Is Preoperative Moderate to Severe Varus Alignment Associated With Survivorship and Outcome Scores at a Minimum of 5 Years After Mobile-bearing Total Ankle Arthroplasty With the Hintegra Device?

BACKGROUND

Analyses of long-term results after mobile-bearing total ankle arthroplasty (TAA) in ankles with preoperative moderate to severe varus deformity with adequate sample sizes remain limited. Because preoperative moderate to severe varus alignment may influence implant survival and functional outcomes, clarifying its long-term impact is important.

QUESTIONS/PURPOSES

(1) Do the clinical and radiologic outcomes of mobile-bearing TAA differ between ankles with preoperative neutral alignment and those with moderate to severe varus alignment? (2) What are the 5- and 10-year prosthesis survivorship, survivorship free from any revision including polyethylene exchange, and survivorship free from any unplanned reoperation in each group after mobile-bearing TAA? (3) Did the incidence of asymmetric polyethylene wear differ between the groups?

METHODS

Between September 2004 and May 2019, a single nondeveloper surgeon performed 417 TAAs. All procedures were performed using a single-design mobile-bearing device. The general indications for TAA were painful end-stage ankle arthritis. Of the 382 eligible ankles, 44% (168 ankles) were in patients with varus ankles (a preoperative coronal tibiotalar ankle ≥ 10° of varus) and 56% (214 ankles) were in neutral ankles (defined as < 10° of varus or valgus). Sixty-one percent (103 of 168) of the varus group and 61% (131 of 214) of the neutral group were available for follow-up with complete radiographic imaging and patient-reported outcome scores at a minimum of 5 years, and these patients were the focus of this retrospective, comparative study. The median (range) follow-up time was 123 months (60 to 230). The groups were similar with respect to age (63 versus 64 years; p = 0.34), gender (53% versus 44% men; p = 0.19), BMI (25.1 versus 25.5 kg/m2; p = 0.58), and follow-up duration (124 versus 116 months; p = 0.09). Although posttraumatic osteoarthritis was more common in the varus group and inflammatory arthritis in the neutral group, baseline demographic characteristics were otherwise comparable. Additional procedures to correct coronal alignment were performed at the discretion of the surgeon when necessary. Clinical outcomes were evaluated using VAS pain scores, Ankle Osteoarthritis Scale pain and disability subscores, as well as ankle ROM. Radiologic assessment included measurements of the postoperative coronal tibiotalar angle and development of asymmetric polyethylene inlay wear. CT scans with metal artifact reduction were performed to evaluate osteolysis. Survivorship was analyzed using the Kaplan-Meier method at 5 and 10 years for three endpoints: (1) revision or removal of a metal component, (2) revision of any component (including polyethylene exchange), and (3) any unplanned reoperation.

RESULTS

There were no clinically important differences in patient-reported outcome scores between the neutral and varus groups at a minimum of 5-year follow-up. The varus group had greater preoperative varus deformity (3° ± 4° versus 18° ± 6°, mean difference 15° [95% confidence interval (CI) 14° to 17°]; p < 0.001). Postoperative coronal plane alignment differed between groups, with the varus group demonstrating 1° more residual varus (2° ± 2° versus 3° ± 2°, mean difference 1° [95% CI 0° to 1°]; p = 0.01). Survivorship free from metal component revision did not differ between the neutral and varus groups at a minimum of 10-year follow-up (93.7% [95% CI 89.9% to 99.4%] versus 94.2% [95% CI 89.8% to 98.9%]; p = 0.88). Survivorship free from all-kind revision (including polyethylene exchange) did not differ between the neutral and varus groups at a minimum of 10-year follow-up (68.7% [95% CI 60.3% to 78.3%] versus 75.1% [95% CI 66.3% to 85.1%]; p = 0.19). Survivorship free from any unplanned reoperation did not differ between the neutral and varus groups at a minimum of 10-year follow-up (63.4% [95% CI 54.8% to 73.3%] versus 63.1% [95% CI 53.6% to 74.3%]; p = 0.94). The varus group had a higher proportion of patients who developed asymmetric polyethylene inlay wear than did the neutral group (42% [43 of 103] versus 17% [22 of 131]; p < 0.001).

CONCLUSION

In patients with moderate to severe preoperative varus deformity treated with this mobile-bearing TAA, we found no difference in patient-reported outcomes and implant survivorship compared with neutral ankles. However, varus ankles demonstrated a higher proportion of asymmetric polyethylene inlay wear, which may increase the risk of subsequent revision. Future studies should determine which patterns of varus deformity and residual malalignment are most strongly associated with edge-loading and how surgical correction strategies may mitigate this risk.

LEVEL OF EVIDENCE

Level III, therapeutic study.