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Comparison of Dorsal Plate Fixation versus Intramedullary Headless Screw Fixation of Metacarpal Shaft Fractures: A Biomechanical Study
Eitan Melamed, MD; Richard M. Hinds, MD; Michael Gottschalk, MD; Oran Kennedy, MD; John T. Capo, MD
NYU Hospital for Joint Diseases, New York, NY

Introduction: Operative metacarpal fractures are often treated with dorsal plate fixation. Recently, intramedullary headless screw (IMHS) fixation has shown promise as an alternative fixation strategy. The purpose of this study was to assess the biomechanical performance of IMHS versus dorsal plate fixation. We hypothesized that IMHS fixation provides equivalent fixation stability to dorsal plating.

Methods: Our hypothesis was tested in a transverse metacarpal fracture model using forty-four human metacarpals harvested from 8 fresh-frozen cadavers. The specimens were divided into 5 fixation groups: 1.5-mm non-locking plate; 1.5-mm locking plate; 2.0-mm non-locking plate; 2.0-mm locking plate; and 2.4-mm short cannulated IMHS. A 4-point bending model was used to assess load-to failure (LTF) and stiffness. Failure was defined as a marked change in the load versus displacement curve. Stiffness was determined from the slope of the elastic region of the load versus displacement curve. A one-way ANOVA test was used to identify statistically significant differences in LTF and stiffness among groups with a Wilcoxon test utilized for pairwise comparisons. The level of significance for all tests was P < 0.05.

Results: IMHS had significantly lower LTF (P < 0.001) than all of the dorsal plate fixation groups. Additionally, 2.0-mm non-locking plates (P = 0.01) and 2.0-mm locking plates (P = 0.023) demonstrated significantly greater LTF than 1.5-mm locking plates (Figure 1). There was a trend towards a significant difference for LTF between 1.5-mm non-locking plates and 1.5-mm locking plates (P = 0.092). No significant differences in LTF were found between 2.0-mm non-locking plates and 2.0-mm locking plates (P = 0.144). IMHS demonstrated the lowest stiffness in all groups, and was significantly less than 3 of the 4 dorsal plate groups (Figure 2). Bending stiffness in 2.0-mm locking plates was significantly greater than in the 2.0-mm non-locking plates (P = 0.022). No significant differences were found in stiffness between 1.5-mm locking plates and 1.5-mm non-locking plates (P = 0.999), or between 1.5-mm non-locking plates and 2.0-mm non-locking plates (P = 0.835).

Discussion and Conclusion: IMHS fixation of unstable metacarpal shaft fractures offers less stability compared to dorsal plate constructs when loaded in bending. The LTF and structural stiffness of IMHS versus dorsal plate fixation of metacarpal shaft fractures has not been previously quantified.

Figure 1. Chart displaying load to failure data. Values are displayed as mean and standard deviation.

Figure 2. Chart displaying stiffness data. Values are displayed as mean and standard deviation.

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