Evaluation of Nitinol Staples for the Lapidus Arthrodesis in a Reproducible Biomechanical Model

Abstract

While the Lapidus procedure is a widely accepted technique for treatment of hallux valgus, the optimal fixation method to maintain joint stability remains controversial. The purpose of this study is to evaluate the biomechanical properties of new shape memory alloy (SMA) staples arranged in different configurations in a repeatable first tarsometatarsal arthrodesis model. Ten sawbones models of the whole foot (n = 5 per group) were reconstructed using a single dorsal staple or two staples in a delta configuration. Each construct was mechanically tested non-destructively in dorsal four-point bending, medial four-point bending, dorsal three-point bending, and plantar cantilever bending with the staples activated at 37°C. The peak load (newton), stiffness (newton per millimeter), and plantar gapping (millimeter) were determined for each test. Pressure sensors were used to measure the contact force and area of the joint footprint in each group. There was a statistically significant increase in peak load in the two staple constructs compared to the single staple constructs for all testing modalities with P values range from 0.016 to 0.000. Stiffness also increased significantly in all tests except dorsal four-point bending. Pressure sensor readings showed a significantly higher contact force at time zero (P = 0.037) and contact area following loading in the two staple constructs (P = 0.045). Both groups completely recovered any plantar gapping following unloading and restored their initial contact footprint. The biomechanical integrity and repeatability of the models was demonstrated with no construct failures due to hardware or model breakdown. SMA staples provide fixation with the ability to dynamically apply and maintain compression across a simulated arthrodesis following a range of loading conditions.

Radiographic Results of Nitinol Compression Staples for Hindfoot and Midfoot Arthrodeses

“…Advantages of the new generation of nitinol staples are dynamic continuous compression that increases after time zero, full recovery of plantar gapping with 3- and 4-point bending, and new delivery instrumentation that does not require refrigeration or heating of the staple. 15 This study found that the staples also have a high union rate for both hindfoot and midfoot fusions, comparable to other constructs reported in the literature.…”

“…In contrast, nitinol staples completely recover plantar gapping following 3-point and 4-point bending secondary to their dynamic compression property. 15 Crossed screws for foot fusions are known to have high rigidity and high force to failure. 2,7,13 It is unclear if the combination of a staple and screw is superior to the use of a staple alone biomechanically and with regard to fusion.…”

First Metatarsophalangeal Joint Arthrodesis: A Narrative Review of Fixation Constructs and Their Evolution

“…This potentially offers a measurable decrease in operative time due to the simplicity of inserting a staple versus placement of an interfragmentary screw. Additionally, the continuous compression afforded by the use of nitinol staples is important, as it serves to help prevent the formation of gaps that can occur due to osteoclastic resorption or by other means when using constructs that utilize a static compression construct, such as an interfragmentary compression screw [39][40]. Figure 6A and Figure 6B show anterior-posterior and oblique views of the foot, respectively.…”

Finite element analysis of locking plate and 1/4 tubular plate for first tarsometatarsal joint fracture-dislocation

“…An improper implant may cause changes in the local biomechanical environment of the feet, leading to complications such as implant breakage, loss of reduction, and malunion. 2 Therefore, the biomechanical characteristics of different plates must be evaluated.…”