Magnetic resonance imaging findings in acute elbow dislocation: insight into mechanism.

PURPOSE: To identify with magnetic resonance imaging the location and severity of ligamentous injury after acute elbow dislocations. Based on observations that many elbow dislocations arise from an initial acute valgus load, we hypothesized that all patients would have a high-grade medial injury but not all would demonstrate injury of the lateral ligaments.

METHODS: The medial collateral ligament was subdivided into anterior bands of the anterior bundle of the medial collateral ligament (MCL) and posterior bands of the anterior bundle of the MCL, whereas the lateral collateral ligament was divided into the lateral ulnar collateral ligament and the radial collateral ligament. Distinction on magnetic resonance imaging was made between normal morphology and low-grade partial tear (< 50% of the ligament fibers), high-grade partial tear (≥ 50%), and full-thickness disruption. The site of disruption was also characterized.

RESULTS: Acute magnetic resonance imaging studies for 16 patients were included. No low-grade tears or intact evaluations of either the anterior or posterior bands of the anterior bundle of the MCL were observed; most demonstrated complete tears. The lateral ulnar collateral ligament most frequently showed complete disruption but was occasionally intact. The radial collateral ligament infrequently showed full disruption. Complete tears involving either the anterior or posterior portions of the anterior band of the MCL were significantly more common than complete tears involving the ligaments on the lateral side.

CONCLUSIONS: After elbow dislocation, complete ligamentous tears were more common on the medial versus the lateral side. Whereas the lateral ligaments were occasionally preserved, this was never observed on the medial side. These data suggest a sequence of failure starting on the medial side with subsequent variable energy dissipation laterally.

TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic IV.