The Effect of Anteromedial Facet Fractures of the Coronoid and Lateral Collateral Ligament Injury on Elbow Stability and Kinematics

BACKGROUND: It is postulated that fractures of the anteromedial facet of the coronoid process and avulsion of the lateral collateral ligament lead to posteromedial subluxation and arthritis of the elbow. It is not clear which injuries require internal fixation and whether repair of the lateral collateral ligament is sufficient. We hypothesized that increasing sizes and subtypes of anteromedial facet fractures cause increasing instability and that isolated lateral collateral ligament repair without fracture fixation would restore elbow stability in the presence of small subtype-I fractures. METHODS: Ten fresh-frozen cadaveric arms from donors with a mean age of 66.3 years at the time of death were used in this biomechanical study. Passive elbow flexion was performed with the plane of flexion oriented horizontally to achieve varus and valgus gravitational loading. An in vitro unconstrained elbow-motion simulator was used to simulate active elbow flexion in the vertical position. Varus-valgus angle and internal-external rotational kinematics were recorded with use of an electromagnetic tracking system. Testing was repeated with the coronoid intact and with subtype-I, subtype-II, and subtype-III fractures. Instability was defined as an alteration in varus-valgus angle and/or in internal-external rotation of the elbow. All six coronoid states were tested with the lateral collateral ligament detached and after repair. RESULTS: In the vertical position, the kinematics of subtype-I and subtype-II anteromedial coronoid fractures with the lateral collateral ligament repaired were similar to those of the intact elbow. In the varus position, the kinematics of 2.5-mm subtype-I fractures with the lateral collateral ligament repaired were similar to those of the intact elbow. However, 5-mm fractures demonstrated a mean (and standard deviation) of 6.2 degrees +/- 4.5 degrees of internal rotation compared with a mean of 3.3 degrees +/- 3.1 degrees of external rotation in the intact elbow (p < 0.05). In the varus position, subtype-II 2.5-mm fractures with the lateral collateral ligament repaired demonstrated increased internal rotation (mean, 7.0 degrees +/- 4.5 degrees; p < 0.005). Subtype-II 5-mm fractures demonstrated instability in both the varus and valgus positions (p < 0.05). Subtype-III fractures with the lateral collateral ligament repaired were unstable in all three testing positions (p < 0.05). CONCLUSIONS: This study suggests that the size of the anteromedial coronoid fracture fragment affects elbow kinematics, particularly in varus stress. The size of an anteromedial coronoid fracture and the presence of concomitant ligament injuries may be important determinants of the need for open reduction and internal fixation.