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Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 235 records · Page 13Linked to original sources
PubMed1990

Glenohumeral muscle force and moment mechanics in a position of shoulder instability.

The three-dimensional orientation of the shoulder girdle musculature was studied in five cadaver shoulders in the position of function at 90 degrees of abduction and 90 degrees of external rotation using a method of computer assisted gross muscle cross-section analysis. The muscle volume, muscle fiber length, and physiological cross-sectional area were obtained by dissecting two specimens. The line of action, the magnitude and orientation of the moment were calculated for each muscle crossing the shoulder joint. The quantitative description of the moment potential of muscle forces influencing shoulder function was thus obtained. The most effective flexors of the shoulder which also appear to resist anterior dislocation in the position studied are the pectoral, the short head of the biceps, coracobrachialis, anterior deltoid, and the subscapularis. Most of the rotator cuff muscles and the posterior deltoid acted as adductors, while the anterior deltoid, long and short head of the biceps, and supraspinatus were abductors. In this position, external rotation was effected by the long head of the biceps, coracobrachialis, and the posterior deltoid, while the majority of the remaining muscles acted as internal rotators.

Aged↗
PubMed1990

Structural consequences of transcortical holes in long bones loaded in torsion.

Finite element models were used to predict the structural consequences of transcortical holes through long bones loaded in torsion. Several parameters were investigated including hole size, anelastic behavior of the bone, cortical wall thickness, cortical wall symmetry, curvature along the bone's long axis and the axial length of the defect. Finite element model predictions of percent intact bone strength were compared to experimental data for sheep femora with transcortical drill holes loaded to failure in torsion. Hole size was expressed as hole diameter divided by the outer bone diameter. Linear finite element model predictions were in conservative agreement with the experimental data for large hole sizes. A transcortical hole with a diameter 50% of the outer bone diameter reduced the torsional strength by 60%. However, the linear models predict a 40% drop in strength for small holes whereas in vitro data suggest that small holes have no significant effect on strength. Models which represent non-linear anelastic behavior in bone overpredicted torsional strengths. Asymmetric cortical wall thickness and long bone bowing have minor effects, while the length of an elongated defect strongly influences the torsional strength. Strength reductions are greatest for bones with thin cortical walls.

Animals↗
PubMed1990

Mechanical properties of human pulleys.

In order to determine the mechanical properties of the fibro-osseous pulleys in the hand, the diaphyseal annular pulleys, the volar plate annular pulleys and the cruciate or condensable portions were tested. A custom-made loading device provided proper fit of the soft tissues for a uniform distribution of the pulley load during testing. The A2 pulley was found to be the strongest of the pulleys; the A1 and A4 were the next strongest. The A3 pulley was nearly equal in mean breaking strength to the other annular pulleys, but in absolute breaking load was considerably weaker because of its shortness. The A4 was the least compliant of the pulleys. We concluded that the fibro-osseous A2 and A4 were mechanically stronger and stiffer pulleys than the A1, A3, A5 (volar plate) pulleys. In testing one type of pulley reconstruction, we found that the "belt loop" technique of Karev nearly matched the annular pulleys in strength and energy absorption.

Biomechanical Phenomena↗
PubMed1990

Intraarticular pressure and capacity of the elbow.

The compliance, capacity, and the position of minimum intraarticular pressure were measured in 13 thawed, fresh-frozen human elbows. The capacity of the joint capsule was 23 +/- 4 ml. The intraarticular pressure was the lowest at 80 degrees of flexion. Capsular rupture occurred at relatively low intraarticular pressures--80 +/- 42 mm Hg. Knowledge of the capacity of the normal elbow joint combined with the fact that this joint capsule tends to rupture or permit extravasation of fluid into the periarticular soft tissues should be considered when infusing fluids during arthroscopy. Finally, the "resting position" of 80 degrees of flexion minimizes capsular tension and therefore might contribute to the development of joint contracture associated with prolonged immobilization in this position. This would be consistent with the observation that patients with posttraumatic elbow stiffness have an average arc of flexion of 60-90 degrees.

Elbow Joint↗
PubMed1990

A biplanar cephalometric stereoradiography technique.

A biplanar cephalometric stereoradiography (BCSR) technique was developed for accurate three-dimensional assessment of structures that can be identified by markers or anatomical landmarks that are visible on both lateral closed and posteroanterior cephalometric radiographs. The accuracy and precision of the technique were determined by means of a phantom and clinical radiographs. On the phantom, three-dimensional coordinates were determined by the BCSR technique and were measured directly with an electronic digital caliper. The accuracy of the BCSR technique was found to be within 0.5% of the measured distances. On clinical radiographs, the lengths of plates and screws, used as rigid fixation devices, were measured on two subsequent sets of biplanar radiographs and were found to be within the accuracy of our current digitizer (+/- 0.381 mm). The stability of interosseous wires was tested against implants and other interosseous wires on two subsequent sets of biplanar radiographs through a comparison of the distances between two devices. These comparisons confirmed the stability of interosseous wires. The BCSR technique proved to be an accurate method for measurements in three dimensions.

Cephalometry↗
PubMed1990

Glenohumeral elevation studied in three dimensions.

We studied the position and rotational changes associated with elevation of the glenohumeral joint, using a three-dimensional magnetic-field tracking system on nine fresh cadaveric shoulders. The plane of maximal arm elevation was shown to occur 23 degrees anterior to the plane of the scapula. Elevation in any plane anterior to the scapula required external humeral rotation, and maximal elevation was associated with approximately 35 degrees of external humeral rotation. Conversely, internal rotation was necessary for increased elevation posterior to the plane of the scapula. The observed effects of this rotation were to clear the humeral tuberosity from abutting beneath the acromion and to relax the inferior capsular ligamentous constraints. Measurement of the obligatory humeral rotation required for maximal elevation helps to explain the relationship of the limited elevation seen in adhesive capsulitis and after operations which limit external rotation.

Biomechanical Phenomena↗
PubMed1990

Analysis of upper-extremity performance in athletes and musicians.

Injuries can result from direct or indirect trauma and overuse in sports and the performing arts. These injuries occur when the objective exceeds the physiologic tolerance. Biomechanics analysis enables the estimation of the capacities of the body as well as the loading environment encountered by the tendons, muscles, bones, and joints during various types of sports and musical activities.

Biomechanical Phenomena↗
PubMed1990

Stabilizing mechanism of the glenohumeral ligaments.

By using the electromagnetic tracking system, the kinematics of the glenohumeral joint in the shoulder complex was studied. With the location of the glenohumeral ligament insertions digitized, the change of ligament length and direction could then be calculated throughout a given movement. This technique provided a useful method for in vitro assessment of the capsuloligamentous constraints of the shoulder joint.

Biomechanical Phenomena↗
PubMed1990

Kinematic and kinetic analysis of push-up exercise.

The purpose of this study was to experimentally measure and analytically determine the load across the wrist, elbow, and shoulder joints during push-ups to better understand the nature of this exercise. A piezoelectric force platform was used to measure the vertical and two shear forces as well as the moment and the location of the center of pressure on the hand during a push-up. The electromagnetic tracking system was utilized to associate the force and moment measurement on the hand to the joints of the upper limbs. Factors which affect the intersegmental loads on the joints during push-ups include the location of the palm relative to the shoulder joint, the plane of arm movement, and the relative foot positions. In addition, the speed of push-ups also affects the amount of inertial load on top of the base static load.

Arm↗
PubMed1989

Effects of a scaphoid waist osteotomy on carpal kinematics.

The effects of a scaphoid osteotomy on the kinematics of the carpal bones were determined in five cadaveric wrist specimens. Minute radiographic markers were inserted into the distal radius and selected carpal bones through limited arthrotomies between the intercarpal ligaments. Simultaneous biplanar radiographs were obtained in neutral and the extreme wrist positions of extension, flexion, radial deviation, and ulnar deviation, both before and after a scaphoid waist osteotomy. The positions of each of the carpal markers and their corresponding carpal bones were digitized for each wrist position , and a computer-assisted motion analysis was performed for each specimen before and after transverse scaphoid waist osteotomy. Following the osteotomy, there was a tendency for the scaphoid osteotomy to collapse into a dorsally angulated or "humpback collapse" deformity during each extreme wrist position. There was also multiplanar osteotomy site motion as well as complex collapse deformities of the midcarpal joint associated with loss of the mechanical tie-rod function of the scaphoid. These findings reveal the importance of the scaphoid in maintaining normal kinematics and the inherent instability of these fractures with loss of scaphoid integrity.

Carpal Bones↗
PubMed1989

Transverse stability of the carpus. An analytical study.

The stabilizing structures of the transverse carpal arch were studied utilizing an analytical model based on a rigid body spring model theory. This method was used to calculate the relative motion between carpal bones, the distribution of compressive forces in the intercarpal joints, and the tensions in the ligaments under simulated dorsopalmar compression. The contribution of each ligament against the effect of compression was determined by removing ligaments from the model. A multivariate analysis of variance disclosed that sectioning the flexor retinaculum alone does not significantly modify the distribution of forces in ligaments and joints (p = 0.33), and decreases dorsopalmar carpal stiffness by only 7.8%. In contrast, isolated removal of the palmar hamate-capitate ligament causes a pronounced weakening of the carpal structure, from an average of 232 to 131 N/mm (p less than 0.01). If the flexor retinaculum is removed in addition to releasing one palmar intercarpal ligament, a gross instability of the carpal arch is created.

Biomechanical Phenomena↗
PubMed1989

Incorporation of muscle architecture into the muscle length-tension relationship.

A mathematical model of the muscle active length-tension relationship has been developed. It integrates the functional basis of different muscle arrangements into a mathematical description of the contractile element. The model is complex enough to represent many of the mechanical and architectural properties of active muscle. Yet, it is simple enough that only two parameters (muscle fiber optimal length, muscle belly optimal length) are needed to scale the model to a specific actuator.

Elastic Tissue↗
PubMed1989

Physiological considerations of muscle force through the elbow joint.

An analytical model for the determination of muscle forces across the elbow joint during isometric loading conditions has been developed. The model incorporates the muscle length-tension relationship, while considering the muscle architecture. Sensitivity analyses were performed to study the effects of the geometric and architectural factors of the muscles on the distribution of muscle forces.

Biomechanical Phenomena↗
PubMed1989

Biomechanical analysis of finger flexor pulley reconstruction.

Fifty cadaver digits were used to study the mechanical properties of five different methods of pulley reconstruction and the effectiveness of three different pulley reconstructive arrangements in restoring a normal relationship between tendon excursion and joint motion. All reconstructed pulleys showed less stiffness and more displacement before failure than normal intact pulleys. Although reconstruction using a length of another tendon woven through the remaining fibrous rim of the pulley and both double and triple tendon graft loops around bone absorbed more energy to failure than a normal pulley, only the triple loop around bone could withstand as much load before failure as a normal pulley. No reconstruction restored a normal tendon excursion/joint motion relationship, but reconstruction of the A2 and A4 pulleys restored a more normal relationship than either the "belt loop" reconstruction or a combination belt loop, A2 and A4 reconstruction.

Biomechanical Phenomena↗
PubMed1989

An anatomic and mechanical study of the interosseous membrane of the forearm: pathomechanics of proximal migration of the radius.

The interosseous membrane of the forearm of 12 fresh cadaver specimens was studied anatomically and mechanically to better understand its role in stabilization of the radius after radial head excision. A central band of ligamentous tissue, approximately twice the thickness of the membrane on either side was identified in all specimens. Mechanical studies determined the relative contribution to longitudinal stiffness of the forearm. The central band was responsible for 71% of the longitudinal stiffness of the interosseous membrane after radial head excision. The contribution of the triangular fibrocartilage complex was 8%. Silicone radial head implants were much less stiff than the intact interosseous membrane. Injury to the central band of the interosseous membrane may be crucial to the development of proximal migration of the radius after radial head excision.

Biomechanical Phenomena↗
PubMed1989

Stability of the transverse carpal arch: an experimental study.

The mechanical characteristics of the transverse carpal arch were studied using fresh-frozen human cadaveric wrists. Tensile properties of the ligaments involved in this structure were also analyzed. The flexor retinaculum did not prove to be a major factor in the maintenance of the carpal arch since its division only reduced the global transverse carpal arch stiffness an average of 7.5%. On the contrary, the transverse intercarpal ligaments connecting the bones of the distal carpal row were shown to have an essential role in providing stability to the carpal tunnel.

Biomechanical Phenomena↗