Medial wear of the polyethylene component associated with heterotopic ossification after reverse shoulder arthroplasty

Discussion

Polyethylene wear on retrieved implants has been observed in up to 50% of patients who undergo RSA.1^,2 Fluoroscopic examination attributes this to impingement of the humeral cup on the scapular neck, which can also result in scapular notching.1^,2 The notching phenomenon is of some concern because large or progressive lesions can negatively affect clinical outcomes and increase the risk of glenoid loosening.3 Some authors have suggested that impingement may simply be the initiating factor, with further osteolysis being triggered by polyethylene particles from cup wear.1^,2 In our patient’s case, revision surgery only 8 weeks after the initial RSA led us to believe that heterotopic ossification was the primary mechanical source of impingement leading to medial wear of the polyethylene component.

Conventional total shoulder arthroplasty has been known to result in post-operative heterotopic ossification. Sperling and colleagues4 found radiographic evidence of heterotopic ossification in 24.1% of 58 conventional total shoulder arthroplasties performed between 1989 and 1992. In most cases, the heterotopic ossification was present on early radiographs (1–2 mo postoperatively) and had developed inferior to the humeral head near the inferolateral aspect of the glenoid. Boehm and colleagues5 noted that patients with a primary diagnosis of cuff tear arthropathy who underwent total shoulder arthroplasty appeared to be at higher risk for the development of heterotopic ossification (36.4%) than patients with primary diagnoses such as osteoarthritis, avascular necrosis or fracture (< 14.5%).

We are not aware of any reports specifically documenting the incidence of heterotopic ossification after RSA. However, patients who have RSA may be at higher risk for the development of heterotopic ossification owing to a combination of factors: primary diagnosis of rotator cuff arthropathy; the amount of tissue damage from the surgical approach, which may include an extensive anterior and inferior capsular release; and the need to release the long head of the triceps from the inferior aspect of the glenoid to facilitate optimal inferior glenoid screw placement.5 The unique prosthetic design of RSA implants — an almost horizontal orientation of the RSA humeral cup combined with the absence of a prosthetic neck on the glenoid side — can predispose the polyethylene humeral cup inlay to excessive medial wear.1 The presence of heterotopic ossification inferolateral to the glenoid could trigger or exacerbate this problem.

We recommend a meticulous surgical technique to minimize tissue damage during the surgical approach and copious irrigation intraoperatively to limit osteogenic cell contamination that may contribute to heterotopic ossification. Although prophylactic nonsteroidal anti-inflammatory drug treatment does not appear to decrease the incidence of heterotopic ossification after total shoulder arthroplasty,5 no specific study of prophylaxis after RSA has been performed. Consideration should therefore be given to empiric nonsteroidal antiinflammatory drug prophylaxis. We also suggest close monitoring of post-operative radiographs for the first 8 weeks to identify any increased incidence of heterotopic ossification.