Radiographic Outcomes of a Mobile-Bearing Total Ankle Replacement.

BACKGROUND

Contemporary total ankle prostheses embody design changes intended to address weaknesses in first-generation implants. Due to these changes, outcomes of the newer designs are of particular interest. We have previously published self-reported patient outcomes for the STAR (Scandinavian Total Ankle Replacement) prosthesis. The present study documents radiographic outcome measurements for the STAR prosthesis at intermediate to long-term follow-up.

METHODS

Of 89 consecutive ankle replacements performed between July 1998 and April 2007, 79 had a minimum follow-up of 2 years and were followed prospectively. Serial radiographs were measured by 2 of the authors, including varus, valgus, alpha, beta, and gamma angles, as well as point contact ratio. Inter- and intrarater reliability was calculated and reported. A "severe" subgroup of patients with preoperative coronal plane deformity exceeding 10 degrees was assessed separately. Preoperative and immediate postoperative measurements were compared and maintenance of correction evaluated on subsequent radiographs. Heterotopic ossification and pericomponent lucency were documented and followed, and subsequent procedures were recorded to follow survivorship. The mean follow-up was 8.0 years.

RESULTS

Of the 79 ankles, 25 underwent a secondary surgery (31.6%). Coronal correction averaged 5.1 degrees (P < .001), and this was maintained to final follow-up. The severe subgroup (n = 21), with a mean preoperative coronal angulation of 16.1 degrees, was corrected to 4.6 degrees at final follow-up (P < .001). The severe subgroup had a higher secondary surgery rate at 33.3%, with metallic component revision or failure occurring in 3 cases (14.3%) compared to 8 (10.1%) in the entire cohort. The heterotopic ossification rate was 100%, slightly higher than prior reports.

CONCLUSIONS

STAR prosthesis survivorship was similar to that documented in prior studies of second-generation implants in European patient cohorts. Statistically significant correction in coronal alignment was achieved immediately after surgery and maintained until a final mean follow-up of 8 years, even in patients with preoperative deformity greater than 10 degrees.

LEVEL OF EVIDENCE: Level III, retrospective cohort study.