We present minimum 20 year results of a randomized, prospective double blinded trial (RCT) of cross-linked versus conventional polyethylene (PE), using a computer assisted method of PE wear measurement.

After Ethics Committee approval, 122 patients were enrolled into an RCT comparing Enduron (non cross-linked PE) and highly cross-linked Marathon PE (DePuy, Leeds, UK). Other than the PE liners, identical components were used, a Duraloc 300 metal shell with one screw, a 28mm CoCr femoral head and a cemented Charnley Elite femoral stem. All patients were followed with anteroposterior (A∼P) and lateral radiographs at 3 days, 6 weeks, 3 months, 6 months, 1, 2, 3, 4, 5, 10 and 20 years. PE wear was measured with PolyMig, which has a phantom validated accuracy of ± 0.09mm.

At minimum 20 year follow-up, 47 patients had died, 5 of which had been revised prior to their death. Another 32 patients were revised and alive, leaving 43 patients unrevised and alive (15 Enduron, 28 Marathon). No patients were lost to follow-up, but 2 were not able to be radiographed (dementia), leaving 41 patients (15 Enduron, 26 Marathon) available for PE wear measurement. After the bedding-in period, Enduron liners had a wear rate of 0.182 mm/year, and Marathon liners had a wear rate of 0.028 mm/year. At 20 years follow-up, 37 patients had required revision. Patients with conventional PE had three times the revision rate (28/37) of those who received XLPE (9/37).

This is the longest term RCT showing substantially improved clinical and radiological results when XLPE is used as the bearing surface.

Aims

This paper describes the methodology, validation and reliability of a new computer-assisted method which uses models of the patient’s bones and the components to measure their migration and polyethylene wear from radiographs after total hip arthroplasty (THA).

Introduction: Hip Simulator studies show that use of highly cross-linked polyethylene in total hip replacement reduces polyethylene (PE) wear by a factor of 85–98%. Early clinical studies using RSA or computer-aided techniques of polyethylene wear measurement show a reduction of 50–80%. There is speculation about why this discrepancy in the clinical and laboratory data should exist. The results of a randomized, prospective double blinded (surgeon and patient) trial (RCT) of cross-linked versus conventional polyethylene, using a 100% reproducible method of PE wear measurement, are reported.

Materials And Methods: After Ethics Committee approval, the two authors enrolled 124 patients onto an RCT comparing Enduron (non cross-linked PE) and highly cross-linked Marathon PE (DePuy, Leeds, UK). Randomization was performed by the circulating nurse intra-operatively opening an envelope which determined whether the patient received an Enduron or Marathon liner appropriate to the size of the metal shell. Liners were implanted into identical metal shells (Duraloc 300) with one screw. They articulated with identical 28mm CoCr femoral heads and cemented Charnley Elite femoral stems. All patients were followed with anteroposterior and lateral radiographs at 3 days, 6 weeks, 3 months 6 months, 1, 2, 3 and 4 years. PE wear was measured with PWAuto, a validated computer-assisted technique with 100% reproducibility and accuracy of ±0.13mm.

Results: One hundred and thirteen patients had appropriate radiographs and follow-up interval. Mean follow-up was 2.6 years (range 2–4 years). Fifty-eight patients received Enduron liners and 55 patients received Marathon liners. At 6 months (E=0.32, M=0.31mm) and one year (E=0.37, M=0.31mm) the three-dimensional PE wear was identical in both groups. Thereafter, all PE wear measurements showed a significant difference in PE wear between the two groups. Wear of the conventional Enduron group continued (0.51mm at 2 years, 0.70 at 3 years, 0.97 at 4 years), while the crosslinked Marathon group showed virtually no further wear (0.32mm at 2 years, 0.32mm at 3 years, 0.33mm at 4 years).

Conclusions: This is the first study to confirm that Hip Simulator predictions of cross-linked PE wear can be reproduced in-vivo. Randomization, double-blinding, and the use of a 100% reproducible technique for wear measurement add further weight to this data.

Introduction: Long waits for total hip joint replacement (THJR) surgery affect quality of life and are likely to impose significant medical, personal and other costs on individuals and society.

Aim: To define the economic and health costs of waiting for THJR surgery.

Method: A prospective study of 130 patients requiring primary THJR is being undertaken. Data on health related quality of life (HRQL), using self completed EQ-5D and WOMAC questionnaires, are collected on enrolment, and every month before surgery and continuing for six months after surgery. Monthly cost diaries are used to record medical, personal and other costs. Inferential statistics and regression analyses will be used to test the strength of associations between costs and waiting times, and changes in HRQL before and after surgery.

Results: Preliminary results indicate that costs are greatest before surgery (mean=$70.41 per person, per month), remain high during the first month after surgery (mean=$53.24 pp pm), and drop significantly (p< 0.05) within six months after surgery (mean=$12 pp pm). WOMAC scores of pain, stiffness and physical function show significant improvements (p< 0.05) within three months after surgery. The EQ-5D also indicated significant (p< 0.05) positive changes.

Conclusions: The preliminary results suggested that patients had high dependency levels for the first month after surgery. Consequently, costs associated with recuperation after surgery may have shifted from the public hospitals onto the community and family. Significant improvements in HRQL by three months after surgery indicated that THJR is a successful intervention for osteoarthritis.

Introduction: Hip fractures in the elderly create an economic and social burden on individuals and society. Earlier predictions of the incidence of hip fractures in the older adult population showed that by the year 2011 the rate would rise to epidemic proportions.

Aim: To analyse the actual hip fracture rate from 1988 to 1999 and then to compare it with the hip fracture rate predicted by Rockwood, Horne and Cryer in 1990.

Method: Data on the number of patients admitted to New Zealand hospitals with a diagnosis of fractured neck of femur were obtained, and compared with Rockwood’s (1990) weighted regression and baseline predictions. Poisson regression was used to test for changes in hip fracture rates over time.

Results: The numbers of hip fractures for females, from 1988 to 1993, were similar to the numbers predicted, yet have been significantly lower than stated predictions since 1995 (all age bands, P < 0.002; in the 85+ group, p < 0.0001). For males, hip fracture numbers are closer to those predicted, and since 1995 are less than the weighted regressions predicted. The difference was not statistically significant.

Conclusions: Despite the absence of a nationally agreed and coordinated strategy aimed at osteoporosis prevention, it appears that the use of risk assessments, osteoporosis prevention strategies, in combination with improved retirement home and personal care interventions and treatments are likely to have contributed to this situation. The 4.6% drop in the age group most at risk of hip fracture (85+), may be a contributing factor.