During our casuistry of treatment to gain external rotation (ER) of the shoulder in patients with late obstetric paralysis (OP), we observed ectoscopy morphological changes in the lower portion of the pectoralis major (PM).

To accurately analyze the PM muscle in its lower region and its alterations both macroscopically and histopathologically in late cases of patients with obstetric brachial palsy.

Evaluation of samples from 5 patients with late OP with retraction of anterior shoulder structures who underwent orthopedic procedures to gain ER. Samples for histological study were collected when there was an indication of PM muscle release.

Surgical Technique: After identifying the PM and visualizing its portions macroscopically, we found a lower portion with a different color that we considered to be a retraction zone. We then release this retracted portion of the muscle and this segment is removed in the proximal-distal axis for anatomopathological evaluation.

Histopathological Evaluation: Equidistant cross-sections were performed with a regular thickness of approximately 2.0mm. The evaluation was simplified and quantified in degrees of intensity of the sampled tissue (mild, moderate or severe), or variable foci of inflammatory component/fibrosis were noted along the muscular cross-sections.

In all cases, the area of muscle retraction was found along the lower PM region. After the excision of this segment and consequent release of the PM, the maneuver of passive movements of ABD and RE was repeated and a visible improvement of the ROM was observed in all cases. In the microscopic analysis, all the samples taken showed fibrotic or inflammatory tissue of varying degrees and it was verified that the latter was more intense in the proximal-distal direction.

The literature does not cite the pectoralis major muscle as one of the main structures to be released, and in many cases, its release is not included in the surgical technique.

With the knowledge of such anatomical changes, we can infer that in a patient with OBPP who requires the release of retracted muscular structures to gain ER and ABD, the release of the pectoralis major muscle should be performed by excising its inferior segment, which is altered and in retraction.

In cases of OP, the inferior portion of the PM muscle can be the determining cause of its retraction. Histopathological, the lower portion of the PM shows varying degrees of fibrosis.