[Biomechanical study on posterolateral rotatory instability of elbow in coronoid process fracture with anterior bundle injury of medial collateral ligament].

OBJECTIVE

To investigate whether or not posterolateral rotatory instability of the elbow is due to type-I and type-II coronoid process fracture together with anterior bundle of medial collateral ligament (AMCL) injury so as to provide a theoretic basis for its clinical treatment.

METHODS

Ten fresh-frozen upper extremities were collected from cadavera which was donated voluntarily with no evidence of fracture, dislocation, osteoarthritis, mechanical injury of the surrounding ligament and joint capsule. They included 9 males and 1 female with an average age of 25.1 years (range, 19-40 years), including 3 cases at left sides and 7 cases at right sides. All specimens were transected at the upper midhumeral and carpal levels preserving the distal radioulnar joints to get the bone-ligament specimens. An axial load of 100 N compressing the elbow joint was applied along the shaft of the forearm in the sagittal plane through the biomechanical study system. The load-displacement plot was measured and analyzed at elbow flexion of 90, 60, and 45 degrees and under four conditions (intact elbow, type-I coronoid process fracture, type-I coronoid process fracture with AMCL deficient, and type-II coronoid process fractures with AMCL deficient).

RESULTS

The posterior displacements were maximum at 90 degrees elbow flexion. Hence, the results at 90 degrees elbow flexion were analyzed: under condition of intact elbows, the posterior displacement was the smallest (2.17 +/- 0.42) mm and the posterolateral rotatory stability was the greatest; under condition of type-I coronoid process fracture, the posterior displacement was (2.20 +/- 0.41) mm, showing no significant difference compared with that of the intact elbow (P > 0.05); under condition of type-I coronoid process fracture with AMCL deficient, the posterior displacement was (2.31 +/- 0.34) mm, showing no significant difference compared with that of intact elbow (P > 0.05); and under condition of type-II coronoid process fracture with AMCL deficient, the posterior displacement was (2.65 +/- 0.38) mm, showing a significant difference compared with that of intact elbow (P < 0.05). There was no macroscopic ulnohumeral dislocation or radial head dislocation during the experiment.

CONCLUSION

An simple type-I coronoid process fracture or with AMCL deficient would not cause posterolateral rotatory instability of elbow and may not need to be repaired. But type-II coronoid process fractures with AMCL deficient can cause posterolateral rotatory instability of elbow, so the coronoid process and the AMCL should be repaired or reconstructed to restore posterolateral rotatory stability as well as valgus stability.