Fred Wentorf - Academia.edu (original) (raw)
Papers by Fred Wentorf
Journal of wrist surgery, Jul 31, 2014
A loss of forearm rotation, particularly supination, is frequently seen as a consequence of dista... more A loss of forearm rotation, particularly supination, is frequently seen as a consequence of distal radius fractures. 1 This may cause functional difficulties in daily activities such as supporting heavy loads, receiving coins or other small objects, and perineal hygiene. 2 Previous studies have identified distal radius fracture malalignment as a cause of restriction in forearm rotation and have implicated distal radioulnar joint (DRUJ) incongruency or capsular scarring. 3,4 When bone alignment of the distal radius and ulna have been maintained or restored, Kleinman and Graham have implicated DRUJ capsular scarring alone as a cause of limited forearm rotation. 5 Separately, a distal radius fracture with or without open reduction and plating may damage the pronator quadratus (PQ) muscle secondary to fracture displacement. Experientially, we have noted during open surgery for fracture management that the PQ muscle is often contused, lacerated, or entrapped in the fracture site. It seems probable that scarring of the muscle would limit its function. Research examining this question related to any muscle is not abundant. However, in a rabbit model, Chung et al showed that muscle injury left to heal in shortened position would restrict function and that proactive maintenance of muscle length was necessary to preserve best function. 6 The purpose of our study was to determine whether restricted excursion of the PQ muscle alone could affect forearm rotation. Materials and Methods Specimen Preparation Eight adult, fresh-frozen, unmatched upper extremities were amputated at the mid-humerus. All of the specimens used appeared free from any prior trauma. The skin, subcutaneous tissue, and forearm flexor and extensor muscles were excised to the level of the wrist joint. The biceps tendon, elbow Keywords ► pronator quadratus ► distal radius fractures ► volar approach to ORIF of distal radius ► fracture ► complications of distal radius fracture ► forearm rotation
Spine, Aug 1, 2000
Study Design. A biomechanical study of the rigidity of various scoliosis constructs instrumented ... more Study Design. A biomechanical study of the rigidity of various scoliosis constructs instrumented with and without caudal pedicle screw anchors and with none, one, or two cross-link devices. Objectives. To determine whether the increased torsional rigidity provided by distal pedicle screw fixation might make cross-linking unnecessary. Summary of Background Data. Pedicle screws and cross-linking devices have been shown to increase the structural rigidity of spinal constructs. Their relative contributions to scoliosis construct rigidity has not been determined. Methods. "Short" (T2-T11) and "long" (T2-L3) scoliosis constructs were mounted on an industrially fabricated spine model and tested in a hydraulic testing machine. Four different short and four different long constructs were tested: hooks only, hooks with concave side thoracic sublaminar wires, hooks with distal pedicle screw anchors, and hooks, distal pedicle screw anchors, and concave thoracic sublaminar wires. There were four iterations for each construct tested: no cross-links, one superior cross-link at T4-T5, one inferior cross-link at T9-T10, and two cross-links. Torsional rigidity was tested by applying a rotational torque at T2. Vertebral body motion was recorded with a three-dimensional video analysis system. Results. Constructs with distal pedicle screws were statistically more rigid in torsion than those with hooks as distal anchors. The additional torsional rigidity from one or more cross-links was negligible compared with that provided by pedicle screws. Conclusions. With pedicle screws as distal anchors in scoliosis constructs, cross-linking with one or two devices adds very little additional rotational stiffness and may be unnecessary in many cases.
The Physician and Sportsmedicine, Feb 15, 2011
An athlete who has an acute knee injury should be assessed rapidly on the field and then more tho... more An athlete who has an acute knee injury should be assessed rapidly on the field and then more thoroughly on the sideline or in the training room. On-the-field assessment includes questions about the mechanism of injury and any similar previous injuries, a visual check for knee deformities and skin injuries, a neurovascular exam, and, ideally, tests for flexion and hyperextension. On the sideline or in the training room, standard physical tests are likely to reveal any significant injuries. These include the patellar apprehension, Lachman, posterior sag, quadriceps active, posterior drawer, posterolateral drawer, valgus and varus stress, pivot-shift, and dial tests.
The Journal of Hand Surgery, Sep 1, 1999
Flexor carpi ulnaris (FCU) transfer to the extensor carpi radialis brevis (ECRB) and/or the exten... more Flexor carpi ulnaris (FCU) transfer to the extensor carpi radialis brevis (ECRB) and/or the extensor carpi radialis longus (ECRL) has been commonly used to provide wrist extension. The ability of this wrist extension transfer to also provide forearm supination has been inferred but not formally investigated. This laboratory study investigated the forearm supination effect of FCU transfer to the ECRB and to the ECRL in a cadaveric model. Two vectors of pull were investigated: freeing either the distal one third or the distal two thirds of the FCU ulnar origin. Five fresh-frozen, above-elbow, non-matched cadaveric specimens placed in a mounting device that allowed the arm to rotate about its ulnar axis starting from a full pronated position were measured for resultant supination after tendon transfer and loading. This study showed that the transfer of the FCU into either the ECRB or the ECRL resulted in no significant difference in maximum supination. The vector of origin, however, did significantly affect the maximum supination obtained. Releasing the distal two thirds of the FCU ulnar origin resulted in a mean supination that was significantly greater than the mean supination achieved with releasing the distal one third of the FCU ulnar origin. We concluded that in the cadaveric model, transfer of the FCU into either the ECRB or ECRL provided similar resultant supination and that freeing the distal two thirds of the FCU ulnar origin provided significantly more supination than freeing only the distal one third. For the hand surgeon treating wrist flexion in combination with forearm pronation deformity, transfer of the FCU into the ECRB and/or the ECRL can be used to concomitantly provide wrist extension and forearm supination.
Total ankle replacement designs have evolved since their introduction in the mid 1970s. While the... more Total ankle replacement designs have evolved since their introduction in the mid 1970s. While the first-generation total ankle replacement (TAR) designs had unacceptably high failure rates, recent designs have demonstrated improved outcomes [1]. Two philosophies are commonly used in TAR design: mobile-bearing and fixed-bearing. Unlike mobile-bearing designs which have two articulating surfaces, fixed-bearing designs have only one articulating surface. While fixed-bearing designs have lower risk of dislocation than mobile-bearing designs, the single articulation feature can produce higher contact stress on the articulating surface, increasing the potential for polyethylene wear [1, 2].
Knee Surgery, Sports Traumatology, Arthroscopy, Oct 2, 2014
appropriate implant component size, having the appropriate size available and the effect of downs... more appropriate implant component size, having the appropriate size available and the effect of downsizing. The laxity of the implanted knee contributes to how the implant feels to the patient and ultimately the patient's satisfaction with their new knee.
Annals of Biomedical Engineering, May 1, 1998
The effects of osteoarthrosis inducing surgery on the kinematics of the rabbit knee were evaluate... more The effects of osteoarthrosis inducing surgery on the kinematics of the rabbit knee were evaluated in vivo. A video motion analysis system was used to track reflective markers attached to two pins fixed in both femur and tibia, and from these data knee kinematics were computed. The control for all measurements was the gait after pins were implanted, but the knee was unaltered. Both a release of the anterior cruciate ligament and a partial medial meniscectomy were then performed, and the animals' gait was recorded at 4, 8 and 12 weeks after knee surgery. Knee kinematics were described by three translations and three rotations and were analyzed in terms of maximum and minimum values and range of motion. Statistical comparisons of these data between control and operated knees were made using Wilcoxon's signed rank test. Results showed an initial increase in maximum anterior displacement which returned to normal after 12 weeks. In addition there was a persistent increase in knee adduction and an increase in the minimum value of external rotation over the 12 week period. At 12 weeks after surgery there was no change in range of any measurable kinematic parameter. Overall, the changes in joint kinematics following partial medial meniscectomy and release of the anterior cruciate ligament were small, suggesting that altered joint kinematics might not be a critical factor in the development of osteoarthrosis in this animal model.
Blackwell Science Ltd eBooks, Jan 28, 2008
INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for th... more INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for the development of shoulder pain and associated rotator cuff tendonitis is compression of the soft tissues within the subacromial space of the shoulder as the arm is elevated. However, current methods of subacromial space measurement are limited. The purpose of this study was to develop and validate a volumetric description of the subacromial space at the shoulder, and describe changes in this space during passive humeral scapular plane abduction.
Journal of Bone and Joint Surgery-british Volume, 2017
Introduction In total knee arthroplasty (TKA), non-cemented implants rely on initial fixation to ... more Introduction In total knee arthroplasty (TKA), non-cemented implants rely on initial fixation to stabilize the implant in order to facilitate biologic fixation. The initial fixation can be affected by several different factors from type of implant surface, implant design, patient factors, and surgical technique. The initial fixation is traditionally quantified by measuring the motion between the implant and underlying bone during loading (micromotion). Extraction force has also been quantified for cementless devices. The question remains does an increase or decrease in extraction force affect micromotion based on the fact that most loading at the knee joint is in compression. The objective of this research is to investigate if there is any correlation between extraction force and implant micromotion. Methods The relationship between extraction force and micromotion was evaluated by performing a series of experiments using a synthetic bone analog and a tibial baseplate with hexagon p...
Journal of Bone and Joint Surgery-british Volume, 2017
Purpose The goal of Total Ankle Arthroplasty (TAA) is to relieve pain and restore healthy functio... more Purpose The goal of Total Ankle Arthroplasty (TAA) is to relieve pain and restore healthy function of the intact ankle. Restoring intact ankle kinematics is an important step in restoring normal function to the joint. Previous robotic laxity testing and functional activity simulation showed the intact and implanted motion of the tibia relative to the calcaneus is similar. However there is limited data on the tibiotalar joint in either the intact or implanted state. This current study compares modern anatomically designed TAA to intact tibiotalar motion. Method A robotic testing system including a 6 DOF load cell (AMTI, Waltham, MA) was used to evaluate a simulated functional activity before and after implantation of a modern anatomically designed TAA (Figure 1). An experienced foot and ankle surgeon performed TAA on five fresh-frozen cadaveric specimens. The specimen tibia and fibula were potted and affixed to the robot arm (KUKA Robotics Inc., Augsburg, Germany) while the calcaneus...
Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chro... more Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chromium alloys articulating on ultrahigh molecular weight polyethylene (UHMWPE). Articulation of these surfaces during in vivo loading can generate UHMWPE wear particles, which may then result in osteolysis and component loosening [1]. Osteolysis has been observed following TAA in 15-22% of patient populations [2,3]. Use of highly crosslinked UHMWPE (HXPE) has been shown to reduce wear in other joint systems [4] compared to conventional UHMWPE (CPE); and thus has the potential to improve wear performance of TAA. The goal of this study was to quantify the impact of crosslinking on wear within TAA using loading parameters biomechanically relevant to the ankle joint.
INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for th... more INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for the development of shoulder pain and associated rotator cuff tendonitis is compression of the soft tissues within the subacromial space of the shoulder as the arm is elevated. However, current methods of subacromial space measurement are limited. The purpose of this study was to develop and validate a volumetric description of the subacromial space at the shoulder, and describe changes in this space during passive humeral scapular plane abduction.
Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chro... more Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chromium alloys articulating on ultrahigh molecular weight polyethylene (UHMWPE). Articulation of these surfaces during in vivo loading can generate UHMWPE wear particles, which may then result in osteolysis and component loosening [1]. Osteolysis has been observed following TAA in 15-22% of patient populations [2,3]. Use of highly crosslinked UHMWPE (HXPE) has been shown to reduce wear in other joint systems [4] compared to conventional UHMWPE (CPE); and thus has the potential to improve wear performance of TAA. The goal of this study was to quantify the impact of crosslinking on wear within TAA using loading parameters biomechanically relevant to the ankle joint.
Thedevelopment of an in vivo animalmodel of posterolateral knee instability is desired for devisi... more Thedevelopment of an in vivo animalmodel of posterolateral knee instability is desired for devising effective interventions for this injury. Sequential sectioning of the popliteus tendon, lateral collateral ligament, and lateral capsule was done in cadaveric goat knees to create knee joint instability, followed by in vivo studies (Studies 1 and 2) of 7 and 3 months duration, respectively. In Study 1, the popliteus tendon and lateral collateral ligament were sectioned; in Study 2, these structures as well as the lateral joint capsulewere sectioned. Biomechanical testing and histological assessments were done to determine the severity of the instability and the morphological changes. Sectioning the lateral collateral ligament and popliteus tendon (Study 1) resulted in a significant increase in varus instability at 908. Sectioning the lateral collateral ligament, popliteus tendon, and lateral capsule (Study 2) resulted in significant varus instability at 308, 608, and 908, and signific...
The American Journal of Sports Medicine, 1999
To determine if untreated grade III injuries of the posterolateral structures contribute to incre... more To determine if untreated grade III injuries of the posterolateral structures contribute to increased force on an anterior cruciate ligament graft, we measured the force in the graft in cadaveric knees during joint loading after reconstruction with otherwise intact structures and in the same reconstructed knees after selected cutting of specific posterolateral knee structures. Tests were first performed on the knee with the posterolateral structures intact and then after sequential sectioning of the fibular collateral ligament, popliteofibular ligament, and popliteus tendon. The graft force was significantly higher after fibular collateral ligament transection during varus loading at both 0° and 30° of knee flexion than it was for the same loading of the joint with intact posterolateral structures. In addition, coupled loading of varus and internal rotation moments at 0° and 30° of flexion further increased graft force beyond that with varus force alone. The increase in graft force ...
The American Journal of Sports Medicine, 2000
The purpose of this study was to contrast the magnetic resonance imaging appearance of uninjured ... more The purpose of this study was to contrast the magnetic resonance imaging appearance of uninjured components of the posterolateral knee with that of injured structures, and to assess the accuracy of magnetic resonance imaging in identifying posterolateral knee complex injuries. Thin-slice coronal oblique T1-weighted images through the entire fibular head were used to identify the posterolateral structures in seven uninjured knees. The appearance of corresponding grade III injuries to these structures was identified prospectively in 20 patients and verified at the time of surgical reconstruction. The sensitivity, specificity, and accuracy of imaging for the most frequently injured posterolateral knee structures in this series were as follows: iliotibial band-deep layer (91.7%, 100%, and 95%), short head of the biceps femoris-direct arm (81.3%, 100%, and 85%), short head of the biceps femoris-anterior arm (92.9%, 100%, and 95%), midthird lateral capsular ligament-meniscotibial (93.8%, ...
The American Journal of Sports Medicine, 2000
To determine if helmet removal causes a significant increase in lordosis of the cervical spine in... more To determine if helmet removal causes a significant increase in lordosis of the cervical spine in ice hockey players, we radiographically assessed the position of the cervical spine in subjects immobilized to a standard spine backboard wearing shoulder pads both with and without a helmet. Ten adult male volunteers (ages, 18 to 28 years) with no previous history of cervical spine injuries were fitted with an appropriately sized ice hockey helmet and shoulder pads and immobilized in a supine position to a standard spine backboard. Computerized tomographic lateral scout scans were obtained of the cervical spine for three conditions: 1) no equipment (control), 2) helmet and shoulder pads, and 3) shoulder pads only (helmet removed). With the helmet removed and the shoulder pads remaining, a significant increase in C2 to C7 lordosis was found when compared with the other two conditions. Individual segmental measurements revealed a significant increase in cervical lordosis at the C6—7 leve...
Bone Joint Journal Orthopaedic Proceedings Supplement, Dec 1, 2013
Introduction: Following total knee arthroplasty, patients often complain of an unnatural feeling ... more Introduction: Following total knee arthroplasty, patients often complain of an unnatural feeling in their knee joint, which in turn limits their activities [Noble et al, CORR 2006]. To develop an implant design that recreates the motion of the natural knee, both the functional kinematics as well as the laxity of the joint need to be understood. In vitro testing that accurately quantifies the functional kinematics and laxity of the knee joint can facilitate development of implant designs that are more likely to result in a natural feeling, reconstructed knee. The objective of this study is to demonstrate that robotic in vitro testing can produce clinically relevant functional kinematics and joint laxities. Methods: All testing was performed using a KUKA (KUKA Robotics, Augsburg, Germany) 6 degree of freedom robotic arm and a six degree of freedom load cell (ATI Industrial Automation, Apex, North Carolina, USA), attached to the arm (Figure 1). FUNCTIONAL KINEMATICS: Eight cadaveric specimens implanted with contemporary cruciate retaining implants were used for this evaluation. The functional activity, lunge, was simulated using kinematic control for flexion/extension and force-torque control for the other degrees of freedom. The inputs for the force-torque control were obtained from e-tibia data from live patients during the lunge activity [Varadarajan et al, J Biomech 2008]. At a given flexion angle, the robot moved in force-torque control to obtain the desired values within given tolerances (± 2.5N & ± 0.1 Nm). When these tolerances were met the position of femur with respect to the tibia was recorded and the knee flexed to the next level. The lunge simulation began at full extension and ended at 120 degrees of knee flexion, through 1 degree increments. The kinematic data from the contemporary CR implants were compared to in vivo kinematics of patients that were implanted with the same knee replacements performing a lunge activity [Varadarajan et al, Med Eng Phys 2009]. JOINT LAXITY: Eight native, unimplanted knees were used for this evaluation. Joint laxity of the knee joint was evaluated at 0, 30, 60, 90, and 120 degrees of knee flexion by applying various loads to the tibia and quantifying the resulting motion of the tibia. The resulting laxities were compared to various knee laxity studies in the literature. Results: The in vitro functional kinematics correlated well with the in vivo results. Femoral external rotation and tibial varus angulation were found not be statistically different between the in vitro and in vivo results (Figure 2). The laxities measurements correlated well with reported values in the literature. Discussion: In vitro robotic evaluations allow for a better understanding of the motion at the knee joint by simulating clinically relevant functional kinematics as well as quantifying joint laxities in the same testing system. Both of these metrics are needed to understand how the knee moves and should be used to evaluate the performance of new knee designs (Figure 3).
Journal of wrist surgery, Jul 31, 2014
A loss of forearm rotation, particularly supination, is frequently seen as a consequence of dista... more A loss of forearm rotation, particularly supination, is frequently seen as a consequence of distal radius fractures. 1 This may cause functional difficulties in daily activities such as supporting heavy loads, receiving coins or other small objects, and perineal hygiene. 2 Previous studies have identified distal radius fracture malalignment as a cause of restriction in forearm rotation and have implicated distal radioulnar joint (DRUJ) incongruency or capsular scarring. 3,4 When bone alignment of the distal radius and ulna have been maintained or restored, Kleinman and Graham have implicated DRUJ capsular scarring alone as a cause of limited forearm rotation. 5 Separately, a distal radius fracture with or without open reduction and plating may damage the pronator quadratus (PQ) muscle secondary to fracture displacement. Experientially, we have noted during open surgery for fracture management that the PQ muscle is often contused, lacerated, or entrapped in the fracture site. It seems probable that scarring of the muscle would limit its function. Research examining this question related to any muscle is not abundant. However, in a rabbit model, Chung et al showed that muscle injury left to heal in shortened position would restrict function and that proactive maintenance of muscle length was necessary to preserve best function. 6 The purpose of our study was to determine whether restricted excursion of the PQ muscle alone could affect forearm rotation. Materials and Methods Specimen Preparation Eight adult, fresh-frozen, unmatched upper extremities were amputated at the mid-humerus. All of the specimens used appeared free from any prior trauma. The skin, subcutaneous tissue, and forearm flexor and extensor muscles were excised to the level of the wrist joint. The biceps tendon, elbow Keywords ► pronator quadratus ► distal radius fractures ► volar approach to ORIF of distal radius ► fracture ► complications of distal radius fracture ► forearm rotation
Spine, Aug 1, 2000
Study Design. A biomechanical study of the rigidity of various scoliosis constructs instrumented ... more Study Design. A biomechanical study of the rigidity of various scoliosis constructs instrumented with and without caudal pedicle screw anchors and with none, one, or two cross-link devices. Objectives. To determine whether the increased torsional rigidity provided by distal pedicle screw fixation might make cross-linking unnecessary. Summary of Background Data. Pedicle screws and cross-linking devices have been shown to increase the structural rigidity of spinal constructs. Their relative contributions to scoliosis construct rigidity has not been determined. Methods. "Short" (T2-T11) and "long" (T2-L3) scoliosis constructs were mounted on an industrially fabricated spine model and tested in a hydraulic testing machine. Four different short and four different long constructs were tested: hooks only, hooks with concave side thoracic sublaminar wires, hooks with distal pedicle screw anchors, and hooks, distal pedicle screw anchors, and concave thoracic sublaminar wires. There were four iterations for each construct tested: no cross-links, one superior cross-link at T4-T5, one inferior cross-link at T9-T10, and two cross-links. Torsional rigidity was tested by applying a rotational torque at T2. Vertebral body motion was recorded with a three-dimensional video analysis system. Results. Constructs with distal pedicle screws were statistically more rigid in torsion than those with hooks as distal anchors. The additional torsional rigidity from one or more cross-links was negligible compared with that provided by pedicle screws. Conclusions. With pedicle screws as distal anchors in scoliosis constructs, cross-linking with one or two devices adds very little additional rotational stiffness and may be unnecessary in many cases.
The Physician and Sportsmedicine, Feb 15, 2011
An athlete who has an acute knee injury should be assessed rapidly on the field and then more tho... more An athlete who has an acute knee injury should be assessed rapidly on the field and then more thoroughly on the sideline or in the training room. On-the-field assessment includes questions about the mechanism of injury and any similar previous injuries, a visual check for knee deformities and skin injuries, a neurovascular exam, and, ideally, tests for flexion and hyperextension. On the sideline or in the training room, standard physical tests are likely to reveal any significant injuries. These include the patellar apprehension, Lachman, posterior sag, quadriceps active, posterior drawer, posterolateral drawer, valgus and varus stress, pivot-shift, and dial tests.
The Journal of Hand Surgery, Sep 1, 1999
Flexor carpi ulnaris (FCU) transfer to the extensor carpi radialis brevis (ECRB) and/or the exten... more Flexor carpi ulnaris (FCU) transfer to the extensor carpi radialis brevis (ECRB) and/or the extensor carpi radialis longus (ECRL) has been commonly used to provide wrist extension. The ability of this wrist extension transfer to also provide forearm supination has been inferred but not formally investigated. This laboratory study investigated the forearm supination effect of FCU transfer to the ECRB and to the ECRL in a cadaveric model. Two vectors of pull were investigated: freeing either the distal one third or the distal two thirds of the FCU ulnar origin. Five fresh-frozen, above-elbow, non-matched cadaveric specimens placed in a mounting device that allowed the arm to rotate about its ulnar axis starting from a full pronated position were measured for resultant supination after tendon transfer and loading. This study showed that the transfer of the FCU into either the ECRB or the ECRL resulted in no significant difference in maximum supination. The vector of origin, however, did significantly affect the maximum supination obtained. Releasing the distal two thirds of the FCU ulnar origin resulted in a mean supination that was significantly greater than the mean supination achieved with releasing the distal one third of the FCU ulnar origin. We concluded that in the cadaveric model, transfer of the FCU into either the ECRB or ECRL provided similar resultant supination and that freeing the distal two thirds of the FCU ulnar origin provided significantly more supination than freeing only the distal one third. For the hand surgeon treating wrist flexion in combination with forearm pronation deformity, transfer of the FCU into the ECRB and/or the ECRL can be used to concomitantly provide wrist extension and forearm supination.
Total ankle replacement designs have evolved since their introduction in the mid 1970s. While the... more Total ankle replacement designs have evolved since their introduction in the mid 1970s. While the first-generation total ankle replacement (TAR) designs had unacceptably high failure rates, recent designs have demonstrated improved outcomes [1]. Two philosophies are commonly used in TAR design: mobile-bearing and fixed-bearing. Unlike mobile-bearing designs which have two articulating surfaces, fixed-bearing designs have only one articulating surface. While fixed-bearing designs have lower risk of dislocation than mobile-bearing designs, the single articulation feature can produce higher contact stress on the articulating surface, increasing the potential for polyethylene wear [1, 2].
Knee Surgery, Sports Traumatology, Arthroscopy, Oct 2, 2014
appropriate implant component size, having the appropriate size available and the effect of downs... more appropriate implant component size, having the appropriate size available and the effect of downsizing. The laxity of the implanted knee contributes to how the implant feels to the patient and ultimately the patient's satisfaction with their new knee.
Annals of Biomedical Engineering, May 1, 1998
The effects of osteoarthrosis inducing surgery on the kinematics of the rabbit knee were evaluate... more The effects of osteoarthrosis inducing surgery on the kinematics of the rabbit knee were evaluated in vivo. A video motion analysis system was used to track reflective markers attached to two pins fixed in both femur and tibia, and from these data knee kinematics were computed. The control for all measurements was the gait after pins were implanted, but the knee was unaltered. Both a release of the anterior cruciate ligament and a partial medial meniscectomy were then performed, and the animals' gait was recorded at 4, 8 and 12 weeks after knee surgery. Knee kinematics were described by three translations and three rotations and were analyzed in terms of maximum and minimum values and range of motion. Statistical comparisons of these data between control and operated knees were made using Wilcoxon's signed rank test. Results showed an initial increase in maximum anterior displacement which returned to normal after 12 weeks. In addition there was a persistent increase in knee adduction and an increase in the minimum value of external rotation over the 12 week period. At 12 weeks after surgery there was no change in range of any measurable kinematic parameter. Overall, the changes in joint kinematics following partial medial meniscectomy and release of the anterior cruciate ligament were small, suggesting that altered joint kinematics might not be a critical factor in the development of osteoarthrosis in this animal model.
Blackwell Science Ltd eBooks, Jan 28, 2008
INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for th... more INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for the development of shoulder pain and associated rotator cuff tendonitis is compression of the soft tissues within the subacromial space of the shoulder as the arm is elevated. However, current methods of subacromial space measurement are limited. The purpose of this study was to develop and validate a volumetric description of the subacromial space at the shoulder, and describe changes in this space during passive humeral scapular plane abduction.
Journal of Bone and Joint Surgery-british Volume, 2017
Introduction In total knee arthroplasty (TKA), non-cemented implants rely on initial fixation to ... more Introduction In total knee arthroplasty (TKA), non-cemented implants rely on initial fixation to stabilize the implant in order to facilitate biologic fixation. The initial fixation can be affected by several different factors from type of implant surface, implant design, patient factors, and surgical technique. The initial fixation is traditionally quantified by measuring the motion between the implant and underlying bone during loading (micromotion). Extraction force has also been quantified for cementless devices. The question remains does an increase or decrease in extraction force affect micromotion based on the fact that most loading at the knee joint is in compression. The objective of this research is to investigate if there is any correlation between extraction force and implant micromotion. Methods The relationship between extraction force and micromotion was evaluated by performing a series of experiments using a synthetic bone analog and a tibial baseplate with hexagon p...
Journal of Bone and Joint Surgery-british Volume, 2017
Purpose The goal of Total Ankle Arthroplasty (TAA) is to relieve pain and restore healthy functio... more Purpose The goal of Total Ankle Arthroplasty (TAA) is to relieve pain and restore healthy function of the intact ankle. Restoring intact ankle kinematics is an important step in restoring normal function to the joint. Previous robotic laxity testing and functional activity simulation showed the intact and implanted motion of the tibia relative to the calcaneus is similar. However there is limited data on the tibiotalar joint in either the intact or implanted state. This current study compares modern anatomically designed TAA to intact tibiotalar motion. Method A robotic testing system including a 6 DOF load cell (AMTI, Waltham, MA) was used to evaluate a simulated functional activity before and after implantation of a modern anatomically designed TAA (Figure 1). An experienced foot and ankle surgeon performed TAA on five fresh-frozen cadaveric specimens. The specimen tibia and fibula were potted and affixed to the robot arm (KUKA Robotics Inc., Augsburg, Germany) while the calcaneus...
Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chro... more Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chromium alloys articulating on ultrahigh molecular weight polyethylene (UHMWPE). Articulation of these surfaces during in vivo loading can generate UHMWPE wear particles, which may then result in osteolysis and component loosening [1]. Osteolysis has been observed following TAA in 15-22% of patient populations [2,3]. Use of highly crosslinked UHMWPE (HXPE) has been shown to reduce wear in other joint systems [4] compared to conventional UHMWPE (CPE); and thus has the potential to improve wear performance of TAA. The goal of this study was to quantify the impact of crosslinking on wear within TAA using loading parameters biomechanically relevant to the ankle joint.
INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for th... more INTRODUCTION Shoulder pain is a common and debilitating condition. One theorized mechanism for the development of shoulder pain and associated rotator cuff tendonitis is compression of the soft tissues within the subacromial space of the shoulder as the arm is elevated. However, current methods of subacromial space measurement are limited. The purpose of this study was to develop and validate a volumetric description of the subacromial space at the shoulder, and describe changes in this space during passive humeral scapular plane abduction.
Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chro... more Introduction: Bearing couples within total ankle arthroplasty (TAA) typically utilize cobalt chromium alloys articulating on ultrahigh molecular weight polyethylene (UHMWPE). Articulation of these surfaces during in vivo loading can generate UHMWPE wear particles, which may then result in osteolysis and component loosening [1]. Osteolysis has been observed following TAA in 15-22% of patient populations [2,3]. Use of highly crosslinked UHMWPE (HXPE) has been shown to reduce wear in other joint systems [4] compared to conventional UHMWPE (CPE); and thus has the potential to improve wear performance of TAA. The goal of this study was to quantify the impact of crosslinking on wear within TAA using loading parameters biomechanically relevant to the ankle joint.
Thedevelopment of an in vivo animalmodel of posterolateral knee instability is desired for devisi... more Thedevelopment of an in vivo animalmodel of posterolateral knee instability is desired for devising effective interventions for this injury. Sequential sectioning of the popliteus tendon, lateral collateral ligament, and lateral capsule was done in cadaveric goat knees to create knee joint instability, followed by in vivo studies (Studies 1 and 2) of 7 and 3 months duration, respectively. In Study 1, the popliteus tendon and lateral collateral ligament were sectioned; in Study 2, these structures as well as the lateral joint capsulewere sectioned. Biomechanical testing and histological assessments were done to determine the severity of the instability and the morphological changes. Sectioning the lateral collateral ligament and popliteus tendon (Study 1) resulted in a significant increase in varus instability at 908. Sectioning the lateral collateral ligament, popliteus tendon, and lateral capsule (Study 2) resulted in significant varus instability at 308, 608, and 908, and signific...
The American Journal of Sports Medicine, 1999
To determine if untreated grade III injuries of the posterolateral structures contribute to incre... more To determine if untreated grade III injuries of the posterolateral structures contribute to increased force on an anterior cruciate ligament graft, we measured the force in the graft in cadaveric knees during joint loading after reconstruction with otherwise intact structures and in the same reconstructed knees after selected cutting of specific posterolateral knee structures. Tests were first performed on the knee with the posterolateral structures intact and then after sequential sectioning of the fibular collateral ligament, popliteofibular ligament, and popliteus tendon. The graft force was significantly higher after fibular collateral ligament transection during varus loading at both 0° and 30° of knee flexion than it was for the same loading of the joint with intact posterolateral structures. In addition, coupled loading of varus and internal rotation moments at 0° and 30° of flexion further increased graft force beyond that with varus force alone. The increase in graft force ...
The American Journal of Sports Medicine, 2000
The purpose of this study was to contrast the magnetic resonance imaging appearance of uninjured ... more The purpose of this study was to contrast the magnetic resonance imaging appearance of uninjured components of the posterolateral knee with that of injured structures, and to assess the accuracy of magnetic resonance imaging in identifying posterolateral knee complex injuries. Thin-slice coronal oblique T1-weighted images through the entire fibular head were used to identify the posterolateral structures in seven uninjured knees. The appearance of corresponding grade III injuries to these structures was identified prospectively in 20 patients and verified at the time of surgical reconstruction. The sensitivity, specificity, and accuracy of imaging for the most frequently injured posterolateral knee structures in this series were as follows: iliotibial band-deep layer (91.7%, 100%, and 95%), short head of the biceps femoris-direct arm (81.3%, 100%, and 85%), short head of the biceps femoris-anterior arm (92.9%, 100%, and 95%), midthird lateral capsular ligament-meniscotibial (93.8%, ...
The American Journal of Sports Medicine, 2000
To determine if helmet removal causes a significant increase in lordosis of the cervical spine in... more To determine if helmet removal causes a significant increase in lordosis of the cervical spine in ice hockey players, we radiographically assessed the position of the cervical spine in subjects immobilized to a standard spine backboard wearing shoulder pads both with and without a helmet. Ten adult male volunteers (ages, 18 to 28 years) with no previous history of cervical spine injuries were fitted with an appropriately sized ice hockey helmet and shoulder pads and immobilized in a supine position to a standard spine backboard. Computerized tomographic lateral scout scans were obtained of the cervical spine for three conditions: 1) no equipment (control), 2) helmet and shoulder pads, and 3) shoulder pads only (helmet removed). With the helmet removed and the shoulder pads remaining, a significant increase in C2 to C7 lordosis was found when compared with the other two conditions. Individual segmental measurements revealed a significant increase in cervical lordosis at the C6—7 leve...
Bone Joint Journal Orthopaedic Proceedings Supplement, Dec 1, 2013
Introduction: Following total knee arthroplasty, patients often complain of an unnatural feeling ... more Introduction: Following total knee arthroplasty, patients often complain of an unnatural feeling in their knee joint, which in turn limits their activities [Noble et al, CORR 2006]. To develop an implant design that recreates the motion of the natural knee, both the functional kinematics as well as the laxity of the joint need to be understood. In vitro testing that accurately quantifies the functional kinematics and laxity of the knee joint can facilitate development of implant designs that are more likely to result in a natural feeling, reconstructed knee. The objective of this study is to demonstrate that robotic in vitro testing can produce clinically relevant functional kinematics and joint laxities. Methods: All testing was performed using a KUKA (KUKA Robotics, Augsburg, Germany) 6 degree of freedom robotic arm and a six degree of freedom load cell (ATI Industrial Automation, Apex, North Carolina, USA), attached to the arm (Figure 1). FUNCTIONAL KINEMATICS: Eight cadaveric specimens implanted with contemporary cruciate retaining implants were used for this evaluation. The functional activity, lunge, was simulated using kinematic control for flexion/extension and force-torque control for the other degrees of freedom. The inputs for the force-torque control were obtained from e-tibia data from live patients during the lunge activity [Varadarajan et al, J Biomech 2008]. At a given flexion angle, the robot moved in force-torque control to obtain the desired values within given tolerances (± 2.5N & ± 0.1 Nm). When these tolerances were met the position of femur with respect to the tibia was recorded and the knee flexed to the next level. The lunge simulation began at full extension and ended at 120 degrees of knee flexion, through 1 degree increments. The kinematic data from the contemporary CR implants were compared to in vivo kinematics of patients that were implanted with the same knee replacements performing a lunge activity [Varadarajan et al, Med Eng Phys 2009]. JOINT LAXITY: Eight native, unimplanted knees were used for this evaluation. Joint laxity of the knee joint was evaluated at 0, 30, 60, 90, and 120 degrees of knee flexion by applying various loads to the tibia and quantifying the resulting motion of the tibia. The resulting laxities were compared to various knee laxity studies in the literature. Results: The in vitro functional kinematics correlated well with the in vivo results. Femoral external rotation and tibial varus angulation were found not be statistically different between the in vitro and in vivo results (Figure 2). The laxities measurements correlated well with reported values in the literature. Discussion: In vitro robotic evaluations allow for a better understanding of the motion at the knee joint by simulating clinically relevant functional kinematics as well as quantifying joint laxities in the same testing system. Both of these metrics are needed to understand how the knee moves and should be used to evaluate the performance of new knee designs (Figure 3).