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Biomedical subjects

M J Pearcy

Publications and source records attributed to M J Pearcy.

At least 37 records · Page 2Linked to original sources
PubMed1995

Failure strengths of different meniscal suturing techniques.

The aim of this study was to measure the failure strengths of three arthroscopic meniscal suturing methods. The techniques investigated were a single horizontal loop, a double vertical loop, and a single vertical loop. Eleven human, lateral menisci obtained at autopsy were cut with a scalpel to simulate peripheral longitudinal tears. The menisci were then repaired with one suture at a time, using each of the three methods in turn. The two parts of the meniscus were then pulled apart using a computer-controlled materials testing machine until failure occurred, either by the suture itself failing or by the suture pulling out because of tearing of the meniscus. The horizontal sutures had a mean failure strength of 29.3 N, whereas the double vertical loop failed at 63.2 N and the single vertical loop at 67.3 N. The horizontal loop sutures and the double vertical loop sutures all failed by pulling out of the meniscus. The single vertical loop sutures failed by rupture of the suture itself. This study showed the superior mechanical characteristics of the single vertical loop suturing system over the other techniques tested. Owing to the more consistent failure strength, decreased costs, and shorter surgical time over the double vertical loop system, the single vertical loop technique is recommended for arthroscopic meniscal repair.

Aged↗
PubMed1993

The effects of flexion on the geometry and actions of the lumbar erector spinae.

A modeling study was undertaken to determine the effects of flexion on the forces exerted by the lumbar back muscles. Twenty-nine fascicles of the lumbar multifidus and erector spinae were plotted onto tracings of radiographs of nine normal volunteers in the flexion position. Moment arms and force vectors of each fascicle were calculated. The model revealed that moment arms decreased slightly in length resulting in no more than an 18% decrease in maximum extensor moments exerted across the lumbar spine. Compression loads were not significantly different from those generated in the upright posture. However, there were major changes in shear forces, in particular a reversal from a net anterior to a net posterior shear force at the L5/S1 segment. Flexion causes substantial elongation of the back muscles, which must therefore reduce their maximum active tension. However, if increases in passive tension are considered it emerges that the compression forces and moments exerted by the back muscles in full flexion are not significantly different from those produced in the upright posture.

Adult↗
PubMed1993

A method for production and characterization of metal prosthesis wear particles.

The wear of joint prostheses generates wear particles that produce an inflammatory response in the surrounding tissues and may contribute to bone resorption resulting in prosthetic loosening. Although the effects of particles produced from prosthetic materials have been studied extensively in vitro and in vivo, little attention has been paid to the standardisation of methods for the generation and characterization of these particles. This paper describes a reproducible method for generation of metal particles by the abrasive shaking of joint replacement components. Particular attention was given to the production of metal particles that closely resembled particles found around solid and loose human prostheses. To achieve this, particle size, size distribution, chemical composition, and shape were characterized. Particles that were 0.5-3.0 microns in diameter were isolated by differential sedimentation, and the distribution of particle sizes was determined with use of a Coulter Multisizer. Chemical composition was measured by atomic absorption spectrophotometry, and transmission electron microscopy was used to characterize particle shape. The techniques were shown to be reproducible, since there was little variation between batches over a lengthy time period. These or similar methods of particle production and characterization should be an essential part of future in vitro and in vivo studies of wear particles.

Alloys↗
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

Twisting mobility of the human back in flexed postures.

The twisting mobility of the back was measured using an electromagnetic measuring device, the 3SPACE Isotrak, in ten healthy subjects in five postures: standing upright, in two forward-leaning positions, and two seated positions. In the forward-leaning positions the subjects flexed with mean values of 28 degrees and 53 degrees and had no difference in their active twisting compared with that experienced in the upright position. The two seated positions induced mean flexion values of 32 degrees and 44 degrees and were associated with statistically significant increases in active twisting compared with the upright position of 38% and 46%, respectively, at the level of P < 0.0001. These increases suggest that the wedge morphology of the zygapophysial joints permits greater twisting when the intervertebral joints flexed, but postural muscle action in forward leaning restricts active twisting. This study suggests a mechanism for increased vulnerability of the posterior anulus to injury when twisting is combined with flexion.

Adult↗
PubMed1993

The axial torque of the lumbar back muscles: torsion strength of the back muscles.

The maximal, axial torque generated by the lumbar back muscles was determined by modelling the action of the 49 fascicles of longissimus thoracis, iliocostalis lumborum and the lumbar multifidus on radiographs of the lumbar spine of nine young male subjects in upright standing and in full lumbar flexion. No single fascicle exerted more than 2 Nm of axial torque in the upright posture, and the collective torque of all muscles acting a segment did not exceed 5 Nm. All torques were considerably less in full flexion. The lumbar back muscles exert very little torque on the lumbar spine, and contribute only about 5% of the total torque involved in trunk rotation. None of the lumbar back muscles can be considered a rotator. The oblique abdominal muscles are the principal rotators of the trunk. Preventative and rehabilitation programmes concerned with torsion injuries should focus on the abdominal muscles rather than the back muscles for stability in axial rotation.

Back↗
PubMed1993

The differences in toxicity and release of bone-resorbing mediators induced by titanium and cobalt-chromium-alloy wear particles.

We investigated the relationship between the toxic effects of metal wear particles and their ability to stimulate the release of inflammatory mediators implicated in bone resorption. In vitro studies were carried out with use of rat peritoneal macrophages, which were exposed to either cobalt-chromium-alloy or titanium-aluminum-vanadium particles, milled from the metal components of hip prostheses. The particles were in the size-range of, and at concentrations similar to, those found in the tissues surrounding failed prostheses in humans. The titanium-aluminum-vanadium particles showed little toxicity even at high concentrations, while the cobalt-chromium particles were very toxic. The titanium-aluminum-vanadium particles induced significantly more release of prostaglandin E2 than did the cobalt-chromium particles, and this was true for a wide range of concentrations. Exposure to titanium-aluminum-vanadium increased the release of prostaglandin E2, interleukin-1, tumor necrosis factor, and interleukin-6. In contrast, exposure to cobalt-chromium particles was associated with a decreased release of prostaglandin E2 and interleukin-6, and it had little effect on the release of interleukin-1 and tumor necrosis factor.

Alloys↗
PubMed1993

The response to particulate debris.

The most common cause of failure of total hip and other arthroplasties is aseptic loosening of the prosthesis. Substantial evidence suggests that the adverse tissue response to prosthesis wear particles is an important contributor to bone loss around implants. The results may be an increased risk of loosening and severe bone loss, which makes revision surgery more difficult. Studies in humans have demonstrated that the appearances of the periprosthetic tissues are related to the type, number, and size of wear particles. The appearance and tissue response around any given prosthesis is related to the balance among the rate of production of wear particles, the ability of the tissues to deal with the particles, and the rate of clearance of the particles from the joint. Prosthesis wear particles may be produced by wear at the articulating surface, particularly if there is three-body wear, by abrasion due to movement at the prosthesis-bone interface of uncemented prostheses, by abrasion at the prosthesis-cement and cement-bone interfaces of cemented prostheses, or at any articulation of the components of modular prostheses. Future in vivo and in vitro studies of the effects of wear particles should focus on quantitative measurement of the effects of particles and on the use of particles of comparable size and in concentrations similar to those found in the tissues surrounding failed prostheses.

Animals↗
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

A universal model of the lumbar back muscles in the upright position.

A model of the lumbar back muscles was constructed incorporating 49 fascicles of the lumbar erector spinae and multifidus. The attachment sites and sizes of fascicles were based on previous anatomic studies, and the fascicles were modeled on radiographs of nine normal volunteers in the upright position. Calculations revealed that the thoracic fibers of the lumbar erector spinae contribute 50% of the total extensor moment exerted on L4 and L5; multifidus contributes some 20%; and the remainder is exerted by the lumbar fibers of erector spinae. At upper lumbar levels, the thoracic fibers of the lumbar erector spinae contribute between 70% and 86% of the total extensor moment. In the upright posture, the lumbar back muscles exert a net posterior shear force on segments L1 to L4, but exert an anterior shear force on L5. Collectively, all the back muscles exert large compression forces on all segments. A force coefficient of 46 Ncm-2 was determined to apply for the back muscles. These results have a bearing on the appreciation of the effects on the back muscles of surgery and physiotherapy.

Adult↗
PubMed1991

Axial rotation of lumbar intervertebral joints in forward flexion.

This paper examined the mobility of intervertebral joints in axial rotation in a neutral and in two flexed positions. Torsion tests were conducted in vitro on specimens of isolated intervertebral joints in a rig specifically designed to apply torsion without imposing a fixed axis. This permitted the specimens to rotate about their own mobile axis of axial rotation. In addition the specimens were flexed about previously defined physiological axes of sagittal flexion in order to simulate movements as close as possible to those seen in life. It was shown that some intervertebral joints do exhibit an increased ability to rotate when in some degree of sub-maximal flexion dependent on the morphology of the zygapophysial joints. In full flexion axial rotation is limited, most probably by tightening of the posterior ligaments and zygapophysial joint capsules. This study lends evidence to the argument that torsion alone is insufficient to damage the intervertebral disc but a combination of flexion and torsion will increase its vulnerability to injury.

Aged↗
PubMed1990

Mechanical function of the human lumbar interspinous and supraspinous ligaments.

The mechanical function of the interspinous and supraspinous ligaments has been examined by simulating, on excised specimens, the deformation caused during forward flexion of the spine in real life. The load extension curves showed that during the first half of flexion the ligaments carried very little load but towards the end of the range of flexion they resisted up to 134N. When the supraspinous ligament was sectioned the interspinous ligament alone resisted 75% of this load. Testing at high strain rates showed an increase in load-carrying capacity of up to 30%. The maximum extension moment that can be produced by these ligaments was calculated to be approximately 7 Nm, or 5% of the moment the back muscles can produce across any intervertebral joint. Hence, during active lifting, these ligaments in isolation provide little mechanical assistance.

Aged↗
PubMed1989

Rotational mobility of the human back in forward flexion.

This paper describes the measurement of the ability of the human back to twist when in flexed postures using a new electromagnetic measurement device. The mobility of the lumbar spine in 12 normal male subjects was investigated and it was demonstrated that increased rotation was possible when in a flexed posture. This suggests that the intervertebral disc may be vulnerable to torsion when twisting is combined with sub-maximal sagittal flexion.

Adult↗
PubMed1989

Twisting of the human back in forward flexion.

This paper addresses the role of torsion in the production of spinal injury and in particular the possibility of injury resulting from torsion combined with flexion. The back movement of 16 normal male subjects was measured using a non-invasive, three-dimensional measurement system for assessing spinal mobility, the opto-electronic CODA-3 scanner. Measurements were made of the ability to twist the back while standing upright and in two flexed postures. Rotational ability was shown, in general, to be increased in a flexed posture, presumed to be due to an opening of the lumbar zygapophysial joints. This suggests that twisting in a flexed posture could be a mechanism for intervertebral disc injury.

Adult↗
PubMed1988

Instantaneous axes of rotation of the lumbar intervertebral joints.

Lateral radiographs of ten normal individuals were studied to determine the location of the instantaneous axis of rotation (IAR) of every lumbar vertebra for the movements of flexion and extension from the upright position and flexion from the fully extended position; and errors involved in the technique were quantified to establish confidence limits for the results of the calculations. The distribution of the IARs was found to fall within a small range from the mean location at each level, particularly for the movement of flexion from the extended position. Within-observer and between-observer errors occurred in tracing and superimposing radiographs and marking x and y coordinates. Unacceptably large errors occur when the movement of the joint is less than 5 degrees, and only the IAR for flexion from extension can be plotted with acceptable confidence. This result invalidates the notion that plotting centrodes may be of diagnostic value in recognizing mechanical disorders. The determination of a single extension to flexion IAR may be of more value clinically, to which end this study provides essential normative data.

Humans↗