Timing of radiographic healing for distal femur fractures treated with intramedullary nails

Objectives: This study aimed to profile modified Radiographic Union Scale for Tibia (mRUST) scores over time in distal femur fractures treated with intramedullary nails and identify predictors of radiographic union timing and delayed progression.

Methods: Design: Multicenter retrospective cohort study.

Setting: Ten Level I Trauma Centers.

Patient selection criteria: The inclusion criteria were patients with distal femur fractures (OTA/AO 33A and 33C) treated with intramedullary nails, with a minimum follow-up of one year or until radiographic union or reoperation. The exclusion criteria were fractures treated with combination nail-plate constructs, pathologic fractures, and patients under 18 years old.Outcome Measures and Comparisons: The primary outcome was the mRUST score at 3, 6, and 12 months post-operatively. Receiver operating characteristic (ROC) curve analysis identified the optimal 3-month mRUST score predicting reoperation. Multivariable models were used to identify predictors of radiographic union timing and delayed progression.

Results: The study included 155 fractures in 152 patients, with a mean patient age of 51 and a mean follow-up of 17 months. A 3-month mRUST score of ≤8 predicted reoperation with a PPV of 25%, and a NPV of 99%. The timing of radiographic union was associated with tobacco use (1.2 months later; p = 0.04), open fracture (1.4 months later; p = 0.04), and the use of topical antibiotics (2.1 months longer; 95% CI: 0.33 - 3.84; p = 0.02), however topical antibiotics was at high risk of being confounded by injury severity. Delayed progression to fracture healing, wherein the most rapid radiographic healing occurs more than 3 months post-operatively, was predicted by chronic kidney disease (p < 0.01).

Conclusions: A 3-month mRUST score >8 suggests a very high likelihood of avoiding reoperation for nonunion.Tobacco use and open fractures were associated with a longer time to radiographic union. Chronic kidney disease is associated with a delayed radiographic progression, suggesting a need for adjusted expectations and management strategies in these patients.

Level of evidence: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.