Aims. This study reports the ten-year wear rates, incidence of osteolysis, clinical outcomes, and complications of a multicentre randomized controlled trial comparing oxidized zirconium (OxZr) versus cobalt-chrome (CoCr) femoral heads with ultra-high molecular weight polyethylene (UHMWPE) and highly cross-linked polyethylene (XLPE) liners in total hip arthroplasty (THA). Methods. Patients undergoing primary THA were recruited from four institutions and prospectively allocated to the following treatment groups: Group A, CoCr femoral head with XLPE liner; Group B, OxZr femoral head with XLPE liner; and Group C, OxZr femoral head with UHMWPE liner. All study patients and assessors recording outcomes were blinded to the treatment groups. The outcomes of 262 study patients were analyzed at ten years’ follow-up. Results. Patients in Group C were associated with increased mean liner wear rates compared to patients in Group A (0.133 mm/yr (SD 0.21) vs 0.031 mm/yr (SD 0.07), respectively; p < 0.001) and Group B (0.133 mm/yr (SD 0.21) vs 0.022 mm/yr (SD 0.05), respectively; p < 0.001) at ten years’ follow-up. Patients in Group C were also associated with increased risk of osteolysis and aseptic loosening requiring revision surgery, compared with patients in Group A (7/133 vs 0/133, respectively; p = 0.007) and Group B (7/133 vs 0/135, respectively; p = 0.007). There was a non-statistically significant trend towards increased mean liner wear rates in Group A compared with Group B (0.031 mm/yr (SD 0.07) vs 0.022 mm/yr (SD 0.05), respectively; p = 0.128). All three groups were statistically comparable preoperatively and at ten years’ follow-up when measuring normalized Western Ontario and McMaster Universities Osteoarthritis Index (p = 0.410), 36-Item Short Form Health Survey (p = 0.465 mental, p = 0.713 physical), and pain scale scores (p = 0.451). Conclusion. The use of UHMWPE was associated with progressively increased annual liner wear rates after THA compared to XLPE. At ten years’ follow-up, the group receiving UHMWPE demonstrated an increased incidence of osteolysis and aseptic loosening requiring revision surgery compared to XLPE. Femoral heads composed of OxZr were associated with trend towards reduced wear rates compared to CoCr, but this did not reach statistical significance and did not translate to any differences in osteolysis, functional outcomes, or revision surgery between the two femoral head components. Cite this article: Bone Joint J 2022;104-B(7):833–843

We have reviewed 70 patients with bilateral simultaneous total hip arthroplasties to determine the rate of failure and to compare polyethylene wear and osteolysis between an implant with a cobalt-chrome head and Hylamer liner with that of a zirconia head and Hylamer liner. The mean thickness of the polyethylene liner was 11.0 mm (8.8 to 12.2) in the hip with a zirconia head and 10.7 mm (8.8 to 12.2) in that with a cobalt-chrome head. At follow-up at 6.4 years no acetabular or femoral component had been revised for aseptic loosening and no acetabular or femoral component was loose according to radiological criteria in both the cemented and cementless groups. The mean rate of linear wear and annual wear rate were highest in the 22 mm zirconia femoral head (1.25 mm (SD 1.05) and 0.21 mm (SD 0.18), respectively) and lowest in the 22 mm cobalt-chrome femoral head (0.70 mm (SD 0.39) and 0.12 mm (SD 0.07), respectively). The mean volumetric wear was highest in the 28 mm zirconia femoral head (730.79 mm. 3. ) and lowest in the 22 mm cobalt-chrome femoral head (264.67 mm. 3. ), but if the results were compared by size of the femoral head and type of material there was no statistical difference (p > 0.05). Sequential measurements of annual wear showed that the zirconia femoral head had a relatively higher rate of penetration than the cobalt-chrome head over the first three years; thereafter the rate of wear was reduced and compared favourably with that of cobalt-chrome heads. There was a statistically significant relationship between the wear of the polyethylene liner and the age of the patient, male gender and the degree of abduction angle of the cup, but not diagnosis, weight, hip score, range of movement, or amount of anteversion. Osteolysis was identified on both sides of the acetabulum in six patients (9%). Of 12 hips with acetabular osteolysis, six had a 28 mm cobalt-chrome femoral head and the remaining six a 28 mm zirconia head. Osteolysis was observed in zones 1A and 7A of the femur in two hips (3%) with a 28 mm zirconia head (cemented hip) and in four (6%) with a 28 mm cobalt-chrome femoral head (cementless hip). Our findings suggest that although the performance of a zirconia femoral head with a Hylamer liner was not statistically different from that of a cobalt-chrome femoral head and Hylamer liner, there was a trend for the zirconia head to be worse than the cobalt-chrome femoral head

Thirty total hip replacements in twenty-eight patients in which a Zirconia/Polyethylene articulation was utilized were compared to a control group undergoing total hip replacement utilizing Cobalt-Chrome/Polyethylene articulation. These patients were matched for gender, BMI and pre-operative diagnosis. At nine years after implantation there was no difference in the functional outcome between the two groups and no difference in liner wear rate on x-ray (Livermore technique). There was a 27% revision rate in the Zirconia group compared to the 11.5% revision rate in the Cobalt-Chrome group. Bearing surfaces require long- term clinical follow-up to validate in vitro performance. To determine the benefit of Zirconia on polyethylene versus cobalt-chrome on polyethylene in total hip articulation. Zirconia offers no advantage over a cobalt-chrome head in decreasing in vivo polyethylene wear at ten- year follow-up. Newer bearing surfaces require long- term clinical follow-up to validate in vitro laboratory performance. All primary total hip replacements at this institution are entered prospectively in a database and are assessed on an annual basis. All patients in this study were followed for a mean of nine years with a range of six to thirteen years. Thirty cementless total hip arthroplasties were performed in twenty-eight patients utilizing a Zirconia head coupled with a polyethylene acetabular component. Twenty-six hips have been followed for a mean of nine years. These were matched to a control group of twenty-six hips in twenty-six patients utilizing a cobalt-chrome head coupled with an identical polyethylene liner followed for a mean of ten years (range five to fourteen years). There was no functional difference in outcome at nine years between the two groups utilizing the Livermore technique there was no difference in the liner wear rate between the two patient groups. However, seven hips (27%) of the Zirconia group required revision due to loosening and/or extensive osteolysis around the cup and only three hips (11.5%) required revision in the cobalt-chrome group. Our study demonstrates that although changes in component designs and materials may offer theoretical advantages over current components their effect in vivo remains questionable

At yearly intervals we compared the radiological wear characteristics of 81 alumina ceramic femoral heads with a well-matched group of 43 cobalt-chrome femoral heads. Using a computer-assisted measurement system we assessed two-dimensional penetration of the head into the polyethylene liner. We used linear regression analysis of temporal data of the penetration of the head to calculate the true rates of polyethylene wear for both groups. At a mean of seven years the true rate of wear of the ceramic group was slightly greater (0.09 mm/year, SD 0.07) than that of the cobalt-chrome group (0.07 mm/year, SD 0.04). Despite the numerous theoretical advantages of ceramic over cobalt-chrome femoral heads, the wear performance in vivo of these components was similar

Introduction. Large diameter metal-on-metal hip arthroplasty (LDMMTHA) provides benefits of reduced dislocation rates and low wear. The use of modular systems allows better restoration of hip biomechanics. There have been reports of modular LDMMTHAs with tapered sleeves generating excessively high metal ions, due to possible mismatch between the titanium stem and the cobalt-chrome sleeve and the dual Morse tapers involved. We evaluated metal ion levels in LDMMTHA patients with and without a cobalt-chrome (CoCr) tapered sleeve. Methods. A cross-sectional series of 91 patients with proximal porous titanium alloy stem LDMMTHA with identical design CoCr bearings, attending a 1 to 2-year review were assessed with routine clinical and radiographic examinations, hip scores and metal ion analysis. Of these 65 had a single Morse taper between monoblock CoCr heads and the stems. Twentysix had a tapered cobalt-chrome sleeve in addition, with the resultant dual taper. Mean bearing diameter was 46 mm in both groups and mean age was 58 years in the monoblocks and 66 years in the tapered sleeve group. Results. Mean Oxford Hip score is worse in the tapered group (14.7) than in the monoblocks (12.6). All patients had well-functioning hips clinically and radiologically. Median blood cobalt and chromium are higher in the tapered sleeve (2.3μg/L and 1.8 μg/L) compared to the monoblocks (1.8 μg/L and 1.1 μg/L). Urine cobalt and chromium levels in the tapered sleeve (13.8 μg/24 hr and 5.3 μg/24 hr) also are higher than those in the monoblocks (12.2 μg/24 hr and 4.5 μg/24 hr respectively). Discussion and Conclusion. The limitation of this study is that it is a cross-sectional study. The results indicate that the use of a tapered sleeve in total hip arthroplasty does lead elevation of cobalt and chromium levels and the difference is statistically significant. However these levels are not as high as the levels reported with some other hip systems which have been withdrawn and the clinical significance of the elevated levels in the present study is unknown

This study reports the ten-year outcomes of a three-arm, multicentre randomised controlled trial comparing Cobalt-Chrome (CoCr) and Oxidised Zirconium (OxZr) femoral heads with ultra-high molecular weight polyethylene (UHMWPE) versus highly cross-linked polyethylene (XLPE) liners in total hip arthroplasty (THA). Patients undergoing THA from four institutions were prospectively randomised into three groups. Group A received a CoCr femoral head and XLPE liner; Group B received an OxZr femoral head and XLPE liner; and Group C received an OxZr femoral head and UHMWPE liner. The outcomes of 262 study patients were analysed at ten years follow-up. At ten years, increased linear wear rates were recorded in group C compared to group A (0.133 ± 0.21 mm/yr vs 0.031 ± 0.07 mm/yr respectively, p<0.001) and group B (0.133 ± 0.21 mm/yr vs 0.022 ± 0.05 mm/yr respectively, p<0.001). Patients in group C had increased risk of osteolysis and aseptic loosening requiring revision surgery compared with group A (7/133 vs 0/133 respectively, p=0.007) and group B (7/133 vs 0/135 respectively, p=0.007). There was a non- significant trend towards increased liner wear rates in group A compared to group B (0.031 ± 0.07 mm/yr vs 0.022 ± 0.05 mm/yr respectively, p=0.128). All three groups were statistically comparable preoperatively and at ten years follow-up from a clinical score perspective. The use of UHMWPE was associated with progressively increased annual liner wear rates. At ten years follow-up, this translated to an increased incidence of osteolysis and aseptic loosening requiring revision, compared with XLPE. Femoral heads composed of OxZr were associated with a non-significant trend towards reduced wear rates compared to CoCr, but this did not translate to any differences in osteolysis, functional outcomes, or revision surgery between the two treatments groups

Background: Patients with femoral head osteonecrosis usually tend to be younger and more active when compared with osteoarthritis patients. Second generation metal-on-metal THA was reintroduced to reduce poly-ethylene-induced wear debris, and therefore increase longevity of implants. The aim of this retrospective study was to compare full blood cobalt-chrome levels, patient activity, clinical/radiological outcome and implant survival in patients with osteonecrosis and osteoarthritis after a minimum follow up of 12 years. Methods: Full blood cobalt-chrome levels of a consecutive series of 125 patients, consisting of 40 patients (38 male, 2 female, average age 35 years, range 28 to 46 years) with osteonecrosis (ON group) and 85 patients (60 male, 25 female, average age 58 years, range 52 to 68 years) with osteoarthritis (OA group) as primary diagnosis were retrospectively compared. Patient activity level was assessed using UCLA Score and clinical outcome was evaluated using HHS. Radiological outcome and implant survival (Kaplan Meyer analysis) was determined in both groups. Results: Patients with osteonecrosis of the femoral head showed significant higher UCLA scores when compared to OA group (4 versus 7) (p < 0.05). Despite this higher patient activity no significant difference was found between cobalt-chrome full blood levels (2.1/1.6 μg/l, ON group, 1.9/1.8 μg/l OA group, respectively) (p > 0.05). No positive correlation between patient activity, acetabular cup abduction angle and cobalt-chrome levels was found (r. 2. < 0.01). Clinical and radiological outcome were equal in both groups. Harris hip score was 91 points in the OA and 92 in the ON group (p > 0.05). Average cup inclination angle was 47° (range 32° to 55°) and 44° (range 30° to 56°) respectively (p > 0.05). Implant survival at 12 years follow up was 96% in the OA and 97% in the ON group. Conclusion: After a minimum follow up of 12 years, we could not find increased metal levels in osteonecrosis patients when compared to the osteoartrithis group. Regarding our clinical and radiological outcome we cannot confirm previously published reports showing suboptimal results of THA in patients with osteonecrosis. Implant survival data did not differ among both group. Metal on metal THA seems to be an effective and safe treatment option for these patients

Fifty-four cobalt-chrome alloy femoral heads were retrieved at revision surgery or at post-mortem; 23 came from uncemented, eight from hybrid and 23 from cemented hip arthroplasties. The uncemented and hybrid implants had porous coating, metal backing and modular femoral heads; with one exception none of the cemented implants had any of these. Twenty-five of the 31 heads from uncemented and hybrid arthroplasties, and 11 of the 23 heads from cemented arthroplasties showed surface damage involving more than 25% of the surface. Scanning electron microscopy revealed multidirectional fine scratches 1 micron to 10 microns in depth and width which appeared to have been made by fine, hard particles. There was a higher rate of such damage in the uncemented and hybrid arthroplasties than in the cemented implants, suggesting that the abrasive particles were mainly released from the metal, rather than from the cement or polyethylene components of the implants

While Oxidized Zirconium (OxZr) femoral heads matched with highly cross-linked polyethylene (XLPE) have demonstrated the lowest rate of revision compared to other bearing couples in the Australian National Joint Registry, it has been postulated that these results may, in part, be due to the fact that a single company offers this bearing option with a limited combination of femoral and acetabular prostheses. The purpose of this study was to assess clinical and radiographic outcomes in a matched cohort of total hip replacements (THR) utilizing an identical cementless femoral stem and acetabular component with either an Oxidized Zirconium (OxZr) or Cobalt-Chrome (CoCr) femoral heads at a minimum of 10 years follow-up. We reviewed our institutional database to identify all patients whom underwent a THR with a single cementless femoral stem, acetabular component, XLPE liner and OxZr femoral head with a minimum of 10 years of follow-up. These were then matched to patients who underwent a THR with identical prosthesis combinations with CoCr femoral head by gender, age and BMI. All patients were prospectively evaluated with WOMAC, SF-12 and Harris Hip Score (HHS) preoperatively and postoperatively at 6 weeks, 3 months, 1 and 2 years and every 2 years thereafter. Charts and radiographs were reviewed to determine the revision rates and survivorship (both all cause and aseptic) at 10 years for both cohorts. Paired analysis was performed to determine if differences exist in patient reported outcomes. There were 208 OxZr THRs identified which were matched with 208 CoCr THRs. There was no difference in average age (OxZr, 54.58 years, CoCr, 54.75 years), gender (OxZr 47.6% female, CoCr 47.6% female), and average body max index (OxZr, 31.36 kg/m2, CoCr, 31.12 kg/m2) between the two cohorts. There were no significant differences preoperatively in any of the outcome scores between the two groups (WOMAC (p=0.449), SF-12 (p=0.379), HHS(p=0.3718)). Both the SF12 (p=0.446) and the WOMAC (p=0.278) were similar between the two groups, however the OxZr THR cohort had slightly better HHS compared to the CoCr THR cohort (92.6 vs. 89.7, p=0.039). With revision for any reason as the end point, there was no significant difference in 10 years survivorship between groups (OxZr 98.5%, CoCr 96.6%, p=0.08). Similarly, aseptic revisions demonstrated comparable survivorship rates at 10 year between the OxZr (99.5%) and CoCr groups (97.6%)(p=0.15). Both THR cohorts demonstrated outstanding survivorship and improvement in patient reported outcomes. The only difference was a slightly better HHS score for the OxZr cohort which may represent selection bias, where OxZr implants were perhaps implanted in more active patients. Implant survivorship was excellent and not dissimilar for both the OxZr and CoCr groups at 10 years. Therefore, with respect to implant longevity at the end of the first decade, there appears to be no clear advantage of OxZr heads compared to CoCr heads when paired with XLPE for patients with similar demographics. Further follow-up into the second and third decade may be required to demonstrate if a difference does exist

Hypersensitivity to metal alloy orthopaedic implants has become identified increasingly as a cause of implant failure. Because of their hypoallergenic properties, ceramic materials have been recommended as an alternative to metals. Unfortunately, the cost of ceramics and limitations imposed by their material properties has restricted these applications. The metalloceramic composite Oxinium® has been suggested as asubstitute. This is the first study to prospectively compare these materials in patients with documented cobalt-chrome hypersensitivity. Over a period of ten years, preoperative screening using skin patch testing and in vitro leukocyte stimulation testing of patients with gonarthrosis and a history of metal hypersensitivity identified sixteen patients with allergy to cobalt-chrome alloy. Twelve (all& ) underwent primary, and four underwent revision (3& , 1%) knee replacement surgery using either alumina ceramic femoral components (3 primary, 2 revisions) or Oxinium® femoral components (9 primary, 2 revisions) All implants were fixed with acrylic cement, and all-polyethylenetibial implants were used in each procedure. None of the patients in the primary groups developed symptoms of allergic reaction at a minimum of one year following surgery. Serial serum antibody and leukocyte stimulation studies have shown no reaction following placement of either type of prosthetic knee. Those undergoing revision surgeries had rapid resolution of preoperative symptoms of pain, effusion and eczematous rash. Serum studies showed a concomitant fall inantibody levels. The two patients undergoing revision surgery with alumina femoral implants subsequently underwent second revisions (both at 8 years) using Oxinium® femoral implants. Neither developed clinical symptoms orchanges in antibody profile. While the number of patients in the present study is relatively small, it is the only independent, prospective, clinical comparison of these materials. The uniformly good results suggest implants of Oxinium® offer the hypoallergenic properties of alumina without adverse-material properties and at a lower cost

We studied the wear generated by motion between polished and shot-blasted titanium-alloy (Ti-6Al-4V) or cobalt-chrome alloy (Co-Cr) surfaces and cortical bone in vitro. Semicircular sections of human proximal femoral cortex were reamed to fit metal cylinders of each alloy. The cylinders were then fitted in the bone, loaded and rotated in physiological saline. Ti-alloy resulted in more wear both of the bone and of the metal than did Co-Cr alloy. Metal wear was reduced and bone wear was increased by shot-blasting, a procedure which introduces surface residual stresses and roughens the metal surface. We conclude that when there is gross motion between a metal implant and bone, Ti-alloy is likely to generate more wear debris than Co-Cr alloy. The least wear both of bone and of metal was produced by polished Co-Cr

We implanted 57 uncemented cobalt-chrome porous-coated collarless femoral components into 51 patients (mean age 49 years). At review, five to eight years postoperatively, good or excellent results were recorded in 70% by the Mayo Clinic hip evaluation and in 84% by the Harris hip score. Revision for aseptic loosening of the femoral stem was necessary in only one hip. Thigh pain diminished with time and was present in only two hips at the time of review. Endosteal bone formation was seen at the junction of the smooth and the porous segments of the stem in 94% of hips and in 60% it continued after three years. In 90% of hips, proximal femoral atrophy did not progress after three years. Discontinuous radiolucent lines were seen around 30% of stems, most commonly in zones I, IV and VII. They were not progressive in 94% and their presence did not correlate with the clinical outcome

Oxidized Zirconium (OxZr), metallic zirconium alloy oxidized to form a ceramic surface, was developed as an alternative bearing material to cobalt-chrome (CoCr) alloy for improvements in roughening resistance, frictional behavior, and biocompatibility without a risk of brittle fracture. Knee simulator testing without intentional addition of abrasives demonstrated that the ultra-high molecular weight polyethylene (UHMWPE) wear rate was 85% less with OxZr than with CoCr femorals. The relative performance of articulating materials can change when tested under abrasive conditions, so test protocols were investigated with abrasives added directly to the simulator test lubricant. Testing was conducted on a six-station, four-axis, physiological knee simulator. OxZr and CoCr medium-sized, cruciate-retaining, femoral components were tested against UHMWPE tibial inserts sterilized by ethylene oxide. Alumina powder was mixed into 50% bovine serum lubricant at a concentration of 0.2 mg/cm3. Tests were conducted with different powder sizes in the range of 0.3 to 150 μm. Measurements included tibial insert weight and femoral surface roughness. The lubricant in CoCr tests became opaque with gray debris while the femoral condyles became scratched. In contrast, the lubricant in OxZr tests remained normal (as in tests without abrasives), and femoral condyle scratching was much less severe. Despite these obvious effects, the UHMWPE wear produced by each material did not increase appreciably over that of tests without abrasives, with OxZr maintaining a wear rate about 85% less than for CoCr. It was noted that the scratches were aligned, or became realigned, with the translation motion and had little evidence of the swirls or cross-hatching often observed on retrieved components. Previous testing indicates that UHMWPE wear increases significantly only if scratches are oblique to the sliding direction. Thus, a test technique that produces scratches with more clinically relevant orientations is needed for a performance comparison between femoral materials under abrasive conditions

Recently, monoblock cups have increased in popularity for hip resurfacing and large femoral head total hips. However, there have been no studies specifically evaluating the durability of this type of cup. The purpose of this study was to define the mid-term survivorship of cobalt-chrome alloy, monoblock acetabular components. A retrospective radiographic review of 426 consecutive hip resurfacings using the ConserveÒPlus prosthesis was performed with specific attention to the acetabular component. Radiographs were analyzed for cup position, the presence of radiolucencies, cup migration, bead shedding, osteolysis and stress remodeling of the pelvic bone. Kaplan-Meier (KM) survival estimates were calculated using revision for aseptic loosening of the acetabular component as the end point. Average follow-up was 8.6 years (range 5.4 to 12.3). Mean abduction angle and anteversion angle were 46.6° (± 6.8°), and 21.6° (± 8.6°), respectively. Radiolucent gaps behind the cup from incomplete seating were visible in zone 2 in 16% of cases. These were typically 1 to 2 mm in size and radiographically filled in all but 2 cases. No cups with early lucencies went on to fail. Late radiolucencies developed in zone 1 in 8 cups (1.9%), in zone 2 in 8 cups (1.9%), and in zone 3 in 19 cups (4.5%). Radiolucencies in multiple zones were seen in 6 cups (1.4%). Small amounts of socket migration (2mm or less) were suspected in 3 cups (0.7%) but each of these has remained stable. There were no cases of bead shedding. Small osteolytic lesions were suspected in 12 hips (2.8%). There were 2 revisions for aseptic loosening of the cup at 5 and 8 years, and one revision for protrusion of the cup through the medial wall 4 days after surgery. Additionally, one cup at 9 years follow-up is believed to be loose but has yet to be revised. The KM survival estimate was 99.6% at 5 years (95% C.I. 98.4% to 99.9%) and 98.7% at 10 years (95% C.I. 94.5% to 99.7%). In conclusion, this study demonstrates excellent mid-term survivorship of a cobaltchrome alloy monoblock acetabular component, which matches that of conventional titanium implants. Small early gaps seen behind the cup from incomplete seating do not appear to effect cup survivorship as long as a good peripheral press-fit is obtained. Osteolysis with this prosthesis is rare but does occur

Aims

Oxidized zirconium (OxZi) and highly cross-linked polyethylene (HXLPE) were developed to minimize wear and risk of osteolysis in total hip arthroplasty (THA). However, retrieval studies have shown that scratched femoral heads may lead to runaway wear, and few reports of long-term results have been published. The purpose of this investigation is to report minimum ten-year wear rates and clinical outcomes of THA with OxZi femoral heads on HXLPE, and to compare them with a retrospective control group of cobalt chrome (CoCr) or ceramic heads on HXLPE.

Although total knee arthroplasty (TKA) has been a reliable procedure providing durable pain relief, polyethylene (PE) wear remains a major limitation of the long-term success of TKA. One potential method of lowering PE wear in TKA is to use oxidized zirconium (OxZr)-bearing surface. Although wear simulating testing of an OxZr counter surface of femoral component produced less PE wear and fewer particles than did cobalt-chrome (Co-Cr) counter surface of femoral component [1–4], this finding has not been demonstrated in vivo to our knowledge. We measured in vivo PE wear by isolating and analyzing PE wear particles in synovial fluid from wellfunctioning TKA [5]. The purpose of the current study was to determine the size, shape, and amount of PE wear particles isolated from synovial fluid of patients who underwent a bilateral simultaneous TKA prosthesis, but different materials of femoral components. We performed a bilateral simultaneous TKA in 100 patients (200 knees) who received an OxZr femoral component in one knee and a Co-Cr femoral component in the other. Mean age was 55.6 (44–60) years. Synovial fluid was obtained from 28 patients (56 knees) who had undergone a simultaneous bilateral TKA under completely sterile conditions at one or two years after the operation. Randomization to an OxZr or Co-Cr femoral component was accomplished with use of a sealed study number envelope, which was opened in the operating room before the skin incision had been made. After the opening the randomization envelope, the first knee received prosthesis indicated by the envelope (OxZr or Co-Cr component) and the contralateral (second TKA) knee received the other prosthesis (OxZr or Co-Cr component). All operations were performed by one surgeon using the same design of total knee prosthesis: Genesis II (Smith and Nephew, Memphis, Tennessee). Only the material of the femoral component differed between two groups. The preoperative diagnosis was osteoarthritis in all patients. Preoperative and post operative KS and HSS knee scores, KS functional scores and UCLA activity scores were evaluated. The amount of polyethylene wear particles in the aspirated synovial fluid sample was analyzed by thermogravimetic analysis (TGA) using a TGA instrument (TGA/SDTA 84le model, Mettler Toledo CO., Greifensee, Switzerland). The weight of the sample solution was measured before and after removing the organic content by heating the sample solution. The sample solution was casted onto petri dishes. The petri dish was covered and kept in a dry oven at 60°C for 2 days. While the sample solution was kept in a dry oven for 2 days, a small hole was made on the cover of the petri dish to allow water to evaporate slowly for 2 days. After this procedure, the cover of petri dish was removed and TGA sample was dried at 60°C for another 2 days. After the sample was completely dried out, the dried sample was measured using analytical balance. TGA was used to determine the weight change profiles of polyethylene subject to heating under a nitrogen atmosphere. The nitrogen flow rate was kept constant at 50mL per minute. TGA data were taken at heating rate as 5°C per minute in the temperature range of 20° to 1000°C. The weight loss data were recorded as a function of time and temperature using special software in computer. When the temperature reached to the point of decomposition of the sample, the sample started to lose weight. By calculating the weight of the sample around the temperature which led to start to decomposition, real amount of polyethylene in the sample was measured. The size and shape of PE particles were examined using scanning electron microscopy (JSH-6360A model, Jeol Co., Tokyo, Japan). The samples were coated using a platinum sputtering machine for 20 sec. ANOVA, nonparametric chi square test, nonpaired t-test and Mann-Whitney U-test were used for statistical analyses. Differences of P< 0.05 were considered statistically significant. Mean preoperative KS (27.5 vs 27.2 points) scores, HSS (51.1 vs 51.2 points) knee scores, KS functional scores (55.4 vs 55.4 points) and UCLA activity scores (2.8 vs 2.8 point) were not significantly different between two groups. Mean postoperative KS (93 vs 92 points), HSS knee scores (90 vs 89 points), KS functional scores (78 vs 78 points), and UCLA activity scores (7.8 vs 7.8) were not significantly different. Mean weight of the polyethylene particles was 0.0219 g (SD, 0.0058) in the Co-Cr femoral component groups and it was 0.0214 g (SD, 0.005) in the OxZr group. This difference was not significant (P=0.711139, paired t-test). The size of particles was not different between the two groups. Also, shape of particles was not different between the two groups. Under the condition and the duration of this study in this specific group of patients, TKA with OxZr or Co-CR femoral knee component had excellent clinical and radiographic outcomes with no osteolysis. While the wear simulator test in vitro demonstrated significant decrease in PE particles in the knees with an OxZr femoral component, our study in vivo revealed that total particle weight, size, and shape of PE wear particles were similar in the knees with an OxZr femoral component and in those with a Co-Cr femoral component

Purpose

The success of total knee replacement (TKR) surgery can be attributed to improvements in TKR design, instrumentation, and surgical technique. Over a decade ago oxidized zirconium (OxZr) femoral components were introduced as an alternative bearing surface to cobalt-chromium (CoCr), based on strong in-vitro evidence, to improve the longevity of TKR implants. Early reports have demonstrated the clinical success of this material however no long-term comparative studies have demonstrated the superiority of OxZr implants compared to a more traditional CoCr implant. This study aims to compare long-term survivorship and outcomes in OxZr and CoCr femoral components in a single total knee design.

Summary Statement

CXCR4 gene and protein expression is regulated in a dose and time-dependent manner by metallic wear debris but not polyethylene wear debris in vitro and in vivo.

A recent French report suggested that cobalt metal ions released from total hip replacements (THRs) were associated with an increased risk of dilated cardiomyopathy and heart failure. If the association is causal the consequences would be significant given the millions of Orthopaedic procedures in which cobalt-chrome is used annually. We examined whether cobalt-chrome containing THRs were associated with an increased risk of all-cause mortality, heart failure, cancer, and neurodegenerative disorders. Data from the National Joint Registry was linked to NHS English hospital inpatient episodes for 375,067 primary THRs with up to 14·5 years follow-up. Implants were grouped as either containing cobalt-chrome or not containing cobalt-chrome. The association between implant construct and the risk of all-cause mortality and incident heart failure, cancer, and neurodegenerative disorders was examined. There were 132,119 individuals (35·2%) with an implant containing cobalt-chrome. There were 48,106 deaths, 27,406 heart outcomes, 35,823 cancers, and 22,097 neurodegenerative disorders. There was no evidence of an association that patients with cobalt-chrome implants had higher rates of any of the outcomes. For all-cause mortality there was a very small survival advantage for patients having a cobalt-chrome implant (restricted mean survival time 13·8=days, 95% CI=6·8-20·9). Cobalt-chrome containing THRs did not have an increased risk of all-cause mortality, heart failure, cancer, and neurodegenerative disorders into the second decade post-implantation. Our findings will reassure clinicians and patients that primary THR is not associated with systemic implant effects