Similar 5-year total ankle outcomes seen with mobile vs fixed bearings

Clinical outcomes favored mobile-bearing and fixed-bearing implants for total ankle replacement, according to published results.

“[At] a minimum of 2 to 5 years after implantation of a mobile-bearing vs. a fixed-bearing ankle replacement there appears to be little to no difference in patient-reported outcomes [PROs],” James A. Nunley II, MD, told Orthopedics Today. “Nevertheless, this preliminary data in the study will need to be followed for at least 10 years ...”

“[The] incidence of tibial lucency and cyst formation, while similar for the mobile-bearing and fixed-bearing tibial components, the mobile-bearing has greater talar lucency and tibial-talar subsidence,” Nunley said in his presentation of the study, which was a finalist for the Roger A. Mann Award at the American Orthopaedic Foot & Ankle Society Annual Meeting.

Nunley and colleagues compared mobile-bearing STAR Total Ankle Replacement (Stryker) and fixed-bearing Salto Talaris Total Ankle Replacement (Tornier) implants for total ankle replacement (TAR) in 84 patients with end-stage ankle osteoarthritis who failed nonoperative treatment. On average, the follow-up was 4.5 years. At 6 and 12 months postoperatively, investigators collected PROs, VAS, SF-36, foot and ankle disability index, short musculoskeletal functional assessment (SMFA) and AOFAS ankle-hindfoot scores.

All patients had statistically significant improvements from the preoperative to the most recent evaluation. Their clinical outcomes were not statistically significantly different. The area that showed statistical improvement of the fixed-bearing ankle over the mobile-bearing ankle was the SMFA.

Based on radiographs, tibial lucency/cyst formation for mobile-bearing and fixed-bearing TAR was 26.8% and 20.9%, respectively. Investigators found tibial settling/subsidence in 7.3% of the mobile-bearing group. Talar lucency/cyst formation occurred in 24.3% of the mobile-bearing group vs. 2% of the fixed-bearing group. In 21.9% of mobile-bearing TARs, investigators observed talar subsidence compared with 2% in the fixed-bearing TARs.

There were eight reoperations in the mobile-bearing group and three reoperations in the fixed-bearing group, mostly for impingement or to treat cysts.

The debate continues concerning whether mobile-bearing or fixed-bearing ankle designs are better, Nunley said.

“The mobile bearing has an unfixed polyethylene component with two fully conforming surfaces that articulate with metal,” he said, noting it optimizes conformity. The fixed bearing, which is poly fixed, is partially conforming which eliminates risk of subluxation, but is prone to eccentric load.” – by Monica Jaramillo