Posterior Condyle Offset and Maximum Knee Flexion Following a Cruciate Retaining Total Knee Arthroplasty

Inconsistent data has been reported on the effect of the femoral posterior condyle offset (PCO) on the maximal knee flexion after total knee arthroplasty (TKA). This study investigated the relationship between the postoperative changes of the PCO and the changes of maximal knee flexion after a cruciate retaining (CR) TKA. Nine patients with medial osteoarthritis (OA) in one knee were investigated. Before operation, each index knee was magnetic resonance imaging (MRI) scanned for construction of a three-dimensional (3D) knee model. The patient then performed a maximal weight-bearing (WB) flexion and the index knee flexion was measured using a dual fluoroscopy technique. At an average of 8 months after a CR TKA, all patients performed the same WB knee flexion. The postoperative changes of the PCO, the posterior cruciate ligament (PCL) elongation, and the posterior tibial slope (PTS) were determined. The postoperative changes of maximal knee flexion were determined by comparing with the preoperative maximal flexion angles of the knee. The correlations of the postoperative changes of PCO and PTS with the postoperative changes of the maximal flexion angle and PCL elongation of the knee were analyzed. The preoperative PCO (28.5 ± 4.5 mm) was significantly smaller than the postoperative PCO (31.1 ± 5.1 mm) (p < 0.05). The increasing of PCO after surgery is correlated with the decreasing of maximal knee flexion angle (r = 0.74) and the increasing of PCL elongation (r = 0.64) after the TKA. The PTS was not found to change significantly after the TKA and was not significantly correlated to the maximal knee flexion angle and PCL elongation. The postoperative increases of the PCO were shown to cause overstretching of the PCL and poor flexion angle of the knee after the CR TKA. Restoration of PCO could help optimize the maximal flexion of the knee after the TKA with consideration about PCL tension.