Koen Smet

Abstract: The comparison of hip resurfacing arthroplasty (HRA) with total hip arthroplasty (THA) seems straightforward since both procedures are performed to treat diseases of the hip joint. However, besides biomechanical distinctions, differences in indications, treatment timing, surgical experience and technique have been demonstrated. This chapter compares the outcomes of HRA and THA from a clinical, radiographic and survivorship point of view focusing especially on the group of young and/or active patients for whom HRA was primarily developed. Objective, multi-factorial weighing of the current knowledge leads to the conclusion that hip resurfacing is the better reconstructive option for specific patient groups such as young and active males with osteoarthritis. Other patient groups such as females or patients with anatomic deformities should be assessed thoroughly and considered as HRA candidates with certain reservations.

Postoperative dislocations are known to be a big problem in revision surgery. In literature dislocation rates vary from 4.8% to 33% after previous surgery. In revision surgery, impingement of the implant components, the capsular and soft tissue release, muscular weakness and greater trochanter problems can give additional instability. The reason for revision is important, where instability, infection and tumour cases will lead to a higher percentage of dislocations. The use of big metal heads on polyethylene should be avoided because of the higher volumetric wear. With the new developments of metal-on-metal hip resurfacing and the production of big modular metal heads, the metal-on-metal bearing should guarantee a low-wear result without osteolysis. Between November 2000 and December 2003 45 patients requiring a revision were treated with a Birmingham Hip Resurfacing cup (MMT, UK) and a big metal-on-metal modular head. All surgery was done with a posterolateral approach. Cup sizes r...

Introduction: The purpose of this retrospective study is to compare long-term whole blood metal ion concentrations (Co, Cr, Ni, Mo) between two different metal-on-metal total hip arthroplasties and a metal-on-polyethylene control group, in relationship with physical activity. Materials and methods: Between 1996 and 2000, different conventional prosthetic designs were implanted at our hospital. For this study, three groups were chosen according to the bearing surfaces used. Patients who had undergone other surgical interventions with implantation of potential sources of Cr/Co were excluded. Patients taking medication or dietary supplements containing Cr/Co were also excluded. In group 1, 17 patients with a 28 mm metal-on-metal bearing, type Metasul (Zimmer), were included. Group 2 comprised 11 patients with a 28 mm metal-on-metal bearing, type M2a (Biomet). The control group consisted of 9 patients with a 28 mm metal-on-polyethylene bearing in combination with a cemented CoCr stem. T...

INTRODUCTION Metal-on-metal hip resurfacing arthroplasty (MoMHRA) is a surgical option in the treatment of end-stage hip disease. The measurement of systemic levels of metal ions gives an insight into the wear occurring and is advocated by regulatory bodies as routine practice in the assessment of resurfaced hips. However, the acceptable upper levels of Chromium (Cr) and Cobalt (Co) ions concentration with clinical significance still have to be established. The aim of this study is to address this issue in unilateral and bilateral resurfaced hips. METHODS 453 patients with unilateral MoMHRA and 139 patients with bilateral MoMHRA at >12 months postoperative were retrospectively identified from an independent hip specialist9s database. Routine metal ion levels were measured at last follow-up (ICPMS protocol). Radiological assessment included measurement of acetabular component orientation using EBRA, calculation of contact patch to rim (CPR) distance, and evaluation for any adverse X-ray findings. The cohort was divided into the well functioning group (Group A) and the non-well functioning group (Group B). A well functioning resurfacing gad to fulfil all of the following criteria (bilateral patients had to fulfil criteria for both hips): no patient reported hip complaints, no surgeon detected clinical findings, HHS> 95, CPR distance> 10mm, no abnormal radiological findings and no further operation scheduled. Upper levels (acceptable limits) of Cr/Co were considered to be represented by the top margin of the box-whisker plot [upper limit = 75 th quartile value + (1.5 x interquartile range)] in Group A. RESULTS 251 unilateral MoMHRAs patients (55%) and 58 patients with bilateral MoMHRAs (42%) comprised Group A. The majority of males were in Group A compared to the majority of females who belonged in Group B (p The upper levels (safe were: Cr: 4.6µg/l / Co: 4.0µg/l for unilateral MoMHRAs and Cr: 7.4µg/l / Co: 5.0µg/l for bilateral MoMHRAs. Unilateral MoMHRAs had significantly higher ion levels compared to bilateral patients (p DISCUSSION The findings of this study suggest that both unilaterally and bilaterally resurfaced patients with well functioning implants have low metal ion levels with upper levels of Cr: 4.6µg/l / Co: 4.0µg/l for unilateral MoMHRAs and Cr: 7.4µg/l / Co: 5.0µg/l for bilateral MoMHRAs These results indicate that the upper acceptable limit of metal ion levels in resurfaced hips is lower than the previously MHRA recommended threshold, however the study was conducted with very low tolerance for what was considered a clinically problematic hip. Well-functioning bilateral resurfacing have higher ion levels compared to well-functioning unilateral resurfacing.

Surface arthroplasty or resurfacing represents a significant development in the evolution of hip replacement. A hip resurfacing arthroplasty (HRA) is a bone conserving alternative to total hip arthroplasty (THA) that restores normal joint biomechanics and load transfer and ensures joint stability. Metal-on-metal (MoM) bearings have been preferred for these large diameter articulations because of their lower volumetric wear and smaller particulate debris compared to metal-on-poly-ethylene bearings. Of the many engineering factors which have contributed to the success of the MoM bearing, the metallurgy, diametral clearance, sphericity and surface finish were thought to be most important. More recently, adverse reactions to metal particles and ions generated by wear and corrosion of the metal surfaces have focused the attention on the importance of coverage angle and cup positioning. Currently, the scientific consensus is that cup coverage angle, diametral clearance and metallurgy have their importance in that order. Precise understanding of manufacturing variables is imperative in obtaining clinical consistency and safety in the patient. It is important to examine femoral fixation, bone remodelling, and wear of MoM implants. For the second and third generation MoM HRA various designs and biomaterials have been used. We have conducted a randomised, controlled trial comparing 9 different hip resurfacing prostheses. Clinical and radiographic outcome and whole blood, serum and urine metal ion levels are evaluated at 6 months, 1 year and 2 years in 180 patients with 9 different HRA designs and the differences are analyzed. Besides, the design quality of the 9 different metal-on-metal prostheses and their accessory instruments have been judged during the operation. The Durom with its Metasul history may claim a metallurgic advantage, and in combination with the highest coverage angle of all cups, it may be the best wear couple, as suggested by low ion measurements. However, as discussed above, an optimal bearing alone is not sufficient to achieve a successful hip resurfacing.

Introduction Hip resurfacing (HRA) designer centres have reported survivorships between 88.5–96% at 12 years. Arthroplasty Registries (AR) reported less favourable results especially in females gender and small sizes. The aim of this study was to evaluate the minimum 10-year survival and outcome of the Birmingham Hip Resurfacing (BHR) from an independent specialist centre. Methods Since 1998, 1967 BHRs have been implanted in our centre by a single hip resurfacing specialist. The first 249 BHR, implanted between 1999 and 2001 in 232 patients (17 bilateral) were included in this study. The majority of the patients were male (163; 69%). The mean age at surgery was 50.6 years (range: 17–76), with primary OA as most common indication (201; 81%), followed by avascular necrosis (23; 9.2%) and hip dysplasia (11; 4.4%). Mean follow up was 10.2 years (range: 0.1 (revision) to 13.1). Implant survival was established with revision as the end point. Harris Hip Scores (HHS), radiographs and metal ion levels were assessed in all patients. Sub-analysis was performed by gender, diagnosis and femoral component size (Small: Results Of the 232 patients, 15 were deceased (4 bilateral BHR), 16 lost to follow-up and 9 revised. 205 BHR were evaluated at minimum 10 years postoperatively. Failure modes included 2 component malpositioning, 2 loose femoral heads, 1 fracture, 1 metal sensitivity, 2 impingement and 1 with high metal ions. The overall survival was 95.1% (95% CI: 93.6–96.6) at 12.8 years. The mean HHS was 97.8 (range: 65–100). Survivorship in men was 98.6% (95%CI: 97.4–99.8%) at 13 years. Survivorship in women was inferior to men (log rank = 0.003): 87.9% (95%CI: 84.3–91.5%) at 12 years. There was no difference in HHS between genders in the non-revised cases (p = 0.46). There was no difference in survivorship with different pre-operative diagnosis (log-rank = 0.83) but a significant difference in 12-year survivorship between Small (90.1%) and Large components (97.2%) (log rank = 0.01). After adjusting for head size, the difference in survival between males and females was no longer significant (log-rank = 0.125). The median ion levels were Cr:2.0μg/l; Co:1.0μg/l. In 24 patients the ion levels were undetectable. Four patients (1.9%) had ions above the upper acceptable limits of Cr:4.6μg/l;Co:4.0μg/l for unilateral or Cr:7.4μg/l;Co:5.0μg/l for bilateral HRA. In 67 patients with consecutive ion measurements, levels decreased significantly with time with a mean decrease of 0.97μg/l for Cr and 0.60μg/l for Co. Discussion This study reports the more than 10-year survival of BHR and reflects an experienced specialist9s practice, including his learning curve of the procedure. The overall 12.8-year survival was superior to registry reported figures of THA amongst young patients and corresponded well with reports from designer centres. Survivorship and clinical outcome were excellent in men. In women survivorship was significantly inferior and related to smaller component sizes, but the >10-year clinical outcome in non-revised cases was excellent. In well-functioning BHR, the metal ions decrease significantly with time. The results of this study support the use of HRA with a good design.

Background: Potential systemic toxicity of metal ions from metal-on-metal hip arthroplasties (MoMHA) is concerning. High blood cobalt (Co) levels have been associated with neurological, cardiac and thyroid dysfunctions. Questions/purposes: The aim of this research was to investigate the prevalence of systemic Co toxicity in a MoMHA population, to identify confounding factors, and to indicate a Co level above which there is a high risk for systemic toxicity. Patients and Methods: We conducted a cross-sectional study of patients with a MoMHA, using questionnaires validated to detect cobaltism in cobalt industry workers. We retrospectively identified 161 patients with Co levels >4 μg/L and 337 patients with Co levels 20 μg/L groups. Results: There were significant correlations (p ≤ 0.003) between increasing Co levels and prevalence of sleeping disorders, cognitive problems, equilibrium disturbances, neuropathic symptoms, fatigue, somatic disorders and mood changes. More frequent and severe symptoms were found with Co > 20 μg/L (p = 0.017). Several years post-revision, some patients still complained of chronic symptoms possibly associated with longer exposure. Female gender and age ≤50 years were confounding factors. Conclusions: We demonstrated a correlation between increasing Co levels and toxicity symptoms (p ≤ 0.003). As in the published case reports of MoMHA related cobaltism, the highest incidence of symptoms was found with Co > 20 μg/L. Patients with repeated Co measurements >20 μg/L are at risk for systemic toxicity.

Introduction Tribological studies have described a characteristic wear pattern of metal-on-metal hip resurfacings (MoMHRAs) with a run-in period followed by a ‘bedding-in’ phase minimising wear or by an increasing wear patch with edge loading. The use of metal ions as surrogate markers of in-vivo wear is now recommended as a screening tool for the performance of MoMHRAs. The aims of this retrospective, single-surgeon study were to measure ion levels in unilateral MoMHRAs at different stages during the steady-state in order to study the evolution of wear and factors affecting it. Methods 218 consecutive patients with minimum two serum ion measurements were included. The mean age at surgery was 52.3 years, the first assessment was made at a mean of 2.5 years (11 months–8 years) and the last assessment at a mean of 4.6 years post resurfacing (2– 12 years). Ion level change was defined as Ion level at last assessment minus Ion level at first assessment. Ten different resurfacing designs were implanted, the majority being BHR (n=104), Conserve plus(n=55) and ASR (n=25). The median femoral component size was 50 mm (38–59mm). Radiological assessment of acetabular component orientation was made with EBRA. Results For the whole cohort a significant reduction in Chromium (Cr) levels between initial [2.6 μg/ml (SD: 6.8)] and last assessment [1.9 μg/ml (SD: 8.3)] was found (p= 0.004). Cobalt (Co) levels were similar at initial [1.7 (SD: 7.7)] and last [1.8 (SD: 10.6)] follow-up (p=0.78). Cr levels increased in 31% and Co increased in 46% of patients. There was a significant ion level increase in 5% of patients. There was no significant difference between genders (p= 0.4) or implant designs (p = 0.07), but a trend of higher ions at last follow up with the ASR implants in comparison to BHR and C+. Neither component size (p=0.4) nor acetabular orientation (p=0.46) correlated with change in ion levels. However, a CPR distance (contact patch-rim) of Discussion The analysis of the evolution of ion levels in unilateral hip resurfacing after the run-in phase demonstrates an overall decrease of Cr levels but no significant change in Co levels. This in vivo finding is consistent with tribocorrosion studies showing the formation of a passive protective film on the articulating surfaces after the initial wear-in, preventing further corrosion. From that point on, provided there is no edge loading causing increased surface wear, ions are mainly formed by corrosion of the particulate debris generated during the run-in phase. In vitro studies have shown a higher dissolution of the more soluble Co from the debris while Cr remains in solid form with less ion formation. In a number of cases in our study, ion levels continued to increase, indicating ongoing surface wear. These increasing ion levels were correlated with a lower coverage angle more prone to edge loading and with the development of clinical symptoms.

Recently, a new generation of metal-on-metal total hip resurfacing arthroplasty devices has been introduced with the aim of preserving proximal femoral bone stock, minimizing the risk of postoperative dislocation of large femoral heads and reducing wear of the articulation for longer prosthetic survivorship. Resurfacing arthroplasty also has the advantage of ensuring a more biomechanical loading pattern of the proximal femur.

The difference in outcome after uncemented ceramic-on-ceramic total hip and metal-on-metal resurfacing is looked at in comparable patient groups. Theoretical advantages in resurfacing are less bone resection, normal femoral loading, avoidance of stress shielding and restoration of normal anatomy. In addition, reduced risk of dislocation, less leg lengthening and easier revision should convince us to perform metal-on-metal resurfacing. These advantages of resurfacing, the subjective “better feeling” and having a more “normal” joint is illustrated by objective proof with functional scores and activity. The first 250 cases of 1067 (September 1998 –March 2004) performed Birmingham Hip resurfacings (MMT, UK) (follow up 2–5 years, mean age 49.54) were scored clinically and functionally. In the same period (July 1996 – September 2003) 164 ceramic-on-ceramic Ancafit total uncemented prostheses (Wright Medical, US) were implanted inthe same age and activity group as the resurfacings. The fir...

INTRODUCTION Metal-on-metal hip resurfacing (MoMHRA) requires a new standardized radiographic evaluation protocol. Evaluation of the acetabular component is similar to total hip arthroplasty but the femoral component requires different criteria since there is no component in the femoral canal and the metallic femoral implant overlies the junctions between bone-cement and cement-prosthesis. Lucencies around the metaphyseal HRA femoral stem can be described with the femoral zonal system into 3 peg-zones (Amstutz9 et al) but this doesn9t account for bony changes of the femoral neck away from the stem. This study proposes a new femoral zonal system for radiographic HRA assessment. We tested the efficacy of radiographs in identifying a problem by reviewing 711 radiographs of resurfaced hips and correlating radiographic features to outcome. METHODS 611 in-situ HRA (one surgeon) with minimum two radiographs at >12 months postoperatively and 100 revised HRA (55 referred) were assessed for component positioning, reactive lines±cortical thickening±cancellous condensation (borderline) and lucent lines±osteolysis±bone resorption (sinister). Findings around the acetabular implant were classified in six zones: Zones I-III equally distributed acetabular zones (DeLee-Charnley); Zone IV, V and VI situated in the iliac, pubic and ischial bone respectively. Findings around the proximal femur are defined with a new zonal system, dividing the implant-cement-bone interfaces and the femoral neck into 7 areas. Zones 1,7 at the superior and inferior part of the femoral neck-head, zones 2,3 at the proximal and distal halves of the superior aspect of the stem, zone 4 at the tip, zones 5,6 at the distal and proximal inferior aspects of the stem). Radiological findings and zones were correlated with gender, size, survival, Harris Hip Scores (HHS), metal ions, and adverse soft tissue reactions (ALTR). RESULTS Radiological changes were found in 260 cases (36.7%), 151 sinister (21.2%) and 110 borderline (15.5%). 82% of revisions had sinister findings versus 11.3% of in-situ HRA (p 3 4 zones had a sensitivity of 50% and specificity of 94.2% (AUC=0.898) in detecting hips with ALTR (risk ratio=19.6). DISCUSSION Radiographic assessment of HRA provides valuable information: 82% of problematic hips had sinister changes and 90.4% of cases with proven ALTR. In order to accurately evaluate progressive radiographic changes in HRA, specific zones have been established around the HRA femoral component. There was a high correlation between radiographic findings, clinical outcome and metal in levels. However, the absence of sinister radiologic findings does not eliminate a problematic HRA and further investigations (ion levels, imaging) would be indicated in symptomatic patients.

The surgical treatment of young adults with end-stage hip disease has been a challenge. Inferior THA survival in the young, perceived advantages of hip resurfacing versus THA and advancements in tribology, led to the introduction of 3rd generation Metal-on-Metal-Hip-Resurfacing-Arthroplasty (MoMHRA). To-date, thousands of such prostheses have been implanted worldwide in younger patients, yet little is known regarding long-term outcome. The only studies reporting greater than 10 year outcome come from designer centres with survivorship varying between 88.5–96% at 12 years. Arthroplasty Registries (AR) have reported less favourable survivorships with female gender and size having a negative effect on survival. In our independent hip resurfacing centre in Ghent, Belgium, a single surgeon has implanted more than 3500 HRA over more than 12 years. A cohort of 149 patients who received a Birmingham Hip Resurfacing (BHR) at a mean age of 50 years at surgery have now reached a minimum 10 years follow-up. The overall 12-year survival in these young adults is 93.1% (95% CI: 88.3–98.0), 99% in males and 87.3% in females. These survivorship data are superior to registry reported figures of THA amongst young patients and correspond well with previous reports from designer centres. The long-term survivorship and clinical outcome of the BHR are excellent in men, uninfluenced by preoperative diagnosis or age. However, survivorship in women is inferior and usually related to increased wear and reactions to metal debris. Malpositioning of components with associated wear-induced soft tissue fluid collections is the most frequent factor leading to failure of a HRA. In our experience, mid-term outcome following revision is good and complication and re-revision rates can be low. Surgical experience, early intervention in cases of mal-positioned implants, clinical use of ion levels, implantation of larger ceramic-on-ceramic THA femoral heads and patient education are factors in improving outcome and reducing complication and re-revisions following HRA revision.

Introduction Metal-on-metal hip resurfacings (MoMHRAs) have a characteristic wear pattern initially characterised by a run-in period, followed by a lower-wear steady-state. The use of metal ions as surrogate markers of in-vivo wear is now recommended as a screening tool for the in-vivo performance of MoMHRAs. The aims of this retrospective study were to measure ion levels in MoMHRAs at different stages during the steady-state in order to study the evolution of wear at minimum 10 years postoperatively and describe factors that affect it. Materials and methods A retrospective study was conducted to investigate the minimum 10-year survivorship of a single-surgeon Birmingham Hip Resurfacing (BHR) series, and the evolution of metal ion levels. Implant survival, Harris Hip Scores (HHS), radiographs and serum metal ion levels were assessed. The evolution of metal ion levels was evaluated in 80 patients for whom at least two ion measurements were available at more than 12 months postoperatively, i.e. past the run-in phase. Ion level change (Delta Cr; Delta Co) was defined as Cr or Co level at last assessment minus Cr or Co level at initial assessment. Sub-analysis was performed by gender, diagnosis, age, femoral component size and cup inclination angle. Results Overall Cr and Co levels were low (Cr: 1.3 μg/L; Co: 1.0 μg/L for unilateral and Cr: 3.2 μg/L; Co: 2.3 μg/L for bilateral resurfacings) and decreased significantly (p 2.5 μg/L, associated with head sizes £50 mm and with clinical symptoms and high cup inclination angles. There was no significant difference in the change of ion levels between genders (Cr: p = 0.845; Co: p = 0.310) although Cr levels at initial and last assessments were higher in females (p = 0.008). Component size did not correlate with change in ion levels (Cr: p = 0.505; Co: p = 0.370). Patients with increased ion levels at follow-up had lower Harris Hip Scores (p = 0.038). Discussion Low serum Cr and Co ion levels were found in patients with well-functioning unilateral and bilateral MoMHRA. In well-functioning MoMHRA ion levels continue to be low even after 3 10 years in situ. In this series, there were no symptomatic patients with low metal ion levels. Increasing metal ion levels >10 μg/l were invariably associated with poorly functioning MoMHRA. The analysis of consecutive ion levels demonstrated a statistically significant overall decrease of Cr and Co levels with time in well-functioning BHR. In 25% of patients ion levels were undetectable at 3 10 years postoperatively. Our data are in accordance with tribocorrosion studies indicating a lower-wear bedding-in phase after the initial running-in phase of higher wear. An increase in ion levels after the run-in phase is an indication of continued surface wear which may eventually lead to implant failure potentially associated with soft tissue and bone destruction.

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 Pearson's correlation coefficient with other validated hip questionnaires.

The purpose of this study was to compare clinical outcomes between ceramic-on-ceramic total hip replacement and metal-on-metal hip resurfacing arthroplasty in comparable groups of young active patients at a 3- to 6-year follow-up. The first 250 patients (mean age, 49.54 years) of a series of 930 resurfacing arthroplasties were compared clinically and functionally with a series of 190 patients (mean age, 46.76 years) with ceramic-on-ceramic uncemented total hip prostheses. The total Harris hip score was 97.9 in the resurfacing group vs 92.1 in the ceramic group. In the resurfacing group, 60.71% had a strenuous activity level vs 30.43% in the ceramic group.

Hip resurfacing arthroplasty has increased in popularity as a viable treatment option for young, active patients with osteoarthritis that find in this procedure the real option to return to their old habits of life. Early literature show that resurfacing hip arthroplasty patients had kinematics and kinetics (abduction moments, extension moments, and walking velocities) that approached normal values for patients without hip osteoarthritis. Many of the technical problems that affected resurfacing implants have been identified and resolved with improved engineering and manufacturing techniques. At the present time, failure for THA for all diagnoses in patients younger than fifty years old, as reported by the Swedish Arthroplasty Registry, was associated with a ten-year survival rate of 85%. In contrast HRA failure for any reason is rare and the ten-year survival rate from the best cohort were 95.5%- 96.1%. We do agree hip resurfacing arthroplasty only finds its place in high volume cen...

We report the consensus of surgical opinions of an international faculty of expert metal-on-metal hip resurfacing surgeons, with a combined experience of over 18,000 cases, covering required experience, indications, surgical technique, rehabilitation and the management of problematic cases.

This paper reports the consensus of an international faculty of expert metal-on-metal (MoM) hip resurfacing surgeons, with a combined experience of over 40,000 cases, on the current status of hip resurfacing arthroplasty. Indications, design and metallurgy issues, release of metal ions and adverse soft tissue reactions to particles, management of problematic cases and revisions, as well as required experience and training are covered. The overall consensus is that MoM hip resurfacing should not be banned and should be viewed separately from MoM total hip arthroplasty (THA) with a large diameter head because of the different design and wear behaviour related to the taper/trunnion connection. The use of hip resurfacing has decreased worldwide but specialist centres continue to advocate hip resurfacing in young and active male patients. Regarding age the general recommendation is to avoid hip resurfacing in men older than 65 and in women older than 55, depending on the patient activity...