Rare Shoulder Birth Defect Linked to Twin Fractures Once Suspected as Abuse

When a five-week-old boy arrived at a pediatric emergency department with a sudden reluctance to move his right arm, the clinical picture pointed toward one of the most feared diagnoses in pediatric medicine. Radiographs revealed a fracture through the basi-acromion, the lateral extension of the scapular spine that forms the root of the acromion and represents the ossified portion of the shoulder blade’s bony prominence at birth. Because scapular fractures are extraordinarily rare in infants and are considered a high-specificity marker of physical abuse when they occur in the absence of high-energy trauma, the finding immediately triggered a full child-abuse workup. What followed over the next several weeks, however, would challenge that initial interpretation and ultimately document what its authors believe is the first reported association between a congenital shoulder deformity and these telling fractures.

The infant, a fraternal twin delivered by unremarkable cesarean birth, had no history or visible signs of trauma, no pre-existing pain or weakness, and only questionable tenderness when his right shoulder was palpated. He was admitted to the hospital, and the Child Abuse Pediatrics team was consulted. The ensuing evaluation was exhaustive: a non-sedated MRI of the brain and cervical spine was normal, screening for occult abdominal trauma including liver transaminases and pancreatic enzymes was unremarkable, and a complete skeletal survey identified nothing beyond the known right acromion fracture. His twin sister underwent her own medical evaluation and skeletal survey, both of which were entirely normal. A report was made to child protective services, and the infant was discharged home to his parents under the supervision of a relative while the investigation continued.

Ten days later, the story took a decisive turn. The boy, now six weeks old, was brought to a pediatric orthopedic office because of decreased movement in his left arm. Bilateral humerus radiographs demonstrated a new fracture through the left basi-acromion, while the earlier right-sided injury showed signs of subacute healing, including peri-fracture resorptive changes and mild increased displacement. The symmetry of the two injuries, occurring on opposite sides of the body within days of each other in an otherwise healthy infant, suggested that something intrinsic to the child’s anatomy, rather than repeated external trauma, might be responsible. He was readmitted for a second round of testing.

That second workup was equally thorough and equally unrevealing. A repeat brain MRI remained normal. A metabolic bone disease screen measured free T4, thyroid-stimulating hormone, calcium, magnesium, phosphorus, alkaline phosphatase, parathyroid hormone, and 25-hydroxy-vitamin D, all of which fell within normal limits. A geneticist evaluated the child, and both whole-exome sequencing and an Ehlers-Danlos syndrome panel failed to identify an underlying genetic condition. A follow-up skeletal survey performed sixteen days after the first was negative for any additional fractures. The clinical picture simply did not fit the typical pattern of abusive injury, in which scapular fractures are usually accompanied by other traumatic findings such as additional fractures or central nervous system injury.

The breakthrough came from imaging review. An outside radiologist raised the possibility of glenoid hypoplasia, prompting bilateral shoulder MRI interpreted by a pediatric musculoskeletal radiologist. The study confirmed symmetric congenital glenoid dysplasia, a primary abnormality of the formation and ossification of the bony glenoid and adjacent scapular neck, along with healing fractures traversing the ossified basi-acromions on both sides. The quantitative findings were striking. Axial imaging showed exaggerated glenoid retroversion of 36 degrees on the right and 40 degrees on the left, compared with normal values of less than 10 degrees before age two. Coronal imaging revealed an exaggerated downward tilt of the glenoid fossae, with declination angles of approximately 45 degrees, in sharp contrast to the expected upward glenoid tilt of 0 to 15 degrees normally seen in childhood.

Congenital glenoid dysplasia must be distinguished from glenohumeral dysplasia, a secondary and usually unilateral deformity most often seen as a sequela of brachial plexus birth palsy, in which muscle imbalance drives progressive glenoid retroversion and posterior subluxation of the humeral head. The congenital form, by contrast, is typically bilateral and often asymptomatic, which helps explain why it usually escapes detection until adolescence, frequently after sports-related injuries, or until adulthood, when it can present as early-onset shoulder osteoarthritis. Recent studies suggest the condition may be substantially underdiagnosed, with reported incidence figures ranging from 19 to 35 percent. It can occur in isolation or in association with syndromes including Apert, Cornelia de Lange, Holt-Oram, Grant, aglossia-adactylia, and Hurler syndromes, and acquired unilateral deformities that mimic it must be ruled out during evaluation.

The multidisciplinary team ultimately classified the case as indeterminate for abusive injury, acknowledging that the effects of altered shoulder mechanics from congenital glenoid dysplasia were unknown and that abuse could not be completely excluded. Nevertheless, the consensus was that the fractures most likely resulted from restriction of the normal range of glenohumeral motion caused by the glenoid deformity. The reasoning is biomechanically coherent: a glenoid fossa tilted downward and rotated posteriorly would mechanically restrict cross-body adduction, vertical abduction, and forward flexion, precisely the motions routinely used in the everyday care of an infant, such as dressing and undressing. Ordinary handling, the team concluded, could plausibly have stressed the basi-acromion through its restricted arc of motion until it fractured, first on one side and then, symmetrically, on the other.

The discussion surrounding the case touches on one of the most delicate balances in pediatric medicine. Underdiagnosis of physical abuse leaves a child at risk of recurrent harm, but overdiagnosis carries its own serious consequences, including unnecessary removal of a child from the home and emotional trauma for everyone involved. Reaching the correct diagnosis requires the careful integration of patient history, physical examination, laboratory findings, and radiologic review, ideally through a collaborative multidisciplinary approach. In this instance, the symmetric appearance of isolated acromion fractures in a child with confirmed congenital glenoid dysplasia, combined with an otherwise entirely normal repeated evaluation, made abuse much less likely, though the authors emphasize that careful radiologic review remains essential in every suspected case.

The boy’s long-term outcome offers a reassuring epilogue. The bilateral fractures were treated conservatively, and he received weekly physical therapy from six months to three years of age, followed by twice-weekly occupational therapy from fourteen months to four years, with goals of increasing range of motion, strengthening the shoulder girdle, and improving flexion and abduction. By age four he had achieved full flexion and abduction in both upper extremities, and his orthopedic surgeon lifted activity restrictions. Now an active child participating in a variety of sports, he is monitored annually with imaging, which confirms ongoing joint laxity and persistent glenoid morphologic deficiencies, including non-visualization of the posterior glenoid rim, scalloped margination, and periosteal spurs on axillary views, along with posterior subluxation of the right humeral head.

Beyond its value to the individual family, the case carries a broader message for clinicians who evaluate infant fractures. Atypical fracture patterns do not always signal trauma, and congenital anomalies deserve a place in the differential diagnosis, particularly when injuries appear symmetric, isolated, and unaccompanied by other findings. Because congenital glenoid dysplasia is often silent in early childhood, its early manifestations remain poorly characterized, and its potential relationship to fracture risk has never before been documented. The authors call for further investigation into early presentations of the condition so that future clinicians can better distinguish congenital findings from those associated with abuse, protecting children on both sides of a diagnostic knife-edge: those who are being harmed and those whose unusual anatomy has been mistaken for evidence of harm.

Subject of Research: Congenital glenoid dysplasia associated with bilateral infantile acromion fractures initially suspected as child abuse

Article Title: Case report: Bilateral infantile acromion fractures in the setting of congenital glenoid dysplasia

Article References: Case report: Bilateral infantile acromion fractures in the setting of congenital glenoid dysplasia. (n.d.). https://doi.org/10.1007/s00247-026-06802-z

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06802-z

Keywords: congenital glenoid dysplasia, acromion fractures, child abuse pediatrics, pediatric radiology, scapular fractures, glenoid retroversion, shoulder biomechanics, infant fractures, MRI, skeletal survey, basi-acromion, orthopedics