Two Orthogonal Nitinol Staples and Combined Nitinol Staple-Screw Constructs for a First Metatarsophalangeal Joint Arthrodesis: A Biomechanical Cadaver Study

Abstract

Background: End-stage hallux metatarsophalangeal (MTP) joint arthritis is commonly treated with arthrodesis using stainless steel or titanium implants. These implants provide static compression that is maximal at the time of implant insertion. Alternatively, nitinol staples are capable of dynamic compression. They have most frequently been used for midfoot arthrodesis procedures. However, their biomechanical performance during hallux MTP arthrodesis has not been described. Methods: 8 matched pairs of cadaveric feet (4 female, 4 male) were prepared for hallux MTP arthrodesis using cup and cone reamers. Cadaveric pairs were then instrumented with either (1) a transarticular lag screw and dorsal nitinol staple or (2) orthogonal nitinol staples placed dorsally and medially. Walking in a short leg cast for 6 weeks was simulated by applying 90-N forces at 3 Hz to the plantar proximal phalanx for up to 250 000 cycles. Failure was defined as catastrophic implant failure or plantar gapping beyond 7 mm. Results: 15 of 16 specimens failed cyclic loading. All 8 specimens fixed with orthogonal staples failed at an average of 37 ± 81 cycles. 7 of 8 specimens fixed with a dorsal staple and crossed screw failed at 14 900 ± 39 000 cycles. Collectively, 5 specimens failed because of bone fracture (1 in orthogonal staples, 4 in staple-screw group) and 10 failed because of excessive gap formation (7 in orthogonal staples, 3 in staple-screw group). The number of cycles to failure was significantly lower ( P = .0469) in the orthogonal staple constructs compared with the dorsal staple and crossed screw constructs. Conclusion: The tested constructs permit significant motion at the first MTP fusion surface during simulated protected weightbearing. Although multiple in vivo factors should be considered when extrapolating results from this cadaveric study, this motion may result in clinical failure with early postoperative weightbearing protocols. Clinical Relevance: We report the first biomechanical evaluation of hallux MTP arthrodesis using modern nitinol staples in 2 separate constructs.

Evaluating the Biomechanical Integrity of Various Constructs Utilized for First Metatarsophalangeal Joint Arthrodesis: A Systematic Review

“…Across the 20 included articles, there were a total of 143 pairs of human cadaveric toes, 16 pairs of porcine cadaveric toes, and 92 synthetic bone models for a total of 446 cases of first MTP arthrodesis [1,9,11,13,19,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Arthrodesis was achieved using a variety of modalities including dorsal plates, interfragmentary lag screws, K-wires, wire sutures, and staples.…”

“…Neufeld et al also compared shape-memory staples to cross-cannulated screws as well as a dorsal plate, finding that the staples did indeed fail at significantly lower loads than the crossed-cannulated screws (p < 0.029) and the dorsal plate (p < 0.002) [36]. Schafer et al similarly compared orthogonal nitinol staples to a dorsal staple with a crossed screw [30]. All eight specimens implanted with orthogonal staples failed at an average of 37 ± 81 cycles of a 90 N, 250,000 cycle protocol designed to simulate 6 weeks of postoperative weightbearing due to excessive gap formation > 7 mm.…”

“…Despite the growing interest within the literature and the variety of fixation methods, there currently exists no consensus on the ideal fixation method for first MTP arthrodesis or the biomechanical underpinnings of these treatments [1,9,19,[22][23][24][25]. In the past decade alone, there have been 12 published primary studies describing the biomechanics of the first MTP joint [1,11,13,19,22,23,[25][26][27][28][29][30], warranting a systematic analysis of the existing literature. However, to date, no systematic review has synthesized and evaluated the biomechanical properties of the variety of fixation and joint resection methods described in the literature for first MTP arthrodesis.…”

Comparison of plate and compression screw in the treatment of hallux rigidus with arthrodesis: a retrospective study

“…The MPA1 procedure can vary depending on the type of joint surface resection and fixation method. For instance, these surgeries may rely on different types of joint surface resections, such as flat, concave, or convex, and various fixation methods, including screws, plates, or staples [10][11][12]. These different techniques can affect the effectiveness and outcomes of the surgical procedure.…”

Nitinol Staples in Foot and Ankle Surgery: Panacea or the Next Bubble?

“…Notwithstanding the positive clinical results, and the ever-increasing number of commercially available nitinol staple products, there are potential inherent limitations to nitinol staples as a sole tool for midfoot and forefoot fusions and trauma. Schafer et al 8 reported a biomechanical comparison of a 90-degree orthogonal nitinol staple construct vs a compression screw and staple construct for metatarsophalangeal fusion. They found that 15 of 16 specimens failed during cyclic loading, with significantly earlier failure in the orthogonal staple group.…”