New parameters describing morphological variations in the suprascapular notch region as potential predictors of suprascapular nerve entrapment

BACKGROUND The suprascapular notch (SSN), bridged by the superior transverse scapular ligament (STSL), creates a pathway for the suprascapular nerve (SN). Morphological variations in the SSN region are common and can increase the risk of neuropathy by constricting the space for the nerve. The aim of this study was to establish new objective parameters that take this complex morphology into account. METHODS The SSN region of 100 formalin-fixed cadaveric shoulders was dissected. The dimensions of the SSN, the STSL and the anterior coracoscapular ligament (ACSL), as well as diameters of the SN, associated vessels and SN passage area, were measured by means of quantitative visual data analysis software to assign those structures to present classifications. The area reduction coefficient (ARC) and the ambit occupation coefficient (AOC) were defined and calculated for each shoulder. RESULTS The mean ARC and AOC for ligaments in the suprascapular region were: ARCSTSL = 71.6%, ARCACSL = 9.6%, AOCSTSL = 56.8% and AOCACSL = 9.1%. The SN passage area, ARC and AOC did not differ significantly between SSN types. The SN passage area and ARC differed significantly between band- and fan-shaped types of STSL. A significant relationship was observed between ARC and AOC (R=0.6855; p<0.0001). The SN passage area correlated significantly with ARC (R=-0.7555; p<0.0001) and AOC (R=-0.5609; p<0.0001). CONCLUSIONS The proposed parameters convey the complex morphology of the SSN region in a quantitative manner. The area reduction coefficient seems to be a more relevant indicator than the AOC as it better correlates with the SN passage area. Contrary to the SSN type, the STSL type significantly influences SN passage area and ARC.