Does the inferior transverse scapular ligament cause distal suprascapular nerve entrapment? An anatomic and morphologic study.

The number of reports on entrapment of the distal suprascapular nerve is increasing, but the incidence with regard to the inferior transverse scapular ligament remains controversial. Therefore, we investigated its incidence and anatomy in a series of cadaveric specimens; 115 shoulders (62 cadavers) were examined. The ligament was classified as either ligament- or membrane-type depending on its thickness. The width of the ligament and its maximal distance to bone and nerve were measured. Among the 115 specimens, the ligament was absent in 21 cases (18.3%), the ligament-type was present in 25 (21.7%), and the membrane-type was present in 69 (60.0%). The ligament width varied from 1.8 to 9.0 mm (mean, 5.4 mm), the maximal distance from ligament to bone varied from 3.0 to 11.1 mm (mean, 5.7 mm), and the distance from ligament to nerve was from 0.1 to 7.0 mm (mean, 3.1 mm). As there was considerable variation in the distances from the ligament to bone and nerve, the ligament may play a role in paralysis of the infraspinatus muscle, depending on these distances.