Preoperative Joint Line Convergence Angle as an Indicator of Clinical Outcomes and Accuracy of Alignment Correction After Double-Level Osteotomy

Background: The relationship between postoperative alignment and clinical outcomes after double-level osteotomy (DLO) has not been clarified. Purpose: To examine the radiological and clinical outcomes after DLO and specifically evaluate the influence of the joint-line convergence angle (JLCA) on the accuracy of alignment correction and surgical outcomes. Study Design: Case-control study; Level of evidence, 3. Methods: Included were 74 knees in 51 patients (mean age, 61.0 years) who underwent DLO for varus osteoarthritic knees and who had a minimum of 2 years of follow-up. The target hip-knee-ankle angle (HKAA) for the intended limb alignment was set to 1° valgus. The lateral distal femoral angle, medial proximal tibial angle, JLCA, and HKAA were measured on preoperative and postoperative radiographs. Outliers in alignment correction were defined as a deviation of ≥3° from the originally intended HKAA. Clinical outcomes were assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS). In the data analysis, the influence of the radiological parameters on the postoperative outcomes was statistically assessed. Results: Radiological and clinical evaluation at 2-year follow-up showed significant improvement from preoperative values (P < .001). The HKAA was corrected from 13.4°± 3.0° varus preoperatively to 0.5°± 2.8° varus at 2 years, indicating a slight undercorrection. Regarding clinical outcomes, significant pre- to postoperative improvement was found on the KOOS (from 185.0 ± 71.2 to 387.9 ± 70.5; P < .001). Overall, 22 of the 74 knees (29.7%) were deemed to be outliers at the 2-year follow-up (19 knees [25.7%] in undercorrection, 3 knees [4.1%] in overcorrection). Postoperative KOOS values were significantly worse in the outliers than in the nonoutliers (344.4 ± 77.7 vs 405.8 ± 59.3; P < .001), and both pre- and postoperative JLCA was significantly larger in the outlier group. The receiver operating characteristic curve analysis indicated a preoperative cutoff JLCA of 6.0° for predicting postoperative alignment outliers. Conclusion: A preoperative JLCA of ≥6° was found to be a significant prognostic factor affecting the radiological and clinical outcomes after DLO for varus osteoarthritic knees by compromising the accuracy of deformity correction, resulting in suboptimal postoperative alignment.