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Biomedical subjects

P J Gregg

Publications and source records attributed to P J Gregg.

At least 19 recordsLinked to original sources
PubMed2000

Graded compression stockings in elective orthopaedic surgery. An assessment of the in vivo performance of commercially available stockings in patients having hip and knee arthroplasty.

We recruited 89 patients who had hip or knee replacements to assess the performance of below-knee graded compression stockings. The pressure gradients generated by the stockings were measured and all patients had venography of the ipsilateral leg. We found that 98% of stockings failed to produce the 'ideal' pressure gradient (+/- 20%) of 18, 14 and 8 mmHg from the ankle to the knee, while 54% produced a 'reversed gradient' on at least one occasion during the course of the study. The overall rate of deep-venous thrombosis was 16.7%. Stockings which produced reversed gradients were associated with a significantly higher incidence of deep-venous thrombosis (p = 0.026) than those with the correct gradient (25.6% v 6.1%). This suggests that the performance of graded compression stockings can be improved if reversed pressure gradients are detected and prevented.

Arthroplasty, Replacement, Hip↗
PubMed1999

Osteoarthritic cartilage loses its ability to remain avascular.

OBJECTIVE: To determine whether human osteoarthritic (OA) cartilage loses its ability to remain avascular when placed into the in-vivo model of angiogenesis, the chick embryo chorio-allantoic membrane (CAM), and to determine specific changes that occur in the cartilage matrix when the cartilage is exposed to an active vasculature. DESIGN: Articular cartilage from OA and non-OA joints was grafted onto the CAM for up to 5 days before fixing and processing for histological, histochemical and immunological examination for specific changes in proteoglycan and collagen. RESULTS: OA cartilage, but not non-OA cartilage, showed invasion of its matrix by blood vessels from the CAM to various extents. Associated with these blood vessels was a loss of staining for proteoglycans and cartilage specific glycosaminoglycans (GAG). A deposition of collagen types I and X was also visualized around the invasive vessels. CONCLUSIONS: OA cartilage loses or has already lost its ability to remain avascular when placed onto the chick CAM. Changes occur in the matrix around the invasive blood vessels, specifically a loss of proteoglycan and GAG, and the deposition of new collagen types, notably I and X.

Aged↗
PubMed1999

Manipulation of total knee replacements. Is the flexion gained retained?

As part of a prospective study of 476 total knee replacements (TKR), we evaluated the use of manipulation under anaesthesia in 47 knees. Manipulation was considered when intensive physiotherapy failed to increase flexion to more than 80 degrees. The mean time from arthroplasty to manipulation was 11.3 weeks (median 9, range 2 to 41). The mean active flexion before manipulation was 62 degrees (35 to 80). One year later the mean gain was 33 degrees (Wilcoxon signed-rank test, range -5 to 70, 95% CI 28.5 to 38.5). Definite sustained gains in flexion were achieved even when manipulation was performed four or more months after arthroplasty (paired t-test, p < 0.01, CI 8.4 to 31.4). A further 21 patients who met our criteria for manipulation declined the procedure. Despite continued physiotherapy, there was no significant increase in flexion in their knees. Six weeks to one year after TKR, the mean change was 3.1 degrees (paired t-test, p = 0.23, CI -8.1 to +2).

Aged↗
PubMed1999

Outcome of Charnley total hip replacement across a single health region in England: the results at five years from a regional hip register.

Using a regional arthroplasty register we assessed the outcome at five years of 1198 primary Charnley total hip replacements (THRs) carried out in 1152 patients across a single UK health region in 1990. Information regarding outcome was available for 1080 hips (90%) and 499 had an independent clinical and radiological assessment. By five years the known rate of aseptic loosening was 2.3%, of deep infection 1.4%, of dislocation 5.0% and of revision 3.2%. The radiological assessment of 499 THRs revealed gross failure in a further 5.2%, which had been previously unrecognised. The combined rate of failure of nearly 9% is higher than those published from specialist centres and surgeons, but is probably more representative of the norm. Our study supports the need for a national register and surveillance of THRs. It emphasises that all implants should be followed, and suggests that the results of such surgery, when performed in the general setting, may not be as good as expected.

Arthroplasty, Replacement, Hip↗
PubMed1999

The inadequacy of standard radiographs in detecting flaws in the cement mantle.

Radiological assessment of the cement mantle is used routinely to determine the outcome of total hip replacement. We performed a simulated replacement arthroplasty on cadaver femora and took standard postoperative radiographs. The femora were then sectioned into 7 mm slices starting at the calcar, and high-resolution faxitron radiographs were taken of these sections. Analysis of the faxitron images showed that defects in the cement mantle were observed up to 100 times more frequently than on the standard films. We therefore encourage the search for a better technique in assessing the cement mantle.

Arthroplasty, Replacement, Hip↗
PubMed1998

In vivo pressure profiles of thigh-length graduated compression stockings.

BACKGROUND: The aim of the study was to assess whether the appropriate pressure profile is generated by thigh-length graduated compression stockings in human subjects. The effect of leg posture on the pressure profile was assessed in three commonly used brands of graduated compression stockings. METHODS: The study involved 17 human volunteers from the Department of Orthopaedic Surgery. Three different brands of stockings commonly recommended for the prevention of deep vein thrombosis were applied to each individual and the interface pressure profile under the stocking was measured. The effect of posture was assessed by comparing the interface pressure profile with the subject supine and in standing and sitting positions. RESULTS: Appropriate median pressure profiles were achieved only with the subject standing or supine. In the sitting position with the knee flexed, a high median interface pressure in excess of 28 mmHg was generated at the popliteal fossa. Overall, inconsistent performance was found in all three brands of stockings; fewer than 30 per cent of the pressure readings fell within 20 per cent of the 'ideal'. Reversed pressure profile was observed in over 70 per cent of subjects. CONCLUSION: Thigh-length graduated compression stockings may be most effective in bedridden patients. Knee-length stockings may be more suitable for the prevention of deep vein thrombosis in ambulant patients.

Bandages↗
PubMed1998

Cement as a risk factor for deep-vein thrombosis. Comparison of cemented TKR, uncemented TKR and cemented THR.

A total of 110 total knee replacements (TKRs) was randomised to receive either a cemented or an uncemented prosthesis. Postoperative venography at five to seven days was used to compare the prevalence, site and size of deep-vein thrombosis (DVT). We also compared the findings with those of postoperative venography in a group of patients with cemented total hip replacements (THRs). The total prevalence of DVT was significantly greater after uncemented (81%) than after cemented TKR (55%). Both knee groups had a significantly higher prevalence of DVT than in cemented hip replacements (32%). We found no difference in the proportion with proximal DVT in the three groups (14%, 15% and 16%). The median length of the thrombi was significantly greater after cemented (26.5 cm) than after uncemented TKR (11 cm) or after cemented THR (7 cm). This difference was mainly due to greater lengths of distal rather than proximal thrombi. We conclude that the use of cement may affect the formation of DVT after joint replacement, but does not appear to lead to an increased incidence.

Arthroplasty, Replacement, Hip↗
PubMed1998

Randomised, prospective study comparing cemented and cementless total knee replacement: results of press-fit condylar total knee replacement at five years.

Early implants for total knee replacement were fixed to bone with cement. No firm scientific reason has been given for the introduction of cementless knee replacement and the long-term survivorship of such implants has not shown any advantage over cemented forms. In a randomised, prospective study we have compared cemented and uncemented total knee replacement and report the results of 139 prostheses at five years. Outcome was assessed both clinically by independent examination using the Nottingham knee score and radiologically using the Knee Society scoring system. Independent statistical analysis of the data showed no significant difference between cemented and cementless fixation for pain, mobility or movement. There was no difference in the radiological alignment at five years, but there was a notable disparity in the radiolucent line score. With cemented fixation there was a significantly greater number of radiolucent lines on anteroposterior radiographs of the tibia and lateral radiographs of the femur. At five years, our clinical results would not support the use of the more expensive cementless fixation whereas the radiological results are of unknown significance. Longer follow-up will determine any changes in the results and conclusions.

Adult↗
PubMed1998

Further uses of polymethylmethacrylate in orthopaedic surgery.

For over 30 years polymethylmethacrylate (PMMA) has been used in orthopaedic surgery to fix prosthetic components. Two additional uses, relying on the moulding properties previously utilized in dentistry, are described here: the use of PMMA as a bone graft template and as a femoral window plug in total hip replacement.

Arthroplasty, Replacement, Hip↗
PubMed1998

Current practice in primary total hip replacement: results from the National Hip Replacement Outcome Project.

As part of the National Study of Primary Hip Replacement Outcome, 402 consultant orthopaedic surgeons from three regions were contacted by postal questionnaire which covered all aspects of total hip replacement (THR). There was a 70% response rate of which 71 did not perform hip surgery, a further 33 refused to take part, leaving 181 valid responses. Preoperative assessment clinics were used by 89% of surgeons, but anaesthetists and rehabilitation services were rarely involved at this stage. Of respondents, 99% used routine thromboprophylaxis, with 79% using a combination of mechanical and chemical methods. Of surgeons, 84% routinely used stockings, whereas 95.5% used chemical prophylaxis, 63% employed low molecular weight heparins. Theatre facilities were shared with other surgical specialties by 6% of surgeons and 18% regularly used body exhaust suits for THR. Antibiotic loaded cement was used by 69% of surgeons, the majority (65%) used a single brand of normal viscosity cement with 9% using reduced viscosity formulations. Modern cementing techniques were commonly used at least in part, 87% used a cement gun and 94% a cement restrictor for femoral cementing. On the acetabulum, 47% pressurised the cement. In all, 36 different femoral stems and 35 acetabular cups were in routine use, but the majority of surgeons (55%) used Charnley type prostheses. Of the surgeons, 57% performed only cemented THR, while 3% exclusively used uncemented THR. Of consultants, 21% followed up their patients to 5 years, the majority discharge patients within the first year. Of concern is a large proportion of surgeons using low molecular weight heparins despite a lack of evidence with regard to reducing fatal pulmonary embolism, and also the small number of surgeons using prostheses of unproven value. Third generation cementing techniques have yet to be fully adopted. The introduction of a national hip register could help to resolve some of these issues.

Arthroplasty, Replacement, Hip↗
PubMed1997

Intrinsic control of vascularization in developing cartilage rudiments.

The vascularization of developing cartilage rudiments is temporally and spatially defined. By using an in vivo angiogenesis model, the chorioallantoic membrane (CAM) of the chick embryo and chick embryo cartilage rudiments, we conclude that the factors controlling the vascular invasion of cartilage rudiments are intrinsic. Intact rudiments, separate hypertrophic zones and separate rounded cell zones, when grafted onto the CAM, become vascularized in the same temporal and spatial manner as occurs in ovo. When grown as organ cultures prior to CAM grafting, rudiments still become vascularized in the same temporal and spatial manner. The integrity of the extracellular matrix and the presence of the periosteum are two physical factors regulating the control of vascularization. Removal of the periosteum from hypertrophic regions caused a cessation of the invasion. Insults to the matrix via brief enzymatic degradation of extracellular matrix components resulted in invasion and erosion of rounded cell zones at an earlier time than is ordinarily seen both in ovo and on the CAM.

Animals↗
PubMed1997

Cement pressurisation during hip replacement.

The newer techniques of cementing aim to improve interlock between cement and bone around a femoral stem by combining high pressure and reduced viscosity. This may produce increased embolisation of fat and marrow leading to hypotension, impaired pulmonary gas exchange and death. For this reason the use of high pressures has been questioned. We compared finger-packing with the use of a cement gun by measuring intramedullary pressures during the cementing of 31 total hip replacements and measuring physiological changes in 19 patients. We also measured pressure in more detail in a laboratory model. In the clinical series the higher pressures were produced by using a gun, but this caused less physiological disturbance than finger-packing. The laboratory studies showed more consistent results with the gun technique, but for both methods of cementing the highest pressures were generated during the insertion of the stem of the prosthesis.

Bone Cements↗
PubMed1997

Screening for deep-venous thrombosis after hip and knee replacement without prophylaxis.

We performed routine venography after operation in a consecutive series of 252 patients with total joint arthroplasties in whom no form of routine chemical or mechanical prophylaxis had been used. The prevalence of deep-vein thrombosis (DVT) was 32% (16% distal, 16% proximal) after total hip replacement and 66% (50% distal, 16% proximal) after total knee replacement (p < 0.001). We did not treat distal DVT. There were only two readmissions within three months of surgery because of thromboembolic disease. There were two deaths within this period, neither of which was due to pulmonary embolism.

Cause of Death↗
PubMed1997

Mortality and fatal pulmonary embolism after primary total hip replacement. Results from a regional hip register.

We calculated the rates for perioperative mortality and fatal pulmonary embolism (PE) after primary total hip replacement in a single UK health region, using a regional arthroplasty register and the tracing service of the Office of National Statistics. During 1990, there were 2111 consecutive primary replacements in 2090 separate procedures. Within 42 days of operation a total of 19 patients had died (0.91%, 95% CI 0.55 to 1.42). Postmortem examination showed that four deaths (0.19%, 95% CI 0.05 to 0.49) were definitely due to PE. The overall perioperative mortality and fatal PE rates are low and in our study did not appear to be altered by the use of chemical thromboprophylaxis (perioperative mortality rate: one-tailed Fisher's exact test, p = 0.39; fatal PE rate: one-tailed Fisher's exact test, p = 0.56). The routine use of chemical thromboprophylaxis for primary THR is still controversial. The issue should be addressed by an appropriate randomised, prospective study using overall mortality and fatal PE rate as the main outcome measures, but the feasibility of such a study is questioned.

Adult↗
PubMed1997

Sectioning fresh human bone: the reduction of aerosol and physical hazards.

Musculoskeletal research demands an accurate model on which to work, and fresh frozen human bone is an ideal material. However, there is increasing concern over the biohazard that this represents. A method is reported that reduces the biohazard, and two research situations are described. Both use polymethylmethacrylate (PMMA) bone cement as an interface between the human tissue and the cutting device, which allows solid and suitable geometry for vice fixation. A method of bone cutting that enables remote operation is described; this method may reduce the risk of disease transmission by aerosol, and prove useful to all in this field of research.

Aerosols↗
PubMed1996

Vibration analysis in the detection of total hip prosthetic loosening.

This present paper reports on experiments which seek to obtain evidence of the usefulness of vibration in the diagnosis of implant loosening by utilizing extra information by considering the amplitude response at all frequencies (within a certain range) as well as spectral analysis of particular waveforms. This frequency response is essentially a study of the manner in which the amplitude of vibration of a system varies as the frequency of an input force of fixed amplitude is varied. The experimental technique involved the application of a sinusoidal force to the distal end of a femur containing an implanted prosthesis and collecting the output signal using an accelerometer placed at the proximal end. The output signal was stored on a computer with a digital signal processing board and subsequently analysed using the two signal processing techniques mentioned above. Data were collected when the implanted prosthesis was secure, and at various stages of loosening. Analysis of these data shows that prosthetic instability can be detected using both modalities of vibration analysis.

Hip Prosthesis↗