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A Comparison Of Two Pyrolytic Carbon Hemiarthoplasty Implants In The Treatment Of Trapezial-metacarpal Arthritis
Mark A. Vitale, MD, MPH; Marco Rizzo, MD; Steven L. Moran, MD; Mayo Clinic
Mayo Clinic, Rochester, MN, USA

Introduction: The treatment of trapezial-metacarpal (TM) arthritis of the thumb with prosthetic arthroplasty remains poorly characterized. The present study examines a cohort of patients with TM arthritis treated with two different pyrocarbon hemiarthroplasty prostheses. The hypothesis is that those treated with a second generation pyrocarbon prosthesis (NuGrip) will have a better range of motion (ROM), strength and lower complication and revision rate than those treated with the first generation of this prosthesis (PyroHemiSphere).

Methods: The cohort consisted of 46 arthritic TM joints in 36 patients with a diagnosis of osteoarthritis (n=36), post-traumatic arthritis (n=5), or rheumatoid/inflammatory arthritis (n=5) treated with prosthetic replacement with one of two implants (22 NuGrip versus 24 PyroHemiSphere). Patients were followed for an average of 27.4 months postoperatively.

Results: The average patient age at time of surgery was 56.0 years (SD=11.3). Compared to preoperative measurements, postoperatively those treated with the PyroHemiSphere prosthesis had an average decrease in radial abduction of -3.1° (SD=17.9), palmar abduction of -5.7° (SD=17.6), grip strength of -0.8-kg (SD=20.5), opposition pinch strength of -0.9-kg (SD=7.9) and apposition pinch strength of -0.9-kg (SD=4.6). Those treated with the NuGrip prosthesis had an average increase in radial abduction of 17.1° (SD=8.1), palmar abduction of 14.3° (SD=4.4), grip strength of 8.4-kg (SD=6.0), opposition pinch strength of 7.3-kg (SD=14.8) and apposition pinch strength of 11.3-kg (SD=14.9). Those treated with the NuGrip prosthesis had significantly greater increase in palmar abduction (p<0.01), grip strength (p<0.05) and apposition strength (p<0.05) than those treated with the PyroHemiSphere prosthesis. There was a 33.3% complication rate (n=8/24) and 37.5% revision rate (n=9/24) with the PyroHemiSphere compared to a 36.4% complication rate (n=8/22) and a 22.7% revision rate (n=5/22) with the NuGrip prosthesis, which was not statistically different. Overall, complications and revision surgery were most common in patients with rheumatoid/inflammatory arthritis (both 60.0%, n=3/5), although these rates were not significantly higher than other groups. There were no complications or revisions in patients with post-traumatic arthritis.

Conclusion: The second generation NuGrip prosthesis appears to offer an advantage in ROM and grip and pinch strength postoperatively compared to the PyroHemiSphere prosthesis at medium-term follow-up. Complication rates and revision rates, however, are high in both groups. Given the high rate of complications and revisions in those with rheumatoid or inflammatory arthritis, we do not recommend TM arthroplasty in this group, and we caution against use in patients with any evidence of STT arthritis or TM instability.

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