Alessandro Calistri

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 …

The 2012 Otto Aufranc Award: The interpretation of metal ion levels in unilateral and bilateral hip resurfacing.

BackgroundThe interpretation of metal ion concentrations and their role in clinical management of patients with metal-on-metal implants is still controversial.Questions/PurposesWe questioned whether patients undergoing hip resurfacing with no clinical problems could be differentiated from those with clinical (pain, loss of function) and/or radiographic (component malpositioning, migration, bone loss), problems based on metal ion levels, and if there was a threshold metal level that predicted the need for clinical intervention. Furthermore, we asked if patient and implant factors differed between these functional groups.MethodsWe retrospectively identified 453 unilateral and 139 bilateral patients with ion measurements at minimum followup of 12 months (mean, 4.3 years; range, 1–12.9 years). Patients were designated as well functioning or poorly functioning based on strict criteria. The acceptable upper levels within the well-functioning group were determined from the 75th percentile plus 1.5× interquartile range. The sensitivity and specificity of these levels to predict clinical problems were calculated.ResultsWell-functioning group ions were lower than the poorly functioning group ion levels. The acceptable upper levels were: chromium (Cr) 4.6 μg/L, cobalt (Co) 4.0 μg/L unilateral and Cr 7.4 μg/L, Co 5.0 μg/L bilateral. The specificity of these levels in predicting poor function was high (95%) and sensitivity was low (25%). There were more males in the well-functioning group and more females and smaller femoral components in the poorly functioning group.ConclusionsMetal levels higher than these proposed safe upper limits can predict problems with metal-on-metal resurfacings and are important parameters in the management of at-risk patients.Level of EvidenceLevel II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

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.

Italian Version of University of California at Los Angeles (UCLA) Activity Score: Cross-Cultural Adaptation

Over the last 10 years, patient-oriented evaluations using questionnaires have become an important aspect of clinical outcome studies. Any questionnaire must be translated and culturally adapted in order to be used with different language groups, and the translated version must then be evaluated for reliability, validity and responsiveness which are fundamental attributes of any measurement tool. The aim of this study is the validation, translation and cross-cultural adaptation of the Italian version of UCLA activity Score, following the Guillemin criteria. The results show that our Italian version of the UCLA score has the following: reproducibility expressed as ICC=0.994, an internal consistency calculated as Spearman-Brown coefficient=0.754 and finally the construct validity has demonstrated a significant Pearsons correlation coefficient with other validated hip questionnaires.

Hip resurfacing arthroplasty complicated by mismatched implant components

Metal-on-metal hip resurfacing has gained popularity as a feasible treatment option for young and active patients with hip osteoarthritis and high functional expectations. This procedure should only be performed by surgeons who have trained specifically in this technique. Preoperative planning is essential for hip resurfacing in order to execute a successful operation and preview any technical problems. The authors present a case of a man who underwent a resurfacing arthroplasty for osteoarthritis of the left hip that was complicated by mismatched implant components that were revised three days afterwards for severe pain and leg length discrepancy. Such mistakes, although rare, can be prevented by educating operating room staff in the size and colour code tables provided by the companies on their prostheses or implant boxes.

The use of radiography to evaluate hip resurfacing

Abstract: The introduction of hip resurfacing with metal-on-metal bearings required a new standardised radiographic evaluation protocol to assess the clinical performance of the components. This chapter provides detailed methods for pre-operative templating, radiographic technique, and the post-operative evaluation of the acetabular and femoral components with particular emphasis on the measurement of component placement. The radiographic features associated with well-functioning and poorly functioning components are described. A new method for the zonal demarcation of bone surrounding the hip resurfacing is introduced.

The use of bone scintigraphy to evaluate hip resurfacing

Abstract: Bone scintigraphy involves the use of a radiolabelled bone seeking agent. It is a highly sensitive method that can be used for the pre-operative diagnosis of a hip disorder such as avascular necrosis or for the post-operative differential diagnosis between an infection, aseptic loosening or soft tissue reaction. This chapter describes the bone scan features of a normal hip and different hip diseases as well as normal and pathological findings after a total hip replacement and a hip resurfacing.