Biomechanical Evaluation of Metacarpal Fracture Fixation: Application of a 90° Internal Fixation Model

Abstract

Purpose Complications in metacarpal fracture treatment increase in proportion to the severity of the initial injury and the invasiveness of the surgical fixation technique. This manuscript evaluates the feasibility of minimizing internal fixation construct size and soft tissue dissection, while preserving the advantages of stable internal fixation in a biomechanical model. We hypothesized that comparable construct stability could be achieved with mini-plates in an orthogonal (90/90) configuration compared with a standard dorsal plating technique. Methods This hypothesis was evaluated in a transverse metacarpal fracture model. Twelve metacarpals were subject to either placement of a 2.0-mm six-hole dorsal plate or two 1.5-mm four-hole mini-plates in a 90/90 configuration. These constructs were tested to failure in a three-point bending apparatus, attaining failure force, displacement, and stiffness. Results Mean failure force was 353.5±121.1 N for the dorsal plating construct and 358.8±77.1 N for the orthogonal construct. Mean failure displacement was 3.3±1.2 mm for the dorsal plating construct and 4.1±0.9 mm for the orthogonal construct. Mean stiffness was 161.3±50.0 N/mm for the dorsal plating construct and 122.1±46.6 N/mm for the orthogonal construct. Mean failure moment was 3.09±1.06 Nm for the dorsal plating construct and 3.14±0.67 Nm for the orthogonal construct. The dorsal plating group failed via screw pullout, whereas the orthogonal failed either by screw pullout or breakage of the plate. Conclusions When subject to apex dorsal bending, the orthogonal construct and the standard dorsal plate construct behaved comparably. These data suggest that despite its shorter length, lower profile, and less substantial screws, the orthogonal construct provides sufficient rigidity. Clinical Relevance This study represents a "proof of concept" regarding the applicability of orthogonal plating in the metacarpal and provides the foundation for minimizing construct size and profile.

Intramedullary screw fixation for metacarpal shaft fractures: a biomechanical human cadaver study

“…(2019) reported higher peak loads between 119 N and 212 N for intramedullary screw fixation of midshaft transverse osteotomies in a 3-point bending test protocol. In our model, we used cantilever bending instead of 3-point bending because this technique may mimic the in vivo configuration after metacarpal fracture fixation most accurately (Nicklin et al., 2008; Watt et al., 2015). However, due to the fixation of the specimen at its base, cantilever bending may be associated with system failure rather than construct failure (Watt et al., 2015).…”

“…In the present experiments, 3/24 specimens fractured at the base before construct failure. Failure at the bone/PMMA interface is not unusual for cantilever bending and does not depend on the type of specimen (Sohn et al., 2008; Watt et al., 2015).…”

Headless Screw Fixation of Metacarpal Neck Fractures: A Mechanical Comparative Analysis

“…5,17,18,21 In addition, biomechanical studies have found dorsal plating, KW pinning, and intramedullary nailing to have reasonable stability across a metacarpal fracture site with dorsal plating being the most stable. 2,16,32 While clinically successful and biomechanically sound, the utility of these strategies is limited by a complication rate of up to 36%. 5,17,18,21 These complications include infection, 3,18 tendon injury, 21 malunion, 22 nonunion, 22 avascular necrosis, 15 stiffness, 17,21 and tendon adhesions.…”

Effect of oblique headless compression screw fixation for metacarpal shaft fracture: a biomechanical in vitro study

“…As a practical matter, no in vitro biomechanical tests can authentically reflect physiological loadings. In addition to the modified three-point bending test [ 15 , 30 , 31 ], cantilever bending tests [ 32 , 35 ], three-point bending tests [ 36 ], four-point bending tests [ 19 , 37 ], and torsional tests [ 32 , 38 ] have been adopted in previous studies. In this study, the cantilever bending test was not used because our pilot experiment revealed that the proximal end of the metacarpal bone was removed from the custom fixture with bone cement clamps during the cantilever bending loading.…”