Glenoid hypoplasia

Glenoid hypoplasia, also known as glenoid dysplasia, is an uncommon congenital condition resulting from underdevelopment of inferior glenoid ossification centre.

Epidemiology

Although previously considered rare, there is increasing recognition of a spectrum of glenoid hypoplasia with the increasing use of CT and MRI for shoulder assessment. Reports estimate a prevalence ~20% (range 14 to 35%) ^2,6, and possibly varying by race ⁷.

Glenoid hypoplasia is likely under-diagnosed since it is frequently asymptomatic or minimally symptomatic, particularly early in life and in cases of mild deformity. 

Clinical presentation

Glenoid hypoplasia is commonly asymptomatic or only mildly symptomatic, particularly in younger patients ^1,6. 

Symptomatic presentations are most common in middle-aged or elderly, and include ^1-4:

• limited range of motion

• shoulder pain

• shoulder dislocation (posterior glenohumeral instability): rare

Pathology

There are two glenoid ossification centres - superior and inferior ⁵. The typical pattern in glenoid hypoplasia involves the failure of the inferior glenoid epiphysis to ossify properly. Depending on the degree of development, there is variably deficiency of the inferior glenoid, compensatory hypertrophy of the articular cartilage/labrum, and variable glenoid retroversion relative to the scapular body/neck. 

The abnormal morphology may predispose to early degenerative changes such as glenohumeral osteoarthritis and posterior labral tears, resulting from altered glenohumeral mechanics ^1,3,6.

Radiographic features

• widened appearance of inferior glenohumeral joint interval ⁴

  • secondary to deficient inferior osseous glenoid, often with associated hypertrophy of the glenoid articular cartilage

• irregular glenoid articular surface

  • uniconcave

  • undulating "dentate" or biconcave appearance ⁴

• early-onset secondary osteoarthritis ^3,4

  • depends on the degree of underlying morphologic abnormality

• +/- posterior labral tears

• +/- additional osseous morphologic abnormalities, usually limited to adjacent shoulder bones ²

  • hypoplasia of proximal humerus

  • bossing or "hooking" of the distal clavicle

  • hypertrophy of coracoid process