Biomechanical comparison of elbow stability constructs

Abstract

Background: Despite surgical stabilization of complex elbow trauma, additional fixation to maintain joint congruity and stability may be required. Multiple biomechanical constructs include a static external fixator (SEF), a hinged external fixator (HEF), an internal joint stabilizer (IJS), and a hinged elbow orthosis (HEO). The optimal adjunct fixation to surgical reduction is yet to be determined.

Methods: Eight matched cadaveric upper extremities were tested in a biomechanical model. Anteroposterior stress radiographs were obtained of the elbow in full supination at 0° and 45° of elbow flexion with the weight of the hand serving as a varus load as the baseline. A 360° capsuloligamentous soft-tissue release was performed around the elbow. The biomechanical constructs were applied in the same sequential order: SEF, HEF, IJS, and HEO. For each construct, 0 kg (0-lb) and 2.3 kg (5-lb) of weight were applied to the distal arm. At both weights, radiographs were obtained with the elbow at 0° and 45° of flexion, with subsequent measurement of displacement, congruence at the ulnohumeral joint, and the ulnohumeral opening angle. Statistical analysis was performed to quantify the strength and stability of each construct.

Results: Compared with the control group at 0° with and without 2.3 kg (5-lb) of varus force and at 45° with and without 2.3 kg (5-lb) of varus force, no difference was noted in the medial ulnohumeral joint space, lateral ulnohumeral joint space, or ulnohumeral opening angle between the SEF, HEF, and IJS. The gap change after exertion of a 2.3-kg (5-lb) force between the control condition and application of each construct demonstrated no difference between the SEF, HEF, and IJS. Comparison among destabilized elbows showed no significant difference between the SEF, HEF, and IJS. The HEO catastrophically failed in each position at 0 kg (0-lb) of weight.

Conclusion: The SEF, HEF, and IJS are neither superior nor inferior at maintaining elbow congruity with the weight of the arm and 2.3 kg (5-lb) of varus stress. The HEO did not provide additional stability to the unstable elbow.

Keywords: Elbow instability; biomechanical stability; biomechanical strength; complex elbow injury; hinged elbow brace; hinged external fixator; internal joint stabilizer; static external fixator.