Comparison of Dorsal Plate Fixation Versus Intramedullary Headless Screw Fixation of Unstable Metacarpal Shaft Fractures: A Biomechanical Study

Abstract

Background: Recently, intramedullary headless screw (IMHS) has shown promise as an alternative to dorsal plate fixation of metacarpal fractures. The purpose of this study was to assess the biomechanical performance of IMHS versus plating. We hypothesized that IMHS fixation provides inferior stability to plating. Methods: Metacarpal fracture model with 3-mm of volar gapping in forty-four human cadaveric metacarpals was created. The specimens were divided into 5 groups: Group 1, 1.5-mm non-locking plate; Group 2, 1.5-mm locking plate; Group 3, 2.0-mm non-locking plate; Group 4, 2.0-mm locking plate; and Group 5, 2.4-mm short cannulated IMHS. A 4-point bending model was used to assess load-to failure (LTF) and stiffness. Results: Mean LTF was 364 ± 130 N for 1.5-mm non-locking plates, 218 ± 94 N for 1.5-mm locking plates, 421 ± 86 N for 2.0-mm non-locking plates, 351 ± 71 N for 2.0-mm locking plates, and 75 ± 20 N for IMHS. Mean stiffness was 91 ± 12 N/mm for 1.5-mm non-locking plates, 110 ± 77 N/mm for 1.5-mm locking plates, 94 ± 20 N/mm for 2.0-mm non-locking plates, 135 ± 16 N/mm for 2.0-mm locking plates, and 55 ± 15 N/mm for IMHS. IMHS demonstrated significantly lower LTF and stiffness than plates. Conclusions: IMHS fixation of unstable metacarpal shaft fractures offers less stability compared to plating when loaded in bending. The LTF and stiffness of IMHS versus plating of metacarpal shaft fractures has not been previously quantified. Our results reveal that IMHS fixation is less favorable biomechanically and should be carefully chosen in regards to fracture stability.

Keywords: biomechanical; fracture; intramedullary; metacarpal; stiffness.

Figure 1.

A 2.0-mm nonlocking plate construct positioned for testing in the biomechanical jig.

Figure 2.

Example of a typical load versus displacement graph. Note. LTF was defined a marked change in the load versus displacement curve as indicated in this figure. Stiffness was determined from the slope of the elastic region of the load versus displacement curve. LTF, load to failure.

Figure 3.

(a) 1.5-mm nonlocking plate constructs, (b) 1.5-mm locking plate constructs, (c) 2.0-mm nonlocking plate constructs, (d) 2.0-mm locking plate constructs, and (e) 2.4-mm intramedullary headless screws after biomechanical testing to failure. Note. Values are displayed as mean and standard deviation. IMHS, intramedullary headless screw.

Figure 4.

Chart displaying load-to-failure data. Note. Values are displayed as mean and standard deviation. IMHS, intramedullary headless screw.

Figure 5.

Chart displaying stiffness data. Note. Values are displayed as mean and standard deviation. IMHS, intramedullary headless screw.