Paper 45: Varus malalignment is associated with increased failure risk following medial compartment oca transplantation

Objectives: Osteochondral allograft (OCA) transplantation is a well-established joint-preserving treatment for focal chondral defects of the knee, particularly in young, active patients. Coronal plane malalignment is known to affect joint loading and may influence graft survival. While large deformities are routinely addressed with realignment osteotomy, the role of subtle malalignment remains unclear. This study aimed to evaluate the association between preoperative coronal alignment and graft survivorship following medial compartment OCA transplantation in patients without concomitant realignment. It was hypothesized that greater varus alignment would be associated with an increased risk of graft failure.
Methods: Patients who underwent OCA transplantation for medial femoral condyle lesions between 2011 and 2022 were retrospectively reviewed. All included patients had preoperative standing long-leg alignment radiographs and no history of concomitant realignment osteotomy. Patients were excluded if they underwent concomitant major procedures (e.g., meniscal allograft transplantation) or underwent reoperation on the index knee that was not the terminal failure event. Radiographic parameters included hip-knee angle (HKA), percent mechanical axis deviation (PMAD), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), and joint line obliquity (JLO). Graft failure was defined using both clinical and imaging criteria. Primary failure included revision OCA, conversion to arthroplasty, or reoperation at the same site. Secondary failure was defined as imaging-confirmed structural graft compromise, such as subchondral collapse, fragmentation, or resorption, with corresponding clinical symptoms. Cox regression was performed to identify predictors of failure while controlling for age, sex, and BMI. Receiver operating characteristic (ROC) analysis with Youden's index was used to identify optimal cutoff values for significant predictors. Kaplan-Meier survival analysis compared graft survivorship above and below these thresholds using the log-rank test. Statistical significance was set at p < 0.05.
Results: Fifty-four patients were included (mean age 32.5 +- 10.8 years; BMI 25.9 +- 4.4; 31 male, 23 female) with a mean follow-up of 3.2 +- 2.7 years. Eight patients (14.8%) experienced graft failure, including two revision OCAs, two conversions to arthroplasty, and four structural failures confirmed by imaging and clinical symptoms.Cox regression analysis identified three alignment parameters significantly associated with graft failure, independent of age, sex, and BMI. Greater varus alignment was significantly associated with failure across HKA (HR = 0.59, 95% CI: 0.40-0.87; p = 0.0078), PMAD (HR = 0.90, 95% CI: 0.83-0.98; p = 0.013), and MPTA (HR = 0.70, 95% CI: 0.49-0.98; p = 0.040). No significant associations were observed for LDFA, JLCA, or JLO.ROC analysis demonstrated acceptable discrimination for HKA (area under the curve 0.731), PMAD (0.740), and MPTA (0.664), with optimal thresholds identified as HKA <= -1.8°, PMAD <= 38.4%, and MPTA <= 85.7°. Kaplan-Meier analysis confirmed significantly lower 5-year graft survival below each threshold. For patients with HKA <= -1.8°, survival was 70.3% (95% CI: 53.9-91.6%) compared to 88.9% (95% CI: 70.6 - 100.0%) above the threshold (p = 0.0048). PMAD <= 38.4% was associated with 65.8% survival (95% CI: 48.0 - 90.2%) versus 91.7% (95% CI: 77.3 - 100.0%) for higher PMAD (p = 0.0062). MPTA <= 85.7° had the poorest survival: 42.6% (95% CI: 19.1 - 95.0%) vs. 89.3% (95% CI: 77.7 - 100.0%) for higher values (p = 0.00023).
Conclusions: Greater varus malalignment was associated with a significantly increased risk of graft failure following OCA transplantation for medial compartment defects. HKA was an independent predictor of failure, with each 1° increase in varus alignment associated with a 41% increase in failure risk. Similarly, each 1% medial shift in PMAD was associated with a 10% increase in failure risk, while each 1° decrease in MPTA conferred a 30% increase in failure risk. These relationships remained significant after adjusting for age, sex, and BMI. Importantly, the alignment thresholds associated with inferior survivorship fell within ranges often considered acceptable in standard clinical practice. These findings suggest that even mild varus deformity may compromise graft success and support the consideration of adjunctive realignment procedures in select patients. Further research is warranted to determine whether concomitant osteotomy improves outcomes near these alignment cutoffs in patients with medial femoral condyle OCA.