K-wire Pull-Out Force After Multiple Redirection Attempts

Purpose: To evaluate if redirecting a Kirschner wire (K-wire) through the same proximal hole will weaken the pull-out force and to test if multiple redirections will result in a continued stepwise decrease in pull-out force.

Methods: An Instron was used to test the pull-out force of K-wires using the peak initial failure load as a measure of failure of K-wire fixation. K-wires 0.062 inches in diameter were inserted with an angled drill guide into a bicortical bone substrate. Trials were divided into 7 groups with the first group having the K-wires placed through both cortices and then tested without redirection. In groups 2-6, the K-wire was placed bicortically and then withdrawn and redirected through the same proximal hole with 1, 2, 3, 4, and 5 redirections. A control group in which the K-wire was only unicortical was also tested.

Results: Compared with the control group of no redirects, any number of redirections weakened the pull-out force. There was no difference between redirected groups and the unicortical group. When comparing between redirections, there were no significant differences in pull-out force. Regression analysis showed that, after the first redirection, there was no stepwise change in pull-out force with additional redirection.

Conclusions: There was a significant decrease in pull-out force with any redirections, but there was no stepwise decrease in failure force after multiple redirections. The failure force of any redirection was similar to a unicortically placed wire.

Clinical relevance: Any K-wire redirection attempts in hand bone fixation can result in a considerably weakened construct.