The coronoid opening angle: a novel radiographic technique to assess bone loss in coronoid trauma

Elbow fracture dislocations are complex injuries that often require surgical treatment in order to obtain a stable and congruent elbow joint. The coronoid plays a key role in the stability of this joint. Accurately identifying the degree of coronoid bone loss in the setting of traumatic elbow injuries is challenging. The purpose of this study is to describe a new radiographic measure, the coronoid opening angle (COA), to assist in estimating bone loss in these challenging fractures.

Radiographs were drawn from a regional database in a consecutive fashion. Candidate radiographs were excluded on the basis of radiographic evidence of degenerative changes, previous surgery or injury, bony deformity, and inadequate lateral view of the elbow. Normal COA, coronoid height, and calculated COA at varying amounts of bone loss were determined by 3 reviewers.

A total of 120 subjects were included. The normal coronoid opening angle was 34° (95% CI 32.9°-34.0°) and the coronoid height, 18.8 mm (18.1-19.6). Ninety-five percent of the population had an opening angle greater than 29° (95% CI 27.2°-29°). The COA limit was calculated at 20%, 33%, and 50% of baseline coronoid height corresponding to degree of bone loss. Coronoid opening angles of 24°, 20°, and 16°, respectively, indicate the minimum bone loss of interest in 95% of the population. The intraclass correlation coefficient was found to be 0.89 or higher.

In the setting of elbow trauma, it is often challenging to predict the amount of coronoid bone loss. The coronoid opening angle is a new technique and an adjunct for lateral elbow radiographs to predict the minimum coronoid bone loss. This can be used to guide clinical decision making, aid in predicting instability, and guide treatment. Future research will aim to validate this tool in the clinical trauma setting.