Clinical and Radiographic Outcomes of Nitinol Compression Staples for Midfoot and Chopart Arthrodesis

Abstract

Category: Midfoot/Forefoot; Hindfoot Introduction/Purpose: Continuous compression implant (nitinol staples) use in orthopaedic surgery has increased in recent years. There are several advantages of nitinol staples, including a lower profile when compared to traditional fixation methods. They are easy to apply and take up a smaller footprint than most plating techniques, thus decreasing surgical time and dissection. Additionally, continuous compression across the fusion site is maintained during the resorptive phase of bone healing. Biomechanical studies provide useful data supporting the use of nitinol staples in the foot and ankle; however, clinical data is limited. This study’s purpose is to determine the efficacy of nitinol staples to achieve stable, bony healing in midfoot and Chopart joint arthrodesis, and examine their clinical outcomes, complications, and pain scores. Methods: A retrospective chart review was performed on 127 midfoot/Chopart joints (71 patients) that underwent arthrodesis using nitinol staples in isolation over a five-year period (January 2017 – February 2022). The primary outcome variable was radiographic evidence of healing. Radiographs were blinded, randomized, and independently reviewed by three board certified foot and ankle surgeons. Each investigator reviewed digital radiographs independently and recorded their radiographic finding responses. Fusions were deemed healed if greater than 50% of the arthrodesis site contained bridging bone. A partially healed arthrodesis was defined as some bridging bone, but less than 50% of the overall arthrodesis site, and a nonunion was defined as no healing seen radiographically or loss of reduction. There were no cases of complete inter-surgeon radiographic disagreement in this study. Pain scores and clinical outcomes were also collected. Smokers and diabetics represented 27% (n = 19) and 13% (n=9) of the patient population, respectively. Results: Complete/partial union was seen in 89% of all joints (113/127) and 93% of midfoot joints (98/106). Chopart joints had a significantly lower healing rate (15/21; 71%) compared to midfoot joints (p = 0.013) and TMT joints in isolation (86/91; 95%) (p = 0.006). Neuropathy and smoking had no effect on healing but diabetes did (p = 0.004). Joints requiring bone grafting had a worse healing rate (38/49; 76%) (p = 0.002). For all joints, post-operative VAS scores were significantly lower than pre-operative (p < 0.00001). Midfoot and Chopart pre-operative pain scores did not differ (p= 0.30), but differed post-operatively (p = 0.003). Midfoot joints had significantly lower pain scores post-operatively than pre-operatively (p < 0.00001). No such significance existed in Chopart joints (p = 0.070). Conclusion: Isolated nitinol staples are a viable option for midfoot arthrodesis, especially TMT joints, and offer significant pain improvement. Staples are lower profile, decreasing hardware irritation and potential secondary surgeries, and ease of use makes insertion efficient and reproducible. They offer the benefit of continuous compression of the fusion site, and are rigid enough to maintain reduction. Chopart joints, however, may require a more rigid fixation than nitinol staples can provide, given the lower healing rate. Caution should be exercised in diabetics and joints that may require bone grafting.