Suprascapular nerve entrapment caused by the superior transverse scapular ligament (STSL) causes pain, and limitation of motion in the shoulder. To relieve these symptoms, suprascapular nerve decompression is performed through the resection of STSL. To describe and classify the topographic anatomy of the suprascapular notch, 103 cadaveric shoulders were dissected. The mean length and width of STSLs were 11.2 and 3.4 mm, respectively. The bony bridges replacing STSL in four shoulders were 8.2 mm long and 3.5 mm wide on average. The suprascapular nerve always ran through the notch under the STSL. All shoulders had a single suprascapular artery, while multiple suprascapular veins appeared in 21.3%. The arrangement of the suprascapular vessels was classified into three types: in Type I (59.4%), all suprascapular vessels ran over the STSL; in Type II (29.7%), the vessels ran over and under the STSL simultaneously; in Type III (10.9%), all vessels ran under the STSL. In 48.9% of cadavers, these types were bilaterally matched. The omohyoid muscle originated distantly from the STSL in 38.0%, was adjacent to it in 44.0%, and was partially over the STSL in 18.0%. The number of suprascapular vessels running under the STSL was positively correlated with the size of the STSL and the middle diameter of the suprascapular notch. Age was inversely correlated with the length of STSL. The STSL was wider in males than in females. This study provides details of the structural variations in the region of the suprascapular notch.

These results suggest that the fan-shaped area bounded by LP2, LP3, and the mandibular border is the safest and most effective depressor anguli oris muscle injection site.