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Findings: AP film of the right shoulder with the humerus in external rotation (Fig. 1) demonstrates a short scapular neck with notching of the inferior portion of the glenoid fossa. The scapular neck is retroverted, resulting in retroversion of the articular surface. The humeral head has an abnormal contour with flattening and varus angulation.Subsequent CT images (Figs 2a, 2b) confirm the plain film findings and show an enlarged coracoid process. Similar findings are seen involving the left shoulder.

Diagnosis: Bilateral glenoid hypoplasia.

Discussion: Glenoid hypoplasia is a relatively rare developmental abnormality affecting males and females with equal frequency. It may be sporadic or can be transmitted in an autosomal dominant fashion with variable penetrance. Patients are usually asymptomatic. Symptoms may develop (i.e., shoulder pain, especially with exercise, limited range of motion, especially on abduction), usually in the 2nd and 3rd decades.

The glenoid is formed from two ossification centers, the subcoracoid and the secondary glenoid centers. It is thought that maldevelopment of the more inferior secondary glenoid center is the primary abnormality, which leads to bony undergrowth of the glenoid. The articular cartilage of the glenoid is thickened in a compensatory fashion. Altered dynamics about the shoulder joint lead to secondary changes involving the acromion and coracoid processes, humeral head and clavicle. This is analogous to changes seen in congenital dysplasia of the hips.

The basic radiographic findings in glenoid hypoplasia is underdevelopment of the inferior aspect of the scapular neck and glenoid rim. In the more severe forms, the inferior portion of the glenoid appears confluent with the lateral scapular border. A notch is frequently seen involving the inferior aspect of the glenoid and is referred to as a dentate deformity. The acromion process can enlarge and override the superior aspect of the joint, limiting abduction. The coracoid process is also often prominently enlarged. Changes in the humeral head include flattening of the articular surface, small size of the humeral head, elevation of the humeral head relative to the glenoid and slight varus deformity of the humeral neck. Hooking of the distal aspect of the clavicle can occur. On CT or MR, the articular cartilage may appear thickened, especially inferiorly. Thickening of the glenohumeral ligaments has also been described.

Glenoid hypoplasia may be unilateral or bilateral. In the series by Wirth et al (5), the unilateral cases were more symptomatic and radiographically more severe. When bilateral, glenoid hypoplasia is usually an isolated finding. The main differential considerations include bony dysplasias (multiple epiphyseal dysplasia, pelvis-shoulder dysplasia, spondylo-epiphyseal dysplasia, metaphyseal dysplasia, Apert's syndrome) which can usually easily be excluded by physical exam findings or skeletal survey demonstrating skeletal abnormalities at other sites, or Erb's Palsy, related to neurologic injury with birth trauma.

The mainstay of treatment of glenoid hypoplasia is physical therapy directed at strengthening the muscles of the shoulder girdle with avoidance of activities which exacerbate symptoms. Surgical intervention is rarely indicated.

References:
1.Borenstein ZCF, et al. Case Report 655. Skeletal Radiology 1991, 20:134-136.

2.Collins JS, et al. Case Report: MR Findings in Congenital Glenoid Dysplasia.
Journal of Computer Assisted Tomography, 1995, 19(5):819-821.

3.Kozlowski K, et al. Case Reports: congenital Bilateral Glenoid Hypoplasia:
A Report of Four Cases. The British Journal of Radiology 1987, 60:705-706.

4.Manns RA, et al. Glenoid Hypoplasia: Assessment by Computed Tomographic Arthrography.
Clinical Radiology 1991, 43:316-320.

5.Wirth MA, et al. Hypoplasia of the Glenoid: A Review of Sixteen Patients.
The Journal of Bone and Joint Surgery, 1993, 75(8):1174-1184.

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