Aims

The Birmingham Hip Resurfacing (BHR) was introduced in 1997 to address the needs of young active patients using a historically proven large-diameter metal-on-metal (MoM) bearing. A single designer surgeon’s consecutive series of 130 patients (144 hips) was previously reported at five and ten years, reporting three and ten failures, respectively. The aim of this study was to extend the follow-up of this original cohort at 25 years.

Aims

The aims of the study were to report for a cohort aged younger than 40 years: 1) indications for HRA; 2) patient-reported outcomes in terms of the modified Harris Hip Score (HHS); 3) dislocation rate; and 4) revision rate.

Polyimide (MP-1, MMATech, Haifa, Israel), is a high performance aerospace thermoplastic used for its lubricity, stability, inertness and radiation resistance. A wear resistant thin robust bearing is needed for total hip arthroplasty (THR). After independent laboratory testing, in 2006, the author used the material as a bearing in two Reflection (Smith and Nephew, USA) hip surgeries. The first, a revision for polyethylene wear, survives with no evidence of wear, noise, new osteolysis or complications related to the MP-1 bearing after 16 yrs. The second donated his asymptomatic MP-1 hip at 6.5yrs for post-mortem examination. There were no osteoclasts, cellular reaction bland in contrast to that of polyethylene. In 2013 a clinical study with ethical committee approval was started using a Biolox Delta (Ceramtec, Germany) head against a polyimide liner in 97 patients. MMATech sold all liners, irradiated: steam 52:45. Sixteen were re-machined in New Zealand. Acetabular shells were Delta PF (LIMA, Italy). The liner locked by taper. The cohort consisted of 46:51 M:F, and ages 43 to 85, mean 65. Ten received cemented stems. For contralateral surgery, a ceramic or polyethylene liner was used. Initial patients were lower demand, later, more active patients, mountain-biking and running. All patients have on-going follow up, including MP-1 liner revision cases. There has been no measurable wear, or osteolysis around the acetabular components using weight-bearing radiographs. Squeaking within the first 6 weeks was noted in 39 number of cases and subtle increase in palpable friction, (passive rotation at 50 degrees flexion), but then disappeared. There were 6 revisions, four of which were related to cementless Stemsys implants (Evolutis, Italy) fixed distally with proximal linear lucencies in Gruen zones 1 and 7, and 2 and 6. No shells were revised and MP-1 liners were routinely changed to ceramic or polyethylene. The liners showed no head contact at the apex, with highly polished contact areas. There were no deep or superficial infections, but one traumatic anterior dislocation at 7 years associated with 5 mm subsidence of a non-collared stem. The initial squeaking and increased friction was due to the engineering of the liner / shell composite as implanted, not allowing adequate clearance for fluid film lubrication and contributed to by shell distortion during impaction. The revised bearings were “equatorial” rather than polar, and with lack of wear or creep this never fully resolved. Where the clearance was better, function was normal. The “slow” utilization was due to my ongoing concern with clearances not being correct. The revision of 4 Stemsys stems, tribology issues may have contributed, but non “MP-1” / Stemsys combinations outside this study have shown the same response, thought to be due to de-bonding of the hydroxyapatite coating. With correct engineering and clearances, a 3.6 mm thick MP-1 bearing, a surface Ra<0.5, steam sterilized, shows no appreciable wear, and with confidence, can be used as a high performance THR bearing

Aims. The optimum clearance between the bearing surfaces of hip arthroplasties is unknown. Theoretically, to minimize wear, it is understood that clearances must be low enough to maintain optimal contact pressure and fluid film lubrication, while being large enough to allow lubricant recovery and reduce contact patch size. This study aimed to identify the relationship between diametrical clearance and volumetric wear, through the analysis of retrieved components. Methods. A total of 81 metal-on-metal Pinnacle hips paired with 12/14 stems were included in this study. Geometrical analysis was performed on each component, using coordinate and roundness measuring machines. The relationship between their as-manufactured diametrical clearance and volumetric wear was investigated. The Mann-Whitney U test and unpaired t-test were used, in addition to calculating the non-parametric Spearman's correlation coefficient, to statistically evaluate the acquired data. Results. The hips in this study were found to have had a median unworn diametrical clearance of 90.31 μm (interquartile range (IQR) 77.59 to 97.40); 32% (n = 26) were found to have been below the manufacturing tolerance. There was no correlation found between clearance and bearing (r. s. = -0.0004, p = 0.997) or taper (r. s. = 0.0048, p = 0.966) wear rates. The wear performance of hips manufactured within and below these specifications was not significantly different (bearing: p = 0.395; taper: p = 0.653). Pinnacles manufactured from 2007 onwards had a greater prevalence of bearing clearance below tolerance (p = 0.004). Conclusion. The diametrical clearance of Pinnacle hips did not influence their wear performance, even when below the manufacturing tolerance. The optimum clearance for minimizing hip implant wear remains unclear. Cite this article: Bone Joint Res 2020;9(8):515–523

Aims

This study reports the mid-term results of total hip arthroplasty (THA) performed using a monoblock acetabular component with a large-diameter head (LDH) ceramic-on-ceramic (CoC) bearing.

Aims

This study presents the long-term survivorship, risk factors for prosthesis survival, and an assessment of the long-term effects of changes in surgical technique in a large series of patients treated by metal-on-metal (MoM) hip resurfacing arthroplasty (HRA).

Introduction. Because of concerns regarding excessive wear and short-term failures attributed to the metal-on-metal bearings, the use of metal-on-metal hip resurfacing arthroplasty (MOMHRA) has been greatly reduced since 2008, despite great mid-term results for well-designed implants and in certain patient populations. The true cause of excessive wear was then unknown. Therefore, identification of true risk factors for the procedure became paramount to refine indications and improve survivorship outcomes. Methods. Over the last 10 years, a systematic search of the US national library of Medicine and National institutes of health with the key words “metal-on-metal” and hip resurfacing” was conducted and returned 2186 items. Of these items, 862 were deemed relevant to our research purposes and entered in our center's reference database from which this review was performed. Results. Edge loading is the main culprit for high wear and high serum Co and Cr ion concentrations because it disrupts the fluid film lubrication of the device. Computation of the contact patch to rim distance (CPR), an estimate of the joint's functional coverage, is the best predictor of potential edge loading and excessive wear. Both in vivo and in vitro studies show that the wear of well-designed and well-positioned MOM bearings diminishes over time with continued use, an advantage only featured by MOM bearings. Systemic wear-related complications and hypersensitivity to metal once thought to be common are in fact rare occurrences. In addition, metal-related revisions only represent a small portion of the various modes of failure encountered with well-designed HRA. In our series of 1321 hips with only 0.5% lost to follow-up, 11 patients underwent revision surgery for excessive wear or adverse local tissue reaction. All but 2 had mal-positioned acetabular components (CPR distance <10mm). One of these 2 patients had serum cobalt and chromium levels of 13 and 9 µg/L respectively, despite a CPR distance of 18.3 mm, while the other showed a peri-prosthetic fluid collection estimated at 111cc on MRI. Component aseptic loosening (acetabular or femoral) remains, as is also the case for total hip arthroplasty (THA), the leading indication for revision surgery, even though substantial progress has been reported to reduce its incidence. Femoral neck fractures and loosening are associated with the surgeon's learning curve which can be avoided with proper training. The survivorship of the femoral component in our series after implementation of surgical technique changes is 99.2% at 10 years for an overall survivorship of 95.5%. A diagnosis of DDH is associated with a higher failure rate, particularly from socket loosening, while women without risk factors have a survivorship of 98.6% at 15 years. Conclusion. HRA has often been, but should not be associated with the results of large head metal-on-metal THA which often present with a different set of failure mechanisms. Now that most of the risk factors for HRA have been identified, and solutions found, a balanced perspective of its results is needed because the long-term data available validate the low wear of MOM bearings which was predicted in the early hip simulator studies. Considering the tremendous progress made in surgical technique and the advanced tribological knowledge acquired with the last 20 years of investigations related to MOM HRA, all the conditions are present to make this procedure a success for lifetime durability as shown in our series where 44 patients (54 hips) have died without a revision at a mean follow-up time of 9.7 years (range, 1.8 to 19.7). For HRA, when devices with adequate coverage and clearance of the ball by the socket are used, severe developmental dysplasia and inadequate surgical technique are responsible for most failures at 10 to 15 years of follow-up. It is our opinion that the advantages of HRA over THA (such as absence of thigh pain, a low dislocation rate, no taper corrosion, and the preservation of proximal femoral bone mineral density and the ability to maintain high activity levels without penalty) now outweigh the risks of using a MOM bearing

There is increasing global awareness of adverse reactions to metal debris and elevated serum metal ion concentrations following the use of second generation metal-on-metal total hip arthroplasties. The high incidence of these complications can be largely attributed to corrosion at the head-neck interface. Severe corrosion of the taper is identified most commonly in association with larger diameter femoral heads. However, there is emerging evidence of varying levels of corrosion observed in retrieved components with smaller diameter femoral heads. This same mechanism of galvanic and mechanically-assisted crevice corrosion has been observed in metal-on-polyethylene and ceramic components, suggesting an inherent biomechanical problem with current designs of the head-neck interface.

We provide a review of the fundamental questions and answers clinicians and researchers must understand regarding corrosion of the taper, and its relevance to current orthopaedic practice.

Cite this article: Bone Joint J 2016;98-B:579–84.

Hip resurfacing using metal-on-metal bearings has a number of purported advantages over traditional total hip replacement in the young, active patient. Males in particular can benefit from the bone preservation, stability, and higher activity levels seen with this procedure. As more is learned about the factors affecting long-term outcome of hip resurfacing, component position has emerged as one major predictor of success. Given a well-selected patient, and a well-designed device, acetabular positioning is perhaps the most important determinant of long-term survivorship in hip resurfacing. One feature of resurfacing socket design which has not been widely disseminated is the sub-hemispheric arc of the bearing surface. While the outer circumference of the socket represents a complete hemisphere, and radiographic evaluation may assume that the apparent socket angle is satisfactory, the actual bearing is less than a hemisphere, so that the true abduction of the bearing is considerably more vertical. This important fact leads to excessive bearing inclination, edge loading, and all that follows, including runaway wear, metallosis, ALVAL, and pseudotumors. Inadequate socket anteversion can expose the psoas tendon to abrasion and tendonitis. Too much acetabular anteversion, especially when combined with increased femoral neck anteversion, can result in an overall decrease in bearing contact area, and excessive wear. Femoral component positioning is critical in the prevention of femoral neck fractures, which are a chief cause of early failure. Varus placement increases the tensile stresses on the superior femoral neck. Excessive valgus threatens notching. Both increase femoral neck fractures. Sufficient malposition will ultimately result in edge loading. Edge wear is incompatible with fluid film lubrication, the key to longevity of these bearings

Squeaking arising from a ceramic-on-ceramic (CoC) total hip replacement (THR) may cause patient concern and in some cases causes patients to seek revision surgery. We performed a meta-analysis to determine the incidence of squeaking and the incidence of revision surgery for squeaking. A total of 43 studies including 16 828 CoC THR that reported squeaking, or revision for squeaking, were entered into the analysis. The incidence of squeaking was 4.2% and the incidence of revision for squeaking was 0.2%. The incidence of squeaking in patients receiving the Accolade femoral stem was 8.3%, and the incidence of revision for squeaking in these patients was 1.3%.

Cite this article: Bone Joint J 2014;96-B:181–7.

Head sizes used in total hip arthroplasty (THA) has increased drastically from the original 22mm used by Charnley. This is due to two factors: the use of hard-on-hard materials for the bearing articulation and the increasing problem of dislocation. The tribological aspect. Hard-on-hard materials enable mixed or fluid film lubrication due to their good wettability. The development of a fluid film layer is encouraged by smaller surface pressures (larger area) and higher velocity at the articulating interface (larger radius), suggesting that larger diameters exhibit better lubrication and such less wear. This was effectivly proven in pre-clinical simulator studies and used as argument to increase the diameters of metal-on-metall and ceramic-on-ceramic bearings. Clinically the tribological advantage of larger diameters has not yet been shown. For hard-on-soft bearings the situation is different. Due to the bad wettability of Polyethylene (PE), the abrasive wear regime is dominant. This means that the longer wear path of a larger diameter will inevitably carry a larger amount of wear debris. Despite this relation, the heads used in combination with PE were also increased up to 40mm diameter, justified by the overall greatly reduced wear amount of the new generation(s) of cross-linked PE and favourable simulator results. First in-vivo studies have shown that larger heads carry larger amounts of wear particles. Whether this increase is relevant with respect to osteolysis is still unclear and will have to be shown in longer term studies. The biomechanical aspect. Larger heads require a larger “jumping” distance until they dislocate. Consequently the use of larger heads reduces dislocation rates, which was shown in multiple clinical studies. However, the reduction in dislocation rate achieved by increasing diameters varies greatly. Some centres achieve dislocation rates below 1% with 28mm heads, other centres require 36mm heads to achieve the same result. No study shows any further advantage with head diameters larger than 36mm. Despite their obvious biomechanical advantage with regard to stability, larger heads also have large disadvantages. Larger heads carry inevitably larger friction moments, requiring better anchoring of the components. In unfavourable conditions (start-up, break-down of lubrication film), friction moments of hard-on-hard bearings can get very high and reach or even exceed the losening torque of the head on the taper. Depending on the head impaction foce during assembly, the loosening torques amount to 8 to 17Nm. Movement at the head-taper connection possibly causes wear and increased corrosion at this interface. Larger head diameters also require thinner shells and/or liners, leading to problems with liner chipping or incomplete seating. Large head diameters have also lead to the use of sub-hemispherical cups with reduced covering surface, increasing the risk of fluid film break down due to edge loading if not well positioned. Finally, larger heads might give the surgeon a wrong feeling of security regarding a sub-optimal positioned cup. The question regarding “the optimal” head diameter is open for discussion and needs to consider the bearing material used. Head size should be limited to a reasonable compromise, which based on the information currently available, could be 36mm. Join the “36 and under” club

Fluid film lubricating ability of a total hip prosthesis depends on the profile accuracies including surface-roughness or the sphericity of a head or a cup. Therefore, surface polishing is important. It was, however, difficult to polish the central portion of a cup or head using the conventional rotating machine. In the present study, we developed a polishing method combining a pendulum machine and a robotic arm. The effect of the accuracy improvement by this method was evaluated by the friction measurements on some test specimens. Nine balls and a cup of Co-Cr-Mo alloy that were polished by a conventional process using a rotating machine were prepared for the prototype. The average diameter of the balls was 31.9648 mm with the sphericity of 0.0028 μm. The inside diameter of the cup was 31.9850 mm with the sphericity of 0.0044 μm. We combined a robotic arm and a pendulum apparatus to enable the further polishing. The ability of both automatic centering and change in the sliding direction was accomplished by this system. The sliding direction has been changed 180 times every ten degrees. The total distance of polishing was 120 m under vertical load of 100 N in a bath of saline solution containing abrasive grains of silicate of the diameter of 2μm. The surface roughness of the central portion of the cup, which is important area for the fluid film lubrication decreased from Ra 20.2 μm before the polishing to Ra 18.7 μm after the polishing. A pendulum type friction tester was used for the assessment of the improvement of the lubricating ability by the polishing. The measurement was run over at 10 times under the conditions of the load of 600 N in a bath of saline solution. As the result, the frictional coefficients decreased from 0.1456–0.1720 before polishing to 0.1250–0.1300 after polishing. The polishing effect was, however, observed only at the specimens that radial clearances did not exceed the value of 50 μm. The present results indicated that the surface polishing of the central portion of hip prostheses must improve the lubrication ability and the radial clearance before the finishing process should be chinked as possible

The ACCIS system comprises a bearing of a 5 micron surface ceramic upon a Chrome Cobalt Molybdenum (CrCoMo) substrate which allows for a homogeneous couple. The Titanium Niobium Nitride (TiNbN) microceramic applied by Plasma Vapour Deposition. In comparison with CrCoMo alloy, TiNbN gives a hard (2800 vs 489V), smooth (0.23 vs 0.55Rz), low friction (0.079–0.1 vs 0.11–0.56mu pin on disk test), wetable surface which when combined allows for the potential of gaining fluid film lubrication (lambda>3) on a smaller head diameter than an untreated surface. These properties are postulated to reduce wear and hence lower the release of Cr and Co ions in vivo. The surface microceramic also prevents exposure to release of Cr and Co by corrosion. The surface modified implants were first used in 2003 in large head arthroplasty and later in 2005 with resurfacing implants. Two series of patients implanted by a single surgeon were examined to elucidate the metal ion release of the ACCIS system. The first series retrospectively examined 52 consecutive Large Head Arthroplasty cases for [Cr], [Co] and [Mo] levels. A mean follow-up time of 7.5 yrs (77–101mths) with 9 patients being lost to revision and death by the time of the study. Median levels of [Cr] 1.6, [Co] 4.76 and [Mo] 2.5 µg/l were obtained. The second series prospectively examined the [Cr] and [Co] levels with the pre-operative values as controls in 125 resurfacing cases with the ACCIS microceramic. The second series gave no rising trend observed at up to 5 years ([Cr & Co] (range < 0.5–1.6 µg/l). It is postulated that the ACCIS surface microceramic reduces wear and also reduces the effective patch size for a given load thus allowing for a greater Patch to Edge Distance allowing a greater tolerance to cup positioning. A RCT is currently underway

Introduction. Metal-on-polycarbonate urethane (MPU) is a cutting-edge new bearing technology for hip arthroplasty. The acetabular component consists of a 2.7mm-thick polycarbonate-urethane liner inserted into a specially manufactured uncemented titanium shell coated with hydroxyapatite [(HA) Fig. 1]. The liner is pliable and biomechanically mimics human cartilage. In vitro studies have shown minimal wear, fluid film lubrication, physiological load transmission and shock absorption capacity equal to the normal hip. This system includes prosthetic heads of a diameter 12mm less than the socket diameter. The aim of this study was to clinically assess patients treated with this novel technology in a retrospective single centre study. Methods. Twenty-seven patients with osteoarthritis treated with MPU bearing arthroplasty were included. Mean patient age was 67.9±10.35 years (44–84). Sixteen patients were female and 11 were male. Twenty-four of these had an uncemented HA-coated stem while 3 had a hip resurfacing metal femoral component. All patients were operated on by a single surgeon using a postero-lateral approach. Results. No patients were lost to follow-up. Mean follow-up time was 29 months (minimum 24 months). There were no major complications. At follow-up, the mean Harris hip score was 98 points (80–99). X-rays showed good bone-implant contact without any osteolysis or bone rarefaction. Discussion and conclusion. Our promising short-term results confirm the in vitro findings. Advantages of this new bearing technology include the possibility to use large diameter metal heads without exposing the patients to elevated levels of metal ions as is the case with metal-on-metal bearings, the minimal wear and the superior biomechanical characteristics

ABSTRACT. The viscosity and shear stress versus shear rate relationship for pure bovine serum (BS) and its aqueous solutions with and without carboxymethyl cellulose (CMC) were investigated. BS and diluted BS without CMC showed pseudoplastic flow curves up to a critical shear rate of ∼100 s-1 above which a Newtonian flow with significant rise in shear stress was observed. The viscosity flow curve for the diluted BS+5g CMC showed only shear thinning up to a shear rate of 3000 s-1 whereas diluted BS+1g or +2g CMC showed similar flow curves to pure BS. The shear rate application modified the flow behaviour of BS from a pseudoplastic to a Newtonian flow depending on its purity and CMC content. Friction factor was dependent on viscosity and clearance with mixed lubrication as the dominant mode within the viscosity range 0.001-0.044 Pas. INTRODUCTION. Pure BS and diluted BS are used as in vitro lubricants for tribological studies. Boundary, mixed and fluid film lubrication are the mechanisms involved in the lubrication of both natural and artificial joints. Clearance and lubricant viscosity will influence the nature of contact between the articulating surfaces. The objectives of this work were to study the flow properties of serum-based lubricants with different viscosities and the correlation between the rheological properties and frictional (and lubrication) behaviour of large diameter Biomet ReCaps with various clearances. MATERIALS AND METHODS. Rheological analysis was performed using a cone-on-plate rheometer (RHEOPLUS/32 V3.40) with a gap of 0.049mm at a constant temperature of 25°C on pure BS as base, 25BS+75 distilled water (DW), and 25BS+75DW+1g, +2g, or +5g CMC. The viscosity and shear stress were measured within shear rates of 0.3-3000 s-1. Frictional measurements of all the joints were carried out at the University of Bradford using a Prosim Friction Simulator on four, as-cast, high carbon, cobalt-chrome resurfacing systems (supplied by Biomet UK Healthcare Ltd., Swindon) with a nominal diameter of 52 mm each and diametral clearances of 167-178 μm. Stribeck plots were used to determine the lubrication mode. RESULTS AND DISCUSSION. Pure BS and diluted BS without and with CMC (1g and 2g) showed similar flow curves with viscosity decreasing from ∼1 to ∼0.001 Pas as shear rate increased from 0.3 up to ∼100 s-1 indicating shear thinning behaviour. A Newtonian flow with a significant rise in shear stress (from ∼0.2 to ∼3.5 Pa) was then observed above ∼100 s-1. Diluted BS+5g CMC showed the pseudoplastic flow only with viscosity decreasing from ∼12 to ∼0.236 Pas as shear rate increased up to 3000 s-1 with a significant rise in shear stress from 3.84 to 708 Pa in the range 0.3-3000 s-1. The Biomet ReCap with a clearance of 167 μm had lower friction factors (0.07 at a viscosity of 0.044 Pas) as compared to that with 178 μm clearance (0.1 at 0.044 Pas). All the ReCaps showed a mixed lubrication up to a viscosity of 0.044 Pas, above which the friction factor increased to 0.13 at a viscosity of 0.236 Pas for the 178 μm clearance

This multicentre study analysed 12 alumina ceramic-on-ceramic components retrieved from squeaking total hip replacements after a mean of 23 months in situ (11 to 61). The rates and patterns of wear seen in these squeaking hips were compared with those seen in matched controls using retrieval data from 33 ‘silent’ hip replacements with similar ceramic bearings. All 12 bearings showed evidence characteristic of edge-loading wear. The median rate of volumetric wear was 3.4 mm³/year for the acetabular component, 2.9 mm³/year on the femoral heads and 6.3 mm³/year for head and insert combined. This was up to 45 times greater than that of previously reported silent ceramic-on-ceramic retrievals. The rate of wear seen in ceramic components revised for squeaking hips appears to be much greater than in that seen in retrievals from ‘silent’ hips.

Although the number of displaced femoral neck fractures treated with hip arthroplasty is steadily growing, the outcomes are not as good as for other surgical indications. As a result, there is no consensus on the ideal type of arthroplasty for these patients. Unipolar and bipolar arthroplasty have a low dislocation rate but implant longevity and functional results are suboptimal. Total hip arthroplasty (THA) provides better functional outcomes and implant longevity but it is associated with a high incidence of postoperative dislocation. This constitutes a significant limiting factor for a more widespread use of this procedure. The TriboFit. ®. Buffer (Active Implants Corporation, Memphis, Tennessee, USA) is a 2.7 mm-thick cup made of polycarbonate-urethane which mimics the mechanical characteristics of human cartilage. It is a pliable, hydrophilic, biocompatible, endotoxin-resistant material and acts as a stress-absorber, transmitting loads to the subchondral bone in a physiological manner. The TriboFit. ®. Buffer shows excellent tribology, including ideal fluid film lubrication, low friction, high load carrying capabilities and long endurance. The TriboFit. ®. Buffer is fixed using flexible mechanical fixation. With a special instrument, a circumferential groove is cut into the patients’ socket. The TriboFit. ®. Buffer is seated by applying gentle pressure, with its ledge snapping tightly into the groove. The surgical technique is bone sparing as no acetabular bone reaming is required whatsoever. The TriboFit. ®. Buffer can be coupled with large diameter cobalt-chromium femoral prosthetic heads of the same dimensions as the patients’ femoral head. By restoring the correct hip anatomy and preserving the original size of the femoral head, hip range of motion (ROM) and stability are optimised. Within a multi-centre study, 224 patients (63 male and 161 female) with femoral neck fractures were treated with the TriboFit. ®. Buffer, a large diameter head and either cemented (192) or uncemented femoral stems (32). The mean patient age was 83 years (range 65 to 96). All surgeries were performed using a standard antero-lateral approach. Rehabilitation was fast and weight-bearing was as tolerated by the patients. There were no major complications, and in particular, no postoperative dislocations were reported. At a mean follow-up of one year, X-rays showed good implant stability. The mean Harris hip score (HHS) after one month was 58 points and increased to 80 points at one year (p = < 0.05). The ROM was the same as in the intact hip. Only one patient was revised because of nonimplant-related pain. This patient complained of pain in the surgically treated limb which was in actual fact related to spinal stenosis. Analysis of the retrieved implant revealed a loss of thickness in the superior area as well as minimal weight (approximately 2.4%). The backside revealed evidence of macroscopic wear in the area of directional loading from the femoral head to the acetabulum. The bearing surface showed minimal wear (less than 15 mm3), indicating that the primary wear location was on the backside. Retrieved synovial fluid and tissue analysis confirmed that there was no reactivity and no sign of synovitis. With femoral neck fracture patients, TriboFit. ®. Buffer arthroplasty is theoretically superior to both hemiarthroplasty and THA as it should involve the same low risk of dislocation and acetabular bone preservation associated with hemiarthroplasty, together with the same good functional results and consistent implant longevity of THA. Other advantages of this technique include reduced bleeding and short surgical times. The results of this study show that the new TriboFit. ®. Buffer arthroplasty technology has the potential to revolutionize the surgical treatment of displaced femoral neck fracture

The Articular Surface Replacement (ASR) hip resurfacing arthroplasty has a failure rate of 12.0% at five years, compared with 4.3% for the Birmingham Hip Resurfacing (BHR). We analysed 66 ASR and 64 BHR explanted metal-on-metal hip replacements with the aim of understanding their mechanisms of failure. We measured the linear wear rates of the acetabular and femoral components and analysed the clinical cause of failure, pre-revision blood metal ion levels and orientation of the acetabular component.

There was no significant difference in metal ion levels (chromium, p = 0.82; cobalt, p = 0.40) or head wear rate (p = 0.14) between the two groups. The ASR had a significantly increased rate of wear of the acetabular component (p = 0.03) and a significantly increased occurrence of edge loading (p < 0.005), which can be attributed to differences in design between the ASR and BHR. The effects of differences in design on the in vivo wear rates are discussed: these may provide an explanation as to why the ASR is more sensitive to suboptimal positioning than the BHR.

Introduction: Pseudotumours (soft-tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated serum and hip aspirate metal ion levels, suggesting that pseudotumours occur when there is increased wear. This study aimed to quantify in vivo wear of implants revised for pseudotumours and a control group of implants revised for other reasons of failure. Methods: A total of 30 contemporary MoMHRA implants in two groups were investigated in this Institutional Review Board approved study:. 8 MoMHRA implants revised due to pseudotumour;. 22 MoMHRA implants revised due to other reasons of failure (femoral neck fracture and infection). The linear wear of retrieved implants was measured using a Taylor-Hobson Roundness machine. The average linear wear rate was defined as the maximum linear wear depth divided by the duration of the implant in vivo. Results: In comparison with the non-pseudotumour implant group, the pseudotumour implant group was associated with:. significantly higher median linear wear rate of the femoral component: 8.1um/year (range 2.75–25.4um/year) vs. 1.79um/year (range 0.82–4.15um/year), p=0.002; and. significantly higher median linear wear rate of the acetabular component: 7.36um/year (range1.61–24.9um/year) vs. 1.28um/year (range 0.18–3.33um/year), p=0.001. Similarly, differences were also measured in absolute wear values. The median absolute linear wear was significantly higher in the pseudotumour implant group:. 21.05um (range 2.74–164.80um) vs. 4.44um (range 1.50–8.80um) for the femoral component, p=0.005; and. 14.87um (range 1.93–161.68um) vs. 2.51um (range 0.23–6.04um) for the acetabular component, p=0.008. Wear on the acetabular cup components in the pseudotumour group always involved the edge, indicating edge-loading of the bearing. In contrast, edge-loading was observed in only one acetabular component in the non-pseudotumour group of implants. The deepest wear was observed well within the bearing surface for the rest of the non-pseudotumour group. The difference in the incidence of edge-loading between the two groups was statistically significant (Fisher’s exact test, p=0.03). Discussion: Significantly greater linear wear rates of the MoMHRA implants revised due to pseudotumour support the in vivo elevated metal ion concentrations in patients with pseudotumours. This study provides the first direct evidence to confirm that pseudotumour is associated with increased wear at the MoM articulation. Furthermore, edge-loading with the loss of fluid film lubrication may be the dominant wear generation mechanism in patients with pseudotumour

We investigated factors that were thought to be associated with an increased incidence of squeaking of ceramic-on-ceramic total hip replacements. Between June 1997 and December 2008 the three senior authors implanted 2406 primary total hip replacements with a ceramic-on-ceramic bearing surface. The mean follow-up was 10.6 years. The diagnosis was primary osteoarthritis in each case, and no patient had undergone previous surgery to the hip. We identified 74 squeaking hips (73 patients) giving an incidence of 3.1% at a mean follow-up of 9.5 years (4.1 to 13.3).

Taller, heavier and younger patients were significantly more likely to have hips that squeaked. Squeaking hips had a significantly higher range of post-operative internal (p = 0.001) and external rotation (p = 0.003) compared with silent hips. Patients with squeaking hips had significantly higher activity levels (p = 0.009). A squeaking hip was not associated with a significant difference in patient satisfaction (p = 0.24) or Harris hip score (p = 0.34). Four implant position factors enabled good prediction of squeaking. These were high acetabular component inclination, high femoral offset, lateralisation of the hip centre and either high or low acetabular component anteversion.

This is the largest study to date to examine patient factors and implant position factors that predispose to squeaking of a ceramic-on-ceramic hip. The results suggest that factors which increase the mechanical forces across the hip joint and factors which increase the risk of neck-to-rim impingement, and therefore edge-loading, are those that predispose to squeaking.