The medial forearm fascia and lateral forearm fascia contribute to overhead elbow extension in displaced olecranon fractures: a biomechanical study

Abstract

Background: In nonoperative management of displaced olecranon fractures, patients are able to maintain overhead extension despite a persistent nonunion. It has been hypothesized that this is feasible because of an intact lateral cubital retinaculum. The purpose of this biomechanical study was to determine the contribution of the medial and lateral cubital retinacula to overhead extension in the setting of a displaced olecranon fracture.

Methods: Eight fresh-frozen cadaveric upper-extremity specimens were used in this study. The triceps muscle was loaded through a pulley system operated by an Instron 8874 Biaxial Servohydraulic Fatigue Testing System at a rate of 10 mm/second to simulate overhead elbow extension. Each specimen was tested in 4 states: (1) native state with an intact olecranon; (2) transverse olecranon fracture; (3) transection of 1 cubital retinaculum (medial or lateral); and (4) transection of both medial and lateral cubital retinacula. The primary outcome was the ability to perform overhead extension. The secondary outcome was the force needed to generate extension.

Results: Elbow extension was noted in each specimen for trials 1, 2, and 3. Only when both the lateral fascia and medial fascia were transected was elbow extension not achieved. There was no significant difference in the force required to generate extension in the first 3 trials (P = .99). There was no significant difference in the change in the maximum force required to achieve extension between the specimens with only the medial side transected and the specimens with only the lateral side transected (P = .07).

Discussion: In the setting of an olecranon fracture, this biomechanical study suggests that if either the lateral or medial cubital retinaculum remains in continuity with the distal ulna, active overhead extension can be maintained. This finding may explain the positive clinical outcomes of nonoperative management of displaced olecranon fractures in the elderly patient population. Determining the integrity of the fascial structures preoperatively may help select candidates for nonoperative treatment of displaced olecranon fractures.

Keywords: Olecranon fractures; anconeus; biomechanics; elbow extension; lateral cubital retinaculum; medial forearm fascia; triceps.