Heterotopic Ossification After Acute Acromioclavicular Joint Dislocation—Effect on Radiographic and Clinical Outcomes

Background: Heterotopic ossification (HO) frequently occurs after treatments for acute acromioclavicular (AC) joint dislocations, and is often considered a complication. Hypothesis/Purpose: This study aimed to evaluate and compare HO severity and configuration after single-suture button (SSB) and double-suture button (DSB) stabilization, and nonoperative treatment. It was hypothesized that the extent of HO after Rockwood (RW) type V injuries is associated with increased vertical stability, without substantially impairing clinical results. Study Design: Cohort study; Level of evidence, 3. Methods: Patients with acute RW type V dislocations treated with SSB (group 1), DSB (group 2), or nonoperatively (group 3) were analyzed with a 2-year follow-up. The exclusion criteria were previous shoulder surgery or concomitant fractures. HO was evaluated on anteroposterior stress radiographs in the conoid ligament area (CLA) and trapezoid ligament area (TLA), graded by severity and configuration. Radiographic parameters (coracoclavicular difference, RW classification, DPT, and osteoarthritis) and clinical outcomes (Constant Score, Subjective Shoulder Value, Taft score (TF), and Acromioclavicular Joint Instability score were assessed. Group differences were tested using the Kruskal-Wallis test, and associations between HO severity and outcomes were assessed using linear regression. Results: A total of 85 patients were included (group 1, n = 36; group 2, n = 28; and group 3, n = 21), with a mean age of 39.3 ± 11 and a mean follow-up of 44 ± 21.5 months. HO occurred in 71.3% of cases (CLA) and 58.7% of cases (TLA), with no group differences ( P = .390). Severity was predominantly mild across all groups, and the configuration was mostly clavicular. Severity showed no group difference (CLA, P = .703; TLA, P = .132). Configuration differed for the TLA ( P = .042), but not for the CLA ( P = .178). Severity of HO in the CLA correlated with higher TF scores (B = 0.902; P = .003), whereas TLA severity correlated negatively (B = −0.823; P = .034). Conclusion: When present, HO was mostly mild and clavicular, without relevant radiographic or clinical effects. Severity in the CLA correlated with a higher TF, whereas severity in the TLA correlated negatively. Given that the other radiographic and clinical parameters are unaffected, the term complication should be used with caution.