Scaphoid Healing Required for Unrestricted Activity: A Biomechanical Cadaver Model.

PURPOSE: To determine if scaphoid fractures with bridging bone of 50% of their width treated with a centrally placed screw will restore biomechanical integrity equivalent to that of the intact scaphoid.

METHODS: Twenty-four fresh cadaver scaphoids were used. Six were left intact to serve as the control group. Six were osteotomized 50% of their width and made up the osteotomy without screw group. Six were included in the 50% osteotomy plus compression screw group. The remaining 6 were to be treated with an osteotomy of 25% or 75% with a screw, based upon the results of the 50% osteotomy with screw group. Biomechanical testing was performed using an Instron testing machine, with a load applied to the scaphoid's distal pole. Load to failure and stiffness were measured.

RESULTS: Intact scaphoids had an average load to failure of 610.0 N. The average load to failure of the 50% osteotomy group without a screw was 272.0 N and with a screw was 666.3 N. There was no significant difference in load to failure between the 50% osteotomy plus screw and the intact scaphoid. The 75% osteotomy plus screw was found to have a load to failure of 174.0 N, significantly lower than the intact scaphoid. The 50% osteotomy plus screw had a significantly higher stiffness than the intact scaphoid control.

CONCLUSIONS: A 50% intact scaphoid with a centrally placed screw showed similar load to failure and significantly higher stiffness than the intact scaphoid when tested in cantilever bending.

CLINICAL RELEVANCE: This study demonstrates that patients with scaphoid waist fractures who undergo surgery with a compression screw may be able to return to unrestricted activity with 50% partial healing.