Radiographic Comparison of Heterotopic Ossification After Primary Total Ankle Arthroplasty in Fourth-Generation Implants

Heterotopic ossification (HO) is a known sequela in total ankle arthroplasty. The purpose of this study was to determine the radiographic incidence of HO in fourth-generation total ankle implants including the INFINITY, CADENCE, and VANTAGE. Radiographs were assessed for the incidence and location of HO in each implant using the modified Brooker classification. Seventy-one patients were included. There were 41 INFINITY, 16 CADENCE, and 14 VANTAGE implants. The average radiographic follow-up was 19.7 months. The incidence of HO was 69.0%. Overall, the HO was Class I in 31 cases (63.3%); Class II in 7 cases (14.3%); Class III in 10 cases (20.4%); and Class IV in 1 case (2.0%). For INFINITY; n = 33 patients (80.5%), CADENCE; n = 8 patients (50%); VANTAGE n = 8 patients (57.1%). When comparing INFINITY with CADENCE/VANTAGE, there was a statistically significant difference in presence of HO (P = 0.01). When comparing INFINITY with CADENCE, there was a statistically significant difference in presence of HO (P = 0.04). In the 33 cases of INFINITY with HO, 30 had neutral or posterior coverage, and in 4 cases, the prosthesis did not extend to the posterior tibial cortex (P = 0.005). This study demonstrates a continued high rate of HO with 3 fourth-generation ankle implants in the short term, although many were Class 1 and posterior. The INFINITY had a higher overall incidence of HO. Adequate posterior cortical coverage did not play a role in radiographic presence of HO. Further research is warranted with longer-term follow-up to determine the clinical and radiographic significance of HO.