Radiographically undetectable periprosthetic osteolysis with ASR implants: the implication of blood metal ions

Isolated acetabular cup revision in Metal-on-Metal total hip arthroplasty: a low-complication strategy feasible in only half of cases

PURPOSE

There is still a debate regarding the removal of the femoral stem due to the risk of trunnion. To answer this question, we conducted a study to compare long terms outcomes of isolated acetabular to total revision of MoM THA using an institutional arthroplasty registry.

METHODS

From 1996 to 2019, 150 patients (12.5%) of the 1202 revision THAs (rTHA) recorded in Geneva Arthroplasty Registry (GAR) underwent a revision of a MoM THA. After matching the two groups,126 patients were finally included: 63 in each group. The mean age was 64.4 (SD 11.6) years, 48.4% (61/126) were women with a mean BMI of 27.2 (SD 5.5) Kg/m2.

RESULTS

The overall survival rate was 88.1% [79.9-97.2%] at ten years. 10-year survival rate was 93.5% [86.2-100.0%] after isolated acetabular rTHA and 79.5% [61.7-100.0%] after total rTHA (p = 0.16). Regarding Hip Harris score and Merle d'Aubigne score, no difference at last follow-up was observed between the two groups (respectively: p = 0.39; p = 0.33). Regarding the chrome, cobalt, and nickel level reduction, no difference was observed between the two groups (respectively, p = 0.38, 0.81 and 0.97).

CONCLUSION

No difference was observed between isolated acetabular and total revision of MoM THAs regarding survival rate and ions levels at long term. It seems advisable to perform an isolated acetabular revision of a MoM THA when it is indicated.

LEVELS OF EVIDENCE

Level III, case control studies.

Radiographic evaluation of hip resurfacing: the role of x-rays in the diagnosis of a problematic resurfaced hip

INTRODUCTION

Hip resurfacing (HRA) requires a new standardised radiographic evaluation protocol. Evaluation of acetabular components is similar to total hip arthroplasty (THA) but femoral components require different criteria. This study evaluates the efficacy of a new femoral zonal system for radiographic HRA assessment in identifying clinical problems.

METHODS

A new proximal femoral zonal system divides implant-cement-bone interfaces at head and neck into 7 DeSmet zones. 611 in situ and 100 revised HRA were assessed for component positioning, borderline findings (reactive lines, cortical thickening, cancellous condensation) or sinister findings (lucent lines, bone resorption, osteolysis). Findings were correlated with gender, size, implant survival, clinical scores, metal ions, and adverse soft tissue reactions (ALTR).

RESULTS

Radiological changes were found in 265 hips (37.3%), 154 sinister (21.7%) and 111 borderline (15.6%). 84% of revisions had sinister findings versus 11.4% of in situ HRA (p < 0.001). The mean number of abnormal acetabular and femoral zones was 3.3 in revised compared to 0.6 in situ HRA (p < 0.001). Sinister findings were associated with female gender, lower clinical scores, smaller sizes or ASR design (all: p < 0.001). Metal ions were higher with sinister (p < 0.001) and borderline (p < 0.01) findings compared to normal radiographs. Pathological findings in ⩾4 zones had a sensitivity of 50% and specificity of 94.2% (AUC = 0.898) in detecting hips with ALTR (odds ratio = 49).

CONCLUSION

In order to accurately evaluate progressive radiographic changes in HRA, specific zones have been established around the femoral component. There was a high correlation between radiographic findings and outcome measures. 84% of problematic hips and 90.4% of proven ALTR had sinister changes.

Ultrasound-based decision making following metal-on-metal hip arthroplasty

BACKGROUND

Metal-on-Metal (MoM) total hip arthroplasty (THA) represents a very controversial procedure because of the possibility of postoperative adverse local tissue reaction (ALTR). This study investigates the reliability of the ultrasound scan as a diagnostic tool to quantify a clinically useful threshold in the level of periprosthetic fluid collection to suggest implant revision.

METHODS

This study includes 116 patients (123 implants) who received an Articular Surface Replacement XL (ASRTMXL, De Puy Synthes, USA) MoM THA. The study group included 56 males and 60 females with a mean age of 66.6 years (range, 15-86 years). All patients were clinically and radiologically annually evaluated (according to the Harris Hip Score) up to a mean follow-up of 7.5 years (min. 1.4 - max. 10.3 years) from the primary surgery: all patients underwent standard ultrasound evaluation of the affected hip and Cobalt/Chromium blood detection testing according to a custom-made diagnostic algorithm for MoM THA revision.

RESULTS

At final follow-up, 51 (43.1%) of 117 implants underwent revision after a mean of 6 years (1.79-9.26) from the primary ASR implant. The authors found a statistically significant correlation between Cr (p = 0.015) and Co (p = 0.009) blood values and different ultrasound grades. Statistical analysis showed a significant association between periprosthetic fluid collection and revision surgery (p < 0.0001) and the final revision risk was estimated to be 7 times greater in patients with ultrasound grade ≥ 2 (peri-prosthetic collection ≥ 20 mm).

CONCLUSIONS

This study confirms the reliability of ultrasound evaluation in detecting clinically significant peri-prosthetic joint effusions: a new diagnostic algorithm for MoM THA revision is here presented. Longer follow up studies are mandatory to better understand the potential advantages of this diagnostic protocol.

Revisions of Modular Metal-on-metal THA Have a High Risk of Early Complications

BACKGROUND

The risk of early complications is high after monoblock acetabular metal-on-metal (MoM) THA revisions. However, there is a paucity of evidence regarding clinical complications after isolated head-liner exchange of modular MoM THA.

QUESTIONS/PURPOSES

The purposes of this study were (1) to describe the frequency of early complications after an isolated head-liner exchange revision of modular MoM THA; and (2) to determine whether patients who experienced complications or dislocation after head-liner exchanges had higher serum chromium (Cr) or cobalt (Co) ion levels than those who did not.

METHODS

A review of our institution's total joint registry retrospectively identified 53 patients who underwent 54 liner exchange revisions of a modular acetabular MoM THA. The study period was from April 2008 to April 2016 at a single tertiary care center. During this period, isolated head-liner exchanges (rather than more extensive revisions) were performed in patients if they did not have evidence of loosening of the acetabular or femoral components. Reasons for revision surgery included pain, mechanical symptoms, radiographic evidence of osteolysis, elevated serum metal ions, and MRI abnormalities with 40 of the 54 hips having pain or mechanical symptoms and 38 of 54 hips having multiple reasons for revision before surgery. Patients were excluded if they did not meet the minimum postrevision followup or had the modular liner exchange secondary to infection. All revisions were from a single manufacturer with one head-liner exchange of a MoM THA from another manufacturer excluded during the study period. The mean time from index MoM THA to modular exchange was 96 (SD ± 36) months. Because the focus of this study was early complications, we had a minimum 90-day followup duration for inclusion. Mean followup after revision was 15 months (SD ± 12); a total of 56% (30 of 54) had followup of at least 12 months' duration. Complications (dislocation, infection) and reoperations were obtained by chart review performed by individuals other than the treating physician(s). Serum metal ion levels were obtained before head-liner exchange. The median serum Cr and Co levels were 6 µg/L (range, 0-76 µg/L) and 12 µg/L (range, 0-163 µg/L), respectively.

RESULTS

Of the 54 revision THAs, 15 (28%) developed complications. Nine (17%) occurred within 90 days of the revision surgery and 11 (20%) resulted in reoperation. The most common complication was dislocation (12 of 54 [22%]) with recurrent dislocation noted in eight of these 12 patients. All patients with recurrent dislocation continued to dislocate and underwent repeat revision. Patients with dislocation had higher median serum Cr and Co ion levels than those without dislocation (Cr: 24 [range, 11-76] versus 4 [range, 0-70], p = 0.001 [95% confidence interval {CI}, 10-57]; Co: 41 [range, 6-163] versus 8 [range, 0-133], p = 0.016 [95% CI, 6-141]). Three (6%) of the 54 patients underwent repeat surgery for deep space infection.

CONCLUSIONS

Complications and reoperations are common after modular head-liner exchange in the setting of a failed MoM THA. Our study likely underestimates the frequency of complications and revisions because the followup period in this report was relatively short. Dislocation is the most common complication and elevated serum metal ion levels may be a predictor of dislocation. These findings are concerning and surgeons should be aware of the high complication risk associated with this procedure.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Periprosthetic acetabular radiolucency progression in mid-term follow-up of the articular surface replacement hip system

INTRODUCTION

Recent registry studies show that aseptic loosening secondary to osteolysis is the second leading cause of hip implant failure in patients implanted with metal-on-metal (MoM) bearings. The primary aim of our study was to report on the progression of acetabular osteolysis during mid-term follow-up in patients treated with MoM hip resurfacing arthroplasty (HRA) and MoM total hip arthroplasty (THA). The secondary aim was to identify independent predictors of osteolytic lesion progression.

MATERIALS AND METHODS

A total of 805 patients (805 hips) were included in this study (541 MoM HRA, 264 MoM THA) from a prospective, international clinical registry of the Articular Surface Replacement Hip System. Patients were enrolled a median of 6.6 years from surgery. Osteolytic lesion progression was defined either as any lesion developing de novo, or as an existing lesion progressing from radiolucency to osteolysis during the study period (range 0.5-4.3 years).

RESULTS

The number of cases with any osteolysis or radiolucency was 21 (3.9%) for ASR HRA and 29 (11.0%) for ASR XL THA at enrollment and increased to 69 (12.8%) for ASR HRA and 41 (15.5%) for ASR XL THA after follow-up. Osteolytic lesion progression was found in 66 (12.2%) ASR HRA patients and 31 (11.7%) ASR XL THA patients. Multivariate models determined that lower acetabular version angle (OR 0.963, p = 0.011) and elevated whole blood chromium (OR 1.110, p = 0.044) were independent predictors of osteolytic lesion progression in ASR HRA.

CONCLUSION

We suggest that physicians of patients implanted with ASR HRA implants closely monitor patients with higher chromium levels and lower version angles, as they are at increased risk for osteolytic lesion progression, and we recommend annual radiographic follow-up on all patients with ASR implants.

Relationship of Blood Metal Ion Levels and Leukocyte Profiles in Patients With Articular Surface Replacement Metal-on-Metal Hip Replacement

The purpose of this study was to compare blood leukocyte profiles and metal ion concentrations between hip resurfacing arthroplasty (articular surface replacement) patients with and without revision. A total of 25 articular surface replacement patients were recruited (10 with stable implants and 15 undergoing revision). Blood concentrations of chromium (Cr) and cobalt (Co) were measured. Flow cytometry was used to quantify the subpopulations of leukocytes, including CD14⁺ monocytes, CD16⁺ monocytes, CD3⁺ T-lymphocytes, CD19⁺ B-lymphocytes, CD4⁺ helper T-cells, and CD45⁺RA memory vs naïve T-cells. Patients undergoing revision had higher blood Co (mean, 10.85 µg/L) and Cr (mean, 3.19 µg/L) levels than patients with stable implants (mean Co, 3.06 µg/L; mean Cr, 1.07 µg/L) (P<.05). The number of CD4⁺ helper T-cells was higher in patients with stable implants (mean, 842±311 cells/µL) than in patients undergoing revision (mean, 591±208 cells/µL) (P<.05). There was a significant association between total metal ion levels (Co+Cr) and the number of CD14⁺ monocytes (P=.045) and inflammatory CD16⁺ monocytes (P=.046). The authors observed that the increase in blood metal ions was associated with an increase in CD16⁺ monocytes. They believe that continued analysis of blood leukocyte profiles may be helpful in defining differences among failed articular surface replacement, stable articular surface replacement, and failed metal-on-polyethylene implants. [Orthopedics. 2018; 41(3):e424-e431.].

Fluoroscopy- vs ultrasound-guided aspiration techniques in the management of periprosthetic joint infection: which is the best?

BACKGROUND

Fluid samples obtained from an affected joint still play a central role in the diagnosis of periprosthetic joint infection (PJI). It is the only preoperative test able to discover the causative microbiological agent. In the hip, fluid aspiration can be performed through fluoroscopy, ultrasound, or, less commonly, computed tomography. However, there is still a lack of consensus on which method is preferable in terms of efficacy and costbenefit.

PURPOSES

We, therefore, asked whether (1) the benefits in terms of sensitivity and specificity and (2) the costs were comparable between fluoroscopy- and ultrasound-guided joint aspirations in a suspicious of hip PJI.

METHODS

Between 2013 and 2016, 52 hip aspirations were performed on 49 patients with clinical, radiological, or serological suspicion of PJI, waiting for a revision surgery. The patients were divided in two groups: fluoroscopy- (n = 26) vs ultrasound-guided hip aspiration group (n = 26). These groups were also divided in control and infected patients. The criteria of MusculoSkeletal Infection Society (MSIS) were used, as gold standard, to define PJI.

RESULTS

(1) Ultrasound-guided aspiration revealed valid sensitivity (89% vs 60%) and specificity (94% vs 81%) in comparison with fluoroscopic-guided aspiration. (2) The cost analysis was also in favor of ultrasound-guided aspiration (125.30€) than fluoroscopic-guided aspiration (343.58€).

CONCLUSIONS

We concluded that ultrasound-guided hip aspiration could represent a valid, safe, and less expensive diagnostic alternative to fluoroscopic-guided aspiration in hip PJI.

Heart failure after conventional metal-on-metal hip replacements

Background and purpose - It is unclear whether metal particles and ions produced by mechanical wear and corrosion of hip prostheses with metal-on-metal (MoM) bearings have systemic adverse effects on health. We compared the risk of heart failure in patients with conventional MoM total hip arthroplasty (THA) and in those with metal-on-polyethylene (MoP) THA. Patients and methods - We conducted a retrospective cohort study using data from the Australian Government Department of Veterans' Affairs health claims database on patients who received conventional THA for osteoarthritis between 2004 and 2012. The MoM THAs were classified into groups: Articular Surface Replacement (ASR) XL Acetabular System, other large-head (LH) (> 32 mm) MoM, and small-head (SH) (≤ 32 mm) MoM. The primary outcome was hospitalization for heart failure after THA. Results - 4,019 patients with no history of heart failure were included (56% women). Men with an ASR XL THA had a higher rate of hospitalization for heart failure than men with MoP THA (hazard ratio (HR) = 3.2, 95% CI: 1.6-6.5). No statistically significant difference in the rate of heart failure was found with the other LH MoM or SH MoM compared to MoP in men. There was no statistically significant difference in heart failure rate between exposure groups in women. Interpretation - An association between ASR XL and hospitalization for heart failure was found in men. While causality between ASR XL and heart failure could not be established in this study, it highlights an urgent need for further studies to investigate the possibility of systemic effects associated with MoM THA.

Densitometric evaluation might prevent failure of knee artroplasty for aseptic loosening. An 8-year observational controlled study

OBJECTIVES

To study the correlation between quantitative ultrasound (QUS) expressed as stiffness index (SI) and the risk of aseptic loosening of knee arthroplasty. 

METHODS

An observational retrospective controlled study was performed on 85 female patients (mean age: 73.3 years) divided into 2 groups from January 2007 to March 2015 and carried out at the Orthopedic Rehabilitation Unit, Casa di Cura Eremo, Arco, Trento, Italy. Group A included 42 patients who had undergone a revision of knee prosthesis for aseptic-loosening, and group B included 43 age-matched patients who underwent primary replacement of the knee without following aseptic loosening. Patients in both groups were evaluated for SI with Achilles - QUS system at the same side of the surgery.

RESULTS

In group A, 20/42 patients (47.6%) had an SI T-score below -2.5. In group B, 14/43 (32.5%) patients had a SI T-score below -2.5. The difference between the 2 groups was statistically significant (p=0.015). 

CONCLUSION

Stiffness index appears to be an important predictor of aseptic loosening of the knee prosthesis. Therefore, densitometric evaluation, including SI, may be recommended before surgical knee replacement.

Outcomes of the Recalled Articular Surface Replacement Metal-on-Metal Hip Implant System: A Systematic Review

BACKGROUND

The aim of this review was to synthesize the main findings of clinical studies that have evaluated outcomes of the articular surface replacement (ASR) Hip System.

METHODS

We performed a systematic literature search to identify all articles published between January 2008 and June 2015 that included ASR hip resurfacing arthroplasty (ASR HRA) or ASR total hip arthroplasty (ASR XL THA) outcomes according to the PRISMA statement.

RESULTS

A total of 56 studies were assessed. The prevalence of adverse local tissue reactions (ALTRs) and revision rates were found to be high. ALTR prevalence varied from 12.5% to 69% (mean, 33.5%). Mean revision rate for any reason at 4-year to 7-year follow-up was 13.8% (range, 5.6%-31%) for ASR HRA and 14.5% (range, 0%-37%) for ASR XL THA. Femoral head size <53 mm was found to correlate with higher blood metal ion levels. Femoral head size >44 mm was not associated with higher ALTR prevalence or revision rates in ASR XL THA. High blood metal ion levels (>7 μg/L Co, >7 μg/L Cr) were associated with higher failure rates and bearing-related complications. The role of cup positioning was found to be controversial.

CONCLUSION

ALTR prevalence and failure rates were high. High blood metal ion levels were a risk factor for ALTR and failure. Surprisingly, the role of cup positioning and large femoral head size in ASR XL THA were controversial. These findings should be considered in the clinical follow-up and risk stratification of patients with the ASR Hip System.

[Are the cobalt hip prosthesis dangerous?]

The placement of a hip prosthesis is one of the most common orthopedic surgical procedures. Some implants contain metal and are therefore capable of releasing metal particles like cobalt in patients who wear metal prostheses. Cobalt can be responsible of local toxicity (including metallosis, hypersensitivity reaction, and benign tumor) or systemic toxicity (including cardiomyopathy, polycythemia, hypothyroidism, and neurological disorders). To monitor potential toxicity of metal hip prostheses, an annual monitoring of patients implanted is recommended and includes clinical examination, radiological examination and blood cobalt determination. The cobalt concentration in blood allows to estimate the risk of toxicity and to evaluate the performance of the implant. The currently recommended threshold value is equal to 7 µg of cobalt per liter of blood. Our study, conducted on 251 patients over a period of 4 years, has shown that the cobalt concentration average was 2.51 µg/l in blood, with 51 patients having a cobaltemia higher than the threshold of 7 µg/l.

International metal-on-metal multidisciplinary teams: do we manage patients with metal-on-metal hip arthroplasty in the same way? An analysis from the International Specialist Centre Collaboration on MOM Hips (ISCCoMH)

AIMS

There are many guidelines that help direct the management of patients with metal-on-metal (MOM) hip arthroplasties. We have undertaken a study to compare the management of patients with MOM hip arthroplasties in different countries.

METHODS

Six international tertiary referral orthopaedic centres were invited to participate by organising a multi-disciplinary team (MDT) meeting, consisting of two or more revision hip arthroplasty surgeons and a musculoskeletal radiologist. A full clinical dataset including history, blood tests and imaging for ten patients was sent to each unit, for discussion and treatment planning. Differences in the interpretation of findings, management decisions and rationale for decisions were compared using quantitative and qualitative methods.

RESULTS

Overall agreement between the orthopaedic centres and the recommended treatment plans for the ten patients with MOM hip implants was moderate (kappa = 0.6). Full agreement was seen in a third of cases, however split decisions were also seen in a third of cases. Units differed in their interpretation of the significance of the investigation findings and put varying emphasis on serial changes, in the presence of symptoms.

DISCUSSION

In conclusion, the management of raised or rising blood metal ions, cystic pseudotumours and peri-acetabular osteolysis led to inconsistency in the agreement between centres. Coordinated international guidance and MDT panel discussions are recommended to improve consensus in decision making.

TAKE HOME MESSAGE

A lack of evidence and the subsequent variation in regulator guidance leads to differences in opinions, the clinical impact of which can be reduced through a multi-disciplinary team approach to managing patients with MOM hip implants. Cite this article: Bone Joint J 2016;98-B:179-86.

Management of metal-on-metal hip implant patients: Who, when and how to revise?

The debate on how best to manage patients with metal-on-metal (MOM) hip implants continues. With over 1 million patients affected worldwide, the impact is far reaching. The majority of the aggressive failures of MOM hip implants have been dealt with by revision hip surgery, leaving patients with a much more indolent pattern of failure of devices that have been in situ for more than 10 years. The longer-term outcome for such patients remains unknown, and much debate exists on how best to manage these patients. Regulatory guidance is available but remains open to interpretation due to the lack of current evidence and long-term studies. Metal ion thresholds for concern have been suggested at 7 ppb for hip resurfacing arthroplasty and below this level for large diameter total hip arthroplasties. Soft tissue changes including pseudotumours and muscle atrophy have been shown to progress, but this is not consistent. New advanced imaging techniques are helping to diagnose complications with metal hips and the reasons for failure, however these are not widely available. This has led to some centres to tackle difficult cases through multidisciplinary collaboration, for both surgical management decisions and also follow-up decisions. We summarise current evidence and consider who is at risk, when revision should be undertaken and how patients should be managed.

Revision of Articular Surface Replacement (ASR) Total Hip Arthroplasty: Correlation of Perioperative Data and Early Post-Revision Outcome Results

The articular surface replacement (ASR) total hip arthroplasty (THA) showed accelerated failure rates due to adverse-reaction to metal debris (ARMD). Literature correlating preoperative with intraoperative revision findings respectively post-revision outcome results are rare. 30 of 99 available ASR THA were revised due to ARMD. Mean post-revision follow-up term was 2.3 years. In part, preoperative data did not correlate with intraoperative revision findings. ARMD was even found in asymptomatic patients with non-elevated ion levels. Postoperative pain and metal ions decreased significantly (P ≤ 0.016). Cobalt decreased faster than chrome. Patients with intraoperative pseudotumors, osteolysis or bilateral THA did not have higher pre- or postoperative ion values (P ≥ 0.053). Females showed higher postoperative chrome levels (P=0.031). One major post-revision complication (femoral nerve palsy) and one re-revision (late onset infection) occurred.

A High Prevalence of Corrosion at the Head-Neck Taper with Contemporary Zimmer Non-Cemented Femoral Hip Components

Mechanically assisted crevice corrosion (MACC) occurs at metal/metal modular junctions in which at least one of the components is fabricated from cobalt-chromium alloy and may lead to adverse local tissue reaction (ALTR) in patients with metal-on-polyethylene (MoP) total hip arthroplasty. This type of reaction has been previously described in hips with head/neck modularity, but the prevalence is unknown. We found a prevalence of 1.1 percent in a consecutive series of 1356 contemporary Zimmer non-cemented femoral hip components followed for a minimum of 2years. The average time to presentation was 3.7years (range, 9-105months); delay in treatment led to irreversible soft tissue damage in three patients. We recommend usage of ceramic heads until this problem is further understood.

Mechanically assisted crevice corrosion of the head-neck taper in a large head metal-on-metal total hip arthroplasty

Taper corrosion of the head-neck junction is a potentially significant and devastating problem facing orthopedic surgeons. We present a case of a 53 year old male who presented for routine follow up for a left, large head, metal on metal total hip arthroplasty five years out. The patient was asymptomatic at the visit. X-rays at the time demonstrated a large amount of medial calcar osteolysis. Serum ion levels revealed a mildly increased cobalt and normal chromium level and hip aspiration revealed brownish fluid. At the time of revision surgery, corrosion of the head-neck taper was found with a normal appearing bearing surface leading to the diagnosis of mechanically assisted crevice corrosion of the head-neck taper with medial calcar osteolysis.

A case series of 35 hip revisions for adverse reactions to metal debris following Cormet hip resurfacing

The primary aim of this study was to analyse our painful metal-on-metal (MoM) hip resurfacing revisions with evidence of 'adverse reactions to metal debris' (ARMD). In our series of 35 revisions the median whole blood Cobalt levels were 58 nmols/l (range 12-1407 nmols/l), and whole blood Chromium levels were 73 nmols/l (range 2-353 nmols/l). Thirty-four of our 35 patients had abnormal imaging on Ultrasound scanning (USS). The mean histological Campbell grading of ARMD was 4, and ranged from 0-9. The mean Oxford Hip Score (OHS) increased from 19 pre-revision (range 4-46) to 33 post-revision surgery (range 23-47).We found no correlation between the preoperative metal ion levels, and the severity of the disease or the outcome.Pain following hip resurfacing may arise from a number of causes and when groin pain arises in conjunction with abnormal cross sectional imaging we have offered our patients revision surgery regardless of raised metal ions or grossly abnormal imaging, with good results.

Assessment of Patients with a DePuy ASR Metal-on-Metal Hip Replacement: Results of Applying the Guidelines of the Spanish Society of Hip Surgery in a Tertiary Referral Hospital

The prognosis associated with the DePuy ASR hip cup is poor and varies according to the series. This implant was withdrawn from use in 2010 and all patients needed to be assessed. We present the results of the assessment of our patients treated with this device, according to the Spanish Society of Hip Surgery (SECCA) algorithm published in 2011. This retrospective study evaluates 83 consecutive ASR cups, followed up at a mean of 2.9 years. Serum levels of chromium and cobalt, as well as the acetabular abduction angle, were determined in order to assess their possible correlation with failure, defined as the need for revision surgery. The mean Harris Hip Score was 83.2 (range 42–97). Eight arthroplasties (13.3%) required revision due to persistent pain and/or elevated serum levels of chromium/cobalt. All the cups had a correct abduction angle, and there was no correlation between elevated serum levels of metal ions and implant failure. Since two previous ASR implants were exchanged previously to the recall, the revision rate for ASR cups in our centre is 18.2% at 2.9 years.

MRI does not detect acetabular osteolysis around metal-on-metal Birmingham THA

OBJECTIVE

Osteolysis has not been recognized as a common failure mode of the Birmingham modular metal-on-metal (MoM) total hip arthroplasty (THA). The clinical value of metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) to assess the periprosthetic soft tissue is well documented; however, the appropriate image modalities to detect periacetabular osteolysis remain unclear. Eleven patients with periacetabular osteolysis within 3-6 years after uncemented Birmingham modular MoM THA with a synergy stem are presented. All 11 patients received corresponding standardized AP pelvis radiographs, high-quality MARS MRIs and CT scans with a metal artifact reduction sequence. While periacetabular osteolysis around MoM THA was not detected on MARS MRI in ten patients, CT imaging identified osteolysis in all patients. Periacetabular osteolysis appears to be a failure mechanism of the Smith & Nephew Birmingham MoM THA.

DISCUSSION

There is no evidence in the literature to support the effectiveness of MARS MRI to detect periacetabular osteolysis around cobalt chromium alloy metal-on-metal total hip arthroplasties. Osteolysis due to corrosion-related particles seems to be one of the primary modes of failure in modular MoM THA.

CONCLUSIONS

MRI is not a sensitive test to identify periacetabular osteolysis. The authors recommend CT for the screening of implants with this failure mode. Our study suggests that patients with a Birmingham modular MoM THA are at increased risk to develop acetabular osteolysis and should be carefully monitored for this failure mode.