Anatomic and biomechanical study of the biceps vinculum, a structure within the biceps sheath.

PURPOSE To evaluate the anatomic, biomechanical, and histologic properties of the biceps vinculum and its potential role as a restraint to distal migration of the biceps after tenotomy. METHODS Eight human shoulders were dissected to define the anatomic parameters of the biceps vinculum. Histologic studies were performed by sectioning through the vinculum-tendon attachment and performing H&E staining. The strength of the vinculum was tested biomechanically after sectioning the biceps origin and applying a uniaxial tension at a rate of 1 mm/s until failure. RESULTS With regard to anatomy, the vinculum was present in all specimens, attached to the biceps tendon and proximal humerus. Excursion testing showed that the vinculum prevented the biceps origin from migrating distal to the groove entrance. The mean dimensions of the structures and excursion were as follows: biceps origin to vinculum, 43.4 mm; vinculum width on biceps side, 46.2 mm; vinculum width on bone side, 69.3 mm; length of tendon with proximal pull, 42.6 mm; and length of tendon with distal pull, 2.25 mm. With regard to histology, the membranous tissue of the biceps vinculum consisted of loose soft tissue with fat, arteries, and veins. The vinculum was seen to loosely attach to the biceps tendon and more intimately attach to the periosteal/bone side. With regard to biomechanical testing, the maximum force to failure of the vinculum was variable, ranging from 17.4 N to 227.6 N, with a mean value of 102.7 +/- 76 N. CONCLUSIONS The biceps vinculum was a consistent membranous structure intimately associated with the biceps tendon and attached to the proximal humerus. After tenotomy at the biceps origin, the vinculum prevented distal migration of the proximal biceps tendon past the groove entrance in all specimens. Biomechanical testing showed that the vinculum provided variable resistance to distal pull. CLINICAL RELEVANCE The properties described may help to explain why biceps tenotomy does not routinely result in a Popeye biceps deformity.