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.

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.

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.

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.