Tendinous muscular insertions onto the deep fascia of the upper limb. First part: anatomical study.

We examined 30 upper limbs in order to study the tendinous muscular insertions into the deep fascia and to verify whether they have a specific anatomical arrangement and to measure their resilience to traction. We have found that the fascia receives many tendinous muscular insertions, which are always present and exhibit a constant anatomical structure. In particular, the pectoralis major fascia always continues with the brachial fascia in two distinct ways: the fascia overlying the clavicular part of pectoralis major had an expansion towards the anterior brachial fascia, whereas the fascia covering its costal part extended into the medial brachial fascia and the medial intermuscular septum. The lacertus fibrosus was also composed by two groups of fibres: the main group was oriented downwards and medially, the second group longitudinally. The palmaris longus opened out into a fan-shape in the palm of the hand and sent some tendinous expansions to the flexor retinaculum and fascia overlying the thenar eminence muscles. In the posterior region of the arm, the fascia of the latissimus dorsi sent a fibrous lamina to the triceps brachial fascia. The triceps tendon inserted partially into the antebrachial fascia, while the extensor carpi ulnaris sent a tendinous expansion to the fascia of the hypothenar eminence. It is hypothesized that the tendinous muscular insertions maintain the fascia at a basal tension and create myofascial continuity between the different muscles actuating flexion and extension of the upper limb, stretching the fascia in different ways according to the different motor directions.