Morphology and Prevalence of the Inferior Transverse Scapular Ligament: Systematic Review, Meta-Analysis, and Proposal for Classification.

: The suprascapular nerve is most vulnerable to entrapment at the suprascapular and spinoglenoid notches, causing neuropathy. Numerous studies have examined the suprascapular notch and ligament and its relationship with suprascapular nerve entrapment, but few have examined the spinoglenoid notch and the inferior transverse scapular ligament (ITSL). This study summarizes all existing ITSL morphology studies and presents a simple and comprehensive classification system for different ITSL subtypes. A systematic review of the literature was conducted according to the PRISMA guidelines, searching the online databases PubMed and Embase. The references of each relevant article were further screened to find more eligible studies. The Anatomical Quality Assessment tool was used in order to further evaluate the quality of the records extracted. STATA MP 14 was used for the analysis in this study. : In total, 14 studies (995 scapulae; minimum: 1 and maximum: 268) were included in the present study. The overall ITSL prevalence was 5.8 (95% CI: 4.5-7.1) and the estimated odds for ligamentous vs. membranous type was 0.5 (95% CI: 0.3-0.7). The basic different morphological subtypes of the ITSL reported in the included studies are the band-like ligament, the fan-shaped ligament, the membranous ITSL, and the perforated membranous types. The ITSL represents an anatomical structure of mostly ligamentous nature. A single ITSL definition and standardization of its basic morphological subtypes along with an easy-to-remember and thus widely used classification system could greatly facilitate the comprehensive description, identification, and proper handling of this element across many surgical procedures.