Lateral nail entry increases valgus risk, but coronal plane deformity does not affect knee function after femoral locked nailing

BACKGROUND: Closed locked intramedullary nailing (IMN) of femoral diaphyseal fractures (FDF) is the gold standard treatment. Postoperative frontal plane deformities can still occur following locked IMN. OBJECTIVES: The primary aim of this study was to evaluate the effect of coronal plane deformities on knee joint function and overall functional outcomes in adults with FDF treated using static locked IMN. MATERIAL AND METHODS: One hundred and twenty patients treated with locked IMN for FDF were divided into 2 groups based on coronal plane angulation measured on long-leg radiographs: group A (<5° deformity, n = 100) and group B (≥5° deformity, n = 20). Factors potentially influencing coronal plane deformity were compared between the groups. Radiographic parameters, including the mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), and postoperative lower extremity mechanical axis angle (MA), as well as intraoperative factors and complications, were analyzed. Functional outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) knee score, the Lower Extremity Functional Scale, and the Kujala patellofemoral scoring system. RESULTS: There were no significant differences between the groups in terms of age, gender, AO classification, or mechanism of injury. Coronal plane deformity was found to be independent of fracture localization, fracture type, and use of a traction table. However, nails implanted laterally to the greater trochanter were associated with significantly more valgus deformity (p < 0.001). No significant differences were observed in postoperative mLDFA, mMPTA, or MA between the groups at the final follow-up. Functional scores also showed no significant differences. CONCLUSIONS: After a minimum follow-up of 5 years, no adverse effects on knee or patellofemoral joint function were observed in patients with coronal plane deformities. Coronal plane deformity following locked IMN for FDF was independent of fracture location, classification, and traction table use. However, lateral entry to the greater trochanter was associated with increased valgus deformity.