Optimal acetabular orientation for hip resurfacing

Revision of metal-on-metal hip replacements and resurfacings for adverse reaction to metal debris: a systematic review of outcomes

PURPOSE

This systematic review assessed evidence on outcomes following revision of MoM hip resurfacings (HRs) and total hip replacements (THRs) for adverse reaction to metal debris (ARMD).

METHODS

Four electronic databases were searched between January 2009 and July 2013 to identify studies reporting clinical outcomes following revision of MoM HRs and THRs for ARMD. Only studies reporting cohorts with more than 10 metal-on-metal (MoM) hips revised for ARMD were included. Outcomes of interest following ARMD revision were: (1) complication rates; (2) re-revision rates; (3) surgical intervention other than re-revision; (4) functional outcome.

RESULTS

Of 148 unique studies identified, six studies were eligible for inclusion containing 216 MoM hips (197 HRs and 19 THRs) revised for ARMD. Mean follow-up time from ARMD revision ranged between 21-61 months. Complication rates were 4%-50% for HR and 68% for THR. Re-revision rates were 3%-38% for HR and 21% for THR. Dislocation (n = 14), ARMD recurrence (n = 11), and acetabular loosening (n = 9) were the three commonest complications and indications for re-revision. All six studies reported between one and three cases of ARMD recurrence during follow-up. One study specifically reported on performing procedures other than re-revision with 26% requiring closed reductions for dislocated THRs. Functional outcomes following ARMD revision were good or satisfactory in all but two studies.

CONCLUSIONS

Limited evidence exists regarding outcomes following revision of MoM hips for ARMD, especially for THRs. This should be addressed in future studies and may be important when counselling asymptomatic individuals in whom revision is considered for raised blood metal ions.

Factors affecting squeaking in metal on metal hip resurfacings

We reviewed 380 hip resurfacings cases between December 1999 and Dec 2012. 11 cases (2.89%) squeaked postoperatively. Mean follow-up was 88.6 months (19-130 months). Mean time to squeak was 11.3 months (3-22 months). Ten (91%) cases were male and nine (81%) cases had a Birmingham hip resurfacing. Cases were matched for age, gender, BMI and implant to three controls. Radiographs were analysed using EBRA (Einzel-Bild-Roentgen-Analysis, University of Innsbruck, Austria) software to evaluate cup orientation. There was no significant difference between the mean inclination angle of the cups (p = 0.26) or the mean anteversion angle (p = 0.29). There was no difference in serum cobalt (p = 0.20) or serum chromium (p = 0.45) levels at latest follow-up. Three of the 11 (27.3%) cases had revision surgery at a mean follow-up of 101 months (72-117 months). Squeaking was not influenced by patient demographic parameters and resolved in all cases that did not undergo revision surgery. Males with a resurfacing head size <50 mm had significantly increased odds of squeaking when compared to controls (odds ratio = 26.6; 95% CI = 1.2-573.3; p<0.05). Based on our findings, we do not recommend that squeaking on its own should be an indication for revision of hip resurfacing components.

The effect of orientation of the acetabular component on outcome following total hip arthroplasty with small diameter hard-on-soft bearings

We assessed the orientation of the acetabular component in 1070 primary total hip arthroplasties with hard-on-soft, small diameter bearings, aiming to determine the size and site of the target zone that optimises outcome. Outcome measures included complications, dislocations, revisions and ΔOHS (the difference between the Oxford Hip Scores pre-operatively and five years post-operatively). A wide scatter of orientation was observed (2sd 15°). Placing the component within Lewinnek's zone was not associated withimproved outcome. Of the different zone sizes tested (± 5°, ± 10° and ± 15°), only ± 15° was associated with a decreased rate of dislocation. The dislocation rate with acetabular components inside an inclination/anteversion zone of 40°/15° ± 15° was four times lower than those outside. The only zone size associated with statistically significant and clinically important improvement in OHS was ± 5°. The best outcomes (ΔOHS > 26) were achieved with a 45°/25° ± 5° zone. This study demonstrated that with traditional technology surgeons can only reliably achieve a target zone of ±15°. As the optimal zone to diminish the risk of dislocation is also ±15°, surgeons should be able to achieve this. This is the first study to demonstrate that optimal orientation of the acetabular component improves the functional outcome. However, the target zone is small (± 5°) and cannot, with current technology, be consistently achieved.

Predictors of time to revision and clinical outcomes following revision of metal-on-metal hip replacements for adverse reaction to metal debris

We undertook a retrospective cohort study to determine clinical outcomes following the revision of metal-on-metal (MoM) hip replacements for adverse reaction to metal debris (ARMD), and to identify predictors of time to revision and outcomes following revision. Between 1998 and 2012 a total of 64 MoM hips (mean age at revision of 57.8 years; 46 (72%) female; 46 (72%) hip resurfacings and 18 (28%) total hip replacements) were revised for ARMD at one specialist centre. At a mean follow-up of 4.5 years (1.0 to 14.6) from revision for ARMD there were 13 hips (20.3%) with post-operative complications and eight (12.5%) requiring re-revision. The Kaplan-Meier five-year survival rate for ARMD revision was 87.9% (95% confidence interval 78.9 to 98.0; 19 hips at risk). Excluding re-revisions, the median absolute Oxford hip score (OHS) following ARMD revision using the percentage method (0% best outcome and 100% worst outcome) was 18.8% (interquartile range (IQR) 7.8% to 48.3%), which is equivalent to 39/48 (IQR 24.8/48 to 44.3/48) when using the modified OHS. Histopathological response did not affect time to revision for ARMD (p = 0.334) or the subsequent risk of re-revision (p = 0.879). Similarly, the presence or absence of a contralateral MoM hip bearing did not affect time to revision for ARMD (p = 0.066) or the subsequent risk of re-revision (p = 0.178). Patients revised to MoM bearings had higher rates of re-revision (five of 16 MoM hips re-revised; p = 0.046), but those not requiring re-revision had good functional results (median absolute OHS 14.6% or 41.0/48). Short-term morbidity following revision for ARMD was comparable with previous reports. Caution should be exercised when choosing bearing surfaces for ARMD revisions.

Prevalence of a soft-tissue lesion after small head metal-on-metal total hip replacement: 13- to 19-year follow-up study

We investigated the incidence of soft-tissue lesions after small head metal-on-metal total hip replacement (MoM THR). Between December 1993 and May 1999, 149 patients (195 hips) underwent primary cementless MoM THR. During the follow-up period, three patients (five THRs) died and eight patients (14 THRs) were lost to follow-up. We requested that all patients undergo CT evaluation. After exclusion of five patients (six THRs) who had undergone a revision procedure, and 22 (28 THRs) who were unwilling to take part in this study, 111 patients (142 THRs) were evaluated. There were 63 men (88 THRs) and 48 women (54 THRs) with a mean age of 45.7 years (37 to 56) at the time of surgery. The mean follow-up was 15.4 years (13 to 19). A soft-tissue lesion was defined as an abnormal peri-prosthetic collection of fluid, solid lesion or asymmetrical soft-tissue mass. At final follow-up, soft-tissue lesions were found in relation to 28 THRs (19.7%), including 25 solid and three cystic lesions. They were found in 20 men and eight women; 26 lesions were asymptomatic and two were symptomatic. The mean maximal diameter of the soft-tissue lesion was 42.3 mm (17 to 135). The relatively high rate of soft-tissue lesions observed with small head MoM THR remains a concern.

Finite element modelling for assessing effect of acetabular component orientation on the basic stress path above acetabular dome

OBJECTIVE

To investigate the effect of acetabular component orientation on the basic stress path above the acetabular dome in the recommended safe zone.

METHODS

A subject-specific normal hip finite element model was generated and a convergence study carried out to determine the number of material properties for trabecular bone using a normal hip model. Four abduction angles (35°, 40°, 45° and 50°) and four anteversion angles (10°, 15°, 20° and 25°) from the recommended safe zone of acetabular cup orientation were chosen to simulate acetabular reconstruction. The distribution and level of periacetabular stress was assessed using a normal hip model as a control and 16 reconstructed acetabula in simulated single-legged stances.

RESULTS

The error of the average stress between plans four and five (50 and 100 materials for trabecular bone respectively) was 4.8%, which is less than the previously defined 5% error. The effect of acetabular component orientation on stress distribution in trabecular bone was not pronounced. When the acetabular component was at 15° anteversion and the abduction angle was 40° or 45°, the stress level on posterolateral cortical bone above the acetabular dome was as stable as that in the normal hip model.

CONCLUSIONS

Acetabular component orientation affects the basic stress path above the acetabular dome. Thus, orientation should be considered when attempting to restore normal biomechanics in the main load-bearing area.

Influence of implant design on blood metal ion concentrations in metal-on-metal total hip replacement patients

PURPOSE

Most factors considered to affect blood metal ions following metal-on-metal hip replacement are based on hip resurfacing patients. The study aims were to determine which factors affect blood metal ion concentrations following metal-on-metal total hip replacement (MoM THR).

METHODS

All unilateral MoM THR patients at one centre with whole-blood cobalt (Co) and chromium (Cr) concentrations measured up to May 2013 were included. Blood sampling was at a mean of 4.5 years (range 1.1-11.8 years) postoperatively.

RESULTS

Of 496 patients (mean age 59.1 years; 52.8% male), blood metal ions >7 μg/l were observed in 9.7% (n = 48). Large femoral head sizes (≥38 mm) had significantly higher (p < 0.0001) blood metal ions than smaller sizes (28/36 mm). Corail-Pinnacle implants produced significantly lower blood metal ions compared to other implant designs (p < 0.01 Co and Cr). Univariate linear regression demonstrated the only significant predictors of both blood Co and Cr concentrations were femoral head size (R(2) = 8.6% Co and R(2) = 3.3% Cr, both p < 0.0001) and implant design (R(2) = 8.8%, p = 0.005 Co and R(2) = 5.1%, p = 0.003 Cr). When the three THR implant design groups (Corail-Pinnacle, Synergy, Other) were analysed separately, femoral head size no longer significantly affected blood metal ions in any of the three implant design groups.

CONCLUSIONS

Implant design was the most important factor affecting blood metal ion concentrations. We recommend the regularity of follow-up be tailored to survival rates of various MoM THR designs rather than according to femoral head size.

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.

Self-reported neurological clinical manifestations of metal toxicity in metal-on-metal hip arthroplasty

Adverse reactions to metal particle debris have been increasingly reported as a complication following large head metal-on-metal (MoM) hip arthroplasty. Elevated metal ion levels are a cause for concern. The aim of this study is to evaluate whether exposure to cobalt is associated with patient characteristics and symptoms of neuropathy, representing nervous system dysfunction. A cross-sectional study was conducted comparing patients with a MoM total hip arthroplasty and patients with a conventional hip arthroplasty. They received three questionnaires, one to assess neurotoxic complaints and two standardised self-administered questionnaires to identify symptoms that are suggestive of peripheral neuropathy. Current and historical data were available for whole blood cobalt levels in all patients. We analysed potential predictive factors for cobalt based on five different cut-off levels (0-2, 2-4, 4-10, 10-20, >20 µg/L). We performed 723 MoM total hip arthroplasties in 643 patients in our clinic. The response rate was 89%. Male-female ratio was 236/280, median age 63.6 years (30-72) with a mean follow-up of 50.6 months (20-86). We also sent the questionnaires to 98 patients in the control group. An increase in the incidence of reported symptoms was not consistent with higher serum cobalt levels. Female gender was the only consistent predictive factor for serum cobalt at different cobalt cut-off levels in the multivariate analysis. The study population did not show an increase in reported symptoms with elevated cobalt levels. Neurotoxic symptoms and whole blood cobalt levels did not show a consistent relationship with different dichotomised levels of cobalt exposure.

Optimal acetabular component orientation estimated using edge-loading and impingement risk in patients with metal-on-metal hip resurfacing arthroplasty

Edge-loading in patients with metal-on-metal resurfaced hips can cause high serum metal ion levels, the development of soft-tissue reactions local to the joint called pseudotumours and ultimately, failure of the implant. Primary edge-loading is where contact between the femoral and acetabular components occurs at the edge/rim of the acetabular component whereas impingement of the femoral neck on the acetabular component's edge causes secondary or contrecoup edge-loading. Although the relationship between the orientation of the acetabular component and primary edge-loading has been identified, the contribution of acetabular component orientation to impingement and secondary edge-loading is less clear. Our aim was to estimate the optimal acetabular component orientation for 16 metal-on-metal hip resurfacing arthroplasty (MoMHRA) subjects with known serum metal ion levels. Data from motion analysis, subject-specific musculoskeletal modelling and Computed Tomography (CT) measurements were used to calculate the dynamic contact patch to rim (CPR) distance and impingement risk for 3416 different acetabular component orientations during gait, sit-to-stand, stair descent and static standing. For each subject, safe zones free from impingement and edge-loading (CPR <10%) were defined and, consequently, an optimal acetabular component orientation was determined (mean inclination 39.7° (SD 6.6°) mean anteversion 14.9° (SD 9.0°)). The results of this study suggest that the optimal acetabular component orientation can be determined from a patient's motion and anatomy. However, 'safe' zones of acetabular component orientation associated with reduced risk of dislocation and pseudotumour are also associated with a reduced risk of edge-loading and impingement.

The relationship between operative and radiographic acetabular component orientation

There is great variability in acetabular component orientation following hip replacement. The aims of this study were to compare the component orientation at impaction with the orientation measured on post-operative radiographs and identify factors that influence the difference between the two. A total of 67 hip replacements (52 total hip replacements and 15 hip resurfacings) were prospectively studied. Intra-operatively, the orientation of the acetabular component after impaction relative to the operating table was measured using a validated stereo-photogrammetry protocol. Post-operatively, the radiographic orientation was measured; the mean inclination/anteversion was 43° (sd 6°)/ 19° (sd 7°). A simulated radiographic orientation was calculated based on how the orientation would have appeared had an on-table radiograph been taken intra-operatively. The mean difference between radiographic and intra-operative inclination/anteversion was 5° (sd 5°)/ -8° (sd 8°). The mean difference between simulated radiographic and intra-operative inclination/anteversion, which quantifies the effect of the different way acetabular orientation is measured, was 3°/-6° (sd 2°). The mean difference between radiographic and simulated radiographic orientation inclination/anteversion, which is a manifestation of the change in pelvic position between component impaction and radiograph, was 1°/-2° (sd 7°).

This study demonstrated that in order to achieve a specific radiographic orientation target, surgeons should implant the acetabular component 5° less inclined and 8° more anteverted than their target. Great variability (2 sd about ± 15°) in the post-operative radiographic cup orientation was seen. The two equally contributing causes for this are variability in the orientation at which the cup is implanted, and the change in pelvic position between impaction and post-operative radiograph.

Cite this article: Bone Joint J 2014;96-B:1290–7

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 patient's 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.

Predictivity and fate of metal ion release from metal-on-metal total hip prostheses

Blood metal ion levels in 72 patients with large head metal-on-metal hip arthroplasty were studied to determine the correlation between the values measured in whole blood and urine. Urinary cobalt and chromium levels of 30μg and 21μg, respectively, adjusted to creatinine were found to correspond to the 7μg/l cut-off value that has been accepted in whole blood. Cobalt and chromium levels in whole blood and urine both significantly correlated with increased acetabular component inclination angle over 50 degrees and pain scores. There was no correlation with socket anteversion angle or femoral head diameter. The data support the use of urinary measurement of metal ions adjusted to creatinine to monitor patients with large head metal-on-metal total hip arthroplasty.

Risk of edge-loading and prosthesis impingement due to posterior pelvic tilting after total hip arthroplasty

BACKGROUND

Proper implant orientation is essential for avoiding edge-loading and prosthesis impingement in total hip arthroplasty. Although cup orientation is affected by a change in pelvic tilt after surgery, it has been unclear whether surgeons can prevent impingement and edge-loading by proper positioning by taking into account any change in pelvic alignment associated with alteration of hip range of motion.

METHODS

We simulated implant orientation without edge-loading and prosthesis impingement, even with a change in pelvic tilt and associated change in hip range of motion after surgery, by collision detection using implant models created with computer-aided design.

FINDINGS

If posterior pelvic tilting with a corresponding hyperextension change in hip range of motion after surgery remains within 10°, as occurs in 90% of cases, surgeons can avoid edge-loading and impingement by correctly orienting the implant, even when using a conventional prosthesis. However, if a 20° change occurs after surgery, it may be difficult to avoid those risks.

INTERPRETATION

Although edge-loading and impingement can be prevented by performing appropriate surgery in most cases, even when taking into account postoperative changes in pelvic tilt, it may also be important to pay attention to spinal conditions to ensure that pelvic tilting is not extreme because of increasing kyphosis.

Hip resurfacing arthroplasty at a non-specialist centre

INTRODUCTION

Few studies have reported the outcome of hip resurfacing arthroplasty (HRA) with respect to implant characteristics from non-specialist centres. We report the survival, clinical and radiological outcomes of a single surgeon series of HRA with an average follow-up duration of five years.

METHODS

All consecutive HRAs performed by a single surgeon between 2003 and 2011 at a district general hospital were retrospectively examined clinically and radiologically.

RESULTS

A total of 85 patients underwent 109 HRAs (58 male [53.2%] and 51 female patients [46.8%]) with a mean follow-up period of 62 months (range: 12-102 months). The median age was 57 years (range: 25-75 years). The mean acetabular and femoral head component sizes were 54 mm (range: 48-64 mm) and 48 mm (range: 42-58 mm) respectively with a mean acetabular inclination angle of 42.9° (range: 20-75°). The survival rate was 95% with five revisions due to aseptic loosening (n=3) and fracture (n=2): these were predominantly for female patients (n=4), with significantly smaller mean acetabular (51 mm, p=0.04) and femoral (44 mm, p=0.02) implant sizes. Furthermore, they had a higher mean acetabular inclination angle of 48.1° (p=0.74). The mean Oxford hip score was 43.8 (range: 25-48) and the mean University of California Los Angeles (UCLA) activity score was 6.8 (range: 3-10). Radiological findings included heterotopic ossification in 13 (11.9%), radiolucent lines in 6 (5.5%), femoral neck thinning in 2 (1.8%) and femoral neck notching in 5 patients (4.6%).

CONCLUSIONS

We have shown that HRA at a non-specialist centre has short to medium-term outcomes comparable with those at specialist centres. HRA therefore remains a viable option although vigilance is required in case selection and follow-up according to national guidance.

A new technique for radiographic measurement of acetabular cup orientation

Accurate radiographic measurement of acetabular cup orientation is required in order to assess susceptibility to impingement, dislocation, and edge loading wear. In this study, the accuracy and precision of a new radiographic cup orientation measurement system were assessed and compared to those of two commercially available systems. Two types of resurfacing hip prostheses and an uncemented prosthesis were assessed. Radiographic images of each prosthesis were created with the cup set at different, known angles of version and inclination in a measurement jig. The new system was the most accurate and precise and could repeatedly measure version and inclination to within a fraction of a degree. In addition it has a facility to distinguish cup retroversion from anteversion on anteroposterior radiographs.

Wear analysis of 39 conserve plus metal-on-metal hip resurfacing retrievals

There have been increasing concerns regarding adverse local tissue reactions (ALTR) following metal-on-metal (MOM) hip arthroplasties. This study examined wear rates in retrievals of one design of MOM resurfacing arthroplasty, and assessed the differences in wear between those with and without ALTR. Wear measurements were made on 39 MOM resurfacing components (30 femoral, 9 acetabular) which were at least 2years in vivo. Seven hips (6 patients; 4 acetabular components, 7 femoral components) were identified to have ALTR. Acetabular component abduction and anteversion angles were determined using EBRA, and the contact-patch-to-rim (CPR) distance was calculated. The ALTR group had higher linear femoral and acetabular wear rates, acetabular anteversion and abduction angles, lower CPR, and longer time to revision. Given the increased risk for ALTR associated with acetabular component malpositioning, patients with malpositioned acetabular components may require closer clinical follow-up and monitoring.

The painful total hip replacement: diagnosis and deliverance

Total hip replacement (THR) is a very common procedure undertaken in up to 285 000 Americans each year. Patient satisfaction with THR is very high, with improvements in general health, quality of life, and function while at the same time very cost effective. Although the majority of patients have a high degree of satisfaction with their THR, 27% experience some discomfort, and up to 6% experience severe chronic pain. Although it can be difficult to diagnose the cause of the pain in these patients, this clinical issue should be approached systematically and thoroughly. A detailed history and clinical examination can often provide the correct diagnosis and guide the appropriate selection of investigations, which will then serve to confirm the clinical diagnosis made.

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.

Squeaking: Current knowledge and how to avoid it

This review aims to update the reader with current thinking and research related to the well documented phenomenon of squeaking hip arthroplasties. The etiology of squeaking is multifactorial and still not well understood. We aim to share our own experience and views on the combination of factors we believe increases the likelihood of squeaking, along with mechanisms by which the sound may be generated. Recent published findings from other groups are summarized along with an appropriate management algorithm we recommend for this cohort of patients.

Is second generation metal-on-metal primary total hip arthroplasty with a 28 mm head a worthy option?: a 12- to 18-year follow-up study

To determine whether MoM THA with a small head is still worthy of use, we investigated survivorship, complications, and factors influencing failure. Of 149 consecutive patients (195 hips), 141 (180 hips) of mean age 43 (19-55) years were available for review at a mean of 14.4 years postoperatively. Survivorship for cup revision for any cause was 97.8% at 18.4 years postoperatively. Nine hips generated complaints of groin pain; six showed periacetabular osteolysis, one had pain without radiological change, and two were diagnosed as symptomatic pseudotumors. Four of six hips with periacetabular osteolysis or aseptic loosening were revised. Surgery- and patient-related factors had no effect in results. Our results are encouraging, however, further study will be necessary to determine the incidence and fates of pseudotumors after MoM THA with a small head.

Poor short term outcome with a metal-on-metal total hip arthroplasty

Metal-on-metal (MoM) bearings for total hip arthroplasty (THA) have come under scrutiny with reports of high failure rates. Clinical outcome studies with several commercially available MoM THA bearings remain unreported. We evaluated 78 consecutive MoM THAs from a single manufacturer in 68 patients. Sixty-six received cobalt-chrome (CoCr) monoblock and 12 received modular titanium acetabular cups with internal CoCr liners. Femoral components were titanium with modular necks. At average 2.1 years postoperatively, 12 THAs (15.4%) demonstrated aseptic failure (10 revisions, 2 revision recommended). All revised hips demonstrated capsular necrosis with positive histology reaction for aseptic lymphocytic vasculitis-associated lesions/adverse local tissue reactions. Prosthetic instability following revision surgery was relatively common. Female gender was a strong risk factor for failure, though smaller cups were not. Both monoblock and modular components fared poorly. Corrosion was frequently observed around the proximal and distal end of the modular femoral necks.

Incidence of pseudotumor and acute lymphocytic vasculitis associated lesion (ALVAL) reactions in metal-on-metal hip articulations: a meta-analysis

We systematically reviewed the peer-reviewed literature to determine a pooled estimate of the incidence of pseudotumor and acute lymphocytic vasculitis associated lesions (ALVAL) in adult patients with primary metal-on-metal (MoM) total hip arthroplasty or resurfacing. Fourteen eligible articles were identified, with a total of 13,898 MoM hips. The incidence of pseudotumor/ALVAL ranged from 0% to 6.5% of hips with a mean follow-up ranging from 1.7 to 12.3 years across the studies. The pooled estimated incidence of pseudotumor/ALVAL is 0.6% (95% CI: 0.3% to 1.2%). The rate of revision for any reason ranged from 0% to 14.3% of hips, with a pooled estimate of 3.9% (95% CI: 2.7% to 5.3%).

The Canadian Arthroplasty Society’s experience with hip resurfacing arthroplasty

The purpose of this study was twofold: first, to determine whether the five-year results of hip resurfacing arthroplasty (HRA) in Canada justified the continued use of HRA; and second, to identify whether greater refinement of patient selection was warranted.

This was a retrospective cohort study that involved a review of 2773 HRAs performed between January 2001 and December 2008 at 11 Canadian centres. Cox’s proportional hazards models were used to analyse the predictors of failure of HRA. Kaplan–Meier survival analysis was performed to predict the cumulative survival rate at five years. The factors analysed included age, gender, body mass index, pre-operative hip pathology, surgeon’s experience, surgical approach, implant sizes and implant types. The most common modes of failure were also analysed.

The 2773 HRAs were undertaken in 2450 patients: 2127 in men and 646 in women. The mean age at operation was 50.5 years (sd 8.72; 18 to 82) and mean follow-up was 3.4 years (sd 2.1; 2.0 to 10.1). At the last follow-up a total of 101 HRAs (3.6%) required revision. Using revision for all causes of failure as the endpoint, Kaplan–Meier survival analysis showed a cumulative survival of 96.4% (95% confidence interval (CI) 96.1 to 96.9) at five years. With regard to gender, the five-year overall survival was 97.4% in men (95% CI 97.1 to 97.7) and 93.6% in women (95% CI 92.6 to 94.6). Female gender, smaller femoral components, specific implant types and a diagnosis of childhood hip problems were associated with higher rates of failure. The most common cause of failure was fracture of the femoral neck, followed by loosening of the femoral component.

The failure rates of HRA at five years justify the ongoing use of this technique in men. Female gender is an independent predictor of failure, and a higher failure rate at five years in women leads the authors to recommend this technique only in exceptional circumstances for women.

Cite this article: Bone Joint J 2013;95-B:1044–50.

Revision of metal-on-metal hip arthroplasty in a tertiary center: a prospective study of 39 hips with between 1 and 4 years of follow-up

BACKGROUND AND PURPOSE

Operative findings during revision of metal-on-metal hip arthroplasty (MOMHA) vary widely and can involve massive soft tissue and bone disruption. As a result, planning of theater time and resources is difficult, surgery is challenging, and outcomes are often poor. We describe our experience with revision of MOMHA and provide recommendations for management.

PATIENTS AND METHODS

We present the findings and outcomes of 39 consecutive MOMHAs (in 35 patients) revised in a tertiary unit (median follow-up time 30 (12-54) months). The patients underwent a preoperative work-up including CT, metal artifact reduction sequence (MARS) MRI, and blood metal ion levels.

RESULTS

We determined 5 categories of failure. 8 of 39 hips had conventional failure mechanisms including infection and impingement. Of the other 31 hips, 14 showed synovitis without significant disruption of soft tissue; 6 had a cystic pseudotumor with significant soft tissue disruption; 7 had significant osteolysis; and 4 had a solid pseudotumor. Each category of failure had specific surgical hazards that could be addressed preoperatively. There were 2 reoperations and 1 patient (2 hips) died of an unrelated cause. Median Oxford hip score (OHS) was 37 (9-48); median change (ΔOHS) was 17 (-10 to 41) points. ΔOHS was similar in all groups-except those patients with solid pseudotumors and those revised to metal-on-metal bearings, who fared worse.

INTERPRETATION

Planning in revision MOMHA is aided by knowledge of the different categories of failure to enable choice of appropriate personnel, theater time, and equipment. With this knowledge, satisfactory outcomes can be achieved in revision of metal-on-metal hip arthroplasty.

A review of hip resurfacings revised for unexplained pain

BACKGROUND

Adverse reaction to metal debris (ARMD) has come to prominence as a mode of failure for metal-on-metal hip resurfacings. These patients frequently present with unexplained groin pain.

AIMS

1) To review all metal-on-metal hip resurfacings revised for unexplained pain seeking evidence for ARMD; 2) To determine the clinical outcome following revision arthroplasty.

METHODS

The hospital database was searched (1997-2009) to identify all cases of Birmingham Hip Resurfacings (BHRs) revised for unexplained pain. ARMD was diagnosed using specific clinical, radiological, and histopathological criteria. Postoperatively all patients were assessed in clinic and completed an Oxford Hip Score (OHS) questionnaire.

RESULTS

Of 3076 BHRs implanted 149 were revised. Of these, 20 BHRs in 17 patients were revised for unexplained pain (mean age at BHR 50.5 yr; 55% female). Unexplained pain requiring revision had a prevalence of 0.65% of all hip resurfacings performed (20/3076). ARMD was the mode of failure in 50% (n = 10). Common features observed in ARMD patients included hip-joint effusions, femoral neck thinning, intraoperative macroscopic granulomas, and lymphocytic infiltrates on histopathological examination. No ARMD patients had macroscopic soft-tissue destruction. A range of mechanical causes were responsible for the remaining failures. At a mean 3.6 year follow-up (range 1.1-8.0) one ARMD patient experienced a dislocation. There were no further complications or need for surgical re-intervention. Median OHS for the cohort was 25.0%.

CONCLUSIONS

Hip resurfacings revised for unexplained pain comprise a diverse group of conditions with ARMD being the commonest. ARMD probably contains subgroups yet to be defined, some of which may be related to mechanical rather than immunological factors.

Assessment of cup orientation in hip resurfacing: a comparison of TraumaCad and computed tomography

Purpose

The orientation of the acetabular component in metal-on-metal hip resurfacing arthroplasty affects wear rate and hence failure. This study aimed to establish if interpretation of pelvic radiographs with TraumaCad software can provide a reliable alternative to CT in measuring the acetabular inclination and version.

Methods

TraumaCad was used to measure the acetabular orientation on AP pelvis radiographs of 14 painful hip resurfacings. Four orthopaedic surgeons performed each measurement twice. These were compared with measurements taken from CT reformats. The correlation between TraumaCad and CT was calculated, as was the intra- and inter-observer reliability of TraumaCad.

Results

There is strong correlation between the two techniques for the measurement of inclination and version (p <0.001). Intra- and inter-observer reliability of TraumaCad measurements are good (p <0.001). Mean absolute error for measurement of inclination was 2.1°. TraumaCad underestimated version compared to CT in 93% of cases, by 12.6 degrees on average.

Conclusions

When assessing acetabular orientation in hip resurfacing, the orthopaedic surgeon may use TraumaCad in the knowledge that it correlates well with CT and has good intra- and inter-observer reliability but underestimates version by 12° on average.

The incidence of noise generation arising from the large-diameter Delta Motion ceramic total hip bearing

Noise generation has been reported with ceramic-on-ceramic articulations in total hip replacement (THR). This study evaluated 208 consecutive Delta Motion THRs at a mean follow-up of 21 months (12 to 35). There were 141 women and 67 men with a mean age of 59 years (22 to 84). Patients were reviewed clinically and radiologically, and the incidence of noise was determined using a newly described assessment method. Noise production was examined against range of movement, ligamentous laxity, patient-reported outcome scores, activity level and orientation of the acetabular component. There were 143 silent hips (69%), 22 (11%) with noises other than squeaking, 17 (8%) with unreproducible squeaking and 26 (13%) with reproducible squeaking. Hips with reproducible squeaking had a greater mean range of movement (p < 0.001) and mean ligament laxity (p = 0.004), smaller median head size (p = 0.01) and decreased mean acetabular component inclination (p = 0.02) and anteversion angle (p = 0.02) compared with the other groups. There was no relationship between squeaking and age (p = 0.13), height (p = 0.263), weight (p = 0.333), body mass index (p = 0.643), gender (p = 0.07) or patient outcome score (p = 0.422). There were no revisions during follow-up. Despite the surprisingly high incidence of squeaking, all patients remain satisfied with their hip replacement.

Strict component positioning is necessary in hip resurfacing

BACKGROUND

Hip resurfacing arthroplasty has some advantages, including improved metal-on-metal articulation, a lower dislocation rate and preserved femoral bone. This procedure is a surgical option for younger and more active patients with osteoarthritis and osteonecrosis of the femoral head. Although there have been some reports about the efficacy of this technique, others report serious complications caused by metal debris. Additionally, femoral neck preservation adversely decreases the head-neck ratio and results in postoperative impingement.

METHODS

We evaluated the range of motion after hip resurfacing with various component orientations and optimal component orientations to avoid postoperative impingement using computer simulations in 10 male patients with osteonecrosis.

RESULTS

The mean ranges of motion in flexion, extension, abduction, adduction and internal rotation at 90° of flexion were 92.4° ± 13.8°, 25.7° ± 13.8°, 38.0° ± 11.1°, 29.1° ± 10.0° and 20.9° ± 11.5°, respectively. The oscillation angle in flexion and extension motion was 118.1° ± 10.3°. More than 100° of flexion was acquired in 79 of 240 simulations (32.9 %), and more than 20° extension was acquired in 142 simulations (59.2 %). Combined anteversion was significantly correlated with maximal flexion and extension angles. The component safe zone to fulfill the range of motion criteria varied among patients, and 4 of 10 patients had no safe zone.

CONCLUSIONS

Postoperative impingement occurs relatively frequently in hip resurfacing because of preservation of the femoral neck and component malpositioning. The safe zone of the acetabular component to avoid postoperative impingement is very narrow. Greater care should be taken regarding patient selection, rigorous preoperative planning and accurate component positioning.

Flexion following hip resurfacing and factors that influence it

Flexion following arthroplasty of the hip is important for activities of daily living. Studies have highlighted a possible reduction in flexion following Metal-on-Metal Hip Resurfacing Arthroplasty (MoMHRA) but failed to account for inter-subject variability and the possible etiology for this reduction. This in vivo study aims to determine whether flexion is restored following MoMHRA and identify factors that influence it. Charnley Class A patients (n=112) that underwent MoMHRA were reviewed in a dedicated clinic assessing flexion (resurfaced and contra-lateral hips) and outcome. The difference in flexion between both hips was defined as flexion deficit (δflexion). Various patient (age, gender, BMI) and surgical (component orientation, size, head-neck-ratio, offset) factors were examined in terms of their effect on δflexion. MoMHRA-hips had significantly reduced flexion as compared to the native hips. This flexion-deficit correlated with contra-lateral maximum flexion, component size, head-neck-ratio and component orientation. The findings demonstrate that flexion following MoMHRA is strongly correlated to but is reduced in comparison to the native, disease-free, hip flexion. Surgical practice can minimise flexion-deficit and optimise function.

Metal-on-metal hip arthroplasty

In this paper, we will consider the current role of metal-on-metal bearings by looking at three subtypes of MoM hip arthroplasty separately: Hip resurfacing, large head (> 36 mm) MoM THA and MoM THA with traditional femoral head sizes.

The ten-year survival of the Birmingham hip resurfacing: an independent series

Recent events have highlighted the importance of implant design for survival and wear-related complications following metal-on-metal hip resurfacing arthroplasty. The mid-term survival of the most widely used implant, the Birmingham Hip Resurfacing (BHR), has been described by its designers. The aim of this study was to report the ten-year survival and patient-reported functional outcome of the BHR from an independent centre. In this cohort of 554 patients (646 BHRs) with a mean age of 51.9 years (16.5 to 81.5) followed for a mean of eight years (1 to 12), the survival and patient-reported functional outcome depended on gender and the size of the implant. In female hips (n = 267) the ten-year survival was 74% (95% confidence interval (CI) 83 to 91), the ten-year revision rate for pseudotumour was 7%, the mean Oxford hip score (OHS) was 43 (SD 8) and the mean UCLA activity score was 6.4 (SD 2). In male hips (n = 379) the ten-year survival was 95% (95% CI 92.0 to 97.4), the ten-year revision rate for pseudotumour was 1.7%, the mean OHS was 45 (SD 6) and the mean UCLA score was 7.6 (SD 2). In the most demanding subgroup, comprising male patients aged < 50 years treated for primary osteoarthritis, the survival was 99% (95% CI 97 to 100). This study supports the ongoing use of resurfacing in young active men, who are a subgroup of patients who tend to have problems with conventional THR. In contrast, the results in women have been poor and we do not recommend metal-on-metal resurfacing in women. Continuous follow-up is recommended because of the increasing incidence of pseudotumour with the passage of time.

Anatomical hip range of motion after implantation during total hip arthroplasty with a large change in pelvic inclination

The supine functional pelvic plane is the recommended reference pelvic plane for acetabular cup planning in navigation-assisted total hip arthroplasty. However, it is unclear whether it can be used in patients with a large preoperative positional change in pelvic inclination (PC) from the supine to the standing position because it is unknown whether these patients have a different hip range of motion (ROM). We measured the anatomical hip ROM after implantation by computed tomography-based navigation in 91 patients and found it to be similar between those with a small PC (<10°) and those with a large PC (≥10°). There was no significant correlation between ROM and preoperative PC. The supine functional pelvic plane is adequate for cup planning whether the PC is small or large.

Posterior femoral neck impingement secondary to excess acetabular anteversion in hip resurfacing arthroplasty

Component malposition in resurfacing arthroplasty can cause impingement, reduced range of motion, increased metal wear, and early failure. It is therefore important that any component malposition is recognized early and monitored carefully. We present a case of delayed diagnosis of excess acetabular component anteversion causing posterior femoral neck impingement and pain. We correlate the degree of damage found intraoperatively with the degree of component malposition on the radiographs. This is used as a platform to discuss the optimum positioning of hip resurfacing components and the radiographic methods used to determine component position postoperatively.

Results of Conserve Plus® metal-on-metal hip resurfacing for post-traumatic arthritis and osteonecrosis

The safety and efficacy of metal-on-metal surface arthroplasty in post-traumatic arthritis and post-traumatic osteonecrosis (PT OA and PT ON) cases has not previously been thoroughly investigated. This study compared the outcomes of metal-on-metal hip resurfacing (HR) in patients performed for an indication of OA secondary to trauma to compared to PT ON. Metal-on-metal resurfacing arthroplasties were performed on 62 hips, 43 with PT OA and 19 with PT ON with secondary osteoarthritis. There were 51 males and 11 females. All patients were followed up clinically and radiographically with a mean follow-up of 87.2 months. Clinical outcome scores, survivorship, and radiographs were compared between the PT OA and PT ON group. The clinical outcomes for the PT ON and PT OA groups were similar with a survival rate of 95% (95% CI 82.1% to 98.8%) for the PT OA group alone at 8 years and 91% for those with PT OA with ON at 8 years (95% CI 50.8%-98.7%). The Kaplan-Meier survivorship curves for the cohorts of PT OA and PT ON patients were not statistically significantly different (Log rank, p=0.6036). Metal-on-metal hip resurfacing appears to be a safe and effective procedure for the treatment of both post-traumatic osteoarthritis and osteonecrosis.

High incidence of pseudotumour formation after large-diameter metal-on-metal total hip replacement: a prospective cohort study

Peri-articular soft-tissue masses or 'pseudotumours' can occur after large-diameter metal-on-metal (MoM) resurfacing of the hip and conventional total hip replacement (THR). Our aim was to assess the incidence of pseudotumour formation and to identify risk factors for their formation in a prospective cohort study. A total of 119 patients who underwent 120 MoM THRs with large-diameter femoral heads between January 2005 and November 2007 were included in the study. Outcome scores, serum metal ion levels, radiographs and CT scans were obtained. Patients with symptoms or an identified pseudotumour were offered MRI and an ultrasound-guided biopsy. There were 108 patients (109 hips) eligible for evaluation by CT scan at a mean follow-up of 3.6 years (2.5 to 4.5); 42 patients (39%) were diagnosed with a pseudotumour. The hips of 13 patients (12%) were revised to a polyethylene acetabular component with small-diameter metal head. Patients with elevated serum metal ion levels had a four times increased risk of developing a pseudotumour. This study shows a substantially higher incidence of pseudotumour formation and subsequent revisions in patients with MoM THRs than previously reported. Because most revision cases were identified only after an intensive screening protocol, we recommend close monitoring of patients with MoM THR.

Metal-on-metal total hip arthroplasty: causes and high incidence of early failure

Early failures of metal-on-metal total hip arthroplasty (THA) occur due to aseptic loosening, metal hypersensitivity reactions, pseudotumor formation, and component seizing. The purpose of this study was to investigate the timing, common modes of failure, clinical outcomes, and incidence of metal-on-metal THA revisions. A review was performed of 80 patients who underwent revision of a failed metal-on-metal THA for any reason. The most common reason for metal-on-metal failure was aseptic acetabular loosening, with a rate of 56.25% (45/80 patients). Early failure of metal-on-metal THAs was noted, with 78% of these revisions being performed within 2 years of the index operation and 92.5% within 3 years. Furthermore, 13% of patients experienced significant localized soft tissue reactions. Mean preoperative Harris Hip Score was 42.35 ± 14.24 and mean postoperative Harris Hip Score was 66.5 ± 23.2 (range, 9.55-95.4), with an average follow-up of 438 ± 492 days (range, 40-2141), or 1.2 years.It is imperative that clinicians be cognizant of the fact that the proposed advantages of metal-on-metal THA are not without potential detrimental sequelae. This article proposes an algorithm to aid in diagnosing the etiology of a painful metal-on-metal THA, as well as 2 classification schemes regarding metal-on-metal THA complications to help direct treatment.

Independent predictors of revision following metal-on-metal hip resurfacing

Modern metal-on-metal hip resurfacing has been widely performed in the United Kingdom for over a decade. However, the literature reports conflicting views of the benefits: excellent medium- to long-term results with some brands in specific subgroups, but high failure rates and local soft-tissue reactions in others. The National Joint Registry for England and Wales (NJR) has collected data on all hip resurfacings performed since 2003. This retrospective cohort study recorded survival time to revision from a resurfacing procedure, exploring risk factors independently associated with failure. All patients with a primary diagnosis of osteoarthritis who underwent resurfacing between 2003 and 2010 were included in the analyses. Cox’s proportional hazard models were used to analyse the extent to which the risk of revision was related to patient, surgeon and implant covariates.

A total of 27 971 hip resurfacings were performed during the study period, of which 1003 (3.59%) underwent revision surgery. In the final adjusted model, we found that women were at greater risk of revision than men (hazard ratio (HR) = 1.30, p = 0.007), but the risk of revision was independent of age. Of the implant-specific predictors, five brands had a significantly greater risk of revision than the Birmingham Hip Resurfacing (BHR) (ASR: HR = 2.82, p < 0.001, Conserve: HR = 2.03, p < 0.001, Cormet: HR = 1.43, p = 0.001, Durom: HR = 1.67, p < 0.001, Recap: HR = 1.58, p = 0.007). Smaller femoral head components were also significantly more likely to require revision (≤ 44 mm: HR = 2.14, p < 0.001, 45 to 47 mm: HR = 1.48, p = 0.001) than medium or large heads, as were operations performed by low-volume surgeons (HR = 1.36, p <  0.001). Once these influences had been removed, in 4873 male patients < 60 years old undergoing resurfacing with a BHR, the five-year estimated risk of revision was 1.59%.

In summary, after adjustment for a range of covariates we found that there were significant differences in the rate of failure between brands and component sizes. Younger male patients had good five-year implant survival when the BHR was used.

Theoretical relationships between component design, patient bone geometry and range-of-motion post hip resurfacing

Clinical studies indicate that range of motion until prosthetic impingement is important in understanding unexplained failures of hip resurfacings, yet the underlying biomechanical principles have received little attention. This study investigates the mathematical relationships between component design, position, patient bone geometry and range of motion in hip resurfaced prostheses. Variations in range of motion and impingement-free safe-zones for cup position were calculated using an established method of vector analysis that facilitated parametric analysis in a time efficient manner. The alpha angle, defined as the angle between the centreline of the femoral neck and the waist of the femoral head/neck junction, was used to represent the natural femoral neck. Range of motion and impingement-free safe-zones were inversely proportional to the alpha angle and cup inclusion angle. The size of the safe-zone was most sensitive to the alpha angle with a 6 degrees reduction, decreasing the range of cup positions without impingement by 80-100%. Lowering the upper limit of cup inclination from 55 degrees to 45 degrees reduced the range of cup positions that allow impingement-free motion by 47-94%. No common safe-zone was observed for the range of component sizes and positions investigated. This offers an explanation to why clinic studies have failed to associate outcome with standardised positioning criteria.

A hierarchy of computationally derived surgical and patient influences on metal on metal press-fit acetabular cup failure

The impact of anatomical variation and surgical error on excessive wear and loosening of the acetabular component of large diameter metal-on-metal hip arthroplasties was measured using a multi-factorial analysis through 112 different simulations. Each surgical scenario was subject to eight different daily loading activities using finite element analysis. Excessive wear appears to be predominantly dependent on cup orientation, with inclination error having a higher influence than version error, according to the study findings. Acetabular cup loosening, as inferred from initial implant stability, appears to depend predominantly on factors concerning the area of cup-bone contact, specifically the level of cup seating achieved and the individual patient's anatomy. The extent of press fit obtained at time of surgery did not appear to influence either mechanism of failure in this study.

In vivo evaluation of edge-loading in metal-on-metal hip resurfacing patients with pseudotumours

Objectives

Pseudotumours (abnormal peri-prosthetic soft-tissue reactions) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated metal ion levels, suggesting that excessive wear may occur due to edge-loading of these MoM implants. This study aimed to quantify in vivo edge-loading in MoMHRA patients with and without pseudotumours during functional activities.

Methods

The duration and magnitude of edge-loading in vivo was quantified during functional activities by combining the dynamic hip joint segment contact force calculated from the three-dimensional (3D) motion analysis system with the 3D reconstruction of orientation of the acetabular component and each patient’s specific hip joint centre, based on CT scans.

Results

Edge-loading in the hips with pseudotumours occurred with a four-fold increase in duration and magnitude of force compared with the hips without pseudotumours (p = 0.02).

Conclusions

The study provides the first in vivo evidence to support that edge-loading is an important mechanism that leads to localised excessive wear (edge-wear), with subsequent elevation of metal ion levels in MoMHRA patients with pseudotumours.

Disappointing short-term results with the DePuy ASR XL metal-on-metal total hip arthroplasty

Outcomes of ultralarge-diameter femoral heads used in metal-on-metal (MOM) total hip arthroplasty (THA) are relatively unknown. This study reports on early failures of the ASR XL (Depuy, Warsaw, Ind) and assesses whether a correlation with cup positioning exists. A retrospective review of 70 consecutive MOM THAs with ultralarge-diameter femoral head and monoblock acetabular component was conducted. Minimum follow-up was 24 months. Of 70 THAs, 12 (17.1%) required revision within 3 years for pain (7), loosening (3), and squeaking (2). Three additional THAs noted squeaking, 2 noted grinding, and 3 additional hips had persistent pain. In total, 20 (28.6%) of 70 demonstrated implant dysfunction. Acetabular components for all symptomatic hips were in acceptable range of cup abduction and anteversion. The failures noted with this design do not correlate to cup placement. The high rate of implant dysfunction at early follow-up suggests serious concerns with the concept of MOM THA with an ultralarge-diameter femoral head paired with a monoblock acetabular cup.

Minimum 5-year results of modular metal-on-metal total hip arthroplasty

This study reports minimum 5-year results of 95 hips implanted with a Pinnacle (DePuy, Warsaw, Ind) modular metal-on-metal acetabular prosthesis. Clinical scores such as the Harris Hip and Western Ontario and McMaster Universities Arthritis Index revealed excellent clinical outcomes at mean 6-year follow-up. With the use of large-diameter femoral heads, dislocation was rare, occurring in only 1 hip. Moreover, no acetabular and only 3 femoral osteolytic lesions were detected. Kaplan-Meier survivorship at 7 years after arthroplasty was 97.8% for the total hip arthroplasty construct and 100% for the acetabular shell. No unexplained pain or other complication attributable to wear debris or the metal-on-metal articulation was observed. These findings indicate that total hip arthroplasty with this specific modular metal-on-metal bearing performed well in a high-demand population at midterm follow-up.

Current controversies in hip surgery

An international faculty of orthopaedic surgeons presented their work on the current challenges in hip surgery at the London Hip Meeting which was attended by over 400 delegates. The topics covered included femoroacetabular impingement, thromboembolic phenomena associated with hip surgery, bearing surfaces (including metal-on-metal articulations), outcomes of hip replacement surgery and revision hip replacement. We present a concise report of the current opinions on hip surgery from this meeting with appropriate references to the current literature.

The influence of acetabular inclination angle on the penetration of polyethylene and migration of the acetabular component

In this prospective study we studied the effect of the inclination angle of the acetabular component on polyethylene wear and component migration in cemented acetabular sockets using radiostereometric analysis.

A total of 120 patients received either a cemented Reflection All-Poly ultra-high-molecular-weight polyethylene or a cemented Reflection All-Poly highly cross-linked polyethylene acetabular component, combined with either cobalt–chrome or Oxinium femoral heads. Femoral head penetration and migration of the acetabular component were assessed with repeated radiostereometric analysis for two years. The inclination angle was measured on a standard post-operative anteroposterior pelvic radiograph. Linear regression analysis was used to determine the relationship between the inclination angle and femoral head penetration and migration of the acetabular component.

We found no relationship between the inclination angle and penetration of the femoral head at two years’ follow-up (p = 0.9). Similarly, our data failed to reveal any statistically significant correlation between inclination angle and migration of these cemented acetabular components (p = 0.07 to p = 0.9).