Introduction: Previous in vivo kinematic studies have assessed total knee arthroplasty (TKA) motion under weight-bearing conditions. This in vivo study analyzed and compared posterior cruciate retaining (PCR) and posterior stabilized (PS) kinematics under passive and weight-bearing conditions in subjects implanted with both a PCR and PS TKA.

Methods: Eighteen subjects were implanted with a PCR and a PS TKA, by a single surgeon using a similar surgical technique. Both implant designs had similar condylar geometry. Femorotibial contact positions for all 18 subjects (PCR and PS), implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject,while under fluoroscopic surveillance, performed a weight-bearing deep knee bend and a passive, nonweight-bearing flexion. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and femoral condylar lift-off were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: Under passive and weight-bearing conditions, the PCR TKA experienced more paradoxical anterior translation than the PS TKA. Under passive, non weight-bearing conditions, the PS TKA, on average, experienced 3.5 mm of posterior femoral rollback, compared to only 0.6 mm for the PCR TKA. Under weight-bearing conditions, the PS TKA experienced only 0.6 mm of posterior femoral rollback, compared to 0.9 mm for the PCR TKA. The maximum anterior slide was 10.0 mm for the PCR TKA and only 2.7 mm for the PS TKA. There was greater variability in both the PCR and PS anteroposterior data. Subjects having a PCR TKA experienced more normal axial rotation patterns. Sixteen of 18 PCR TKA experienced a normal axial rotation pattern under weight-bearing conditions, while only 9/18 PS TKA experienced a normal pattern. Nonweight-bearing, passive axial rotation patterns were more abnormal for both groups than the weight-bearing patterns. The greatest difference between passive and weight-bearing conditions occurred in the condylar lift-off data. Under passive conditions, both TKA groups experienced significantly greater magnitude and incidence of condylar lift-off. The maximum amount of condylar lift-off under passive conditions was 5.0 mm for the PCR TKA and 6.4 mm for the PS TKA.

Discussion: This is the first in vivo kinematic study to assess a comparison between PCR and PS TKA implanted by the same surgeon in the same patient. Subjects in this study experienced more abnormal kinematic patterns, especially condylar lift-off, when tested under passive, nonweight-bearing conditions. Subjects having a PS TKA experienced less variability in their kinematic data, but PCR TKA, on average, experienced more normal axial rotation and less condylar lift-off.

Introduction: Previous in vivo kinematic analyses of the hip joint have determined that femoral head separation from the medial aspect of the acetabular component occurs in metal-on-polyethylene THA. The present study analyzes subjects having either an alumina-on-alumina (AOA),alumina-on-polyethylene (AOP),metal-on-metal (MOM) or metal-on-polyethylene (MOP) THA during gait to determine if the incidence of hip joint separation varies based on articular surface material.

Methods: Forty subjects were analyzed in vivo using video fluoroscopy. Ten subjects had a AOA THA, ten an AOP THA, ten a MOM THA, and ten having a MOP THA. All THA subjects were implanted by two surgeons and were judged clinically successful (Harris hip scores > 90.0). Each subject performed normal gait on a treadmill and an abduction/adduction leg lift maneuver while under fluoroscopic surveillance. The two-dimensional (2D) fluoroscopic videos were converted into 3D using a computer automated model-fitting technique. Each implant was analyzed at varying flexion angles to assess the incidence of hip joint separation.

Results: During gait and the abduction/adduction leg lift, no separation was observed in subjects having an AOA THA or in subjects having a MOM THA. Similar to our previous studies pertaining to subjects having a THA with a polyethylene acetabular insert, all ten subjects having a MOP THA and 6/10 subjects having an AOP THA experienced hip joint separation. The maximum amount of separation was 7.4 mm for a subject having an AOP THA and 3.1 mm for a subject having a MOP THA.

Discussion: This study shows femoral head separation from the medial aspect of the acetabular component can occur in the presence of a polyethylene liner. The femoral head often remains in contact with the liner, hinging superolaterally. Potential detrimental effects resulting from hip joint separation include premature polyethylene wear, component loosening (secondary to impulse loading conditions) and hip instability. Wear may be enhanced due to creation of multidirectional wear vectors or excessive loads due to eccentric femoral head pivoting. The absence of separation observed in AOA and MOM THA designs may be related to increased wettability of these materials and tighter radial tolerances resulting in a cohesive lubrication film. This data may be of value in hip simulation studies to better duplicate wear patterns observed in retrieval analyses and assist in the understanding of the lubrication regime and wear rates in AOA and MOM designs, allowing for the synthesis of prosthetic components that minimize wear and optimize kinematics.

Introduction: Previously, in vivo kinematic studies have determined the in vivo kinematics of the femur relative to the metal base-plate. These kinematic studies have reported posterior femoral rollback in posterior stabilized (PS) TKA designs, but the actual time of cam/post engagement was not determined. The objective of this present study was to determine, under in vivo conditions, the time of cam/post engagement and the kinematics of the femur relative to the polyethylene insert.

Methods: Femorotibial contact positions for twenty subjects having a PS TKA, implanted by two single surgeons, were analyzed using video fluoroscopy. Ten subjects were implanted with a PS TKA that is designed for early cam/post engagement (PSE) and ten subjects with a PS TKA designed for later cam/post engagement (PSL). Each subject, while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion. Video images were downloaded to a workstation computer and analyzed at ten-degree increments of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and condylar lift-off were then determined using a computer automated model-fitting technique.

Results: Subjects implanted with the PSE TKA experienced, on average, the cam engaging the post at 48° (10 to 80°). Subjects having the PSL TKA experienced more consistent results and did experience engagement in deep flexion (Average 75°). Subjects having the PSE TKA experienced, on average, −5.5 mm (1.5 to −9.3) of posterior femoral rollback (PFR), while subjects having the PSL TKA experienced only −2.6 mm (8.5 to −9.0) of PFR. Subjects having the PSE TKA experienced more normal axial rotation patterns. Nine subjects having the PSE TKA experienced condylar lift-off (maximum = 1.9 mm), while only 4/10 having the PSL TKA experienced condylar lift-off (maximum = 2.7 mm).

Discussion: This is the first study to determine the in vivo contact position of the cam/post mechanism. Subjects having a PSE TKA experienced earlier cam/post engagement than subjects having the PSL TKA. Some subjects did not experience any cam/post engagement throughout knee flexion. Subjects having the PSE TKA experienced more PFR and better axial rotation patterns, but subjects having a PSL TKA experienced lesser incidence of condylar lift-off. Results from this study suggest that there may be an advantage to early cam/post engagement, which leads to more normal axial rotation patterns caused by the medial condyle moving in the anterior direction as the lateral condyle rolls in the posterior direction.

Introduction: Previously, in vivo kinematic studies have determined that posterior stabilized (PS) TKA experienced posterior femoral rollback during deep flexion, while posterior cruciate retaining (PCR) experience a paradoxical anterior slide during both gait and deep flexion. The objective of this present study was to analyze the in vivo kinematics for subjects implanted with a PS mobile bearing TKA to determine if there are any distinct advantages.

Methods: Femorotibial contact positions for ten subjects having a mobile bearing PS TKA, implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject,while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion and normal gait. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and condylar lift-off were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: During a deep knee bend, subjects having the Sigma PS rotating platform experienced minimal motion of their medial condyle and posterior femoral rollback of their lateral condyle. On average, the subjects experienced −2.3 mm of posterior femoral rollback (PFR) of their lateral condyle. Nine of ten subjects experienced PFR of their lateral condyle. During gait, on average, subjects experienced minimal motion of their medial (0.8 mm) and lateral condyles (−0.4 mm) from heel-strike to toe-off. During a deep knee bend all ten subjects experienced normal axial rotation (average = 4.0°). During gait, 6/10 subjects experienced normal axial rotation, while four subjects experienced less than 0.8 degrees of reverse rotation. Only 1/10 of the subjects experienced greater than 1.0 mm of condylar lift-off during gait or a deep knee bend.

Discussion: Subject in this study experienced normal kinematic patterns during gait and a deep knee bend. Only one subject experienced greater than 1.0 mm of condylar lift-off, during a deep knee bend and gait. At the present time, it is uncertain if the excellent kinematic patterns for the subjects in this study were related to the chosen surgeon, surgical technique or implant design. If implant design was an influencing factor, subjects requiring a TKA may receive benefit from having a PS mobile bearing type TKA.

Introduction: Previously, in vivo kinematic studies have determined that axial rotation patterns are quite variable between implant type and specific subjects. Previously, kinematic studies have determined that subjects having a mobile bearing TKA experience axial rotation, but it was unknown as to whether the bearing was rotating. Therefore, the objective of this present study was to analyze the in vivo kinematics for subjects having a mobile bearing prosthesis to determine if the polyethylene rotates relative to the femoral and/or the tibial components.

Methods: Femorotibial contact positions for ten subjects having a mobile bearing TKA, implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject, while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Each polyethylene component had four metallic beads, inserted at known positions. Using a 3D model-fitting process, the femoral, tibial and polyethylene insert components were overlaid onto the fluoroscopic images. Initially, the polyethylene insert was made transparent, but the computer would overlay the four metal beads. Then, the polyethylene insert was made viewable and analyzed relative to the metal femoral and tibial components.

Results: All of the subjects experienced polyethylene bearing rotation relative to the metal tibial component and minimal rotation relative to the metal femoral component. On average, relative to the metal tibial component, the subjects experienced 4.7° (2.1 to 7.9°) of polyethylene bearing rotation. The subjects experienced a similar amount of metal femoral component rotation, relative to the metal tibial component. On average, the subjects experienced 4.0° (−0.7 to 10.0°) of rotation of the metal femoral component relative to the metal tibial component. Therefore, on average, subjects experienced only 0.7° of rotation for the metal femoral component relative to the polyethylene bearing. Also, on average, from full extension to 90° of knee flexion the subjects experienced −2.9 mm of posterior femoral rollback of their lateral condyle and –0.4 mm of their medial condyle.

Discussion: This is the firs study to determine the in vivo rotation of the polyethylene bearing for subjects having a mobile bearing TKA. The results from this study determined that the polyethylene bearing is rotating relative to the metal tibial component, but not relative to the metal femoral component. Therefore, as the metal femoral component axially rotates the polyethylene bearing is rotating a similar amount in the same direction. Since bearing rotation does occur under in vivo conditions, subjects implanted with a mobile bearing prosthesis may be subjected to lesser amounts of contact stresses, which may be beneficial to them.

Introduction: The goal of this study was to determine the difference between weight-bearing and non weight-bearing range of motion (ROM) for Japanese subjects having either a fixed or mobile bearing TKA with either a resurfaced (RP) or unresurfaced (UP) patella.

Methods: Forty subjects were evaluated using video fluoroscopy. Twenty subjects had a fixed bearing posterior cruciate retaining (PCR) TKA (10 RP, 10 UP) and twenty subjects had a mobile bearing (MB) TKA (10 RP, 10 UP). Under weight-bearing conditions, each subject performed successive deep knee bends to maximum flexion. Then, under passive, non weight-bearing conditions the subjects stood on one leg and passively flexed their knee to maximum flexion. Each trial was recorded and analyzed digitally. The angle between the femoral and tibial longitudinal axes was subtracted from 180o to obtain the amount of flexion.A single surgeon control was used. The average age of the subjects was 66.4, 78.1, 70.3, and 71.1 for subjects having PCR RP, PCR UP, MB RP, and MB UP, respectively. All total knee subjects were judged excellent clinically with HSS scores > 90 points. None complained of pain during testing.

Results: The preoperative ROM for the implanted knee groups was 115, 122, 110, and 120 degrees for subjects having a PCR RP, PCR UP, MB RP, and MB UP, respectively. The average passive ROM was 106 (90–131) and 108 (72–128) degrees for subjects having a PCR RP and PCR UP, respectively. Subjects having a MB TKA experienced greater passive ROM, 120 degrees for both the MB RP (105–136o) and MB UP (105–167o). Under weight-bearing conditions, ROM decreased for all groups, with the average ROM of 101 (90–125), 108 (86–128), 109 (92–134), and 114 (94–142) degrees for subjects having a PCR RP, PCR UP, MB RP, and MB UP, respectively. The greatest amount of ROM occurred for a subject having a MB UP, 167o during passive ROM and 142o during a weight-bearing ROM.

Discussion: Subjects in this study having a MB TKA experienced greater ROM for all of the compared four parameters. Subjects having a MB RP experienced greater passive (120 vs. 106) and weight-bearing (109 vs. 101) ROM compared to the PCR RP group. Similarly, subjects having a MB UP experienced greater passive (120 vs. 108) and weight-bearing (114 vs. 108) ROM compared to the PCR UP group. Interestingly, subjects having an UP TKA experienced greater ROM compared to subjects having a RP TKA. The results from this study may suggest that a mobile bearing TKA may lead to greater ROM for the Japanese populations, where achieving deep flexion is essential for normal daily activities.

Introduction: Recently, many different mobile bearing TKA designs are being implanted throughout the world. Also,fluoroscopy has been used to evaluate variousTKA under in vivo conditions to determine the kinematics. The objective of this study was to utilize a randomized prospective study to evaluate the kinematic patterns, for Japanese subjects implanted with two different mobile bearing TKA.

Methods: Twenty Japanese subjects were entered into a prospective study. Ten subjects were implanted with a mobile bearing TKA, which is free to rotate around the longitudinal axis of the tibia (MB1). The other ten subjects were implanted with a mobile bearing TKA that allows for unrestricted translation and rotation (MB2). Femorotibial contact positions were analyzed using video fluoroscopy. Each subject, while under fluoroscopic surveillance, was asked to perform gait. Video images were downloaded to a workstation computer and analyzed at varying degrees of gait stance. Femorotibial contact paths for the medial and lateral condyles were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: During gait, on average, subjects implanted with MB1 experienced minimal A/P translation of either condyle. Also, all subjects having MB1 experienced similar motion patterns throughout the stance phase of gait. Axial rotation was evident in these subjects, as one condyle would move in the anterior direction, a similar amount to the other condyle moving posterior. On average, subjects implanted with MB2 experienced both translation and rotation. The amount of translation for subjects with MB2 was greater than subjects with MB1. The kinematic patterns for subjects having MB2 were also more variable than subjects having MB1. Axial rotation was also evident for subjects having MB1.

Discussion: This study has shown that the kinematic patterns for subjects having two different mobile bearing TKA designs differed considerably. Subjects implanted with a mobile bearing TKA that only allows for free rotation, experienced minimal A/P motion and significant axial rotation (MB1). Subjects implanted with a mobile bearing TKA that allows for free translation and rotation did experience both types of motions (MB2). There was minimal variability in the kinematic patterns for subjects implanted with MB1, while subjects implanted with MB2 experienced more variable kinematic patterns.

Purpose: Cinematic studies after total knee arthroplasty without an anterior cruciate ligament demonstrate abnormal behaviour compared with the normal knee. The purpose of this cinematic analysis was to examine the knee behaviour after implantation of single-compartment prostheses with an intact anterior cruciate ligament.

Material and methods: The femorotibial contact points were analysed by videofluoroscopy in 20 patients executing a complete weight-bearing extension to flexion movement. These patients had medial (n=16) or lateral (n=4) single-compartment implants. The clinical result in all patients was considered to be very good with a mean HSS score of 97.9 points at a mean 56 months postoperatively. The femorotibial contact points were determined using an automatic computerised adaptation-modelling system. An anterior contact on the medial tibial line in the sagittal plane was positive and a posterior contact was negative. The rotation axis in the craniopodal direction was measured between the anteroposterior longitudinal axis of the femoral component and the fixed axis of the tibial component.

Results: The mean position of the contact point for medial single-compartment prostheses was −90.8 mm in complete extension, −1.4 mm at 30° flexion, −2.4 mm at 60°, and −1.7 mm at 90°. Mean position of the contact point for lateral single-compartment prostheses was −4.0 mm at complete extension, −7.9 mm at 30° flexion, −5.7 mm at 60° and −5/7 mm at 90°. Seven patients with a medial implant and two patients with a lateral implant exhibited paradoxical anterior translation of the femur during flexion. On the average, patients with a medial implant had normal 3.3° axial rotation at 90°; axial rotation was 11.2° for patients with a lateral implant.

Discussion and conclusion: Cinematic analysis of the normal knee has demonstrated anterior femorotibial contact in extension and 14.2 mm posterior rolling of the femoral component during flexion. After total knee arthroplasty without preservation of the anterior cruciate ligament, the rolling movement is limited or absent and a paradoxical anterior translation can be observed. In the present study, the first reported on single-compartment implants, demonstrates that movement is similar to that in the normal knee but with major interindividual variability. A posterior contact at extension and a paradoxical anterior translation can also be observed. This suggests progressive development of anterior cruciate ligament laxity over time, which can at least in part explain the premature polyethylene wear observed after implantation of single-compartment knee implants.