Mechanical properties of the bicipital aponeurosis

As a biarticular muscle, the biceps brachii both supinates the forearm and flexes the elbow and shoulder, thus allowing the upper limb to perform a variety of activities of daily living (ADL). The biceps brachii originates on the coracoid apex as well as the supraglenoid tubercle and inserts on the radial tuberosity. At the distal end, the bicipital aponeurosis (BA) provides a transition of the biceps tendon into the antebrachial fascia. Previous work has reported the importance of the bicipital aponeurosis in stabilizing distal tendons. Other studies have reported the supination effect that the BA has on the forearm at the radioulnar joint, where it also protects the brachial artery and median nerve (neurovascular bundle). In addition, it has been speculated to have a proprioceptive function. However, despite the important functions fulfilled by this structure, the mechanical properties of the BA are yet to be quantified.

Mechanical properties for eight fresh frozen BA specimens (82 ± 12 years, 5 females, 5 right) were quantified using a Cellscale Biaxial (Waterloo, ON) testing machine. Three samples (approximately 7 × 7mm each) were harvested from the proximal, middle and distal regions along the length of the BA. Samples were tested on a biaxial testing machine while maintaining the alignment of the longitudinal collagen fiber orientation with the X-axis of the tester. The testing protocol included 10 preconditioning sinusoidal cycles at 9% strain, at a strain rate of 1%/s, followed by biaxial testing to a maximum strain of 12% at a strain rate of 1%/s. Young's modulus was quantified for all biaxial tests from the linear portion of the resulting stress-strain relation. Results showed that elastic modulus values were significantly greater in the longitudinal direction aligned with the collagen fibers. The outcomes of this study will provide input values for future models of distal biceps repair, thus aiding surgical planning by providing insight into the potential load sharing contributions of the BA.