PRIMARY SURGICAL RECONSTRUCTION OF JOINT STABILIZERS VERSUS HINGED EXTERNAL FIXATOR AUGMENTATION IN THE TREATMENT OF ACUTE ELBOW INSTABILITY – A BIOMECHANICAL STUDY

Abstract

In the treatment of acute elbow dislocation promising clinical results have been reported on articulated external fixation and surgical reconstruction of major joint stabilizers. However, it remains unclear whether or not surgical reconstruction of the major joint stabilizers sufficiently stabilizes the elbow joint or if augmentation by a hinged elbow fixator is beneficial to provide early stability and motion capacity. The aim of the present study was to compare the stabilizing potential of surgical reconstruction versus augmentation by a hinged external elbow in a model of sequentially induced intability of the elbow.

Materials and Methods: 8 unpreserved human upper extremities were mounted to a testing apparatus which was integrated within a material testing machine. In a first series, varus and valgus moments were induced to the intact elbow joint at full extension, as well as at 30°, 60°, 90° and 120° of flexion and the mean angular displacement at 2.5, 5, an 7.5 Nm was calculated. Instability was then induced by sequentially dissecting the lateral and the medial collateral ligament, the radial head, and the posterior capsule. The elbow joint was then sequentially restabilized by osteosynthesis of the radial head and refixation of the lateral and medial collateral ligament using bone anchors. In each sequence, elbow stability was tested with and without augmentation by a hinged external fixator according to the first testing series described above. Biomechanical data of surgical reconstruction alone and surgical reconstruction augmented by external fixation were compared using an analysis of variance.

Results: In the intact elbow, varus-valgus displacement with 7.5 Nm ranged from 8,3 ± 2,4° (0°) to 11,4 ± 4,2° (90°). With the fixator applied, varus-valgus displacement was significantly lower and ranged from 4,2 ± 1,3° (0°) to 5,3 ± 2,2° (90°). After complete destabilization of the elbow joint, maximum varus-valgus displacement ranged from 17,4 ± 5,3° (0°) to 23,6 ± 6,4° (90°). Subsequent reconstruction of the collateral ligaments, the posterior capsule, and the radial head proved to stabilize the elbow joint compared with the unstable situation, however, mean varus-valgus displacement remained significantly higher when compared to the intact elbow joint. During each sequence of instability, the hinged external fixator provided constant stability not significantly different to the intact elbow joint while guiding the elbow through the entire range of motion.

Conclusion: The stabilizing potential of surgical reconstruction alone is inferior to augmentation of a hinged external elbow fixator. In order to proved primary stability and early motion capacity, augmentation of a hinged external elbow fixator in the treatment of acute dislocation of the elbow is recommended.