Abstract
It is widely accepted that a tip apex distance of greater than 25mm is associated with dynamic hip screw (DHS) failure and cut-out. The aim was to devise an accurate and easy method for calculation of DHS tip apex distance (TAD) from intraoperative imaging using the tools available on Kodac Picture Archiving and Communications System. This method was applied to all patients treated with a DHS for intertrochanteric hip fracture during a six month period. Any subsequent radiographs were assessed for evidence of failure within 18 months.
The TAD was calculated using a modification of a previously described method using a similar imaging system (Johnston et al, Injury 2008) which has been shown to be accurate and reproducible. Scaling was based on the 12.5mm thread diameter of all Synthes (Switzerland) DHS screws.
60 patients underwent a DHS during the study. Nine patients were excluded who had an additional method of fixation or an intracapsular fracture. Four patients had insufficient xrays for analysis. Data was gathered for 47 patients and showed a mean TAD of 17mm (range 8.2–30.6mm). Three patients had a TAD greater than 25mm. 22 patients had a post-operative xray within 18 months. There were two cut-outs identified and both were from patients with a TAD of greater than 25mm (25.7 and 30.6mm). No incidences of implant failure or complications were identified for patients with acceptable TADs.
93.6% of screws were therefore inserted satisfactorily. Two out of the three patients with a TAD greater than 25mm had xray evidence of screw cut-out. This study supports previous evidence that a DHS lag screw should be positioned with a TAD within 25mm and a distance greater than this is associated with screw cut-out. TAD can be easily calculated using intraoperative xrays and scaled using the screw itself.
