Large articulations are increasingly being used to reduce dislocation, the most common early complication following THR. However, potential benefits of large articulations in reducing dislocation have not been proven in a well-controlled clinical trial. The aim of our randomised controlled trial was to compare the one-year incidence of dislocation between 36 and 28 mm metal on highly cross-linked polyethylene articulations. Patients were excluded if they had a high risk of dislocation due to, for example, abnormal anatomy, neuromuscular disease, previous infection or dislocation. Eligible patients were stratified according to a number of other factors which may influence dislocation risk, including primary or revision THR and, if primary THR, by surgeon, age, diagnosis, sex and Charnley grade. Patients were randomised intra- operatively to either a 28 or 36 mm articulation. Dislocation incidence was determined using a hip instability questionnaire and a hospital visit questionnaire. A dislocation was diagnosed if there was radiological evidence and reduction by a doctor was required. Six-hundred-and-forty-four patients undergoing primary or revision THR were entered into the study. Overall, the incidence of dislocation at one year following THR was 5.4% with a 28 mm articulation and 1.3% with a 36 mm articulation (p=.004). Incidence in primary THR patients was 4.4% with a 28 mm articulation, compared to 0.8% with a 36 mm articulation (p=.007). Incidence in revision THR patients was 12.2% and 4.9% with 28 and 36 mm articulations, respectively. For both primary and revision THR patients, sex distribution, age and BMI of patients who dislocated were similar to those of the total samples of primary or revision patients. This large randomised study unequivocally shows for the first time that, compared to a 28 mm articulation, a 36 mm articulation in THR is efficacious in reducing the incidence of dislocation in the first year following THR

The selection of an acetabular component for primary hip arthroplasty has narrowed significantly over the past 10 years. Although monoblock components demonstrated excellent long-term success the difficulty with insertion and failure to fully appreciate full coaptation of contact with the acetabular floor has led to almost complete elimination of its utilization. Modular acetabular components usually with titanium shells and highly crosslinked polyethylene are by far the most utilised today. This is particularly true with mid-term results demonstrating excellent wear rates and extremely low failure rates and the concern of possible mechanical failure of highly crosslinked polyethylene not being a clinical problem. Ceramic liners are also used but problems with squeaking articulations and liner chipping have made highly crosslinked polyethylene the preferred liner material. Metal-on-metal except in surface replacement arthroplasty is rarely used in primary hip arthroplasty. With instability in total hip replacement still being a significant and the leading cause of revision hip replacement the dual mobility articulation has emerged as an increasingly used acetabular component. This is composed of either a monoblock cobalt chrome socket articulating with a large polyethylene liner into which the femoral head is constrained. The polyethylene liner becomes essentially a larger femoral head articulation and hip stability is significantly improved. A modular dual mobility can also be utilised with a titanium shell and a cobalt chrome liner inserted into the shell and then a dual mobility articulation. In a recent series of 182 dual mobility cups, all monoblock ADM, in high risk patients undergoing primary total hip replacement there was 1 interprosthetic dislocation which occurred during reduction of a dislocation. Average follow up was 4.4 years with a range of 2–6.6 years

Surface arthroplasty or resurfacing represents a significant development in the evolution of hip replacement. A hip resurfacing arthroplasty (HRA) is a bone conserving alternative to total hip arthroplasty (THA) that restores normal joint biomechanics and load transfer and ensures joint stability. Metal-on-metal (MoM) bearings have been preferred for these large diameter articulations because of their lower volumetric wear and smaller particulate debris compared to metal-on-poly-ethylene bearings. Of the many engineering factors which have contributed to the success of the MoM bearing, the metallurgy, diametral clearance, sphericity and surface finish were thought to be most important. More recently, adverse reactions to metal particles and ions generated by wear and corrosion of the metal surfaces have focused the attention on the importance of coverage angle and cup positioning. Currently, the scientific consensus is that cup coverage angle, diametral clearance and metallurgy have their importance in that order. Precise understanding of manufacturing variables is imperative in obtaining clinical consistency and safety in the patient. It is important to examine femoral fixation, bone remodelling, and wear of MoM implants. For the second and third generation MoM HRA various designs and biomaterials have been used. We have conducted a randomised, controlled trial comparing 9 different hip resurfacing prostheses. Clinical and radiographic outcome and whole blood, serum and urine metal ion levels are evaluated at 6 months, 1 year and 2 years in 180 patients with 9 different HRA designs and the differences are analyzed. Besides, the design quality of the 9 different metal-on-metal prostheses and their accessory instruments have been judged during the operation. The Durom with its Metasul history may claim a metallurgic advantage, and in combination with the highest coverage angle of all cups, it may be the best wear couple, as suggested by low ion measurements. However, as discussed above, an optimal bearing alone is not sufficient to achieve a successful hip resurfacing

Background:. Dual mobility components in total hip arthroplasty have been successfully in use in Europe for greater than 25 years. However, these implants have only recently obtained FDA approval and acceptance among North American arthroplasty surgeons. Both decreased dislocation rate and decreased wear rates have been proposed benefits of dual mobility components. These components have been used for primary total hip arthroplasty in patients at high risk for dislocation, total hip arthroplasty in the setting of femoral neck fracture, revision for hip instability, and revision for large metal-on-metal (MoM) hip articulation. The literature for the North American experience is lacking. Purpose:. We report indications, short term outcomes, and complications of a series of subjects who received dual mobility outcomes at one institution. Study Design:. Consecutive subjects who received dual mobility total hip arthroplasty components from February 2010 and April 2013 were identified. Charts were retrospectively reviewed for surgical indications, comorbidities, component sizes, and perioperative complications including infection, dislocation, mechanical failure, and reoperation. Results:. 86 hips in 83 subjects underwent total hip arthroplasty or revision total hip arthroplasty using dual mobility components. There were 56 primary total hips and 30 revision total hips. Indications included small acetabular components in the setting of AVN (13 hips), DDH (12 hips) or severe inflammatory arthritis (5 hips), femoral neck fracture (5 hips), intraoperative instability (6 hips), recurrent postoperative instability (5 hips), and revision of large MoM articulations in the setting of failed hip resurfacing (10 hips) or failed MoM total hip arthroplasty (6 hips). Mean follow up was 1 year (3 months to 3.3 years). There were no complications in the primary total hip group. In the revision total hip group, only one hip dislocated and this was in a patient with familial dysautonomia and insensitivity to pain. One subject underwent reoperation for acute prosthetic joint infection. No other complications were encountered. Overall dislocation rate was 1.1% and overall complication rate was 2.2%. Conclusions:. These results closely mirror that of the European literature. Dual mobility articulations in total hip arthroplasty have a low short term complication rate in this cohort and provide a simple solution to difficult cases. Indications for these implants include primary and revision total hip arthroplasty in patients at high risk for instability and revision of large MoM implants including hip resurfacing

Purpose. Total disc replacement (TDR) devices have been restricted to designs with large, congruent articulations due to the limited wear properties of available materials. TDRs with more natural motion could be designed if materials were available which could resist the higher wear conditions. A novel TriLobe TDR design is self-centering and energetically stable, emulating the natural motion of the intact motion segment, but is not feasible using traditional materials due to small incongruent articulating surfaces. The objective of this study was to compare the wear properties of a medical grade polycrystalline diamond with wear properties of cobalt chrome (CoCr) and ultrahigh molecular weight polyethylene (UHMWPE) in aggressive high wear conditions. Methods. A modified pin-on-disc, crossing-path wear test was used to measure the wear rates of PCD-on-PCD, CoCr-on-CoCr, and CoCr-on-UHMWPE. The discs were placed in the inferior position on an oscillating plate, moving in a 10mm by 5mm figure-eight pattern. Pins had an initial 11.5mm radius and were loaded at 133N normal to the disc. In a typical pin-on-disc test, a wear flat develops on the pin and the wear rate is reduced as the contact area increases. The TriLobe design uses three lobes sliding in three non-conforming lenses which prevents wear flats from developing. To approximate this condition, the fixture holding the disc was placed on an air bearing and was allowed to rock in concert with movement of the load. The test was conducted in 25% bovine serum at a speed of less than two Hertz. Two sets of each material were tested, one set to 2.0 million cycles and the other set to 14.0 million cycles. Wear rates on the rocking-discs were measured using a high resolution coordinate measuring machine because the wear in the PCD specimens was not detectable gravimetrically. Results. The diamond specimen averaged 0.0036mm. 3. /MC of wear over the first 2 million cycles. The CoCr-on-CoCr specimens averaged 1.4mm. 3. /MC and the CoCr-on-UHMWPE averaged 4.7mm. 3. /MC over 2 million cycles. The PCD specimen taken to 14 million cycles had and average wear of 0.0022mm. 3. /MC compared to 2.4mm. 3. /MC and 9.5mm. 3. /MC for CoCr-on-CoCr and CoCr-on-UHMWPE respectively. Conclusions. Using the pin-on-rocking-disc test to approximate small, non-congruent articulating surface wear, both CoCr-on-CoCr and CoCr-on-UHMWPE wore at rates that were orders of magnitude greater than medical grade PCD. At two million cycles, CoCr-on-CoCr had worn nearly 400 times more than PCD and CoCr-on-UHMWPE wore more than 1300 times greater. During the last 12 million cycles the wear in non-diamond specimen accelerated, while the diamond wear rate decreased. At the end of 14 million cycles CoCr on itself and on UHMWPE specimens had worn at more than 1100 times and nearly 4300 times greater than PCD, respectively. Coupled with the inherent biocompatibility, high strength and toughness, and ultra low friction of diamond, the performance of PCD makes it an attractive material for TDR applications. PCD could be used in current designs to alleviate concern over wear debris and ion release and to increase the space for the next generation of TDR devices