Polymethylmethacrylate (PMMA) Augmentation Increases the Strength of Midfoot Beam Constructs in Charcot Neuroarthropathy Model: A Biomechanical Study

Category: Basic Sciences/Biologics; Diabetes Introduction/Purpose: Even with the best conservative care, patients with Charcot Neuroarthropathy (CN) of the foot and ankle often ulcerate, increasing their risk of infection, amputation, and death. Surgical fixation has a 30% risk of recurrent ulceration, likely due to poor host bone quality which is prone to deformity recurrence and subsequent ulceration. We propose midfoot beam reconstruction with PMMA augmentation as a novel means of improving fixation. Methods: A protocol was developed to create the characteristic CN midfoot fragmentation both visually and fluoroscopically in each of tweleve matched-pair cadaveric feet. Afterward, the pairs were divided into two groups (1) Midfoot beam fusion alone, and (2) Midfoot beam fusion augmented with PMMA. In both groups, a solid 7.0 mm beam was placed into the medial column and a solid, 5.5 mm beam was placed across the lateral column. In the PMMA group, 8-10 mL of PMMA was inserted into the medial column. The hindfoot of each specimen was potted and the metatarsal heads were cyclically loaded for 1800 cycles, followed by load to failure while load and displacement were continually recorded. Results: One specimen in the beam only group failed before reaching the 1800th cycle and therefore was not included in the failure analysis. The midfoot beam only group demonstrated greater mean displacement during cycle testing compared to the PMMA group, p< 0.05. The maximum force (N), stiffness (N/mm) and toughness (Nmm) were all significantly greater in group augmented with PMMA, p< 0.05. Conclusion: In a CN cadaveric model, PMMA augmentation significantly decreased gapping during cyclic loading and nearly doubled the load to failure compared to midfoot beams alone. Clinical Relevance: The results of this biomechanical study demonstrate that augmentation of midfoot beams with PMMA increases the strength and stiffness of the fusion construct, which may reduce the risk of nonunion and infection in patients with neuropathic midfoot collapse.