K. De Smet

Correlation between inclination of the acetabular component and metal ion levels in metal-on-metal hip resurfacing replacement.

We examined the relationships between the serum levels of chromium and cobalt ions and the inclination angle of the acetabular component and the level of activity in 214 patients implanted with a metal-on-metal resurfacing hip replacement. Each patient had a single resurfacing and no other metal in their body. All serum measurements were performed at a minimum of one year after operation. The inclination of the acetabular component was considered to be steep if the abduction angle was greater than 55 degrees. There were significantly higher levels of metal ions in patients with steeply-inclined components (p = 0.002 for chromium, p = 0.003 for cobalt), but no correlation was found between the level of activity and the concentration of metal ions. A highly significant (p < 0.001) correlation with the arc of cover was found. Arcs of cover of less than 10 mm were correlated with a greater risk of high concentrations of serum metal ions. The arc of coverage was also related to the design of the component and to size as well as to the abduction angle of the acetabular component. Steeply-inclined acetabular components, with abduction angles greater than 55 degrees, combined with a small size of component are likely to give rise to higher serum levels of cobalt and chromium ions. This is probably due to a greater risk of edge-loading.

Adverse reaction to metal debris following hip resurfacing: the influence of component type, orientation and volumetric wear.

We sought to establish the incidence of joint failure secondary to adverse reaction to metal debris (ARMD) following metal-on-metal hip resurfacing in a large, three surgeon, multicentre study involving 4226 hips with a follow-up of 10 to 142 months. Three implants were studied: the Articular Surface Replacement; the Birmingham Hip Resurfacing; and the Conserve Plus. Retrieved implants underwent analysis using a co-ordinate measuring machine to determine volumetric wear. There were 58 failures associated with ARMD. The median chromium and cobalt concentrations in the failed group were significantly higher than in the control group (p < 0.001). Survival analysis showed a failure rate in the patients with Articular Surface Replacement of 12.8% [corrected] at five years, compared with < 1% at five years for the Conserve Plus and 1.5% at ten years for the Birmingham Hip Resurfacing. Two ARMD patients had relatively low wear of the retrieved components. Increased wear from the metal-on-metal bearing surface was associated with an increased rate of failure secondary to ARMD. However, the extent of tissue destruction at revision surgery did not appear to be dose-related to the volumetric wear.

Metal Ion Measurement as a Diagnostic Tool to Identify Problems with Metal-on-Metal Hip Resurfacing

Metal-on-metal bearings for hip replacement are gaining popularity as an alternative to the most widely used bearing couple of metal on polyethylene1. The recent resurgence of hip resurfacing with the so-called third and fourth generations of hip resurfacing arthroplasty devices has played a substantial role in the wider use of metal-on-metal bearings2-4. Concerns about the wear of polyethylene and the role of polyethylene wear debris in the process of aseptic loosening have also increased the use of hard-on-hard bearing couples. However, wear still takes place with metal-on-metal bearings, and there is concern about the relatively high levels of metallic ions released into the body as a consequence. Cobalt-chromium alloy is the metal used for metal-on-metal implants and, while these elements are required for normal biological function, high concentrations of cobalt and chromium are toxic and are known to interfere with a number of biological processes5,6. The metal ion levels typically seen in patients with well-functioning metal-on-metal implants are not thought to be close to toxic levels7 and in many instances are not much higher than those in patients with metal-on-polyethylene implants8. However, there is a potential for much higher concentrations of metal wear products in the joint fluid in the vicinity of the bearing surfaces of poorly functioning metal-on-metal implants. It is these very high levels that are thought to be responsible for adverse reactions such as osteolysis9 and the formation of soft-tissue masses10,11 and that give rise to metallosis (defined as gray discoloration of the hip joint)12. It is not clear whether the levels of metal ions measured in blood serum are indicative of the metal ion concentrations in the joint fluid. Perhaps more importantly, the serum concentrations that are …

Revision of metal-on-metal resurfacing arthroplasty of the hip: THE INFLUENCE OF MALPOSITIONING OF THE COMPONENTS

We have reviewed 42 patients who had revision of metal-on-metal resurfacing procedures, mostly because of problems with the acetabular component. The revisions were carried out a mean of 26.2 months (1 to 76) after the initial operation and most of the patients (30) were female. Malpositioning of the acetabular component resulted in 27 revisions, mostly because of excessive abduction (mean 69.9 degrees ; 56 degrees to 98 degrees ) or insufficient or excessive anteversion. Seven patients had more than one reason for revision. The mean increase in the diameter of the component was 1.8 mm (0 to 4) when exchange was needed. Malpositioning of the components was associated with metallosis and a high level of serum ions. The results of revision of the femoral component to a component with a modular head were excellent, but four patients had dislocation after revision and four required a further revision.

Fluorine-18 fluorodeoxyglucose-positron emission tomography: A highly accurate imaging modality for the diagnosis of chronic musculoskeletal infections.

Background: The noninvasive diagnosis of chronic musculoskeletal infections remains a challenge. Recent studies have indicated that fluorine-18 fluorodeoxyglucose-positron emission tomography is a highly accurate imaging technique and is significantly more accurate than the combination of a bone scan and a white blood-cell scan for the diagnosis of chronic infection in the central skeleton (p < 0.05). However, patients who had had surgery within the previous two years were excluded from study. It was our aim to evaluate the technique in an unselected, clinically representative population. Methods: Sixty patients with a suspected chronic musculoskeletal infection involving the central skeleton (thirty-three patients) or the peripheral skeleton (twenty-seven patients) were studied with fluorine-18 fluorodeoxyglucose-positron emission tomography. Thirty-five patients had had surgery within the previous two years. The fluorine-18 fluorodeoxyglucose-positron emission tomography studies were read in a blinded, independent manner by two experienced readers. The final diagnosis was based on histopathological studies or microbiological culture (eighteen patients) or on clinical findings after at least six months of follow-up (forty-two patients). Results: On the final composite assessment, twenty-five patients had infection and thirty-five did not. All twenty-five infections were correctly identified by both readers. There were four false-positive findings; in two of these cases, surgery had been performed less than six months prior to the study. The sensitivity, specificity, and accuracy were 100%, 88%, and 93% for the whole group; 100%, 90%, and 94% for the subgroup of patients with a suspected infection of the central skeleton; and 100%, 86%, and 93% for the subgroup of patients with a suspected infection of the peripheral skeleton. Interobserver agreement was excellent (kappa = 0.97). Conclusions: Fluorine-18 fluorodeoxyglucose-positron emission tomography is highly accurate as a single technique for the evaluation of chronic musculoskeletal infections. It is especially valuable in the evaluation of the central skeleton, where white blood-cell scans are less useful. Because of its simplicity and high degree of accuracy, it has the potential to become a standard technique for the diagnosis of chronic musculoskeletal infections. Further studies are needed to assess its ability to identify infections at the sites of total joint replacements and to distinguish infection from aseptic loosening of these prostheses.

Reduction of the potential for thermal damage during hip resurfacing

Resurfacing arthroplasty of the hip is being used increasingly as an alternative to total hip replacement, especially for young active patients. There is concern about necrosis of the femoral head after resurfacing which can result in fracture and loosening. Most systems use a cemented femoral component, with the potential for thermal necrosis of the cancellous bone of the reamed femoral head. We used thermal probes to record temperatures close to the cement-bone interface during resurfacing arthroplasty. The maximum temperature recorded at the cement-bone interface in four cases was approximately 68 degrees C which was higher than that reported to kill osteocytes. A modified surgical technique using insertion of a suction cannula into the lesser trochanter, generous pulsed lavage and early reduction of the joint significantly reduced the maximum recorded cancellous bone temperature to approximately 36 degrees C in five cases (p = 0.014). We recommend the modified technique since it significantly reduces temperatures at the cement-bone interface.

Early results of primary Birmingham hip resurfacing using a hybrid metal-on-metal couple

None.

Metal ion levels from well-functioning Birmingham Hip Resurfacings decline significantly at ten years

A retrospective study was conducted to investigate the changes in metal ion levels in a consecutive series of Birmingham Hip Resurfacings (BHRs) at a minimum ten-year follow-up. We reviewed 250 BHRs implanted in 232 patients between 1998 and 2001. Implant survival, clinical outcome (Harris hip score), radiographs and serum chromium (Cr) and cobalt (Co) ion levels were assessed. Of 232 patients, 18 were dead (five bilateral BHRs), 15 lost to follow-up and ten had been revised. The remaining 202 BHRs in 190 patients (136 men and 54 women; mean age at surgery 50.5 years (17 to 76)) were evaluated at a minimum follow-up of ten years (mean 10.8 years (10 to 13.6)). The overall implant survival at 13.2 years was 92.4% (95% confidence interval 90.8 to 94.0). The mean Harris hip score was 97.7 (median 100; 65 to 100). Median and mean ion levels were low for unilateral resurfacings (Cr: median 1.3 µg/l, mean 1.95 µg/l (< 0.5 to 16.2); Co: median 1.0 µg/l, mean 1.62 µg/l (< 0.5 to 17.3)) and bilateral resurfacings (Cr: median 3.2 µg/l, mean 3.46 µg/l (< 0.5 to 10.0); Co: median 2.3 µg/l, mean 2.66 µg/l (< 0.5 to 9.5)). In 80 unilateral BHRs with sequential ion measurements, Cr and Co levels were found to decrease significantly (p < 0.001) from the initial assessment at a median of six years (4 to 8) to the last assessment at a median of 11 years (9 to 13), with a mean reduction of 1.24 µg/l for Cr and 0.88 µg/l for Co. Three female patients had a > 2.5 µg/l increase of Co ions, associated with head sizes ≤ 50 mm, clinical symptoms and osteolysis. Overall, there was no significant difference in change of ion levels between genders (Cr, p = 0.845; Co, p = 0.310) or component sizes (Cr, p = 0.505; Co, p = 0.370). Higher acetabular component inclination angles correlated with greater change in ion levels (Cr, p = 0.013; Co, p = 0.002). Patients with increased ion levels had lower Harris hip scores (p = 0.038). In conclusion, in well-functioning BHRs the metal ion levels decreased significantly at ten years. An increase > 2.5 µg/l was associated with poor function.

Metal ion levels in a triathlete with a metal-on-metal resurfacing arthroplasty of the hip

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.

Pelvic position and movement during hip replacement

The orientation of the acetabular component is influenced not only by the orientation at which the surgeon implants the component, but also the orientation of the pelvis at the time of implantation. Hence, the orientation of the pelvis at set-up and its movement during the operation, are important. During 67 hip replacements, using a validated photogrammetric technique, we measured how three surgeons orientated the patients pelvis, how much the pelvis moved during surgery, and what effect these had on the final orientation of the acetabular component. Pelvic orientation at set-up, varied widely (mean (± 2, standard deviation (sd))): tilt 8° (2sd ± 32), obliquity -4° (2sd ± 12), rotation -8° (2sd ± 14). Significant differences in pelvic positioning were detected between surgeons (p < 0.001). The mean angular movement of the pelvis between set-up and component implantation was 9° (sd 6). Factors influencing pelvic movement included surgeon, approach (posterior > lateral), procedure (hip resurfacing > total hip replacement) and type of support (p < 0.001). Although, on average, surgeons achieved their desired acetabular component orientation, there was considerable variability (2sd ± 16) in component orientation. We conclude that inconsistency in positioning the patient at set-up and movement of the pelvis during the operation account for much of the variation in acetabular component orientation. Improved methods of positioning and holding the pelvis are required.