[Arthroplasty with a mobile cup for shoulder arthrosis with irreparable rotator cuff rupture: preliminary results and cineradiographic study].

PURPOSE OF THE STUDY

Management of patients with massive irreparable rotator cuff tears associated with severe glenohumeral joint degeneration presents a difficult clinical challenge. The present study reports on 24 patients with disabling shoulder pain due to rotator cuff arthropathy treated using a bipolar arthroplasty.

MATERIAL AND METHODS

Between 1995 and 1997, a bipolar shoulder arthroplasty (Biomet, Warsaw, In) was used in 24 patients (25 shoulders) with rotator cuff arthropathy. Patients were monitored for an average of 14.5 months (range 12 to 24 months). The coracoacromial ligament was maintained in all patients to provide anterosuperior stability. The rotator cuff was irreparable and no attempt was made to cover the superior defect. Postoperative results were reviewed with the Constant score and the Swanson score. In order to verify the head-shell motion and to analyze the dynamic comportement of bipolar arthroplasties, we recorded anterior active elevation and active rotations with video-fluoroscopy.

RESULTS

At final the follow-up, 21 shoulders had no or slight pain. Average active flexion improved to 84.8 degrees after operation from 62.4 degrees beforehand. 13 patients achieved more than 90 degrees of active flexion after operation. Active external rotation improved from a mean 3 to 28.8 degrees. Before surgery the average Constant score was 17.62. Postoperatively, the average Constant score was 46.97 and the average Swanson score was 23.13. Complications requiring reoperation occurred in 2 cases: 1 component dislocation (Head-shell), 1 subluxation of the long head of the biceps. Radiographic evaluation at follow up demonstrated no humeral stem loosening or component migration and no bony erosion of the coracoacromial arch. Rupture of the infraspinatus tendon (absolute Constant score: p = 0.04, adjusted Constant score: p = 0.02, Swanson score: p = 0.03, Functional score: p = 0.04), preoperative anterior subluxation of the humeral head (absolute Constant score: p = 0.03, adjusted Constant score: p = 0.05, anterior elevation: p = 0.01, functional score: p = 0.04), preoperative narrowing of the acromio-humeral interval (adjusted Constant score: p = 0.02, overall mobility: p = 0.02, anterior elevation: p = 0.03) may jeopardize the subsequent success of bipolar shoulder arthroplasty. The results of this study suggest that the radius curvature of the shell must match that of the bony surface of the glenoid and the coracoacromial arch (absolute Constant score: p = 0.003, adjusted Constant score: p = 0.005, overall mobility: p = 0.002, anterior elevation: p = 0.0008, functional score: p = 0.002). Recording of anterior active elevation with video-fluoroscopy allowed to identify 3 different types of movements after bipolar shoulder arthroplasty. Recording of internal and external rotation allowed to distinguish 2 differents types of movements. Motion appeared to occur between the bipolar shell and the head. The amount of motion was variable and depended on the biomechanics.

DISCUSSION AND CONCLUSION

Bipolar shoulder arthroplasty is an effective surgical option for patients with massive irreparable tears of the rotator cuff with concomitant glenohumeral arthritis. Satisfactory pain relief and modest gains in motion result in significant functional improvement in this "low functional demand" population. Predictive factors have been identified and should be discussed before surgery.