Long Term Survivorship of InBone II Total Ankle Arthroplasty

Research Type: Level 2 - Prospective comparative study, Meta-analysis of Level 2 studies or Level 1 studies with inconsistent results Introduction/Purpose: As total ankle arthroplasty (TAA) continues to be indicated for more active patients with more complex deformity and at younger ages, understanding implant longevity and survivorship expectations is critical for patient counseling and decision making. Utilization of the INBONE II TAA system has increased with midterm survivorship studies demonstrating promising results of up to 98% survivorship at 5 years, but long-term results are lacking since its introduction in 2010. The purpose of this study was to determine the long-term survivorship of the prosthesis at a minimum follow-up of ten years with accompanying radiographic and patient reported outcome reports at a single institution. Methods: Patients enrolled in a prospective TAA registry with 10-year minimum follow-up after INBONE II TAA were retrospectively identified. Those deceased prior to minimum follow-up, unable to return for medical/travel reasons, lost to follow-up within the first 6 postoperative months, or unable to be contacted were excluded. Chart review captured operative data, prior/concomitant surgeries, reoperations, and revision details. Preoperative and postoperative radiographs were measured to assess coronal/sagittal alignment and presence of periprosthetic lucency (radiolucent line adjacent to implant interface >1 mm thick and >5mm long, at least 50% of the implant “zone”) and osteolysis (hypodense zone > 5 mm without inner bone trabeculae but with new peripheral sclerosis). Available patient recorded outcomes were analyzed. Survivorship was determined by incidence and timing of metal component revision (MCR). Data was then stratified by those who failed (MCR) and those who did not. Of 179 TAAs screened, 72 ankles (69 patients) met inclusion criteria. Results: Median age at surgery was 60.6y (range 38.7-78.4) with median 10.4y follow-up (IQR 9.8-11.1). Overall survivorship was 93.1% (Figure 1); reoperation rate was 17.4% (19 reoperations, 12 patients). Peri-implant lucencies were found in 20.8% of tibias and 11.0% of taluses; periprosthetic cyst formation was noted in 15.3% of tibias and 9.7% of taluses. True MCR rate was 6.9% (3 talus, 2 both components), secondary to failure of ingrowth (2), osteolysis/polyethylene wear (2), and infection (1). Patients with MCR trended towards larger preoperative varus talar tilt (9.6 vs. 2.8) and varus tibiocalcaneal angle (-5.6 vs. 9.1) (p=0.24 and 0.07, respectively); trends were also noted towards larger changes in pre vs. postoperative tibiotalar and distal tibial angles versus non-failures (-16.2 vs. -1.9, p=0.11; -7.3 vs. -0.8, p=0.07). Conclusion: Long term survivorship of the INBONE II TAA was 93% in this cohort at minimum ten years. Despite the presence of periprosthetic osteolysis and/or peri-implant lucency in 9-21% of components, overall reoperation rate was 17.4%, and MCR remained under 10%. While a small number of failures led to no statistically significant conclusions, trends in the pre and postoperative radiographic data suggest possible higher risk of failure in those with greater varus deformity, especially with greater talar tilt, which require more correction. Additional research is required to confirm these suspicions with statistical confidence.