The Use of a Sustained Dynamic Compression Intramedullary Nail for Subtalar Arthrodesis

Abstract

Category: Hindfoot; Other Introduction/Purpose: Subtalar arthrodesis has traditionally been performed using fixation made of titanium or stainless steel. While these devices can provide initial compression, the compressive loads can be lost soon after surgery as bone settling or resorption occurs at the joint spaces. The DynaNail® Mini is a subtalar arthrodesis intramedullary nail that allows for compression during surgery and has a stretched nitinol element that attempts to contract but is held by talus and calcaneus screws providing sustained dynamic compression across the joint. There is minimal clinical data evaluating the effects of sustained compression devices on isolated subtalar arthrodesis. The goal of this study was to prospectively follow patients undergoing subtalar arthrodesis with the DynaNail® Mini and evaluate its clinical efficacy via fusion rate and patient reported outcomes. Methods: We prospectively enrolled patients aged 18-85 who underwent subtalar arthrodesis with the DynaNail® Mini from one of two academic surgeons. Demographic data and patient reported outcomes were collected preoperatively and at follow-up visits including Visual Analog Pain Scale (VAS), Foot Function Index (FFI), Foot and Ankle Ability Measure (FAAM) Sports Subscale, and Veterans Rand 12 (VR-12) physical and mental subscores. Patients were followed at 2 weeks, 6 weeks, 3 months, 6 months, 1 year, and 2 years postoperatively. The primary outcome measure was fusion rate via CT scan at 4 months with secondary outcomes consisting of the patient reported outcome data and rate of revisions. Results: 21 patients met inclusion criteria, 14 patients had a 4-month postoperative CT scan to assess for fusion with 78.6% of the CT scans (11 out of 14) demonstrating fusion at that time. 20 of the patients were followed through their 6 month visits, 16 patients through 1 year, and 16 patients were seen for their 2-year follow-up visit. All patient reported outcomes demonstrated improvement from preoperatively to final follow-up with VAS scores improving from 5.69 to 3.84, FFI improving from 56.43 to 37.88, FAAM-sports improving from 20.31 to 30.47, VR-12 Physical improving from 28.70 to 34.41, and VR-12 Mental improving from 43.64 to 49.81. Conclusion: This prospective study demonstrates that patients undergoing subtalar arthrodesis with the DynaNail® Mini demonstrate favorable clinical outcomes that are comparable to existing methods of subtalar arthrodesis with 78.6% of patients achieving fusion on a 4-month postoperative CT scan and with steady noted improvement in multiple validated patient-reported outcome measures.