'Superior biceps aponeurosis'-Morphological characteristics of the origin of the short head of the biceps brachii muscle

Abstract

Purpose: Our aim was to characterize the morphology of the proximal attachment of the biceps brachii short head. We hypothesize that it has an aponeurotic component that may affect shoulder joint biomechanics.

Methods: The coracoacromial region and the biceps brachii muscle were dissected in 30 cadaveric shoulders. The course and dimensions of the tendon and aponeurosis were evaluated. The cross-sectional area of the belly of the short head and the length of the whole muscle were measured. Correlations between the aponeurosis and dimensions of the muscle were tested with the Spearman's rank correlation coefficient.

Results: Aponeurosis was present in all specimens, although in 10 cases it was vestigial. The aponeurotic part of the muscle (mean length 90.7 ± 16.3 mm, mean width 12.5 ± 2.9 mm) branched off laterally and traveled to the acromion, blending with the coracoacromial ligament creating the aponeurotic membrane. We named this structure the "superior biceps aponeurosis". The mean length of the biceps brachii was 31.3 ± 2.1 cm and the mean cross-sectional area of the short head was 210.7 ± 54.3 mm². The dimensions of the "superior biceps aponeurosis" correlated positively with the cross-sectional area of the muscle (R² from 0.37 to 0.52, p from 0.014 to 0.001).

Conclusion: The origin of the short head of the biceps brachii muscle has a varied aponeurotic component combining the aponeurotic part of the muscle and the aponeurotic membrane. Together, they create the "superior biceps aponeurosis".

Clinical relevance: The morphology of the origin of the biceps brachii short head is relevant in Bristow/Latarjet procedures. This aponeurotic component may affect the shoulder joint biomechanics after the coracoid process transfer.

Keywords: Anatomical variations; Biceps brachii; Superior biceps aponeurosis.