Review Question - QID 219943

This 24-year-old male presents with an os acromiale following a mechanical fall. Os acromiale result due to failure of fusion between ossification centers (Answer 2).

Os acromiale are commonly encountered in practice, being present in approximately 1 to 15% of the population. The condition is most commonly seen incidentally, when patients receive imaging for other reasons, often trauma. The key to differentiating between fractures and congenital malformations comes down to radiographic findings, where the latter exhibits rounded edges with corticalization of the entirety of the fragment. With os acromiale, the acromion consists of four ossification centers: the pre-, meta-, meso-, and basi-acromion (Illustration A). The pathophysiology behind the entity involves failure of fusion between ossification centers, most commonly at the meta- and meso-acromion. When os acromiale are symptomatic, the preferred treatment includes activity modifications, NSAIDs, and possible corticosteroid injection. Only after 6–12 months of nonoperative treatment is surgical management considered, which includes excision or open reduction and internal fixation (ORIF).

You et al. performed a review of os acromiale, detailing their prevalence, pathoanatomy, presentation, and management. The acromion is formed with several ossification centers, including the pre-, meta-, meso-, and basi-acromion. The most common site for failure of fusion occurs between the meso- and meta-acromion. The majority of os acromiale are found incidentally and are thus treated non-operatively. Only after exhaustive nonoperative management including NSAIDs, activity modifications, and possible steroid injections, is surgical management indicated, which may consist of ORIF or excision of the fragment indicated.

Spiegl et al. similarly performed a review of os acromiale. They note the condition is most often encountered incidentally, but when symptomatic, patients often report symptoms similar to subacromial impingement, which includes tenderness overlying the anterolateral acromion, as well as difficulty with overhead activities. The authors encourage diagnostic injection with 1% lidocaine in unclear presentations in order to elucidate the source of pain. In cases where surgical management is warranted, multiple techniques (ORIF, resection) have shown good outcomes.

Hurst et al. also performed a review of the incidence, pathophysiology, and clinical management of os acromiale. The authors note fusion of the ossification typically occurs between 15 and 18 years of age. The presence of the anomaly has been believed to play a role in unsatisfactory outcomes with unrelated surgeries involving the shoulder. The authors similarly recommend exhausting non-operative treatments before entertaining surgical options.

Figures A and B demonstrate orthogonal views demonstrating an os acromiale at the junction of the meso- and meta-acromion. Illustration A is a depiction of the ossification centers as shown in the Hurst review.

Incorrect Answers:
Answer 1: Failure of mesenchymal segmentation occurs in tarsal coalitions.
Answer 3: Defects in chondrocyte proliferation are classically associated with achondroplasia.
Answer 4: Abnormal collagen cross-linking via a glycine substitution is characteristic of osteogenesis imperfecta.
Answer 5: Failure of cartilaginous differentiation most classically occurs in congenital radioulnar synostosis.