Search PubMed⌕ Search

Biomedical subjects

A Unsworth

Publications and source records attributed to A Unsworth.

At least 73 records · Page 4Linked to original sources
PubMed1994

Changes in stiffness following short- and long-term application of standard physiotherapeutic techniques.

A computer-controlled MCP joint arthrograph was developed to measure the stiffness of finger joints objectively. This was used to study the short-term (one application) and long-term (multiple applications over 6 weeks) effects of several physiotherapeutic methods on the reduction in joint stiffness. The techniques used were hot wax baths, pulsed ultrasound alone, wax baths plus pulsed ultrasound and exercise. In the short-term (i.e. after each application) wax plus ultrasound produced a statistically significant reduction in elastic torque range (P < 0.01) and dissipated energy (P < 0.05). However, the reductions in these stiffness parameters were temporary. Long-term no significant reductions in stiffness were measured. In other words, stiffness was reduced by each therapy session, but it then increased again before the next session. Wax, ultrasound alone or exercise produced no short- or long-term effects.

Adult↗
PubMed1994

A comparative study of the frictional properties of emollient bath additives using porcine skin.

The coefficient of friction of 14 prescribable bath emollients was determined using porcine skin attached to a loaded plunger placed through a bearing in a friction-measuring carriage, held above a reciprocating table powered by a DC motor. The carriage was mounted in low-friction rollers, and restrained by a piezo-electric force transducer connected to an amplifier and recorder. Friction was measured at room temperature, and at 45 degrees C. Emulsifying ointment and Bath E45 had the highest coefficients of friction, at room temperature and 45 degrees C, respectively, and Emmolate and Hydromol had the lowest. Nine of the 14 emollients had a lower coefficient of friction at 45 degrees C, one had a coefficient of friction which was the same at both temperatures, and four had a coefficient of friction which was higher at 45 degrees C.

Animals↗
PubMed1993

Measurement of the range and coupled movements observed in the lumbar spine.

The aim of this study was to set up a data base, using the Polhemus Navigation Sciences 3Space Isotrak system, of the range and coupled movements expected to be seen in the lumbar spine of people not experiencing spinal problems. Measurements were taken from groups of volunteers who had not previously experienced any form of serious back pain and who were not suffering from any pathology known to affect the spine. The 'normal' group was split into sections determined by age an dsex. Age was split into five categories, those aged 20-29 years, 30-39 years, 40-49 years, 50-59 years and 60-69 years. Range of motion was seen to be affected by both the age and sex of subjects. Lateral bend and axial rotation, flexion and lateral bend and flexion and axial rotation were all strongly coupled. The younger age groups tested exhibited a greater degree of coupled movement than the older groups.

Adult↗
PubMed1993

The effect of exercise on ankylosing spondylitis--a preliminary study.

The Polhemus Navigation Sciences 3Space Isotrak system was used to measure the range of lumbar spinal motion of 57 patients with ankylosing spondylitis. Forty-three of these attended voluntary exercise sessions for an average of one and a half hours per week while 14 did not participate in any formal exercise groups. Exercising patients fell into two groups: those attending moderate and those attending vigorous exercise sessions. Results for exercising patients obtained immediately pre- and post- a single exercise session showed a small but significant increase in extension for the vigorous exercise group but no significant changes in any other movement for either of the groups. In a group of 44 patients (33 exercising, 11 non-exercising) who were followed-up over a 2 to 6 month period, slight loss of flexion (5.5 degrees) and lateral bend (3 degrees) was observed but there was no change in range of extension.

Adult↗
PubMed1993

Asperity lubrication in human joints.

The asperity lubrication in human joints is examined in the present paper, with particular reference to the tertiary undulation with wavelengths of around 20-45 microns. It was found that, under dynamic physiological loading conditions, the secondary waviness of the cartilaginous surface (typically 0.5 mm wavelength) could be effectively flattened to sustain a fluid film of 0.1-0.3 micron thick, while the tertiary waviness could be squashed to sustain a much thinner fluid film of 0.01 micron (10 nm) thick with normal synovial fluid as the lubricant. The calculated film thickness for the tertiary undulation was less than 5 nm when the ankle joint was lubricated by Ringer's solution or pathological synovial fluids, or when only quasi-static loading conditions were considered, while a sufficiently thick fluid film could still be formed when the secondary undulations were considered alone. It was thus suggested that the fluid film lubrication mechanism was operative for human joints with normal synovial fluid as the lubricant under physiological dynamic loading conditions and the mixed lubrication mechanism could take over when static loading conditions prevailed or when watery lubricants (eta approximately 0.001 Pa s) were used.

Ankle Joint↗
PubMed1992

Variation in lumbar spine mobility measured over a 24-hour period.

An electronic device for the measurement of three-dimensional movements, the Polhemus Navigation Sciences 3Space Isotrak system, was used to measure the range of movement in the lumbar spine of: (1) 10 young adults pre- and post-normal night-time sleep; (2) 10 young adults tested every 2 h over a 24-h period. The results obtained for the 10 subjects tested pre-/post-sleep showed there to be significant decreases in flexion, extension and lateral bend post-sleep. Axial rotation was not seen to alter significantly. The results obtained for the 10 subjects tested over a 24-h period showed movement during the day to be significantly more than at night. A decrease in the range of all movements except extension was observed when testing subjects in the early hours of the morning (after they had been supine for a minimum of 4 h) relative to the range observed from mid-afternoon to early evening.

Adult↗
PubMed1992

The function of bipolar hip prostheses--a laboratory study using cadaveric acetabula.

Cadaveric acetabula were mounted in a hip simulator and the friction developed in each during articulation with a series of metal femoral head prostheses of differing sizes was measured. In a separate study, assembled Hastings bipolar hip prostheses were subjected to weight-bearing forces in the same acetabula and their self-righting mechanism was observed. The self-righting mechanism was found to function efficiently, in most cases overcoming the combined friction of the inner and outer articulations of the Hastings hip. However, during motion in the hip simulator a wide variation of friction was observed between different acetabula and within the same acetabulum with differing head size. In several cases this acetabular friction was found to be less than the friction in the inner articulation of the Hastings bipolar hip prosthesis, and this may explain some cases of reported failure of biarticular function.

Acetabulum↗
PubMed1991

Soft layered prostheses for arthritic hip joints: a study of materials degradation.

A great deal of interest is being shown in complaint bearing surfaces for artificial joints. These produce very low friction because of the fluid-film lubrication that they exhibit, and therefore should produce lower wear than current prosthetic materials as the two surfaces of the joint are completely separated by a film of synovial fluid. However, one problem with soft elastic materials in vivo is that the elastomers may degrade with time. Specimens of four polyurethanes were kept in Ringer's solution at 37 degrees C for about 4 months to investigate changes in mechanical properties and the mode of lubrication with time of immersion. The materials tested were a polyether-urethane (E57), a polyester-urethane (E58), an aromatic polyether-urethane (P1) and an aliphatic polyether-urethane (A1). Samples of E57 showed a decrease in hardness and elastic modulus of 21% and 28% respectively. This was much better than E58 which showed decreases of 32% and 42% respectively. Better results were achieved with A1 (hardness change 2%) and P1 (decrease in hardness of 14% and modulus 17%). When tested in a hip-function simulator, A1 showed virtually no change in its very low coefficient of friction (0.004), P1 showed an increase of 60%, while E57 and and E58 both showed a doubling in friction over the course of the study. The modes of in vitro degradation were considered and surface effects determined to be most damaging. Currently the best candidate for a compliant material in hip replacement is the aliphatic polyether-urethane which maintains fluid-film lubrication.

Compliance↗
PubMed1991

Wear of cross-linked polyethylene against itself: a material suitable for surface replacement of the finger joint.

Cross-linking of polyethylene (XLPE) has dramatically improved its properties in industrial applications, and it may also have some application in the field of human joint replacement. Additionally it has the advantage of permitting a lower molecular weight base material to be used, so that components may be injection moulded rather than machined. This study therefore investigates the wear resistance of medical grade cross-linked polyethylene (XLPE), cross-linked by a silane-grafting process, with a molecular weight between cross links of 5430 g mol(-1). This first report investigates the wear resistance of XLPE against itself, because for certain joints, such as the metacarpo-phalangeal joint, the material may have a high enough wear resistance to allow both bearing surfaces to be made from it. Tests were carried out both on a reciprocating pin and plate machine with pins loaded at 10 and 40 N and also on a new finger joint simulator, which simulates the loads applied to and the movements of, the metacarpo-phalangeal joint. An average wear rate of 1.8 x 10(-6) mm3 N-1 m-1 was found (range 0.9-2.75 x 10(-6) mm3 N-1 m-1). This is about six times greater than the wear rate of non-cross-linked ultra high molecular weight polyethylene (UHMWPE) against stainless steel, but for applications with low loading, such as the metacarpo-phalangeal joint, this material is shown to have adequate wear resistance. The coefficient of friction was 0.1, which is similar to that of UHMWPE on stainless steel.

Humans↗
PubMed1991

Tribology of human and artificial joints.

Studies of human joint lubrication mechanisms have led to the conclusion that under normal healthy conditions they are fluid film lubricated. The main features responsible for allowing this mechanism to operate are the dynamic nature of the loading and the compliance of the bearing surfaces (articular cartilage). In contrast, artificial joints, being made of much more rigid materials, have been demonstrated to be lubricated by a mixed regime, where some load is carried by the fluid film and some by solid to solid contact. Since some surface contact takes place then wear remains a problem and friction is much higher than in human joints. The use of compliant surface bearings for artificial joints has been explored and shown to be of great advantage, reproducing the effects of natural joints. However, elastomeric materials are known to degrade in aqueous solutions so this aspect has been examined to ensure a reasonable life in the human body. Joints of the lower limb--hip, knee, and ankle--have similar load and motion patterns and behave in a similar way in terms of lubrication. Joints of the hand are not in any way similar in their behaviour and so a typical upper limb joint, the finger, has been studied to see if improvements can be made to the design of replacement artificial joints. Novel suggestions like plastic on plastic joints have been shown to be an alternative which is worthy of further consideration.

Cartilage, Articular↗
PubMed1991

Fixation of a surface replacement endoprosthesis of the metacarpophalangeal joint.

Surface replacement of the metacarpophalangeal joint would provide many benefits over current conservative treatment or the use of hinged spacers in excision arthroplasty. One of the main problems in surface replacement is securing adequate fixation of the prosthesis, especially if cement is not to be used. The direction and size of the forces that cause loosening have been described and a series of experiments in cadaveric bone have been used to elucidate the best shape of the component and stem to resist these forces. A 5 mm square section stem of 30 mm length gave the best overall result when combined with a flat on the palmar aspect of the inner bearing surface.

Aged↗
PubMed1990

A laboratory and clinical study of pneumatic 'grip strength' devices.

The use of inflated bags or cuffs to measure grip strength is now a well established technique. The method does have a number of problems. Bags of different diameter and volume were seen to give statistically significantly different pressure readings when squeezed by the same subjects. Different initial pressures (from 20 mmHg to 60 mmHg) also gave significantly different results both in laboratory tests on a materials testing machine and when patients with rheumatoid arthritis squeezed the bag. The technique of squeezing also affected the results. Despite the intrinsic drawbacks of the system, it is likely to remain in general use because of familiarity and convenience. We recommend the minimum details required when pneumodynamometer-derived data are published.

Adult↗
PubMed1990

A finger function simulator and the laboratory testing of joint replacements.

The design of a metacarpophalangeal (MCP) joint function simulator was undertaken and resulted in a versatile machine which offers the facility to apply both dynamic and static loading to a joint, following closely the physiological levels and patterns imposed in vivo. An additional feature was the opportunity to investigate the effect of varying the degree of joint instability. Long-term tests performed on Swanson silastic implants have produced failures of the kind seen clinically, which is very encouraging since it would seem to validate the claim that the simulator successfully imitates the finger function.

Biomechanical Phenomena↗
PubMed1987

Assessment of stiffness in rheumatology: the use of rating scales.

A study of 100 patients with rheumatoid arthritis has shown good correlation amongst three rating scales when used for measuring severity of morning stiffness and severity of stiffness present at the time of interview. Duration of morning stiffness was found to correlate only moderately well with severity of morning stiffness and poorly with severity of stiffness present at the time of interview. Investigation of the patients' definitions of stiffness, with and without the aid of a list of descriptive words, indicated an inter-relationship of pain and limited movement in the majority. This linking of the two symptoms under the term 'stiffness' may explain why some objective methods of measurement do not appear to reflect the subjective stiffness of which patients complain.

Arthritis, Rheumatoid↗