Initial Patella Vertical Fracture Displacement is a Predictor of Nonunion and Hardware Failure.

OBJECTIVES To determine if initial vertical fracture displacement affects postoperative outcomes following operative treatment of patella fractures.

METHODS Design: Prognostic retrospective study.

SETTING Single multi-site urban academic institution.

PATIENT SELECTION CRITERIA Included were patients aged ≥18 years who underwent open reduction internal fixation of a patella fracture (AO/OTA 34A-C) with minimum 6-month follow-up, and complete trauma knee x-ray series. Vertical fractures and those without significant vertical displacement (<2mm) were excluded.

OUTCOME MEASURES AND COMPARISONS Initial vertical fracture displacement was recorded. Follow-up data included knee range-of-motion and post-operative complications: nonunion, fracture related infection (FRI), hardware failure, suspected FRI, knee contracture, inferior sleeve displacement, and venous thromboembolism events. Comparisons were made between the initial amount of displacement and postoperative complications.

RESULTS 229 patients with a median follow-up duration of 12 months (IQR: 6-14) were included. The mean age was 61.2 ± 15.1 years, BMI was 25.4 ± 4.7 kg/m2, and 69.0% (n = 158) were female. OTA fracture classification was: 35.4% C1, 32.3% C3, 17.9% C2, and 14.4% A1. Fixation methods included 63.8% tension band wiring, 17.9% suture repair, 13.5% plate and screws, and 4.8% screws with suture. 33 (14.4%) patients sustained complications. The mean displacement was significantly higher in patients who developed complications (21.6 mm ± 15.0 mm vs. 14.8 mm ± 10.1 mm, p=0.018), particularly for nonunion (29.8 mm ± 13.5 mm vs. 15.1 mm ± 10.6 mm, p<0.001) and hardware failure (30.8 mm ± 12.0 mm vs 15.4 mm ± 10.9 mm, p<0.001). Suture-only and screw-with-suture fixation had higher nonunion rates (p=0.004, p=0.005) than other fixation methods independent of displacement. Initial displacement predicted nonunion and hardware failure (AUROCs=0.818 and 0.838). Youden Index thresholds of >26.6mm and >21.7mm identified patients at increased risk for nonunion and hardware failure. Each millimeter increase in displacement raised nonunion and hardware failure risk by 14.9% (OR=1.1, p=0.003) and 14.6% (OR=1.1, p=0.003).

CONCLUSIONS This study supports the future use of initial vertical fracture displacement as a prognostic tool for nonunion and hardware failure after patella ORIF. Displacement >2cm placed patients at high risk for these complications. Nonunion rates were higher in both suture only and screw-with-suture fixation when compared to other fixation constructs.

LEVEL OF EVIDENCE III.