Jason Koh | University of Chicago (original) (raw)

Papers by Jason Koh

Knee Surgery, Sports Traumatology, Arthroscopy, 2017

23 high school or recreational athletes. All patients had a positive posterior impingement test f... more 23 high school or recreational athletes. All patients had a positive posterior impingement test for posterior pain with extension and limitations of activity. Arthroscopic debridement and additional surgical procedures were performed, and patients underwent follow-up visits at a median 51 months (range 14-81). Results Significant improvements were seen in pain, motion, and function. No neurovascular complications were seen related to the arthroscopic debridement. The mean Andrews and Timmerman elbow score improved from 159 ± 27 to 193 ± 11 (p < 0.01). Thirty-five of thirtysix (97%) patients returned to their previous level of activity, including all professional athletes. Conclusions Arthroscopic management of posterior elbow impingement is safe and effective and can return patients, including professional athletes, to high-level athletic activity. Athletes with symptomatic posterior elbow impingement can be successfully and safely treated with arthroscopic debridement and typically will return to preinjury levels of activity. Level of evidence IV.

Journal of Bone and Joint Surgery, 2016

Background: The meniscus is known to increase the contact area and decrease contact pressure in t... more Background: The meniscus is known to increase the contact area and decrease contact pressure in the tibiofemoral compartments of the knee. Radial tears of the meniscal root attachment along with partial resections of the torn meniscal tissue decrease the contact area and increase pressure; however, there is a lack of information on the effects of a horizontal cleavage tear (HCT) and partial leaf meniscectomy of such tears on tibiofemoral contact pressure and contact area. Methods: Twelve fresh-frozen human cadaveric knees were tested under 10 conditions: 5 serial conditions of posterior medial meniscectomy (intact meniscus, HCT, repaired HCT, inferior leaf resection, and resection of both inferior and superior leaves), each at 2 knee flexion angles (0°and 60°) under an 800-N axial load. Tekscan sensors (model 4000) were used to measure the contact pressure and contact area. Results: HCT and HCT repair resulted in small changes in the contact area and an increase in contact pressure compared with the intact condition. Resection of the inferior leaf resulted in significantly decreased contact area (to a mean 82.3% of the intact condition at 0°of flexion and 81.8% at 60°of flexion; p < 0.05) and increased peak contact pressure (a mean 36.3% increase at 0°flexion and 43.2% increase at 60°flexion; p < 0.05) in the medial compartment. Further resection of the remaining superior leaf resulted in additional significant decreases in contact area (to a mean 60.1% of the intact condition at 0°of flexion and 49.7% at 60°of flexion; p < 0.05) and increases in peak contact pressure (a mean 79.2% increase at 0°of flexion and 74.9% increase at 60°of flexion; p < 0.05). Conclusions: Resection of meniscal tissue forming the inferior leaf of an HCT resulted in substantially decreased contact area and increased contact pressure. Additional resection of the superior leaf resulted in a further significant decrease in contact area and increase in contact pressure in the medial compartment. Clinical Relevance: Repair or minimal resection of meniscal tissue of an HCT may be preferred to complete leaf resection to maintain knee tibiofemoral contact mechanics. K nee menisci help to provide optimal knee function and stability through load-sharing, stress distribution, and shock absorption. The meniscus is known to increase the contact area and decrease peak contact pressure in the tibiofemoral joint of the human knee 1-4. A tear in the meniscus often causes mechanical symptoms of catching, locking, effusion, stiffness, and pain. When conservative nonoperative treatment fails, arthroscopy with partial medial meniscectomy is often performed for pain relief 5,6. Partial meniscectomy is one of the most commonly performed orthopaedic procedures in the United States 7. However, a partial meniscectomy is not completely benign. Several studies have revealed its negative effects on the knee joint 4,8-10. Fairbank first noted an increased incidence of degenerative changes on knee radiographs after meniscectomy and questioned the sequela of meniscectomies 9. Studies have examined the biomechanical sequela of sequential partial meniscectomies. Lee et al. showed that peak contact stresses increase proportionally to the amount of meniscus removed in their study Disclosure: This study received no external funding. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked "yes" to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work.

HIP International, 2017

IntroductionRepairs of labral tears are performed for unstable tears, hip instability, and after ... more IntroductionRepairs of labral tears are performed for unstable tears, hip instability, and after detachment concomitant to the treatment of femoroacetabular impingement (FAI), but limited data is known about the strength of repair. This study evaluated the effect of simulated axial weight-bearing on suture anchor based repair of the acetabular labrum.Methods3 cadaveric pelvises underwent creation of a 1.5 cm anterior-superior labral tear in each hip. The tears were then repaired using 2 suture anchors per hip. Following repair, the hip joint underwent axial cyclic loading to 756 N, and were inspected for separation of the labrum from the acetabulum. The strength of the suture anchor repair was evaluated by testing load to failure, in-line with insertion.ResultsUpon visual examination, all 6 repairs remained fully intact following loading with no visible gap formation or damage at the repair site. In all cases an arthroscopic probe could not be inserted under the edge of the repair. ...

Arthroscopy: The Journal of Arthroscopic & Related Surgery, 2016

The American journal of sports medicine

To date, stress injury of the proximal ulna has been infrequently reported as a cause of elbow pa... more To date, stress injury of the proximal ulna has been infrequently reported as a cause of elbow pain in the throwing athlete. We describe a syndrome of osseous stress injury of the proximal ulna in the professional throwing athlete. Retrospective review. We evaluated the clinical, radiographic, and magnetic resonance imaging findings of seven professional baseball players with osseous stress injury of the proximal ulna. Plain radiographs of the involved elbows failed to demonstrate any significant findings. All of the clinically significant lesions were detected with magnetic resonance imaging. In addition, magnetic resonance imaging was found to be of value in following the course of healing of the injuries. All of the lesions originated on the posteromedial aspect of the proximal ulna. The ulnar collateral ligament was intact in all seven athletes. One athlete had two occurrences of this injury. Six of the seven athletes returned to their previous level of play after a nonoperative...

Medicine & Science in Sports & Exercise, 2004

Purpose: Unbalanced actions of the quadriceps components are closely linked to patellar mal-track... more Purpose: Unbalanced actions of the quadriceps components are closely linked to patellar mal-tracking and patellofemoral pain syndrome. However, it is not clear how individual quadriceps components pull and rotate the patella three dimensionally. The purpose of this study was to investigate in vivo and noninvasively patellar tracking induced by individual quadriceps components. Methods: Individual quadriceps component was activated selectively through electrical stimulation at the muscle motor point, and the resulting patellar tracking was measured in vivo and noninvasively in 18 knees of 12 subjects. The in vivo and noninvasively patellar tracking was corroborated with in vivo fluoroscopy and in vitro cadaver measurements. Results: Vastus medialis (VM) mainly pulled the patella first in the medial and second in the proximal directions and vastus lateralis (VL) pulled first in the proximal and second in the lateral directions. The oblique portion (VMO) of the VM pulled the patella mainly medially and the longus portion (VML) more proximally. Medial tilt was the major patellar rotation induced by VMO contraction at full knee extension. With the knee at the more flexed positions, the amplitude of patellar movement induced by comparable quadriceps contractions was reduced significantly compared to that at full knee extension, and VMO changed its main action from extending to flexing the patella. Conclusions: The medial and lateral quadriceps components moved the patella in rather different directions, and rotated the patella differently about the mediolateral tilt and mediolateral rotation axes but similarly in extension. The approach can be used to investigate patellar tracking in vivo and noninvasively in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.

Journal of Orthopaedic Research, 2003

Annals of Joint, 2017

Hill-Sachs lesions can be seen in 65-80% of initial glenohumeral dislocations, and up to 100% of ... more Hill-Sachs lesions can be seen in 65-80% of initial glenohumeral dislocations, and up to 100% of recurrent instability episodes. Engaging Hills-Sachs lesions have been described as those that occur when the long axis of the humeral head defect is parallel to the anterior glenoid rim, allowing the humeral head defect to fall off of the glenoid fossa in essence becoming levered anteroinferiorly to the glenoid fossa. More recently, an arthroscopic technique, which involves soft tissue interposition into the humeral defect, known as remplissage (French: to fill in) procedure, has been developed to prevent Hill-Sachs lesion engagement on the glenoid rim. The purpose of this paper is to review the current literature surrounding the technique, indications, outcomes, and complications of this procedure.

Introducton: Repairs of labral tears are performed for unstable tears, hip instability, and afer ... more Introducton: Repairs of labral tears are performed for unstable tears, hip instability, and afer detachment concomitant to the treatment of femoroacetabular impingement (FAI), but limited data is known about the strength
of repair. This study evaluated the eﬀect of simulated axial weight-bearing on suture anchor based repair of the
acetabular labrum.
Methods: 3 cadaveric pelvises underwent creaton of a 1.5 cm anterior-superior labral tear in each hip. The tears
were then repaired using 2 suture anchors per hip. Following repair, the hip joint underwent axial cyclic loading to
756 N, and were inspected for separaton of the labrum from the acetabulum. The strength of the suture anchor
repair was evaluated by testng load to failure, in-line with inserton.
Results: Upon visual examinaton, all 6 repairs remained fully intact following loading with no visible gap formaton or damage at the repair site. In all cases an arthroscopic probe could not be inserted under the edge of the
repair. The mean failure force of the 12 suture anchors, in-line with inserton, was 154 N ± 44 N.
Conclusions: Acetabular labral suture anchor repairs may be able to immediately withstand the physiological
loads of axial weight-bearing. Labral repair may be able to tolerate axial weight-bearing immediately afer repair,
preserving the strength and integrity of muscles and sof tssues.
Keywords: Biomechanics, Femoroacetabular impingement (FAI), Hip, Labrum, Suture anchor

Injury, 2015

Since the first description of autologous chondrocyte implantation (ACI) in 1994 different method... more Since the first description of autologous chondrocyte implantation (ACI) in 1994 different methods and improvements were established for this regenerative treatment option of large chondral defects. This study analyzes safety and short-term clinical results from characterized ACI using a collagen based biphasic scaffold and evaluates prognostic factors. 433 patients with a mean age of 33.4 years and localized grade III to IV cartilage defects (ICRS classification) in the knee or ankle were included. Mean defect size was 5.9 cm(2). Prior seeding of the scaffold, expanded chondrocytes were characterized by RT-PCR on 6 different marker genes (type I and II collagen, aggrecan, interleukin-1 β (IL-1β), vascular endothelial growth factor receptor 1 (FLT-1) and bone sialoprotein-2 (BSP-2)). Clinical outcome was evaluated using a questionnaire for defect history, basic demographics, time elapsed from surgery, 10-point outcome assessments of pain, function and swelling. Moreover, adverse events (AEs) or subsequent treatments were recorded and analysed. Patients improved significantly over baseline (p < 0.0001) in pain, function and swelling. Subjects with later than 12 months follow-up reported nominally greater mean changes. Graft failure incidence was 6% for patients with greater than one year follow-up. Graft-related complications were significantly higher for patellar (p < 0.0001) and degenerative defects (p = 0.005). Elevated expression of FLT-1 (p = 0.02) or IL-1 β mRNA (p = 0.03) was associated with graft-related AEs. A bor derline association was found for low collagen type II expression (p = 0.08). Early graft-related AEs after ACI with a biphasic collagen scaffold are related to defect type, location and marker gene expression. The levels of significance observed for gene expression with respect to graft-related AEs were subordinate to those identified in the analysis of lesion history and location.

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2010

Anterior cruciate ligament (ACL) injuries have become more common in recent years as more young p... more Anterior cruciate ligament (ACL) injuries have become more common in recent years as more young people participate in risky sporting activities [1]. Most ACL injuries occur as a result of noncontact mechanisms. Previous in vitro studies of ACL strain have found significant increases in ACL strain primarily with anterior directed force on the tibia relative to the femur and with internal rotation and often with valgus torque [2,3]. However, there remains significant controversy over the mechanisms of ACL failure and the forces on the knee that lead to injury. Some studies have also shown that isolated valgus loading may not load the ACL strongly. The goal of this study was to investigate the mechanism underlying valgus-related ACL injuries. An improved understanding of ACL failure may lead to improved ACL injury prevention programs. A novel 6 degrees of freedom (DOF) knee driving robot was developed in this study with a unique multi-axis simultaneous torque/position control. It was f...

Clinics in Sports Medicine, 2014

Patella instability can cause significant pain and functional limitations. Several factors can pr... more Patella instability can cause significant pain and functional limitations. Several factors can predispose to patella instability, such as ligamentous laxity, increased anterior TT-TG distance, patella alta, and trochlear dysplasia. Acquired factors include MPFL injury or abnormal quadriceps function. In many cases, first-time dislocation can successfully be managed with physical therapy and other nonoperative management; however, more than one dislocation significantly increases the chance of recurrence. Surgical management can improve stability, but should be tailored to the injuries and anatomic risk factors for recurrent dislocation. Isolated lateral release is not supported by current literature and increases the risk of iatrogenic medial instability. Medial repair is usually reserved for patients with largely normal anatomy. MPFL reconstruction can successfully stabilize patients with medial soft tissue injury but is a technically demanding procedure with a high complication rate and risks of pain and arthrosis. Tibial tubercle osteotomy can address bony malalignment and also unload certain articular cartilage lesions while improving stability. Trochleoplasty may be indicated in individuals with a severely dysplastic trochlea that cannot otherwise be stabilized. A combination of procedures may be necessary to fully address the multiple factors involved in causing pain, loss of function, and risk of recurrence in patients with patellar instability.

The Journal of Bone and Joint Surgery (American), 2012

American Journal of Sports Medicine, 2004

Incongruity of the articular cartilage following osteochondral transplantation affects surface co... more Incongruity of the articular cartilage following osteochondral transplantation affects surface contact pressure. An 80 N load was applied for 120 seconds to the femoral condyles of 10 swine knees. Contact pressures were measured using Fuji prescale film. Seven conditions were tested: (1) intact articular surface; (2) 4.5-mm diameter defect; (3) grafted with 4.5-mm diameter plug elevated 1 mm above adjacent cartilage; (4) plug elevated 0.5 mm; (5) plug flush; (6) plug sunk 0.5 mm below surface; and (7) sunk 1.0 mm. Peak contact pressures were significantly (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001) elevated by approximately 20% after defect creation and were reduced to normal when plugs were flush. There were large and significant (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.001) increases in pressure with plugs elevated 1 and 0.5 mm. Contact pressures with plugs sunk 0.5 and 1 mm were significantly (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.01) higher than intact cartilage but were significantly (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;.01) lower than an empty defect. Normal contact pressures and patterns can be duplicated with flush articular surface grafts. However, small incongruities, particularly when the plug is elevated, can lead to significantly increased pressure. This reinforces the importance of articular surface congruity in the initial biomechanical state following osteochondral implantation.

The Knee, Jan 6, 2015

Anterior cruciate ligament injuries are closely associated with excessive loading and motion abou... more Anterior cruciate ligament injuries are closely associated with excessive loading and motion about the off axes of the knee, i.e. tibial rotation and knee varus/valgus. However, it is not clear about the 3-D mechanical actions of the lateral and medial hamstring muscles and their differences in loading the ACL. The purpose of this study was to investigate the change in anterior cruciate ligament strain induced by loading the lateral and medial hamstrings individually. Seven cadaveric knees were investigated using a custom testing apparatus allowing for six degree-of-freedom tibiofemoral motion induced by individual muscle loading. With major muscles crossing the knee loaded moderately, the medial and lateral hamstrings were loaded independently to 200N along their lines of actions at 0°, 30°, 60° and 90° of knee flexion. The induced strain of the anterior cruciate ligament was measured using a differential variable reluctance transducer. Tibiofemoral kinematics was monitored using a...

Clinical Orthopaedics and Related Research®, 2015

Few studies have analyzed the association between elevated BMI and complications after total shou... more Few studies have analyzed the association between elevated BMI and complications after total shoulder arthroplasty (TSA). Previous studies have not consistently arrived at the same conclusion regarding whether obesity is associated with a greater number of postoperative complications. We used a national surgical database to compare the 30-day complication profile and hospitalization outcomes after primary TSA among patients in different BMI categories. We asked: (1) Is obesity associated with an increased risk of complications within 30 days of primary TSA? (2) Is obesity associated with increased operative time? The American College of Surgeons National Surgical Quality Improvement Program(®) database for 2006 to 2012 was queried to identify all patients who underwent a primary TSA for osteoarthritis of the shoulder. The ACS-NSQIP(®) database was selected for this study as it is a nationally representative database that provides prospectively collected perioperative data and a comprehensive patient medical profile. Exclusion criteria included revision TSA, infection, tumor, or fracture. We analyzed 4796 patients who underwent a primary TSA for osteoarthritis of the shoulder. Patients who underwent a TSA were divided in four BMI categories: normal (18.5-25 kg/m(2)), overweight (25-30 kg/m(2)), obesity Class 1 (30-35 kg/m(2)), and obesity Class 2 or greater (&amp;amp;amp;amp;amp;amp;amp;gt; 35 kg/m(2)). Perioperative hospitalization data and 30-day postoperative complications were compared among different BMI classes. Differences in patient demographics, preoperative laboratory values, and preexisting patient comorbidities also were analyzed among different BMI groups, and multivariate analysis was used to adjust for any potential confounding variables. There was no association between BMI and 30-day complications after surgery (normal as reference, overweight group relative risk: 0.57 [95% CI, 0.30-1.06], p = 0.076; obesity Class 1 relative risk: 0.52 [95% CI, 0.26-1.03], p = 0.061; obesity Class 2 or greater relative risk: 0.54 [95% CI, 0.25-1.17], p = 0.117). However, greater BMI was associated with longer surgical times (for normal BMI control group: 110 minutes, SD, 42 minutes; overweight group: 115 minutes, SD, 46 minutes, mean difference to control: 5 minutes [95% CI, -1 to 10 minutes], p = 0.096; obesity Class 1: 120 minutes, SD, 43 minutes, mean difference: 10 minutes [95% CI, 5-15 minutes], p &amp;amp;amp;amp;amp;amp;amp;lt; 0.001; obesity Class 2 or greater: 122 minutes, SD, 45 minutes, mean difference: 12 minutes [95% CI, 6-18 minutes], p &amp;amp;amp;amp;amp;amp;amp;lt; 0.001). Although the surgical time increased for patients with greater BMI, the 30-day complications and perioperative hospitalization data after TSA were not different in patients with increased BMI levels. Obesity alone should not be a contraindication for TSA, and obese patients can expect similar incidences of postoperative complications. The preoperative medical optimization plan should be consistent with that of patients who are not obese who undergo TSA. Level III, therapeutic study.

Of the multiple murine models of autoimmunity, the three most closely resembling human systemic l... more Of the multiple murine models of autoimmunity, the three most closely resembling human systemic lupus erythematosus (SLE) are the MRL/lpr, New Zealand Black/White F(1), and male BXSB. Although these strains share many disease characteristics, no common cellular defect has previously been found in prediseased mice from all these strains. We show in this study that macrophages from prediseased mice of all three SLE-prone strains, as well as macrophages from mice whose genomes contribute to the development of SLE (MRL/+, New Zealand White, New Zealand Black, female BXSB, and LG/J), have an identical and profound defect in cytokine expression that is triggered by apoptotic cells. Strikingly, none of 13 nonautoimmune strains tested exhibited this defect. Given that apoptotic Ags have been increasingly recognized as the target of autoantibodies, a defect in cytokine expression that is triggered by apoptotic cells has broad potential to upset the balance between tolerance and immunity.

Osteoarthritis and Cartilage, 2007

Journal of Shoulder and Elbow Surgery, 2014