Although day surgery has a good patient satisfaction and safety profile, accurate episode-of-care costs (EOCC) calculation for of this procedure compared to standard same-day admission (SDA), while considering functional outcomes, is not well known. This study assesses the EOCC for patients with a THA while comparing DS and Same Day Admission (SDA) (with a 1-day hospitalization) pathways. The episode-of-care cost (EOCC) of 50 consecutive day surgery and SDA patients who underwent a THA was evaluated. The episode-of-care cost was determined using a bottom-up Time Driven- Activity Based Funding method. Functional outcomes were measured using preoperative and postoperative Harris Hip Score (HHS). Overall, the SDA THA cost 11% more than a DS THA. The mean total EOCC of DS THA was 9 672 CAD compared to 10 911 CAD in the SDA THA group. Both groups showed an improvement in HHS score following the procedure but patients in the DS group had a significantly higher postoperative HHS score and a significantly greater improvement in their HHS score postoperatively. Day surgery THA is cost-effective, safe and associated with high patient satisfaction due to functional improvement. Providing policymakers the information to develop optimal financing methods is paramount for clinicians wishing to develop modern protocols, increase productivity while providing the optimal care for patients.
Patients who are actively smoking at the time of primary total joint arthroplasty (TJA) are at considerably increased risk of perioperative complications. Therefore, strategies to assist patients with smoking cessation before surgery have become routine practice. A secondary benefit is the theoretical catalyst for long-term smoking cessation. However, questions remain as to whether patients actually cease smoking prior to the procedure, and if so, how long this lasts postoperatively. Our high-volume, academic institution documents self-reported smoking status at each clinic visit (at 6-month intervals), as well as at the time of surgery through a total joint registry. As such, all patients who underwent TJA from 2007 to 2018 were identified and grouped as: non-smokers, smokers (regularly smoking cigarettes within 1 year from surgery), and former smokers (those who quit smoking within a year before surgery). Thereafter, smoking status in the postoperative period was assessed, with special attention to the former smokers in order to see who remained smoke-free. From the 28,758 primary TJAs identified, 91.3% (26,244) were non-smokers, 7.3% (2,109) were smokers, and 1.4% (405) had quit smoking before surgery. Among patients who quit smoking before surgery, only 38% were still abstinent at 9 years from surgery. Conversely, 24% of smokers at the time of surgery eventually quit and 3.1% of non-smokers started smoking over the same time period. Despite a concerted effort to help patients stop smoking before TJA, an important proportion (7.3%) are unsuccessful. Among those patients who do manage to stop smoking, only a minority (38%) remain smoke-free after surgery. Compared to current smokers, patients who managed to quit before surgery are more likely to remain smoke-free after surgery. These findings highlight that smoking remains a tremendous challenge in contemporary TJA practices. Additional strategies targeting smoking cessation before after surgery are needed.
Joint replacement is one of the most common orthopaedic procedures, with over 2 million surgeries performed each year across the globe. Loss of implant fixation, or aseptic loosening, is the leading cause of revision following primary joint replacement, accounting for ∼25% of all revision cases [1]. However, diagnosis of aseptic loosening and its underlying causes remain challenging due to the low sensitivity and specificity of plain radiographs. To address this, we propose a novel approach inspired by [2] involving the use of a self-sensing bone cement (by imparting strain-dependent electrical conductivity or piezoresistivity) combined with electrical impedance tomography (EIT). Piezoresistivity is imparted to cement via incorporation of micro/nanoscale conductive fillers. Therefore mechanical effects such as loosening and cracks will manifest as a conductivity change of the cement. This work explores if EIT is able to detect strains and cracks within the bone cement volume. Experiments were designed to determine whether EIT combined with piezoresistive cement can be used to detect strains and cracks (Fig. 1). The setup consists of a tank filled with water, 16 electrodes, sample, a loading machine (MTS), and an EIT system. To develop the piezoresistive bone cement, microscale carbon fibers were used with varying CF/PMMA volumetric ratios (VR) from VR = 0.25% to 3.0%. Three conical samples were made to model a loading condition similar to knee implants (Fig. 1). The samples were compressed while the conductivity map of the tank was measured with the EIT system.INTRODUCTION
METHODS
The use of Additive Manufacturing (AM) to 3D print titanium implants is becoming widespread in orthopaedics, particularly in producing cementless porous acetabular components that are either We examined 11 retrieved 3D printed acetabular cups divided into two groups: “Introduction
Material and methods
Additive manufacturing has enabled a radical change in how surgeons reconstruct massive acetabular defects in revision hip surgery. We report on the early clinical and radiological results from our methods for surgical planning, design, and implantation of 3D printed trabecular titanium implants in a cohort of patients with large unclassifiable pelvic defects. We set up a prospective investigation involving 7 consecutive patients. Inclusion criteria was the following: 1) A history of previous total hip replacement; and 2) Current imaging showing at least a Paprosky 3B defect. Planned acetabular inclination and version was 40° and 20° respectively. Post operatively all patients had a CT scan which was analysed with software to determine component position and compared to planned. Outpatient review was done at 2 weeks (For wound), 6 weeks (for weight bearing and fixation) and 52 weeks (for fixation and infection) post-operative. The median age at surgery was: 65 years (40–78). The median bone defect volume was 140cm3. Median surgery length was 5.2 hours (3–6.25). Median blood loss was 1300mL (450– 2000). Radiologically, components were stable and no screw breakages were identified. Achieved inclination was 41.0° (29.0–55.6) and achieved version was 15.8° (3.8–43.6). Median Oxford Hip score improved from 9 (2–44) to 25 (18–32). We have demonstrated a new series of pre, intra and post-operative methods for reconstruction of unclassifiable acetabular bony defects. Initial clinical and radiological results are excellent considering the severity of the bony defects. We recommend the use of our or similar methods when trying to reconstruct these defects.
Surgeons are waiting for a hassle free, time saving, precise and accurate guide for hip arthroplasty. Industry are waiting for instruments to reduce manufacturing costs associated with washing, assembling, sterilization and transportation. Patient specific / custom made surgical guides may deliver these goals but current systems have had limited assessments. We comprehensively assessed a new guiding system for the acetabular component of hip replacement, “Bullseye”.
Background
Methods
Our study is still in progress. The results mentioned in the abstract are preliminary results. The final results will be provided at the time of presentation. Over the past decade, the widespread availability of high-resolution ultrasonography coupled with advances in regional anaesthesia have popularised peripheral nerve blocks for anterior cruciate ligament reconstructions (ACLRs). The aim of this study is to investigate whether the femoral nerve block (FNB) administered at the time of ACLR has any long-term impact on the quadriceps strength as compared to patients who did not receive a FNB. This is a retrospective study. Four hundred charts of patients who underwent ACLR at our institution and had subsequent Biodex testing (an isokinetic rehabilitation test that provides objective information about muscle strength deficits and imbalances of the operated leg compared to the non-operated leg) from 2004 to 2015 were reviewed. Patients who had prior ipsilateral knee surgery, multi-ligament knee injury or at extreme ages were excluded from the study. The following baseline patient characteristics was recorded for each reviewed chart: age, sex, medical comorbidities, the date of the injury, date of the surgery, surgery technical notes and associated procedures, the surgeon, the hospital were the patient was operated, the Biodex test date and the Biodex test results. Data extraction assessed any association between the ACLR patients' who received FNB with the results of the Biodex test after completing the rehabilitation protocol. Descriptive statistics were used to compare the type of anaesthesia, mode of pain control and the results of the Biodex tests between patients grouped by the mode of anaesthesia used at the time of surgery (FNB versus no FNB). A multivariate regression model then compared quadriceps strength (inferred by Biodex test results) between groups while controlling for baseline differences between groups. Fifty five percent of the ACLR patients received FNB compared to 45% that did not receive FNB over the last 11 years of performing ACLRs (2004–2015) at our institute. Fifty percent of the patients that received FNB failed to achieve more than or equal to 80% quadriceps strength (compared to the contralateral non-operated leg) at 6 months on Biodex test. On the other hand, only 20% of the non-FNB group failed to achieve more than or equal to 80% quadriceps strength. This study lead us to think that ACLR patients that received FNB are significantly weaker in quadriceps strength at 6 months post ACLR in comparison to non-FNB ACLR patients. This finding subsequently might affect the time needed to return to sports and might indicate a considerable clinical consequence of the FNB on ACL-reconstruction patients.
Hip fractures are among the most common orthopaedic injuries and represent a growing burden on healthcare as our population ages. Despite improvements in preoperative optimisation, surgical technique and postoperative care, complication rates remain high. Time to surgery is one of the few variables that may be influenced by the medical team. The aim of the present study was to evaluate the impact of time to surgery on mortality and major complications following surgical fixation of hip fractures. Utilising the American College of Surgeons' National Quality Improvement Program (NSQIP) database, we analysed all hip fractures (femoral neck, inter-trochanteric, and sub-trochanteric) treated from 2011 to 2013 inclusively. We divided patients into three groups based on time to surgery: less than one day (<24h), one to two days (24–48h), and two to five days (48–120h). Baseline characteristics were compared between groups and a multivariate analysis performed to compare 30-day mortality and major complications (return to surgery, deep wound infection, pneumonia, pulmonary embolus, acute renal failure, cerebrovascular accident, cardiac arrest, myocardial infarction, or coma) between groups. A total of 14,730 patients underwent surgical fixation of a hip fracture and were included in our analysis. There were 3,475 (24%) treated <24h, 9,960 (67%) treated 24–48h, and 1,295 (9%) treated 48–120h. Thirty-day mortality and major complication rates were 5.0% and 6.2% for the <24h group, 5.3% and 7.0% for the 24–48h group, 7.9% and 9.7% for the 48–120h group respectively. After controlling for baseline demographic differences between groups (age, sex, race) as well as pertinent comorbidities (diabetes, dyspnea, chronic obstructive pulmonary disease, chronic steroid use, hypertension, cancer, bleeding disorders, and renal failure), time to surgery beyond 48h resulted in greater odds of both mortality (1.45, 95%CI 1.10–1.91) and major complications (1.45, 95%CI 1.12–1.84). Time to surgery is one of the few variables that can be influenced by timely medical assessment and access to the operation room. Expediting surgery within 48h of hip fracture is of paramount importance as it may significantly reduce the risk of mortality as well as major complications.
Metal-on-metal (MOM) total hip arthroplasty using large diameter femoral heads offer clinical advantages however the failure rates of these hips is unacceptably high. Retrieved hips have a wide range of wear rates of their bearing and taper surfaces and there is no agreement regarding the cause of failure. Detailed visual inspection is the first step in the forensic examination of failed hip components and may help explain the mechanisms of failure. The aim of this study was to determine if there was a correlation between the results of detailed inspections and the volumetric wear of the bearing and taper surfaces of retrieved hips. Detailed, non-destructive macroscopic and stereomicroscopic examinations of 89 retrieved MOM hip components were performed by a single experienced examiner using quantitative assessment to document the severity of 10 established damage features: Light scratches, Moderate scratches, Heavy scratches, Embedded particles, Discolouration, Haziness, Pitting, Visible wear zone, Corrosion, Fretting Each surface was considered in terms of zones comprising of quadrants (cup, head, and taper) and subquadrants (cup and head), Figure 1. Each zone was scored on a scale of 0 to 3 by determining the percentage of the surface area of the zone that exhibited the feature in question: a score of 0=0%, 1<25%, 25%<2<75%, 3>75%. The sum of the scores of each zone was used for the assessment of each damage feature. The volume of wear at the surfaces of each hip was measured with a Zeiss Prismo coordinate measuring machine (cup and head) and a Talyrond 365 roundness measurement instrument (taper), using previously reported methods1, 2. Simple linear regression models were used to asses the univariable associations between the inspection scores and wear volumes. Multiple linear regression models were subsequently used to asses the simultaneous contribution of the inspection scores, found significant in univariable analyses, on the wear outcome variables. All statistical analysis was performed using Stata/IC version 12.1 (StataCorp, USA) and throughout a p value < 0.05 was considered statistically significant.Introduction
Method
There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with modular tapers in total hip replacements with a single combination of materials of modular tapers. An inverted hip replacement setup was used (ASTM F1875-98). 28 mm Cobalt Chrome (CoCr) femoral heads were coupled with either full length (standard) or reduced length (mini) 12/14 Titanium (Ti) stem tapers. These Ti stem tapers had either a rough or smooth surface finish whilst all the head tapers had a smooth surface finish. Wear and corrosion of taper surfaces were compared after samples were sinusoidally loaded between 0.1 kN and 3.1 kN for 10 million cycles at 4 Hz. In test 1 rough mini stem tapers were compared with rough standard stem tapers whilst in test 2 rough mini stem tapers were compared with smooth mini stem tapers. Surface parameters and profiles were measured before and after testing. Electrochemical static and dynamic corrosion tests were performed between rough mini stem tapers and smooth mini stem tapers under loaded and non-loaded conditions.Introduction:
Methods:
Tribo-chemical damage of modular taper junctions is often observed at revision THR and may be a contributing factor to chronic inflammation of peri-prosthetic tissues through generation of chromium rich corrosion products. At the time of revision, surgeons may elect to leave the primary femoral stem in situ and replace the original femoral head with a new component. This decision is based on the assumption that the interface formed between the original trunnion and the new bore is capable of withstanding the loads and torques applied during use, without failure of the new interface. This study was performed to determine the extent to which the mechanical properties of the taper interface are degraded with varying degrees of tribo-chemical damage secondary to prior implantation. Fifteen CoCr femoral heads (DePuy: 6, Smith & Nephew: 5; Zimmer: 4) were retrieved at revision THR and were examined with stereomicroscopy. The surface of each bore was scored for the presence of fretting and corrosion using the grading system of Goldberg et al. Nine additional heads in original (unimplanted) condition (3 per manufacturer) were also selected to act as controls. Each head was manually assembled on a matching unimplanted TiAlV trunnion in a mechanical testing machine (MTS Bionix) and loaded at 500N/sec to a maximum assembly load of 4000N. The head/trunnion specimen was then mounted in a torsional loading fixture and immersed in bovine serum. A cyclic torque was applied to the head with an initial maximum value of 2 Nm. The specimen was unloaded and held for a 30 sec wait period and the torsional loading was repeated to a peak value of 4 Nm. With each torsional cycle the peak torque was increased by 2 Nm until the taper junction underwent rotational failure. During testing, relative motion between the femoral head and the trunnion was measured with a displacement transducer (DVRT-3, MicroStrain, accuracy = ± 0.1%, resolution = 1.5 μm, hysteresis & repeatability = ± 1 μm). A separate disassembly test was performed by first assembling each specimen with 4000N and then applying a distraction force at 0.008 mm/sec until separation.Introduction
Materials and Methods
High failure rates with large diameter, metal on metal hip replacements have highlighted a potential issue with the head/stem taper junction as one of the significant sources of metal ion release. Postulated reasons as to why this may be such a problem with large head metal on metal hip replacements is due to the increased torque achieved by the larger head size. This may be responsible for applying greater micromotion between the head and stem taper and consequently greater amounts of fretting corrosion. The aim of this study was to perform short term in vitro electrochemical tests to assess the effect of increasing head diameter and torque on the fretting corrosion susceptibility of the head/stem taper interface and to investigate its effect on different material combinations. 36 mm Cobalt Chrome (CoCr) femoral heads were coupled with either a CoCr or Titanium (Ti) stem with 12/14 tapers, all with a smooth surface finish. Increasing perpendicular horizontal offsets in the sagittal plane created incremental increases in torque. Offset increments of 0 mm, 5.4 mm and 7.5 mm were selected (Figure 1) to simulate the torque force equivalent to 9 Nm, 12 Nm and 17 Nm. An inverted hip replacement setup was used (ASTM F1875-98) (Figure 2). Components were statically loaded at 0 kN and 2.3 kN prior to sinusoidal cyclic loading and electrochemical testing. Mean & fretting currents were calculated every 50 cycles up to a maximum of 1000 cycles of sinusoidal cyclic loading at 3 Hz along with the Overall Mean Current (OMC), Overall Mean Fretting Current (OMFC) and Overall Current change (OCC).Introduction:
Methods:
It has been suggested that corrosion and fretting at the taper junctions of stemmed metal-on-metal hip replacements may contribute to their high failure rates. A peer-reviewed semi-quantitative scoring system [Goldberg et al., 2002] has been used to visually assess the severity of corrosion and fretting of the taper junction but has not been validated using multiple examiners. The aim of this study was to assess the inter-observer variability of this method. Macroscopic and stereomicroscopic examinations of the femoral head and stem tapers of 100 retrieved large diameter metal on metal (MOM) hip components were performed by two independent observers using the methods defined by Goldberg et al. [2002] to quantify corrosion and fretting. Scores ranging from 1 (none) to 4 (severe) were assigned to the medial, lateral, posterior and anterior quadrants of the neck taper and the distal and proximal regions of the head taper. An overall score was then assigned to each surface as a whole. Cohen's weighted Kappa statistic (κ) was used to measure the inter-observer agreement. A quadratic weighting scheme, that allocated weights to the importance of disagreements that are proportional to the square of the number of categories apart, was used to take account of scaled disagreement. Kappa values were assessed using previously established criteria where κ ≤ 0 = poor, 0.01 to 0.20 = slight, 0.21 to 0.40 = fair, 0.41 to 0.60 = moderate, 0.61 to 0.80 = substantial, 0.81 to 1 = almost perfect. A sample size of 100 was used in order to detect a coefficient of 0.60 to within 0.25 with 95% confidence with two experienced observers. Statistical analysis was performed using Stata/IC version 12.1 (StataCorp, College Station, TC, USA) and a p value < 0.05 was considered statistically significant.Introduction
Method
The changes in surface roughness occurring during the wear process at the bearing surface are of great importance in trying to understand the failure mechanism of large head metal-on-metal hip replacements. The aim of the study is to identify and characterise the areal surface parameter variation between the worn and unworn areas. Surface topography variations at the bearing surface have an effect on the lubrication regime [1]. In vitro tests of these components have suggested a “self-polishing” of the surface [2]. Traditionally A total of 50 retrieved metal-on-metal hip replacements were assessed using white light scanning interferometry (Talysurf CCI, Ametek, UK) to determine the difference in the areal surface topography parameters between the worn and unworn regions of the bearing surface. The worn area was identified by use of a previously described method [3] to produce a wear map of the bearing surface, this allows the identification of the regions of interest. A series of six measurements were taken on each component (figure 1) comprising of: 2 measurements at the equator of the head representing the unworn region, one measurement at the pole and just off centre from the pole and the rest of the measurements were taken inside and at the boundary of the wear area. Each measurement covered an area of 1 mm2 therefore it is crucial that the location of the measurement be established as accurately as possible. Data was analysed to determine the most relevant parameters that could be used to describe and highlight the changes in surface roughness that occur during the wear process.Background
Methods
Recent retrieval studies and registry reports have demonstrated an alarming incidence of early failure of metal-on-metal THR. This appears to be due to fretting and corrosion at the taper junction (trunnion) between the neck and large diameter heads in metal-on-metal hip implants. It has been proposed that designs with lower bearing clearances and greater cup flexibility deform during implantation leading to increased frictional torque and micromotion at the head-neck taper junction. Small movements at the trunnion may suggest elastic deformation, but large movements may suggest slippage at the friction interface. This study was conducted using retrieved metal-on-metal components to test the hypotheses that: 1. Cup deformation through localized compression leads to increased bearing torque, and 2. Increased torques generated in large head metal-on-metal bearings cause motion of the head-neck taper junction. Nine metal-on-metal hip implants were received from a national joint retrieval service and tested in a mechanical testing machine. The components were of three different designs (ASR, BHR, and Durom) and ranged in diameter from 42–54 mm. A custom jig was constructed to generate controlled radial compression at opposite points on the rim of an acetabular component. The jig was positioned inverted to the normal anatomical position and was angled to simulate the anatomical orientation of the cup (35° inclination, 10° anteversion). With the exception of an initial compression load of 100N, the cups were compressed at 200N intervals to a maximum of 2000N. Three trials at each cup compression load were performed. The torque developed about the trunnion axis was measured as the head articulated through a motion arc of 60° and the friction factor was calculated. Head–neck micromotion was continuously monitored using a non-displacement inductive transducer. Changes in micromotion from the 100N compression load were calculated.Introduction
Materials and Methods
A disturbing prevalence of painful inflammatory reactions has been reported in metal-on-metal (MoM) hip resurfacing arthroplasty. A contributing factor is localized loading of the acetabular shell leading to “edge wear” which is often seen after precise measurement of the bearing surfaces of retrieved components. Factors contributing to edge wear include adverse cup orientation leading to proximity (<10 mm) of the hip reaction force to the edge of the acetabular component. As this phenomenon is a function of implant positioning and patient posture, this study was performed to investigate the occurrence of edge loading during different functional activities as a function of cup inclination and version. We developed a computer model of the hip joint through reconstruction of CT scans of a proto-typical pelvis and femur and virtually implanting a hip resurfacing prosthesis in an ideal position. Using this model, we examined the relationship between the resultant hip force vector and the edge of the acetabular shell during walking, stair ascent and descent, and getting in and out of a chair. Load data was derived from 5 THR patients implanted with instrumented hip prostheses (Bergmann et al). We calculated the distance from the edge of the shell to the point of intersection of the load vector and the bearing surface for cup orientations ranging from 40 to 70 degrees of inclination, and 0 to 40 degrees of anteversion.Introduction:
Methods:
Metal-on-metal (MOM) total hip arthroplasty and hip resurfacing using large diameter femoral heads offer clinical advantages, however the failure rates of these hips are unacceptably high. Retrieved MOM hips have a wide range of wear rates of their bearing surfaces and there is ongoing research to identify the causes of failure. Detailed visual inspection is the first step in the forensic examination of failed hip components, but there is no universally accepted description or process. Visible features may help explain the mechanism of failure of MOM hips. During our analysis of 2000 MOM hip components, we have developed protocols to undertake detailed, non-destructive macroscopic and stereomicroscopic examinations of each component, using quantitative assessment to document the presence of types of damage. We have established a systematic terminology to describe the types of damage that are observed, allowing for consistency and clarity in the vocabulary used. These include (but are not limited to):
Scratching – when there is an increase in the number and/or magnitude of scratches present on the surface, typically increasing measured roughness parameters. The severity of scratching is determined by rubbing a 0.18 mm thickness acetate gage or fingernail over the surface:
Light –visible but not detectable with gage. Moderate – visible and detectable with gage. Heavy – depth clearly visible and will catch a fingernail or gage. Pitting – indentations in the surface for which the dimensions are similar in all directions. Embedded Particles – hard particles that have become embedded in the bearing surface. Discolouration – observed as a change in the appearance of the surface, often as colour diffraction patterns. Polishing, gouges, etching (from corrosion), surface films, surface deposits and tribochemical reaction layers. To assess the distribution of these types of damage on the components, each surface is considered in terms of zones defined by quadrants (cup, head, stem and taper) and sub-quadrants (cup and head only), Figure 1. Each zone is scored on a scale of 0 to 3 by determining the percentage of the surface area of the quadrant that exhibits the feature in question:
a score of 0 indicates 0%
indicates greater than 0% but less than 25% indicates between 25% and 75% inclusive indicates greater than 75%. The use of zones to differentiate between the polar and equatorial regions of the cup and head surfaces can offer important information relating to the articulation of the bearing surfaces. For example in a cohort of 90 inspections, a score of 3 for light scratching was recorded in all areas of the bearing surface in 40% of cups, whilst approximately 5% had evidence of pitting, occurring near the rim. Current research at our retrieval centre involves correlating the results of detailed inspections with a range of variables, including implant design, size and surgical position.
A disturbing prevalence of short-term failures of metal-on-metal (MoM) hip resurfacings has been reported by joint registries. These cases have been primarily due to painful inflammatory reactions and, in extreme cases, formation of pseudotumors within periarticular soft-tissues. The likely cause is localized loading of the acetabular shell leading to “edge wear” which is often seen after precise measurement of the bearing surfaces of retrieved components. Factors contributing to edge wear of metal-on-metal arthroplasties are thought to include adverse cup orientation, patient posture, and the direction of hip loading. The purpose of this study was to investigate the role of different functional activities in edge loading of hip resurfacing prostheses as a function of cup inclination and version. We developed a computer model of the hip joint through reconstruction of CT scans of a proto-typical pelvis and femur and virtually implanting a hip resurfacing prosthesis in an ideal position. Using this model, we examined the relationship between the resultant hip force vector and the edge of the acetabular shell during walking, stair ascent and descent, and getting in and out of a chair. Load data was derived from 5 THR patients implanted with instrumented hip prostheses (Bergmann et al). We calculated the distance from the edge of the shell to the point of intersection of the load vector and the bearing surface for cup orientations ranging from 40 to 70 degrees of inclination, and 0 to 40 degrees of anteversion.Introduction
Methods
The articulating surface replacement (ASR) XL stemmed total hip replacement and ASR resurfacing hip systems were recalled by DePuy due to a high prevalence of early failure. The ASR XL has a greater failure rate than the ASR resurfacing, which has been increasingly attributed to wear and corrosion at the taper interface between the female taper surface of the femoral head and the male taper (trunnion) of the femoral stem. The aim of this study was to quantify the prevalence and severity of taper corrosion in retrieved ASR XL hip components. A peer-reviewed subjective corrosion scoring system was used to quantify corrosion in a consecutive series of the 50 ASR XL hip components (head components – n=44; femoral stems – n=6) at our retrieval centre. Bearing surface wear (femoral head and acetabular cup combined) was quantified and a value of <5 microns was defined as low-wearing. Subsequent profilometry analysis was undertaken in the low-wearing hips to quantify material loss from the taper interface. 90% of components showed evidence of corrosion, with at least moderate corrosion observed in 58%. There were 17 low-wearing hips which had a median material loss from the taper interface of 3.51mm3 (range: 0.612–9.443). The median linear depth of material loss was 33μm (range: 8.5–78.0). No relationship was observed between taper corrosion and serum cobalt (r=0.204, p=0.2712) or chromium (r=0.146, p=0.432) metal ions. Wear and material loss from metal-on-metal (MoM) hips is associated with pseudotumour formation and adverse soft-tissue reactions. We have shown that taper corrosion is extremely common in failed ASR XL hips and that wear occurs in the same degree of magnitude as at the bearing surface also occurs at the taper interface. Therefore our findings support the emerging concept of ‘taper failure’, whereby the taper is the predominate reason for failure of MoM hips. Future work must determine the relative contributions of the bearing surface and the taper interface to serum cobalt and chromium metal ion levels.
Corrosion at the taper interface between the femoral head and the femoral stem is well described in metal-on-polyethylene (MoP) hips but previously was undetermined in large diameter head metal-on-metal (LHMoM) hips. The high failure rate of the articulating surface replacement (ASR) XL hip system has been partly attributed to susceptibility to corrosive damage at the taper interface. It was not known if other hip manufacturers are liable to taper corrosion. Therefore the aim of this study was to quantify the prevalence and severity of taper corrosion in LHMoM hips and compare corrosion across five different current generation manufacturers. Taper corrosion was analysed in a consecutive series of the five most common hip types at our retrieval centre: ASR XL, Evidence of corrosion was observed in 86% of components, with at least moderate corrosion observed in 61%. No difference in corrosion was observed between the ASR XL and the other manufacturers (p=0.202). There was still no difference seen when all manufacturers were compared individually (p=0.363). A positive correlation was observed between corrosion and femoral head diameter (r=0.224, p=0.021). However no relationship was observed with implantation time (r=0.163, p=0.118). Our study indicates that taper corrosion is common in LHMoM hips and affects all hip types equally. The clinical significance of this finding is that all hip types will be susceptible to the complications of corrosion, such as third body wear and osteolysis. Furthermore recent reports indicate that corrosive debris released from the taper interface may play a role in the formation of pseudotumours and adverse soft-tissue reactions. We found that larger femoral head sizes showed greater corrosion, which suggests that high torque increases fretting corrosion of the taper interface. Future work must determine the optimum femoral head size and investigate the chemical composition of the corrosive debris.
