Previously, fluoroscopy has been used to determine the in vivo kinematics during gait, step-up maneuvers and flexion to nine tydegrees. Recently, TKAs have been designed for deep flexion maneuvers. Therefore, the objective of this study is to determine the in vivo kinematics for subjects implanted with either a fixed or mobile bearing deep flexion TKA from full extension to maximum knee flexion

Three-dimensional femorotibial contact positions for thirty-nine subjects, implanted by two surgeons, were evaluated using fluoroscopy into deep flexion. Nineteen subjects had a fixed bearing PS deep flexion TKA and 20 subjects were implanted with a mobile bearing deep flexion TKA. Both TKA designs have similar design features, including condylar geometries.

Seventeen of nineteen subjects implanted with a fixed bearing deep flexion TKA experienced posterior femoral rollback, while all 20subjects having a mobile bearing deep flexion TKA experienced poster iorfemoral rollback. On average, subjects experienced -5.1 and -8.1 mm of posterior femoral rollback, for the fixed and mobile bearing TKA, respectively. The maximum amount of posterior femoral rollback was -11.8 and -12.4 mm for subjects having a fixed and mobile bearing TKA, respectively. On average, subjects experienced 6.5 and 5.4 degrees of normal axial rotation for a fixed and mobile bearing TKA, respectively. The average amount of weight-bearing range of motion was 116 and 125 degrees for a fixed and mobile bearing TKA, respectively. Also, subjects having both TKA types evaluated in this study experienced excellent patellofemoral kinematics

This is the first study to evaluate femorotibial and patellofemoral knee kinematics into deep flexion for a fixed and mobile bearing TKA, designed for deep flex-ion activities. Both groups in this study experienced, on average and subject-to-subject comparison, excellent kinematic patterns. Also, both TKA types evaluated in this study achieved excellent weight-bearing range-of-motion, supporting the design goal for these TKA.

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.