Pyrocarbon interposition shoulder arthroplasty: preliminary results from a prospective multicenter study at 2 years of follow-up.

BACKGROUND: The concept of free interposition arthroplasty proved successful for small joints of the hand, wrist, and foot, particularly after the use of implants coated with pyrocarbon, which enhanced their tribologic and elastic properties. The present study reports preliminary outcomes of a pyrocarbon-coated interposition shoulder arthroplasty (PISA) implant.

METHODS: This was a prospective study of 67 consecutive patients who underwent shoulder PISA at 9 centers. The mean age at surgery was 51 years, with only 12 patients older than 60 years. The indications for surgery were primary glenohumeral arthritis in 42, avascular necrosis in 13, and secondary arthritis in 12 patients.

RESULTS: Revision surgery was performed in 7 patients (10.4%), 2 (3.0%) were lost to follow-up, and the outcome assessments were incomplete in 3 (4.4%). This left 55 patients, aged 49.3 ± 12.0 years, with complete outcomes assessments at a mean follow-up of 26.8 ± 3.4 months. The Constant score improved from 34.1 ± 15.1 preoperatively to 66.1 ± 19.7 postoperatively. The radiographic findings revealed erosion in 6 glenoids and thinning of 3 humeral tuberosities.

CONCLUSION: In a cohort of young arthritic patients, PISA renders clinical scores and implant survival comparable to those of hemishoulder arthroplasty but remain inferior to those results reported for total shoulder arthroplasty. The study enabled identification of contraindications and potential causes of failure that wererelated to the concept of free interposition and smaller radius of curvature of the sphere. Until long-term results are available, this type of innovative implant should remain to be tested in a few specialized shoulder centers.