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.

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.

Introduction: In a pioneer study Oonishi et al (1988) found reduced socket wear with the use of polyethylene subjected to high radiation doses. This observation has stimulated the development of a new generation polyethylene. In addition to high radiation doses the plastic is also subjected to various types of heat treatment to reduce the amount of free radicals. The purpose of the present study is to evaluate one of the new highly cross-linked polyethylenes in a randomized controlled study of cemented THA. The hypothesis is that the improved wear resistance will reduce the prevalence of osteolytic lesions with long-term follow-up.

Methods and materials: Patients in clinical and radiographic need of a THR with non-inflammatory osteoarthritis of the hip were randomized in two groups. Group 1 received a cemented Weber cup (Sulzer®, Switzerland) made of highly cross-linked (WIAM) polyethylene, group 2 got a conventional cup. All patients received a cemented Spectron (Smith & Nephew, USA) with a 28mm cobalt-chromium head.

So far 15 patients, (6 male and 9 females) with a median age of 55 years (range 42–62) have been evaluated in group 1 and 14 (9 male and 5 females) with a median age of 55 years (range 45–70) in group 2. The penetration of the femoral heads has so far been measured postoperatively (all hips supine), after 3 month (17 hips supine and standing) and after 6 month (11 hips supine and standing) using radiostereometry.

Results: The median proximal and three-dimensional (3-D) penetration (total wear) 0–6 month (supine position) was almost equal in the two groups. Group 1 had a proximal penetration of 0.08 mm (range 0.00–0.17) and a total penetration of 0.11 mm (range 0.06–0.14). The corresponding values for group 2 were 0,10 mm (0.05–0.21) for proximal penetration and 0.13 mm (0.10–0.16) for total penetration. Between 3 and 6 month the penetration (median values) was 0.04 mm/0.10 mm (proximal/3-D) for group 1 and 0.07 mm/0.12 mm for group 2. With the patients standing we found a proximally migration of the socket (0–6 month) in group 1 of 0,08 mm (−0.07 – 0.21) and 0.12 mm (0.1–0.13) in group 2.

Discussion: Use of a highly cross-linked polyethylene in the socket did not influence the early penetration rate after THR. Early creep of the material is possible explanation.

1-year follow-up on approximately 50% of the patients will be presented at the meeting.

We studied the kinetics of the knee in 20 patients (22 knees) 12 months after total knee arthroplasty (TKA), by using three-dimensional radiostereometry and film-exchanger techniques. Eleven knees had a concave (constrained) tibial implant and 11 a posterior-stabilised prosthesis. Eleven normal knees served as a control group.

In the posterior-stabilised knees there was less proximal and posterior displacement of the centre of the tibial plateau during extension from 45° to 15°, with a decrease in the anterior translation of the femoral condyles of 4 mm at 45°. There was less internal tibial rotation and increased distal positioning of the centre of the tibial plateau with both designs when compared with the normal knees, and in both the centre of the plateau was displaced posteriorly by more than 1 cm.

Increased AP translation has been recorded in all prosthetic designs so far studied by radiostereometry. The use of a posterior-stabilised design of tibial insert could reduce this translation but not to that of the normal knee.

We analysed synovial fluid from 88 hips, 38 with osteoarthritis and 12 with well-functioning and 38 with loose hip prostheses. The levels of TNF-α, IL-1ß (71 hips) and IL-6 (45 hips) were measured using the ELISA technique. Joints with well-functioning or loose prostheses had significantly increased levels of TNF-α compared with those with osteoarthritis. Hips with aseptic loosening also had higher levels of IL-1ß but not of IL-6 compared with those without an implant. The levels of TNF-α and IL-1ß did not differ between hips with stable and loose prostheses.

Higher levels of TNF-α were found in hips with bone resorption of type II and type III (Gustilo-Pasternak) compared with those with type-I loosening.

The level of cytokines in joint fluid was not influenced by the time in situ of the implants or the age, gender or area of the osteolysis as measured on conventional radiographs.

Our findings support the theory that macrophages in the joint capsule increase the production of TNF-α at an early phase probably because of particle load and in the absence of clinical loosening. Since TNF-α has an important role in the osteolytic process, the interfaces should be protected from penetration of joint fluid.

We revised 24 consecutive hips with loosening of the femoral stem using impaction allograft and a cemented stem with an unpolished proximal surface. Repeated radiostereometric examinations for up to two years showed a slow rate of subsidence with a mean of 0.32 mm (−2.0 to +0.31). Fifteen cases followed for a further year showed the same mean subsidence after three years, indicating stabilisation. A tendency to retroversion of the stems was noted between the operation and the last follow-up. Retroversion was also recorded when displacement of the stem was studied in ten of the patients after two years. Repeated determination of bone mineral density showed an initial loss after six months, followed by recovery to the postoperative level at two years. Defects in the cement mantle and malalignment of the stem were often noted on postoperative radiographs, but did not correlate with the degrees of migration or displacement. After one year, increasing frequency of trabecular remodelling or resorption of the graft was observed in the greater trochanter and distal to the tip of the stem. Cortical repair was noted distally and medially (Gruen regions 3, 5 and 6). Migration of the stems was the lowest reported to date, which we attribute to the improved grafting technique and to the hardness of the graft.

We enrolled 98 patients (107 hips) with a mean age of 47 years (SD 8.6) into a prospective study of the Madreporic Lord THR; 34 hips had primary and 73 secondary osteoarthritis.

After ten years, the survival rate using revision as the endpoint for failure was 70% (±9) for the cup and 98% (±0.3) for the stem. The combined clinical and radiological survival rates were 46% (±11) and 81% (±10), respectively. Osteoporosis due to stress-shielding was observed in the proximal femur. Hips with radiologically dense bone postoperatively showed the most pronounced bone loss.

We recommend continued radiological follow-up of patients with this type of implant to allow revision to be performed before there is severe bony destruction of the pelvis.