Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 163 records · Page 9Linked to original sources

PubMed1996

Calibration of measured center of pressure of a new stairway design for kinetic analysis of stair climbing.

A stairway that allows the collection of kinetic data is essential for biomechanical studies on stair climbing. There is a need to validate the measured center of pressure (COP) on the surface of a stair in order to verify the accuracy of the calculation of joint kinetics. The purpose of this study was to validate a new stairway design for kinetic analysis of stair climbing through a calibration and error analysis of the COP obtained from this system. The new stairway design allows the collection of kinetic data for multiple steps without any constraint to foot placement. Known vertical forces were applied to known locations on the surface of each stair and each force plate. Multiple regression analyses were conducted to determine the distribution pattern of the error in the measured COP. It was found that the error in the COP was a function of location on the stair or force plate. The magnitude of the vertical force had no significant effect on the error in the measured COP. The distribution pattern of the error in the measured COP on the force plates used in this study matched the results in the literature. A healthy female subject was used as a subject in a stair climbing test. The error in the measured COP had a significant effect on the calculated joint resultant moments, especially the abduction-adduction and internal-external rotation moment. The correction of these errors should make the kinetic calculation in stair climbing more accurate.

Adult↗

PubMed1995

Method for the measurement of friction between tendon and pulley.

An experimental system was developed that allows direct measurement of friction at the tendon-pulley interface, and the results were interpreted by use of a theoretical model for friction of a cable around a fixed pulley. Validation experiments were conducted with a nylon cable around a nylon rod. One end of the cable was connected to an actuator via a load cell, and the other end was connected to a 4.9 N load via a similar load cell. The cable was passed around the nylon rod and then pulled toward the actuator. Tests were performed at five different arcs of contact. The friction forces, as measured by the difference between two load transducers, were compared with those determined for a theoretical model and were used for calculation of the friction coefficient. The measurement system then was used to study the friction force between the flexor digitorum profundus tendon and the A2 pulley on nine fresh frozen index digits. The method allows us to measure the direct interaction between the tendon and pulley and could be used to evaluate and compare procedures for tendon-pulley and pulley repair and reconstruction, as well as for the study of tendon-pulley friction in various pathological conditions.

Fingers↗

PubMed1995

Effects of freeze/thaw conditioning on the tensile properties and failure mode of bone-muscle-bone units: a biomechanical and histological study in dogs.

Eight pairs of canine supraspinatus bone-muscle-bone units were mechanically tested to failure in tension. One side was tested immediately post mortem, and the other side was tested after exposure to a standard freeze/thaw process (-60 degrees C). The failure site was analyzed histologically. Fresh specimens had greater values for ultimate strength (p < 0.001), stiffness (p < 0.001), and energy to failure (p < 0.001). All specimens failed in the muscle close to the musculotendinous junction. The length of muscles subjected to the freezing process was reduced (9.3%). In addition, the load-displacement curves for the fresh and frozen specimens showed marked differences in shape. The loss of tensile strength in muscle tissue is due to damage of the intracellular contractile elements caused by postmortem autolysis; this type of damage is increased as a result of the freeze/thaw process. The freeze/thaw process significantly altered the tensile properties of normal muscle tissue, no matter how carefully it was done. One cannot expect to receive representative data if muscle is frozen and thawed.

Animals↗

PubMed1995

Tensile properties of the supraspinatus tendon.

The tensile properties of the supraspinatus tendon were investigated in 11 shoulders from fresh cadavers. The tendon was divided into three longitudinal strips: anterior, middle, and posterior. Each specimen was mounted on a materials testing machine, with four fluorescent markers placed on both surfaces of the tendon strip. The positions of these markers were recorded during the test by two synchronized video cameras. Load-deformation and strain curves were determined, and the stress-strain curve, strength, and modulus of elasticity were calculated. The posterior strip was thinner in cross section than the others (p = 0.0355). The ultimate load and ultimate stress were significantly greater in the anterior strip (16.5 +/- 7.1 MPa) than in the middle (6.0 +/- 2.6 MPa) and posterior (4.1 +/- 1.3 MPa) strips (p < 0.0001). The modulus of elasticity also was significantly greater in the anterior strip (p < 0.0001), but there was no significant difference between the superficial and deep surfaces. It is concluded that the anterior portion of the supraspinatus tendon is mechanically stronger than the other portions, and it seems to perform the main functional role of the tendon.

Aged↗

PubMed1995

Force and pressure transmission through the normal wrist. A theoretical two-dimensional study in the posteroanterior plane.

Force transmission through the wrist in the normal population was investigated using the rigid body spring modeling (RBSM) technique (assuming carpal bones are rigid bodies interposed by series of springs simulating articulating cartilage and constraining ligaments). One-hundred and twenty normal wrist posteroanterior X-rays of adults (evenly divided to represent both genders and two age groups) provided the anatomical data. Reaction forces between the carpal bones were modeled using a system of compression linear springs, representing cartilage and subchondral bone, and of tensile linear springs, representing ligaments. The spring constants were determined based on the material properties of wrist cartilage and ligaments. Assumed axial loads were applied along the metacarpals to simulate a grasp strength of 10 N with active stabilization of the wrist in neutral position. The force transmission ratio at the radio-ulno-carpal joint was 55% through the radio-scaphoid and 35% through the radio-lunate joints. The remaining 10% of the load was passing through the triangular fibrocartilage with minor differences between genders. Among the intercarpal joints, a large percentage of the load of the wrist was transmitted to the scaphoid. The peak pressure was highest at the proximal pole of the radio-scaphoid, with a radio-scaphoid versus radio-lunate peak pressure ratio of 1.6. The most important ligaments in terms of load transmission were those opposing ulnar translation of the carpus. The wrist morphology had little influence on the magnitude and pattern of load distribution. There was no effect of age on wrist force distribution.

Adult↗

PubMed1995

A comparison of intersegmental joint dynamics to isokinetic dynamometer measurements.

This study quantified the errors associated with measurements obtained using an isokinetic dynamometer for knee evaluation at 60 degrees and 180 degrees s-1. Five normal subjects were tested. A triaxial electrogoniometer was used to measure the kinematics. A custom-designed load cell was used to measure the three orthogonal components of the reaction force applied by the isokinetic dynamometer to the leg. The inverse dynamics problem was solved to obtain the intersegmental dynamics at the knee joint. These data were compared to those obtained from the isokinetic dynamometer. The results indicate that the knee motion recorded by the isokinetic dynamometer was in error by 7-9 degrees during flexion and 10-13 degrees during extension. The isokinetic dynamometer recorded knee flexions which were less than actual during the flexion portion of the exercise and greater than actual during extension. The duration of constant velocity was limited based on the speed selected. The knee moment was in error by 5 Nm during flexion and 25-29 Nm during extension. The use of a gravity correction factor reduced the knee moment error during extension, but increased it during flexion.

Biomechanical Phenomena↗

PubMed1995

Flexor tendon-pulley interaction after tendon repair. A biomechanical study.

Ten normal ring fingers from ten donors were used to determine the effect of flexor tendon repair on the gliding resistance between the tendon and the A2 pulley. Gliding resistance was measured for the intact FDP tendon and for the same tendon after it was cut transversely and repaired with a 4/0 Ticron core suture and a 6/0 running epitendinous nylon suture. After repair, the gliding pattern of the tendon through the A2 pulley changed significantly. The resistance and the friction coefficient were approximately doubled (P < 0.005).

Biomechanical Phenomena↗

PubMed1995

Externally applied forces to the palm increase carpal tunnel pressure.

Change in carpal tunnel pressures that result from externally applied forces to the palm of the hand were assessed in five cadaveric specimens. MIKRO-TIP transducers were percutaneously placed into the carpal tunnel at the level of the hook of the hamate. A 1 kg force was applied to the palm of the hand in 16 separate locations. Significant elevations in carpal tunnel pressure were observed for external forces applied over the flexor retinaculum (103 mm Hg) and also for the hypothenar (37 mm Hg) and thenar (75 mm Hg) areas adjacent to the distal aspect of the carpal tunnel. These data demonstrate that the application of external forces on the palm of cadaver hands increases carpal tunnel pressure and the magnitude of the pressure change in the carpal tunnel depends on the location of the applied force.

Analysis of Variance↗

PubMed1995

Effect of lumbrical muscle incursion within the carpal tunnel on carpal tunnel pressure: a cadaveric study.

Lumbrical muscle incursion within the carpal tunnel has been implicated as a possible cause of carpal tunnel syndrome. During finger flexion, surgeons have observed the presence of lumbrical muscles in the carpal tunnel. However, the significance of this incursion has not been evaluated. To evaluate the effect of lumbrical muscle incursion within the carpal tunnel as a cause of carpal tunnel syndrome, carpal canal pressures were measured in cadaver hands at the level of the hamate hook for four finger positions: (1) 100% finger flexion; (2) 75% finger flexion; (3) 50% finger flexion; and (4) full extension. After measuring carpal tunnel pressures for each position, the lumbrical muscles were excised and the pressures were again recorded. A progressive increase in carpal tunnel pressure was noted for each degree of finger flexion in the group with intact lumbricals. This is in sharp contrast to a relatively stable carpal tunnel pressure during finger flexion for the group without lumbrical muscles. Two-way repeated measures analysis of variance revealed a significant difference in carpal tunnel pressure for both variables, lumbrical muscles and finger position. One-way repeated measures analysis of variance for carpal tunnel pressures demonstrated that the effect of finger position was significant for the group with intact lumbricals but not for the group with lumbricals removed. We conclude that lumbrical muscle incursion into the carpal tunnel can result in elevation of carpal tunnel pressure in cadaver hands and could be a variable in the cause of work-related carpal tunnel syndrome.

Analysis of Variance↗

PubMed1995

Pressure dynamics of the carpal tunnel and flexor compartment of the forearm.

Although carpal tunnel pressures have been observed to increase as a result of repetitive flexion and extension of the wrist, and forearm compartment pressures have been shown to rise during and after muscle activity, the relationship between those two observations has not been studied. The flexor compartments of five cadavers were perfused with saline to determine whether elevated pressure in the flexor compartment of the forearm is transmitted to the carpal tunnel. The pressure in the carpal tunnel after the infusion was significantly different from the pressure in the flexor compartment of the forearm. Furthermore, pressures recorded in the carpal tunnel at the conclusion of the study were not statistically different from the preinfusion pressures. While the carpal tunnel may appear to be an open compartment anatomically, it functions as a relatively closed compartment with respect to transfer of pressure from the flexor compartment of the forearm under conditions that mimic elevated tissue pressure.

Carpal Tunnel Syndrome↗

PubMed1995

Rotational stability of the carpus relative to the forearm.

To perform rotational tasks adequately, the rotational laxity between the radius and the carpus must be constrained within a certain limit. The contribution of nine individual capsuloligamentous structures to the rotational stability of the radiocarpal joint was studied using 14 fresh-frozen human cadaveric specimens. Torque-rotation curves, with sequential section of the soft-tissue structures, were used to calculate the percentage contribution of each individual structure. The primary pronation constraint was the palmar radioscaphocapitate ligament. The contributions to supination constraint were more complex; the dorsal radiotriquetral ligament was dominant, assisted by the palmar ulnolunate ligament. Structures originating from the ulna changed their major constraint contribution with forearm orientation, whereas those with a radial origin had a constant contribution independent of forearm rotation. Injury of these structures may lead to rotational instability at the radiocarpal level and should be considered when treating carpal instabilities.

Adult↗

PubMed1995

Loose-hinge total elbow arthroplasty. An experimental study of the effects of implant alignment on three-dimensional elbow kinematics.

A previous study suggested that the kinematics of a loose-hinge total elbow arthroplasty (TEA) are those of a truly semiconstrained joint. This study addresses the effects of malposition of the implant. The three-dimensional elbow kinematics during simulated active motion were studied in six cadaver specimens using an electromagnetic tracking device. In addition to simulated active elbow flexion, flexion arcs were obtained under an elbow varus or valgus moment, to calculate the structural varus-valgus laxities. The results after four different Coondrad-Morrey TEA positions of implantation were compared with those of the intact elbow. The flexion-extension amplitudes were not significantly decreased after TEA implantation, except with external rotation of the ulnar component, which resulted in a loss of extension. In the intact elbow and after TEA implantation in any position, the mean varus-valgus deviations throughout elbow flexion were in a narrower range than the structural limits imposed by the ligaments (intact elbow) or the TEA hinge design. With internal malrotation of the humeral component over 10 degrees, however, the valgus structural limit was reached and, conversely, the varus limit with external rotation over 10 degrees. The clinical improvement observed with the semiconstrained TEA is derived from the benefits of the less constrained articulation. The proximodistal changes of TEA implantation have no consequence on the kinematic pattern. Rotational malpositioning of either humeral or ulnar component should be avoided, the first because it changes the kinematic pattern toward the structural limits of the implant and, therefore, may lead to excessive stresses at the bone-cement-implant interfaces and to early loosening, and the latter because it causes loss of extension.

Biomechanical Phenomena↗

PubMed1995

Kinematics of the normal arch of the foot and ankle under physiologic loading.

We studied 15 cadaver feet to determine three-dimensional motion of selected tarsal bones under axial loading at three different loading levels. We determined the motion of individual joints and also the rotation of the tarsal bones in relation to the tibia. Joint rotations increased consistently with higher loads. The naviculartalar joint had the greatest total screw axis rotation, which averaged 9.4 degrees +/- 2.2 degrees at 667 N of load, followed by the first metatarsal-navicular (mean, 7.2 degrees +/- 1.5 degrees), talartibial (mean, 5.2 degrees +/- 1.6 degrees), and calcaneal-talar (mean, 4.4 degrees +/- 1.7 degrees) joints. The observed changes indicate the need for assessment of foot and ankle alignment clinically and radiologically while the patient is weightbearing.

Aged↗

PubMed1995

Effect of femoral offset on range of motion and abductor muscle strength after total hip arthroplasty.

At a minimum of one year after operation, we studied 64 patients with 86 total hip arthroplasties (THA) by standard anteroposterior hip and pelvic radiographs and measurement of range of motion and of isometric abduction strength. The femoral offset correlated positively with the range of abduction (p = 0.046). Abduction strength correlated positively with both femoral offset (p = 0.0001) and the length of the abductor lever arm (p = 0.005). Using multiple regression, abduction strength correlated with height (p = 0.017), gender (p = 0.0005), range of flexion (p = 0.047) and the abductor lever arm (p = 0.060). Our findings suggest that greater femoral offset after THA allows both an increased range of abduction and greater abductor strength.

Adult↗

PubMed1995

Morphology of the torn rotator cuff.

The morphological characteristics of shoulders with torn rotator cuffs were determined using 41 embalmed specimens. The following parameters were measured in the supraspinatus (SSP), infraspinatus (ISP) and subscapularis (SSC) muscles: the length, thickness and width of the extramuscular tendon; the length of the intramuscular tendon; the length and width of a tear, if present, muscle fibre length; and muscle volume. The cross-sectional area (CSA) of the tendon was measured on the photographic image of slices of the tendon using an image analysis system, and the CSA of the muscle was calculated by dividing the muscle volume by muscle fibre length. The rotator cuff was intact in 11 shoulders. A partial-thickness tear of the cuff was present in 12 shoulders, a full-thickness tear of the SSP in 11 shoulders, and a full-thickness tear of more than 2 tendons in 7. Overall incidence of full-thickness tears of the rotator cuff was 44%, and that of partial-thickness tears 29%. With increase of tear size, the functional tendon length (extramuscular tendon length plus tear length) increased by a statistically significant amount in the SSP, ISP and SSC, whereas muscle fibre length decreased in SSP and ISP. It is concluded that the increased functional tendon length and decreased muscle fibre length are the main morphological changes that make the rotator cuff a physiologically abnormal unit. Surgical repair of the torn cuff would be expected to improve these anatomical changes and restore the kinetics of the glenohumeral joint.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1995

Late versus early repair of Achilles tendon rupture. Clinical and biomechanical evaluation.

Eleven patients who had late reconstruction for Achilles tendon rupture were compared with 10 patients who had immediate repair. The followup period averaged 8 years for both groups. Results, based on a clinical score, were successful (excellent or good) for all but 1 patient. Although manual testing demonstrated normal plantar flexion strength in all but 1 patient, significant differences were seen in isometric and isokinetic plantar flexion strength of the involved sides as compared with the uninvolved sides of these patients. The patient with the unsuccessful result had abnormalities in vertical, foreaft, and medial-lateral force components of the ground reaction force. Three-dimensional motion analysis showed decreased total motion in the sagittal plane on the operated side as compared with the unoperated side in this patient. The data indicated that patients with late reconstruction of Achilles tendon rupture have successful clinical results comparable with those of early repair.

Achilles Tendon↗

PubMed1994

Kinematics of the normal trapeziometacarpal joint.

Motion of the trapeziometacarpal joint was studied in 12 hands from fresh human cadavera. By use of a magnetic tracking system, a full range of motion of the first metacarpal was analyzed with respect to a defined trapezial coordinate system. The traces of the reference points on the head and base of the first metacarpal were monitored, and the instantaneous centers of rotation were calculated. During circumduction, the reference points on the head and base followed elliptical paths but in opposite directions. The average instantaneous center of circumduction was at approximately the center of the trapezial joint surface. In flexion-extension, the axis of rotation was located within the trapezium, and the path of the head was identical to the path of the base. In abduction-adduction, the axis of rotation was located distal to the trapezium within the base of the first metacarpal, and the base and head moved in opposite directions. There was no single center of rotation; rather, instantaneous motion occurred reciprocally between these centers of rotation within the trapezium and metacarpal base in the normal thumb. This changing instantaneous center of rotation results in a unique pattern of motion which is related to congruent, tightly constrained joint surfaces of two reciprocal saddle joints and to precisely positioned extraarticular ligaments.

Humans↗

PubMed1994

Kinematics of the trapeziometacarpal joint after sectioning of ligaments.

This study was designed to examine the roles of ligaments in the maintenance of the articular kinematics of the trapeziometacarpal joint. Circumduction of the trapeziometacarpal joint was studied in 12 hands from fresh human cadavera. With use of a magnetic tracking system, changes in the motion of the base of the first metacarpal after ligament sectioning were analyzed and compared with those of the normal joint. Two sets of ligaments were sectioned: (a) the anterior oblique and ulnar collateral ligaments and (b) the first intermetacarpal ligament and the ulnar joint capsule. Sectioning of the anterior oblique and ulnar collateral ligaments resulted in a significant dorsal-ulnar shift in the path of the base of the first metacarpal. However, sectioning of the first intermetacarpal ligament did not affect the movement pattern of the center of the base. The anterior oblique and ulnar collateral ligaments provided constraint of the trapeziometacarpal joint during circumduction of the thumb.

Humans↗