Abstract
BackgroundThe alignment correction after high tibial osteotomy (HTO) is made both by bony correction and soft-tissue correction around the knee. Change of the joint-line convergence angle (JLCA) represents the soft-tissue correction after HTO, which is the angle made by a tangential line between the femoral condyles and the tibial plateau. We described the patterns of JLCA change and related factors after HTO and investigated the appropriate preoperative planning method.MethodsEighty patients who underwent HTO between 2013 and 2016 were included for this retrospective study. Standing, whole-limb radiograph, supine knee anteroposterior (AP) and lateral were measured on the preoperative and postoperative radiographs. The patterns of JLCA changes and related factors were analyzed.ResultsJLCA decreased by a mean of 0.9° ± 1.2° (P < 0.001) after HTO. Sixteen patients (20%, group II) showed a greater JLCA decrease ≥ 2°, while 64 (80%, group I) patients remained in a narrow range of JLCA change < 2°. Group II showed more varus deformity (varus 8.1° vs. varus 4.7° in the mechanical femorotibial angle, P < 0.001), greater JLCA on standing (4.9° vs. 2.1°, P < 0.001), and the difference of JLCA in the standing and supine positions (2.8° vs. 0.7°, P < 0.001) preoperatively compared to group I. The risk of a greater JLCA decrease ≥ 2° was associated with greater preoperative JLCA in the standing position and the difference between the JLCA in the standing and supine positions. Postoperative JLCA correlated better with preoperative JLCA in the supine position than those in the standing position. A preoperative JLCA ≥ 4° or the difference of preoperative JLCA in the standing and supine positions ≥ 1.7° was the cut-off value to predict a large JLCA decrease ≥ 2° after HTO in the receiver operating characteristic (ROC) curve analysis.ConclusionsSurgeons should consider the effect of the JLCA change during the preoperative planning and intraoperative procedure to avoid unintended overcorrection.
Highlights
The alignment correction after high tibial osteotomy (HTO) is made both by bony correction and soft-tissue correction around the knee
joint-line convergence angle (JLCA) decreased by a mean of 0.9° ± 1.2° after HTO
When dividing the patients by the preoperative JLCA of 2°, 3°, and 4°, the proportion of patients with a JLCA change of ≥ 2° after HTO was significantly higher if the preoperative JLCA was greater than the cut-off values (Table 2 and Fig. 2)
Summary
The alignment correction after high tibial osteotomy (HTO) is made both by bony correction and soft-tissue correction around the knee. Change of the joint-line convergence angle (JLCA) represents the soft-tissue correction after HTO, which is the angle made by a tangential line between the femoral condyles and the tibial plateau. The change of the joint-line convergence angle (JLCA), defined as the angle made by a tangential line between the femoral condyles and the tibial plateau, can represent the soft-tissue correction after HTO [13, 16]. JLCA change is a risk factor for the discrepancy of limb alignment both checked intraoperatively using fluoroscopy and measured on the postoperative, standing, whole-leg radiograph [19, 20]. This phenomenon can cause unintended overcorrection of the limb alignment [13, 15]. Several studies have reported methods to consider the change of the JLCA [8, 14, 21, 22], Postoperative JLCA change is not easy to be expected and difficult to calcuate the estimated amount during the preoperative planning [15]
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