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Publications (13)17.76 Total impact

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    ABSTRACT: Widespread concern exists about adverse tissue reactions after metal-on-metal (MoM) total hip replacement (THR). Concerns have also been expressed with wear and corrosion of taper junctions in THR. We report the effect of surface finish and contact area associated with a single combination of materials of modular tapers. In an in vitro test, we investigated the head/neck (CoCrMo/Ti) interface of modular THRs using commercially available heads. Wear and corrosion of taper surfaces was compared following a 10 million loading cycle. Surface parameters and profiles were measured before and after testing. Electrochemical static and dynamic corrosion tests were performed under loaded and non-loaded conditions. After the load test, the surface roughness parameters on the head taper were significantly increased where the head/neck contact area was reduced. Similarly, the surface roughness parameters on the head taper were significantly increased where rough neck tapers were used. Corrosion testing showed breaching of the passive film on the rough but not the smooth neck tapers. Thus, surface area and surface finish are important factors in wear and corrosion at modular interfaces. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.
    Journal of Orthopaedic Research 08/2013; · 2.88 Impact Factor
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    ABSTRACT: Determining the relationship between clinical factors and engineering analysis of retrieved hip implants can help our understanding of the mechanism of device failure. This is particularly important for metal-on-metal hip arthroplasties because the most common cause of failure is unexplained. We sought to understand the variation in wear rates in a large series of retrieved metal-on-metal hip arthroplasty components. We prospectively recorded preoperative, intraoperative, and postoperative data to study the effect on both head and cup wear rates of the following variables: patient sex, cause of failure, manufacturer type, resurfacing or modular design, blood cobalt and chromium levels, edge-loading, femoral head size, and cup inclination angle. We analyzed 276 components (138 femoral head and acetabular cup couples) retrieved from failed metal-on-metal hip replacements. We found a high rate of edge-loading (64%), but only forty-three (31%) of 138 hips had a cup inclination angle of >55°. Multivariate analysis showed that the most important factor responsible for the variation in wear rate was the presence or absence of edge-loading, even when adjusted for cup inclination angle. Strong positive correlations were found between acetabular cup and femoral head wear rates and between wear rates and both blood cobalt and chromium ion levels. Multivariate analysis of nine factors found that edge-loading was the most important predictor of wear rate and occurred in two-thirds of failed metal-on-metal hip replacements. The majority did not have excessive cup inclination angles: 68% had an inclination angle of ≤55°. This finding, together with the relatively low median wear rate of the components in our study, suggests that cup position and/or wear rate may not be the only outcome related to failure of metal-on-metal hip replacements. Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.
    The Journal of Bone and Joint Surgery 04/2013; 95(8):678-85. · 3.23 Impact Factor
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    ABSTRACT: PURPOSES: Post arthroplasty gait analysis has up till now been performed on subjects walking slowly on flat ground rather than challenging them at faster speeds or walking uphill. We therefore asked: (1) Is there a measurable difference in the performance of hip resurfacing arthroplasty (HRA) and total hip arthroplasty (THA) limbs at patients' self-determined fastest walking speeds and steepest inclines? and (2) Is there a relationship between the observed differences between the gait of HRA and THA implanted limbs and patient walking speeds and inclines. METHODS: In an ethically approved study we recruited patients with bilateral hip arthroplasties: one HRA and one THA. Nine subjects were assessed using an instrumented treadmill at a range of speeds and inclines by a blinded observer. The ground reaction forces of subjects were recorded and an age, sex and BMI matched control group was used for comparison. RESULTS: Increasing walking speed correlated strongly with between leg differences in weight acceptance (r = 0.9, p = 0.000) and push-off force (r = 0.79, p = 0.002). HRA implanted limbs accepted significantly more weight at top walking speeds (1208 N ± 320 versus 1279 N ± 370, p = 0.026) and pushed off with greater force when walking uphill (818 N ± 163 versus 855 ± 166, p = 0.012). HRA limbs more closely approximated to the gait of the normal control group. CONCLUSIONS: Arthroplasty implants do have an impact on the gait characteristics of patients. Differences in gait are more likely to be evident when assessment is made at fast speeds and walking uphill. This study suggests that HRA may enable a more normal gait.
    International Orthopaedics 02/2013; · 2.32 Impact Factor
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    ABSTRACT: Due to an increasing lifespan, patients with osteogenesis imperfecta have a high incidence of hip osteoarthritis. The presence of recurrent fractures and deformities make primary and particularly revision total hip arthroplasty challenging. We present a series of patients with osteogenesis imperfecta undergoing total hip arthroplasty at a tertiary referral centre with a median follow-up of 7.6 years (4 to 35 years). There were four primary total hip arthroplasties and eight revision total hip arthroplasties performed in four patients. Three femoral components were custom computer assisted design computer assisted manufactured. The survival rate of the primary total hip arthroplasty was 16% and there were ten complications: five intraoperative fractures, one case of septic loosening and four cases of aseptic loosening. Patients with pre-operative acetabular protrusio were significantly more likely to require revision surgery (p = 0.02). At latest follow-up, the median Oxford hip score was 41 (37 to 46). As the largest series of primary and revision total hip arthroplasty performed in patients with osteogenesis imperfecta, we report good medium to long-term outcomes. Preoperative planning and consideration of custom made prostheses have an important role in these complex cases.
    Hip international: the journal of clinical and experimental research on hip pathology and therapy 01/2013; · 0.34 Impact Factor
  • Luthfur Rahman, Justin Cobb, Sarah Muirhead-Allwood
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    ABSTRACT: Polyethylene wear is an important factor in failure of total hip arthroplasty (THA). With increasing numbers of THAs being performed worldwide, particularly in younger patients, the burden of failure and revision arthroplasty is increasing, as well, along with associated costs and workload. Various radiographic methods of measuring polyethylene wear have been developed to assist in deciding when to monitor patients more closely and when to consider revision surgery. Radiographic methods that have been developed to measure polyethylene wear include manual and computer-assisted plain radiography, two- and three-dimensional techniques, and radiostereometric analysis. Some of these methods are important in both clinical and research settings. CT has the potential to provide additional information on component orientation and enables assessment of periprosthetic osteolysis, which is an important consequence of polyethylene wear.
    The Journal of the American Academy of Orthopaedic Surgeons 12/2012; 20(12):735-43. · 2.46 Impact Factor
  • Nemandra A Sandiford, Sarah Muirhead-Allwood, John Skinner
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    ABSTRACT: Revision of well fixed uncemented Birmingham Hip Resurfacing (BHR) acetabular components is challenging due to their dual radius design and their stabilising fins. These features preclude use of the standard Explant device. We investigated a novel device designed to simplify revision of this socket. This prospective study included 6 male and 14 female patients. The reasons for revision, technique of revision and the scientific basis for use of this device are discussed. The sizes of revised and implanted components were measured and the amount of bone loss was calculated. Patient satisfaction was assessed as well as pre and post operative hip scores. Six men and fourteen women were included. Average ages were 58 and 623 years respectively. The average diameters of the explanted and re-implanted sockets were 50.7 and 54.6 mm respectively. Average time for revision of the cup was less than 5 minutes. The average duration of follow-up was 13.2 months. All patients were satisfied with their outcomes. This device simplifies the use of the Explant in removing well fixed BHR sockets with predictably minimal loss of host bone.
    Acta orthopaedica Belgica 02/2012; 78(1):49-54. · 0.63 Impact Factor
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    ABSTRACT: We prospectively evaluated the long-term outcome of 158 consecutive patients who underwent revision total hip replacement using uncemented computer-assisted design-computer-assisted manufacture femoral components. There were 97 men and 61 women. Their mean age was 63.1 years (34.6 to 85.9). The mean follow-up was 10.8 years (10 to 12). The mean Oxford, Harris and Western Ontario and McMaster hip scores improved from 41.1, 44.2 and 52.4 pre-operatively to 18.2, 89.3 and 12.3, respectively (p < 0.0001, for each). Six patients required further surgery. The overall survival of the femoral component was 97% (95% confidence interval 94.5 to 99.7). These results are comparable to those of previously published reports for revision total hip replacement using either cemented or uncemented components.
    Journal of Bone and Joint Surgery - British Volume 10/2010; 92(10):1370-5. · 2.69 Impact Factor
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    ABSTRACT: We carried out a cross-sectional study with analysis of the demographic, clinical and laboratory characteristics of patients with metal-on-metal hip resurfacing, ceramic-on-ceramic and metal-on-polyethylene hip replacements. Our aim was to evaluate the relationship between metal-on-metal replacements, the levels of cobalt and chromium ions in whole blood and the absolute numbers of circulating lymphocytes. We recruited 164 patients (101 men and 63 women) with hip replacements, 106 with metal-on-metal hips and 58 with non-metal-on-metal hips, aged < 65 years, with a pre-operative diagnosis of osteoarthritis and no pre-existing immunological disorders. Laboratory-defined T-cell lymphopenia was present in 13 patients (15%) (CD8(+) lymphopenia) and 11 patients (13%) (CD3(+) lymphopenia) with unilateral metal-on-metal hips. There were significant differences in the absolute CD8(+) lymphocyte subset counts for the metal-on-metal groups compared with each control group (p-values ranging between 0.024 and 0.046). Statistical modelling with analysis of covariance using age, gender, type of hip replacement, smoking and circulating metal ion levels, showed that circulating levels of metal ions, especially cobalt, explained the variation in absolute lymphocyte counts for almost all lymphocyte subsets.
    Journal of Bone and Joint Surgery - British Volume 06/2009; 91(6):835-42. · 2.69 Impact Factor
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    ABSTRACT: Periprosthetic fractures which occur in close proximity to an in situ hip resurfacing prosthesis can pose a technically demanding challenge to orthopaedic surgeons. While this is currently an uncommon problem, it is logical to assume that as the numbers of hip resurfacing arthroplasties increase, we are likely to see larger numbers of patients with this presentation. In these cases, if the resurfacing prosthesis in not functioning well, the choice to replace it is easy. If it is well functioning, this decision becomes more difficult however. We present a case illustrating our experience with this unusual problem. We discuss our treatment strategy, the issues and options which need to be considered before treating these patients and review the current literature addressing this topic.
    European Journal of Orthopaedic Surgery & Traumatology 03/2009; 19(3):159-162. · 0.18 Impact Factor
  • Nemandra A Sandiford, Sarah Muirhead-Allwood, John Skinner, Chindu Kabir
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    ABSTRACT: We report the early results of 10 consecutive metal-on-metal resurfacing arthroplasties performed between May 2006 and July 2007 in young, active patients with gross femoral head defects. Failure was classified as revision for any reason. The mean age of our cohort at the time of surgery was 42.8 years and the minimal period of follow-up was 6.9 months. No patients were lost to follow-up. Up to the time of last review, there were no failures and all patients have returned to their preoperative levels of activity. This study shows promising early results of a bone-conserving, hydroxyapatite-coated, uncemented metal-on-metal bearing prosthesis in young, active patients with bony defects of the femoral head.
    Surgical technology international 02/2009; 18:195-200.
  • Sarah Muirhead-Allwood, Nemandra Sandiford, Chindu Kabir
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    ABSTRACT: The concept of hip resurfacing arthroplasty is not new. Early designs by pioneers including Wagner, Freeman and Charnley failed mainly due to material, design and manufacturing flaws. Modern metal on metal hip resurfacing has become increasingly popular over the last decade however. Good early and intermediate results have been reported in young, active patients using this prosthesis. Theoretical benefits compared to conventional total hip arthroplasty (THA) include bone stock preservation, particularly on the femoral side, improved stability due to the large diameter bearing, improved range of motion and proprioception and technically less difficult revision to a total hip arthroplasty if necessary. This prosthesis must be used with strict indications however as the technique is more demanding than conventional THA and imperfect positioning of either the acetabular or femoral component are associated with complications. Unique complications thought to be due to hypersensitivity reactions have also been reported. This article outlines the evolution of hip resurfacing arthroplasty and discusses new designs, surgical techniques and potential complications, all of which the surgeon needs to be familiar with.
    Seminars in Arthroplasty 01/2008; 19(4):274-282.
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    ABSTRACT: With the increased use of metal-on-metal as a bearing surface, complications and side effects are being recognised more frequently. We present a small series of a previously unreported complication, which appears specific to metal-on-metal bearing surface arthroplasties: three cases of infection in the presence of local metal debris and histological features of aseptic lymphocytic vasculitis associated lesions (ALVAL). Each case is associated with significant soft tissue loss and bone destruction to such an extent that pelvic discontinuity has occurred. We postulate that the combination of metal debris, ALVAL and tissue necrosis provides a unique environment for peri-prosthetic bacterial growth and rapid spread of infection.
    Hip international: the journal of clinical and experimental research on hip pathology and therapy 20(2):242-7. · 0.34 Impact Factor