Knee Osteoarthritis (KOA) Severity Influences Proximal Femoral Biomechanics and Predicts Pertrochanteric Fracture Instability: A Retrospective Radiographic Study.

Background and Objectives: Intertrochanteric hip fractures (ITFs) are common in older adults and frequently coexist with knee osteoarthritis (KOA). Although both conditions share key biomechanical risk factors, the specific relationship between KOA severity and ITF stability has not been well defined. Recent evidence suggests that degenerative knee changes may alter lower-limb load distribution and increase susceptibility to unstable fracture patterns. This study evaluated whether KOA severity, graded using the Kellgren-Lawrence (KL) system, is associated with ITF stability according to the 2018 AO/OTA classification. Materials and Methods: A retrospective observational study was conducted on 138 patients with IHFs treated between 2018 and 2023. KOA severity was assessed using KL grades I-IV on non-weight-bearing anteroposterior knee radiographs. Lateral wall thickness (LWT) was measured using the Hsu method, with <20.5 mm indicating fracture instability. Statistical analyses included correlation, linear regression, logistic regression, and receiver operating characteristic (ROC) curve analysis to examine the association between KL grade and fracture stability. Results: Among 138 patients, 98 (71.0%) had unstable ITFs. Advanced KOA was significantly more common in the unstable group (KL III 45.9%, KL IV 48.0%; p < 0.001). KL grade showed a significant inverse correlation with LWT (Pearson's r = -0.394, p < 0.001). Each one-grade increase in KL severity was associated with a 3.8 mm reduction in LWT (p < 0.001). In multivariable logistic regression, KL grade remained an independent predictor of fracture instability (adjusted OR = 4.9, 95% CI: 2.8-8.8, p < 0.001), whereas age and comorbidities were not significant. ROC analysis demonstrated good discriminatory power (AUC = 0.79). A KL ≥ III threshold achieved 95% sensitivity and 56% specificity for predicting instability. Conclusions: Higher KOA severity is strongly associated with unstable ITF patterns. KL grade independently predicts instability and may serve as a simple, accessible radiographic indicator of biomechanical vulnerability and fracture risk in older adults. Incorporating KOA severity into the preoperative evaluation may enhance risk stratification, guide selection of fixation strategy, and support individualized rehabilitation planning.