Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 19 recordsLinked to original sources

PubMed1999

Chimpanzee thumb muscle cross sections, moment arms and potential torques, and comparisons with humans.

This study investigates the morphological basis of differences between humans and chimpanzees in the kinematical and dynamical parameters of the musculature of the thumb. It is partly intended to test an hypothesis that human thumb muscles can exert significantly greater torques, due to larger muscle cross-sectional areas or to longer tendon moment arms or to both. We focus on the estimation of the potentials of thumb muscles to exert torques about joint axes in a sample of eight chimpanzee cadaver hands. The potential torque of a muscle is estimated by taking the product of a muscle's physiological cross-sectional area (an estimator of force) with its dynamical moment arm (derived from the slope of tendon excursion versus joint angular displacement, obtained during passive movements of cadaver thumb joints). Comparison of our results with similar data obtained for humans at the same Mayo Clinic laboratory shows significant differences between humans and chimpanzees in potential torque of most thumb muscles, those of humans generally exhibiting larger values. The primary reason for the larger torques in humans is that their average moment arms are significantly longer, permitting greater torque for a given muscle size. An additional finding is that chimpanzees and humans differ in the direction of secondary thumb metacarpal movements elicited by contraction of some muscles, as shown by differences in moment arm signs for a given movement in the same muscle. The differences appear to be related to differences in the musculo-skeletal structures of the trapeziometacarpal joint.

Animals↗

PubMed1999

Periosteum responds to dynamic fluid pressure by proliferating in vitro.

Periosteum provides a source of undifferentiated chondrocyte precursor cells for fracture healing that can also be used for cartilage repair. The quantity of cartilage that can be produced, which is a determining factor in fracture healing and cartilage repair, is related to the number of available stem cells in the cambium layer. Cartilage formation during both of these processes is enhanced by motion of the fracture or joint in which periosteum has been transplanted. The effect of dynamic fluid pressure on cell proliferation in periosteal tissue cultures was determined in 452 explants from 60 immature (2-month-old) New Zealand White rabbits. The explants were cultured in agarose suspension for 1-14 days. One group was subjected to cyclic hydrostatic pressure, which is referred to as dynamic fluid pressure, at 13 kPa and a frequency of 0.3 Hz. Control explants were cultured in similar chambers without application of pressure. DNA synthesis ([3H]thymidine uptake) and total DNA were measured. The temporal pattern and distribution of cell proliferation in periosteum were evaluated with autoradiography and immunostaining with proliferating cell nuclear antigen. Dynamic fluid pressure increased proliferation of periosteal cells significantly, as indicated by a significant increase in [3H]thymidine uptake at all time points and a higher amount of total DNA compared with control values. On day 3, when DNA synthesis reached a peak in periosteal explants, [3H]thymidine uptake was 97,000+/-5,700 dpm/microg DNA in the group exposed to dynamic fluid pressure and 46,000+/-6,000 dpm/microg in the controls (p < 0.001). Aphidicolin, which blocks DNA polymerase alpha, inhibited [3H]thymidine uptake in a dose-dependent manner in the group subjected to dynamic fluid pressure as well as in the positive control (treated with 10 ng/ml of transforming growth factor-beta1) and negative control (no added growth factors) groups, confirming that [3H]thymidine measurements represent proliferation and dynamic fluid pressure stimulates DNA synthesis. Total DNA was also significantly higher in the group exposed to dynamic fluid pressure (5,700+/-720 ng/mg wet weight) than in the controls (3,700+/-630) on day 3 (p < 0.01). Autoradiographs with [3H]thymidine revealed that one or two cell cycles of proliferation took place in the fibrous layer prior to proliferation in the cambium layer (where chondrocyte precursors reside). Proliferating cell nuclear antigen immunophotomicrographs confirmed the increased proliferative activity due to dynamic fluid pressure. These findings suggest either a paracrine signaling mechanism between the cells in these two layers of the periosteum or recruitment/migration of proliferating cells from the fibrous to the cambium layer. On the basis of the data presented in this study, we postulate that cells in the fibrous layer respond initially to mechanical stimulation by releasing growth factors that induce undifferentiated cells in the cambium layer to divide and differentiate into chondrocytes. These data indicate that cell proliferation in the early stages of chondrogenesis is stimulated by mechanical factors. These findings are important because they provide a possible explanation for the increase in cartilage repair tissue seen in joints subjected to continuous passive motion. The model of in vitro periosteal chondrogenesis under dynamic fluid pressure is valuable for studying the mechanisms by which mechanical factors might be involved in the formation of cartilage in the early fracture callus and during cartilage repair.

Aging↗

PubMed1999

Normative values of agonist-antagonist shoulder strength ratios of adults aged 20 to 78 years.

OBJECTIVE: To determine normative values for isometric flexion/extension, abduction/adduction, and external/internal rotation strength ratios about the shoulder and to determine if these ratios are affected by age or gender. STUDY DESIGN: A cross-sectional study of 120 healthy volunteers (60 men, 60 women) aged 20 to 78 years. SETTING: Orthopedic research laboratory. METHODS: Flexion and extension strengths were measured isometrically using a Cybex II dynamometer at arm flexion angles of 30 degrees, 60 degrees, and 90 degrees. Abduction and adduction strengths were measured at 30 degrees, 60 degrees, and 90 degrees abduction. Internal and external rotation strengths were measured (1) with the arm abducted 15 degrees and neutral external/internal rotation and (2) with the arm abducted 90 degrees and externally rotated 30 degrees above the transverse plane. OUTCOME MEASURES: Isometric strength ratios for flexion/extension, abduction/adduction, and external/internal rotation. RESULTS: No statistically significant differences in agonist/antagonist strength ratios were found between dominant and nondominant sides or between genders. Age was associated with changes in strength ratios for measurements taken with the arm flexed or abducted 90 degrees. Posture was found to affect strength ratios. CONCLUSIONS: These data can serve as a normative reference for clinical use.

Adult↗

PubMed1999

The effects of wrist distraction on carpal kinematics.

Changes in carpal kinematics under wrist distraction were studied in fresh cadaveric specimens. A magnetic tracking device measured kinematic motions of the scaphoid, lunate, and third metacarpal relative to the fixed radius in 3 planes of passive motion (coronal, sagittal, and "dart throwers") under progressive distraction loads. The change in percent contribution of the radiocarpal and midcarpal joints was calculated. Radiocarpal motion during extension was decreased as increasing traction was applied, but it increased with flexion. Motion of the scaphoid relative to the lunate was smaller in the oblique plane, resulting in less radiocarpal motion than in the sagittal plane. In the coronal plane, traction had little effect on radial deviation, but ulnar angulation of the scaphoid was greater with ulnar deviation of the wrist. These results suggest that different degrees of tension exist in the palmar and dorsal ligaments with the wrist under traction and during different planes of wrist motion. If wrist motion is desired during fixed traction, such as used clinically with external fixation, the dart-throwers motion (wrist extension with radial deviation and wrist flexion with ulnar deviation) appears to have the least impact on radiocarpal motion. If greater radiocarpal motion is desired, however, such as during postoperative mobilization, flexion-extension and radioulnar deviation will create more radiocarpal motion than the dart-thrower's motion.

Biomechanical Phenomena↗

PubMed1999

Optimum length of muscle contraction.

OBJECTIVE: The purpose of this study was to develop a mathematical method to determine optimum muscle length and muscle stress based on the measurable physiological and biomechanical data. DESIGN: The values of optimum muscle length and muscle stress are investigated. BACKGROUND: Understanding the characteristics of muscle function in vivo is important for assisting the design of the tendon transfer and other rehabilitation procedures. In vivo determination of the physiological and anatomical parameters of muscle contraction is difficult but not impossible. Optimum muscle length and muscle stresses are important parameters for understanding muscle function. METHODS: A Cybex dynamometer was used to measure isometric elbow flexion torque in eight different joint positions in seven subjects. Then the optimization method was used to determine optimum muscle length and muscle stress of three major elbow flexors, the biceps brachii, the brachialis, and the brachioradialis based on the model and joint torque data. RESULTS: The calculated muscle stress for each subject was on average 109 N/cm(2), while the optimum muscle length for the biceps brachii, the brachialis, and the brachioradialis was on average 14.05, 6.53, 17.24 cm, respectively. The joint angles corresponding to these optimum muscle lengths are 110 degrees, 100 degrees and 50 degrees of elbow flexion, respectively. CONCLUSIONS: Optimum muscle length and muscle stress can be properly predicted using an analytical mathematical model along with an experimentally measured joint torque. RELEVANCE: The estimate of optimum muscle length is important for muscle modeling and tendon transfer surgery by taking advantage of length-tension relationship of individual muscles.

Adult↗

PubMed1999

Identification of optimal strategies for increasing whole arm strength using Karush-Kuhn-Tucker multipliers.

OBJECTIVE: The purpose of this study was to develop a computer model for identifying muscles critical to improving functional upper extremity strength. DESIGN: A three-dimensional biomechanical model of the upper extremity was developed, and the predictions were compared to maximal arm strength data collected from healthy volunteers. BACKGROUND: Although several optimization-based mathematical models of the shoulder have been developed, none have utilized the mathematical properties of the Karush-Kuhn-Tucker multipliers to efficiently estimate the effect of strengthening individual muscles on functional strength of the whole arm. METHODS: A static three-dimensional biomechanical model of the glenohumeral, radio-humeral, ulno-humeral and wrist joints was developed for predicting maximal hand exertion forces. The model was formulated as a linear program. Constraints consisted of moment equilibrium conditions and limits on maximum and minimum allowable muscle forces. Predicted arm strengths were compared to maximal pull strength measurements made on 10 subjects (5 male; 5 female). The task involved pulling toward the mid-sagittal plane of the body with the arm flexed 45 degrees. The Karush-Kuhn-Tucker variables associated with the maximal limits on muscle force were computed to estimate the effect of altering the strength of individual muscles on functional arm strength. RESULTS: Maximum pull strengths were predicted well by the model. Karush-Kuhn-Tucker values ranged from 0 (for muscles not at their upper force limits) to 0.11 for the flexor carpi radialis and pectoralis major muscles. Karush-Kuhn-Tucker multipliers were found to be insensitive to the assumed specific tension of muscle. CONCLUSIONS: Upper extremity strength can be predicted from musculoskeletal geometry and physiology using linear programming. RELEVANCE: Karush-Kuhn-Tucker multipliers associated with the muscle force upper limits give insight into the effect of strengthening individual muscles on whole arm exertion strength. Such an analysis may provide insight into the development of optimal rehabilitation protocols.

Adult↗

PubMed1999

Biomechanical analysis of the trapeziometacarpal joint after surface replacement arthroplasty.

A biomechanical analysis of the trapeziometacarpal joint was performed in 7 fresh-frozen normal human cadaveric hands to compare the kinematics of the trapeziometacarpal joint before and after surface total joint replacement. Using a 3-space magnetic Isotrak system (Polhemus, Colchester, VT), which provides a 3-dimensional analysis of motion of joints as well as translation, we found that kinematics and stability of the trapeziometacarpal joint could be duplicated by joint surface replacement arthroplasty provided that normal ligament tensions were present.

Arthroplasty, Replacement↗

PubMed1999

An anatomic study of the stabilizing ligaments of the trapezium and trapeziometacarpal joint.

We provide a detailed and comprehensive anatomic description of the ligaments stabilizing the trapezium and trapeziometacarpal joint. Sixteen ligaments were identified. Fourteen ligaments inserted onto the trapezium and 2 others attached independently to the thumb metacarpal. The ligaments inserting onto the trapezium were the superficial anterior oblique, deep anterior oblique (beak ligament), dorsoradial, posterior oblique, ulnar collateral, dorsal trapezio-trapezoid, volar trapezio-trapezoid, dorsal trapezio-second metacarpal, volar trapezio-second metacarpal, trapezio-third metacarpal, volar scaphotrapezial, radial scaphotrapezial, transverse carpal, and trapezio-capitate ligaments. The remaining 2 ligaments attach onto the thumb metacarpal and are the proper intermetacarpal and the dorsal intermetacarpal. The dorsoradial and deep anterior oblique ligaments play a substantial role in stabilizing the trapeziometacarpal joint, and the deep anterior oblique ligament may function as a pivot for the first metacarpal during palmar abduction to allow rotation (pronation). The dorsal trapezio-second metacarpal, volar trapezio-second metacarpal, and trapezio-third metacarpal ligaments function as tension bands and are required to prevent instability from cantilever bending forces on the trapezium.

Aged↗

PubMed1999

Constraint and material properties of the subregions of the scapholunate interosseous ligament.

The material and constraint properties of the dorsal, proximal, and palmar regions of the scapholunate ligament were studied using isolated bone-ligament-bone preparations from 24 adult intact cadaver wrists. Determinations of constraint to differential rotation and translation as well as failure strength were made using a servohydraulic testing machine incorporating an additional rotatory actuator. The dorsal region of the scapholunate ligament offered the greatest constraint to differential translation, while both the dorsal and palmar regions demonstrated statistically significant combined constraints to differential rotation between the scaphoid and lunate. The greatest yield strength was found in the dorsal region (260.3 N +/- 118.1 N), followed by the palmar region (117.9 N +/- 21.3 N) and the proximal region (62.7 N +/- 32.2 N).

Adult↗

PubMed1999

Flexor tendon-tendon sheath interaction after tendon grafting: a biomechanical study in a human model in vitro.

A human cadaver tendon sheath model was used to study the differences in excursion resistance of tendons that might be considered as sources of clinical tendon grafts. The flexor digitorum profundus and superficialis tendons, the extensor indicis proprius tendon used in its normal proximal-distal orientation, the extensor indicis proprius tendon used in a reversed distal-proximal orientation, and the palmaris longus tendon were studied in 7 fingers. The intrasynovial tendons (the flexor digitorum profundus and superficialis tendons and the reversed extensor indicis proprius tendon) produced less excursion resistance (p < .05) than the extrasynovial tendons (the normally oriented extensor indicis proprius tendon and the palmaris longus tendon). In contrast to studies measuring resistance against a single pulley, resistance within a complete tendon sheath may be affected by contact with other structures, particularly in joint extension.

Aged↗

PubMed1999

The static rotator cuff does not affect inferior translation of the humerus at the glenohumeral joint.

BACKGROUND: The static contribution of the rotator cuff to the inferior stability of the shoulder is poorly understood. The purpose of this study was to determine the effect of static rotator cuff muscles on the inferior stability of the glenohumeral joint. METHODS: The humeral head positions relative to the glenoid were obtained in 12 shoulder specimens under the following conditions: with and without a 1.5-kg load; with the humerus adducted and abducted 90 degrees; and in three stages of dissection: (1) before release of any of the rotator cuff muscles, (2) after release of the supraspinatus or the cuff muscles other than the supraspinatus, and (3) after release of all of the cuff muscles. The order of release was changed in two ways: release of the supraspinatus followed by the release of other muscles in one group, and the opposite order in the other group. RESULTS: In both adduction and abduction, there were no significant differences in the positions of the humeral head either among the three stages of release or between the two different orders of release. CONCLUSION: The static contribution of the cuff muscles to the inferior stability of the shoulder is insignificant.

Biomechanical Phenomena↗

PubMed1999

Biomechanical analysis of prophylactic fixation for middle third humeral impending pathologic fractures.

For determination of the most biomechanically desirable construction for prophylactic fixation of impending central 1/3 humeral fractures, 24 matched pairs of fresh frozen skeletonized human cadaveric humeri were divided randomly into four groups. Group 1 compared intact humeri with matched humeri that had a 50% hemicylindrical cortical central 1/3 defect to show reproducible failure at the defect with significant reduction in strength. Groups 2 through 4 compared prophylactic fixation of the defect combined with cementation and dynamic compression plating, Rush rodding, or locked intramedullary nailing. Each specimen was tested in external rotation torsion to failure by fracture. In Group 1, test specimens with defects failed with significantly lower rotation to failure, peak torque, stiffness, and total energy absorbed to failure. In Groups 2 through 4, intramedullary nailing provided statistically significantly better total energy absorbed to failure and stiffness than did dynamic compression plating. The proximally and distally locked intramedullary nail seems to have biomechanical advantages in the prophylactic stabilization of an impending pathologic fracture of the central 1/3 of the humerus. These biomechanical findings must be considered in light of the clinical context when a means of fixation is selected.

Analysis of Variance↗

PubMed1999

Biomechanical evaluation of a proximal tibial opening-wedge osteotomy plate.

This biomechanical study evaluated the static response of a new opening-wedge osteotomy plate to compression and torsion loads in a human cadaver model. This plate incorporates a metal block that distracts the medial tibial cortices to ensure precise correction and prevent bone collapse. The 15-mm plate was inserted into 23 fresh cadaver specimens using a standard surgical technique. Axial loading of 13 specimens (compression) and external rotation loading of 10 specimens (torsion) was performed using a servohydraulic-testing machine. Compression loading resulted in failure at a mean of 1810 N due to bone collapse, fracture, or translation. Torsional loading resulted in failure at a mean of 10 Nm due to fracture of the lateral tibial cortex in all specimens. The ratio of the experimental failure load to the calculated estimate of the knee joint forces during gait were 1.07 in axial compression and 0.925 in torsion. This opening-wedge osteotomy plate construct appears marginally strong enough to withstand the estimated axial load on the proximal tibia during gait. Estimated torsional load on the knee during level walking slightly exceeds the failure load prior to osteotomy healing. This information can be used to guide further experimental protocols for static and dynamic testing of this device to determine the appropriate rehabilitation guidelines following opening-wedge proximal tibial osteotomy.

Aged↗

PubMed1999

Reoperation for failed prosthetic replacement used for limb salvage.

Patients with segmental bone and joint replacement prostheses because of tumors increasingly need revision surgery because of their long term survival. Between 1970 and 1990, 208 custom prosthetic replacements were performed for limb salvage in patients with tumors. Reoperations were required in 52 patients. The mean time to reoperation was 37 months. The reoperation procedures included 35 prosthetic revisions, 11 amputations, four arthrodeses, one vascularized fibular graft, and one open reduction and internal fixation of a fracture with supplemental bone graft. Functional assessment using the new Musculoskeletal Tumor Society scoring system was available for the 36 living patients, and their mean rating was 63% (18.9) at 12 years' mean followup. Of the 35 patients who received a new prosthesis, 12 (33%) patients needed a third operation at mean followup of 68 months. The probability of prosthetic survival in the group of 35 patients needing revision to the same or another prosthesis was 79% at 5 years and 65% at 10 years. The chance and frequency of needing reoperation increased as patients survived longer. Reoperations for tumor recurrence or infection usually resulted in amputation. Reoperation for failed initial segmental bone and joint prosthetic replacement is feasible and effective and can be done without jeopardizing subsequent patient and implant survival or without significantly affecting functional results compared with the values before reoperation.

Adolescent↗

PubMed1998

EMG study of hand muscle recruitment during hard hammer percussion manufacture of Oldowan tools.

The activity of 17 hand muscles was monitored by electromyography (EMG) in three subjects during hard hammer percussion manufacture of Oldowan tools. Two of the subjects were archaeologists experienced in the replication of prehistoric stone tools. Simultaneous videotapes recorded grips associated with the muscle activities. The purpose of the study was to identify the muscles most likely to have been strongly and repeatedly recruited by early hominids during stone tool-making. This information is fundamental to the identification of skeletal features that may reliably predict tool-making capabilities in early hominids. The muscles most frequently recruited at high force levels for strong precision pinch grips required to control the hammerstone and core are the intrinsic muscles of the fifth finger and the thumb/index finger regions. A productive search for skeletal evidence of habitual Oldowan tool-making behavior will therefore be in the regions of the hand stressed by these intrinsic muscles and in the joint configurations affecting the relative lengths of their moment arms.

Animals↗

PubMed1998

A theoretical model to predict distribution of the fabric tensor and apparent density in cancellous bone.

The adaptation of cancellous bone to mechanical forces is well recognized. Theoretical models for predicting cancellous bone architecture have been developed and have mainly focused on the distribution of trabecular mass or the apparent density. The purpose of this study was to develop a theoretical model which can simultaneously predict the distribution of trabecular orthotropy/orientation, as represented by the fabric tensor, along with apparent density. Two sets of equations were derived under the assumption that cancellous bone is a biological self-optimizing material which tends to minimize strain energy. The first set of equations provide the relationship between the fabric tensor and stress tensor, and have been verified to be consistent with Wolff's law of trabecular architecture, that is, the principal directions of the fabric tensor coincide with the principal stress trajectories. The second set of equations yield the apparent density from the stress tensor, which was shown to be identical to those obtained based on local optimization with strain energy density of true bone tissue as the objective function. These two sets of equations, together with elasticity field equations, provide a complete mathematical formulation for the adaptation of cancellous bone.

Bone Density↗

PubMed1998

Comparison of two methods for computing abduction moment arms of the rotator cuff.

Biomechanical models of the shoulder mechanism require estimates of muscle moment arm magnitude. Some shoulder models have estimated muscle moment arms by assuming an idealized minimum distance path from the origin to insertion that passes around the bony geometry. Alternatively, the principle of virtual work can be used to estimate moment arms from tendon excursion and joint-angle data. The purpose of this study was to determine if these two methods give different estimates of abduction moment arms for the supraspinatus, infraspinatus, and subscapularis muscles. Muscle moment arms were estimated for these muscles on ten fresh frozen cadaver specimens. The results showed a significant difference between the two estimation methods. Average differences were 3.1 mm (10.6%), 3.9 mm (43.9%), and 7.2 mm (70.3%) for the supraspinatus, subscapularis, and infraspinatus muscles, respectively. These results suggest that shoulder models based on the origin-insertion method may give higher rotator cuff muscle force estimates than methods using the slope of the tendon excursion vs joint angle relationship.

Adult↗

PubMed1998

Mechanical advantage of the thumb muscles.

The purpose of this study was to measure the moment arms of four extrinsic muscles (flexor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus) and four intrinsic muscles (flexor pollicis brevis, abductor pollicis brevis, adductor pollicis, and opponents pollicis) of the thumb at the interphalangeal, the metacarpophalangeal, and the carpometacarpal joints in the same cadaver specimens and to examine the specific role of each muscle. Measurements were made on seven fresh frozen cadaver hands. The moment arms were measured during flexion/extension of the interphalangeal joint, flexion/extension and adduction/abduction of the metacarpophalangeal joint, and flexion/extension and adduction/abduction of the carpometacarpal joint. Moment arms were computed using the slope of the tendon excursion joint angle relationship. The specific function of each muscle was determined by multiplying the measured moment arms by the maximum force that each muscle can generate. It was found that the flexor pollicis longus was a pure flexor while flexor pollicis brevis was an adductor as well as a flexor, the extensor pollicis longus was an extensor and an adductor, extensor pollicis brevis was an extensor and a mild abductor, the abductor pollicis longus was an extensor as well as an abductor, the abductor pollicis brevis was mainly an abductor, the adductor pollicis was a major flexor as well as an adductor, and the opponents pollicis was a flexor and an abductor.

Aged↗