Comparison of screw trajectory on stability of oblique scaphoid fractures: a mechanical study.

PURPOSE

To determine whether a screw placed perpendicular to the fracture line in an oblique scaphoid fracture will provide fixation strength that is comparable with that of a centrally placed screw.

METHODS

Oblique osteotomies were made along the dorsal sulcus of 8 matched pairs of cadaveric scaphoids. One scaphoid from each pair was randomized to receive a screw placed centrally down the long axis. In the other scaphoid, a screw was placed perpendicular to the osteotomy. Each scaphoid underwent cyclic loading from 80 N to 120 N at 1 Hz. Cyclic loading was carried out until 2 mm of fracture displacement occurred or 4,000 cycles was reached. The specimens that reached the 4,000-cycle limit were then loaded to failure. Screw length, number of cycles, and load to failure were compared between the groups.

RESULTS

We found no difference in number of cycles or load to failure between the 2 groups. Screws placed perpendicular to the fracture line were significantly shorter than screws placed down the central axis.

CONCLUSIONS

A perpendicularly placed screw provides equivalent strength to one placed along the central axis.

CLINICAL RELEVANCE

Compared with a screw placed centrally in an oblique scaphoid fracture, a screw placed perpendicular to the fracture line allows the use of a shorter screw without sacrificing strength of fixation.