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)

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.

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.

On the relationship between resultant joint torques and muscular activity.

This paper is an investigation of the relationship between resultant joint torques and in vivo muscular activity. This relationship is currently inaccessible by direct experimental measurements due to the limited usefulness of electromyographic (EMG) data to indicate muscle force reliably and to proscriptions and experimental difficulties related to in vivo measurements on human subjects. The standard indirect method for inferring information about this relationship, using model studies in conjunction with temporal EMG data, is discussed. Key assumptions incorporated in these model studies, which lead to values for the joint force and torque resultants, are reviewed. The general distribution problem is formulated, and key assumptions associated with generating the simplified distribution problem that governs muscle activity are described. Two basically different methods for solving the simplified distribution problem and therefore determining the approximate relationship between resultant joint torques and muscular activity, including methods that attempt to account for the effect of antagonistic muscular activity, are discussed.

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.

A mechanical analysis of a special class of rebound phenomena.

An analytical method is presented for determining the post-impact motion of a rough elastic ball which collides with and rebounds from an arbitrarily oriented rough inertial surface. Pre-impact ball motion is completely general, and the contact interface is assumed to be sufficiently rough to provide a no-slip condition during the restitution phase of the short impact interval. A solution to the impulse-momentum equations is obtained by using Newton's linear coefficient of restitution, and by introducing a torsional coefficient of restitution to account for changes in the magnitude and direction of the component of the ball's angular velocity vector perpendicular to the inertial surface. This method is used to analyze the hop or hook-serve used in advanced-level handball play. An expression for the hop angle gamma is derived, which depends on the components of the mass center velocity and angular velocity vectors imparted to the ball by the server. These results are consistent with the natural tendency for right- and left-handed servers to generate characteristic hops to the left and right, respectively. These same results also indicate, however, that many handball authorities are not giving proper instructions when teaching hop servers how the ball should be spinning after hand impact.

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.

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.

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.

Closed loop problems in biomechanics. Part II--an optimization approach.

A closed loop problem in biomechanics may be defined as a problem in which there are one or more closed loops formed by the human body in contact with itself or with an external system. Under certain conditions the problem is indeterminate--the unknown forces and torques outnumber the equations. Force transducing devices, which would help solve this problem, have serious drawbacks, and existing methods are inaccurate and non-general. The purposes of the present paper are (1) to develop a general procedure for solving closed loop problems; (2) to illustrate the application of the procedure; and (3) to examine the validity of the procedure. A mathematical optimization approach is applied to the solution of three different closed loop problems--walking up stairs, vertical jumping and cartwheeling. The following conclusions are drawn: (1) the method described is reasonably successful for predicting horizontal and vertical reaction forces at the distal segments although problems exist for predicting the points of application of these forces; (2) the results provide some support for the notion that the human neuromuscular mechanism attempts to minimize the joint torques and thus, to a certain degree, the amount of muscular effort; (3) in the validation procedure it is desirable to have a force device for each of the distal segments in contact with a fixed external system; and (4) the method is sufficiently general to be applied to all classes of closed loop problems.

Closed loop problems in biomechanics. Part I--a classification system.

Biomechanics researchers have relied heavily on the inverse dynamics approach for calculating the forces and torques at human joints. However, implicit in this approach is the assumption that there are sufficient independent equations of motion to uniquely determine these unknown kinetics. There exists a class of problems, commonly referred to as closed loop problems, when there are insufficient equations and indeterminacy arises. The purposes of the present paper are (1) to develop a general classification system of closed loop problems for whole body movements; and (2) to identify the minimum number of force transducing devices necessary to uniquely determine joint kinetics for these problems. The classification system is based on the human subject's interaction with his environment and with himself. Two criteria are considered: first, the number of the subject's extremities in contact with fixed external reference systems, and second, the number of closed loops formed by those extremities not in contact with fixed external systems. Different combinations of these two criteria are examined and grouped into five cases according to the degree to which the equations of motion are over-determined, determined, or under-determined. Examples are given to illustrate the concepts. It is felt that the use of this system should aid in the understanding of joint force and torque calculations, especially with regard to the under-determined cases.

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.

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.

Medial and anterior-posterior ligament stability of the human knee, measured with a stress apparatus.

The five ligaments studied act with a symphonic harmony to provide stability to the knee. The SMCL was of major importance in medial knee stability. The other ligament which provided the most dramatic contribution to knee stability was the PC. It was the only ligament which when sectioned resulted in a significant posterior anterior drawer instability and on three occasions produced a jerk test.

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.

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.

55 Nitinol wire: force developed as a function of "elastic memory".

Closing spaces is done either by translation of the edgewise brackets over an archwire or by the use of closing loops of some common design. This investigation suggests the concept of the further refinement of the "wire rubber band" as a means of closing spaces. Advantages of such a wire hypothetically would be to level the dentition, align the dentition, and condense spaces in the dentition with only one or two stretched nickel titanium wires having the proper temperature transition range (TTR). The temperature of the mouth would make such wires return to their original prestretched length. A correctly-sized wire would have sufficient stiffness at mouth temperature, and it would be kept at or above its TTR. The system eliminates friction from edgewise bracket translation and also the use of many auxiliary closing devices as well as reducing the number of archwire changes, thus saving chairside time.