Intra-articular alignment after distal femoral osteotomy: A multicenter analysis of intra-articular changes

BACKGROUND: Distal femoral osteotomy (DFO) influence on intra-articular parameters, particularly joint line convergence angle (JLCA), joint line obliquity (JLO), remains under-investigated. HYPOTHESIS: This study aimed to assess the impact of DFO on JLCA and JLO and to identify potential "tipping points" of correction influencing JLCA changes, hypothesizing that large femoral corrections affect intra-articular alignment. Secondly, to correlate preoperative deformity and postoperative intra-articular parameters with clinical outcomes. PATIENTS AND METHODS: A retrospective multi-center analysis of patients undergoing isolated varus- or valgus-producing DFO between 2019 and 2024 by three different surgeons. Radiological analysis involved assessment of hip knee ankle angle (HKA), mechanical lateral distal femoral angle (mLDFA), JLCA, JLO and related phenotype. Patients were clinically evaluated at a minimum 12-month follow-up. Multivariate linear regression models identified significant (p < 0.05) predictors of Δ JLCA and postoperative JLO, as well as tipping correction threshold associated with soft tissue-driven JLCA variation. RESULTS: Final analysis included 56 patients. The degree of femoral correction was the only significant predictor of Δ JLCA (p = 0.017) and of JLO phenotype shift (p = 0.011), although these changes were not associated with differences in clinical outcomes. A femoral correction > 7.4° or postoperative mLDFA > 91.4° only in valgus deformities were associated with a marked absolute JLCA increase (2.2° and 2.6°, respectively), suggesting a soft tissue-driven tipping point. Post-operative JLO correlated strongly with postoperative mLDFA and JLCA (p < 0.001), and nearly half of the patients changed JLO phenotype, without affecting clinical outcomes. All clinical scores improved significantly postoperatively (p < 0.001). DISCUSSION: DFO improved outcomes in femoral-based varus and valgus malalignment. Δ mLDFA primarily drived JLCA and JLO changes. A soft tissue driven effect beyond 7.4° Δ mLDFA and 91.4° mLDFA was noted only in valgus cases, without adversely impacting outcomes. These intra-articular variations should be considered in case of large femoral corrections. LEVEL OF EVIDENCE: IV; retrospective cohort study.