Minimal versus maximal plate fixation techniques of the ulna: the biomechanical effect of number of screws and plate length

Abstract

Objective: To test the hypothesis that longer plates with the minimum number of screws provide equivalent or superior strength of fixation to standard compression plating using the maximum number of screws.

Design: Prospective analysis of biomechanical data was performed.

Setting: In vitro experimentation.

Interventions: A reproducible osteotomy was made in formalin-fixed ulnae. The osteotomies were stabilized employing six-, eight-, or ten-hole plates with two screws in the outermost holes and two screws in the innermost holes, and compared to stabilization with a six-hole plate with six screws.

Main outcome measure: Four-point mechanical testing to failure was performed in both apex-dorsal (tension-band) or medial-lateral bending modes. Load-displacement curves were obtained.

Results: All of the longer plates with the minimum number of screws were stronger than the six-hole plate with six screws when tested in the medial-lateral and the tension-band mode. The eight-hole plate with four screws, however, was statistically inseparable from the fully loaded six-hole plate. There was no statistical difference between any of the configurations in regard to the stiffness of the fixation.

Conclusions: In a cadaveric ulnar osteotomy model stripped of soft tissue, the number of screws is less important than the length of the plate in providing bending strength to the construct.