Variations in bifid superior transverse scapular ligament as a possible factor of suprascapular entrapment: an anatomical study

PURPOSE: The suprascapular region is the most common place for suprascapular nerve entrapment. The purpose of this research was to investigate the influence of the superior transverse scapular ligament (STSL) on the reduced space for suprascapular nerve passage at the suprascapular notch. Additionally, we precisely described other structures that seem important during arthroscopic and open procedures in this region. METHODS: The study was carried out on 96 formalin-fixed cadaveric shoulders. After dissection of the suprascapular region the superior transverse scapular ligament was visualised. Measurements of the ligaments and area of the opening for the passage of the suprascapular nerve were taken using two independent methods: MultiScanBase v.14.02 software and electronic digimatic caliper. RESULTS: In three of 96 dissected shoulders (3.1 %), a bifid superior transverse scapular ligament was discovered. Morphologically, two subtypes of bifid STSL were distinguished. The first has medially separate superior and inferior bands and a common lateral attachment. In the second subtype, independent anterior and posterior parts are fixed to the lateral border of the suprascapular notch with a common medial attachment. Singular STSL in 93 of 96 shoulders was found. The mean area of the suprascapular opening in the specimens with singular STSL was larger than in the first subtype of bifid STSL and in the second subtype of bifid STSL with anterior coracoscapular ligament. CONCLUSION: Knowledge of the variations of the superior transverse scapular ligament is important for better understanding of the possible anatomical conditions that can promote suprascapular nerve entrapment. Its morphology should also be taken into particular consideration during surgical and arthroscopic procedures.