Biomedical subjects

M Pearcy

Publications and source records attributed to M Pearcy.

12 recordsLinked to original sources

PubMed2006

Modelling external bone adaptation using evolutionary structural optimisation.

External remodelling is significant in the bone healing process, and it is essential to predict the bone external shape in the design of artificial bone grafts. This paper demonstrates the effectiveness of the evolutionary structural optimisation (ESO) method for the simulation of bone morphology. A two-dimensional ESO strategy is developed which is capable of finding the modified bone topology beginning with any geometry under any loading conditions. The morphology of bone structure is described by the quantitative bone adaptation theory, which is integrated with the finite element method. The evolutionary topology optimisation process is introduced to find the bone shape. A rectangle, which occupies a larger space than the external shape of the bone structure, is specified as a design domain; the evolutionary process iteratively eliminates and redistributes material throughout the domain to obtain an optimum arrangement of bone materials. The technique has been tested on a wide range of examples. In this paper, the formation of trabecular bone architecture around an implant is studied; as another example, the growth of the coronal section of a vertebral body is predicted. The examples support the assertion that the external shape of bone structure can be successfully predicted by the proposed ESO procedure.

Adaptation, Physiological↗

PubMed2006

Comparison of two numerical approaches for bone remodelling.

This paper addresses the "checkerboard" phenomenon, which occurs in numerical simulation of bone remodelling. It attempts to answer the question: is an element-based approach suitable for bone remodelling? Two different numerical approaches, the element-based and the node-based finite element analyses, are implemented using ABAQUS. A comparison of the numerical results demonstrates that the checkerboard phenomenon occurs only in the element-based finite element analyses; the node-based approach eradicates the checkerboard phenomenon but requires much more computational time. This study shows that it is essential to enforce the continuity of bone density across the element boundaries. As the node-based approach requires much more computational time, the first-order Adams-Bashforth integration method is introduced to reduce computational cost. The comparisons with Euler's forward method demonstrate that the first-order Adams-Bashforth method indeed enhances accuracy and reduces computational cost. This study concludes that the node-based approach with the first-order Adams-Bashforth integration scheme is to be recommended for computational bone remodelling studies.

Algorithms↗

PubMed2006

Thelytokous parthenogenesis and its consequences on inbreeding in an ant.

Thelytokous parthenogenesis, that is, the production of diploid daughters from unfertilized eggs, may involve various cytological mechanisms, each having a different impact on the genetic structure of populations. Here, we determined the cytological mechanism of thelytokous parthenogenesis and its impact on inbreeding in the ant Cataglyphis cursor, a species where queens use both sexual and asexual reproduction to produce, respectively, workers and new queens. It has been suggested that thelytokous parthenogenesis in C. cursor might have been selected for to face high queen mortality and, originally, to allow workers to replace the queen when she passes away. We first determined the mode of thelytokous parthenogenesis by comparing the rate of transition to homozygosity at four highly polymorphic loci to expectations under the different modes of parthenogenesis. Our data show that thelytoky is achieved through automictic parthenogenesis with central fusion. We then estimated the proportion of colonies headed by worker-produced queens in a natural population. We designed a model linking the observed homozygosity in queens to the proportion of queens produced by workers, based on the assumption that (i) parthenogenesis is automictic with central fusion and (ii) queen lineage is asexually produced, resulting in an increase of the inbreeding over generations, whereas workers are sexually produced and therefore not inbred. Our results indicate that more than 60% of the colonies should be headed by a worker-produced queen, suggesting that queen's lifespan is low in this species.

Animals↗

PubMed2001

Modelling the line of action for the oblique abdominal muscles using an elliptical torso model.

When modelling the line of action of a muscle, anatomical considerations must be included if the model is to realistically mimic the muscle behaviour. The internal and external oblique muscles are examples of muscles that do not follow a straight line between origin and insertion, instead having to wrap around the torso. A model is presented which describes the shape of the torso using a right elliptical cylinder of varying dimensions. The muscle lines of action are then calculated based on this underlying torso shape. The model has been successfully fitted to the data reported by Stokes and Gardner-Morse (Journal of Biomechanics 32(3) (1999) 311). When compared to a linear model, the use of the torso model results in a 15% increase in the axial twist moment, and decreases in the lateral bend and extension moments (5% and 2%, respectively), able to be generated by the internal and external oblique muscles combined in upright stance. These differences become larger (up to 37%) when the torso is flexed, extended or twisted. The structure of the torso model allows it to be used to model any posture without significant increases in the overall model complexity.

Abdominal Muscles↗

PubMed2001

Graphical presentation of the range of hip and knee rotations for clinical evaluation of gait.

OBJECTIVE: This paper reports a method of using a multi-axis graph to represent the range of rotations at the hip and knee joints during gait for clinical evaluation of a patient's performance. DESIGN AND METHODS: The multi-axis graph uses 12 symmetrically arranged axes to represent each component of range of rotations at the hip and knee joints of both legs. The range of joint rotations of thirteen normal subjects and two patients were measured using an electromagnetic motion tracking system with four foot switches. RESULTS: The range of joint rotations of normal subjects shows a symmetrical star in the multi-axis graph. Abnormal function of a patient shows an asymmetrical star. CONCLUSIONS: This representation provides a simple way to examine a patient's performance in a time effective manner. Relevance. In clinical practice, the multi-axis representation of joint rotations can be used as an initial evaluation of a patient's performance to identify problems for further investigation.

Adult↗

PubMed1999

A three-dimensional definition for the flexion/extension and abduction/adduction angles.

Flexion/extension and abduction/adduction, two major parameters for the description of joint rotations, are used to define planer anatomical orientations of body segments. These two-dimensional definitions have been used extensively in the biomechanical literature for reporting and representing both two-dimensional and three-dimensional joint rotations. Whether these traditional two-dimensional measurements represent true joint rotations in three dimensions has not been investigated. A quantitative error analysis is presented to show how large an error can be produced in the flexion/extension and abduction/adduction angles when using two-dimensional measurements to represent three-dimensional joint rotations. The results indicate that for an out-of-plane flexion the error in abduction angle measured by previous methods increases with both flexion and initial abduction angle and become very sensitive when the flexion angle exceeds 40 degrees. Although the error can be less than 2 degrees for flexion below 20 degrees when the initial abduction angle is at 30 degrees, it can be as large as 9 degrees for 60 degrees of flexion with an initial 10 degrees of abduction; nearly double the real abduction angle. Therefore, two-dimensional measurements of flexion/extension and abduction/adduction can be erroneous and overestimated for a three-dimensional joint rotation. To overcome the problem new definitions are proposed for the true flexion/extension and abduction/adduction angles as two independent parameters for three-dimensional joint rotation.

Biomechanical Phenomena↗

PubMed1998

Total wrist arthroplasty: a quantitative review of the last 30 years.

OBJECTIVE: To investigate the suitability of design of 3 generations of wrist prostheses. METHODS: A comparative review was performed on the Swanson, Volz, Meuli, Trispherical, Biaxial, and MWP III total wrist prostheses. RESULTS: The review revealed a sharp rise in fracture and revision rates for the Swanson prosthesis after 55 months followup, with the most likely site for fracture at the junction of the distal stem and barrel. The Volz prosthesis had initial problems with a postoperative resting stance of ulnar deviation, due to the radial shift of the axis of the prosthesis to that of the normal wrist. A modified prosthesis corrected the problem of ulnar deviation; however, problems with bone resorption under the collar of the radial component and metacarpal loosening were seen. The majority of complications occurred in patients with post-traumatic degenerative joint disease. The remaining prostheses have had only a few clinical studies, and are presented to illustrate the different design concepts adopted. CONCLUSION: Total wrist arthroplasty has less satisfactory clinical outcomes compared to hip and knee arthroplasty. The changes in design from the first to the third generation, with closer approximation to the wrist joint's center of rotation, have led to encouraging results. The comparison of the clinical outcome of different prostheses has been difficult due to the lack of uniformity of outcome measures used.

Arthroplasty↗

PubMed1995

A biological basis for instantaneous centres of rotation of the vertebral column.

The instantaneous centre of rotation has proven to be a useful parameter of vertebral motion. The normal location of instantaneous centres has been determined in cadavers and in normal volunteers for the cervical, thoracic and lumbar spines, and abnormal location of centres has been shown to correlate with spinal pain. However, to date, an instantaneous centre has constituted no more than a convenient mathematical summary of vertebral kinematics. It has defied resolution into biologically meaningful parameters. This study offers a novel model of vertebral motion in which the instantaneous centre of rotation can be shown to be a function of the location of the centre of reaction of a vertebra, and the intrinsic rotation and translation it undergoes. These parameters are strictly linked by equations that determine the location of an axis of rotation. These equations allow aberrations in the location of an axis to be interpreted in terms of the anatomical and pathological factors that affect the centre of reaction of the vertebra and the rotation and translation it undergoes.

Biomechanical Phenomena↗

PubMed1985

The effect of low-back pain on lumbar spinal movements measured by three-dimensional X-ray analysis.

Back pain patients have restricted spinal movements, and the pattern of disturbance from normal movements may indicate the pathology and the functioning of the lumbar spine. Biplanar radiography was used to measure the three-dimensional intervertebral movements of patients with back pain alone and with back pain plus nerve tension signs demonstrated by restricted straight leg raise. Statistically significant decreases in flexion/extension compared with a normal control group were demonstrated for both groups. Accompanying coupled movements were increased only in those patients without nerve tension signs indicating asymmetrical muscle action, while those with tension signs had symmetric splinting particularly of the lower levels. Conservative treatments had no effect either clinically or on the movements. Caudal epidural injections produced clinical improvement and increased movements demonstrating relaxation of muscle splinting. Biplanar radiography, although capable of differentiating between the groups was not able to provide clinically useful information concerning individual patients with this type of back pain.

Adult↗

PubMed1985

Is there instability in spondylolisthesis?

Biplanar radiography was used to investigate the three-dimensional intervertebral movements of patients with symptomatic spondylolisthesis to assess whether there was evidence of instability. These movements were also compared with those of a group of normal subjects. The primary movements of flexion and extension were studied, and the three-dimensional analysis enabled intervertebral translations and any coupled movements of lateral bending and axial rotation to be examined. The results showed that symptomatic spondylolisthesis resulted in reduced mobility of all levels of the lumbar spine and the appearance of coupled movements at the higher levels. The pathology did not produce instability at the level of the slip in any of these patients.

Adult↗

PubMed1984

Three-dimensional x-ray analysis of normal movement in the lumbar spine.

Biplanar radiography was used to assess the normal three-dimensional movements of the lumbar spine in the erect posture in a group of asymptomatic volunteers. The primary movements investigated were flexion and extension, while the three-dimensional analysis also measured any associated coupled lateral bends and axial rotations. The results showed that each intervertebral joint had a total range of flexion and extension of approximately 14 degrees, the lower levels moving slightly more than the upper levels. All the intervertebral joints had more movement in flexion than extension from the upright position, except for the L5/S1 joint, which showed no consistent pattern, some subjects extending more than flexing. Coupled movements of 4 degrees or more in flexion and 3 degrees or more in extension were shown to be abnormal.

Adult↗

PubMed1982

Assessment of bony union after interbody fusion of the lumbar spine using a biplanar radiographic technique.

Assessment of bony union after anterior fusion of the lumbar spine has previously relied on the skilled interpretation of plain radiograph. A biplanar radiographic technique was used to measure small movements between vertebrae and to give a quantitative measure of bony union in 11 patients who had undergone interbody fusion with autogenous bone chips at one level in the lumbar spine. The investigation gave three types of results: bony union, where the fused level showed marked restriction of movement relative to the rest of the lumbar spine; paradoxical movement, where the fused joint showed marked reverse movement (when the patient flexed, the fused level of the lumbar spine extended) which was thought to be due to an anterior bony bar which caused an altered pattern of movement; and non-union, where the level of fusion showed no restriction of movement. The intervertebral joint above the level of fusion was shown to move more than the other joints in the lumbar spine. The study showed that bony union is possible with the use of autogenous cancellous bone chips, and that biplanar radiographic technique can determine the extent of union.

Adult↗