A biomechanical study comparing plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to cyclic loading

Abstract

The use of bicortical screws to fix metacarpal fractures has been suggested to provide no added biomechanical advantage over unicortical screw fixation. However, this was only demonstrated in static loading regimes, which may not be representative of biological conditions. The present study was done to determine whether similar outcomes are obtained when cyclic loading is applied. Transverse midshaft osteotomies were created in 20 metacarpals harvested from three cadavers. Fractures were stabilised using 2.0 mm mini fragment plates fixed with either bicortical or unicortical screw fixation. These fixations were tested to failure with a three-point bending cyclic loading protocol using an electromechanical microtester and a 1 kN load cell. The mean load to failure was 370 N (SD 116) for unicortical fixation and 450 N (SD 135) for bicortical fixation. Significant differences between these two constructs were observed. A biomechanical advantage was found when using bicortical screws in metacarpal fracture plating.

Angular stable lateral plating is a valid alternative to conventional plate fixation in the proximal phalanx. A biomechanical study

“…This can be further enhanced by the use of unicortical screws since the far cortex does not need to be bored through, thus eliminating any chance of injury to the structures beyond this cortex by the drill. However, this is only possible with the angular stability offered by locking plate systems (Marti et al, 2001;Szypryt and Forward, 2009) as non-locked unicortical screw fixation has been shown to be inferior to nonlocking bicortical screw fixation (Afshar et al, 2012). Non-locking plates work best when used on the tension side to provide absolute rigid fixation or as a neutralizing plate in addition to a lag screw.…”

“…Rigidity of various fixation methods was investigated in previous studies (Afshar et al, 2012;Black et al, 1986;Lu et al, 1996;Nunley and Kloen, 1991;Ouellette et al, 2004;Prevel et al, 1995). Most of them were conducted applying quasistatic loading, which is less representative for the repetitive movements encountered during rehabilitation, or three-point bending of the fingers with limited physiological relevance.…”

A biomechanical analysis of plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to 4-point bending and dynamical bending test

“…Undisplaced metacarpal fractures may be treated conservatively with cast immobilization in intrinsic plus position for 4 to 6 weeks but the nonstable, dislocated, or complex fractures require a surgical treatment. [2] We define as unstable the fractures that are prone to dislocation, for example, the spiral metacarpal fracture, dislocated the fractures that are displaced more that the half of the shaft width and complex the multifragment and intra-articular fractures.…”

“…And if using locking plates, the biomechanical superiority of bicortical (locking) fixation over unicortical (locking) fixation in transverse metacarpal fracture plating remains also a subject of debate. [2,10,11] Surgeons, who are not used to monocortical fixation get the feeling of “insufficient” stability, whereas bicortical fixation always include the risk of soft tissue affection on the palmar aspect due to the “rolling up” of nerves, vessels, or tendons with the drill. [10,12] …”

Comparison of Dorsal Plate Fixation Versus Intramedullary Headless Screw Fixation of Unstable Metacarpal Shaft Fractures

“…1,8 While the majority of metacarpal fractures may be treated nonoperatively, closed reduction and percutaneous pinning as well as open reduction and internal fixation (ORIF) are recognized options for fixation of metacarpal fractures.…”