Does joint line elevation after revision knee arthroplasty affect tibio-femoral kinematics, contact pressure or collateral ligament lengths? An in vitro analysis

Abstract

Introduction: Correct restoration of the joint line is generally considered as crucial when performing total knee arthroplasty (TKA). During revision knee arthroplasty however, elevation of the joint line occurs frequently. The general belief is that this negatively affects the clinical outcome, but the reasons are still not well understood.

Material and methods: In this cadaveric in vitro study the biomechanical consequences of joint line elevation were investigated using a previously validated cadaver model simulating active deep knee squats and passive flexion-extension cycles. Knee specimens were sequentially tested after total knee arthroplasty with joint line restoration and after 4 mm joint line elevation.

Results: The tibia rotated internally with increasing knee flexion during both passive and squatting motion (range: 17° and 7° respectively). Joint line elevation of 4 mm did not make a statistically significant difference. During passive motion, the tibia tended to become slightly more adducted with increasing knee flexion (range: 2°), while it went into slighlty less adduction during squatting (range: -2°). Neither of both trends was influenced by joint line elevation. Also anteroposterior translation of the femoral condyle centres was not affected by joint line elevation, although there was a tendency for a small posterior shift (of about 3 mm) during squatting after joint line elevation. In terms of kinetics, ligaments lengths and length changes, tibiofemoral contact pressures and quadriceps forces all showed the same patterns before and joint line elevation. No statistically significant changes could be detected.

Conclusions: Our study suggests that joint line elevation by 4 mm in revision total knee arthroplasty does not cause significant kinematic and kinetic differences during passive flexion/extension movement and squatting in the tibio-femoral joint, nor does it affect the elongation patterns of collateral ligaments. Therefore, clinical problems after joint line elevation are probably situated in the patello-femoral joint or caused by joint line elevation of more than 4 mm.

Keywords: collateral ligaments; contact pressure; kinematics; revision.

Figure 1

The experimental set-up with a cadaver specimen mounted on the knee rig, ready for a squat. The rig allows 6° of freedom for the knee joint. Visible are the clamp fixed to the quadriceps tendon (a) and cables attached to medial and lateral hamstring tendons (b); the marker frames on tibia and femur (c) and the Tekscan sensor and handle (d)

Figure 2

Top view of the tibial insert with the medial and lateral femoral condyle centers projected onto it during the different motion cycles (passive cycles on the left, squats on the right). Top row shows knee kinematics after primary TKA with joint line reconstruction, lower row shows knee kinematics after revision TKA with 4 mm joint line elevation M – medial, L – lateral, A – anterior, P – posterior.

Figure 3

Tibial external rotation and tibial adduction as a function of flexion angle during passive flexion-extension cycles (A) and during squatting (B)

Figure 4

Relative length changes of sMCL and LCL with respect to their initial, native length as a function of flexion angle during passive flexion-extension cycles (A) and during squatting (B)

Figure 5

Change in tibio-femoral contact pressure after 4 mm joint line elevation with respect to contact pressure after primary TKA as a function of flexion angle during squatting (A) and quadriceps force as a function of flexion angle during squatting (B)