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D W Murray

Publications and source records attributed to D W Murray.

At least 37 records · Page 2Linked to original sources
PubMed2005

Osteonecrosis in retrieved femoral heads after failed resurfacing arthroplasty of the hip.

We present the histological findings of bone retrieved from beneath the femoral components of failed metal-on-metal hip resurfacing arthroplasties. Of a total of 377 patients who underwent resurfacing arthroplasty, 13 required revision; for fracture of the femoral neck in eight, loosening of a component in three and for other reasons in two. None of these cases had shown histological evidence of osteonecrosis in the femoral bone at the time of the initial implantation. Bone from the remnant of the femoral head showed changes of osteonecrosis in all but one case at revision. In two cases of fracture which occurred within a week of implantation, the changes were compatible with early necrosis of the edge of the fracture. In the remaining six fractures, there were changes of established osteonecrosis. In all but one of the non-fracture cases, patchy osteonecrosis was seen. We conclude that histological evidence of osteonecrosis is a common finding in failed resurfaced hips. Given that osteonecrosis is extensive in resurfaced femoral heads which fail by fracture, it is likely to play a role in the causation of these fractures.

Arthroplasty, Replacement, Hip↗
PubMed2005

Influence of surface geometry and the cam-post mechanism on the kinematics of total knee replacement.

Abnormal sagittal kinematics after total knee replacement (TKR) can adversely affect functional outcome. Two important determinants of knee kinematics are component geometry and the presence or absence of a posterior-stabilising mechanism (cam-post). We investigated the influence of these variables by comparing the kinematics of a TKR with a polyradial femur with a single radius design, both with and without a cam-post mechanism. We assessed 55 patients, subdivided into four groups, who had undergone a TKR one year earlier by using an established fluoroscopy protocol in order to examine their kinematics in vivo. The kinematic profile was obtained by measuring the patellar tendon angle through the functional knee flexion range (0 degrees to 90 degrees ) and the results compared with 14 normal knees. All designs of TKR had abnormal sagittal kinematics compared with the normal knee. There was a significant (p < 0.05) difference between those of the two TKRs near to full extension. The presence of the cam-post mechanism did not influence the kinematics for either TKR design. These differences suggest that surface geometry is a stronger determinant of kinematics than the presence or absence of a cam-post mechanism for these two designs. This may be because the cam-post mechanism is ineffective.

Aged↗
PubMed2005

Influence of stem geometry on the stability of polished tapered cemented femoral stems.

Polished, tapered stems are now widely used for cemented total hip replacement and many such designs have been introduced. However, a change in stem geometry may have a profound influence on stability. Stems with a wide, rectangular proximal section may be more stable than those which are narrower proximally. We examined the influence of proximal geometry on stability by comparing the two-year migration of the Exeter stem with a more recent design, the CPS-Plus, which has a wider shoulder and a more rectangular cross-section. The hypothesis was that these design features would increase rotational stability. Both stems subsided approximately 1 mm relative to the femur during the first two years after implantation. The Exeter stem was found to rotate into valgus (mean 0.2 degrees , sd 0.42 degrees ) and internally rotate (mean 1.28 degrees , sd 0.99 degrees ). The CPS-Plus showed no significant valgus rotation (mean 0.07 [correction] degrees, sd 0.29 [correction] degrees ) or internal rotation (mean -0.03 degrees , sd 0.75 degrees ). A wider, more rectangular cross-section improves rotational stability and may have a better long-term outcome.

Aged↗
PubMed2004

[Medial unicompartmental knee replacement using the "Oxford Uni" meniscal bearing knee].

Medial unicompartmental knee replacement (UKR) has many advantages over total replacement (TKR) including better function and reduced morbidity. However, the long-term failure rates of fixed-bearing UKR are high, especially because of polyethylene wear. The fully congruent mobile bearing of the Oxford UKR exhibits minimal polyethylene wear, failure from this cause does not seem to occur before 10 years. The instrumentation allows precise implantation to restore isometric function of the ligaments. During its 20 years development, the limits of usefulness of the implant have been established and found to include about one in four knees requiring replacement for osteoarthritis. In an independent series, using these criteria, the 15 year survival was 94%. Since 1998, the phase 3 implant has been used with modified instruments through a small incision, avoiding damage to the extensor mechanism. Patients now recover about three times faster than after TKR, and regain much better flexion (mean 135 degrees ). The current evidence supports that the minimally invasive Oxford UKR should be seriously considered as primary treatment for anteromedial compartment osteoarthritis-provided the appropriate surgical expertise is available.

Adult↗
PubMed2004

Minimally invasive Oxford unicompartmental knee arthroplasty: functional results at 1 year and the effect of surgical inexperience.

Oxford medial unicompartmental arthroplasty (UCA) is now routinely performed through a short incision without dislocation of the patella. We present the 1 year results of the first 104 knees operated in Oxford using this technique and the learning curve associated with it. The patient's average age at surgery was 68 years. The average American Knee Society 'knee score' improved from 37 to 94 points and the average 'functional score' from 50 to 92 points. Average maximum flexion improved from 117 to 131 degrees. The average knee score during a surgeon's first 10 cases was 88 points, which was significantly less (P<0.03) than the score achieved for subsequent cases after the first 10 (95 points). These data suggest for the first time that a learning curve exists with worse results being achieved during a surgeon's first 10 cases. However, the results during the learning curve are still similar to that achieved after total knee arthroplasty.

Aged↗
PubMed2004

In vivo measurement of total knee replacement wear.

Polyethylene wear is one of the most important causes of failure of total knee replacements (TKRs). Currently, wear can only be accurately measured by retrieval studies. There is a need for a method to measure wear accurately in vivo. We have developed a Roentgen stereophotogrammetric analysis (RSA) system that can measure penetration of the metallic femoral component into the polyethylene of the tibia. We have used this system to study six AGC TKRs at 6 years postoperatively and six control AGC TKRs at 2 weeks postoperatively. The mean difference between the RSA measured bearing thickness and the manufacturer's quoted values for the control group was -0.03 mm (S.D. 0.17). The average linear penetration in the study group was 0.8 mm (S.D. 0.46). This was significantly (P<0.0001) different from the control group. The average linear penetration rate was 0.13 mm per year (S.D. 0.08). We would expect the penetration to deepen with time. In young active patients, this could be a cause for concern, particularly with a thin bearing. The current system is accurate enough to measure wear at 5 years post TKR. It has the potential for predicting long-term wear problems with new designs of TKR and new materials within 2 years.

Aged↗
PubMed2004

A comparison of Rasch with Likert scoring to discriminate between patients' evaluations of total hip replacement surgery.

The purpose of this study was to examine whether there are advantages in terms of outcome assessment of using Rasch methods of scoring the 12-item Oxford Hip Score (OHS) questionnaire over conventionally Likert scores. As part of a prospective cohort study of total hip replacements in five former regions of England the OHS was sent to patients pre-operatively, at 3 months and 1 year post-operatively. Post-operative data was collected on over 5000 cases. Based on the level of satisfaction with surgery, patients were divided into satisfied and dissatisfied. Analyses were performed to test the relative precision (RP) of Rasch scoring vs. conventionally Likert scores in discriminating the groups experiencing different level of satisfaction. Considerable gains in precision were achieved with Rasch scoring methods when groups were compared 3 and 12 months post-operatively. The results from the current study suggest that in some situations there may be substantial gains in measuring health related outcomes using Rasch-based scoring methods.

Activities of Daily Living↗
PubMed2004

Roentgen stereophotogrammetric analysis of the Birmingham hip resurfacing arthroplasty. A two-year study.

The Birmingham hip resurfacing (BHR) arthroplasty is a metal-on-metal prosthesis for which no medium- or long-term results have been published. Despite this, it is increasing in popularity as an alternative to stemmed prostheses for younger patients. Since the fixation of the socket is conventional, the major concern is long-term failure of the femoral component. This can be predicted by the use of roentgen stereophotogrammetric analysis (RSA). We have therefore undertaken such a study of the BHR femoral component over a period of two years. Twenty patients (22 hips) underwent a standard BHR procedure. Migration of the femoral component was measured by RSA at intervals of three, six, 12 and 24 months. At 24 months the total three-dimensional migration of the head was 0.2 mm. This was not statistically significant. Previous studies have shown that implants which loosen quickly have rapid early migration. Our results therefore suggest that the BHR femoral component is an inherently stable device which is likely to perform well in the long term.

Adult↗
PubMed2003

The influence of cement viscosity on the early migration of a tapered polished femoral stem.

It is unclear whether it is best to use high-viscosity or low-viscosity cement for fixation of total hip replacement (THR) femoral components. This study examines the influence of cement viscosity on the migration of the Exeter femoral component using roentgen stereophotogrammetric analysis (RSA). Simplex, CMW1 and CMW3 G cements were examined in a total of 46 patients over a 12-month period. The overall pattern of migration for all cohorts was one of subsidence and rotation into valgus. There was no significant difference in any aspect of migration between the groups. In vitro studies demonstrate that low-viscosity cement forms a more stable bone-cement interface. Several groups have examined the in vivo effect of cement viscosity on stem longevity with conflicting results. For a polished, tapered implant that is designed to subside, cement viscosity does not influence the 1-year migration, and it is therefore unlikely to affect long-term outcome.

Aged↗
PubMed2003

Development and numerical validation of a finite element model of the muscle standardized femur.

The human femur is one of the parts of the musculo-skeletal system most frequently analysed by means of the finite element (FE) method. Most FE studies of the human femur are based on computed tomography data sets of a particular femur. Since the geometry of the chosen sample anatomy influences the computed results, direct comparison across various models is often difficult or impossible. The aim of the present work was to develop and validate a novel three-dimensional FE model of the human femur based on the muscle standardized femur (MuscleSF) geometry. In the new MuscleSF FE model, the femoral attachment of each muscle was meshed separately on the external bone surface. The model was tested under simple load configurations and the results showed good agreement with the converged solution of a former study. In the future, using the validated MuscleSF FE model for numerical studies of the human femur will provide the following benefits: (a) the numerical accuracy of the model is known; (b) muscle attachment areas are incorporated in the model, therefore physiological loading conditions can be easily defined; (c) analyses of the femur under physiological load cases will be replicable; (d) results based on different load configurations could be compared across various studies.

Compressive Strength↗
PubMed2003

Strain distribution within the human femur due to physiological and simplified loading: finite element analysis using the muscle standardized femur model.

The aim of the current work was to study the effect of simplified loading on strain distribution within the intact femur using the Muscle Standardized Femur finite element model and to investigate whether the interaction between the intact human femur and the muscles which are attached to the bone surface could accurately be represented by concentrated forces, applied through the centroids of their attachment areas. An instant at 10 per cent of the gait cycle during level walking was selected as the reference physiological load case; nine load cases were analysed. Comparison of the calculated results for the physiological load case with muscle forces uniformly distributed over their attachment areas showed good agreement with in vivo measurements of strain values and femoral head displacement in humans. Simplified load cases generated unrealistic displacement results and high strain magnitudes, exceeding the physiological range. It was found that when muscles with large attachment areas are included in the model and the muscle forces are simplified, stress and strain distributions will be affected not only on the external bone surface in the vicinity of the load application node, but also on the internal surface of the cortical bone. However, applying muscle forces as concentrated loads at the centroids of the attachment areas can serve as first indicators of the physiological stress and strain levels, if results from nodes and elements in the vicinity of the load application nodes are discarded. Omitting muscle forces or fixing the femur in mid-shaft leads to large unphysiological strain values.

Compressive Strength↗
PubMed2003

A mobile-bearing total knee prosthesis compared with a fixed-bearing prosthesis. A multicentre single-blind randomised controlled trial.

Before proceeding to longer-term studies, we have studied the early clinical results of a new mobile-bearing total knee prosthesis in comparison with an established fixed-bearing device. Patients requiring bilateral knee replacement consented to have their operations under one anaesthetic using one of each prosthesis. They also agreed to accept the random choice of knee (right or left) and to remain ignorant as to which side had which implant. Outcomes were measured using the American Knee Society Score (AKSS), the Oxford Knee Score (OKS), and determination of the range of movement and pain scores before and at one year after operation. Preoperatively, there was no systematic difference between the right and left knees. One patient died in the perioperative period and one mobile-bearing prosthesis required early revision for dislocation of the meniscal component. At one year the mean AKSS, OKS and pain scores for the new device were slightly better (p < 0.025) than those for the fixed-bearing device. There was no difference in the range of movement. We believe that this is the first controlled, blinded trial to compare early function of a new knee prosthesis with that of a standard implant. It demonstrates a small but significant clinical advantage for the mobile-bearing design.

Aged↗
PubMed2002

Defining the femoral axis on lateral knee fluoroscopy.

The methodological detail about determining the femoral axis on lateral fluoroscopic images of the knee is lacking. This paper reports on the use of the posterior border of the lower femoral diaphysis to represent the axis. This method is accurate, simple, reliable and can be used by researchers studying knee joint kinematics using dynamic video fluoroscopy. It is also useful in the outpatient clinic to assess the flexion/extension position of femoral components after knee arthroplasty.

Arthroplasty, Replacement, Knee↗
PubMed2002

Accelerated recovery for unicompartmental knee replacement--a feasibility study.

A pilot study assessed the feasibility of discharging NHS patients undergoing knee replacement within a day of surgery. Seven patients with medial compartment osteoarthritis were recruited after fulfilling strict exclusion criteria. Pre-operative assessment revealed that all patients had significant dysfunction and pain before operation. They had medial unicompartmental replacement through a short incision without dislocation of the patella. Each patient underwent an accelerated recovery program that included pain control, physiotherapy and self-assessment. Patients were mobilised immediately after operation. Follow-up assessment was performed at 1, 2 and 6 weeks after surgery. All patients, except one (who failed to go home because of an administrative error), returned home the day after surgery. The average pain score for the first 2 weeks after surgery was 2/10. At 6 weeks, knee flexion averaged 125 degrees and all patients were walking independently and painfree. The new protocol allows for early, safe discharge of patients undergoing unicompartmental knee replacement.

Aged↗
PubMed2002

The effect of anteversion on femoral component stability assessed by radiostereometric analysis.

Internal rotation of a femoral stem within the femur, with posterior migration of the femoral head (PHM) relative to the femur, is an important mode of failure. The relationship between anteversion and rotational stability for the Exeter (Howmedica International Ltd, London, UK) and Charnley Elite (DePuy International Ltd, Leeds, UK) stems was investigated using radiostereometric analysis (RSA). For the Elite, there was a significant (P=.01) correlation between anteversion and PHM, whereas for the Exeter, there was no significant correlation (P=.6). Increasing anteversion of the Elite was associated with decreasing PHM and increased stability. Of stems, 20% of the Elite and none of the Exeter were classified as having reduced rotational stability because their PHM was >2 SDs from the mean. All reduced rotational stability implants had anteversion substantially <20 degrees. Polished collarless tapered stems such as the Exeter seem to have enhanced rotational stability. For conventional stems, increasing anteversion increases stability. It is recommended that these stems are anteverted 20 degrees.

Hip Prosthesis↗
PubMed2002

Dislocation of the bearing of the Oxford lateral unicompartmental arthroplasty. A radiological assessment.

When the Oxford unicompartmental meniscal bearing arthroplasty is used in the lateral compartment of the knee, 10% of the bearings dislocate. A radiological review was carried out to establish if dislocation was related to surgical technique. The postoperative radiographs of 46 lateral unicompartmental arthroplasties were analysed. Five variables which related to the position and alignment of the components were measured. Dislocations occurred in six knees. Only one of the five variables, the proximal tibial varus angle, had a statistically significant relationship to dislocation. This variable quantifies the height of the lateral joint line. The mean proximal tibial varus angle for knees the bearings of which had dislocated was 9 degrees and for those which had not it was 5 degrees. In both groups it was greater than would be expected in the normal knee (3 degrees). Our study suggests that a high proximal tibial varus angle is associated with dislocation. The surgical technique should be modified to account for this, with care being taken to avoid damage to or overdistraction of the lateral soft tissues.

Aged↗