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Papers by Kory Charron

Orthopaedic Proceedings, Nov 1, 2011

Purpose: High contact stresses and wear after total knee replacement (TKR) has been a problem. Mo... more Purpose: High contact stresses and wear after total knee replacement (TKR) has been a problem. Mobile bearing TKRs have been advocated as a means to increase load bearing area, reduce contact stresses and minimize wear. The purpose of this study was to compare two, large, consecutive cohorts of TKR patients with greater than 10 years follow-up, one with a fixed bearing and one with a mobile bearing design. Method: One hundred and three SAL II mobile bearing TKR’s were compared to a gender, age, BMI and time from surgery matched fixed bearing Genesis II cohort of equal size. All surgeries were performed between September 1993 and December 2000 (average follow-up, 11.64±1.64 years). Inclusion criteria included patients with osteoarthritis of the knee. Exclusion criteria included revision arthroplasty, inflammatory arthritis, a prior osteotomy or a prior patellectomy. The >10 year Kaplan-Meier survivorship, health-related outcomes (Knee Society scores, WOMAC and SF-12), radiographs and retrieved implants for the fixed and mobile bearing TKR cohorts were compared. Results: Fixed bearing TKRs demonstrated better 10 year Kaplan-Meier survivorships for any re-operation, 1.000±0.000 compared to 0.969±0.018 for mobile bearings (Genesis II and SAL I/II respectively). Revision rates were significantly different between groups with fixed bearing having no revisions and mobile four revisions (3.9%). No cases were revised for sepsis. Mobile bearing revisions were for pain (1), patellar maltracking (1), polyethylene wear (1) and aseptic loosening (1). At 10 years, health-related outcomes were similar between the two cohorts. Fixed bearing TKRs demonstrated more range of motion (111.42±12.76 vs 107.19±14.74 degrees) although not significant (p=0.052). Wear was more frequently noted in mobile bearing TKRs on >10 year radiographs. Conclusion: In this comparison of two contemporary TKRs, the fixed bearing TKR outperformed the mobile bearing TKR.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: Approximately, 10% of two-stage TKA revisions for deep sepsis become re-infected. The pu... more Purpose: Approximately, 10% of two-stage TKA revisions for deep sepsis become re-infected. The purpose of this study was to determine the success in terms of sepsis eradication and factors associated with failure of repeat two-stage revision TKA. Method: Between 1991 and 2006, 129 two-stage revision TKRs for deep sepsis were performed. Ten cases which became re-infected were identified. These unfortunate patients, representing 8% of all the two-stage TKA revisions performed during this time period, are the focus of this study. Their progress and treatment interventions were followed for the purposes of this study. Results: Ten patients were identified with a two-stage revision TKA which became re-infected. Mean patient age was 72 with 40 % being female. Following recurrent sepsis all patients went on to require more than one further two-stage revision (mean 3.67 further revision surgeries). Infection was only successfully eradicated in 28.7% of cases, the remaining require chronic suppressive therapy or have ongoing active infection. Two patients went on to have an arthrodesis (both remain on suppressive anti-biotics) and one patient had trans-femoral amputation. Staph Aureus and Coagulase neg Staph accounted for 80% of primary infective organisms with only one primary infection with methicillin resistant staph aureus (MRSA). Cultures at subsequent revisions were the same organism in 67% cases. Additional organism cultured included Pseudomonas and Propionibacterium. These patients had an increased incidence of multiple medical co-morbidities including Type-2 Diabetes Mellitus and Rheumatoid Arthritis. Conclusion: Patients with recurrent sepsis after a two-stage revision for infection in TKR all required multiple further surgeries. Eradication of infection was only achieved in 28.7% cases. Risk factors for recurrent sepsis include Rheumatoid Arthritis and Type-2 Diabetes Mellitus.

Orthopaedic Proceedings, Mar 1, 2010

Purpose: Gender specific total knee replacement design has been a recently debated controversial ... more Purpose: Gender specific total knee replacement design has been a recently debated controversial topic. The purpose of this study was to investigate the survivor-ship and clinical outcomes of a large primary total knee arthroplasty cohort, specifically assessing any differences between gender groups. Method: A consecutive cohort of 3817 patients with osteoarthritis, having undergone 5289 primary total knee replacements (3100-female, 2179-male) with a minimum of 2 years follow-up were evaluated. All surgeries were performed at the same institution by one of four surgeons. Pre-operative scores, latest scores, and change in clinical outcome scores (KSCRS, SF12, WOMAC) were compared and tested for significance using the students t-test. Kaplan Meier (K-M) survivor-ship was determined and tested for significance and categorical variables were compared using chi-squared. Results: Men were significantly taller and heavier than women, while women had significantly higher BMI’s (p Conclusion: In this cohort of patients undergoing total knee replacements, women demonstrated statistically greater implant survivorship, statistically greater improvement in WOMAC scores and less improvement in KSCR scores, leading one to question the hypothesis of an inferior clinical outcome in total knee arthroplasty that is gender based.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The purpose of this prospective blinded randomized control trial was to compare the stem... more Purpose: The purpose of this prospective blinded randomized control trial was to compare the stem migration of two cemented stem designs using radiostereometric analysis (RSA). This was essentially a safety study in which our hypothesis was that the newer design (CPCS, Smith and Nephew Inc) would demonstrate similar micro-motion to the well-established Exeter (Stryker) design. Method: Thirty patients were consented and enrolled into a blinded RCT in which 15 patients received a dedicated RSA CPCS stem and 15 patients received a RSA Exeter stem. Both stems are collarless tapered polished cemented stems, the only difference being a slight lateral to medial taper with the CPCS design. Outcome measures were compared (Hip Society Score, WOMAC, SF-12). RSA analysis was conducted immediately postoperatively, at 6 weeks, 3 months, 6 months, 1 year and 2 years. Results: No difference was found in any of the outcome measures pre-operatively or postoperatively. At 2 years, stem subsidence for the CPCS stem was approximately half that seen for the Exeter stem (0.565±0.189mm and 0.981±0.209mm respectively, p Conclusion: As expected with this stem design, both stems showed some axial and rotational migration within the cement mantle. The subtle differences in design may explain the differences in migration patterns. Our data suggests that the newer CPCS design should perform well over the long-term.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The purpose of this study was to investigate the mid to long term (minimum 10 years foll... more Purpose: The purpose of this study was to investigate the mid to long term (minimum 10 years follow-up) survivorship of the AMK total knee arthroplasty (TKA), as well as determine the effect of implant fixation on outcome. Method: Between 1988 and 2000, 1074 AMK primary total knee arthroplasties were preformed on 843 patients. All diagnosis included, the distribution was 90% osteoarthritis (971), 7% inflammatory arthritis (76) and 3% other diagnoses (27). Average time from surgery was 15 years (range 10–21 years). Average age at primary procedure was 68 years (range 22–99). Fifty-six percent were female (599) and 44% male (475). Preoperative alignment consisted of 56% varus (601) and 17% valgus (182). Ninety percent (968) had patella resurfacing performed, 62% (661) received cemented TKA fixation, on 32% hybrid fixation (cemented femoral component, cementless tibial tray) was performed and 6% (66) had cementless fixation. Two hundred thirty-seven cases were deceased before 20 years follow-up (22%). Results: At 10 to 21 years follow-up, 129 revisions were performed (12%). The most common reasons for revision were polyethylene wear, particle induced osteolysis, instability and pain (43% of revisions). Implant fixation significantly influenced the rate of revision with cemented fixation having a 6.7% rate of revision (44/661), hybrid fixation a 14% revision rate (47/336) and cementless a 36.4% revision rate (24/66). Excluding infections (11 cases), overall Kaplan-Meier survivorship at five, 10 and 15 years was 96.4%, 91.9% and 85.8%, respectively. At 20 years the predicted Kaplan-Meier survivorship was estimated at 83.5% (no revisions beyond 17.5 years). Cemented fixation was associated with significantly better survivorship than hybrid and cementless fixation (p Conclusion: Cemented fixation had superior outcomes compared to cementless and hybrid fixation with the most common reasons for revision being polyethylene wear and osteolysis. To our knowledge this the first medium to long term follow-up of the AMK TKA and it demonstrates that method of fixation had a major influence on revision rates and survivorship.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The purpose of this study was to determine the greater than 20 year survivorship of the ... more Purpose: The purpose of this study was to determine the greater than 20 year survivorship of the PCA total hip arthroplasty (THA) in patients with severe hip osteoarthritis. Method: A prospective follow-up of 315 consecutive patients treated with a PCA cementless THA in patients with hip osteoarthritis was performed. Patients had postoperative assessments and radiographs every two years. Overall THA, femoral stem and acetabular cup revisions and Kaplan-Meier survivorship was determined. Revision rates and survivorship was also investigated across gender. Results: The mean age of our patients was 61 years old (range 20 to 86) with 47% female patients. 226 cases used a 26mm articulation and 89 cases a 32mm articulation. At 23 years follow-up, 188(60%) patients were alive with retained implants while 85(27%) were deceased with still implants that were functioning well. Forty-two cases (13%) were revised (30 sockets, 13 stems), five of which later deceased. The 20 year Kaplan Meier survivorship for the overall THA, stem component and acetabular cup were 86%, 97% and 90% respectively. Survivorship of the acetabular cup for 26mm and 32mm articulations was 92% and 85% respectively (p=0.016). Females had a worse THA survivorship than males, 82% and 91% respectively (p=0.036). Conclusion: The PCA cementless THA has performed well beyond 20 years with 26 mm articulations doing better than 32 mm, and male gender associated with better outcomes. The authors postulate that polyethylene thickness is key to predicting failure.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: There is no consensus whether the posterior cruciate ligament (PCL)should be preserved (... more Purpose: There is no consensus whether the posterior cruciate ligament (PCL)should be preserved (CR) or sacrificed (CS) during primary total knee replacement (TKR). The purpose of this study was to compare the greater than 10 year survivorship and health related outcomes of CR and CS TKRs using a single implant system. Method: Between 1996 and 2000, 478 Genesis II Primary TKRs were inserted in 414 patients. Excluding those with a primary diagnosis other than osteoarthritis, body mass index greater then 40, history of prior patellectomy, fusion or osteotomy, 358 cases in 310 patients were included. 134 (37%) had a PCL preserving (CR) and 224 (63%) had a PCL sacrificing implant (CS). The two patient cohorts were compared for Kaplan-Meier survivorship, health-related outcomes (Knee Society scores, WOMAC, SF-12), range of motion (ROM) and radiographic loosening or wear. Results: Mean follow-up was 11.87±1.04 years for CR and 10.96±0.87 years for CS (p=0.001). Four cases were revised for infection. No significant differences were noted between the CR and CS Genesis II cohorts at 10 year Kaplan-Meier survivorship excluding infections (CR 0.984±0.011, CS 0.986±0.008, p=0.30). Overall revisions were two for CR (1.5%, no infections) and seven for CS (1.7%, four for infection; 1.3% excluding infections). Revision rates were not significantly different between groups including or excluding infections (p=0.493 and p=1.00 respectively). CS had significantly greater postoperative ROM than CR (CS=114.20±13.60, CR=111.35±12.38, p=0.024). At 10 years, no differences were observed in satisfaction, health-related outcomes or radiographic wear/loosening. Crepitus was reported more frequently in CS design. Conclusion: Most studies comparing PCL sacrificing (CS) versus retaining (CR) TKRs are short term. In this large, long term, single implant CR versus CS study, no differences were found in Kaplan-Meier survivorship, health-related outcomes or patient satisfaction. The CS design had more range of motion, but also a higher incidence of peripatellar crepitus than the CR design. We conclude that both CR and CS TKR designs can yield excellent long term clinical outcomes.

Journal of Bone and Joint Surgery, American Volume, 2012

We previously reported the ten to fourteen-year results for 311 Porous Coated Anatomic total hip ... more We previously reported the ten to fourteen-year results for 311 Porous Coated Anatomic total hip replacements that had been inserted by two surgeons in 279 patients. The purpose of the present report is to update that study and to report the outcome beyond twenty years. The patients were followed prospectively with clinical assessment with use of the Harris hip score and radiographic analysis, and the results were collected in a database. Two hundred and sixty-eight hips were functioning at the time of death or at the time of the latest follow-up. A total of forty-three hips (14%) underwent major revision for all causes, and an additional four hips underwent minor revision. At a mean of twenty-three years of follow-up, Kaplan-Meier analysis revealed a survival rate of 83% with revision for any reason as the end point. The survival rate was 95% for the femoral component and 88% for the acetabular component with revision for any reason as the end point. The rate of survival of the acetabular component was significantly higher in hips with a 26-mm femoral head than in those with a 32-mm femoral head (91% compared with 80%; p = 0.026).

Journal of Bone and Joint Surgery, American Volume, Jul 20, 2011

This study was designed to compare the fixation of a Mallory-Head total hip prosthesis with and w... more This study was designed to compare the fixation of a Mallory-Head total hip prosthesis with and without cement. Two hundred and fifty patients with osteoarthritis of the hip were randomized to receive a Mallory-Head total hip prosthesis designed for insertion with cement or the same prosthesis designed for insertion without cement. Neither the patient nor the outcomes assessor was aware of the type of prosthesis. Outcomes were assessed with respect to mortality, revision arthroplasty, health-related quality of life (evaluated with the Harris hip score, Merle d'Aubign and Postel hip score, McMaster-Toronto Arthritis Patient Preference Disability Questionnaire (MACTAR), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and the time trade-off technique), and the six-minute-walk test. Patients were seen at three, six, and twelve months and yearly thereafter. The prosthesis was inserted with cement in 124 patients and without cement in 126 patients. The mean age of the patients was sixty-four years, 48% were female, and the mean duration of follow-up was 6.3 years. There were thirteen revisions in the group that had fixation with cement and six in the group that had fixation without cement (p = 0.11), and more femoral components were revised in the group that had fixation with cement (twelve versus one; p = 0.002). All health-related quality-of-life measures improved postoperatively in both groups. In this randomized trial, the group that had the cemented Mallory-Head hip prostheses required more revisions of the femoral component than did the group with the cementless Mallory-Head prostheses, which was perhaps related to the titanium-alloy femoral stem. Our findings are specific to the implants evaluated in this study.

Orthopaedic Proceedings, Mar 1, 2010

Purpose: The purpose of this study was to determine the reasons for patient dissatisfaction after... more Purpose: The purpose of this study was to determine the reasons for patient dissatisfaction after primary TKA. Method: Primary TKA patients (n=2513) entered into the Ontario Joint Replacement Registry (OJRR) with decision date and one year follow-up data (WOMAC, expectations, satisfaction and willingness to undergo surgery) were analyzed to determine the factors that might be associated with patients who were not satisfied with their total knee replacement. Results: The majority of patients were satisfied with their TKA (n=1939, 81%), but 169 (7%) were uncertain and 281 (12%) were not satisfied. Pre-operative expectations were important as 89% of patients who did not have their expectations met and 40% who had no expectations were dissatisfied with their TKA. Factors that affected patient satisfaction for their TKA, controlling for age, comorbidity and post-operative complications were better pre-operative WOMAC function scores (p25 point improvement). Conclusion: In this province-wide study, one in five TKA patients were not satisfied with their surgery at one-year follow-up. It is important that patients, surgeons and healthcare payers recognize significant factors that can lead to patient dissatisfaction and help patients establish realistic expectations prior to undergoing TKA surgery.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: Efforts to decrease polyethylene wear have lead to advances in polyethylene and counter-... more Purpose: Efforts to decrease polyethylene wear have lead to advances in polyethylene and counter-face technology for total hip replacement. In particular, the use of highly cross-linked polyethylene (XLPE) and more recently, oxidized zirconium (Oxinium) heads, have demonstrated significant in-vitro improvements in THR wear. This study reports on the early clinical performance and wear (measured with RSA) of an randomized controlled trial (RCT) comparing Oxinium and CoCr heads on XLPE and conventional polyethylene (CPE). Method: Forty patients were enrolled in a RCT and stratified to receive either an Oxinium (Ox) or CoCr head against either XLPE or CPE (ie 10 patients in each group). All patients had otherwise identical THRs and had tantalum beads inserted in the pelvis and polyethylene for wear analysis. There were no significant differences between groups with respect to patient demographics and the average age was 68 years (range 57–76) at index procedure. RSA wear analysis was performed immediately post-op, at six weeks, three and six months and then at one and two years. All patients are a minimum of four years post-op (average 4.6, range 4 – 5.8). Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Harris Hip scores) and radiographs. Results: All health-related outcomes were significantly improved from pre-operative with a mean Harris Hip score and WOMAC at last follow-up of 90.9 and 80.2, respectively. Total 3D femoral head penetration at two years for each group were the following: CoCrXLPE (0.068±0.029mm); OxXLPE (0.115±0.038mm); CoCrCPE (0.187±0.079mm); and OxCPE (0.242±0.088mm). Thus, OxCPE was significantly higher than OxXLPE and CoCrXLPE but not CoCrCPE (p=0.001, p>0.0001 and p=0.094, respectively). In other words, head penetration was higher with CPE compared to XLPE but there was no significant difference between Ox and CoCr heads. Similarily, regardless of head type (ie combining similar poly types), there was a significant difference in 3D head penetration at two years between CPE and XLPE ( CPE 0.213±0.086; XLPE 0.093±0.041, p>0.0001). Conclusion: The early results of this RCT, using RSA as the wear analysis tool, indicate a significant improvement in wear with XLPE compared to CPE. However, it failed to show a clear advantage to the use of Oxinium over CoCr against either polyethylene. Longer follow-up is required to determine steady-state wear rates (after bedding-in) and allow comparison between bearing groups.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: Standardized guidelines for in-vitro wear testing of total knee replacements have recent... more Purpose: Standardized guidelines for in-vitro wear testing of total knee replacements have recently been proposed (ISO-14243). Such ISO guidelines suggest the use of a protein-rich lubricant without giving ranges on the lubricants’ thermal stability. Thermal stability has not received much attention in implant wear testing, but is an important tribological characteristic of a lubricant. This study examines the thermal stability of human synovial fluid (SF) from patients with osteoarthritis, the thermal stability of three artificial lubricants and investigates their effects on PE wear. Method: SF was aspirated from three patients undergoing primary total knee arthroplasty. Three artificial lubricants were mixed using iron-supplemented alpha-calf serum (ACS) as the protein-rich base-lubricant and were diluted with either distilled water (ACS + DW; osmolality = 145 ± 2.00 mmol/kg), phosphate-buffered saline (ACS + PBS; osmolality = 312 ± 1.00 mmol/kg), or with PBS an 1.5 g/L hyaluronic acid (ACS + PBS + HA; osmolality = 321 ± 2.64 mmol/kg). Differential scanning calorimetry was used to determine the thermal stability of the SF and all three artificial lubricants. A 5.5 Million cycle wear test was performed using an AMTI knee simulator to determine the effect of each artificial lubricants thermal stability on PE wear. Additional biochemical analyses included the assessment of protein degradation and the measurements of peptide concentration. Results: The thermal stabilities were significantly different between all three artificial lubricants (ACS + DW Conclusion: Using ACS + PBS instead of ACS + DW increased the lubricants’ osmolality, thus stabilizing the proteins by increasing the thermal stability of the lubricant which reduced the PE wear rate. ACS + PBS + HA increased the lubricants’ thermal stability, which closely matched the thermal stability of SF, and such an increase accelerated the PE wear rate. It was proposed that HA formed a protein-HA network which reduced the lubricating ability of ACS + PBS + HA compared with ACS + PBS, leading to increased protein degradation and increased peptide concentration and thus accelerating the PE wear rate. The findings of the present study strongly suggested to revise ISO-14243 in its current form and to include recommendations on clinically relevant thermal stability levels for artificial lubricants used in in-vitro wear testing of total knee replacements.

Orthopaedic Proceedings, May 1, 2009

Attempts have been made to develop standardise guidelines for knee implant wear testing of polyet... more Attempts have been made to develop standardise guidelines for knee implant wear testing of polyethylene (PE). The current ISO-14243-3 standard recommends the use “calf serum”, without giving ranges on the specific protein constituents and characteristics. In the present study, three types of frequently used calf sera with various protein constituents (albumin, globulins) were utilised. The effect of osmolality and hyaluronic acid (HA) was also assessed. An attempt was made to identify synovial fluid (SF) characteristics that may be responsible for the boundary lubrication in the joint with the goal to develop a more clinically relevant lubricant. Twenty samples of SF were drawn from twenty patients and analyzed. Specific protein constituents and osmolality were then compared to three calf sera used for wear testing. Test One (six million cycles (Mc)): Bovine calf serum (BCS), newborn calf serum (NCS) and alpha-calf serum (ACS) were diluted with distilled water (DW). Test two (5.5Mc): ACS with an osmolality of 312 ± 1.00 mmol/kg (closest to clinical osmolality; diluted with phosphate buffered saline, PBS) and 145 ± 2.00 mmol/kg (diluted with DW) were consecutively tested. HA was added at a concentration of 1.5g/l. Modular total knee replacements of cruciate retaining design (GUR 1050, 10mm PE insert) were used. ACS diluted with PBS appeared to be of closest specific protein constituents and osmolality when compared to SF. The wear rate for BCS was 21.81 ± 2.48 mg/Mc, 17.05 ± 3.25 mg/Mc for NCS, and 13.44 ± 0.79 mg/Mc for ACS (p There was significant difference in PE wear rates between the three calf-sera. BCS and NBC did not have clinically relevant levels of specific protein constituents. This study strongly suggests that current standards for total knee wear testing should be revised to enable more controlled wear testing under more clinically relevant conditions. It is suggested to be of particular importance when new bearing materials, such as cross-linked PE’s, are evaluated and proposed for clinical application.

Orthopaedic Proceedings, Jul 1, 2011

Purpose: The purpose of this study was to determine why some TKR patients are satisfied and other... more Purpose: The purpose of this study was to determine why some TKR patients are satisfied and others are dissatisfied. Method: 2,481 primary TKR patients who had completed a decision date WOMAC were randomly identified within the Ontario Joint Replacement Registry (OJRR) database. One year post-operatively, these patients were mailed a survey to determine satisfaction/expectations, willingness to undergo surgery again, Jaeschke self-reported clinical improvement, WOMAC scores and complications. The satisfied and not satisfied patient groups were identified, statistical analysis employed to determine variables that individually affect satisfaction and logistic regression used to identify significant factors which might lead to patient dissatisfaction. Results: Only 70% of primary TKR patients felt that their expectations had been met and 15% reported that they had no expectations. Only 81% of patients reported that they were satisfied with their TKR. When asked whether they would have their surgery again, 96% of the satisfied patients reported that they would do so as compared to only 63% in the dissatisfied group (p Conclusion: Only one in five primary TKR patients are satisfied with their operative procedure. Significant risk factors for patient dissatisfaction after primary TKR include a pre-operative WOMAC

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The Synergy femoral component was introduced in late 1996 as a second generation titaniu... more Purpose: The Synergy femoral component was introduced in late 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets (standard & high) to help better restore femoral offset at THR. The purpose of this prospective study was to evaluate the long-term (minimum 10 year) clinical and radiographic results and survivorship of this second-generation femoral component at our institution. Method: From December 1996 to December 1999, 256 cementless Synergy femoral components were inserted and followed prospectively in 254 patients requiring THR. 185 were standard offset stems(72.3%) while 71 stems (27.7%) were high offset. The average follow-up was 11.2 years (range 10.0 to 12.9 years). Average age at index THR was 58.9 years (range 19 to 86 years). Two hundred eight stems had standard porous coating while 48 had additional HA coating. Fifty-two cases were either lost to follow-up or had died prior to 10 years follow-up. Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Harris Hip scores) and radiographs. Kaplan-Meier survival analysis was performed. Results: All health-related outcomes were significantly improved from pre-operative with a mean Harris Hip score and WOMAC at last follow-up of 91.6 and 81.8, respectively. From the initial 256 femoral stems inserted, only 5 stems have been revised. Two stems have been revised for infection. To date, only one stem has been revised due to subsidence at nine months following surgery likely, as a result of a calcar fracture occurring at the index THR. Two stems were revised for peri-prosthetic fracture as a result of patient falls at six months and 9.8 years post-op. Radiographic review of remaining stems in-situ identified no cases of loosening with all stems showing evidence of osseous integration. The Kaplan-Meier survivorship analysis of the femoral component, with revision for aseptic loosening, was 99.2%±0.008 at five, 10 and 12 years. Conclusion: The Synergy femoral component, a second generation titanium proximally porous-coated tapered stem design with dual offsets, has demonstrated excellent clinical & radiographic results and long-term survivorship (99% at 10 years) at our institution.

Clinical Orthopaedics and Related Research, 2010

The range of motion after TKA depends on many patient, surgical technique, and implant factors. R... more The range of motion after TKA depends on many patient, surgical technique, and implant factors. Recently, high-flexion designs have been introduced as a means of ensuring or gaining flexion after TKA. We therefore evaluated factors affecting postoperative flexion to determine whether implant design influences longterm flexion. We prospectively collected data on patients receiving a primary Genesis II TM total knee replacement with a minimum of 1-year followup (mean, 5.4 years; range, 1-13 years). We recorded pre-and postoperative outcome measures, patient demographics, and implant design (cruciate retaining [CR, n = 160], posterior stabilized [PS, n = 1177], high-flex posterior stabilized [HF-PS, n = 197]). Backward stepwise linear regression modeling identified the following factors affecting postoperative flexion: preoperative flexion, gender, body mass index, and implant design. Independent of gender, body mass index, and preoperative flexion, patients who received a HF-PS and PS design implant had a mean of 8°and 5°more flexion, respectively, than those who received a CR implant. Patients with low flexion preoperatively (\ 100°) were more likely to gain flexion, whereas those with high flexion preoperatively ([ 120°) were most likely to maintain or lose flexion postoperatively. Controlling for implant design, patients with high flexion preoperatively ([ 120°) were more likely to gain flexion with the HF-PS design implant (HF-PS = 32.0%; PS = 15.1%; CR = 4.5%).

The journal of bone and joint surgery, Mar 1, 2011

We evaluated the outcome of primary total hip replacement (THR) in 3290 patients with the primary... more We evaluated the outcome of primary total hip replacement (THR) in 3290 patients with the primary diagnosis of osteoarthritis at a minimum follow-up of two years. They were stratified into categories of body mass index (BMI) based on the World Health Organisation classification of obesity. Statistical analysis was carried out to determine if there was a difference in the post-operative Western Ontario and McMaster Universities osteoarthritis index, the Harris hip score and the Short-Form-12 outcome based on the BMI. While the pre-and post-operative scores were lower for the group classified as morbidly obese, the overall change in outcome scores suggested an equal if not greater improvement compared with the non-morbidly obese patients. The overall survivorship and rate of complications were similar in the BMI groups although there was a slightly higher rate of revision for sepsis in the morbidly obese group. Morbid obesity does not affect the post-operative outcome after THR, with the possible exception of a marginally increased rate of infection. Therefore withholding surgery based on the BMI is not justified.

Clinical Orthopaedics and Related Research, Nov 1, 2008

Gender-specific total knee replacement design is a recent and debated topic. We determined the su... more Gender-specific total knee replacement design is a recent and debated topic. We determined the survivorship and clinical outcomes of a large primary total knee arthroplasty cohort, specifically assessing any differences between gender groups. A consecutive cohort of 3817 patients with 5279 primary total knee replacements (3100 female, 2179 male) with a minimum of 2 years followup were evaluated. Preoperative, latest, and change in clinical outcome scores (WOMAC, SF-12, KSCRS) were compared. While men had higher raw scores preoperatively, women had greater improvement in all WOMAC domains including pain (29.87 versus 27.3), joint stiffness (26.78 versus 24.26), function (27.21 versus 23.09), and total scores (28.35 versus 25.09). There were no gender differences in improvements of the SF-12 physical scores. Men had greater improvement in Knee Society function (22.1 versus 18.63) and total scores (70.01 versus 65.42), but not the Knee Society knee score (47.83 versus 46.64). Revision rates were 10.2% for men and 8% for women. Women demonstrated greater implant survivorship, greater improvement in WOMAC scores, equal improvements in SF-12 scores, and less improvement in only the Knee Society function and total scores. The data refute the hypothesis of inferior clinical outcome for women following total knee arthroplasty when using standard components. Level of Evidence: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Clinical Orthopaedics and Related Research, 2010

Despite substantial advances in primary TKA, numerous studies using historic TKA implants suggest... more Despite substantial advances in primary TKA, numerous studies using historic TKA implants suggest only 82% to 89% of primary TKA patients are satisfied. We reexamined this issue to determine if contemporary TKA implants might be associated with improved patient satisfaction. We performed a cross-sectional study of patient satisfaction after 1703 primary TKAs performed in the province of Ontario. Our data confirmed that approximately one in five (19%) primary TKA patients were not satisfied with the outcome. Satisfaction with pain relief varied from 72-86% and with function from 70-84% for specific activities of daily living. The strongest predictors of patient dissatisfaction after primary TKA were expectations not met (10.79 greater risk), a low 1-year WOMAC (2.59 greater risk), preoperative pain at rest (2.49 greater risk) and a postoperative complication requiring hospital readmission (1.99 greater risk). Level of Evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Journal of The Mechanical Behavior of Biomedical Materials, Aug 1, 2010

There is currently considerable interest in the use of highly cross-linked polyethylene (XLPE) ac... more There is currently considerable interest in the use of highly cross-linked polyethylene (XLPE) acetabular liners for total hip arthroplasty (THA). In literature, only a single retrieval analysis of one type of XLPE liner implanted for greater than four years exists. The purpose of the present report is to quantify surface deviations in two XLPE liners implanted during revision THA and retrieved between four to five years after implantation. The two XLPE acetabular liners (Reflection, Smith and Nephew Inc., Memphis, TN) were retrieved from patients undergoing their second revision surgery, at 4.90 and 4.07 years. The retrieved liners and a new, non-implanted, unworn liner of the same size were scanned using micro-computed tomography (micro-CT). Articular surface deviation maps were created by comparing the retrievals to the unworn liner, based on the liner geometry obtained from micro-CT. The linear penetration rates were found to be 0.018 and 0.008 mm/year. Localized scratches and pits with deviations greater than 0.205 mm were also found on the articular surfaces of both liners. The XLPE liners retrieved from the two cases demonstrated low linear penetration rates. Regions with greater focal deviations were also apparent, likely due to third-body wear. The results are consistent with previously published clinical followups of other XLPE liners.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: High contact stresses and wear after total knee replacement (TKR) has been a problem. Mo... more Purpose: High contact stresses and wear after total knee replacement (TKR) has been a problem. Mobile bearing TKRs have been advocated as a means to increase load bearing area, reduce contact stresses and minimize wear. The purpose of this study was to compare two, large, consecutive cohorts of TKR patients with greater than 10 years follow-up, one with a fixed bearing and one with a mobile bearing design. Method: One hundred and three SAL II mobile bearing TKR’s were compared to a gender, age, BMI and time from surgery matched fixed bearing Genesis II cohort of equal size. All surgeries were performed between September 1993 and December 2000 (average follow-up, 11.64±1.64 years). Inclusion criteria included patients with osteoarthritis of the knee. Exclusion criteria included revision arthroplasty, inflammatory arthritis, a prior osteotomy or a prior patellectomy. The >10 year Kaplan-Meier survivorship, health-related outcomes (Knee Society scores, WOMAC and SF-12), radiographs and retrieved implants for the fixed and mobile bearing TKR cohorts were compared. Results: Fixed bearing TKRs demonstrated better 10 year Kaplan-Meier survivorships for any re-operation, 1.000±0.000 compared to 0.969±0.018 for mobile bearings (Genesis II and SAL I/II respectively). Revision rates were significantly different between groups with fixed bearing having no revisions and mobile four revisions (3.9%). No cases were revised for sepsis. Mobile bearing revisions were for pain (1), patellar maltracking (1), polyethylene wear (1) and aseptic loosening (1). At 10 years, health-related outcomes were similar between the two cohorts. Fixed bearing TKRs demonstrated more range of motion (111.42±12.76 vs 107.19±14.74 degrees) although not significant (p=0.052). Wear was more frequently noted in mobile bearing TKRs on >10 year radiographs. Conclusion: In this comparison of two contemporary TKRs, the fixed bearing TKR outperformed the mobile bearing TKR.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: Approximately, 10% of two-stage TKA revisions for deep sepsis become re-infected. The pu... more Purpose: Approximately, 10% of two-stage TKA revisions for deep sepsis become re-infected. The purpose of this study was to determine the success in terms of sepsis eradication and factors associated with failure of repeat two-stage revision TKA. Method: Between 1991 and 2006, 129 two-stage revision TKRs for deep sepsis were performed. Ten cases which became re-infected were identified. These unfortunate patients, representing 8% of all the two-stage TKA revisions performed during this time period, are the focus of this study. Their progress and treatment interventions were followed for the purposes of this study. Results: Ten patients were identified with a two-stage revision TKA which became re-infected. Mean patient age was 72 with 40 % being female. Following recurrent sepsis all patients went on to require more than one further two-stage revision (mean 3.67 further revision surgeries). Infection was only successfully eradicated in 28.7% of cases, the remaining require chronic suppressive therapy or have ongoing active infection. Two patients went on to have an arthrodesis (both remain on suppressive anti-biotics) and one patient had trans-femoral amputation. Staph Aureus and Coagulase neg Staph accounted for 80% of primary infective organisms with only one primary infection with methicillin resistant staph aureus (MRSA). Cultures at subsequent revisions were the same organism in 67% cases. Additional organism cultured included Pseudomonas and Propionibacterium. These patients had an increased incidence of multiple medical co-morbidities including Type-2 Diabetes Mellitus and Rheumatoid Arthritis. Conclusion: Patients with recurrent sepsis after a two-stage revision for infection in TKR all required multiple further surgeries. Eradication of infection was only achieved in 28.7% cases. Risk factors for recurrent sepsis include Rheumatoid Arthritis and Type-2 Diabetes Mellitus.

Orthopaedic Proceedings, Mar 1, 2010

Purpose: Gender specific total knee replacement design has been a recently debated controversial ... more Purpose: Gender specific total knee replacement design has been a recently debated controversial topic. The purpose of this study was to investigate the survivor-ship and clinical outcomes of a large primary total knee arthroplasty cohort, specifically assessing any differences between gender groups. Method: A consecutive cohort of 3817 patients with osteoarthritis, having undergone 5289 primary total knee replacements (3100-female, 2179-male) with a minimum of 2 years follow-up were evaluated. All surgeries were performed at the same institution by one of four surgeons. Pre-operative scores, latest scores, and change in clinical outcome scores (KSCRS, SF12, WOMAC) were compared and tested for significance using the students t-test. Kaplan Meier (K-M) survivor-ship was determined and tested for significance and categorical variables were compared using chi-squared. Results: Men were significantly taller and heavier than women, while women had significantly higher BMI’s (p Conclusion: In this cohort of patients undergoing total knee replacements, women demonstrated statistically greater implant survivorship, statistically greater improvement in WOMAC scores and less improvement in KSCR scores, leading one to question the hypothesis of an inferior clinical outcome in total knee arthroplasty that is gender based.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The purpose of this prospective blinded randomized control trial was to compare the stem... more Purpose: The purpose of this prospective blinded randomized control trial was to compare the stem migration of two cemented stem designs using radiostereometric analysis (RSA). This was essentially a safety study in which our hypothesis was that the newer design (CPCS, Smith and Nephew Inc) would demonstrate similar micro-motion to the well-established Exeter (Stryker) design. Method: Thirty patients were consented and enrolled into a blinded RCT in which 15 patients received a dedicated RSA CPCS stem and 15 patients received a RSA Exeter stem. Both stems are collarless tapered polished cemented stems, the only difference being a slight lateral to medial taper with the CPCS design. Outcome measures were compared (Hip Society Score, WOMAC, SF-12). RSA analysis was conducted immediately postoperatively, at 6 weeks, 3 months, 6 months, 1 year and 2 years. Results: No difference was found in any of the outcome measures pre-operatively or postoperatively. At 2 years, stem subsidence for the CPCS stem was approximately half that seen for the Exeter stem (0.565±0.189mm and 0.981±0.209mm respectively, p Conclusion: As expected with this stem design, both stems showed some axial and rotational migration within the cement mantle. The subtle differences in design may explain the differences in migration patterns. Our data suggests that the newer CPCS design should perform well over the long-term.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The purpose of this study was to investigate the mid to long term (minimum 10 years foll... more Purpose: The purpose of this study was to investigate the mid to long term (minimum 10 years follow-up) survivorship of the AMK total knee arthroplasty (TKA), as well as determine the effect of implant fixation on outcome. Method: Between 1988 and 2000, 1074 AMK primary total knee arthroplasties were preformed on 843 patients. All diagnosis included, the distribution was 90% osteoarthritis (971), 7% inflammatory arthritis (76) and 3% other diagnoses (27). Average time from surgery was 15 years (range 10–21 years). Average age at primary procedure was 68 years (range 22–99). Fifty-six percent were female (599) and 44% male (475). Preoperative alignment consisted of 56% varus (601) and 17% valgus (182). Ninety percent (968) had patella resurfacing performed, 62% (661) received cemented TKA fixation, on 32% hybrid fixation (cemented femoral component, cementless tibial tray) was performed and 6% (66) had cementless fixation. Two hundred thirty-seven cases were deceased before 20 years follow-up (22%). Results: At 10 to 21 years follow-up, 129 revisions were performed (12%). The most common reasons for revision were polyethylene wear, particle induced osteolysis, instability and pain (43% of revisions). Implant fixation significantly influenced the rate of revision with cemented fixation having a 6.7% rate of revision (44/661), hybrid fixation a 14% revision rate (47/336) and cementless a 36.4% revision rate (24/66). Excluding infections (11 cases), overall Kaplan-Meier survivorship at five, 10 and 15 years was 96.4%, 91.9% and 85.8%, respectively. At 20 years the predicted Kaplan-Meier survivorship was estimated at 83.5% (no revisions beyond 17.5 years). Cemented fixation was associated with significantly better survivorship than hybrid and cementless fixation (p Conclusion: Cemented fixation had superior outcomes compared to cementless and hybrid fixation with the most common reasons for revision being polyethylene wear and osteolysis. To our knowledge this the first medium to long term follow-up of the AMK TKA and it demonstrates that method of fixation had a major influence on revision rates and survivorship.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The purpose of this study was to determine the greater than 20 year survivorship of the ... more Purpose: The purpose of this study was to determine the greater than 20 year survivorship of the PCA total hip arthroplasty (THA) in patients with severe hip osteoarthritis. Method: A prospective follow-up of 315 consecutive patients treated with a PCA cementless THA in patients with hip osteoarthritis was performed. Patients had postoperative assessments and radiographs every two years. Overall THA, femoral stem and acetabular cup revisions and Kaplan-Meier survivorship was determined. Revision rates and survivorship was also investigated across gender. Results: The mean age of our patients was 61 years old (range 20 to 86) with 47% female patients. 226 cases used a 26mm articulation and 89 cases a 32mm articulation. At 23 years follow-up, 188(60%) patients were alive with retained implants while 85(27%) were deceased with still implants that were functioning well. Forty-two cases (13%) were revised (30 sockets, 13 stems), five of which later deceased. The 20 year Kaplan Meier survivorship for the overall THA, stem component and acetabular cup were 86%, 97% and 90% respectively. Survivorship of the acetabular cup for 26mm and 32mm articulations was 92% and 85% respectively (p=0.016). Females had a worse THA survivorship than males, 82% and 91% respectively (p=0.036). Conclusion: The PCA cementless THA has performed well beyond 20 years with 26 mm articulations doing better than 32 mm, and male gender associated with better outcomes. The authors postulate that polyethylene thickness is key to predicting failure.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: There is no consensus whether the posterior cruciate ligament (PCL)should be preserved (... more Purpose: There is no consensus whether the posterior cruciate ligament (PCL)should be preserved (CR) or sacrificed (CS) during primary total knee replacement (TKR). The purpose of this study was to compare the greater than 10 year survivorship and health related outcomes of CR and CS TKRs using a single implant system. Method: Between 1996 and 2000, 478 Genesis II Primary TKRs were inserted in 414 patients. Excluding those with a primary diagnosis other than osteoarthritis, body mass index greater then 40, history of prior patellectomy, fusion or osteotomy, 358 cases in 310 patients were included. 134 (37%) had a PCL preserving (CR) and 224 (63%) had a PCL sacrificing implant (CS). The two patient cohorts were compared for Kaplan-Meier survivorship, health-related outcomes (Knee Society scores, WOMAC, SF-12), range of motion (ROM) and radiographic loosening or wear. Results: Mean follow-up was 11.87±1.04 years for CR and 10.96±0.87 years for CS (p=0.001). Four cases were revised for infection. No significant differences were noted between the CR and CS Genesis II cohorts at 10 year Kaplan-Meier survivorship excluding infections (CR 0.984±0.011, CS 0.986±0.008, p=0.30). Overall revisions were two for CR (1.5%, no infections) and seven for CS (1.7%, four for infection; 1.3% excluding infections). Revision rates were not significantly different between groups including or excluding infections (p=0.493 and p=1.00 respectively). CS had significantly greater postoperative ROM than CR (CS=114.20±13.60, CR=111.35±12.38, p=0.024). At 10 years, no differences were observed in satisfaction, health-related outcomes or radiographic wear/loosening. Crepitus was reported more frequently in CS design. Conclusion: Most studies comparing PCL sacrificing (CS) versus retaining (CR) TKRs are short term. In this large, long term, single implant CR versus CS study, no differences were found in Kaplan-Meier survivorship, health-related outcomes or patient satisfaction. The CS design had more range of motion, but also a higher incidence of peripatellar crepitus than the CR design. We conclude that both CR and CS TKR designs can yield excellent long term clinical outcomes.

Journal of Bone and Joint Surgery, American Volume, 2012

We previously reported the ten to fourteen-year results for 311 Porous Coated Anatomic total hip ... more We previously reported the ten to fourteen-year results for 311 Porous Coated Anatomic total hip replacements that had been inserted by two surgeons in 279 patients. The purpose of the present report is to update that study and to report the outcome beyond twenty years. The patients were followed prospectively with clinical assessment with use of the Harris hip score and radiographic analysis, and the results were collected in a database. Two hundred and sixty-eight hips were functioning at the time of death or at the time of the latest follow-up. A total of forty-three hips (14%) underwent major revision for all causes, and an additional four hips underwent minor revision. At a mean of twenty-three years of follow-up, Kaplan-Meier analysis revealed a survival rate of 83% with revision for any reason as the end point. The survival rate was 95% for the femoral component and 88% for the acetabular component with revision for any reason as the end point. The rate of survival of the acetabular component was significantly higher in hips with a 26-mm femoral head than in those with a 32-mm femoral head (91% compared with 80%; p = 0.026).

Journal of Bone and Joint Surgery, American Volume, Jul 20, 2011

This study was designed to compare the fixation of a Mallory-Head total hip prosthesis with and w... more This study was designed to compare the fixation of a Mallory-Head total hip prosthesis with and without cement. Two hundred and fifty patients with osteoarthritis of the hip were randomized to receive a Mallory-Head total hip prosthesis designed for insertion with cement or the same prosthesis designed for insertion without cement. Neither the patient nor the outcomes assessor was aware of the type of prosthesis. Outcomes were assessed with respect to mortality, revision arthroplasty, health-related quality of life (evaluated with the Harris hip score, Merle d'Aubign and Postel hip score, McMaster-Toronto Arthritis Patient Preference Disability Questionnaire (MACTAR), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and the time trade-off technique), and the six-minute-walk test. Patients were seen at three, six, and twelve months and yearly thereafter. The prosthesis was inserted with cement in 124 patients and without cement in 126 patients. The mean age of the patients was sixty-four years, 48% were female, and the mean duration of follow-up was 6.3 years. There were thirteen revisions in the group that had fixation with cement and six in the group that had fixation without cement (p = 0.11), and more femoral components were revised in the group that had fixation with cement (twelve versus one; p = 0.002). All health-related quality-of-life measures improved postoperatively in both groups. In this randomized trial, the group that had the cemented Mallory-Head hip prostheses required more revisions of the femoral component than did the group with the cementless Mallory-Head prostheses, which was perhaps related to the titanium-alloy femoral stem. Our findings are specific to the implants evaluated in this study.

Orthopaedic Proceedings, Mar 1, 2010

Purpose: The purpose of this study was to determine the reasons for patient dissatisfaction after... more Purpose: The purpose of this study was to determine the reasons for patient dissatisfaction after primary TKA. Method: Primary TKA patients (n=2513) entered into the Ontario Joint Replacement Registry (OJRR) with decision date and one year follow-up data (WOMAC, expectations, satisfaction and willingness to undergo surgery) were analyzed to determine the factors that might be associated with patients who were not satisfied with their total knee replacement. Results: The majority of patients were satisfied with their TKA (n=1939, 81%), but 169 (7%) were uncertain and 281 (12%) were not satisfied. Pre-operative expectations were important as 89% of patients who did not have their expectations met and 40% who had no expectations were dissatisfied with their TKA. Factors that affected patient satisfaction for their TKA, controlling for age, comorbidity and post-operative complications were better pre-operative WOMAC function scores (p25 point improvement). Conclusion: In this province-wide study, one in five TKA patients were not satisfied with their surgery at one-year follow-up. It is important that patients, surgeons and healthcare payers recognize significant factors that can lead to patient dissatisfaction and help patients establish realistic expectations prior to undergoing TKA surgery.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: Efforts to decrease polyethylene wear have lead to advances in polyethylene and counter-... more Purpose: Efforts to decrease polyethylene wear have lead to advances in polyethylene and counter-face technology for total hip replacement. In particular, the use of highly cross-linked polyethylene (XLPE) and more recently, oxidized zirconium (Oxinium) heads, have demonstrated significant in-vitro improvements in THR wear. This study reports on the early clinical performance and wear (measured with RSA) of an randomized controlled trial (RCT) comparing Oxinium and CoCr heads on XLPE and conventional polyethylene (CPE). Method: Forty patients were enrolled in a RCT and stratified to receive either an Oxinium (Ox) or CoCr head against either XLPE or CPE (ie 10 patients in each group). All patients had otherwise identical THRs and had tantalum beads inserted in the pelvis and polyethylene for wear analysis. There were no significant differences between groups with respect to patient demographics and the average age was 68 years (range 57–76) at index procedure. RSA wear analysis was performed immediately post-op, at six weeks, three and six months and then at one and two years. All patients are a minimum of four years post-op (average 4.6, range 4 – 5.8). Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Harris Hip scores) and radiographs. Results: All health-related outcomes were significantly improved from pre-operative with a mean Harris Hip score and WOMAC at last follow-up of 90.9 and 80.2, respectively. Total 3D femoral head penetration at two years for each group were the following: CoCrXLPE (0.068±0.029mm); OxXLPE (0.115±0.038mm); CoCrCPE (0.187±0.079mm); and OxCPE (0.242±0.088mm). Thus, OxCPE was significantly higher than OxXLPE and CoCrXLPE but not CoCrCPE (p=0.001, p>0.0001 and p=0.094, respectively). In other words, head penetration was higher with CPE compared to XLPE but there was no significant difference between Ox and CoCr heads. Similarily, regardless of head type (ie combining similar poly types), there was a significant difference in 3D head penetration at two years between CPE and XLPE ( CPE 0.213±0.086; XLPE 0.093±0.041, p>0.0001). Conclusion: The early results of this RCT, using RSA as the wear analysis tool, indicate a significant improvement in wear with XLPE compared to CPE. However, it failed to show a clear advantage to the use of Oxinium over CoCr against either polyethylene. Longer follow-up is required to determine steady-state wear rates (after bedding-in) and allow comparison between bearing groups.

Orthopaedic Proceedings, Nov 1, 2011

Purpose: Standardized guidelines for in-vitro wear testing of total knee replacements have recent... more Purpose: Standardized guidelines for in-vitro wear testing of total knee replacements have recently been proposed (ISO-14243). Such ISO guidelines suggest the use of a protein-rich lubricant without giving ranges on the lubricants’ thermal stability. Thermal stability has not received much attention in implant wear testing, but is an important tribological characteristic of a lubricant. This study examines the thermal stability of human synovial fluid (SF) from patients with osteoarthritis, the thermal stability of three artificial lubricants and investigates their effects on PE wear. Method: SF was aspirated from three patients undergoing primary total knee arthroplasty. Three artificial lubricants were mixed using iron-supplemented alpha-calf serum (ACS) as the protein-rich base-lubricant and were diluted with either distilled water (ACS + DW; osmolality = 145 ± 2.00 mmol/kg), phosphate-buffered saline (ACS + PBS; osmolality = 312 ± 1.00 mmol/kg), or with PBS an 1.5 g/L hyaluronic acid (ACS + PBS + HA; osmolality = 321 ± 2.64 mmol/kg). Differential scanning calorimetry was used to determine the thermal stability of the SF and all three artificial lubricants. A 5.5 Million cycle wear test was performed using an AMTI knee simulator to determine the effect of each artificial lubricants thermal stability on PE wear. Additional biochemical analyses included the assessment of protein degradation and the measurements of peptide concentration. Results: The thermal stabilities were significantly different between all three artificial lubricants (ACS + DW Conclusion: Using ACS + PBS instead of ACS + DW increased the lubricants’ osmolality, thus stabilizing the proteins by increasing the thermal stability of the lubricant which reduced the PE wear rate. ACS + PBS + HA increased the lubricants’ thermal stability, which closely matched the thermal stability of SF, and such an increase accelerated the PE wear rate. It was proposed that HA formed a protein-HA network which reduced the lubricating ability of ACS + PBS + HA compared with ACS + PBS, leading to increased protein degradation and increased peptide concentration and thus accelerating the PE wear rate. The findings of the present study strongly suggested to revise ISO-14243 in its current form and to include recommendations on clinically relevant thermal stability levels for artificial lubricants used in in-vitro wear testing of total knee replacements.

Orthopaedic Proceedings, May 1, 2009

Attempts have been made to develop standardise guidelines for knee implant wear testing of polyet... more Attempts have been made to develop standardise guidelines for knee implant wear testing of polyethylene (PE). The current ISO-14243-3 standard recommends the use “calf serum”, without giving ranges on the specific protein constituents and characteristics. In the present study, three types of frequently used calf sera with various protein constituents (albumin, globulins) were utilised. The effect of osmolality and hyaluronic acid (HA) was also assessed. An attempt was made to identify synovial fluid (SF) characteristics that may be responsible for the boundary lubrication in the joint with the goal to develop a more clinically relevant lubricant. Twenty samples of SF were drawn from twenty patients and analyzed. Specific protein constituents and osmolality were then compared to three calf sera used for wear testing. Test One (six million cycles (Mc)): Bovine calf serum (BCS), newborn calf serum (NCS) and alpha-calf serum (ACS) were diluted with distilled water (DW). Test two (5.5Mc): ACS with an osmolality of 312 ± 1.00 mmol/kg (closest to clinical osmolality; diluted with phosphate buffered saline, PBS) and 145 ± 2.00 mmol/kg (diluted with DW) were consecutively tested. HA was added at a concentration of 1.5g/l. Modular total knee replacements of cruciate retaining design (GUR 1050, 10mm PE insert) were used. ACS diluted with PBS appeared to be of closest specific protein constituents and osmolality when compared to SF. The wear rate for BCS was 21.81 ± 2.48 mg/Mc, 17.05 ± 3.25 mg/Mc for NCS, and 13.44 ± 0.79 mg/Mc for ACS (p There was significant difference in PE wear rates between the three calf-sera. BCS and NBC did not have clinically relevant levels of specific protein constituents. This study strongly suggests that current standards for total knee wear testing should be revised to enable more controlled wear testing under more clinically relevant conditions. It is suggested to be of particular importance when new bearing materials, such as cross-linked PE’s, are evaluated and proposed for clinical application.

Orthopaedic Proceedings, Jul 1, 2011

Purpose: The purpose of this study was to determine why some TKR patients are satisfied and other... more Purpose: The purpose of this study was to determine why some TKR patients are satisfied and others are dissatisfied. Method: 2,481 primary TKR patients who had completed a decision date WOMAC were randomly identified within the Ontario Joint Replacement Registry (OJRR) database. One year post-operatively, these patients were mailed a survey to determine satisfaction/expectations, willingness to undergo surgery again, Jaeschke self-reported clinical improvement, WOMAC scores and complications. The satisfied and not satisfied patient groups were identified, statistical analysis employed to determine variables that individually affect satisfaction and logistic regression used to identify significant factors which might lead to patient dissatisfaction. Results: Only 70% of primary TKR patients felt that their expectations had been met and 15% reported that they had no expectations. Only 81% of patients reported that they were satisfied with their TKR. When asked whether they would have their surgery again, 96% of the satisfied patients reported that they would do so as compared to only 63% in the dissatisfied group (p Conclusion: Only one in five primary TKR patients are satisfied with their operative procedure. Significant risk factors for patient dissatisfaction after primary TKR include a pre-operative WOMAC

Orthopaedic Proceedings, Nov 1, 2011

Purpose: The Synergy femoral component was introduced in late 1996 as a second generation titaniu... more Purpose: The Synergy femoral component was introduced in late 1996 as a second generation titanium proximally porous-coated tapered stem with dual offsets (standard & high) to help better restore femoral offset at THR. The purpose of this prospective study was to evaluate the long-term (minimum 10 year) clinical and radiographic results and survivorship of this second-generation femoral component at our institution. Method: From December 1996 to December 1999, 256 cementless Synergy femoral components were inserted and followed prospectively in 254 patients requiring THR. 185 were standard offset stems(72.3%) while 71 stems (27.7%) were high offset. The average follow-up was 11.2 years (range 10.0 to 12.9 years). Average age at index THR was 58.9 years (range 19 to 86 years). Two hundred eight stems had standard porous coating while 48 had additional HA coating. Fifty-two cases were either lost to follow-up or had died prior to 10 years follow-up. Patients were followed prospectively using validated clinical outcome scores (WOMAC, SF-12, Harris Hip scores) and radiographs. Kaplan-Meier survival analysis was performed. Results: All health-related outcomes were significantly improved from pre-operative with a mean Harris Hip score and WOMAC at last follow-up of 91.6 and 81.8, respectively. From the initial 256 femoral stems inserted, only 5 stems have been revised. Two stems have been revised for infection. To date, only one stem has been revised due to subsidence at nine months following surgery likely, as a result of a calcar fracture occurring at the index THR. Two stems were revised for peri-prosthetic fracture as a result of patient falls at six months and 9.8 years post-op. Radiographic review of remaining stems in-situ identified no cases of loosening with all stems showing evidence of osseous integration. The Kaplan-Meier survivorship analysis of the femoral component, with revision for aseptic loosening, was 99.2%±0.008 at five, 10 and 12 years. Conclusion: The Synergy femoral component, a second generation titanium proximally porous-coated tapered stem design with dual offsets, has demonstrated excellent clinical & radiographic results and long-term survivorship (99% at 10 years) at our institution.

Clinical Orthopaedics and Related Research, 2010

The range of motion after TKA depends on many patient, surgical technique, and implant factors. R... more The range of motion after TKA depends on many patient, surgical technique, and implant factors. Recently, high-flexion designs have been introduced as a means of ensuring or gaining flexion after TKA. We therefore evaluated factors affecting postoperative flexion to determine whether implant design influences longterm flexion. We prospectively collected data on patients receiving a primary Genesis II TM total knee replacement with a minimum of 1-year followup (mean, 5.4 years; range, 1-13 years). We recorded pre-and postoperative outcome measures, patient demographics, and implant design (cruciate retaining [CR, n = 160], posterior stabilized [PS, n = 1177], high-flex posterior stabilized [HF-PS, n = 197]). Backward stepwise linear regression modeling identified the following factors affecting postoperative flexion: preoperative flexion, gender, body mass index, and implant design. Independent of gender, body mass index, and preoperative flexion, patients who received a HF-PS and PS design implant had a mean of 8°and 5°more flexion, respectively, than those who received a CR implant. Patients with low flexion preoperatively (\ 100°) were more likely to gain flexion, whereas those with high flexion preoperatively ([ 120°) were most likely to maintain or lose flexion postoperatively. Controlling for implant design, patients with high flexion preoperatively ([ 120°) were more likely to gain flexion with the HF-PS design implant (HF-PS = 32.0%; PS = 15.1%; CR = 4.5%).

The journal of bone and joint surgery, Mar 1, 2011

We evaluated the outcome of primary total hip replacement (THR) in 3290 patients with the primary... more We evaluated the outcome of primary total hip replacement (THR) in 3290 patients with the primary diagnosis of osteoarthritis at a minimum follow-up of two years. They were stratified into categories of body mass index (BMI) based on the World Health Organisation classification of obesity. Statistical analysis was carried out to determine if there was a difference in the post-operative Western Ontario and McMaster Universities osteoarthritis index, the Harris hip score and the Short-Form-12 outcome based on the BMI. While the pre-and post-operative scores were lower for the group classified as morbidly obese, the overall change in outcome scores suggested an equal if not greater improvement compared with the non-morbidly obese patients. The overall survivorship and rate of complications were similar in the BMI groups although there was a slightly higher rate of revision for sepsis in the morbidly obese group. Morbid obesity does not affect the post-operative outcome after THR, with the possible exception of a marginally increased rate of infection. Therefore withholding surgery based on the BMI is not justified.

Clinical Orthopaedics and Related Research, Nov 1, 2008

Gender-specific total knee replacement design is a recent and debated topic. We determined the su... more Gender-specific total knee replacement design is a recent and debated topic. We determined the survivorship and clinical outcomes of a large primary total knee arthroplasty cohort, specifically assessing any differences between gender groups. A consecutive cohort of 3817 patients with 5279 primary total knee replacements (3100 female, 2179 male) with a minimum of 2 years followup were evaluated. Preoperative, latest, and change in clinical outcome scores (WOMAC, SF-12, KSCRS) were compared. While men had higher raw scores preoperatively, women had greater improvement in all WOMAC domains including pain (29.87 versus 27.3), joint stiffness (26.78 versus 24.26), function (27.21 versus 23.09), and total scores (28.35 versus 25.09). There were no gender differences in improvements of the SF-12 physical scores. Men had greater improvement in Knee Society function (22.1 versus 18.63) and total scores (70.01 versus 65.42), but not the Knee Society knee score (47.83 versus 46.64). Revision rates were 10.2% for men and 8% for women. Women demonstrated greater implant survivorship, greater improvement in WOMAC scores, equal improvements in SF-12 scores, and less improvement in only the Knee Society function and total scores. The data refute the hypothesis of inferior clinical outcome for women following total knee arthroplasty when using standard components. Level of Evidence: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Clinical Orthopaedics and Related Research, 2010

Despite substantial advances in primary TKA, numerous studies using historic TKA implants suggest... more Despite substantial advances in primary TKA, numerous studies using historic TKA implants suggest only 82% to 89% of primary TKA patients are satisfied. We reexamined this issue to determine if contemporary TKA implants might be associated with improved patient satisfaction. We performed a cross-sectional study of patient satisfaction after 1703 primary TKAs performed in the province of Ontario. Our data confirmed that approximately one in five (19%) primary TKA patients were not satisfied with the outcome. Satisfaction with pain relief varied from 72-86% and with function from 70-84% for specific activities of daily living. The strongest predictors of patient dissatisfaction after primary TKA were expectations not met (10.79 greater risk), a low 1-year WOMAC (2.59 greater risk), preoperative pain at rest (2.49 greater risk) and a postoperative complication requiring hospital readmission (1.99 greater risk). Level of Evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Journal of The Mechanical Behavior of Biomedical Materials, Aug 1, 2010

There is currently considerable interest in the use of highly cross-linked polyethylene (XLPE) ac... more There is currently considerable interest in the use of highly cross-linked polyethylene (XLPE) acetabular liners for total hip arthroplasty (THA). In literature, only a single retrieval analysis of one type of XLPE liner implanted for greater than four years exists. The purpose of the present report is to quantify surface deviations in two XLPE liners implanted during revision THA and retrieved between four to five years after implantation. The two XLPE acetabular liners (Reflection, Smith and Nephew Inc., Memphis, TN) were retrieved from patients undergoing their second revision surgery, at 4.90 and 4.07 years. The retrieved liners and a new, non-implanted, unworn liner of the same size were scanned using micro-computed tomography (micro-CT). Articular surface deviation maps were created by comparing the retrievals to the unworn liner, based on the liner geometry obtained from micro-CT. The linear penetration rates were found to be 0.018 and 0.008 mm/year. Localized scratches and pits with deviations greater than 0.205 mm were also found on the articular surfaces of both liners. The XLPE liners retrieved from the two cases demonstrated low linear penetration rates. Regions with greater focal deviations were also apparent, likely due to third-body wear. The results are consistent with previously published clinical followups of other XLPE liners.