Abstract
Introduction
In total knee arthroplasty, patients sometimes have pain in the posterolateral part of the knee. One possible cause is the impingement of the popliteus tendon against femoral components. In the literature, the incidence has been reported to be 1–4%. The purpose of this study is to quantify the amount of posterolateral overhang of the femoral component using 3-D templating software.
Methods
We investigated 40 knees with varus osteoarthritic knees (Male 6 knees and Female 34 knees), all cases were grade 2 or lower in Kellgren Lawrence classification. Three-dimensional preoperative planning software was used to simulate the replacement of femoral component. The distal femur was simulated to cut 9 mm thickness on the lowest point of the medial condyles with 6 degrees valgus. The femoral mediolateral axis was simulated to be parallel to the surgical epicondylar axis. The size of femoral components was decided by anteroposteriol dimension of distal femur. Mediolateral location of the femoral component was that the lateral edge of the femoral components is just on the lateral cortex of the femur. In coronal plane, amount of M-L overhang of the femoral component was measured in 3 Zones (distal, proximal, center) on the surface of the posterior condyle cut (Figure 1).
Results
The mean amounts of M-L overhang averaged of 3 zone were 1.0±13 mm in medial condyle and 3.7±1.5 mm in lateral (P<0.01). The number of cases in which M-L overhang was larger than 3 mm were 5 knees (12.5%) in medial condyle and 25 knees (62.5%) in lateral (P<0.01). In lateral condyles, over 3 mm overhanging cases were 25 knees in proximal zone, 21 knees in center zone and 8 knees in distal zone. There were significant differences in each zones (P<0.01).
Discussion and Conclusion
Over 3 mm overhang in the poterolateral part of the fumer was present in 25 knees in 40 knees (62.5%). Furthermore, all cases had over 3 mm overhang in proximal zone. There is the popliteal sulcus in proximal zone of the posterolateral part of the fumer (Figure 2). To our knowledge, this is the first report on the objective data of posterolateral overhang of the femoral component. In view of the case with popliteus tendon impingement, rounded and reduced shape of the posterolateral corner in the femoral component would be beneficial (Figure 3).
