In a „true“ valgus knee the lateral femoral condyle is smaller in both the vertical and anteroposterior dimensions and lateral soft tissue structures are contracted. In a „false“ valgus knee there is no mismatch between anteroposterior dimensions of both condyles. The aim of the study was to preoperatively analyse patterns of passive movement of valgus knees with imageless navigation system to optimise surgical approach during subsequent total knee replacement (TKR).

TKR were prospectively performed in 50 valgus knees. After the data 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“.

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°). The mean difference between axis deviation in 0° to 120° range of flexion was 5.5° (range 10° to 1°) in the „true“ valgus group. In the „false“ valgus group the varus deviation was observed in 90° of flexion in all cases and mean difference between axis deviation in 0° to 120° range of flexion was 12.0° (range 14° to 10°).

Computer navigation can easily help to identify the character of valgus deformity („true“ or „false“) just before skin incision. In „true“ valgus deviation lateral approach may be necessary for appropriate soft tissue balancing during TKR surgery.