Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 217 records · Page 12Linked to original sources

PubMed1992

Compensatory motion in the upper extremity after elbow arthrodesis.

Ten healthy male subjects were asked to complete a series of tasks that represent normal elbow function. They were then fitted with a custom adjustable brace that simulated elbow arthrodesis at 50 degrees, 70 degrees, 90 degrees, and 110 degrees flexion and asked to repeat the tasks. The 3 Space Isotrak system was used to measure shoulder motion; a triaxial wrist goniometer was used to measure wrist compensation; and all subjects were videotaped to qualitatively observe other compensatory motion. Unlike other joints, elbow arthrodesis at any angle results in a significant impairment, since the adjacent shoulder and wrist joints cannot compensate to allow completion of activities.

Activities of Daily Living↗

PubMed1992

Functional anatomy and biomechanics of the thumb.

The thumb is a mechanical unit consisting of strong ligaments and dynamic muscles, providing the resistance to the fingers and palm during pinch and grip. Each thumb joint has a mechanical equivalent that helps explain elements of thumb stability. The trapeziometacarpal joint is potentially the most unstable but has adapted to its unique position by special joint geometry and, in particular, a combination of support ligaments that permit a wide range of motion yet stability. New anatomic and mechanical studies demonstrate the key support structures that must be duplicated by reconstructive surgical procedures if thumb stability is to be maintained.

Biomechanical Phenomena↗

PubMed1992

Elbow subluxation and dislocation. A spectrum of instability.

After sequential releases of the ligaments and capsules of 13 fresh autopsy specimen elbows, external rotation and valgus moments with axial forces resulted in posterior dislocations in 12 of the 13 with the anterior medical collateral ligament (AMCL) intact. Kinematic displacements measured with a three-dimensional electromagnetic tracking device showed that dislocation involved posterolateral rotation of 34 degrees-50 degrees and 5 degrees-23 degrees valgus at about 80 degrees flexion. Dislocation is the final of three sequential stages of elbow instability resulting from posterolateral rotation, with soft-tissue disruption progressing from lateral to medial. In each stage, the pathoanatomy correlated with the pattern and degree of instability. Testing for valgus stability of the elbow during simulated active flexion revealed no significant increase (-0.3 degrees-2.4 degrees) in valgus laxity after reduction compared with the intact specimens (p greater than 0.05, beta = 0.1, delta = 2.5 degrees). In no case did the digitized AMCL origin-to-insertion distance increase beyond normal during the dislocation (p less than 0.01). The mechanism of dislocation during a fall on the outstretched hand would involve the body "rotating internally" on the elbow, which experiences an external rotation/valgus moment as it flexes. Posterior dislocations should therefore be reduced in supination. If valgus stability in pronation is demonstrated, the AMCL can be assumed to be intact, and rehabilitation in a hinged cast-brace with the elbow in full pronation can be commenced immediately.

Autopsy↗

PubMed1992

Intersegmental elbow joint load during pushup.

Intersegmental loading pattern on the elbow joint during a push-up exercise was investigated. Electromagnetic motion sensors and a piezoelectric force plate were used to simultaneously record upper extremity motion and forces on nine healthy male subjects during push-ups in six different hand positions. Peak axial forces exerted on the elbow joint averaged 45 percent of the body weight. Peak torque to produce elbow flexion was 2305.9 N-cm, or 56 percent of maximal isometric extensor torque. The results of this analysis give insight to the biomechanics of a normal elbow and to its load carrying capacity.

Adult↗

PubMed1991

Three-dimensional kinematics of glenohumeral elevation.

To help resolve longstanding uncertainties about kinematics of the shoulder, we studied three-dimensional glenohumeral joint motion during arm elevation. A magnetic tracking system was used to monitor the three-dimensional orientation of the humerus with respect to the scapula. Appropriate coordinate transformations were then performed for the calculation of glenohumeral joint rotation based on the defined Eulerian angle. The effects of the plane of elevation and the humeral rotation on the magnitude of arm elevation were documented. The maximum humeral elevation at the glenohumeral joint took place in a plane anterior to the scapular plane. Maximum elevation in all planes anterior to the scapular plane required external axial rotation of the humerus. Conversely, internal axial rotation was necessary for maximum elevation posterior to the scapular plane. Quantifying the obligatory axial rotation explains the relationship of internal and external rotation with maximum elevation.

Biomechanical Phenomena↗

PubMed1991

Correlation of physiological cross-sectional areas of muscle and tendon.

Muscle physiological cross-sectional area, as defined and measured by dividing the volume of the muscle by its fibre length, is proportional to the maximum strength of the muscle. It is one of the important parameters when considering muscle mechanics in sports science and, clinically in tendon transfer procedures. This study reports that tendon cross-sectional area correlated well with the physiological cross-sectional area of associated muscles.

Adult↗

PubMed1991

Physiological prediction of muscle forces--II. Application to isokinetic exercise.

The successful application of a physiological model of the musculoskeletal system capable of accounting for nonequilibrium dynamic loading and predicting individual muscle forces in the knee is presented. The model incorporates rigid-body mechanics and musculoskeletal physiology. Unknown muscle and joint contact forces outnumber the equilibrium equations resulting in an indeterminant problem. Mathematical optimization is utilized to resolve the indeterminacy. The model is used to estimate individual muscle forces during isokinetic exercise. Five subjects were tested at speeds of 60 degrees/s and 180 degrees/s. A newly proposed optimal criterion, minimizing muscular activation, results in muscle force predictions which have significantly higher correlations with myoelectric activity than other linear and nonlinear optimal criteria. The results demonstrate that properly constrained linear programming methods do not limit the number of active muscles and allow for uniform recruitment of the active muscles.

Adult↗

PubMed1991

Functional ranges of motion of the wrist joint.

We have examined 40 normal subjects (20 men and 20 women) to determine the ideal range of motion required to perform activities of daily living. The amount of wrist flexion and extension, as well as radial and ulnar deviation, was measured simultaneously by means of a biaxial wrist electrogoniometer. The entire battery of evaluated tasks could be achieved with 60 degrees of extension, 54 degrees of flexion, 40 degrees of ulnar deviation, and 17 degrees of radial deviation, which reflects the maximum wrist motion required for daily activities. The majority of the hand placement and range of motion tasks that were studied in this project could be accomplished with 70 percent of the maximal range of wrist motion. This converts to 40 degrees each of wrist flexion and extension, and 40 degrees of combined radial-ulnar deviation. This study provides normal standards for the functional range of motion of the wrist.

Activities of Daily Living↗

PubMed1991

The distal radioulnar ligaments: a biomechanical study.

The mechanical roles of the triangular fibrocartilage have been examined in three experiments. Kinematic analysis by a stereophotogrammetric method revealed that the palmar radioulnar ligament was taut in supination and that the dorsal radioulnar ligament was taut in pronation. In full pronation, the palmar radioulnar ligament decreased to an average of 71% of its length in tension. In full supination, the dorsal radioulnar ligament decreased to an average of 90% of its length. Mechanical testing of the triangular fibrocartilage under axial load disclosed a significant laxity (mean: 10.4 mm), which was decreased in pronation. Transverse loading tests demonstrated that the triangular fibrocartilage is less stiff in neutral forearm rotation. Study of the material properties of the palmar and dorsal parts of the triangular fibrocartilage showed these structures to be strong ligaments with material properties similar to those of the radiocarpal ligaments.

Biomechanical Phenomena↗

PubMed1991

Extensor mechanism of the fingers. I. A quantitative geometric study.

A close-range stereophotogrammetric measurement system was used to determine the three-dimensional geometric characteristics of the extensor assembly in seven human finger specimens and five finger configurations. The numerical data obtained showed that, although changes in length of the different bundles are small, their spatial orientation varies considerably from one to another position. This information should help to improve the accuracy of models derived to understand the extensor assembly behavior in normal and pathological conditions.

Fingers↗

PubMed1991

Extensor mechanism of the fingers. II. Tensile properties of components.

Seven fresh human finger specimens have been studied to determine the differences in structural stiffness between different components of the extensor assembly. Differences were found to be significant, ranging from an average of 275 N/mm for the proximal and distal segments of the central band to an average of 40 N/mm for the central-to-lateral intercrossing fascicles. The terminal tendon of the lateral band was shown to be as stiff as the middle segment of the central band.

Fingers↗

PubMed1991

A kinematic study of luno-triquetral dissociations.

An analysis of carpal motion after sectioning the ligamentous support of the luno-triquetral joints was done by use of stereoradiographic methods. The ligaments were sectioned in two stages. In stage I, a complete sectioning of both the dorsal and palmar luno-triquetral ligaments and the interosseous membrane was done. Stage II consisted of further sectioning of both the dorsal radio-triquetral and dorsal scapho-triquetral ligaments. After both stage I and stage II ligament sectioning, all of the intercarpal joints exhibited altered kinematics. The changes were especially marked at the luno-triquetral joint where motion was increased in all planes of wrist motion. The essential lesion in producing a static palmar flexed intercalated segment instability was division of the dorsal radio-triquetral and dorsal scapho-triquetral ligaments in association with the luno-triquetral ligaments and interosseous membrane sectioning.

Cadaver↗

PubMed1991

Kinetic chain exercise in knee rehabilitation.

Rehabilitation is recognised as a critical component in the treatment of the anterior cruciate ligament (ACL) injured athlete, and has been the subject of intense research over the past decade. As a result, sound scientific principles have been applied to this realm of sports medicine, and have improved the outcome of both surgical and nonsurgical treatment. Possibly the most intriguing of these principles is the use of the kinetic chain concept in exercise prescription following ACL reconstruction. The hip, knee, and ankle joints when taken together, comprise the lower extremity kinetic chain. Kinetic chain exercises like the squat recruit all 3 links in unison while exercises such as seated quadriceps extensions isolate one link of the chain. Biomechanical assessment with force diagrams reveals that ACL strain is reduced during kinetic chain exercise by virtue of the axial orientation of the applied load and muscular co-contraction. Additionally, kinetic chain exercise through recruitment of all hip, knee, and ankle extensors in synchrony takes advantage of specificity of training principles. More importantly, however, it is the only way to reproduce the concurrent shift of 'antagonistic' biarticular muscle groups that occurs during simultaneous hip, knee, and ankle extension. Incoordination of the concurrent shift fostered by exercising each muscle group in isolation may ultimately hamper complete recovery. Modifying present day leg press and isokinetic equipment will allow clinicians to make better use of kinetic chain exercise and allow safe isokinetic testing of the ACL reconstructed knee. Reconstruction of the ACL with a strong well placed graft to restore joint kinematics, followed by scientifically sound rehabilitation to improve dynamic control of tibial translation, will improve the outcome after ACL injury.

Anterior Cruciate Ligament Injuries↗

PubMed1991

The injured upper extremity and the JAMAR five-handle position grip test.

Niebuhr and Marion (Am J Phys Med Rehab 1990;69:96-101) recently presented a study that utilized healthy subjects who were able to control the amount of force exerted during submaximal grip strength efforts. Stokes (J Occup Med 1983;25:683-684) proposed that a true weakness of grip can be distinguished in the injured upper extremity from a feigned effort that yields a flat horizontal type of curve. The purpose of this study was to evaluate the five-handle position JAMAR grip test in an injured population and compare the curves produced with a group of healthy subjects. We found that the patients with well-documented pathology produced a curve that was similar in shape to the healthy group; however, the curve on the injured extremity was reduced in force output.

Adult↗

PubMed1991

Biomechanical study of ligaments around the elbow joint.

The ligamentous contribution to elbow joint stability is a product of morphology and biologic parameters of each of the collateral ligaments. Better understanding of these characteristics is of paramount importance for successful ligament reconstruction in the surgery for joint replacement and traumatic injury. Two experiments were performed. In the first, the arc of elbow flexion where the individual ligament was either taut or slack was measured; in the second, the structural properties of each collateral ligament were determined by using bone-ligament-bone preparations. The anterior medial collateral ligament (AMCL) and radial collateral ligament (RCL) were taut throughout most of the entire arc of flexion. The posterior medial collateral ligament (PMCL) was taut only when the elbow was in a flexed position. Among the collateral ligaments, the AMCL was the strongest and stiffest with an average failure load of 260 N. The palmaris longus tendon, the most frequently used graft for elbow ligament reconstruction, was similar in strength (357 N).

Biomechanical Phenomena↗

PubMed1991

Valgus stability of the elbow. A definition of primary and secondary constraints.

The stabilizing structures of the elbow that resist valgus stress were studied with a tracking device in a model simulating active motion and muscle activity. By varying the order of serial release of the medial collateral ligament complex and removal of the radial head, each structure's contribution to valgus stability against the effect of gravity was determined. In the otherwise intact elbow, absence of the radial head does not significantly alter the three-dimensional characteristics of motion in the elbow joint. Isolated medial collateral release, on the other hand, causes increases in abduction rotation of about 6 degrees-8 degrees in magnitude. Releasing both structures results in gross abduction laxity and elbow subluxation. This study defines the medial collateral ligament (MCL) as the primary constraint of the elbow joint to valgus stress and the radial head as a secondary constraint. This definition facilitates the proper management of patients with radial head fractures and MCL disruption. The comminuted radial head fracture uncomplicated by MCL insufficiency should be treated by excision without the need for an implant and without concern of altering the normal kinematics of the elbow.

Biomechanical Phenomena↗

PubMed1991

Measurement of joint kinematics using ExpertVision system.

Three-dimensional kinematic calculations based on the output from a video-based passive marker detection system was developed. Three-dimensional position data of the markers placed on the limb were obtained with the system and then run through a program that calculated absolute and relative joint kinematics based on Eulerian angle and screw axis description. In this study, the accuracy and limitation of the system for kinematic analysis were examined.

Artificial Intelligence↗

PubMed1990

Torsional strength reduction due to cortical defects in bone.

This study correlated torsional strength reduction with circular defect size in cortical bone, to define the "stress riser" and "open-section" effect of the defects. The experimental model was developed and verified. Circular defects from 10 to 60% of bone diameter were then created in paired sheep femora and the bones loaded to failure. Contrary to theory, this experimental study suggests that small defects (10%) of bone diameter cause no significant torsional strength reduction. A 20% defect caused a 34% decrease in strength, representing the "stress riser" dimension. Defects between 20 and 60% of bone diameter decreased strength linearly as a function of defect size, and thus no discrete "open section" dimension was identified. For circular defects, we were unable to demonstrate a discrete "open-section" effect at which dramatic strength reduction is observed. These data may prove to be helpful when planning surgery that involves placing defects in bone such as for infection, biopsy, and prosthesis removal. The accepted guideline to avoid defects of greater than 50% of the bone diameter may be too great. Our data reveal this 62% reduction in torque strength and 88% energy to failure exist with a 50% circular defect.

Animals↗