Introduction: The Resurfacing Hip has been increasingly popular for younger patients. Femoral neck fractures are still the main complication. The problems associated with cement such as thermal necrosis, cement debris and lack of long-term biological fixation, combined with the general use of cementless fixation in young patients invite the question whether a cementless component can be used for resurfacing hip replacement. Given that the cement may reinforce the femoral head preventing collapse, an additional question regarding the effect of bone density in cemented and cementless fixation can be asked. The hypotheses of the study are that:

High bone density will increase the yield point and stiffness of the femoral head and therefore improve the implant fixation.

Materials and Methods: Thirty-six femoral head specimens were obtained from consented patients receiving routine hip arthroplasty. The heads were stored frozen at −20oC until use. pQCT was used to analyse trabecular bone density within each head. Specimens were ranked according to bone density and were assigned to high and low bone density groups. Cemented and cementless fixations were then alternatively assigned to individual heads in each group. Thus the 4 groups included in the study were: High density cemented, high density cementless, low density cemented, and low density cementless. Implantation of Birmingham resurfacing hips was carried out according to recommended surgical procedures. For cementing groups, surgical simplex P bone cement was used. Each sample was potted in a cylindrical polyethylene block for testing. A compressive load up to 5 or 10 KN using a Hounsfield Universal Testing Machine were applied on each sample at a rate of 1 mm min-1. Load versus displacement graphs were plotted for all tests. Yield point and stiffness were measured for each sample.

Results:

For yield point, there is no significant difference between cemented or cementless resurfacing (4169 ± 1420 N vs. 3789 ± 1461 N; P = 0.434). However, the high density heads provide a significantly higher yield point than low density heads (4749 ± 1145 N vs. 3208 ± 1287 N; P = 0.01).

Discussion: Bone density plays an important role in resurfacing hip arthroplasty. Higher bone density will reduce the incidence of fractures comparing with lower density. Therefore, resurfacing THR for the older patients and those with sub-optimal bone density should be used with caution. Consequently, it is suggested that a bone density scan should be routinely applied for those patients who are considered for resurfacing hip replacement. There is no difference between the cemented and cementless fixation in reducing femoral head failure, though cement will increase the stiffness of the bone. The study suggests that cementless resurfacing hip could be an alternative design with its clinical advantages of long-term osseointegration if implant is coated with bio-active materials.

Here we present the results of functional outcome of 531 patients (aged from 27.6 to 88.7, mean 62.6) who have had the Trilogy (Zimmer; Warsaw IN, USA) acetabular shell implanted for 5 years or longer. All patients operated at our unit between 20/1/1992 and 31/3/2004 were included, looking at both Primary (431) and Revision (100) hip arthroplasties. All surgery was performed by the senior surgeon using the Trilogy shell and liners. The Trilogy acetabular shell was used with either an ultra-high molecular weight polyethylene liner or ceramic liner, along with a wide variety of femoral stems, mainly: Harris Pre-coat stem (183 patients, Zimmer), Versys cemented stem (102 pts, Zimmer), CADCAM (140 pts, Stanmore), and HAC Furlong (96 pts, JRI). There were a variety of other stems, including Exeter and Pro-femur. 48 patients had revision of socket only.

Functional outcome was assessed by three questionnaires: the Oxford Hip Questionnaire (12 best function-60 worst), the Harris Hip Score (100 best to 0 worst), and the WOMAC Hip Score (0 best-96 worst).

Patients filled in these questionnaires at every postoperative follow-up clinic. These were compared with the pre-operative scores obtained from questionnaires which the patients completed retrospectively. Mean follow up questionnaire times were 76.5 months postoperatively for primary arthroplasties, and 70.6 months for the revision arthroplasties.

For primary arthroplasty mean scores improved from 40.8 pre-operatively to 16.4 post-operatively (Oxford), 43.9 to 92.9 (Harris), and 51.8 to 9.4 (WOMAC) (all p< 0.05). For revision arthroplasty mean scores improved from 39.1, 41.7, and 49.3 pre-operatively to 19.6, 88.0, and 12.5 (all p< 0.05).

No patients required re-operation for loosening, one patient dislocated at day 5.

We can conclude that the Trilogy acetabular component is a versatile acetabular implant which can be used with a wide range of femoral components, both in primary and revision Total Hip Arthroplasty, with successful functional outcome scores greater than 5 years after implantation.

An observation was made in our unit that sciatic nerve injury following total hip arthroplasty seemed to be more common in women. This observation has been mentioned in the literature, but no anatomical explanation has been postulated. We aimed to confirm this and suggest an anatomical explanation.

Members of the British Hip Society were approached by means of a postal questionnaire regarding the sex incidence of sciatic nerve injury following both primary and revision hip surgery in their practice. In this cohort of surgeons, of 179 reported sciatic nerve injuries, 77% were in women (80% in primary hip replacement and 69% in revision surgery), which is statistically significant.

We suggest that the wider outlet of the female pelvis causes the path of the sciatic nerve to pass more closely to the posterior wall of the acetabulum so making it more vulnerable to surgical injury. This hypothesis has been explored by measurements taken from CT scans of the pelvis and hips. Results do confirm the closer proximity of the nerve to the hip joint in women. We therefore advise increased care when performing hip replacement in women and suggest that this be mentioned as a gender linked risk when consenting patients prior to surgery.