Compressive Strength of Midfoot Fusion Nail vs Midfoot Fusion Bolt and Role of Subtalar Fusion in Midfoot Charcot Fixation Model.

Abstract

Operative management of midfoot Charcot arthropathy often involves an extended midfoot arthrodesis with intramedullary bolts for fixation, a method called "beaming." Recently intramedullary nails have been introduced for the same indication, presumably providing stronger fixation. This study compares midfoot fusion nails to bolts with regard to stiffness and compressive ability. Additionally, we assessed how the addition of a subtalar fusion affects the construct. Medial column fusions were performed on 10 matched cadaver foot specimens with either a midfoot fusion nail or bolt. Specimens underwent cyclical compression loading, and displacement was measured. Separately, compressive forces produced were compared between the 2 fixation constructs using a synthetic bone block model. Lastly, another 10 matched specimens with midfoot fusion nails were evaluated with or without subtalar fusions. No differences in stiffness were found in comparing matched specimens between nail vs bolt or comparing nail only without subtalar fusion (STF) vs nail with STF. The compressive force produced by the nail specimens was significantly and substantially greater than the bolted specimens (751.7 vs 139.0 N, P = .01). The accumulated height drop at the midfoot after cycling was 0.5 mm more in the nail group than in the bolt group (1.72 vs 1.22 mm, P = .008). The nail with STF group had greater initial height drop at the midfoot than the nail-only group (0.68 vs 0.34 mm, P = .035) with similar initial height drop at the ankle. However, there were no differences in strength among the matched pairs of midfoot nail-only vs midfoot nail with STF as measured by displacement after fatigue or maximum force at load to failure. The overall cadaveric comparisons between matched pairs of nails vs bolts, and nail-only vs nail with STF, did not provide noteworthy differences between the groups with regard to strength or stiffness. However, the compressive force of the midfoot fusion nail was far superior to the bolt in a synthetic bone model. These data provide valuable insight comparing implants used in Charcot midfoot arthrodesis.