Biomedical subjects

M J Pearcy

Publications and source records attributed to M J Pearcy.

At least 19 recordsLinked to original sources

PubMed2001

Impact data for the investigation of injuries in inflatable rescue boats (IRBS).

Inflatable Rescue Boats (IRBs) are arguably the most important rescue tools utilised by Australian Surf Lifesavers. The crews in the IRB are continuously battling the fierce element that is the ocean. This force of nature takes its toll on man and machine. Initial impact data for this unique situation has been gathered as part of a biomechanical study investigating the increasing frequency of injuries to surf lifesavers whilst using an IRB. This paper outlines the scope of the research topic and concentrates on the data gathering equipment and an analysis of this unique data set. This initial testing has revealed impact acceleration peaks up to and exceeding 400 m/s2 (40 g) for a period of about 20 ms. These values were a result of an impact with waves of moderate size (approximately 1 m). It was therefore concluded that the impact is of a significant nature and further work should be performed to determine more concise ride characteristics for the IRB. From that it is hoped that methods will be discovered to lessen the impact on the crew with the aim of decreasing the injury rate.

Acceleration↗

PubMed2000

Disc lesions and the mechanics of the intervertebral joint complex.

STUDY DESIGN: Correlations between tears in the disc and the mechanics of both the intervertebral joint and vertebral body bone were analyzed. OBJECTIVES: To examine the effect of disc degeneration on the mechanics of spinal motion segments. SUMMARY OF BACKGROUND DATA: Degeneration of the intervertebral disc results in changes to the mechanics of the spine. The actual effect of tear type and size on the mechanics of the intervertebral joint is unknown. METHODS: Thirty spinal specimens (median age, 68 years) were divided into T12-L1, L2-L3, and L4-L5 motion segments. Mechanical tests recorded stiffness in flexion, extension, and torsion. Disc morphology was ascertained by taking three transverse sections of the disc and mapping and measuring the concentric tears, radial tears, and rim lesions. The severity of each tear type within each disc then was quantified. Bone cubes from the adjacent vertebral bodies were tested in compression to determine the elastic moduli and tested to failure in the longitudinal direction. RESULTS: Groups with tears were older and had reduced bone elastic moduli than groups without tears. Extension stiffness for the intact joint tended to increase with increasing tear severity. A decrease in torsional stiffness was present with increased severity of rim lesions at both L2-L3 and L4-L5. CONCLUSIONS: Tears in the intervertebral disc are reflected in a reduction in vertebral bone elastic modulus and in changes in the mechanics of the intervertebral joints in flexion, extension, and torsion.

Aged↗

PubMed2000

The skeletal response to matt and polished cemented femoral stems.

We studied the effect of the surface finish of the stem on the transfer of load in the proximal femur in a sheep model of cemented hip arthroplasty. Strain-gauge analysis and corresponding finite-element (FE) analysis were performed to assess the effect of friction and creep at the cement-stem interface. No difference was seen between the matt and polished stems. FE analysis showed that the effects of cement creep and friction at the stem-cement interface on femoral strain were small compared with the effect of inserting a cemented stem.

Animals↗

PubMed2000

Three-dimensional clinical measurement of bilateral hip and knee rotations.

This paper reports a technique of using an electromagnetic system to measure three-dimensional bilateral hip and knee joint rotations during walking and of using peak cross-correlation between rotation angles to describe the pattern of rotations. Three-dimensional rotations of thigh and shank during gait were recorded using five receivers of the electromagnetic system synchronised with four foot-switches. Thirteen normal subjects were tested on two separate occasions to examine repeatability of the measurements. The relationship between the rotations was represented as lags at peak cross-correlation. Twelve parameters of the lags at peak cross-correlation were calculated. The analysis showed that the joint rotation could be measured reliably and the cross-correlation analysis provided parameters that were generally suitable for defining characteristics of hip and knee joint rotations during gait.

Biomechanical Phenomena↗

PubMed1999

Difficulties in estimating muscle forces from muscle cross-sectional area. An example using the psoas major muscle.

Most biomechanical models use muscle cross-sectional area (CSA) as an indicator of maximum isometric muscle force. In general, there are multiple estimates of CSA for the same muscle. For example, numerous studies have estimated the CSA of the psoas major muscle using different subject populations and positions. However, few studies have combined the available information to obtain an overall estimate of CSA or investigated the effect different subject characteristics may have on CSA. In the present update, nine studies that reported psoas major CSA or physiologic CSA were compared with respect to subject characteristics, methodology, and results. Corrections to cadaveric data were made to adjust physiologic CSA to CSA. Comparison of reported values for living subjects indicated that females have smaller mean CSA than males for the psoas major muscle and that body size does not significantly influence muscle CSA in males. Areas derived from cadaveric data were smaller than similar studies on living subjects, possibly because of subject age, removal of tendinous and fatty components of fascicles, and lack of detailed data for fascicle angles in the supine position. Results indicate that researchers who use muscle CSA in biomechanical models should carefully assess the appropriateness of the data used, particularly in relation to potential sex differences and the influence of postural changes on CSA.

Biomechanical Phenomena↗

PubMed1999

Kinematics and movement sequencing during flexion of the lumbar spine.

OBJECTIVES: This study investigated the sequence of intervertebral joint movements and range of motion during three tasks involving lumbar flexion. DESIGN: Position sensors were used to measure position and rotation of lumbar vertebrae during unconstrained flexion. BACKGROUND: In the development of mathematical models, numerous assumptions need to be made. Few studies have attempted to assess the validity of the assumptions regarding kinematics in models of the lumbar spine. METHODS: Position sensors were attached to the skin overlying the lumbar vertebrae of 14 volunteers. Volunteers performed three flexion tasks; unconstrained flexion from upright standing, with and without a mass of 5 kg held close to the body, and the transition from upright standing to a seated position. RESULTS: Four definitive movement sequences were identified for those subjects with consistency between replicates; 'top down' motion (where the top of the lumbar spine starts to move first and the bottom moves last), 'bottom up' (where the bottom of the lumbar spine moves first and the top moves last), 'all together' (where all segments commence movement together), and 'middle last' (where the middle segments of the lumbar spine are last to commence movement). Subjects not fitting one of these sequences were categorised into a miscellaneous group. Only two subjects exhibited the same sequence for each of the three tasks, while other subjects exhibited two or three different sequences for the three tasks, or showed a lack of consistency for one of the tasks. CONCLUSIONS: The results from this study indicate that there is no single movement sequence exhibited by the sample population. RELEVANCE: Incorrect assumptions which are incorporated into mathematical models have the potential to influence model output. Given that output from spinal models is often used to assess ergonomic issues such as safe lifting loads, validation of the assumptions is essential.

Adolescent↗

PubMed1998

Radiographic and histologic analysis of cemented double tapered femoral stems.

The macroscopic, radiographic, and histologic features of the prosthesis-cement and cementbone interfaces and adjacent bone were studied in 21 cemented hemiarthroplasties in sheep that had lived until sacrifice at 9 months. The features were compared with those immediately after implantation of the stem in the contralateral femur. The femoral stem was a double taper that was either polished collarless, matte collarless, or matte collared. There was no prosthesis to cement debonding or cement to bone radiolucent line immediately after implantation, and there was excellent interdigitation at the cement-bone interface. After 9 months there was no evidence of prosthesis to cement debonding and no stem with definite loosening. At 9 months after implantation there was evidence of bone remodeling with new bone filling what were presumed to be gaps at the cement-bone interface from immediately after implantation. Radiolucent lines at the cement-bone interface were found to represent trabeculation of the cortical bone rather than the presence of a complete fibrous interface, which was not seen. There was no difference between stem types. Sheep have been shown to be useful in a model of cemented hip arthroplasty and, although no differences were seen between stem types at 9 months after implantation, long term differences cannot be excluded.

Animals↗

PubMed1997

Power spectrum analysis of human femoral rotations during gait.

Femoral rotational waveforms sampled at 15 Hz for a duration 20 s satisfy the sampling rate and frequency resolution requirements of such waveforms during walking. Spectral analysis provides a unique signature of the frequency composition of such signals. This identity may prove useful in characterising human gait and could be of value in future studies of walking in health and disease.

Biomedical Engineering↗

PubMed1997

The role of polyethylene wear in joint replacement failure.

Aseptic loosening is the major cause of failure of joint replacement prostheses. Polyethylene implants removed at revision surgery regularly show wear. It is proposed that the polyethylene particles released into the tissues as a consequence of this wear induce a tissue response that precedes aseptic loosening. This paper presents the results of recent in vivo and in vitro studies of the biological response to polyethylene wear particles undertaken in the authors' laboratories. A clinical perspective is provided by the inclusion of the authors' recent observations of retrieval analyses of joint replacement implant wear and the tissue response to polyethylene in humans.

Animals↗

PubMed1997

Clinical implications of stiffness and strength changes in fracture healing.

In the assessment of fracture healing by monitoring stiffness with vibrational analysis or instrumented external fixators, it has been assumed that there is a workable correlation between stiffness and strength. We used four-point bending tests to study time-related changes in stiffness and strength in healing tibial fractures in sheep. We aimed to test the validity of the measurement of stiffness to assess fracture strength. At each duration of healing examined, we found marked variations in stiffness and strength. Stiffness was shown to be load-dependent: measurements at higher loads reflected ultimate strength more accurately. There was a biphasic relationship between stiffness and strength: at first there was a strong correlation regardless of loading conditions, but in the second phase, which included the period of 'clinical healing', stiffness and strength were not significantly correlated. We conclude that the monitoring of stiffness is useful primarily in assessing progress towards union but is inherently limited as an assessment of strength at the time of clinical union. Any interpretation of stiffness must take into account the load conditions.

Animals↗

PubMed1997

In vitro human monocyte response to wear particles of titanium alloy containing vanadium or niobium.

Our aim was to determine whether in vitro studies would detect differences in the cellular response to wear particles of two titanium alloys commonly used in the manufacture of joint replacement prostheses. Particles were of the order of 1 microm in diameter representative of those found adjacent to failed prostheses. Exposure of human monocytes to titanium 6-aluminium 4- vanadium (TiAlV) at concentrations of 4 x 10(7) particles/ml produced a mean prostaglandin E2 release of 2627.6 pM; this was significantly higher than the 317.4 pM induced by titanium 6-aluminium 7-niobium alloy (TiAlNb) particles (p = 0.006). Commercially-pure titanium particles induced a release of 347.8 pM. In addition, TiAlV stimulated significantly more release of the other cell mediators, interleukin-1, tumour necrosis factor and interleukin-6. At lower concentrations of particles there was less mediator release and less obvious differences between materials. None of the materials caused significant toxicity. The levels of inflammatory mediators released by phagocytic cells in response to wear particles may influence the amount of periprosthetic bone loss. Our findings have shown that in vitro studies can detect differences in cellular response induced by particles of similar titanium alloys in common clinical use, although in vivo studies have shown little difference. While in vitro studies should not be used as the only form of assessment, they must be considered when assessing the relative biocompatibility of different implant materials.

Alloys↗

PubMed1996

Three-dimensional analysis of active cervical motion: the effect of age and gender.

OBJECTIVE: To describe the effects of age and gender on three-dimensional (3D) active cervical spine motion. DESIGN: This was a descriptive study. BACKGROUND: This study expanded on previous investigations of age and gender effects on single plane motion of the cervical spine. METHODS: Sixty female and 60 male asymptomatic, normal volunteers, aged between 20 and 59 years, were examined in a standardized seated position. The 3 SPACE Isotrak system was used to measure simultaneous 3D motion of the cervical spine. RESULTS: The mean range of all the primary movements decreased significantly with age. For flexion/extension the greatest decrease occurred between the 20- and 30-year-olds, whereas for both lateral flexion and rotation, significant differences were demonstrated in subjects aged two decades apart. The coupling of motion associated with rotation was significantly related to age. CONCLUSION: Age had a significant effect on all of the primary movements. Age had less effect on the range of the coupled movements, in that the only movements to be affected were lateral flexion and extension occurring during cervical rotation. Gender had no marked effect on the primary or the coupled movements. RELEVANCE: This study provides normative data for the effects of age and gender on three-dimensional analysis of active cervical spine motion, which can be used for comparison with specific patient populations. The high level of intra-subject test-retest reliability renders the3 SPACE system of value for clinical measurement of movement pre- and post-treatment intervention for cervical spine disorders.

Journal Article↗

PubMed1996

Bilateral femoral rotations measured during walking: a new parameter to summarize and describe individual gait.

The aim of this study was to develop and assess a method of analysis of femoral rotations to describe and summarize an individual's gait. Twelve normal subjects underwent walking trials at both natural and slow speeds, controlled by a metronome. The three-dimensional rotations of each femur were measured, simultaneously, during walking using a 3SPACE Tracker. The phase lags between the three rotations for each leg, obtained by cross-correlations, provided the primary data. The device was found to be reliable and gave significant test--retest repeatability. The analyses provided summary parameters describing mathematically the patterns of rotations and showed there was repeatability within and between sessions. A strong systematic subject effect in all analyses indicated that these parameters provide a highly specific description of how an individual walks.

Journal Article↗

PubMed1996

Direct measurement of hoop strains in the intact and torn human medial meniscus.

OBJECTIVE: To measure the circumferential or hoop strains generated in the medial meniscus during loading of the knee joint and to examine the effect of longitudinal and radial tears in the meniscus on these strain values. DESIGN: An in vitro investigation measuring the circumferential strains in the medial menisci of cadaveric human knees as they were loaded in a materials testing machine. BACKGROUND: The menisci transmit approximately 50% of the load through the knee, the rest being transmitted by direct contact of the articular cartilage. Damage to the menisci will alter the pattern of load transmission as will meniscectomy. This study examined the changes in the mechanics of the meniscus in situ as a result of simulated tears to assess the effect of its load carrying capacity and the implications of surgery to remove part or all of a damaged meniscus. METHODS: Nineteen human cadaveric knees were tested. Windows were made in the joint capsule and strain gauges inserted into the anterior, middle and posterior sections of the medial meniscus. The knees were then loaded to three times body weight at speeds of 50 and 500 mm/min, with the knee joint at 0 degrees and 30 degrees of flexion. The tests were repeated following the creation of a longitudinal or a radial tear in the meniscus. RESULTS: The intact menisci showed significantly less strain in the posterior section compared to the anterior and middle sections (P < 0.003, with strains of 1.54%, 2.86% and 2.65% respectively). With a longitudinal tear this pattern changed with strains decreasing anteriorly and increasing posteriorly. There were also significant differences at different angles of knee joint flexion not seen in the intact meniscus. 50% radial tears reduced the strains anteriorly whilst a complete radial tear completely defunctioned the meniscus. CONCLUSIONS: This study has shown that there are significantly different hoop strains produced in different sections of the medial meniscus under load and the patterns of strain distribution are disturbed by meniscal tears. RELEVANCE: These results provide important data for mathematical models which must include non-uniform behaviour. They also have implications for the surgical management of torn menisci. Undamaged portions should be preserved and the integrity of the circumferential fibres maintained to ensure the menisci retain a load bearing capability.

Journal Article↗

PubMed1996

The reliability of postural sway measures using the 3SPACE Tracker.

OBJECTIVE: To investigate the reliability of three-dimensional postural control sway measures, in a normal population, using an electromagnetic device. DESIGN: A repeated measures design was used within and between sessions. BACKGROUND: Electromagnetic measurement has been proposed as a method of measuring postural sway; however, reliability within a normal population has not been shown. METHOD: An electromagnetic device, the 3SPACE Tracker, measured postural sway at the pelvis using sway path length and displacements in the anterior-posterior, medial-lateral and vertical direction. Ten subjects performed a postural control task involving two trials for six different sensory conditions, on two separate occasions, two weeks apart. RESULTS: The reliability of the technique was demonstrated by the repeatability of results for individual subjects within and between sessions. Individual subjects and sensory conditions were discriminated. Sway path length was the most consistent of the measures used. CONCLUSIONS: Three dimensional measures of postural sway are reliable and discriminatory in a normal population.

Journal Article↗

PubMed1996

Drug inhibition of the macrophage response to metal wear particles in vitro.

The wear particles of cobalt chrome alloy and titanium alloy have been implicated as a cause of aseptic loosening of prostheses. It is thought that their ability to induce either cell death or the release of mediators that induce bone resorption contributes to this loosening. This study was designed to test the hypothesis that these adverse biologic effects are due to wear particle corrosion at low pH after they have been phagocytosed by macrophages. Cobalt chrome alloy and titanium alloy particles of similar size and concentration to those found in the tissues surrounding failed prostheses were added to cultured rodent peritoneal macrophages. Treatment of macrophages with drugs that prevent a drop in pH within phagosomes significantly reduced the toxicity of phagocytosed cobalt chrome alloy particles. The same drugs also reduced the levels of prostaglandin E2 and interleukin-6 release induced by phagocytosed titanium alloy particles. When both types of particles were incubated at a low pH, similar to that encountered by phagocytosed particles, soluble products were released that induced the same effects as the particles themselves. These results show that enhanced corrosion of wear particles by phagocytic cells may contribute significantly to the adverse biologic effects of wear particles and identify drug therapies that may be investigated further.

Ammonium Chloride↗

PubMed1995

Mechanical properties of the human anterior cruciate ligament.

The aim was to measure the stiffness and strength of the femur-anterior cruciate ligament-tibia complex tested in a physiological manner with a force exerted anteriorly on the tibia, at knee joint flexion angles of 0 degrees, 10 degrees and 30 degrees and at speeds of 50 and 500 mm/min. Ligaments were preconditioned by cycling five times, with data from the fifth cycle used to determine the stiffness of the ligament in a low-load range. The ligaments were then tested to failure with the knee at 30 degrees flexion. The specimens were divided into two groups, middle-aged (40-60) and old (>60). For each group no statistical difference was observed between stiffness of the ligament at different joint flexion angles or speeds. Seven of the 21 specimens in the older age group failed by avulsion at the bone-ligament interface. All the other specimens failed by tears in the substance of the ligament. Ultimate failure load was found to have a significant correlation with bodyweight. It was 1.6 and 1.3 times bodyweight for the middle-aged and older age groups respectively. This study has highlighted the importance of identifying different modes of failure, of making corrections for bodyweight and testing in a physiological manner. The results allow a better understanding of the mechanical behaviour of the anterior cruciate ligament and provide design data for anterior cruciate ligament grafts and prostheses. RELEVANCE:--Our clinical experience indicates that the anterior cruciate ligament is frequently ruptured during uncoordinated contraction of the quadriceps mechanism. The results of this study, in which the mechanical properties of the anterior cruciate ligament have been measured with force exerted anteriorly on the tibia, allow a more complete understanding of the mechanical behaviour of the anterior cruciate ligament and provide design data for anterior cruciate ligament grafts and prostheses.

Journal Article↗

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↗