Difficulty in locking head screw removal.

Background: Locking plates are an internal fixation material useful in the treatment of bone fractures, which provides effective stabilization between the plate and locking head screws (LHSs) via the locking mechanism. However, difficulty in removing LHSs is relatively common, and such cases can require long surgical procedures or use of special removal equipment. The purpose of this study was to report the incidence and risk factors for difficult removal of LHSs.

Methods: During the 5-year-6-month period from April 2006 to September 2011, 83 locking plates containing a total of 482 LHSs were removed in 80 patients at our institution. Out of 482 LHSs, there were 118 LHSs with a 2.4-2.7 mm diameter, 308 LHSs with a 3.5 mm diameter and 56 LHSs with a 5.0 mm diameter. The incidence of removal difficulty was examined on the basis of screw diameter. In addition, the risk factors were assessed in only LHSs with a 3.5 mm diameter. LHSs with a 3.5 mm diameter were divided into 2 groups, the difficult removal group and the easy removal group, and the data were examined based on age, sex, time between insertion and removal, and screw position. The incidence of removal difficulty in LHSs with a 3.5 mm diameter was examined every 6 months between insertion and removal.

Results: Difficulty in removal was encountered in none (0 %) of 118 LHSs with a 2.4-2.7 mm diameter, 15 (4.9 %) of 308 LHSs with a 3.5 mm diameter, and none (0 %) of 56 LHSs with a 5.0 mm diameter. In only LHSs with a 3.5 mm diameter, the mean ages of the patients in the difficult removal group and the easy removal group were 32.1 and 45.6 years, respectively. The average time between insertion and removal in the difficult removal group and the easy removal group was 529.2 and 389.2 days, respectively. There was a statistically significant difference in age and time between insertion and removal. Removal was difficult in 15 (9.1 %) of 165 LHSs with a 3.5 mm diameter in those with >1 year between insertion and removal.

Conclusion: This study suggests that (1) the use of LHSs with a 3.5 mm diameter is a necessary condition for difficulty in screw removal, and that (2) longer time from internal fixation to removal, and (3) younger age, are risk factors for it. When removing LHSs with a 3.5 mm diameter, appropriate instruments and sufficient training are necessary.