Computed Tomography Versus Simple Radiography for Detecting and Classifying Heterotopic Ossification after Reverse Shoulder Arthroplasty.

Backgroud: Heterotopic ossification (HO) is difficult to characterize and classify on simple radiographs. Therefore, we attempted to evaluate intraobserver and interobserver reliability of simple radiography and computed tomography (CT) for detecting and classifying HO after reverse shoulder arthroplasty (RSA). It was hypothesized that CT would provide more reliable results than simple radiography.

Methods: This retrospective study reviewed 30 patients who underwent RSA performed by a single surgeon. Patients were included if they had both postoperative simple radiographs and CT images taken immediately after surgery and at 1 year after surgery and if they had completed clinical assessment at least 1 year after surgery. We first evaluated the intraobserver and interobserver reliability for the detection of the presence of HO and Modified Brooker's classification both on simple radiographs and CT scans with the use of Kappa statistics. Then, we analyzed the correlation of HO observed in simple radiographs and CT scans with clinical outcomes. All radiographic evaluations were performed by 2 independent reviewers in random orders with 3 weeks of intervals.

Results: The intraobserver reliability outcomes of both reviewers in simple radiography and CT were almost perfect or perfect for the detection of HO and classification. However, CT images improved the interobserver reliability for the detection of HO (kappa value for simple radiographs [K_XR] = 0.6018 and kappa value for CT [K_CT] = 0.8316) and classification (K_XR = 0.5300 and K_CT = 0.6964). At a mean follow-up of 25 months (range, 12-54 months), clinical scores were not significantly different according to the presence of HO based on simple radiographs. However, when CT images were used, the University of California, Los Angeles score and physical component score of short-form 36-item health survey were significantly lower in patients with HO than in patients without HO (27.0 vs. 30.4, p = 0.045 and 57.6 vs. 70.7, p = 0.034, respectively).

Conclusions: Both simple radiography and CT provided excellent intraobserver reliability for detecting and classifying HO after RSA. Compared to simple radiography, CT tended to improve interobserver reliability and defined the presence and severity of HO more clearly.