Background

Improving primary care management of musculoskeletal (MSK) pain is a priority. A pilot cluster RCT tested prognostic stratified care for patients with common MSK pain presentations, including low back pain, in 8 UK general practices (4 stratified care; 4 usual care) with 524 patients. GPs in stratified care practices were asked to use i) the Keele STarT MSK tool for risk-stratification and ii) matched treatment options for patients at low-, medium- and high-risk of persistent pain. A linked qualitative process evaluation explored patients' and GPs' views and experiences of stratified care.

Background

Distal femoral replacements (DFR) are used in children for limb-salvage procedures after bone tumor surgery. These are typically modular devices involving a hinged knee axle that has peripheral metal-on-polyethylene (MoP) and central metal-on-metal (M-M) articulations. While modular connections and M-M surfaces in hip devices have been extensively studied, little is known about long-term wear or corrosion mechanisms of DFRs. Retrieved axles were examined to identify common features and patterns of surface damage, wear and corrosion.

Introduction

In 2010, a widely used metal-on-metal hip implant was voluntarily recalled from the market by the manufacturer. Our lab performed detailed retrieval analysis of 548 of the explanted devices and 165 periprosthetic tissue specimens. We reported a high degree of variability in the multiple measurements that we performed on the components, including volumetric wear.

Other studies using semi-quantitative tissue grading methods to describe the histology of the periprosthetic tissues from metal-on-metal hips have looked for relationships between component wear and histological features. Grammatopoulos et al found higher ALVAL scores in 45 hip resurfacing patients with pseudotumors compared to 11 without pseudotumors and a moderately positive correlation between wear and the histological rankings for tissue necrosis and lymphocytic response.

We examined correlations between the component wear measurements from retrieval analysis and the tissue features in this large group of one metal-on-metal hip design.

Background and objectives

Low back pain (LBP) is a major health challenge globally. Research has identified common trajectories of pain over time. We aimed to investigate whether trajectories described in one primary care cohort can be confirmed in another, and to determine the prognostic value of factors collected 5 years prior to the identification of the trajectory.

Recently, a special type of surface pitting found on metal implants was proposed to arise from “inflammatory cell-induced” corrosion (ICI, Figure 1) (1, 2). The actual mechanism of this was unknown, but similar features were suggested to be artefacts of electrocautery damage from revision surgery (3). Under lab conditions and without the influence of any cells, we aimed to reproduce the same surface pits and structures with electrocautery.

Young osteoarthritic male patients have been considered the ideal candidates for Metal-on-Metal (MoM) hip resurfacing arthroplasty (HRA), based on generally good long term results. In contrast, hip resurfacing in young female patients has become controversial. Recently, one implant manufacturer withdrew 46mm and smaller components, citing poorer than expected 10 year outcomes in females with smaller HRAs. Whether this difference is related to gender or to component size is still debated. Possible reasons for higher failure rates reported in females include higher rates of hip dysplasia, poorer bone quality and the risk of higher wear in some smaller sized implants with low cup coverage angles.

We reviewed HRA revision specimens with the aim of comparing mode of failure, time to revision, femoral cement characteristics and acetabular bone attachment in specimens larger and smaller than 46mm and from male versus female patients.

Bone ingrowth fixation of large diameter, beaded cobalt chromium cups is generally considered to be reliable but this is typically judged radiographically. To date, implant retrieval data of attached bone has been limited. This study evaluated correlations between the pre-revision radiographic appearance and the measured amount of bone attachment on one design of porous coated cup.

Avascular necrosis of the femoral head (AVN) is associated with collapse of the femoral head and arthritic degeneration of the joint. The combination of an implant inserted into the femoral head that provides mechanical support and bone grafting to promote bone formation may offer a possible joint-preserving solution1. Seventeen such procedures were performed between November 2012 and March 2014 during an IRB approved clinical trial. Thirteen out of 18 patients remained unrevised at a minimum of 12 months; the results of radiographic and histological analysis of four revisions are presented.

The investigational device (Figure 1) was developed as a joint preserving treatment for AVN with a clinical grade of IIC or less according to the ARCO grading system2.

The device consisted of a braided spherical Nitinol cage with a Titanium / Nitinol orientation feature. It was implanted using fluoroscopic navigation into a spherical cavity cut into the femoral head via an 11mm diameter access tunnel. Once deployed, the implant was filled with a lightly impacted mixture of autologous bone graft and bone marrow soaked Conduit TCP (DePuy CMW, Blackpool, UK). The implant's purpose was to provide mechanical support to the weakened subchondral surface while the bone graft mixture re-integrated with the host bone.

The retrieved femoral heads were trimmed to leave approximately 3mm of bone around the implant, dehydrated, embedded in methacrylate resin, sectioned and thinned into 50–70µm coronal slices for histological analysis. The following observations were made (Figure 2):

Case 1 (Female, age 70, ARCO IIB, revised after 2 days): The patient was revised for spontaneous sub-trochanteric fracture secondary to osteoporosis. Contact between the native bone and bone graft was observed. Marrow elements and repair tissue were visible within the pores in the graft (Figure 2a).

Case 2 (Male, age 67, ARCO IIIC, revised after 82 days): Two wires were broken but retained within the braided structure. A radiolucent gap caused by the presence of fibrous tissue between the graft mixture and native bone was evident suggesting that the implant was unable to prevent progression in this case.

Case 3 (Female, age 70, ARCO IIC, revised after 482 days): The cavity penetrated the subchondral surface; at revision the implant was found to have breached the articular cartilage. There was partial separation of the proximal osteonecrotic fragment and no evidence of graft revascularisation or remodelling within the implant.

Case 4 (Male, age 42, ARCO IIC, revised after 469 days): There was no indication of bone graft re-integration. Collapse of the necrotic bone and deformation of the implant was diagnosed from 1 year follow-up x-rays.

The histopathology of periprosthetic tissues has been important to understanding the relationship between wear debris and arthroplasty outcome. In a landmark 1977paper, Willert and Semlitsch (1) used a semiquantitative rating to show that tissue reactions largely reflected the extent of particulate debris. Notably, small amounts of debris, including metal, could be eliminated without “overstraining the tissues” but excess debris led to deleterious changes. Currently, a plethora of terms is used to describe tissues from metal-on-metal (M-M) hips and corroded modular connections. We reviewed the evaluation and reporting of local tissue reactions over time, and asked if a dose response has been found between metal and tissue features, and how the use of more standardized terms and quantitative methodologies could reduce the current confusion in terminology.

Purpose and Background:

To identify treatment effect modifiers within the STarT Back Trial which demonstrated prognostic stratified care was effective in comparison to standard care for patients with low back pain.

Background

A wide array of measures has been developed to assess the role of psychological factors in the development and persistence of pain. Yet there is likely to be considerable conceptual overlap between such measures, and consequently a lack of clarity about the importance of psychological factors.

Background

People with back pain often experience long-term pain with recurrences and fluctuations. However, few studies have considered which factors predict long-term outcomes.

It has been suggested that metal ion levels are indicative of in vivo bearing performance of metal-on-metal hip replacements. A cobalt or Chromium level of 7μg/L or higher is proposed to be indicative of a bearing malfunction and the need for clinical intervention. Component design, size, acetabular orientation, patient gender and activity level have been suggested as factors leading to accelerated wear and elevated metal ions. The contact patch to rim (CPR) distance is a calculation that describes the distance from the point where a theoretical joint reaction force intersects the cup to the acetabular rim for a patient in standing position, dependent on the coverage, size, and orientation of the acetabular component. It has been suggested that CPR distance determines the hip joint susceptibility to edge loading, and the risk for increased wear and high ion levels (Langton et al JBJS Br 91: 2009). This study examined the effects of patient activity, gender, and CPR distance on serum metal ion concentrations in a series of patients treated with one type of metal on metal hip resurfacing arthroplasty (MMHRA) performed by one surgeon.

182 patients (73 females and 109 males)with a unilateral Conserve Plus (WMT, TN USA) MMHRA and had who had provided blood for metal ion analysis data from December 2000 to June 2011 were retrospectively studied. Only measurements made more than 12 months after surgery were included in order to exclude hips that had yet to reach steady-state wear. For patients with multiple draws, the most recent qualifying draw was used. Activity level was assessed by the UCLA activity score. The mean age was 51.5 years (20.0 to 77.5 years). The mean follow-up time for the last blood draw was 70 months (range, 12 to 165). Serum cobalt (CoS) and chromium (CrS) levels were analyzed using inductively coupled plasma mass spectrometry in a specialized trace element lab. Using acetabular abduction and anteversion measured by EBRA, component size, and reported coverage angle of the acetabular component, the CPR distance was calculated as previously described. Multiple logistic regression was performed to identify significant relationships between high metal ion levels (7 μg/L or greater) and gender, activity and CPR distance.

The median CoS level for the entire cohort was 1.13 μg/L (range, 0.15 to 175.30), and the median CrS level was 1.49 μg/L (range, 0.06 to 88.70). The average CPR distance was 13.8 mm (range, 3.2 to 22.1). There was a significant association between low CPR values and CoS and CrS. There was a 37-fold increase in the risk of CoS >7μg/L (p=0.005) and 11-fold increase in the risk of CrS > 7μg/L (p=0.003) when CPR distance was 10 mm or less. No associations were shown for gender and UCLA activity scores.

CPR distance was found to be a reliable predictor of ion levels > 7μg/L and appears to be a useful indicator to evaluate the multi-factorial process of edge-loading and wear. Patients with a low CPR distance should be monitored for increased metal ion levels.

The Conserve® Plus (Wright Medical Technology Inc., Arlington, TN) was introduced clinically in the United States in 1996. A study of the serum cobalt and chromium ion levels was started in 2000 in our center to monitor the metal ion levels over time as part of an FDA clinical trial.

Thirteen male and five female patients received this resurfacing for idiopathic osteoarthritis (14), post-traumatic degenerative changes (3) or developmental dysplasia (1). Fourteen received a unilateral implant but four subsequently received a contralateral device from 52 to 86 months post-op. Four patients had bilateral resurfacings done in a one-stage procedure. All surgeries were performed by the senior author. None of these patients had known exposure to cobalt or chromium, kidney disease or other metal implants elsewhere in their bodies. Each prospectively provided blood samples and then yearly thereafter to measure cobalt and chromium levels for up to 11 years. Metal levels were measured using atomic absorption spectrophotometry and inductively coupled plasma mass spectrometry by a specialized trace element analysis laboratory. Acetabular component position was evaluated using Einzel-Bild-Röentgen-Analysis (EBRA) software. Contact patch to rim (CPR) distance was computed as described by Langton et al JBJS Br 91: 2009. A mixed model linear regression analysis was performed to evaluate long term trends, and multivariate analysis was performed to examine effects of implant and patient covariates on the metal ion levels.

One bilateral patient underwent revision for femoral loosening, all other patients were clinically well-functioning at the time of last follow-up (ave 89 mos). The median pre-operative Co was below the detection limit (d.l) of 0.3μg/L and the median pre-operative Cr was 0.069μg/L (d.l. 03μg/L). Metal levels increased within the first year then decreased and stabilized (fig 1). For unilaterals over all time intervals, the median Co was 1.06 μg/L, while the median Cr was 1.58 μg/L. For bilaterals, the mean post-operative Co was 2.80 μg/L, while the mean Cr was 5.80 μg/L. Generally, Cr levels were higher at all time points than Co. Bilateral patients had Co values 1.96 times greater on average than the unilateral patients (p<0.001). None of the possible covariates studied (femoral size, cup abduction angle, cup anteversion, CPR distance, activity, BMI and testing method) were related to the assay values.

The results of this study have shown that serum metal levels in well functioning implants can be low and do not increase over time. These are among the lowest levels reported for resurfacing devices and comparable to levels reported for well functioning small diameter metal-on-metal total hips. The study is limited due to the relatively small sample size and limited range of values for the covariates studied. However, it included patients who were active, female or bilateral and we collected ion levels up to 11 years. We now recommend that patients who have well-oriented Conserve Plus components with stable radiographic interfaces and no incidences of unexplained pain or hip noises be scheduled for follow-up every 2–3 years, rather than annually.

In patients with conventional metal-on-Polyethylene (MoP) hip replacements, osteolysis can occur in response to wear debris. During revision hip surgery, surgeons usually remove the source of osteolysis (polyethylene) but cannot always remove all of the inflammatory granulomatous tissues in the joint. We used a human/rat xenograft model to evaluate the effects of polyethylene granuloma tissues on bone healing. Human osteoarthritic and periprosthetic tissues collected during primary and revision hip arthroplasty surgeries were transplanted into the distal femora of athymic (nude) rats. The tissues were assessed before and after implantation and the bone response to the tissues was evaluated after 1 week and 3 weeks using micro-computed tomography, histology, and immunohistochemistry. After 3 weeks, the majority (70%) of defects filled with osteoarthritic tissues healed, while only 21% of defects with polyethylene granuloma tissues healed. Polyethylene granuloma tissues in trabecular bone defects inhibited bone healing. Surgeons should remove polyethylene granuloma tissues during revision surgery when possible, since these tissues may slow bone healing around a newly implanted prosthesis. This model provides a method for delivering clinically relevant sized particles into an in vivo model for investigation.

Background

Pseudotumours have been associated with metal-on-metal (MoM) hip replacements. We define it as a solid mass which may have cystic components that is neither neoplastic nor infectious in aetiology. The cause of a pseudotumour is not fully understood but could be due to excessive wear, metal hypersensitivity or due to an as-yet unknown cause.

Aim

To compare a variety of commercially available bone graft substitutes (BGS) in terms of promoting adherence, proliferation and differentiation of osteoprogenitor cells.

Clinical proteomics is an exciting new sub-discipline of proteomics that involves the application of proteomic technologies at the bedside to identify new biomarkers, associated with specific diseases. In this study to compare serum protein profiles between identical age-matched groups of fracture and non-fracture controls, we looked at the initial proteomic profile of 10 patients who had fractures and compared them to age-matched controls to see if there was any specific difference indicative of fracture.

Background

Social context may be important in chronic pain. One focus is reactions to pain between persons with LBP and their partners. Researchers have investigated partner reactions and found influences on pain levels and psychological outcomes, but little is known about factors underpinning these reactions.

There have been many reports of metal ion levels measured in the bloodstream of patients after metal-on-metal hip replacement, and it is generally accepted that levels of cobalt (Co) and chromium (Cr) are elevated after these types of devices are implanted. However, it is not clear how to interpret these elevated levels; in particular what are the acceptable levels and what levels indicate that close monitoring of the patient is needed. Our aim was to establish the differences in metal ion levels between well functioning patients and those with clinical problems.

We measured serum Co and Cr levels (microgram’s per litre or μg/l) using inductively coupled plasma mass spectrometry with a well established collection protocol of all patients attending follow-up clinics. Our inclusion criteria for this study were all patients unilaterally implanted with a metal-on-metal hip resurfacing with no other metallic implant; patients were categorized as either A. Well Functioning or B. Clinically Problematic (pain, reduced function, reduced ROM, negative x-ray findings) and differences in ion levels between these two groups were examined. Well functioning patient data was only included if measurements were made more than 12 months post-operatively to avoid run-in wear levels. Abduction angle was also measured from x-rays of the pelvis, and the frontal plane coverage arc of each implanted cup calculated (De Haan JBJS[Br] 2008;90(10):1291–7). There were a total of 519 patients, with 358 in Group A and 161 in Group B; patients had a variety of devices with Birmingham Hip Resurfacing (64%) and Conserve Plus (29%) being the most commonly implanted. To establish a guideline upper ion level value for well functioning implants the upper 75th percentile values for Co and Cr levels for Group A patients having 15 mm or more coverage arc were calculated. The risk of having clinical problems was calculated as function of metal ion levels higher or lower than these upper limits.

The ion levels were significantly (Mann Whitney U p< 0.001) higher in Group B (mean [95% confidence intervals], Co 10.2 μg/l [5.9 to 14.5], Cr 10.3 μg/l [6.7 to 14.0]) compared to Group A (Co 2.3 μg/l [1.7 to 2.4], Cr 2.8 μg/l [2.3 to 3.4]). The well functioning upper limit for Co was 4.1 μg/l and for Cr was 5.2 μg/l. Metal ion levels greater than these upper limits were significantly (Chi-square p< 0.001) associated with the presence of clinical problems. The odds ratio for Co greater than 4.1 μg/l was 11.2 [95%CI 5.7 to 22.3] and that for Cr greater than 5.2 μg/l was 4.3 [95%CI 2.6 to 7.0].

There were significantly higher metal ion levels measured in patients with clinical problems after metal-on-metal hip resurfacing than those with well functioning hips. We have proposed upper acceptable limits for Co (4.1 μg/l) and Cr (5.2 μg/l) serum levels. Cobalt levels appear to be more reliable in predicting risk of clinical problems; levels greater than our proposed upper limit have 11 times the odds of developing clinical problems and patients with such levels should be followed closely.

Ion levels in the serum and urine of patients with metal-on-metal hip resurfacing implants can provide a means to monitor bearing wear. This presentation will discuss the current results, now out to 5 years for the Conserve Plus resurfacing. In particular, the effect of bilateral implantation on ion levels was examined

Forty-eight patients were studied. Forty-three of these cases were initially implanted with a unilateral resurfacing. Nine of these cases subsequently were implanted with a resurfacing implant on the contra-lateral side 4 to 48 months following the first implantation (staged implantations). Five cases had bilateral resurfacings done simultaneously. All surgeries were done in one institution by a single surgeon. Serum and urine samples were collected pre-operatively, and at 4 months, 12 months and annually thereafter. The samples were analysed for cobalt and chromium using atomic absorption spectrometry with a detection limit of 0.3 to 0.03ng/ml respectively. The data were compared between the groups and also correlated with UCLA activity scores, cup angle, BMI and component size.

All patients showed a rise in ions following implantation. The simultaneous bilateral levels were higher at all time periods compared with the staged bilaterals monitored at the same time point for the second hip, for example cobalt serum at 12 month uni = 2.24, simultaneous bilat = 2.53, staged bilat = 2.05ng/ml, and at 4 years uni = 1.20, simultaneous bilat = 2.93, staged bilat = 2.27ng/ml. There was no correlation between ion levels and UCLA activity score, gender, component size or cup angle (but only 4 hips had cups > 55 degrees).

Bilateral metal-on-metal hip resurfacings performed simultaneously resulted in higher levels of metal ions, particularly chromium, compared to staged implantations monitored at the same time periods. With the exception of a small number of outliers, the levels in this group of hip resurfacings were within the range of metal levels reported for other metal-on-metal total hips.

Introduction: The Implant Retrieval Laboratory at Orthopaedic Hospital has been collecting and studying retrieved metal-on-metal total hip replacements for over 15 years. The analysis of these implants has provided important insights into their clinical wear performance and the biocompatibility of the wear products. In addition to stem-type implants of first generation (McKee-Farrar) and modern generation (Metasul) implants with metal-on-metal bearings, the lab has performed analysis on over 200 failed metal-on-metal hip resurfacing devices to determine factors relevant to their failure. The primary goal of these analyses was to understand the failure mechanisms and the ways in which failures may be preventable through optimized patient selection and surgical techniques. Lessons learned from these implants include: well-manufactured and well-placed metal-onmetal implants have very low wear rates; conversely poorly manufactured or badly placed implants can have high wear rates; hip resurfacing failures are most often the result of bad bone quality, bad surgical technique or both. Perhaps the most significant finding is that despite the presence of an implant producing wear debris and altering biomechanical stresses, the majority of hip joints heal, adapt and provide a clinically successful outcome.

Femoral neck fracture is a common short-term hip resurfacing failure mode, but later term fractures are starting to be reported. The fracture pattern may indicate whether etiology is primarily mechanical or biological¹. This study evaluated fracture patterns in conjunction with histology to determine etiology in a varied group of hip resurfacings.

Central 3mm thick coronal slices were cut from each of 50 cemented and 2 cementless fractured femoral components (27 males, 25 females). Fracture patterns were grouped as: “edge to edge”, “inside head”, “outside” and “edge to outside”¹. Sections were decalcified and processed for routine histology to examine viability and remodelling. Bone viability was judged on the presence of osteocyte nuclei. Components were judged to be unseated if the cement mantle was more than twice the manufacturers recommended thickness. Histological and clinical data were correlated with fracture pattern.

Overall average time to fracture was 6 months (1–85 months). There were 25 “edge to edge”, 12 “inside head”, 4 “outside” and 11 “edge to outside” fractures, which occurred after a median of 2.0, 13, 1.5, and 2.0 months respectively. The majority of the heads were viable, and the fractures occurred through a region of healing bone involving one or both edges. Fifteen heads with a substantial proximal avascular segment fractured at the interface between necrotic and viable bone, typically inside the component. Eleven implants (21%) were considered unseated. All 4 “outside” fractures were found to be unseated. All “inside head” fractures were seated, but 83% (10/12) of them were found to be avascular. The latest failure (85 months) occurred in association with wear-induced osteolysis. Both cementless components fractured early with an “edge to outside” pattern and were found to be substantially avascular.

Avascular heads failed from one month to four years, usually inside the component. Viable heads tended to fracture early through an area of healing bone at or below the rim. Most fractures were technical failure-sand might be avoided with better patient selection and surgical technique.

Introduction: Management of Ficat stage III and IV hip osteonecrosis remains a formidable challenge in regards to long term care. We report a case of a hemiresurfacing arthroplasty lasting 23 years in a patient who received the implant for osteonecrosis associated with corticosteroid use following kidney transplantation. In 1981, a moderately obese, 27-year-old man presented with bilateral osteonecrotic collapse of the femoral heads secondary to heavy immunosuppressive corticosteroid therapy associated with a kidney transplant. The patient had suffered a loss of both kidneys after a bout of severe nephritis that resulted in replacement with a cadaver kidney in 1979. A cemented THARIES (total hip articular replacement with internal eccentric shells) metal-on-polyethylene resurfacing (Zimmer, Warsaw, Indiana) was implanted in the right hip in 1981. At 3 years post-operatively, the patient complained of acute, exacerbated pain in his right hip. The THARIES components were removed for acetabular and femoral loosening and replaced with a total hip replacement.

Surgery: The acetabular cartilage of the other hip was rated intraoperatively as Grade III (no or minimal acetabular cartilage involvement), and was deemed suitable for hemiresurfacing. A 50 millimeter custom cemented titanium shell (Zimmer, Warsaw, Indiana) was implanted using a lateral incision and a trans-trochanteric approach. The patient continued to be assessed by the surgeon on a regular basis, and returned to an active lifestyle while his kidney function continued to be regulated with corticosteroids and imoran. In 1989, eight years following hemiresurfacing, the left hip radiographs showed a reduced joint space, with further new bone in the acetabular fossa, and the patient continued to do well. UCLA hip scores were 9, 9, 10, and 7 for pain, walking, function and activity, respectively compared with 6, 6, 4, and 4 preoperatively. Radiographs taken at 18 years post-operatively showed further narrowing of the joint space, but the patient continued to be asymptomatic. At the 22-year clinic visit, the patient, now 50 years old, complained of slight groin pain, and some minor limitation in his activities, but was still able to walk without any method of support, and able to participate in recreational exercise including swimming, baseball, and weight lifting. The resurfacing hip was revised to a total hip at 23 years post-op and the specimen was submitted for implant retrieval analysis. This involved sectioning the component into three, 3-millimeter thick coronal slices, which were decalcified and routinely embedded in paraffin.

Results: Hematoxylin and Eosin stained sections showed that the bone within the head was osteopenic but viable with areas of healed old necrotic segments of trabeculae which were surrounded by appositional new bone with some focal areas of recently formed woven bone. A fibrous membrane ranging from a few microns to 1.8 millimeters in thickness was present along most of the cement interface and this contained scattered particle-filled macrophages. There were occasional osteoclastic resorption fronts of bone against this membrane, but osteoblasts were also occasionally seen lining the non-membrane surface. The resurfaced head and neck showed remarkable preservation of bone stock. Although there was minimal cement penetration into the bone, either because of lack of initial penetration or from fragmentation of the cement over the years, the component was functionally well fixed. The bone was viable and there were minimal effects of the small amount of titanium metal debris.

Discussion: Studies report osteonecrosis of the femoral head developing in approximately 11% of hips and 20% of patients receiving organ transplants and for young patients conservative methods need to be pursued. While the best choice of treatment for osteonecrosis is not universally agreed upon, the options are limited once collapse of the femoral head has occurred. Treatment for these patients should be based on the progression of the disease, the age of the patient, and the patient’s long-term needs. This patient had a hemiresurfacing and a metal-on-polyethylene resurfacing; the latter succumbed to polyethylene induced osteolysis, but the hemiresurfacing provided good clinical function in a young, normally active patient for 23 years. While it is recognized that hemiresurfacing is not suitable for every patient with osteonecrosis, it remains a treatment option for some patients.

Introduction: A major concern with cemented hip resurfacing arthroplasty (HRA) femoral components is the thermal damage to femoral head during cement curing; this maybe linked to fracture (reported incidence ~2%) and early failure. We investigated the effect of a modifid surgical technique using pulse lavage, lesser trochanter suction and early reduction on the maximum temperature recorded in the femoral head during HRA, compared to manual lavage and reduction after cement curing.

Methods: Patients undergoing total hip replacement (THR) were given a dummy HRA procedure, during which a temperature probe was inserted into the femoral head and the measuring tip placed close to the reamed surface; the position of the probe was confirmed by inter-operative xray. Four subjects received a dummy HRA femoral component using manual lavage and Simplex cement. The implanted femur was kept dislocated until the cement cured. The implanted heads were then removed and sectioned to locate the temperature probes, the THR surgery was then performed. Five patients receiving a definitive HRA were also measured; for these subjects suction on the lesser trochanter was used, pulse lavage given for 30 seconds prior to cementing with Simplex, and pulse lavage of the femoral head for 2 minutes, applied 1 minute after cementing the femoral component. The implanted joint was then immediately reduced and a further two minutes of pulse lavage applied to the reduced joint. Temperatures were recorded until the cement finally cured. In every case the cement was hand mixed for 1 minute and the component implanted at 2 minutes 30 seconds after mixing began.

Results: Sectioning showed that probe tips were < 0.5mm from cement mantle. The maximum temperature recorded in the femoral head was significantly (p=0.014) greater for the manual technique, median value of 47.2°C (37.0 to 67.9°C), than for the pulse lavage technique, median value of 32.7°C (31.7 to 35.6°C).

Discussion: The results show that excessive bone temperatures can occur during hip resurfacing. Temperatures above 45°C kill bone cells, the manual technique may lead to substantial thermal necrosis. Technique modification, with the use of suction on the lesser trochanter, generous use of pulse-lavage and joint reduction prior to cement curing, significantly reduced the temperatures recorded. With the modified technique, the maximum temperatures were well below the threshold of thermal damage. This modified technique is recommended as the potential for thermal bone necrosis is significantly reduced.

Introduction: Hip resurfacing has been increasingly used procedure for physiologically young and active patients. Wear properties of the implants are considered to be excellent. We present a case of tumor like swelling of the thigh following metal on metal hip resurfacing.

Case report: 56 year old lady underwent metal on metal hip resurfacing for idiopathic osteoarthritis of right hip. Implant size: 38 mm head with 44 mm cup.

After 18 months of successful surgery she presented with short duration (2 weeks) history of thigh swelling with pain and stiffness in hip and knee. Clinically gross circumferential swelling of right thigh from inguinal ligament to the knee joint. She had increased serum cobalt chromium levels. Aspiration of hip revealed high levels of cobalt and chromium. Biopsy and intra operative samples at revision revealed “no infection or tumor but non specific inflammatory reaction.”

The patient underwent revision surgery to ceramic-plastic bearing.(THR).

12 months post operative, the swelling has reduced with painless mobile hip and knee joints.

Discussion: The metal on metal hip resurfacing could have produced high metal ion wear reaction leading to swelling. Which could be because of small diameter prosthesis with valgus position of femoral component with open cup angle of 49 degrees.

Purpose of the study: During resurfacing arthroplasty, excessive valgus of the femoral neck or an insufficient surgical technique can lead to formation of a notch in the femoral head. Although the mechanisms weakening the femoral neck and subsequent fractures are well described, the effects of altered blood supply via the retinacular vessels on potential ischemia of the femoral head are largely unknown. The purpose of our study was to assess blood supply to the femoral head when a notch occurred in the femoral neck during total hip replacement surgery and to deduct possible implications concerning the resurfacing procedure.

Material and methods: Blood supply to the femoral head was measured with laser Doppler fluorometry in 14 hips undergoing total hip replacement for osteoarthritis via a lateral approach with anterior dislocation. An optical laser probe for the fluorometry (Moor Instruments, Wilmington Delewar, 20 mW laser, probe length 780 nm) was introduced via a 3.5 mm hole drilled in the antrolaeral quadrant of the femoral head (leg in neutral position). The position of the probe was checked on the x-ray of the femoral head after resection. A notch was simulated in the lateral posterior portion of the femoral neck using a bone gouge.

Results: Mean patient age was 65 years (range 48–77 years). There were eight men and six women. Two measurements were made: one after dislocation of the hip and the second after simulating the notch. A significant decrease in blood supply measured at more than 50% was observed in all but four hips after simulating the notch. The median decrease in blood flow was 76% (4.4–90.4, p< 0.001).

Conclusion: The retinacular vessels appear to be equally important for the blood supply for osteoarthritic and non-osteoarthritic femoral heads. A notch occurring during hip resurfacing would not only weaken the mechanical resistance of the neck but would also increase the risk of osteonecrosis and subsequent loosening of the femoral component. Consequently, approaches compromising retinacular blood supply (for example the posterior approach) would add a supplementary danger for the integrity and viability of the femoral head.

Fourteen hips with osteoarthritis had femoral head blood flow measured with laser Doppler flowmeter while undergoing during total hip replacement through a modified lateral approach. Mean age sixty-five years (48–77); eight males & six females. Two measurements were taken within the femoral head one after anterior hip dislocation and one after simulated notching of the femoral neck. All hips had a significant decrease in blood flow with a median percentage decrease of 76% (range 4.4–90.4). During surface arthroplasty of the hip, notching of the femoral neck may not only mechanically weaken the bone but also put the femoral head at risk of osteonecrosis.

To evaluate femoral head blood supply in patients with osteoarthrtis of the hip undergoing simulated notching of the femoral neck during total hip replacement and its potential implications in hip resurfacing.

During surface arthroplasty of the hip, notching of the femoral neck may not only mechanically weaken the femoral neck but also put the femoral head at risk of osteonecrosis and subsequent femoral loosening.

It would appear that the retinacular vessels (extraosseous blood supply) are as important in the arthritic femoral head as they are in the nonarthritic state, contradicting the notion that arthritic femoral heads in humans rely mainly on an intraosseous blood supply.

Fourteen hips with a diagnosis of degenerative arthritis had femoral head blood flow measured with laser Doppler flowmeter while undergoing during total hip replacement through a modified lateral approach. With the femoral head exposed and leg in neutral position, a 3.5mm drill hole was made into the anterior lateral quadrant and the fiber optic probe of the laser Doppler flowmeter (Moor Instruments, Wilmington Delaware, 20mW laser, wavelength 780nm) was inserted. Mean age was sixty-five years (48–77). Eight males and six females. Two measurements were taken one after anterior hip dislocation and one after simulated notching of the femoral neck. All but four hips had a significant decrease of more than 50% in blood flow after neck notching with a median percentage change of 76% (range 4.4–90.4), p< 0.001.

Hip resurfacing is a procedure designed to conserve bone stock in the younger patient and facilitate revision to a total hip arthroplasty if the need arises. The Wagner Hip Resurfacing (WHR) was a metal-on- poly implant introduced in 1978.

The notes and radiographs of 16 patients who underwent 19 WHR procedures performed by a single surgeon between 1980 and 1984 were reviewed.

The mean age at primary surgery was 54 (range 41–68). 16 of the WHRs required revision at a mean time of 45 months (range 1–144 months). 3 WHR had not been revised: one is functioning at 22 years, one functioning well 20 years after implantation when the patient died and 1 non-functional 9 years after implantation due to femoral head reabsorption.

The reason for revision was femoral neck fracture (3), femoral head collapse / avascular necrosis or loosening (8), acetabular loosening (5).

Subsequent problems with the revision were noted in 6 patients (2 dislocations, 2 infections, 1 acetabular loosening and 1 femoral loosening). 3 patients ended with a Girdlestone excision arthroplasty and 2 required re-revision.

Hip resurfacing is designed as a conservative option for the young arthritic hip. This prosthesis not only failed catastrophically at an early stage but had a major subsequent impact on revision surgery and complications associated with it.

Cobalt chrome-on-cobalt chrome bearing surfaces have been re-introduced despite some concerns regarding potential risks posed by soluble metallic by-products. We have investigated whether there are metal-selective differences between the levels of genetic damage caused to a human cell line when cultured with synovial fluids retrieved from various designs of orthopaedic joint replacement prostheses at the time of revision arthroplasty.

Synovial fluids were retrieved from revision hip and knee arthroplasty patients with bearings made from cobalt chrome-on-cobalt chrome, cobalt chrome-on-polyethylene and stainless steel-on-polyethylene. Control synovial fluids were retrieved from primary arthroplasty cases with osteoarthritis. Synovial fluid was cultured with human primary fibroblasts for 48 hours in a cell culture system under standardised conditions. The “Comet” assay was used with an image analysis system to measure levels of DNA damage caused by the various synovial fluid samples.

Synovial fluids from cobalt chrome-on-cobalt chrome and cobalt chrome-on-polyethylene joint replacements both caused substantial levels of genetic damage as detected by the Comet assay. Synovial fluids retrieved from stainless steel-on-polyethylene joints caused low levels of damage. The difference between these groups was highly statistically significant (p< 0.001). Control synovial fluids from osteoarthritic joints caused minimal changes. Atomic absorption spectroscopy demonstrated that the metal-on-metal synovial fluids contained the highest levels of cobalt and chromium. Different alloys used in orthopaedic implants are associated with different levels of DNA damage to cultured human cells in vitro. We are able to demonstrate that this damage is attributable at least in part to the metal content of the synovial fluid samples. We have no evidence for any long-term health risk to patients with such implants.

Metal-on-metal bearing surfaces have been reintroduced for use in total hip replacement, despite concerns regarding the potential risks posed by metallic by-products. We have compared periprosthetic tissues from metal-on-metal and metal-on-polyethylene hip replacements at revision surgery with control tissues at primary arthroplasty.

Tissues were obtained from 9 control, 25 contemporary metal-on-metal, 9 CoCr-on-polyethylene and 10 titanium-on-polyethylene hip replacement arthroplasties. Each was processed for routine histology with Haematoxylin and Eosin. Quantitative stereological analysis was performed at the light microscopic level.

Metal-on-metal sections showed more surface ulceration and this was correlated with the density of inflammation in the deeper tissues layers. Metal-on-metal tissues displayed a pattern of well-demarcated tissue layers, which were rarely seen in metal-on-polyethylene cases. In metal-on-polyethylene cases, the inflammation was predominantly histiocytic. Metal-on-metal cases by contrast showed a lymphocytic infiltrate with abundant plasma cells. Metal-on-metal tissues showed a striking pattern of peri-vascular inflammation with prominent lymphocytic cuffs especially deep to areas of surface ulceration. Levels of inflammation were higher in cases revised for failure than in those retrieved at autopsy or exploratory surgery. Total replacement and surface replacement designs of metal-on-metal arthroplasty showed similar histological changes. Plasma cells were not seen in any of the metal-on-polyethylene cases. The differences between the patterns of inflammation and cellular infiltration seen in metal-on-metal and metal-on-polyethylene tissues were highly statistically significant.

The pattern and type of inflammation in periprosthetic tissues from metal-on-metal and metal-on-poly-ethylene arthroplasties is very different. Our findings support the conclusion that metal-on-metal articulations are capable of generating a form of immunological response to metallic wear debris that has not been described previously. The incidence and clinical implications of these immunological responses in failed metal-on-metal joints are unknown.

3-D finite element model of a resurfaced femoral head was composed. Five configurations of cement layer were analyzed and the transient heat transfer analysis during cement polymerization was performed. Peak temperature at the bone-cement interface temperature was lower than 40 oC when there was no or 1.5 mm cement penetration but reached 54 oC and 74 oC with 6 mm penetration and 6 mm penetration plus a cement –filled cyst of 1 cm3, respectively. With deep cement penetration, and a large cement-filled cyst, the peak temperatures exceeded bone thermal osteonecrosis at 55 oC.

To evaluate using a finite element analysis model, the possibility of bone thermal necrosis secondary to cement in resurfacing arthroplasty of the hip.

With deep cement penetration, and the presence of a large cement-filled cyst, the peak temperatures were in the range of bone thermal osteonecrosis 55 oC.

Cementing technique in resurfacing arthroplasty should strive to strike a balance between fixation and avoiding bone thermal necrosis by excessive cement penetration. This information could explain why femoral head cysts > 1cm are a risk factor for femoral loosening after resurfacing arthroplasty and excessive cement penetration could lead to femoral neck fracture.

3-D finite element model of a hemispherical resurfaced femoral head was composed of a metal shell with a diameter of 46 mm. Five configurations of cement layer were analyzed a) no penetration into the bone, b) 1.5 mm penetration, c) 6 mm penetration, d) 6 mm penetration and a 1 cm3 cement filled cyst, and e) 6 mm penetration and 2 cm3 cement-filled cyst. The transient heat transfer analysis during cement polymerization was performed in a series of time steps. The temperature within the bone and cement was lower than 40 oC when there was no or 1.5 mm cement penetration into the femoral head. In contrast, the peak temperature at the bone-cement interface reached 54 oC and 74 oC and 63 oC with 6 mm penetration and 6 mm penetration plus a cement –filled cyst of 1 cm3, respectively.

A prospective study of serum and urinary ion levels was undertaken in a triathlete who had undergone a metal-on-metal resurfacing arthroplasty of the hip four years previously. The one month study period included the final two weeks of training, the day of the triathlon, and the two weeks immediately post-race. Serum cobalt and chromium levels did not vary significantly throughout this period, including levels recorded on the day after the 11-hour triathlon. Urinary excretion of chromium increased immediately after the race and had returned to pre-race levels six days later. The clinical implications are discussed.

The purpose of this study was to present our experience with femoral neck fractures that occurred after metal-on-metal hybrid surface arthroplasty and to assess their causation.

Materials and Methods: A series of 600 metal-on-metal surface arthroplasties was performed from late 1996 to early 2003 by the primary author. Failures during this period were assessed radiographically and with implant retrieval analysis to determine the cause of failure. There were five femoral neck fractures in this series (0.83%).

In addition, a review of the femoral neck fracture cases identified from the Conserve+ Multi-Center IDE was performed (19 femoral neck fractures in 1203 cases, 1.6%).

Results: Lead Author Series: Four of the five fractures occurred at the component–neck junction in the first five months after surgery (average three months). All were associated with a traumatic episode but they also had structural and or technical risk factors, which weakened the constructs. The most important technical deficiency was failure to cover all of the reamed bone with the component in three of the five. One fracture was associated with histological changes consistent with osteonecrosis of the head in a case of overpenetration of cement in very soft bone.

Multi-Center IDE: Additional risk factors were identified among which impingement of the neck with the acetabular component, notching of the lateral femoral neck cortex, and leaving the femoral component proud (not completely seated).

Conclusion: It is important to avoid or at least minimize notching the femoral neck by performing the cylindrical reaming at the recommended angle of 140° and to stop reaming before the reamer touches the lateral cortex. Osteophytes should be judiciously removed only if there is a notable impingement when the hip is at 90° of flexion and internally rotated. We believe that understanding the factors that contribute to femoral neck fracture after surface arthroplasty may reduce the already low incidence of this mode of failure.

Metal-on-metal joint replacements have been reintroduced despite some concerns regarding the potential risks posed by soluble metallic by-products. We have investigated whether there are metal selective differences between the levels of genetic damage caused to a human cell line when cultured with synovial fluids retrieved from orthopaedic joint replacement prostheses at the time of revision arthroplasty.

Methods: Synovial fluids were retrieved from revision hip and knee arthroplasty patients with bearings made from Cobalt chrome-on-Cobalt chrome, Cobalt chrome-on-polyethylene and Stainless Steel-on-polyethylene. Control synovial fluids were retrieved from primary arthroplasty cases with osteoarthritis and no implant in situ. Synovial fluid was cultured with human primary fibroblasts for 48 hours in a cell culture system under standardised conditions. The ‘Comet’ assay was used with an image analysis system to measure levels of DNA damage caused by the various synovial fluid samples. Metal levels were measured in the synovial fluid samples using atomic absorption spectroscopy.

Results: Synovial fluids from Cobalt Chrome-on-Cobalt Chrome and Cobalt Chrome-on-polyethylene joint replacements both caused substantial levels of genetic damage as detected by the Comet assay. Synovial fluids retrieved from Stainless Steel-on-polyethylene joints caused low levels of damage. The difference between these groups was highly statistically significant (p< 0.001). Control synovial fluids from osteoarthritic joints caused minimal changes. Atomic absorption spectroscopy demonstrated that the metal-on-metal synovial fluids contained substantially more cobalt and chromium than the fluids retrieved from cobalt chrome-on-polyethylene joints. Stainless steel-on-polyethylene synovial fluids contained the least metal.

Conclusions: Different alloys used in Orthopaedic implants are associated with different levels of DNA damage to cultured human cells in vitro. We are able to demonstrate that this damage is attributable at least in part to the metal content of the synovial fluid samples. We have no evidence for any long-term health risk to patients with such implants. Further research is needed in this field.

In December 2000, the Inter-Op acetabular component (Sulzer Orthopedics Inc., TX) was recalled. Contamination by an oil-based residue that was inadvertently left in the porous coating following a change in manufacturing processes was suspected to have resulted in lack of fixation. The aim of this study was to characterize the histopathology of the these failures for consistency with this hypothesis.

Materials and methods: Four hundred and fifty cups were submitted for gross and histopathological examination. H& E stained paraffin sections of tissue taken from the socket, membranes and/or capsules from the first 100 cases were reviewed histologically using a new rating scheme which accounts for the presence and extent of inflammatory cells, wear particles, and uncharacteristic tissue features. Immunohistochemical staining was performed on paraffin sections for IL1b, IL6 and TNFa (N=10) and for lymphocytes (CD3, CD4, CD20; N=8), and lipid stains were applied to selected frozen sections.

Results: Cases were revised after ave. 6 months for pain and lack of fixation. Grossly the components had minimal attached tissue, if any. Histologically, the most common finding was extensive chronic inflammation (mostly lymphocytic), although many also had abundant acute inflammation (neutrophils and early granulation tissue). Lymphocytes were mostly common T and helper T cells. Eosinophils (cells associated with intense allergic reactions) were rare. Other uncharacteristic findings included histiocyte-rich granulomas, peculiar metal-like dust associated with silicate-like structures, vacuolated cells and unusual tissue spaces (20 – 50 mm in diameter) some of which were positive with lipid stains. Tissues stained strongly positive for IL-1b and IL-6 but only weakly for TNFa. A similar inflammatory response was noted to have spread into the capsular tissues.

Conclusion: Given the absence of conclusive bacterial cultures in the majority of cases, the histopathology seems consistent with an oil-based contaminant mixed with debris generated from the machines used at the manufacturing plant.

Crosslinking of UHMWPE markedly improves its wear resistance. However, Green et al. (JBMR 53, 490, 2000) have reported that the wear debris from crosslinked PE were smaller than from non-crosslinked PE, and that particles with a mean diameter of 0.24 μm diameter caused more osteolytic activity of mouse macrophages in vitro than 0.45 μm or 1.7 μm particles. In order to predict how a new PE will behave clinically, however, it is desirable to compare its particle morphology to that of the gamma-air sterilized PE that was used in the vast majority of acetabular cups over the past three decades. We compared PE wear debris that were generated in a hip simulator and recovered by digestion and filtration of the serum lubricants, from cups crosslinked at 2.7 Mrads in air (historical controls), and cups machined from extruded bars that had been pre-gamma crosslinked at 4.5 Mrads and remelted (to extinguish free radicals and stabilize against oxidation) prior to cup machining. The debris were 85% and 92% rounded particles, respectively, and the balance were fibrils. The diameters of most of the rounded particles were from 0.07 to 0.3 μm, with very similar distributions in this range for the two materials. The total number of round particles from the 4.5 Mrad remelted PE was 32% and 76% below that of the 2.7 Mrad gamma-air non-aged and aged cups, respectively, the number of fibrils was 66% and 88% lower, respectively, and the total volume of wear debris per million cycles was 71% and 90% lower with the 4.5 Mrad-remelted PE cups, respectively. Since there was little if any systematic change in particle morphology, the substantially reduced wear and high oxidation resistance of the cups fabricated from gamma crosslinked-remelted PE could markedly reduce the incidence of clinical osteolysis.

A recent study of tissues from 14 modern metal-on-metal (MM) total hips reported an intense diffuse and perivascular (p.v.) lymphocytic infiltrate, suggestive of hypersensitivity (Willert et al. Osteologie 2000; 9:2–16). This study evaluated the histopathology of tissues from modern MMs using cases obtained at revision or autopsy.

Materials and methods: 35 MM THRs or surface replacements (SRs) that failed due to dislocation, aseptic loosening, and pain or obtained at autopsy (n = 4) were used. H& E stained sections were rated semiquantitatively. Selected cases were studied by immunohistochemistry for macrophage (CD68) and lymphocyte markers (CD3, 4, 20). Wear was measured with a coordinate measuring machine.

Results: Generally, the THRs without metallosis showed minimal visible wear particles, consistent with their low measured wear (av. total wear depth was 8.25 ± 6.7 um at av. 30 mos). Although SRs had an av. linear wear depth of 46 ± 48 microns at av. 23 mos, the metal rating was also low (av. 0.8), except in 1 case with HA 3rd body induced high wear and subsequent osteolysis. Lymphocytic aggregates were not a common feature but B type cells were extensive in 1 case (THR revised for pain after 36 months) moderate in 1 autopsy SR (with CoCr metallosis due to run-in wear of an out of round component) and minimal in 4 of the SRs.

Discussion and conclusions: Extensive diffuse or p.v. lymphocytes were not a consistent finding in these 35 cases. These features were not seen in well-functioning autopsy retrieved cases with low wear rates, nor in the SR with osteolysis and the highest amount of component wear. Until the long-term local and systemic effects of metal wear products, including hypersensitivity are better understood, continued histopathological assessment of periprosthetic tissues from MM total hips is recommended.

Aims: determine risk factors associated with component loosening so that measures can be implemented to improve component durability. Methods: The þrst 300 patients with Wright Medical Conserve Plusª metal-on-metal hip resurfacings were analyzed radiographically for radiolucencies and failed components were analyzed histologically after the components were sectioned. The group average age was 48 years, 75% were male, and most were operated for OA. At an average of 3 years, 7 hips required revision for femoral loosening, none for acetabular loosening. These included 4 of the þrst 100 cases, 1 in the 2nd 100, 2 in the 3rd 100. Radiographic lucencies were found in 9 of the 1st 100, and 3 in each of the of the 2nd and third 100. Results: The etiology of femoral loosening was found to be multifac-torial and risk factors included: substandard bone preparation, presence of large cysts or bone defects, cement technique, and patient activity.

The short metaphyseal stem serves as a useful Ç barometer È for þxation and impending loosening. Conclusions: Femoral loosening can be minimized by better patient selection and by excellent bone preparation and cement technique. Patients with compromised bone stock may still be successfully resurfaced if the extent of the defects is not excessive and/or the stem is cemented in.

Aims: Measure serum chromium (SrCr) and cobalt (SrCo) and urine chromium (UCr) levels in patients with metal on metal surface arthroplasty of the hip. Methods: Ion levels were measured prospectively in 22 patients implanted with the Conserve Plusª (Wright Medical, TN) CoCr hip resurfacing. There were 15 males and 7 females with an average age of 49 years (range 28 Ð 62 yr). Serum and urine samples were collected using strict anti-contamination techniques pre-operatively and at 3, 6 and 12 months using graphite furnace atomic absorption spectrophotometry. Results: All postoperative metal levels were increased compared to their pre-operative levels. SrCr and SrCo values are at their highest at 3 months post operative and then begin to decrease. UrCr although elevated at 3 and 6 months postoperatively compared to the preop values, the levels continued to increase after the 6-month interval. These values are approximately 4-fold, 7-fold and 3-fold higher in SrCr, UrCr and SrCo, respectively, compared to the values seen in a group of patients with well functioning conventional metal (CoCr) on polyethylene total hips at 84 months postoperative measured by our group. Conclusions: The present levels are 2-fold lower in both SrCr and UrCr and 3-fold lower in SrCo than a group of patients with older generation surface arthroplasties reported previously by our group, suggesting improved manufacturing techniques and material properties have resulted in reduced component wear and generation of wear particles. 12 and 24 month data are currently being collected and analyzed.

Aims: It has been suggested that the capture mechanism of modular polyethylene tibial inserts degrades with time in-situ. This study evaluates micromotion, polyethylene wear and tissue histology in contemporary cemented TKRñs retrieved at autopsy. Methods: Twelve cemented, PCL-retaining TKRñs of the same design were retrieved at autopsy after 41(15–74) months in-situ. Patient age and body weight averaged 73 years and 90 kg, respectively. Insert micromotion was measured according to published protocols on 6 of the 12 TKRñs in which the modular tibial component was undisturbed at retrieval and on 6 unused control components. Tissue histology was evaluated using a semi-quantitative grading system. Articular and backside surface damage was measured using published techniques. Results: There was no signiþcant difference (t-test, p=0.12) between the micro-motion index for retrieved inserts (154±121 um) and control inserts (62±53 um). Backside surface damage covered 38%±23% and was dimpled in appearance without scratching or pitting. Damage covered 46%±8% of the articular surface. Micromotion was negatively correlated with in-situ time (r=−0.94) and backside damage (r=− 0.97). Conclusions: Micromotion for these autopsy-retrieved TKRñs is less than half the 380 micron magnitude measured for other autopsy-retrieved designs, as reported by Engh. Micromotion was greatest on inserts with the least backside wear and the shortest time in-situ. These data suggest that backside damage resulted from axial compression of the polyethylene insert against the baseplate rather than micromotion.

Aims: Examine the short term failures of the Wright Medical Conserve Plusª metal-on-metal hip resurfacing to determine risk factors, so that measures could be implemented to prevent future failures. Methods: Two hundred and ninety six Conserve Plus hip resurfacings were performed in an FDA IDE multi-center trial. 9 femoral neck fractures occurred in 3 of the 9 centers. The time to failure ranged from less than 1 week to 21 weeks. The revised resurfaced heads were sectioned and examined by micro-radiography and histology, along with pre and post-operative radiographs and clinical histories that were discussed with the surgeons. Results: Several risk factors were identiþed including poor bone quality large or multiple cysts in the femoral head or neck, leaving reamed bone uncovered, improper implant placement and incorrect patient selection. Lessons learned from this analysis resulted in no further neck fractures to date in 369 additional Conserve Plus components that have now been implanted. Conclusions: Osteoarthritic femoral necks rarely fracture and neck fracture in resurfaced femoral heads can be largely prevented by better patient selection, improved surgical technique to prevent neck notching and better implant placement.

Aims: To study the levels of genetic damage caused to a cultured human cell line when cultured with synovial ßuid retrieved from revision arthroplasty joints. Methods: Synovial ßuids were retrieved from revision hip and knee arthroplasty patients with bearings made from Cobalt chrome-on-Cobalt chrome, Cobalt chrome-on-polyethylene, Stainless Steel-on-polyethylene and Titanium-onpolyethylene. Control synovial ßuid was retrieved from primary arthroplasty cases. Synovial ßuid was cultured with human primary þbroblasts for 48 hours in a cell culture system under standardised conditions. The ÔCometñ assay was used with an image analysis system to measure levels of DNA damage caused by the various synovial ßu id samples. Results: Synovial ßuids from Cobalt Chrome-on-Cobalt Chrome and Cobalt Chrome-on-polyethylene joint replacements caused signiþcantly (p< 0.05) more genetic damage than synovial ßuids from Stainless Steel-on-polyethylene and Titanium-on-polyethylene cases. Control synovial ßuid caused minimal change. Conclusions: Different alloys used in Orthopaedic implants are associated with different levels of DNA damage to human cells in vitro. We have no evidence for any long-term health risk to patients with such implants. Further research is needed in this þeld.

We describe three prostheses with cemented titanium-alloy stems and Al₂O₃ ceramic femoral heads which had to be revised after a mean period of implantation of 78 months. In each case, the neck of the prosthesis had been so severely worn that the profile was elliptical rather than circular. There was severe metallosis of the periprosthetic tissues. Metal particles isolated from the tissues were approximately one nanometre in size and the ratios of titanium, aluminium and vanadium in the particles were the same as in the original alloy. Histologically, the high concentration of metal particles masked the presence of high-density polyethylene (HDP) debris, but again particles about one nanometre in size were isolated from the tissues. The severe necrobiosis and necrosis noted were consistent with other reports of the presence of extensive wear particles in periprosthetic tissues. Wear is presumed to have occurred as a result of mismatch between the shape or size of the taper cone and the femoral head, or to changes in the geometry of loading due to migration of the cup. To facilitate early intervention, patients with this design of prosthesis should be monitored radiologically.

Cemented Ti-6Al-4V components were used to resurface ten femoral heads in nine young adult patients with osteonecrosis of the femoral head (average age 32 years; range 20 to 51). There were eight hips at Ficat stage III and two at stage IV. Five hips have maintained satisfactory function for an average period of 11.2 years (10 to 12.2) with no radiographic evidence of component loosening or osteolysis; five have been revised after an average period of 7.8 years (3.3 to 10.3) for pain caused by deterioration of the acetabular cartilage. No component required revision for loosening and the specimens retrieved at revision showed no evidence of osteolysis despite burnishing of the titanium bearing surface and the presence of particulate titanium debris in the tissues.

We present three cases of a previously undescribed condition characterised by unilateral tibia vara associated with an area of focal fibrocartilaginous dysplasia in the medial aspect of the proximal tibia. The three children affected were aged 9, 15 and 27 months respectively. Two required tibial osteotomy, but in one the deformity resolved without treatment. The pathogenesis of the focal lesion remains conjectural; the most likely explanation is that the mesenchymal anlage of the tibial metaphysis has, for unknown reasons, developed abnormally at the insertion of the pes anserinus.