PubMed Health⌕ Search

Biomedical subjects

W L Buford

Publications and source records attributed to W L Buford.

15 recordsLinked to original sources
PubMed2001

Internal/external rotation moment arms of muscles at the knee: moment arms for the normal knee and the ACL-deficient knee.

Knowledge of the three-dimensional balance of loads at the knee joint is required to adequately assess the treatment and rehabilitation of the malfunctioning knee. This report focuses upon the moment arms for the knee in internal/external (IE) rotation motion. It augments prior work that defined flexion/extension moment arms. Muscle excursions and angular motion of the lower leg during IE rotation were measured in 17 fresh-frozen hemi-pelvis specimens. Moment arms were calculated as the derivatives of excursion with respect to the angle. Rotational motion was performed for the normal and anterior cruciate ligament (ACL)-deficient knee. Of the 13 muscles measured at the knee, seven were significant contributors to IE rotation: the biceps femoris long and short head externally rotate opposite the gracilis, sartorious, semimembranosis, semitendonosus and popliteus, functioning as internal rotators. Moment arm magnitudes were greatest with the knee in a flexed position (internal [external] rotators peaked at 70 degrees [90 degrees] flexion). At 30 degrees flexion, the IE rotation moment arm minima and maxima were 10.1-11.6, 6.8-9.0, 6.0-15.7, 8.2-14.1 and 0.0-10.4 mm for the semimembranosis, semitendonosus, gracilis, sartorius and popliteus, and 14.7-27.9 and 18.5-31.5 mm for the biceps femoris short and long, respectively. Moment arms for the ACL-deficient condition were significantly changed only at extremes of flexion-extension.

Adult↗
PubMed2000

Femoral surface strain in intact composite femurs: a custom computer analysis of the photoelastic coating technique.

Understanding how forces are distributed through the proximal femur has many clinical applications for surgeons, researchers, and prosthetic designers. A new system for two-dimensional analysis of femoral surface strain was developed and applied to intact composite femurs. The photoelastic coating method was used to resolve the surface strain under axial loading, and strain analysis was performed using digital imaging of the strain patterns and original computer programs. The technique provides qualitative and quantitative data that describes overall femoral surface strains more completely than previous point analysis and strain gauge techniques. Results from repeated testing found the photoelastic process, computer imaging and computer analysis of strain areas to be statistically repeatable.

Biomechanical Phenomena↗
PubMed1997

Muscle balance at the knee--moment arms for the normal knee and the ACL-minus knee.

Forces, moments and stresses at the knee are dependent upon external and internal loading factors including muscle forces, segmental position and velocity, load carried, and the moment arms (mechanical advantage) of the muscle-tendon units. Requisite to prediction of forces and moments is a detailed understanding of effective moment arms throughout the knee range-of-motion (ROM). Existing muscle models for the knee are based upon limited static studies of only a few preserved specimens. The objectives of this report are to develop a comprehensive description of muscle-tendon moment arms for the normal knee and the anterior cruciate ligament (ACL)-minus knee during flexion-extension motion. Recent research results describe two nonorthogonal, nonintersecting axes of motion for the knee--one describing flexion-extension (FE) and the other longitudinal rotation (LR, equivalent to internal-external rotation). The effective flexion-extension moment arms of the muscles crossing the knee were developed with respect to the FE axis in 15 fresh, hemi-pelvis cadaver specimens. The normal moment arms for each of 13 muscles plus the patellar tendon exhibited variable, yet repeatable and recognizable patterns throughout the ROM. For most muscles there was no significant difference between the normal and ACL-minus moment arms. The results provide a basis for more accurate predictions of joint reaction forces and moments as well as useful knowledge for practitioners and therapists to assist in the assessment of muscle balance at the knee following injury, repair, and throughout rehabilitation.

Adult↗
PubMed1995

A virtual five-link model of the thumb.

Most researchers have modelled the thumb as three rigid links with connections of two universal joints (carpometacarpal joint and metacarpo-phalangeal joint), and a hinge joint (interphalangeal joint). Although this produces the required number of degrees of freedom, the resulting motion is not anatomically accurate. In this work, the thumb is modelled as a five-link manipulator with the virtual links connected by hinge joints-one for each degree of freedom of the thumb. The axes of the hinges are not orthogonal to one another, in the long axis of the bones or to the anatomic planes. Four static positions of hand function were analysed-key pinch, screwdriver hold, tip pinch, and wide grasp. The virtual five-link model of the thumb predicted similar muscle recruitment patterns to published EMG data. The force at the distal surface of the trapezium is between 6 and 24 times the applied load depending on the posture.

Biomechanical Phenomena↗
PubMed1995

Carpal bone anatomy measured by computer analysis of three-dimensional reconstructions of computed tomography images.

Using quantitative analysis of three-dimensional reconstructions of computed tomography scan data, a normative database of carpal bone morphology was built. Thirty-five wrists were imaged in a computed tomography scanner. Each slice was processed to determine the bone edges and assembled as a three-dimensional model by stacking. Quantitative measurements of volume, surface area, maximum length, and intercarpal distances were then assessed. A reliable three-dimensional carpal height ratio was calculated by dividing the carpal height (minimum distance between the fourth metacarpal and the radius) by the capitate maximum length. For volume, maximum length, and surface area, the order for the eight carpal bones with respect to size (in descending order) were: capitate, hamate, scaphoid, trapezium, lunate, trapezoid, triquetrum, and pisiform. Male wrists were significantly larger than female wrists. There were no significant differences in the relative dimensions between left and right wrists, or between left and right wrists of matched pairs. This technology offers automated analysis of three-dimensional geometric carpal information and the opportunity to obtain a body of information about normal and abnormal morphology as well as spatial relationships between carpal bones.

Adolescent↗
PubMed1995

Quantification of anatomic, geometric, and load transfer characteristics of the wrist joint.

The work reported here is an assimilation of 8 years of research, the purpose of which was to gain a better understanding of the normal and abnormal workings of the wrist joint. The results are summarized in three major areas of concentration: descriptive anatomic studies, which include direct measurements of cadaver specimens, biomechanical loading studies to define load distribution through normal and abnormal wrists, and three-dimensional (3D) anatomy studies using solid models derived from computed tomographic (CT) images of in vivo and cadaver wrists. The descriptive anatomic studies used 393 cadaver wrists to evaluate the incidence and distribution of anatomic features, arthroses, chondromalacia, and soft-tissue lesions. The data were analyzed for any statistically significant associations among different variables. The biomechanical studies characterized the biomechanics of the human wrist in a variety of normal, simulated traumatic, and surgically treated conditions. The results of the load studies have provided clinically relevant information on the normal anatomy and functional mechanics of the wrist as well as guidelines for the treatment of a number of different fractures and ligament injuries. The 3D anatomic studies use quantitative analysis of 3D reconstructions of CT scan data to build a normative database of carpal bone morphology. Thirty-five wrists were imaged in a CT scanner. Quantitative measurements of volume, surface area, maximum length, and intercarpal distances were than assessed. A reliable 3D carpal height ratio (3DCHR) was calculated by dividing the capitate maximum length by the carpal height, which is the minimum distance between the fourth metacarpal and the radius.

Adolescent↗
PubMed1995

The axes of rotation of the thumb interphalangeal and metacarpophalangeal joints.

The axes of rotation of the thumb interphalangeal and metacarpophalangeal joints were located using a mechanical method. The interphalangeal joint axis is parallel to the flexion crease of the joint and is not perpendicular to the phalanx. This offset of the axis with respect to the phalanx explains the ulnar deviation and pronation that occurs with flexion of the interphalangeal joint. The metacarpophalangeal joint has 2 fixed axes: a fixed flexion-extension axis just distal and volar to the epicondyles, and an abduction-adduction axis related to the proximal phalanx passing between the sesamoids. Neither axis is perpendicular to the phalanges. All physiologic motion for these joints occurs about the axes. These are the mechanical axes of the joints through which the muscles and external forces act. Knowledge of their location should help in constructing prosthetic joints and in planning reconstructive surgery such as tendon transfers.

Finger Joint↗
PubMed1992

The axes of rotation of the thumb carpometacarpal joint.

Two axes of rotation of the carpometacarpal (CMC) joint of seven cadaver thumbs were located using an axis finder. The flexion-extension axis is located in the trapezium and the abduction-adduction axis is in the first metacarpal. These axes are fixed, are not perpendicular to each other or to the bones, and do not intersect. Motion of the first metacarpal on the trapezium can be defined by these two axes. Understanding of the movements of the basal joint of the thumb is essential to the study of its function and reconstruction.

Biomechanical Phenomena↗
PubMed1991

Update in splinting materials and methods.

Current hand splinting methods, materials, and components are reviewed and summarized. Additional subjective and objective tests of thermoplastic materials are performed and results combined with those from other studies. Available samples of thermoplastic materials are tested for fatigue and viscoelastic properties using standard compression cycling methods. Soft splint materials are seeing increased application and appear to be the material for the future.

Hand↗
PubMed1985

Walking casts: effect on plantar foot pressures.

Pressure measurements were made at four sites on the right foot of six normal subjects while they walked in a standard shoe, conventional padded cast, total contact cast, and again in a shoe. No differences in mean relative pressure were found between the padded cast and the total-contact cast. Significant reductions in mean relative pressure were found between the standard shoe and walking casts at the first and third metatarsal head. This study supported the use of walking casts in the management of plantar ulcers. The effectiveness of the cast in reducing plantar pressure was not found to be dependent on the cast padding technique.

Casts, Surgical↗
PubMedDate not supplied

Clinical assessment, objectivity, and the ubiquitous laws of instrumentation.

With the Carville approach to interdisciplinary rehabilitation, special emphasis is placed on improved objective measurement of human function. This article defines essential elements for objective measurement, based on the experiences of a biomedical engineer on the rehabilitation team. Applied to manmade system, these elements are straightforward. Applied to living systems, these elements present difficulties, and special consideration must be given to the methods of measurement applied in the clinical setting. The rules for successful instrumentation and measurement are discussed with respect to the hand therapist's continuing challenge to measure the threshold to tactile sensation.

Humans↗
PubMedDate not supplied

Computer simulation of the upper extremities.

The development of real-time, interactive, three-dimensional, computer graphic simulation of the musculoskeletal system with emphasis on the upper extremities is described. Developments in image analysis, scientific visualization, and interactive computer methods and the continuous improvement in knowledge of musculoskeletal function have combined to provide an exciting new tool for musculoskeletal research. Interactive simulation also has promising applications in medical education and clinical rehabilitation. Only those developments that fit the specific criteria of realism, real-time response, intuitive interaction, three-dimensional structures, and modeling flexibility are discussed. It is hoped that an improved understanding of this emerging tool and an appreciation for its potential applications will be gained.

Arm↗
PubMedDate not supplied

The force/time relationship of clinically used sensory testing instruments.

The stimuli of commonly used sensibility measurement instruments tested in this study demonstrate unequivocally that "hand-held instruments" produce variations in application force from one stimulation to another, one instrument to another, and from one examiner to another. These application force variations cannot be compensated for by care in technique and need to be controlled for measurement reliability. Only the Semmes-Weinstein monofilaments provide some control of force during application and can be considered force controlled if calibrated and applied correctly. The monofilaments, too, become less controllable if applied too quickly and bounced against the skin. Two-point discrimination instruments, in particular, lack control of application force, with the force of one point significantly different from two points. A difference in applied force makes it possible for a patient to solve the two-point discrimination test by discerning the difference between heavier and lighter forces, rather than one or two-point recognition. Tuning fork instruments for vibration testing have even larger variations in application force amplitude rendering their stimulus highly uncontrolled and masking the actual vibration of the tuning fork. Spectral analysis of the force frequency signal produced by hand held sensibility measurement instruments shows they all produce both high and low frequency signals sufficient in strength to stimulate both slowly adapting and quickly adapting end organs, and are not capable of stimulating one particular group. These dynamic properties of testing stimuli explain why our tests are not as repeatable and sensitive as desired. The understanding of these dynamic properties in sensibility measurement is a key for improved instruments and more repeatable findings in clinical testing.

Biomechanical Phenomena↗
PubMedDate not supplied

A comparison of double-plate fixation methods for complex distal humerus fractures.

A modified method of fracture fixation of complex distal humeral fractures with medial and lateral plates and bolts was biomechanically tested and compared with previously described fixation techniques. Compressive stiffness coefficients were determined for three classes of fixation before and after fatigue cycling. This procedure was followed with compressive loading to failure. The results show that in the most unstable fracture type tested this new fixation method provides increased strength and stability. Early clinical follow-up examinations of patients treated with this technique show that this method is a reasonable fixation alternative for the complex distal humerus intercondylar fracture.

Adult↗