Minifragment screw fixation of oblique metacarpal fractures: a biomechanical analysis of screw types and techniques

Abstract

The lag screw technique has historically been a successful and accepted way to treat oblique metacarpal fractures. However, it does take additional time and involve multiple steps that can increase the risk of fracture propagation or comminution in the small hand bones of the hand. An alternate fixation technique uses bicortical interfragmentary screws. Other studies support the clinical effectiveness and ease of this technique. The purpose of this study is to biomechanically assess the strength of the bicortical interfragmentary screw versus that of the traditional lag screw. Using 48 cadaver metacarpals, oblique osteotomies were created and stabilized using one of four methods: 1.5 mm bicortical interfragmentary (IF) screw, 1.5 mm lag technique screw, 2.0 mm bicortical IF screw, or 2.0 mm lag technique screw. Biomechanical testing was performed to measure post cyclic displacement and load to failure. Data was analyzed using one-way analysis of variance (ANOVA). There was no significant difference among the fixation techniques with regard to both displacement and ultimate failure strength. There was a slight trend for a higher load to failure with the 2.0 mm IF screw and 2.0 mm lag screw compared to the 1.5 mm IF and 1.5 mm lag screws, but this was not significant. Our results support previously established clinical data that bicortical interfragmentary screw fixation is an effective treatment option for oblique metacarpal fractures. This technique has clinical importance because it is an option to appropriately stabilize the often small and difficult to control fracture fragments encountered in metacarpal fractures.

Figure 1

a ‘Bicortical interfragmentary’ screws were placed after standard drilling whereas holding the fracture fragments compressed with a clamp. b ‘Lag technique’ screws were placed using standard lag technique: overdrilling near cortex and drilling far cortex.

Figure 2

Oblique, midshaft osteotomy made 45° to long axis.

Figure 3

a Axial loading and cantilever bending force vectors were resolved into single 45° vector. b Specimens loaded at 45° to the long axis.

Figure 4

Mean post cyclic displacement by metacarpal.

Figure 5

Mean load to failure by metacarpal.

Figure 6

Mean post cyclic displacement by fixation type.

Figure 7

Mean load to failure by fixation type.