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Cadaveric Biomechanical Analysis: Intramedullary Screw vs. Dorsal Plate for Metacarpal Base Fixation
Majd Mzeihem, MD
1, Dmitriy Peresada, MD
1, Yeseop Park, PhD
1, Jiries Fakhouri, BS
1, Danil Rybalko, MD
1, Mark Gonzalez, MD, PhD
1; Farid Amirouche, PhD
1,2(1)University of Illinois at Chicago, Chicago, IL, (2)Northshore University Health System, Evanston, IL
IntroductionIntramedullary (IM) screws have shown good results for metacarpal shaft and neck fractures, but extraarticular base fractures are common and lack biomechanical data. This study compares IM screws and dorsal plates for base fractures. Although small clinical reports favor IM screws, no biomechanical studies have tested their proximal stability or directly compared them to plates in this setting.
MethodsThis biomechanical study utilized 24 cadaveric metacarpals (from the thumb and small) from 12 upper extremities to compare the stability and rigidity of IM screw fixation versus dorsal plate fixation for proximal metacarpal base fractures. Each bone was skeletonized, measured, marked at 20% of its length from the base, and distally potted in cement. A standardized transverse fracture was created at this mark with an oscillating saw. Specimens were randomized to IM fixation with antegrade headless cannulated screws buried under the articular surface or dorsal plate fixation. Cantilever bending tests were conducted using an MTS machine at a rate of 0.3 mm/s. The ultimate failure load was the primary outcome, while construct stiffness was the secondary outcome.
ResultsA total of 24 cadaveric metacarpals were randomized to undergo simulated fixation using either dorsal plate or IM screw fixation. Biomechanical testing demonstrated that, when all specimens were combined, plate fixation resulted in a significantly higher load to failure compared to IM fixation (147.54 N vs. 97.44 N,
P = 0.01). However, IM constructs exhibited greater stiffness than plate constructs overall. Subgroup analysis showed a significant difference in the thumb metacarpals, where plate fixation had a higher load to failure than IM fixation (169.93 N vs. 110.98 N,
P = 0.03). In the small finger metacarpals, although plate fixation also had a higher failure load than IM fixation (125 N vs. 84 N), the difference was not statistically significant. Across all subgroups, stiffness was consistently greater in the IM constructs compared to the plate constructs (Table 1).
ConclusionDorsal plating demonstrated a higher load-to-failure than intramedullary screws, with a significant difference observed in the thumb. Both exceeded typical daily metacarpal loads, supporting IM screws as a viable alternative with lower complication and revision risks.
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