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

OBJECTIVES

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

DESIGN

Prognostic retrospective study.

SETTING

Single multisite 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 (<2 mm) were excluded.

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

RESULTS

Two hundred twenty-nine patients with a median follow-up duration of 12 months (Interquartile range: 6-14) were included. The mean age was 61.2 ± 15.1 years, body mass index was 25.4 ± 4.7 kg/m 2 , and 69.0% (n = 158) were female. Orthopaedic Trauma Association 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. Thirty-three (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 >26.6 mm and >21.7 mm 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 open reduction internal fixation. Displacement >2 cm placed patients at high risk for these complications. Nonunion rates were higher in both suture-only and screw-with-suture fixation when compared with other fixation constructs.

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