Morphology of the coracoid process. An anatomical study on 200 dry scapulae.

Previous anatomical studies of dry scapulae have focused on the morphology of the acromion. Very little is known about the morphometric characteristics of the coracoid process. In this study we analysed the morphology, dimensions and orientation of the coracoid process in 200 dry scapulae of adult subjects. Knowledge of these anatomical characteristics is important to evaluate the role of the coracoid in the aetiology of subcoracoid impingement syndrome. MATERIAL AND METHODS: Measurements were performed of the length and thickness of the coracoid process, and the distance between the latter and the antertior border of the glenoid. We also evaluated the inclination ofthe coracoid on the coronal, plane the morphology, on the horizontal plane, of the arch formed the anterosuperior border of the glenoid and the posterolateral margin of the tsoraeoid process. The data were correlated with the length to width ratio of the glenoid and the length to width ratio of the whole scapula. Based on the latter the scapulae were diveded into 3 groups: group I (ratio 1.18-1.34); group I1 l.35-1.50); group III (ratio 1.51-1.75). RESULTS: Group I included 51.5% ofthe scapulae, group II 44.5% and group III 4%. The mean length of the coracoid process was 38.2mm (range 34-47) in group I, 39.1 mm (range 35-47) in group Il, and 44.8 mm (range 38-50) in group III. In all 3 groups, the coracoid tip surpassed laterally the anterior border ofthe glenoid, an average, of 14.9mm, 14.7mm and 15.2mm, respectively; the SDs were as high as 6 mm in each group. The mean thickness ofthe coracoid tip was 7.2mm (range 5.5-10), 7.53 (range 6-10) and 8.50mm (range 7-10.5) in group 1,11 and III, respectively. The shortest mean distance between the anterior border of the glenoid and the lateral margin of the coracoid tip was 16.8 mm (range 12-18) in group 1., 16.0mm (range 14-22) in group ll and 18.5mm (range 15-22) in group III. In the coronal plane, the coracoid was orientated horizontally or inclined slightly caudally. The tangential line to the caudal margin of the coracoid tip running parallel to the articular surface was located cranially (rnax 0.-3mm) or caudally (max 12mm) to the tangen·t line to the cranial end ofthe glenoid. ln the horizontal plane, the anterosuperior border ofthe glenoid and the posterolateral margin ofthe coracoid delimit an arch-like space. We identified 3 configurations of this space: square bracket (33%), round bracket (45%) and fish hook (22%). The 3 configurations were equally distributed in the groups. Among the scapulae with a round bracket configuration, those with the extremities of the bracket very close showed the minimal distance between the coracoid tip and the anterior border of the glenoid. A round bracket configuration was associated with a considerably long and thick coracoid process and a marked prominence of the coracoid beyond the medial glenoid border in 4% ofthe scapulae. None of the parameters examined could be correlated with the length/width ratio of the glenoid. CONCLUSIONS: No correlation was found between the parameters analysed. Coracoid processes with similar length and/or thickness, or equidistant from the anterior border of the glenoid, may be found in each of the 3 groups of scapulae. This study shows that 4% of scapulae have bony motphometric characteristics which may predispose to subcoracoid impingement. Since the prevalence of this condition is not high, it is conceivable that other constitutional or pathological conditions should be present for development of symptomatic impingement.