Anatomical basis of the suprascapular nerve entrapment, and clinical relevance of the supraspinatus fascia

The entrapment of the suprascapular nerve (SSN) is commonly considered at the level of the suprascapular notch and more rarely in the spinoglenoid notch. Recent per-operative findings showed a compression of the SSN along its course in the supraspinatus fossa. The removal of a fascia for releasing the nerve between the suprascapular notch and spinoglenoid notch led us to purchase an anatomical study. 30 cadaver shoulders have been dissected. The morphological features about the suprascapular notch, the supraspinatus fascia, and the spinoglenoid notch have been observed. Histological studies of the fascia and the spinoglenoid ligament have been performed. Morphometric parameters such as shape of the suprascapular notch, diameters of the SSN before and after the suprascapular notch, distance between the two notches, length of the course of the SSN into the supraspinatus fossa, diameters of the spinoglenoid notch have been measured. The shape of the suprascapular notch could be seen as "U"- or "V" as previously reported. The fascia was quite constant (completely identified in 29 shoulders) and was the lateral extension of the supraspinatus fascia. The SSN coursed between the bone and the fascia and was surrounded by fat tissue. This fascia was thickened at the level of the spinoglenoid notch and joined the infraspinatus fascia. The spinoglenoid ligament was seen in 28 shoulders. In pathologic and post-trauma conditions, the fascia can be retracted or thickened and the SSN may be entrapped along its course in the supraspinatus fossa, between the suprascapular notch and the spinoglenoid notch and without any compression in any notch. These anatomical data lead us to consider that a tunnel syndrome may concern the SSN.