The aim of this retrospective study was to evaluate the failure rate among different fixation devices for undisplaced fracture neck of femur. All 52 patients with Garden I and II hip fractures who underwent surgery in a teaching hospital in London from January 2007 to June 2012 were included. Electronic patient records were accessed to collect the patient data.

There were 52% females and the mean age of patients was 70 years. Thirty patients had cannulated screws, 18 – dynamic hip screw (DHS) with de-rotation screw and 4 had DHS alone. Initial results showed that 36% patients had re-operation. 7(77%) had total hip replacement and 1(11%) had metal work removal. The reason for revision was failure of fixation in 8 (88%) and avascular necrosis in 1 (11%). There was significantly higher failure rate in the DHS with derotation screw group (50%) compared to the cannulated screw group (35%) and the DHS alone group (0%). Average time to planned revision was 11.1 months.

Traditionally undisplaced intra capsular hip fractures are treated by in-situ fixation using different devices. Biomechanically DHS with de-rotation screw achieves better rotational and axial stability compared to other fixation devices. However, our study showed a higher failure rate in this group. Inability to achieve a perfectly parallel screw position seems to be a significant factor responsible for high failure. Higher failure rates with fixation may boost the role of replacement arthroplasty as one off surgical treatment in elderly patients.

Hip simulator studies have shown reduced hip offset can cause microseparation and increased wear in hard-on-hard hip bearings. However this has not been analysed yet in vivo. We studied the effect of reduced hip offset on serum metal ion levels in patients with metal-on-metal (MoM) hip arthroplasty.

From all patients who underwent unilateral MoM bearing hip arthroplasty between 2005 and 2009, 63 patients had complete clinical evaluation, measurement of serum chromium and cobalt ion levels as well as biomechanical measurements on pre- and post operative radiographs (cup inclination, head inclination, change in hip offset and change in hip length.)

Ten arthroplasties were revised due to adverse metal reaction and six patients awaiting revision. 55% of ASR hips showed higher metal ions (>7 ppb) whereas only 15% of non-ASR hips had higher ion levels. Patients with reduced postoperative hip offset by more than 5 mm had significantly higher mean metal ion levels compared to the the rest of the hips (31.8 ppb vs. 7.4 ppb, p=0.002). On subgroup analysis this effect was present in non-ASR hips (18.7 ppb vs. 4.7 ppb, p=0.025) but was not significant in ASR hips (29.6 ppb vs. 16.3 ppb, p=0.347).

Our study demonstrated significantly higher serum metal ion levels in patients who lost more than 5 mm hip offset after arthroplasty. Reduced soft tissue tension leading to microseparation of the articulation and edge loading is a theoretical explanation for this effect. This may be relevant in other hard bearings such as ceramic-on-ceramic as well.