Abstract
Introduction
Valgus knee deformity is associated especially with differences in anatomy between medial and lateral femoral condyles. Vertically smaller lateral condyle and more distally located medial condyle cause valgus deformity in extension. The anteroposterior dimensions of both condyles influence the knee axis in flexion. In a „true“ valgus knee there is a mismatch between both condyles in both the vertical and anteroposterior dimensions, the lateral condyle is generally smaller. In a „false“ valgus knee there is no mismatch between anteroposterior dimensions of both condyles, the knee axis changes from valgus into varus with increased degree of flexion and lateral soft tissue structures are that's why not so contracted as in „true“ valgus knee deformity, where the knee stays in valgus deviation during the whole range of motion. The aim of the study was to preoperatively identify and analyse patterns of passive movement of osteoarthritic valgus knees with imageless navigation system to optimise surgical approach and intra-operative tissue handling during subsequent total knee replacement (TKR) surgery.
Material and Methods
TKR were prospectively performed in 50 valgus knees. Cases with severe bony destruction and enormous soft tissue laxity were excluded from the study. The kinematic navigation system used was OrthoPilot® (Aesculap, Tuttlingen, Germany). It is designed to produce a numerical output of varus/valgus deviation of the knee against the degree of flexion. Before skin incision for TKR surgery, active markers were attached percutaneusly to the femur and the tibia with bicortical screws to create two ‘rigid bodies’. After the registration process the kinematic analysis was performed by passive movement of the knee. The mechanical axis was recorded at 0°, 30°, 60°, 90°, and 120° of flexion. The valgus deformity persistent through the whole range of motion was called „true“ and the valgus deformity passing into varus with flexion was called „false“. In „true“ valgus knees the lateral approach according to Keblish was used, in „false“ valgus knees we used standard medial parapatellar approach.
Results
The pre-operative valgus deformity in extension ranged from 13° to 4° (mean 7,8°). We observed „true“ valgus type deformity during passive range of movement in 34 cases (68 %) and „false“ type of kinematics in 16 cases (32 %). The average value of valgus deviation in extension in „true“ group was 7,9° (range, 13° to 4°) and in „false“ group 7,5° (range, 9° to 6°), without statistically significant difference. In the „true“ valgus deviation group the value of deformity gradually decreased with flexion in all cases. The mean difference between axis deviation in 0° and 120° of flexion was 5,5° (range, 10° to 1°) in this group. In the „false“ valgus group the varus deviation was observed either already in 60° of flexion or in most cases in 90° of flexion. The mean difference between axis deviation in 0° and 120° of flexion in this group was much more significant – 12,0° (range, 14° to 10°) – there was statistically significant difference between both groups. The mean time necessary for data collection before surgery was 6 minutes (range, 4 to 11 minutes); afterwards, tha navigation was used for TKR implantation. No complications were observed regarding to the navigation usage. Subsequently correct soft tissue balance was achieved in all TKRs using this method.
Conclusions
Computer navigation assistance can easily and fast help to identify the character of valgus deformity („true“ or „false“) just before skin incision. In „true“ valgus deviation lateral structures (iliotibial band, vastus lateralis tendon, lateral collateral ligament, and the popliteus muscle) are tight and lateral approach according to Keblish may be necessary for appropriate release and soft tissue balancing during TKR surgery. Mostly used standard medial parapatellar approach is always sufficient in „false“ valgus knees. Computer navigation can help surgeon to choose the appropriate parapatellar approach (medial or lateral) just before the surgery without significant time lost.
