Introduction: Many patients eligible for hip arthroplasty suffer from bilateral hip disease with indication for bilateral total hip replacement (BTHR). Traditionally two-stage BTHR is far more common than one-stage procedure due to the risk of complications. However, most studies are in favour of one-stage BTHR in the healthy and young people. This study was designed to further analyse mortality, outcome, complications and cost-effectiveness after one-stage BTHR surgery.

Patients and Methods: In this prospective matched control study we examined 32 patients with BTHR hybrid surgery. The control group of 32 patients with unilateral hybrid THR was derived from Sahlgrenska University hospital. The follow up time was 1 year. Medical records, cost per patient database, records from Swedish Social Insurance Administration and HRQoL outcome measurements from the Swedish Hip Arthroplasty Register were used for the analyses.

Mortality data from the Register regarding all 950 patients with one-stage BTHR surgery during the period 1992 until 2005 were compared to those 2577 who had had a twostage procedure with less than six months between the operations.

Preliminary Results: There were no major differences in complications. The intraoperative bleeding was higher in the BTHR patients and they required more blood transfusion. Length of hospital stay was in average 10,2 days for the one-stage BTHR group and 7,6 days for the unilateral group. Preoperative EQ-5D index was 0,14 in the BTHR group and 0,31 in the control group. Mean EQ-5D gain after 1 year was 0,77 and 0,40 respectively. Hospital costs were only 60% higher in the one-stage BTHR group. Among the employed patients there were no differences in days of sick pay and cost of sick pay in the two groups. Among the 950 subjects with one-stage BTHR surgery, the 90 day mortality was 0,32% compared to 0,42% in the group of 2577 patients with two-stage procedure.

Discussion: In healthy patients with bilateral hip disease requiring bilateral arthroplasty one-stage BTHR is highly cost-effective and safe. There is even lower 90 day mortality for the onestage operated subjects in the register but this is probably due to a natural selection of younger and healthier patients. The one-stage procedure reduces the total time of rehabilitation which is of particular importance for people in working age. Cautiously estimated, performing another 100 one-stage BTHR per year instead of two-stage procedure would save 16–20 million SEK yearly in Sweden.

Introduction: The annual wear rate in polyethylene articulations should be 0.1 mm or less to avoid future osteolysis. Highly Crosslinked polyethylene demonstrates 80–90% wear reduction in hip simulator testing, but the clinical documentation of this new polyethylene is still inadequate. We evaluated the highly crosslink PE in two prospective randomised clinical studies. Patients and Methods: Thirty two patients (12 male, 20 female, 64 hips) with a median age of 48 years (range, 29–70 years) with bilateral primary or secondary arthrosis of the hip received hybrid THA. With liners made of highly cross-link on one side and conventional PE on the other one. Twenty-seven patients in this study have passed 2 years follow up. Further Sixty patients (61 hips) with a median age of 55 years (range, 35–70 years) were randomized to receive either highly crosslink or conventional cemented all PE of the same design. Forty-nine patients have been followed for 3 years. In both studies all patients received Spectron stems with 28mm cobalt-chromium head. Radiostereometric examinations with the patient supine or standing were done at regular intervals. Wear was measured in the supine position from the postoperative week, whereas standing examinations were initiated three months after the operation. Results: The penetration rate was almost identical in the study and control groups in 6 months after the operation. Thereafter the penetration rate levelled out in the 2 groups with highly crosslink PE. At two years the highly crosslink PE liner showed 62% lower proximal penetration and 31% lower total (three-dimensional) penetration when the patients were examined in supine position. The highly crosslink all PE cemented cups showed significantly lower proximal penetration in both position. Discussion: The better wear performance of highly crosslink PE could increase the implant longevity. Longer follow up is needed to evaluate if this new material is associated with less occurrence of osteolysis.

Traditional polyethylene oxidizes, wears and generates particles over time, which most probably contributes to increased risk of periprosthetic osteolysis. Even contemporary sterilization methods such as radiation and package in oxygen reduced or oxygen substituted environment do not eliminate oxidation over time. Thus, there is a need for alternative bearing in total hip replacement surgery and especially in patients with high activity and long life expectancy.

All three major alternate bearings, ceramic-on-ceramic, metal-on-metal and highly crosslinked polyethylene produce major reductions in volumetric wear. The electron beam, melted highly cross-linked polyethylene has an in vivo penetration rate after the bedding in period, which is less than 8 microns per year. This is not substantially different from ceramic on ceramic or metal on metal. Therefore, the inherent risk of periprosthetic osteolysis with these alternate bearings is probably smaller than observed with conventional polyethylene.

In the competition between different articulations highly cross-linked polyethylene has some advantages. The polyethylene is more adaptable than the hard bearing surfaces. This means that extended lip liners, offset liners, constrained liners and further special designs may be used. These options are not possible with any of the hard bearings. Another advantage with polyethylene is forgiveness. Impingement in hard-on-hard bearings may lead to serious complications such as chipping of the ceramics or metallosis in a metal on metal articulation.

Impingement should also be avoided with use of polyethylene, but if it occurs, the consequences are often more benign at least in the short term perspective. Micro-separation results in less material damage with use of polyethylene than with the 2 other types of articulations. A few degrees of additional abduction above the geometrical limits for a particular socket is far less harmful if it is made of polyethylene compared to the situation in ceramic-on-ceramic or metal-on-metal bearings. Polyethylene is also more familiar to the majority of orthopaedic surgeons. In the operating room the cross-linked polyethylene is identical to those types of polyethylene, which have been used fore 3 to 4 decades. Finally the cost is a major factor (Harris 2004). The hard-on-hard bearings are substantially more expensive. The fracture incidence of ceramics components has decreased with improved manufacturing technology, but the risk of polyethylene fracture appears to be still smaller.

On the other hand using highly cross-link polyethylene carries some risks. Particles generated from this new material are smaller with higher inflammatory response. Compared with joints including conventionally sterilised polyethylene the total particle production is, however, reduced with more than 85%, which has implications for the magnitude of the inflammatory response.

The significance and importance of the irradiation and melting induced changes of the mechanical properties of the polyethylene is not known. Long term follow-up is needed to evaluate this issue.

Charnley preferred small head sizes in total hip replacement because they resulted in transmittance of low frictional torque to the acetabular implant. Mueller advocated larger head sizes with improved joint stability and lower contact pressure. Large heads do, however, imply increased volumetric wear. Therefore, 32 mm heads were abandoned in the early 90ties in favour of 28 mm heads. Another consequence of using larger heads is that polyethylene liners are relatively thin. The highly cross-link polyethylene and the hard bearings can be used with bigger femoral heads, which increases the range of motion and the hip joint stability.

Amorphous diamond coatings has been studied as an alternative bearing surface in the laboratory (Santavirta 2003). Such coatings may provide wear rates 104 to 105 times lower than conventional THR articulations, because of their extremely hard surface and low coefficient of friction without any corrosion paths (Santavirta et al. 1999 Lappalainen et al. 2003).

Oxidized Zirconium (OxZr) is another material, which has similar advantages. Oxinium materials are the results of a process that allows thermally–driven oxygen to diffuse and transform the metallic zirconium alloy surface into a durable low-friction oxide. The Oxinium material is harder than commonly used cobalt chrome, and with only the surface changing during the manufacturing process, the rest of the implant remains metal to maintain its overall strength. OxZr provides superior abrasion resistance without the risk of brittle fracture, thereby combining the benefits of metal and ceramics. Knee simulator tests have shown that OxZr can reduce polyethylene wear substantially (Ries et al. 2002). Although promising, these two coatings still lack clinical documentation.

During the last decade it has become evident that many designs of total hip arthroplasty can in patients with normal bone quality be fixed to the bone with a high degree of reproducibility. This has had the effect that younger patients have been operated on in increasing numbers. Wear and periprosthetic bone loss have remained a serious and comparatively frequent complications. The introduction of more wear resistant articulations has the potential to solve these problems making the procedure safer also among these patients. So far there is no or very scarce evidence that these articulations can be used safely during decades without complications causing progressive and often silent bone destruction resulting in difficult revisions with high morbidity. In the case of metal on metal articulations release and accumulation of ions remains a long term concern and especially if the patients will suffer from a temporary or permanent disease associated with impaired renal function.

Because evidence of long term superiority of these new articulations is lacking it is of utmost importance that these new implants and materials are introduced into clinical practice in a controlled way. Careful surveillance of preclinical and gradually enlarged randomised studies followed by multicenter trials is necessary to avoid disastrous mistakes so common in the past.

Aims: The aim of this study was to evaluate a highly cross-linked polyethylene WIAM in cemented hip arthroplasty. This new polyethylene has been resistant to wear in laboratory tests. Methods: 60 patients (30 women, 30 men) with a median age of 55 years (35–70) and a median weight 82 kg (47–120) were included. All patients received a Spectron femoral stem with a 28 mm head in chrome-cobalt. The patients were randomised to acetabular cups made of either WIAM (electron beam irradiation 9.5 Mrad) or conventional polyethylene (CP) sterilized in inert atmosphere. Radiostereometric examinations (supine) were done 7 days after the operation and after 3, 6 12 and 24 months. Examinations (standing) were performed at 3, 6 12 and 24 months. The migration of the femoral head centre in relation to the polyethylene marker represented the femoral head penetration. Results:. 43 hip (19 WIAM 24 CP) were available for 24 months FU. There were no differences in cup migrations between the two groups. The mean proximal penetration (supine and standing) was less than 0.2 mm at 24 months in both groups p> 0,06 Conclusions: The femoral head penetration during the first two years may be dominated by creep. There is tendency for lower proximal penetration at standing examination in the WIAM group. Futher studies and longer follow up is necessary until highly crosslink polyethylene can be recommended for general use.