Biomechanical Evaluation of Popular Lapidus Fixation Plates

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: A 1st Tarsometatarsal (TMT) fusion or Lapidus is increasingly popular for moderate to severe hallux valgus with pronation. Hardware utilized for fixation consists of different combinations of plates, screws, and staples. Prior studies have suggested that constructs including a plate are superior to those consisting of screws or staples only. This biomechanical report compares a novel 1st TMT fusion U-plate to a predicate biplanar locking plating system. Methods: A total of 7 TMT U-plate systems were utilized for mechanical testing, with 3 samples undergoing static testing and 4 samples undergoing dynamic testing. Their mechanical properties were compared to those of one predicate device for static testing and 4 devices for dynamic testing. Standard 4th generation Sawbones models and bicortical screws were utilized in all cases. Static testing consisted of a uniform ramp to catastrophic failure using a cantilever bending model. Dynamic testing consisted of an incremental step procedure. A step size of 50,000 cycles at 3 Hz was used. The peak tensile load defined the step size with the valley tensile loading at one-tenth the peak loading. The first step used a 3.6 Nm moment with a peak tensile loading at 120 N. Results: Static testing of the TMT U-plate system demonstrated comparable or superior performance in load to failure testing than the predicate device (U-plate: mean = 351.3N, SD = 29.6; predicate: 324.4N). Dynamic testing demonstrated that the U-plate system survived 76,602 ± 43,275 cycles which was 261% greater than tested predicate constructs 29,338 ± 33,080 cycles. Additionally, cyclic failure loads were 151.3 ± 23.9 N for the U-plating system which was 120% greater than the predicate constructs at 126.3 ± 12.5 N. Conclusion: The TMT U-Plate demonstrated superior or comparable biomechanical properties to the predicate device in static and dynamic mechanical testing. Further investigation is needed to ascertain if these biomechanical differences have clinical correlations.