PubMed Health⌕ Search

Biomedical subjects

David W Murray

Publications and source records attributed to David W Murray.

10 recordsLinked to original sources
PubMed2007

In vivo sagittal plane kinematics of the Avon patellofemoral arthroplasty.

Isolated patellofemoral osteoarthritis can be treated with patellofemoral arthroplasty (PFA). In contrast to total knee arthroplasty, the effect of PFA on knee joint kinematics is not known. A study was performed to identify the kinematic changes after PFA. The sagittal plane kinematics was examined in 12 patients who had undergone Avon PFA. An established fluoroscopic method was used to examine the patellar tendon angle (PTA)/knee flexion relationship during functional activities. No significant difference existed between the kinematics of PFA knees compared with normal, except for a uniform elevation in PTA throughout the range. This increase in PTA in the PFA joint represents a 1.6-mm anterior displacement of the patella. The kinematic profile after PFA is close to normal and suggests that the knee is exhibiting more normal loading characteristics than those of the total knee arthroplasty joint.

Aged↗
PubMed2006

Recovering articulated pose: a comparison of two pre and postimposed constraint methods.

We contrast the performance of two methods of imposing constraints during the tracking of articulated objects, the first method preimposing the kinematic constraints during tracking and, thus, using the minimum degrees of freedom, and the second imposing constraints after tracking and, hence, using the maximum. Despite their very different formulations, the methods recover the same pose change. Further comparisons are drawn in terms of computational speed and algorithmic simplicity and robustness, and it is the last area which is the most telling. The results suggest that using built-in constraints is well-suited to tracking individual articulated objects, whereas applying constraints afterward is most suited to problems involving contact and breakage between articulated (or rigid) objects, where the ability to test tracking performance quickly with constraints turned on or off is desirable.

Algorithms↗
PubMed2005

Oxford medial unicompartmental arthroplasty for focal spontaneous osteonecrosis of the knee.

BACKGROUND: Spontaneous osteonecrosis of the knee (SONK) is a distinct clinical condition occurring in patients without any associated risk factors. There is controversy as to the best method of treatment, and the available literature would suggest that patients with SONK have a worse outcome than those with primary osteoarthrosis when arthroplasty is performed. We assessed the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK; Ahlbäck grades III and IV). PATIENTS AND METHODS: We assessed 29 knees (27 patients) with spontaneous osteonecrosis of the knee using the Oxford Knee Score. 26 knees had osteonecrosis of the medial femoral condyle and 3 had osteonecrosis of the medial tibial plateau. All had been operated on using the Oxford Medial Unicompartmental Knee Arthroplasty (UKA). This group was compared to a similar group (28 knees, 26 patients) who had undergone the same arthroplasty, but because of primary osteoarthrosis. Patients were matched for age, sex and time since operation. The mean length of follow-up was 5 (1-13) years. RESULTS: There were no implant failures in either group, but there was 1 death (from unrelated causes) 9 months after arthroplasty in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 38, and it was 40 in the group with osteoarthrosis. INTERPRETATION: Use of the Oxford Medial UKA for spontaneous focal osteonecrosis of the knee is reliable in the short to medium term, and gives results similar to those obtained when it is used for patients with primary osteoarthrosis.

Aged↗
PubMed2005

Guided-MLESAC: faster image transform estimation by using matching priors.

MLESAC is an established algorithm for maximum-likelihood estimation by random sampling consensus, devised for computing multiview entities like the fundamental matrix from correspondences between image features. A shortcoming of the method is that it assumes that little is known about the prior probabilities of the validities of the correspondences. This paper explains the consequences of that omission and describes how the algorithm's theoretical standing and practical performance can be enhanced by deriving estimates of these prior probabilities. Using the priors in guided-MLESAC is found to give an order of magnitude speed increase for problems where the correspondences are described by one image transformation and clutter. This paper describes two further modifications to guided-MLESAC. The first shows how all putative matches, ratherthan just the best, from a particularfeature can be taken forward into the sampling stage, albeit at the expense of additional computation. The second suggests how to propagate the output from one frame forward to successive frames. The additional information makes guided-MLESAC computationally realistic at video-rates for correspondence sets modeled by two transformations and clutter.

Algorithms↗
PubMed2004

Equity and need when waiting for total hip replacement surgery.

OBJECTIVES: To explore sociodemographic and health status factors associated with waiting times both for first outpatient appointment and for total hip replacement surgery (THR). METHODS: A survey of THR in five former English regions was conducted between September 1996 and October 1997. Every patient listed for THR was asked to fill out a questionnaire preoperatively. This questionnaire included the 12-item Oxford Hip Score (OHS) questionnaire and two questions on the length of time patients waited for an outpatient appointment and subsequently for their operation. RESULTS: From multiple logistic regression analyses, region, private vs. public sector, housing tenure and preoperative OHS were all independently associated with a waiting time for an outpatient appointment for > 3 months. Region, housing tenure and gender were also independently associated with a wait of >or= 6 months on the surgical waiting list. CONCLUSIONS: A large proportion of patients had long waiting times both for an outpatient appointment and while on a surgical waiting list. There were significant differences in waiting time according to social, geographical and health care system factors. Patients with a worse pain and disability at surgery waited longer for an outpatient appointment. The longer patient waited, the worse was their pain and disability, suggesting that patients were not prioritized by these criteria. Benefits of prioritizing should be tested.

Aged↗
PubMed2002

The effect of millennial-scale changes in Arabian Sea denitrification on atmospheric CO2.

Most global biogeochemical processes are known to respond to climate change, some of which have the capacity to produce feedbacks through the regulation of atmospheric greenhouse gases. Marine denitrification-the reduction of nitrate to gaseous nitrogen-is an important process in this regard, affecting greenhouse gas concentrations directly through the incidental production of nitrous oxide, and indirectly through modification of the marine nitrogen inventory and hence the biological pump for CO2. Although denitrification has been shown to vary with glacial-interglacial cycles, its response to more rapid climate change has not yet been well characterized. Here we present nitrogen isotope ratio, nitrogen content and chlorin abundance data from sediment cores with high accumulation rates on the Oman continental margin that reveal substantial millennial-scale variability in Arabian Sea denitrification and productivity during the last glacial period. The detailed correspondence of these changes with Dansgaard-Oeschger events recorded in Greenland ice cores indicates rapid, century-scale reorganization of the Arabian Sea ecosystem in response to climate excursions, mediated through the intensity of summer monsoonal upwelling. Considering the several-thousand-year residence time of fixed nitrogen in the ocean, the response of global marine productivity to changes in denitrification would have occurred at lower frequency and appears to be related to climatic and atmospheric CO2 oscillations observed in Antarctic ice cores between 20 and 60 kyr ago.

Atmosphere↗
PubMed2002

Mortality, morbidity, and 1-year outcomes of primary elective total hip arthroplasty.

No representative data exist on the risks of adverse outcomes of total hip arthroplasty (THA) in the United Kingdom. A prospective observational study of unselected THA operations was carried out in 5 U.K. regions. Adverse outcomes were assessed from the hospital case notes and general practitioners of 1,100 randomly selected patients and from 7,151 patient-completed questionnaires 3 and 12 months after THA. Three-month mortality was 0.4% to 0.7%. Dislocation and thromboembolic complications were about 3% and 4%. Perioperative fracture, sciatic nerve palsy, aseptic loosening, and revision each had a risk of < or = 1%. At 1 year, 2.6% of patients had undergone another operation on the same hip, 11% reported moderate or severe pain in the operated hip, 23% had severe walking restriction, and 11% were dissatisfied with the operation. Patients and surgeons in the United Kingdom should have access to this information when making a decision about THA.

Arthroplasty, Replacement, Hip↗