INTRODUCTION. Cementless Total Hip Replacement surgery is a well established procedure for relative young patients with severe hip disease. Excellent long term clinical results have been published on the performance of the femoral component. With growing clinical experience, our concern focused on excessive wear of the Ultra High Molecular Weight Polyethylene (UHMWPE) ringloc liner of the Mallory Head cementless Total Hip Prosthesis. After its introduction in our clinic in 1997, this implant is still in use without any modification. We were concerned that due to premature liner wear, the performance of this implant would not be compliant with the international guideline on implant survival (NICE guidelines: at 10 year follow up, 90% of all implants should still be in situ). Our objective was to establish the amount of liner wear in our first 200 MH implants. METHODS. Our first 200 patients consecutively treated with Mallory Head prostheses were followed up to obtain a recent digital image. Follow up was complete for 181 (90.5%) of our 200 patients. Ten had died and nine were not able or willing to come for follow up. The mean duration of follow up was 8.3 years (range: 8–13). The 181 recent digital images were classified as either excessive wear or no excessive wear by two independent orthopedic surgeons. Next, liner wear was measured in the 2D frontal plane using PolyWare Pro/3D Digital Version Rev 5.1 software (Draftware Developers, Conway, USA). A threshold for excessive liner wear was set at 0.2mm/year, according to literature. RESULTS. Using software for measuring PE wear, 46.7% of all patients had excessive UHMWPE wear (> 0.2mm/yr). There was no relation between the amount of wear and BMI, gender, component size or the acetabular inclination angle. Thirteen patients (6.5%) were revised. Nine of these revisions were for excessive liner wear or aseptic loosening (4.5%). For now, our series of cementless Mallory Head prostheses is compliant with the NICE guideline on implant survival. However, with the measured amount of wear we expect to see a significant increase in the number of revisions for liner wear in the near future. DISCUSSION. Our clinical observation of premature UHMWPE wear proved correct. The measured amount of UHMWPE wear is consistent with the few other studies published on this subject. Although we present a retrospective study, limiting the strength of our results, we have included a large group of patients with acceptable loss to follow up. It is unclear if the observed wear will lead to a sharp increase in the number of revisions within the next few years. Possibly, future revisions will be complicated by loss of acetabular bone stock following the pathofysiological reaction to wear particles. Our results can probably be generalised for any district hospital

INTRODUCTION. One of the recent advances in the hard-on-hard hip arthroplasty is the development of a new material of diffusion hardened oxidised zirconium (DHOxZr). The DHOxZr material consists of a ceramic layer on the top surface which is supported by a thick oxygen diffusion hardened (DH) zone underneath. With the desired properties of metal substrate, ceramic surface and a gradient structure of the oxygen diffusion zone, the DHOxZr-on-DHOxZr bearing combination is expected to produce low wear and minimal metal ions. This can possibly address the concerns associated with metal hypersensitivity associated with metal on metal bearings and fracture risk associated with ceramics. The aim of this study was to evaluate the wear of DHOxZr-on-DHOxZr as a possible hard on hard bearing combination in hips. METHODS. Three pairs of 50 mm DHOxZr prototype hip joint devices, each consisting of a DHOxZr modular head and a DHOxZr liner were wear tested in a ProSim hip joint simulator under standard testing conditions used by the Implant Development Centre (IDC), Smith & Nephew, Leamington Spa for 5 million cycles (Mc). The flexion/extension was 30° and 15°. The internal/external rotation was ± 10°. The force was Paul-type stance phase loading, with a maximum load of 3 kN and a standard ISO swing phase load of 0.3 kN. The test frequency was 1 Hz. Gravimetric analysis was carried out at 0, 0.5, 1, 2, 3, 4 & 5 million cycles. The lubricant was new born calf serum with 2 g/l sodium azide concentration diluted with de-ionised water to achieve average protein concentration of 20 g/l. Lubricant was changed every 0.25Mc during the first million cycles of the test and at every 0.33 Mc from 1 to 5Mc. RESULTS. A biphasic wear pattern was observed for the DHOxZr on DHOxZr devices during the test, with a running in phase from 0–1 Mc and a steady state phase from 1–5 Mc. At a confidence level of 95%, the mean wear rate was 0.21 ±0.06 mm3/Mc during the running-in stage, and the wear rate was reduced to 0.01 ±0.03 mm3/Mc during the steady state for the device tested. The wear volume loss of the DHOxZr on DHOxZr devices was significantly lower than that generated by CoCrMo metal on metal (MoM) devices (p < 0.05) under identical simulator test conditions

The prevalent cause of implant failure after total joint replacement is aseptic loosening caused by wear debris. Improvement of the wear behaviour of the articulating bearing between the cup and femoral head is essential for increased survival rate of artificial hip joints. Cross-linking of the polyethylene (PE) material is one attempt to reduce wear particle release at the articulating surface. Various cross-linked polyethylenes (X-PE) are used in orthopaedics since several years. In total hip arthroplasty (THA) the use of larger femoral head sizes has specific reasons. Larger heads lead to a decreased risk of total hip dislocation and impingement as well as an improved range of motion in comparison to smaller head sizes like 28mm or less. However, the increasing diameter of femoral head can be associated with lower thickness of the PE liner and increased wear rate. Cross-linking of PE can improve the wear rate of the liner and hence supports the use of larger femoral heads. The aim of this experimental study was to evaluate the wear of standard vs. sequential X-PE (X3-PE) liner in combination with different ceramic femoral head sizes. Wear testing was performed for 5 million load cycles using standard UHMW-PE liners (N2Vac) and X3-PE liners (each Stryker GmbH & Co. KG, Duisburg, Germany) combined with 28mm ceramic ball heads and the Trident PSL acetabular cup (Stryker). Furthermore, X3-PE liners with an internal diameter of 36mm and 44mm and decreased wall thickness (5.9mm and 3.8mm) were combined with corresponding ceramic heads. An eight station hip wear simulator according to ISO 14242 (EndoLab GmbH, Rosenheim, Germany) was used to carry out the standard wear tests. The tests were realised in temperature-controlled chambers at 37°C containing calf serum (protein content 20g/l). The average gravimetrical wear rates of the standard UHMW-PE (N2Vac) liners combined with 28mm ceramic heads amounted to 12.6 ± 0.8mg/million cycles. Wear of X3-PE liners in combination with 28 mm ceramic heads was not detectable. The average gravimetrical wear rates of the X3-PE liners in combination with 36mm and 44mm ceramic heads amounted to 2.0 ± 0.5mg and 3.1 ± 0.3mg/million cycles, respectively. The purpose of this study was to evaluate the effect of femoral head size at THA on standard and sequential X-PE liner. The wear simulator tests showed that the wear rate of PE liners with small heads (28mm) decreased by cross-linking of the PE significantly. The amount of wear at X-PE increased slightly with larger head size (36mm and 44mm). However, by sequential cross-linking, the wear rate using thinner liners and larger femoral heads is reduced to a fractional amount of wear at conventional UHMW-PE. Hence, the above-mentioned advantages of larger femoral head diameters can be realised by improved wear behaviour of sequential X-PE