Introduction: Dynamisation is a simple method for treating femoral shaft fractures (FSFs) in patients with delayed healing after intramedullary nailing. However, only around half of patients with a slow-healing FSF have been successfully treated with this strategy. Although it is thought that dynamisation with a screw preserved in the dynamic locking hole improves treatment outcome in these patients, to date, no studies have demonstrated empirical evidence supporting this technique. In this study, we investigated the effects of dynamisation with and without rotation and length control as well as timing of dynamisation on treatment outcomes in FSF patients with delayed healing. Patients and methods: Thirty-nine consecutive acute FSF patients with static locking intramedullary nails who subsequently underwent dynamisation were recruited between January 2000 and June 2011. The indication for dynamisation was the presence of gap caused by bone absorption or over-traction at the fracture site when the locking screws were placed. Age, gender, dynamisation method, fracture classification, duration from nail insertion to dynamisation (i.e., timing of dynamisation) and dynamisation outcome were included in the statistical analysis. Results: Patients whose nail was dynamised with a screw preserved in the dynamic locking hole had a significantly higher successful bone union rate (14/15 vs. 14/24, p = 0.028) compared with those with all screws removed from one end of the nail. The patients treated in 10-24 weeks had a significantly increased chance of bone union than those treated after 24 weeks (p = 0.027). A significantly higher bone union rate (p = 0.036) was observed in 10-24 weeks (83.3%) than after 24 weeks (33.3%) in the group of dynamisation with all screws removed from one end of the nail. No statistical difference in bone union success rate was found between patients at 10-24 weeks and after 24 weeks in the group of dynamisation with a screw preserved in the dynamic locking hole. There were no significant differences in outcome based on other variables. Conclusion: (1) Dynamisation with a screw preserved in the dynamic locking hole was associated with a higher success rate in bone union than all screws removed from one end of the nail for patients with delayed healing FSFs. (2) Early dynamisation (10-24 weeks) had a better outcome than late dynamisation (>24 weeks). Late dynamisation with all screws removed from one end of the nails resulted in a poor success rate. Alternative treatment should be considered if the latter approach is to be adopted.
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