Knee joint kinematics and the effects of arthropasty component design

Abstract: Aims: To evaluate the influence of medial osteoarthritis on knee joint kinematics and the effect of design in total knee replacements (TKR) on the kinematics of trunk, hip, knee and ankle. Associations between articulating surface design, clinical outcome and fixation of the tibial component were also evaluated. Materials and methods: Study 1: Knee joint kinematics in 14 patients with non-inflammatory medial gonarthrosis and 10 controls were studied by dynamic radiostereometry during weight-bearing extension. Studies 2-4 and 6: Eighty-three patients (87 knees) were operated with the AMK (DePuy, Johnson&Johnson) TKR. Knees with =5° varus/valgus malalignment received a relatively flat or concave tibial plateau. The posterior cruciate ligament (PCL) was retained. Knees with more malalignment and /or extension deficit =10° received a concave or posterior-stabilized component. The PCL was resected. In study 2, during level walking kinematics of the hip and knee were studied by motion analysis in 39 patients and in study 3 in 20 patients during stair ascent and 17 during descent. Extension-flexion of the trunk, hip, knee and ankle were studied in 28 patients during chair rise (study 4). In study 6 at 5 years, migration of the tibial component was measured with radiostereometry, and radiolucent lines and clinical outcome were evaluated in 72 knees. Study 5: The kinematics of 22 knees operated with the Freeman-Samuelson (Finsbury Instruments Ltd, Surrey, UK) TKR due to non-inflammatory arthrosis were recorded by dynamic radiostereometry during weight-bearing extension. A standard, a mobile bearing, and a spherical medial femoral condyle design were studied.Results: Study 1: Internal tibial rotation was decreased and the lateral femoral condyle was displaced more anteriorly in arthrotic knees. Studies 2-4: There were no major differences related to the articulating surface design. Patients with TKR showed decreased knee and hip extension. During stair walking they also tended to display decreased knee flexion and increased hip flexion moments. Study 5: The mobile bearing implant reduced tibial translations. The spherical design showed abnormal external tibial rotation and valgus with increasing flexion. Study 6: Radiographic or clinical results were not influenced by design. The amount of congruency did not influence migration in the knees with small preoperative deformity. In knees with pronounced preoperative deformity, the posterior stabilized component demonstrated a small increase in varus/valgus tilting compared to the concave insert. Conclusions: Study 1: Arthrotic knees displayed changes in kinematics previously observed in anterior cruciate ligament (ACL) deficient and TKR knees. The abnormal kinematics in TKR knees might originate from preoperative changes. Abnormal kinematics in arthrotic and TKR knees might be at least partly an effect of ACL deficiency.Studies 2-4: A knee replacement should allow full active extension to achieve normal kinematics. Study 5: Modifications of articulating surface design changed kinematics in Freeman-Samuelson TKR. The mobile bearing seemed to improve the tibiofemoral congruity. Study 6: Articulating surface design in AMK TKR had minimum influence on migration and no influence on radiolucent lines or clinical results at 5 years.