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. 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).Introduction
Methods
Restoration of joint line in total knee arthroplasty (TKA) is important for kinematics of knee and ligamentous balance. Especially in revision TKA, it may be difficult to identify the joint line. The aim of this study is to define the relationship between epicondyles and articular surface using CT based three-dimensional digital templating sofware $“Athena” (Soft Cube, Osaka, Japan). 137 knees with osteoarthritis, all caces were grade 2 or lower in Kellgren-Lawrence index, were investigated. Perpendicular lines were dropped from the prominences of the medial and lateral femoral epicondyles to the most distal points of articular surfaces and distances of the lines were measured on the axial and coronal planes. The femoral width was measured as the distance between medial and lateral epicondyles. Each of the distance described above was converted to a ratio by dividing by the femoral width. On the axial plane, the average distance from epicondyles to the posterior articular surfaces were 29.4±2.2mm on the medial side and 21.2±2.3mm on the lateral side. The average of the femoral width was 75.2±4.1mm. On coronal plane, the average distance from epicondyles to the distal articular surfaces were 25.2±2.8mm on the medial side and 21.4±2.5mm on the lateral side. The ratio for the distance from epicondyles to the distal and posterior joint line compared to femoral width was 0.39±0.02, 0.28±0.03, 0.33±0.03 and 0.28±0.03. The distance from epicondyles to the distal and posterior joint line correlates with the femoral width of the distal femur. This information can be useful in determining appropriate joint line.
