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Biomedical subjects

M A Freeman

Publications and source records attributed to M A Freeman.

At least 55 records · Page 3Linked to original sources
PubMed1997

Cost and value of performance indicators. Results from IBH's (Institute for Behavioral Healthcare) National Leadership Council.

Consumer Reports style report cards are becoming commonplace in our industry and will emerge as a necessary component of 21st century behavioral healthcare. As a result, health plans and providers are increasingly required to invest in and maintain an infrastructure for comparative performance measurement and reporting. Policymakers and accrediting agencies must be careful to require reporting about the most cost-effective indicators in order to minimize the extra cost burden imposed upon health plans and providers by this effort. The Institute for Behavioral Healthcare's National Leadership Council evaluated "real life" performance indicators already in use in health plans, facility-based provider settings, community mental health centers, and behavioral group practices. This study shows which performance indicators are most worth measuring and those which are not, and why. Significant implications for policy and accrediting organizations, and for the behavioral healthcare field, are discussed.

Health Care Surveys↗
PubMed1996

Bone formation and bone resorption in failed total joint arthroplasties: histomorphometric analysis with histochemical and immunohistochemical technique.

To elucidate the reactions of bone around aseptically loosened total joint arthroplasties, 24 interface tissues with adjacent bone were obtained in 17 revision operations (11 hips and six knees). The morphology of the bone surface next to the interface membrane was investigated with histochemical and immunohistochemical techniques and then histomorphometrically analysed. One-third of the total bone surface. 32.69 +/- 5.16% (mean +/- SE) (n = 24), showed positive alkaline phosphatase activity. The bone surface in contact with the cells positive for CD11b (a macrophage marker) amounted to 19.33 +/- 5.16% (n = 24). The proportion of the osteoclastic bone resorption estimated by vitronectin receptor expression was 7.67 +/- 1.82% (n = 21). Tissues retrieved from the sites where radiographic evidence of osteolysis was present (n = 12) had a significantly larger extent of the bone surface in contact with CD11b-positive cells than did the tissues from areas without osteolysis (n = 12, p = 0.0067, Mann-Whitney U test), whereas no significant difference was observed in the extent of osteoclastic bone resorption. These data demonstrate that active bone formation, regarded as a repair process, is the most common feature even in revised cases. They also highlight the role played by macrophages, not as cells producing inflammatory mediators that could activate osteoclasts, but as cells primarily responsible for the bone loss in osteolytic lesions.

Adult↗
PubMed1996

Stress and strain distribution within the intact femur: compression or bending?

The aim of this research was to test the hypothesis that the intact femur is loaded predominately in compression. The study was composed of two parts: a finite element analysis of the intact femur to assess if a compressive stress distribution could be achieved in the diaphyseal region of the femur using physiological muscle and joint contact forces; a simple radiological study to assess the in vivo deflections of the femur during one legged stance. The results of this investigation strongly support the hypothesis that the femur is loaded primarily in compression, and not bending as previously thought. The finite element analysis demonstrated that a compressive stress distribution in the diaphyseal femur can be achieved, producing a stress distribution which appears to be consistent with the femoral cross-sectional geometry. The finite element analysis also predicted that for a compressive load case there would be negligible deflections of the femoral head. The radiological study confirmed this, with no measurable in vivo deflection of the femur occurring during one legged stance.

Adult↗
PubMed1996

Acetabular wear.

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Acetabulum↗
PubMed1996

Hydroxyapatite coating of an acetabular prosthesis. Effect on stability.

We report the radiological and clinical outcome of a press-fit (SLF) acetabular component at two to three years in two groups of patients having primary total hip replacement. In 69 the implant was coated with hydroxyapatite (HA) and in 40 it was uncoated. The stability of the cup was assessed by measurement of proximal migration and change in the angle of inclination. The clinical results in the two groups did not differ significantly, and the mean proximal linear wear was similar in both. Fewer radiolucent lines (RLLs) were seen on the radiographs of cups coated with HA. The mean proximal migration was studied by calculating regression lines for each patient using migration measurements: for the SLF+HA group the mean slope was 0.06 mm/year and for the SLF-HA group 0.20 mm/year (p = 0.22). The change in the angle of inclination during follow-up was also consistently smaller in HA-coated cups. Using regression methods the SLF+HA group had a mean slope of 0.08 degrees/year and the SLF-HA group 0.44 degrees/year and the SLF-HA group 0.44 degrees/year (p = 0.023). Partial HA coating appeared to have no effect on the clinical outcome or on the rate of wear of polyethylene, but there was a trend towards a reduced rate of proximal migration, and a significant reduction in rotational migration and the number of radiolucent lines. This suggests that HA coating enhances the stability of this acetabular component.

Acetabulum↗
PubMed1995

Cancellous bone stresses surrounding the femoral component of a hip prosthesis: an elastic-plastic finite element analysis.

The cancellous bone stresses surrounding the femoral component of total hip replacement were investigated using the finite element method. Four versions of a certain femoral hip prosthesis (the Freeman, Corin Medical), cemented, HA coated, press-fit, and press-fit with ridges were analysed. Each model was subjected to two separate load cases with the cancellous bone modelled as an elastic perfectly plastic material. The effect of bone quality was investigated by varying the cancellous bone stiffness. The resulting cancellous bone stress distributions were compared to that of the intact femur. The results were also compared to clinical subsidence data (published elsewhere) for the Freeman femoral prosthesis to determine if the initial cancellous bone stress distribution could be used to predict the migration of the various versions of this prosthesis. The results showed that the press-fit designs of prosthesis generated substantially higher cancellous bone stresses than the cemented and HA coated designs, and that these stresses were up to 6.5 times higher than found in the intact femur. For all forms of fixation the cancellous bone stress distribution was found to be insensitive to changes in the trabecular bone stiffness: thus poor quality cancellous bone is more likely to promote 'plastic' deformation, and therefore subsidence of the prosthesis. Comparison with the clinical migration data showed a good correlation and revealed that it may be possible to use the calculated initial cancellous bone stresses to predict the migration of the implant, and hence the probability of early and mid-term aseptic loosening.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1995

Is stem length important in uncemented endoprostheses?

In an uncemented total hip replacement where the femoral stem is thinner than the medullary canal it may be hypothesized that the distal portion of the stem has no mechanical function. In this study an uncemented total hip replacement has been modelled mathematically using finite element analysis and mechanical tests of a similar system have been carried out loading implants in cadaveric proximal femora. Two implants have been tested mechanically; one with a full length stem and the second with the stem shortened, but three implants have been modelled with an additional intermediate length stem analysed. Additionally the finite element analysis has been done with a high neck resection and a standard level resection. The finite element model showed that the full length stem produced lower interface contact stress levels under the proximal neck, particularly when the nec was resected, and this was borne out by the mechanical testing.

Biomechanical Phenomena↗
PubMed1995

Acetabular cup migration. Prediction of aseptic loosening.

We measured the proximal migration of 265 acetabular cups over seven years and correlated the findings with clinical outcome and acetabular revision for aseptic loosening. Cups which eventually became aseptically loose were shown to migrate more rapidly than successful cups. The average proximal migration at two years postoperatively for four groups of cups showed a monotonic relationship to the acetabular revision rate for aseptic loosening at 6.5 years. We conclude that acetabular cups which develop aseptic loosening as evidenced by pain, revision or screw fracture show increased proximal migration by one year, and that the 'migration rate' at two years can be used to predict the acetabular revision rate from aseptic loosening at 6.5 years.

Acetabulum↗
PubMed1994

Overall long-term impact of total hip and knee joint replacement surgery on patients with osteoarthritis and rheumatoid arthritis.

All patients with OA or RA entering an orthopaedic waiting list for total hip or knee replacement surgery over a period of 2.5 yr were prospectively assessed for overall pain (Visual Analogue Scale) and disability (Health Assessment Questionnaire) prior to and following their operation at annual intervals for up to 5 yr. A total of 293 patients had 335 operations (OA, hip 164; OA, knee 76; RA, hip 41; RA, knee 54). A few patients (14) showed a deterioration in pain and function 1 yr after surgery, but the remainder showed improvements which took 1 yr or more to reach maximum and were maintained for at least 3 yr. Although greater for OA hip patients, improvements occurred and were maintained in all groups, in spite of the polyarticular nature of RA.

Aged↗
PubMed1994

Wear induced by motion between bone and titanium or cobalt-chrome alloys.

We studied the wear generated by motion between polished and shot-blasted titanium-alloy (Ti-6Al-4V) or cobalt-chrome alloy (Co-Cr) surfaces and cortical bone in vitro. Semicircular sections of human proximal femoral cortex were reamed to fit metal cylinders of each alloy. The cylinders were then fitted in the bone, loaded and rotated in physiological saline. Ti-alloy resulted in more wear both of the bone and of the metal than did Co-Cr alloy. Metal wear was reduced and bone wear was increased by shot-blasting, a procedure which introduces surface residual stresses and roughens the metal surface. We conclude that when there is gross motion between a metal implant and bone, Ti-alloy is likely to generate more wear debris than Co-Cr alloy. The least wear both of bone and of metal was produced by polished Co-Cr.

Bone Density↗
PubMed1994

Early migration and late aseptic failure of proximal femoral prostheses.

The vertical migration of four configurations of a proximal femoral prosthesis, followed for up to nine years, was measured on standard radiographs. The same implant was used without cement (group 1) and with cement (group 2). The migration of both groups was linear from six months onwards. The mean migration rate and the incidence of late aseptic loosening were both greater in group 1. Survival analysis of the two groups, however, showed no statistically significant difference. In both groups, hips later destined for revision migrated more rapidly from the initial postoperative period onwards, than did the remainder. A threshold migration of 1.2 mm/year during the first two years after implantation detected hips likely to fail with a specificity of 86% and a sensitivity of 78%. This 'migration test' was applied to the results in two further groups of patients in which a modified femoral prosthesis had been implanted without hydroxyapatite coating (group 3) and with hydroxyapatite coating (group 4). The test distinguished between the four groups and suggested that at least two fixation procedures should be abandoned. We conclude that vertical migration measured on standard radiographs in the first two years after implantation can be used to predict late aseptic loosening. New prosthetic configurations should be evaluated by migration measurements before their general release. Our observations support the view that one cause of late aseptic loosening is imperfect initial fixation.

Adult↗
PubMed1993

Tomlinson report.

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Health Services Needs and Demand↗
PubMed1993

Evaluation of wear in an all-polymer total knee replacement. Part 2: clinical evaluation of wear in a polyethylene on polyacetal total knee.

In an effort to improve the long-term result of total joint replacement arthroplasty, we have investigated the use of a polymer-on-polymer articular replacement arthroplasty. Because of their known biocompatibility and previous use in orthopedic surgery, polyethylene and polyacetal (copolymer, Hoechst) were selected. Polyethylene served in its usual role as the concave member of the articulation; polyacetal formed the convex number. Formal wear testing using a multi-channel hip simulator demonstrated superior wear characteristics of the polymer-on-polymer configuration compared to a conventional chrome-cobalt versus polymer (polyethylene) configuration. A clinical series of relatively high-activity patients having a minimum five-year follow-up (N = 26) showed no specific unfavorable reaction to this material combination in a total knee replacement. Given certain potential advantages of polymeric materials, as well as some theoretical disadvantages of metallic materials, a polymer-on-polymer design for a large joint replacement may have some merit.

Acetals↗