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Biomedical subjects

J G Andrews

Publications and source records attributed to J G Andrews.

At least 19 recordsLinked to original sources
PubMed2004

Cross-match protocols for femoral neck fractures--finding one that can work.

BACKGROUND: Cross-match practice for patients with femoral neck fractures continues to cause concern due to a failure of compliance to the existing protocols. To address this issue, a number of studies were conducted over a 3-year period. METHODS: First, the existing cross-match practice for patients admitted with femoral neck fractures was reviewed to demonstrate the deficiencies within the system. Second, the opinion of anaesthetic and orthopaedic trainees was assessed regarding blood requirements for different femoral neck fractures following surgery and the justification of their perceptions. RESULTS: A summation of the studies is reported which demonstrates the reasons for the poor compliance to previous protocols. CONCLUSIONS: A simple and effective protocol is provided that has helped reduce pre-operative cross-matching of femoral neck fractures from 71% to 16.7% when assessed 2 years after its introduction.

Blood Grouping and Crossmatching↗
PubMed2000

Anxiety and depression in twin and sib pairs extremely discordant and concordant for neuroticism: prodromus to a linkage study.

Multivariate modelling of anxiety and depression data in twins has suggested that the two phenotypes are largely underpinned by one genetic factor, while other studies have indicated a relationship between these disorders and the neuroticism personality trait. As part of a study to identify quantitative trait loci for anxiety and depression, questionnaire responses and interviews of 15,027 Australian twins and 11,389 of their family members conducted during the past 20 years were reviewed to identify individuals with neuroticism, anxiety and depression scores in the upper or lower deciles of the population. This information was then used to identify extreme discordant and concordant (EDAC) sib pairs. 1373 high-scoring and 1571 low-scoring subjects (2357 sib pairs) were selected for participation, and extremely high participation rates were achieved, with over 90% of contactable prospective participants completing the interview phase, and over 90% of these providing blood or buccal samples. Participation bias arising from the nature of the selection variables was minimal, with only a small difference between rates of interview participation among prospective participants with high and low selection scores (89.4% vs 91.6%). The interview permitted the diagnosis of depression and several anxiety disorders (OCD, agoraphobia, panic disorder, generalised anxiety disorder) in this sample according to DSM-IV criteria. The methodology for selection of prospective subjects was demonstrated to be extremely successful, with highly significant differences in depression and anxiety disorder prevalence rates between individuals in the two selection groups. The success of this EDAC sampling scheme will enhance the power for QTL linkage and association analysis in this sample.

Adult↗
PubMed1997

Quantifying osteoarthrotic hip incongruence. An approach to optimizing osteotomies.

Osteoarthrosis of the hip may be treated by osteotomy, but surgeons report variable results, and there is no consensus regarding which method to use in choosing the type of osteotomy. The authors defined three biomechanical measures of hip incongruence (characteristic point locus, joint space, and contact region) and developed a two-dimensional frontal plane model to compute joint incongruence over the joint range of motion during normal activities of daily living. The preoperative measures were calculated for 38 patients who had undergone osteotomy at least 5 years earlier. The authors calculated the measures throughout a functional range of motion after 13 stimulated varus or valgus osteotomies. A logistic regression analysis determined which, if any, of the three measures, in conjunction with other clinical variables, correctly predicted outcome. The average values for the characteristic point locus, joint space, and contact region measures ranged from 0.260 cm to 2.127 cm, 0.963 cm2 to 9.327 cm2, and 0.063 cm to 4.230 cm, respectively. Unimodal behavior between two of the three measures (joint space and contact region) and osteotomy angle were observed, suggesting these two would be the most useful in predicting an optimal osteotomy. The most significant independent variable predicting clinical outcome was the joint space measure. This supports the potential of an optimization approach for determining the best angle for a hip osteotomy.

Acetabulum↗
PubMed1996

Methods for investigating the sensitivity of joint resultants to body segment parameter variations.

Two methods are presented for determining the sensitivity of joint resultants to variations in body segment parameters (BSPs) when solving inverse dynamics problems: the exact sampling method (ESM), and the approximate variational method (AVM). These methods are illustrated by applying them to a single segment in fixed-axis rotation. The results indicate that (a) the AVM provides first-order (linear) approximations to the total variations in joint resultants obtained when using the ESM, (b) the ESM should be used when BSP variations become large and higher-order terms in these variations can no longer be ignored as negligible in the BSP-dependent expansions for the joint resultants, (c) small percent variations in BSPs can propagate into considerably larger percent variations in the joint resultants obtained when solving inverse dynamics problems, and (d) if BSP variations are sufficiently small to allow nonlinear terms in these variations to be ignored as negligible, the AVM is much simpler and easier to use than the ESM.

Algorithms↗
PubMed1990

Contribution of passive tissues to the intersegmental moments at the hip.

Many anatomic structures around the hip contribute either actively (i.e., muscle contractile elements) or passively (i.e., capsule, ligaments, non-contractile portions of muscles) to the intersegmental resultant forces and moments. Investigators have often assumed that the passive elements contribute negligibly to those moments, but without substantial supporting data. We explored this assumption by measuring the 'passive moments' in 15 normal subjects from near full extension to 60 degrees of hip flexion at speeds used in slow and normal walking. The data suggest that throughout most of the gait cycle and normal stair climbing, the passive structures contribute a small portion of the total moment, usually well less than 10%. Thus, for this limited range of activities, the assumption of negligible contribution of passive structures is reasonable.

Activities of Daily Living↗
PubMed1990

The joint distribution problem with multiple articular contact forces.

The single joint distribution problem with two or more unknown bony contact forces is considered, and an optimal solution procedure free of ad hoc assumptions is described. If two bony contact forces are present, a strictly muscle force dependent equality constraint exists that allows for initial independent estimation of muscle forces, followed by unique estimation of all bony contact force components perpendicular to the straight line connecting their known points of application. However, if three or more bony contact forces are present, no strictly muscle force dependent equality constraint exists, solution separability is lost, and optimal muscle and bony contact forces are obtained simultaneously.

Biomechanical Phenomena↗
PubMed1988

Resultant forces and angles of twist about the wrist after ECRL to ECU tendon transfer.

This paper describes an experimental investigation to determine the biomechanical efficacy of the extensor carpi radialis longus (ECRL) to extensor carpi ulnaris (ECU) tendon transfer procedure used in rheumatoid hand reconstruction. Six normal cadaver specimens were tested in an apparatus that measured (a) the forces acting on the hand to restrain it in seven characteristic wrist configurations, and (b) the amount of hand pronation/supination that occurred as a result of loads applied to the tendons of the six major wrist muscles. Each specimen was tested with the ECRL tendon intact, surgically released, and transferred to the insertion point of ECU. In the intact and transferred states, the ECRL tendon was loaded sequentially while the remaining five wrist tendons were subjected to equal constant loads. In all three experimental ECRL test states, forces were also applied to all intact wrist tendons in a manner designed to represent physiologic load sharing. When the ECRL tendon was loaded sequentially, the transfer resulted in the predictable increase in the radially directed restraining force and the predictable supination of the hand relative to the forearm. When all intact tendons were loaded physiologically, the transfer also resulted in an increase in the radially directed restraining force. Significant differences between test states occurred generally only between the intact and release states of the ECRL tendon and not between release and transferred states.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1987

The functional roles of the hamstrings and quadriceps during cycling: Lombard's Paradox revisited.

The purposes of this study were to describe the functional roles of the hamstrings and quadriceps at the hip and knee during cycling as determined both by the standard kinetic (SK) classification method and by the Andrews kinematic (AK) classification method (Andrews, J. biomech Engng 107, 348-353, 1985), and to examine the effect of using these two different methods on the existence of paradoxical muscle behavior (Lombard's Paradox). The results of this study indicated that the functional roles determined by the SK and AK methods differed considerably, and these differences led to the existence of paradoxical behavior in the hamstrings and quadriceps at different regions of the crank cycle. Both classification methods led to the existence of considerable paradoxical muscle behavior, with the SK method predicting somewhat more non-paradoxical activity and somewhat less paradoxical activity than the AK method at both the hip and the knee.

Bicycling↗
PubMed1987

Kinematic analysis of the talocalcaneal/talocrural joint during running support.

The purpose of this investigation was to obtain a comprehensive description of the kinematic behavior of the combined talocalcaneal/talocrural joint during the support phase of running. Considerable variation in kinematic data was exhibited by a heterogeneous subject sample (N = 5). The results indicated that: eversion/inversion may not be the only rotational component that should be considered when examining total talocalcaneal/talocrural joint motion; the common definitions for pronation and supination do not always accurately describe the relative motion of the shank relative to the calcaneus; and a combined talocalcaneal/talocrural joint behaving as an oblique hinge was not an adequate model for describing the relative motion of the shank with respect to the calcaneus. It was concluded that further investigation is needed to categorize subjects according to common kinematic characteristics. This categorization may be necessary to better understand characteristic variations in normal joint behavior, to diagnose joint pathology, and to prescribe effective injury prevention and rehabilitation modalities.

Adult↗
PubMed1986

The in vivo kinematics of the rheumatoid wrist.

The objectives of this study were to describe the three-dimensional in vivo kinematic behavior of wrists affected by rheumatoid arthritis, to correlate kinematic parameters and two radiographic indices of carpal disease, and to describe the in vivo kinematic behavior of the Swanson Silastic wrist implant. Fifteen normal wrists, 17 rheumatoid wrists, and 7 wrists with Silastic wrist implants were tested using a three-dimensional sonic digitizing system. The motion of the hand segment relative to the forearm segment, corresponding to the positions exhibited during flexion-extension motion (FEM) and radial-ulnar deviation (RUD), was described using the equivalent screw displacement (ESD) concept. The mean magnitudes of ESD rotation for both FEM and RUD were statistically different (p less than 0.05) among the normal, rheumatoid, and implant groups. The remaining ESD parameters (i.e., mean values for the translation, the direction angles of the ESD axis, and the intercepts of this axis with the planes of motion), the minimum separation between the FEM and RUD axes, and the coordinates of the midpoint of this separation were not statistically different (p greater than 0.05) among the normal, rheumatoid, and implant groups. The two radiographic indices (carpal collapse and carpal translation) did not correlate with the magnitude of rotation or with any other ESD parameter.

Adult↗
PubMed1986

Actions of hip muscles.

This article describes and explains the moment arm vector (MAV) concept, uses the concept for the quantitative classification of hip muscles according to action, and applies the findings to selected clinical problems. A three-dimensional, straight-line model of hip musculature was used. Measurements made on a matched, dry bone specimen provided muscle attachment point location data for the model. Straight lines of muscle action between attachment sites were simulated for a variety of hip configurations during simple hip motions in three principal anatomical planes. We used the MAV concept to identify the three contributions of a muscle (flexion-extension, abduction-adduction, and internal-external rotation) tending to rotate the thigh segment relative to the pelvis. Muscles were classified according to their action or turning effect at 0, 40, and 90 degrees of hip flexion. Certain muscles exhibited significant changes in their action during these simple motions. Model results were verified using an articulated, dry bone specimen with elastic strings stretched between muscle attachment sites. Based on this geometrical model, a "pathological posture" of hip flexion, adduction, and internal rotation was identified, which is a posture prevalent in spastic, brain damaged patients.

Biomechanical Phenomena↗
PubMed1985

The kinetics of normal and prosthetic wrists.

The purposes of this study were (1) to describe normal wrist kinetics, and (2) to investigate the in-vitro kinetics of four currently available wrist prostheses (Swanson, Meuli, Volz, Hamas). The effective tendon moment arms of the six major wrist muscles were determined through the use of load cells and applied weights. Testing was conducted in a neutral wrist configuration with hand pronation-supination both constrained and unconstrained. The results indicate that each of the muscles studied has a unique set of effective tendon moment arms about the normal wrist as well as about wrists with the implanted prostheses, and that none of the prosthetic wrists studied duplicated normal wrist kinetics.

Humans↗
PubMed1985

A general method for determining the functional role of a muscle.

This paper presents a general classification method for determining the functional role of any muscle, and a procedure for determining the sensitivity of that role to small changes in system parameters. The classification method is based on the premise that the system model, when acted upon solely by the muscle of interest, will depart from any initial rest configuration in such a way as to decrease the muscle's length. This method is particularly useful for multiple-joint muscles, and is illustrated by examining a slider-crank mechanism and straight line muscle model to determine the functional role of the hamstrings during a constrained leg flexion motion.

Biomechanical Phenomena↗
PubMed1985

On the concept of the center of percussion.

This paper briefly reviews the concept of the center of percussion of a rigid body, with special emphasis on the requirements for its existence, the two complementary methods used to determine its location, and the system parameters on which its location depends. A consistent generalization of this concept is then proposed for the case when the rigid body is initially moving arbitrarily in three-dimensional inertial space and is restrained in such a way that no impulsive reaction torque can be applied to the body at the point of restraint. The basic requirement for the existence of a center of percussion in this generalized case is identified, and the location of the center of percussion is obtained using one of the two complementary solution methodologies. Six special cases are considered when the existence requirement is satisfied, and these cases are illustrated using examples from common sport situations.

Biomechanical Phenomena↗
PubMed1983

Biomechanical measures of muscular effort.

This paper identifies those particular force and torque quantities that arise most frequently in biomechanical investigations, and which, when appropriately combined with the system's kinematic behavior, appear to be related most directly to muscular effort, i.e., the metabolic cost associated with producing muscle tension, in a joint neighborhood. Depending upon whether the joint distribution problem has been solved, muscular effort is best determined either by the individual variable muscle force magnitudes or by the magnitude of the variable muscle force-dependent component of the resultant joint torque. Discrete biomechanical measures that can be used to represent these continuously-varying scalar functions are identified and examined critically. These include instantaneous measures (e.g., the extremes and other characteristic force, torque, and power values) and interval measures (e.g., average force, torque, and power values, work performed, change in mechanical energy, and linear and angular impulses). If the variation of the effort function is negligible, instantaneous measures may suffice provided there exists a reliable scaling factor relating these quantities to metabolic cost. If the variation of the effort function is appreciable, then properly weighted impulse measures may be the most appropriate because they appear to reflect muscular effort over the widest range of human activities, including those that involve isometric contractions.

Biomechanical Phenomena↗