Anatomical and morphological study of the subcoracoacromial canal.

INTRODUCTION: Many clinical anatomy studies have looked into how variations in the acromion, coracoacromial ligament (CAL) and subacromial space are associated with rotator cuff injuries. However, no study up to now had defined anatomically the fibro-osseous canal that confines the supraspinatus muscle in the subcoracoacromial space. Through an anatomical study of the scapula, we defined the bone-related parameters of this canal and its anatomical variations. MATERIALS AND METHODS: This study on dry bones involved 71 scapulas. With standardised photographs in two orthogonal views (superior and lateral), the surface area of the subcoracoacromial canal and the anatomical parameters making up this canal were defined and measured using image analysis software. The primary analysis evaluated the anatomical parameters of the canal as a function of three canal surface area groups; the secondary analysis looked into how variations in the canal surface area were related to the type of acromion according to the Bigliani classification. RESULTS: Relative to glenoid width, the group with a large canal surface area (L) had significantly less lateral overhang of the acromion than the group with a small canal surface area (S), with ratios of 0.41±0.23 and 0.58±0.3, respectively (P=0.04). The mean length of the CAL was 46±8mm in the L group and 39±9mm in the S group (P=0.003). The coracoacromial arch angle was 38°±11° in the L group and 34°±9° in the S group; the canal surface area was smaller in specimens with a smaller coracoacromial arch angle (P=0.20). CONCLUSION: Apart from acromial morphology, there could be innate anatomical features of the scapula that predispose people to extrinsic lesions to the supraspinatus tendon (lateral overhang, coracoacromial arch angle) by reducing the subcoracoacromial canal's surface area. LEVEL OF EVIDENCE: Anatomical descriptive study.

The human acromion viewed from an evolutionary perspective.

The high prevalence of rotator cuff tendinopathy in modern humans may be partly related to the shape acquired by the scapula as species changed throughout evolution. Here, we compared the anatomic features of the scapula across members of the Hominoid group. The results support the hypothesis that the scapula of Homo sapiens sapiens exhibits distinctive anatomic characteristics compared to that of other Hominoids. We studied 89 scapulae from five species. For each scapula, we measured eight parameters and determined six index. We then compared the results across species. We identified two distinctive characteristics of the lateral aspect of the human scapula, namely, a lateral orientation of the glenoid cavity and a narrow coraco-acromial arch. Similar to the gorilla acromion, the human one is steeply sloped and, above all, larger and squarer than the acromion of other Hominoids. These features may explain, in part at least, the pathogenesis of rotator cuff tendinopathy in modern man.