Screw fixation of simulated scaphoid waist fractures: a biomechanical comparison of two screw lengths.

TitleScrew fixation of simulated scaphoid waist fractures: a biomechanical comparison of two screw lengths.
Publication TypeConference Abstract
Year of Publication2017
AuthorsM. Ouwendijk, N. Slingerland, J. van Nistelrooij, T. Huysmans, E. Van de Casteele, F. van Glabbeek, G. Meermans, and F. Verstreken
Conference NameEuropean Federation of National Associatinos of Orthopaedics and Traumatology (EFORT), 18th ANNUAL CONGRESS, VIENNA, AUSTRIA
Abstract

Background:
Sixty percent of carpal bone fractures affect the scaphoid. These fractures typically occur in a young and male population, with a mean age of 25 years. Eighty percent of scaphoid fractures are located at the waist and the majority of these fractures is nondisplaced and stable. The poor healing capacity of scaphoid fractures, frequently causes delayed- or nonunion, leading to impaired function, early degenerative changes and chronic wrist pain.. Adequate treatment is therefore essential.
Scaphoid fractures can be managed with a cast or with screw fixation. The latter offers a shorter time of immobilisation with a faster return to function, whilst having the same long-term outcome. Ideal screw length is an area of discussion. Theoretically, longer screws provide more stability, but there is a higher risk of protrusion of the screw in the cartilage resulting in more adverse effects.

Objectives: The goal of this study was to compare the fixation strength for long and short screws in order to evaluate if the choice for the longer screw is worth the increased risk of protrusion.

Study design & methods: Thirteen pairs of fresh frozen cadaveric scaphoids were randomized to have one side fixed with a long and one with a shorter screw (longest screw possible and longest length minus 4 mm). Under fluoroscopic control a central guidewire was inserted and a cannulated screw placed. A wedge osteotomy was made to simulate a horizontal oblique fracture plane. The proximal pole of the scaphoid was placed into a fixture. Load was applied by using a load-controlled test protocol in a hydraulic testing machine and displacement was measured.

Results: There was no significant difference between the load at 1 and 2mm displacement for long and short screws. The load at 1 and 2 mm displacement was 40.9 N (SEM 7.0 N; 90% CI 28.4-53.5 N) and 80.9 N (SEM 11.0 N; 90% CI 61.1-100.7 N) for the short screws compared with 50.4 N (SEM 10.2 N; 32.0-68.8 N) and 92.6 N (SEM 15.6 N; 64.5-120.7 N) for the long screws. An equivalence test based on the mean and 90% CI showed that these values are equivalent.

Conclusions: These data suggest that in oblique waist fracture, fixation with a long or a short screw are equivalent in strength. Given the higher risk of complications with longer screws, a shorter screw is advisable and has no negative impact on the stability of the construct.

Research area: