Description
OBJECTIVE: In recent years, concerns have been raised about the increased load on the lateral compartment of the knee due to postoperative increase of the medial proximal tibial angle (MPTA) in tibial osteotomies for medial knee osteoarthritis (mKOA). In cases of severe varus deformity of the mKOA, a single-level tibial osteotomy requires a large amount of correction, resulting in more excessive obliquity of the knee joint line, which may lead the postoperative osteoarthritis on the lateral compartment of the knee. We investigated the effects of overcorrected MPTA on the lateral compartment of the knee in distal tibial osteotomy with hemicallotasis (DTO-HCO) using three-dimensional gait analysis.
Patients and Methods: Fifteen patients (mean age at surgery 61 years-old) who underwent DTO-HCO for mKOA were divided into two groups according to MPTA at 1 year postoperatively: group A (7 knees) with MPTA≥95° and group B (8 knees) with MPTA<95°. Before and 1 year after surgery, outcome measures including the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Japanese Orthopedic Association (JOA) score, and radiological parameters (MPTA, weight-bearing line ratio: WBLR, correction angle, angle between the ground and the proximal tibial joint line: JLO) were evaluated. In addition, three-dimensional gait analysis was used to measure the external knee joint adduction moment (KAM) and the position of the load line passing through the coronal plane of the knee joint (P-point) during the stance phase. These results were compared between the two groups.
Results: Clinical scores improved significantly in both groups postoperatively, but there were no differences between the groups. No patients had any symptons of the lateral side of the knee postoperatively. In the radiographic evaluation, the mean correction angle (°) in group A was 17.3, which was greater than 14 in group B, but there were no differences between the groups in WBLR and JLO after surgery. There was also no difference in pre- and postoperative KAM between the two groups. The mean pre- and postoperative P-points (distance from the center of the tibial plateau: cm) ranged from 6.3 to 0.1 in group A and from 4.6 to 0.6 in group B, with no differences. In both groups, the postoperative load line was concentrated in the center of the knee joint. Even in the individual cases of group A, where the correction angle was particularly large, none of the P points passed through the lateral compartment of the knee.
Conclusion: In a single-level medial opening wedge proximal tibial osteotomy, it has been reported that the JLO never exceeds 4° even with a postoperative MPTA≥10° due to the compensation of hip and ankle joints. In the present dynamic evaluation, the HCO-DTO did not show a negative KAM (conversion to abduction) even in patients with an MPTA≥95°, and there was no shift of the P-point to the lateral articular surface during gait. This suggests that the possibility of inducing postoperative lateral compartment osteoarthritis of the knee may be low.
