Background and Clinical Rationale
Intertrochanteric hip fractures (ITFs) represent a major cause of morbidity and mortality in older adults, with an estimated annual incidence exceeding 1.5 million worldwide. These fractures frequently coexist with knee osteoarthritis (KOA), a degenerative condition affecting millions globally. While both conditions share common biomechanical risk factors—including altered gait mechanics, reduced mobility, and increased fall risk—the specific relationship between KOA severity and fracture stability has remained poorly defined.
Recent biomechanical evidence suggests that degenerative knee changes may alter lower-limb load distribution through the kinetic chain, potentially increasing susceptibility to unstable fracture patterns. This hypothesis motivated our retrospective investigation, which evaluated whether KOA severity, graded using the Kellgren-Lawrence (KL) system, is associated with ITF stability according to the 2018 AO/OTA classification.
Our findings, published in Medicina, demonstrate a strong, graded association between KOA severity and fracture instability, with KL grade emerging as an independent predictor of unstable fracture morphology. These results carry important implications for preoperative risk assessment and surgical decision-making in elderly patients with hip fractures.
Study Design and Methods
We conducted a retrospective observational study of 138 patients with intertrochanteric hip fractures treated between 2018 and 2023 at a tertiary referral center. 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 values below 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. Multivariable adjustment accounted for potential confounders including age, sex, BMI, and comorbidities.
Key Findings
Demographic and Clinical Characteristics
Among the 138 patients, 98 (71.0%) presented with unstable fracture patterns, while 40 (29.0%) exhibited stable patterns. The mean age was 72.3 ± 16.5 years, with 57.2% male. Patients with unstable fractures were significantly older than those with stable fractures (75.2 ± 13.0 vs. 65.6 ± 21.4 years, p = 0.011). Other baseline variables, including weight, height, BMI, and comorbidities such as hypertension, diabetes mellitus, and heart disease, showed no significant differences between the two groups, supporting the comparability of study populations prior to statistical adjustment.
KOA Severity and Fracture Stability
The severity of KOA showed a strong and graded association with ITF stability. In the stable fracture group, most patients demonstrated mild-to-moderate KOA (KL grade II, 57.5%). In contrast, the unstable fracture group showed a predominance of advanced degenerative changes, with KL grade III in 45.9% and KL grade IV in 48.0% of cases (p < 0.001). A significant linear trend was observed, indicating a clear stepwise increase in instability frequency with higher KL grades (linear-by-linear association: χ² = 41.05, p < 0.001).
Lateral Wall Thickness and Biomechanical Correlation
The mean LWT was significantly lower among patients with unstable fractures compared with those with stable fractures (13.2 ± 5.2 mm vs. 29.9 ± 5.9 mm, p < 0.001). Because the LWT distribution was non-normal, the result was further verified using a Mann-Whitney U test (p < 0.001), confirming robustness. A clear and progressive decrease in LWT was evident with increasing KOA severity, demonstrating a dose-response effect between degenerative grade and cortical thinning.
Correlation analyses revealed a moderately strong inverse relationship between KL grade and LWT across the study cohort (Pearson's r = -0.394, p < 0.001). Nonparametric correlations yielded consistent findings (Spearman's ρ = -0.403, p < 0.001; Kendall's τ = -0.316, p < 0.001). Linear regression analysis indicated that each one-grade increase in KL severity corresponded to an average 3.8 mm decrease in LWT (β = -3.8, 95% CI: -5.0 to -2.6, p < 0.001), confirming a graded biomechanical relationship between KOA severity and cortical integrity.
Predictive Modeling
In the multivariable logistic regression model, KL grade emerged as an independent predictor of fracture instability (adjusted OR = 4.9, 95% CI: 2.8–8.8, p < 0.001). Notably, after adjustment for age, sex, BMI, and comorbidities, no other covariate retained statistical significance in the final model, suggesting that KOA severity independently contributes to the likelihood of an unstable fracture pattern. The model exhibited good calibration (Hosmer-Lemeshow p = 0.25) and moderate explanatory power (Nagelkerke R² = 0.21).
The predictive performance of KL grade as a single diagnostic variable was strong, achieving an area under the ROC curve (AUC) of 0.79 (95% CI: 0.70–0.88). A KL grade ≥ III was identified as the optimal threshold for predicting fracture instability, yielding 95% sensitivity and 56% specificity (Youden Index = 0.51). Overall classification accuracy was 84.1%, with a positive predictive value of 80.0% and a negative predictive value of 85.2%.
Biomechanical Interpretation
The mechanisms linking KOA to fracture instability are likely multifactorial. KOA produces progressive joint malalignment, osteophyte formation, cartilage loss, and subchondral sclerosis. These degenerative changes alter the transmission of mechanical loads through the lower limb, thereby modifying the force vectors acting on the proximal femur during gait or falls.
Neuromuscular deficits commonly associated with KOA—such as quadriceps weakness, impaired proprioception, balance instability, and fear of falling—further affect fall mechanics. These biomechanical and neuromuscular alterations may change the angle and magnitude of ground impact, increasing the likelihood of unstable fracture patterns during a fall.
Our findings align with biomechanical and gait analyses demonstrating that KOA profoundly alters load distribution, stride dynamics, and limb alignment. The functional interdependence of the hip, knee, and ankle joints within the kinetic chain indicates that degenerative changes in one segment affect the entire limb's mechanics.
Clinical Implications
The demonstrated relationship between KOA severity and ITF instability carries significant surgical and rehabilitative implications:
Preoperative Assessment: Preoperative assessment of knee radiographs can provide valuable predictive information, enabling surgeons to anticipate unstable fracture morphology and plan accordingly. In patients with advanced KOA (KL grade ≥ III), more robust fixation strategies may be justified when lateral wall insufficiency is suspected.
Surgical Planning: Surgeons might select longer or static-locking cephalomedullary nails, employ augmentation techniques, and prioritize preservation of the lateral wall. In select cases, consideration of arthroplasty may be warranted.
Postoperative Management: Awareness of the biomechanical vulnerability associated with advanced KOA may inform tailored postoperative protocols, such as delayed or graded weight-bearing and more intensive physiotherapy programs.
Risk Stratification: Incorporating KOA grading into preoperative risk assessment may enhance surgical planning, improve patient counseling, and optimize postoperative management—complementing traditional parameters such as bone mineral density.
Comparison with Previous Literature
Our results are consistent with earlier studies linking KOA severity to unstable proximal femoral fractures. Polat et al. (2025) observed that patients with advanced KOA were more likely to exhibit AO/OTA type II–III fractures than those with milder grades. Similarly, Davut and Kalacı (2022) reported that KOA was significantly more prevalent among individuals with intertrochanteric fractures than among those with femoral neck or subtrochanteric fractures, suggesting a biomechanical influence of degenerative knee changes on fracture type.
Broader epidemiological studies also link KOA with increased fall risk, and studies of fall biomechanics confirm that impact direction, momentum, and velocity substantially influence hip fracture severity and pattern. The present study expands upon this literature by demonstrating that KOA severity not only affects fracture type but also predicts the degree of fracture instability—a distinct and clinically important parameter.
Limitations and Future Directions
We acknowledge several limitations. The retrospective design precludes establishment of causality. The single-center nature may limit generalizability. Additionally, we did not routinely assess bone mineral density or characterize fall mechanisms, which could provide additional insights into the observed associations.
Future prospective studies with larger cohorts are warranted to validate these findings and further clarify the mechanisms linking knee degeneration to hip fracture instability. Such work should integrate BMD assessments, characterization of fall mechanisms, gait analysis, and computational biomechanical modeling to establish causal pathways and inform targeted preventive or therapeutic interventions.
Conclusion
In this cohort, KOA severity was significantly correlated with unstable ITF patterns. The KL grade emerged as an independent predictor of instability and demonstrated strong diagnostic performance. These insights highlight the clinical value of incorporating KOA severity into preoperative assessments—not only for improved risk stratification but also for optimizing surgical planning and rehabilitation strategies. Routine assessment of KOA severity may provide surgeons with a practical, radiographic biomarker for predicting hip fracture stability and optimizing fixation strategy in elderly patients.
A Call for Collaboration
I invite fellow researchers, orthopedic surgeons, biomechanical engineers, and geriatric specialists interested in fracture prevention, musculoskeletal aging, and clinical prediction modeling to connect and explore collaborative opportunities. By integrating biomechanical modeling, imaging biomarkers, and clinical outcomes data, we can advance our understanding of the kinetic chain in aging populations and develop targeted interventions to reduce fracture burden worldwide.
Reference: Hashemi SA, Abedini B, Hosseini H, et al. Knee Osteoarthritis (KOA) Severity Influences Proximal Femoral Biomechanics and Predicts Pertrochanteric Fracture Instability: A Retrospective Radiographic Study. Medicina. 2026;62(3):469. https://doi.org/10.3390/medicina62030469