The concept of stainless steel dual mobility cups in total hip arthroplasty has demonstrated very low long-term instability rates and a 98% survival rate after 12 years. We systematically implanted titanium alloy acetabular cups during a one year period. The purpose of our retrospective study was to report the 18-year clinical outcome data in a homogeneous and continuous series of 103 primary total hip replacements after implantation of a cementless titanium cup. All patients were implanted with NOVAE Ti (SERF) cups made of titanium alloy combined with a retentive polyethylene liner and a 22.2 mm cobalt chrome prosthetic head. Mean patient age at the time of surgery was 53 years. All patients were clinically and radiographically evaluated. The overall 18-year actuarial cup survival rate with a 95% confidence interval was 87.4%. At last follow-up, there was no evidence of implant instability whereas acetabular aseptic loosening was reported in one case and high wear of the retentive liner in 9. The results of this investigation confirmed the long-term stability of dual-mobility implants. The main limitation of this system was early wear of the polyethylene liner in contact with the titanium metal back and reaction with third body along with loss of liner retentivity. In our study, titanium demonstrated favourable osteointegration properties but poor tribologic characteristics, therefore suggesting its interest at the bone-cup interface only

Osteolysis induced by UHMWPE debris has historically been one of the major causes of long term failure of TJR. An increase in concentration of polyethylene particles in the peri-prostheic tissue has been linked to an increased incidence of osteolysis. The dual mobility hip bearing concept mates a femoral head into a polyethylene liner which has an unconstrained articulation into a metal shell. The wear mechanism of the dual mobility hip bearing is distinct from a constrained single articulation design, which may result in a difference in wear debris particles. The aim of this study is to evaluate wear debris generated from a dual mobility hip and compare it to a conventional single articulation design when both are manufactured from sequentially crosslinked and annealed polyethylene. The dual mobility hip (Restoration ADM) incorporated a 28mm CoCr femoral head into a polyethylene liner that articulates against a metal shell (48mm ID). The conventional hip (Trident®) mated a 28mm CoCr femoral head against a polyethylene liner. The polyethylene for all liners was sequentially crosslinked and annealed (X3). A hip joint simulator was used for testing at a rate of 1 Hz with cyclic Paul curve physiologic loading. A serum sample from each testing group was collected. Serum samples were protein digested following the published process by Scott et al. The digested serum was then filtered through a series of polycarbonate filter papers of decreasing size and sputter coated with gold for analysis using SEM. Image fields were randomized and wear debris was compared in terms of its length, width, aspect ration, and equivalent circular diameter (ECD). A total of 149 conventional hip particles and 114 dual mobility hip particles were imaged. Results show a majority of particles are of spherical nature and images do not indicate the presence of fibrillar or larger elongated polyethylene debris. Particle length between designs is not statistically different, while all other comparisons show statistical significance (p<0.05). It is hypothesized that the dual mobility hip system reduces the total amount of cross-shear motion on any one articulation, which aids in the reduction in wear. This design feature may be responsible for the slight difference in morphology of dual mobility wear debris when compared to the constrained hip design. The length of the particles was similar, simply indicating a different shape rather than a marked reduction in overall size. The debris generated is this study was from highly crosslinked polyethylene in two different designs, which produced a very significant decrease in quantity of particles when compared to the quantity of debris from conventional polyethylene. The wear debris was of similar length in both designs and so we do not expect any difference in biological response to debris from either device. The dual mobility design has also shown no effect of cup abduction angle on wear demonstrating forgiveness to implant positioning. This advantage, combined with the low wear rate and similar length wear particles, should lead to good clinical performance of dual mobility cups with sequentially irradiated and annealed polyethylene