Secondary Deformities of the Shoulder in Infants
Object: The authors performed a prospective study in which magnetic resonance (MR) imaging was conducted in 26 consecutive infants (mean age 5.6 months, range 2.7–14.5 months) in whom recovery from an obstetric lesion of the brachial plexus had been inadequate in the first 3 months of life. The purpose was to identify early secondary deformations of the shoulder in obstetrical brachial plexus lesions (OBPLs).
Methods: Features of the shoulders were analyzed according to a standardized MR imaging protocol in patients with OBPLs. Measurements were made of the appearance of the glenoid, glenoid version, and the position of the humeral head.
The appearance of the glenoid on the affected side was normal in only 11 shoulders. In the remainder it was convex in eight and biconcave in seven cases. The degree of humeral head subluxation was significantly greater (p = 0.001) in affected shoulders than in normal shoulders (152 and 170°, respecively). The presence of abnormal glenoid retroversion and humeral head subluxation increased with age: there was a statistical difference (p = 0.001) between infants younger than 5 months of age and those who were older.
Conclusions: Magnetic resonance imaging demonstrates shoulder-related anatomical and nerve root lesion, allowing evaluation of neural, osseous, and cartilaginous structures in younger children.

In most children with an OBPL, improvement of the neurological deficits can be expected within the 1st year of life. At present neurosurgical treatment is considered in infants with (sub)total lesions and those without biceps muscle function at 3 months of age. In these infants neuroimaging is part of the preoperative evaluation and is usually performed at 4 months of age. This examination focuses on diagnosing the type of lesions—that is, distinguishing neurotmesis from avulsion because regenerating axons cannot be expected in preganglionic spinal nerve root avulsions.

For the diagnosis of brachial plexus lesions in infants, MR imaging has surpassed computerized tomography myelography as the modality of choice. In applying different techniques in a noninvasive way, high-power MR images reveal plexus structures with great detail.

Although clinical symptoms are primarily caused by the brachial plexus lesion in infants with an OBPL, secondary deformities of the upper extremity may develop and influence the symptoms, predominantly around the shoulder. Information regarding these secondary shoulder deformities can be acquired during the MR imaging procedure by targeting the relevant neural structures.

Because brachial plexus lesions predominantly affect the upper cervical nerve roots or trunk (C5–6), muscular imbalance results around the shoulder, with paralysis of the abductors and external rotators and relative dominance of internal rotators. Consequently, a characteristic secondary shoulder deformity develops consisting of a flexion and internal rotation contracture of the shoulder as well as a posterior subluxation of the humeral head (referred to as "humeral head subluxation").

It has been shown that secondary structural shoulder deformities develop early in life and may persist despite improvement in neurological status. Although these secondary deformities may be compensatory lesions resulting from the altered muscular balance around the shoulder, in some cases these persistent deformities may even worsen the functional impairment caused by a residual neurological deficit.

The prevalence of shoulder deformities has been reported in 40 to 70% of cases. Until recently standard radiography and computerized tomography scanning were conducted to analyze the developing shoulder deformities. Their shortcoming is that they focus on the osseous structures. In this respect MR imaging better visualizes the predominantly cartilaginous shoulder in young children.

To assess the prevalence of secondary deformities of the shoulder in infants with OBPLs considered for neurosurgical reconstruction, we performed a prospective MR imaging–based study.