Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 109 records · Page 6Linked to original sources

PubMed1998

An instrumented wheel for kinetic analysis of wheelchair propulsion.

An instrumented wheel system for three-dimensional kinetic analysis of upper extremity during wheelchair propulsion has been designed and validated. This system allows the direct measurements of three-dimensional dynamic forces and moments on the handrim during wheelchair propulsion in a laboratory setting as well as in the field. Static loading tests showed a high linearity and little drift (coefficient of determination, r2 > 0.999). Under dynamic loading, the instrumented wheel provided the well-matched measurement forces and moments with the predicted values from the inverse dynamic method using video-based kinematic data (correlation coefficient, p > 0.97). The three-dimensional handrim forces and moments during wheelchair propulsion by a non-disabled subject were demonstrated.

Biomechanical Phenomena↗

PubMed1998

Reconstruction operations for acquired flatfoot: biomechanical evaluation.

A major limitation of operations commonly performed for acquired flatfoot is inadequate correction of alignment. The authors defined the efficacy of two operations, deltoid ligament reconstruction and flexor digitorum longus tendon transfer, for treatment of posterior tibial tendon dysfunction with flatfoot deformity. Twelve fresh-frozen foot specimens were used. A flatfoot deformity was created, and, to simulate the midstance phase of gait, loads were applied axially to the plantar surface of the foot and to appropriate tendons. Foot position improved substantially after deltoid ligament reconstruction but not after flexor digitorum longus tendon transfer. The average increase in arch height after deltoid ligament reconstruction was 10.3 +/- 8.9 mm and after flexor digitorum longus tendon transfer, -0.6 +/- 2.0 mm. Mean arch height after deltoid ligament reconstruction was 2.2 +/- 1.7 mm less than intact arch height and, after flexor digitorum longus tendon transfer, 13.2 +/- 9.0 mm less than intact arch height. Improvement in metatarsal-talar, calcaneal-talar, and talar-tibial positions was significantly greater after deltoid ligament reconstruction than after flexor digitorum longus tendon transfer. Although the authors do not advocate clinical use, the deltoid ligament reconstruction was more effective than flexor digitorum longus tendon transfer in restoring arch alignment in flatfoot.

Adult↗

PubMed1998

Three-dimensional analysis of flatfoot deformity: cadaver study.

Eleven fresh-frozen cadaver foot specimens were tested to define changes in tarsal alignment associated with flatfoot, or pes planus, a common clinical problem. The three-dimensional position of four bones (talus, calcaneus, navicular, and first metatarsal) relative to the fixed tibia was determined with a magnetic tracking system in the intact foot and flatfoot conditions. In the flatfoot, the average metatarsal-to-talar position difference was 11.7 degrees +/-4.4 degrees in abduction (P < 0.0001), 10.4 degrees +/-3.6 degrees in dorsiflexion (P < 0.0001), and 10.9 degrees +/-6.0 degrees in eversion (P < 0.0001) compared with the intact foot. The average calcaneal-to-talar position difference was 2.2 degrees +/-2.6 degrees in abduction (P=0.0171) and 2.7 degrees+/-2.0 degrees in eversion (P=0.0012) compared with the intact foot. The average navicular-to-talar position difference was 13.6 degrees +/-5.0 degrees in abduction (P < 0.0001), 10.5 degrees +/-6.6 degrees in dorsiflexion (P=0.0004), and 8.1 degrees +/-3.8 degrees in eversion (P < 0.0001) compared with normal. The average talar-to-tibial position difference was -8.2 degrees +/-3.2 degrees in dorsiflexion (P < 0.001) compared with the intact foot. The average arch height difference was 6.0+/-2.7 mm (P < 0.0001) less than the normal condition. The deformity associated with flatfoot is complex and occurs in multiple joints and in all three planes. An understanding of the normal and pathologic (flatfoot) conditions is necessary to surgically restore appropriate alignment and function in hindfoot reconstruction operations.

Adult↗

PubMed1998

Contracture of the deltoid muscle. Results of distal release.

We prospectively studied the results of distal release, performed between February 1989 and December 1994 for the treatment of a contracture of the deltoid muscle, in forty patients (forty-nine shoulders). Forty-seven contractures (in thirty-eight patients) developed after multiple intramuscular injections of various medications. The two remaining contractures (in two patients) were congenital. The average age at the onset of the symptoms was thirty-two years (range, birth to fifty-eight years). The primary symptoms included pain around the neck and the shoulder girdle, dimpling of the skin, a palpable fibrous band, winging of the scapula, difficulty in combing the hair or reaching the contralateral side of the body for grooming, and inability to bring the arm adjacent to the body. The average age at the time of the operation was thirty-nine years (range, fifteen to sixty-three years). The average duration of follow-up was three years and eleven months (range, two years to six years and six months). After the distal release of the contracture, but on the same day, the patients started a physical-therapy program. Postoperatively, the pain, dimpling of the skin, palpable fibrous band, and winging of the scapula resolved in forty-eight shoulders (thirty-nine patients). Six patients (six shoulders) no longer had difficulty in combing the hair or adducting the shoulder. There were no infections or neuromuscular complications. Forty-seven (96 per cent) of the forty-nine shoulders (thirty-eight of the forty patients) had a good clinical result, and two shoulders (two patients) had a poor result. Anterosuperior subluxation of the humeral head, noted on preoperative radiographs of twenty-three shoulders (eighteen patients), was not present postoperatively. Drooping of the acromion, seen in six patients (six shoulders) in whom the contracture had developed before they were sixteen years old, improved postoperatively in five shoulders (five patients). Rotation of the scapula, seen in five shoulders (five patients), resolved after release of the contracture in all five. There were no clinical or radiographic signs of osteoarthrosis due to long-term anterior translation of the shoulder joint in the four patients (six shoulders) who had had the contracture for at least twenty years (average, twenty-three years; maximum, twenty-seven years).

Adolescent↗

PubMed1998

Reconstruction of the flexor pulley. The effect of the tension and source of the graft in an in vitro dog model.

Flexor pulleys in the hindpaw digits of twenty-eight adult mixed-breed dogs were reconstructed in order to investigate the influence, on the reconstruction, of the source of the autogenous tissue (intrasynovial compared with extrasynovial tendon) and the tension applied during the repair. The ipsilateral peroneus longus tendon was used to reconstruct the A2 pulley with an around-the-bone technique in twenty-one digits; the graft was sutured at a tension of 0.49, 0.98, and 1.96 newtons in seven digits each. The flexor digitorum profundus tendon of an adjacent digit was used to reconstruct the A2 pulley, at a tension of 0.98 newton, in seven additional digits. The contralateral digits were used as controls for all twenty-eight treated digits. The digits were tested in a custom apparatus designed to measure the frictional force generated between the reconstructed pulley and the tendon beneath it. The frictional force did not differ significantly (p > 0.5) among the three groups repaired with peroneus longus tendon; however, the average value was more than five times that produced in the contralateral, control digits. The average frictional forces created by the flexor digitorum profundus grafts were similar to those in the contralateral, control digits. Reconstruction with the flexor digitorum profundus at a tension of 0.98 newton produced significantly less frictional force (p < 0.05) than that produced by the peroneus longus graft at the same tension. This in vitro model of reconstruction of the A2 pulley demonstrated that tendon from an intrasynovial source (the flexor digitorum profundus) produced less frictional resistance to gliding of the tendon than did tendon from an extrasynovial source (the peroneus longus). This result is consistent with previously published findings that intrasynovial tendons may make better grafts than extrasynovial tendons for the reconstruction of gliding flexor tendons because of decreased friction and better healing qualities. Intrasynovial tendons may also make better grafts for the reconstruction of flexor pulleys.

Animals↗

PubMed1998

Biomechanical effect of medial advancement of the supraspinatus tendon. A study in cadavera.

During the repair of some rotator-cuff tears, the torn tendon cannot be freed up adequately to permit reattachment at its original anatomical site of insertion. An option is to advance the site of insertion medially and reattach the tendon to a trough in the sulcus or to the humeral head. The biomechanical effects of such medial advancement on the moment arm of the supraspinatus muscle during glenohumeral elevation were studied in ten fresh-frozen shoulders from cadavera. Medial advancement of the site of insertion of the supraspinatus tendon was simulated by the placement of suture anchors in the sulcus of the proximal part of the humerus at points three, ten, and seventeen millimeters medial to the junction of the supraspinatus tendon and the bone. These distances were chosen not because they represent clinical options but because the large range allowed biomechanical study of medial advancement. Nylon lines were attached to the suture anchors and were passed back through an eyehook at the midpoint of the supraspinatus muscle. The excursion of each line was measured as the humerus was elevated, and the moment arm was estimated from the joint angle and excursion data with use of the principle of virtual work. Three and ten millimeters of medial advancement of the tendon (attachment in the sulcus) had a minimum (non-significant) effect on the moment arm during elevation compared with the value determined for the intact condition. However, seventeen millimeters of medial advancement was found to reduce the moment arm significantly (p < 0.05).

Adult↗

PubMed1998

Superior-inferior stability of the shoulder: role of the coracohumeral ligament and the rotator interval capsule.

OBJECTIVE: To study the superior-inferior stabilizing functions of the coracohumeral ligament (CHL) and the rotator interval capsule (RIC) with use of a material testing machine. MATERIAL AND METHODS: The axial translations of the humerus with the superior-inferior translation force of 30 N applied were recorded under the following joint capsule conditions: (1) intact, (2) vented, (3) the CHL sectioned, and (4) the RIC incised in six cadaver shoulders. The order of sectioning was changed for conditions 3 and 4 in six other cadaver shoulders. RESULTS: With the arm in internal and neutral rotations, venting the capsule significantly increased the superior-inferior translation, which was unaffected by further sectioning of the CHL and the RIC. With the arm in external rotation, only the CHL contributed significantly to inferior stability, whereas both this ligament and the RIC contributed to superior stability to a lesser degree. CONCLUSION: The CHL is a stabilizer in superior inferior directions with the arm in external rotation, and the intra-articular pressure that is maintained by the intact RIC is a stabilizer in superior-inferior directions with the arm in internal and neutral rotations. These findings may provide a scientific background to support closure of the interval space to stabilize the shoulder and may explain part of the superior instability observed in shoulders with rotator cuff tears.

Aged↗

PubMed1998

Three-dimensional kinematics of the shoulder complex during wheelchair propulsion: a technical report.

Methods for the three-dimensional (3-D) kinematic analysis of the shoulder complex (humerus relative to trunk) are presented and their use demonstrated in this analysis of shoulder motion during wheelchair propulsion. Ten subjects propelled two different wheelchairs (adjustable and conventional chairs) while the motions of the left arm and trunk were measured using a video tracking system. Eulerian angles described the sequence-dependent rotations of the humerus relative to the trunk. Wheel angular velocity and acceleration, hand position on the handrim, and duration of cycle subphases were also measured. Selected temporal and kinematic parameters were derived from the time-normalized average cycle of each subject on each wheelchair. Within-subject variation of these parameters according to wheelchair type were compared using a two-tailed t-test for paired observations. The adjustable chair made available a larger propulsion are compared with the conventional chair. Only the minimum amount of elevation demonstrated a significant difference between chairs (the conventional chair had a smaller minimum than the adjustable chair) at the corrected significance level of p < 0.001. Other differences, though not statistically significant, were still informative. Less shoulder internal rotation but more overall shoulder motion was observed during recovery phase in the adjustable chair as compared with the conventional chair. The methods presented for measuring the 3-D kinematics of the shoulder complex during wheelchair propulsion proved feasible for future use in studies that will address shoulder kinetics, energy requirements, wheelchair design, and chronic use disorders.

Adult↗

PubMed1998

Functional laboratory assessment after oncologic shoulder joint resections.

A laboratory evaluation was undertaken to assess the shoulder range of motion and distal strength after oncologic resection and reconstruction involving the shoulder joint and to compare these functional parameters based on potentially important variables. Inclusion in the study was limited to 32 patients with bone tumors of the proximal humerus or scapula treated surgically by resection of the shoulder joint including the proximal humerus from 1976 through 1992. Active shoulder range of motion and isometric elbow extension and forearm supination strength are significantly less after surgery in patients with greater amounts of bony resection and with resection of the deltoid. Patients who had a modified Tikhoff-Linberg resection were able to achieve 10 degrees to 15 degrees greater shoulder motion in each direction than were patients who had the classic procedure including complete scapulectomy. However, elbow flexion and extension strength and forearm pronation strength were greater for the patients with the classic resection. Osteoarticular allografts as a reconstructive alternative provide as a group the best shoulder motion and overall distal upper extremity strength, but these reconstructions were performed only when the rotator cuff muscles and deltoid were able to be reconstructed. Diminishing elbow strength was seen with longer followup in the patients with osteoarticular reconstructions, corresponding temporally to subchondral collapse observed on radiographs. Range of shoulder motion except rotation was just as good for allograft vascularized fibular arthrodeses as for the osteoarticular allografts, but strength was significantly less with the arthrodeses.

Adolescent↗

PubMed1998

Validation of F-Scan pressure sensor system: a technical note.

This study performed a quantitative validation on a recently developed pressure sensitive transducer system, the F-Scan sensor system. The results indicate that the sensor is adequate for determination of pressure distribution under contact conditions with soft materials. The linear response of the sensor was up to 1.7 MPa with good homogeneity throughout sensor cells. However, the sensor is sensitive to surface conditions, loading speeds, and temperature. Variations also exist from sensor to sensor. In order to have accurate measurement, calibration was recommended in actual clinical or experimental conditions prior to use, including surface contact conditions, loading speeds, and temperature environment. In addition, this sensor system is not suitable for hard surface contact such as plexiglas.

Biomechanical Phenomena↗

PubMed1998

Stability after inferior or anterior maxillary repositioning by Le Fort I osteotomy: a biplanar stereocephalometric study.

A biplanar cephalometric stereoradiographic system was used to measure maxillary positional changes during and after Le Fort I procedures for inferior or anterior repositioning of the maxilla. Of the 29 patients studied, 25 had undergone surgical maxillary advancement, and 15 had undergone inferior repositioning. These cases were divided into subgroups based on fixation technique, presence or absence of bone grafts, age, and surgeon. The postsurgical follow-up period was at least 11 months for each patient. The landmarks used to measure maxillary positional changes consisted of skeletal features and points on wire or rigid fixation devices. Mean magnitudes of postsurgical maxillary landmark displacement were insignificant for all subgroups examined except the advancement group with wire fixation. Individual patients exhibiting the greatest postsurgical displacements tended to have had large surgical advancements and received wire fixation. Magnitudes of surgical and postsurgical change did not seem correlated on the whole, except in the maxillary advancement cases in which bone grafts had not been used. Error analysis results suggest that digitizing consistency was acceptable for maxillary landmarks; however, methodologic improvements with regard to provision of cranial reference landmarks may further minimize errors in future studies.

Adolescent↗

PubMed1997

Biomechanical evaluation of posterior cervical stabilization after a wide laminectomy.

STUDY DESIGN: In vitro biomechanical investigation with nondestructive and destructive testing in a human cadaveric model simulating a wide postlaminectomy condition. OBJECTIVES: To determine the relative stability conferred by a posterior cervical spinal rod system and posterior cervical plating. SUMMARY OF BACKGROUND DATA: Posterior cervical plate fixation has been shown to be biomechanically superior to wiring techniques, but lateral mass screws may injure neurovascular structures or facet joints if they are inserted improperly. A cervical rod system has been developed to enhance the safety of lateral mass instrumentation. METHODS: The cervical spines of 12 cadavers underwent biomechanical testing. After completion of the nondestructive intact testing, a wide laminectomy with subtotal facetectomies from C4 to C6 was performed. The specimens in two subgroups (group A, cervical spine rods with unicortical fixation, and group B, reconstruction plates with bicortical fixation) were tested in flexion, lateral bending, and torsion. Finally, destructive testing in flexion was performed. Stiffness, neutral zone, failure moment, energy to failure, and mechanism of failure were determined for each specimen. The data were analyzed using paired t tests and ANOVA. RESULTS: Group B had a greater mean screw torque value. The instrumented constructs had a greater stiffness ratio (instrumented/intact) than the intact specimens in flexion, lateral bending, and torsional testing. Group A had a significantly greater flexural stiffness than Group B. Neutral zone ratio values were significantly lower during flexural testing for the cervical rod construct. Destructive testing resulted in significantly greater failure moment and energy-to-failure values for group A. In the cervical rod construct, failure occurred primarily by superior screw loosening with pull-out from the lateral mass. Reconstruction plates consistently failed with fracture of the lateral mass and superior screw loosening. CONCLUSION: Significantly greater stability was noted in the cervical rod construct during nondestructive and destructive flexural testing.

Adult↗

PubMed1997

Estrogen regulates the rate of bone turnover but bone balance in ovariectomized rats is modulated by prevailing mechanical strain.

Estrogen deficiency induced bone loss is associated with increased bone turnover in rats and humans. The respective roles of increased bone turnover and altered balance between bone formation and bone resorption in mediating estrogen deficiency-induced cancellous bone loss was investigated in ovariectomized rats. Ovariectomy resulted in increased bone turnover in the distal femur. However, cancellous bone was preferentially lost in the metaphysis, a site that normally experiences low strain energy. No bone loss was observed in the epiphysis, a site experiencing higher strain energy. The role of mechanical strain in maintaining bone balance was investigated by altering the strain history. Mechanical strain was increased and decreased in long bones of ovariectomized rats by treadmill exercise and functional unloading, respectively. Functional unloading was achieved during orbital spaceflight and following unilateral sciatic neurotomy. Increasing mechanical loading reduced bone loss in the metaphysis. In contrast, decreasing loading accentuated bone loss in the metaphysis and resulted in bone loss in the epiphysis. Finally, administration of estrogen to ovariectomized rats reduced bone loss in the unloaded and prevented loss in the loaded limb following unilateral sciatic neurotomy in part by reducing indices of bone turnover. These results suggest that estrogen regulates the rate of bone turnover, but the overall balance between bone formation and bone resorption is influenced by prevailing levels of mechanical strain.

Animals↗

PubMed1997

A method for determination of stiffness of collagen molecules.

This study developed a micromechanical test method for determination of stiffness of collagen molecules. The novelty includes the adoption of an optical tweezer system for loading a single collagen molecule and the development of a binding technique for gripping the collagen molecule termini for the micromechanical test. This methodology will potentially help us to understand the mechanical properties and functions of collagen ultrastructure.

Animals↗

PubMed1997

Quantitative analysis of the intrinsic muscles of the foot.

BACKGROUND: Understanding muscle architecture of the foot may assist in the design of surgical procedures such as tendon transfer, biomechanical modeling of the foot, prosthesis design, and analysis of foot function. There is limited published information regarding foot intrinsic muscle architecture. METHODS: Eleven fresh-frozen cadaveric feet were studied from eight males and three females. Twenty-eight intrinsic muscles were dissected in each foot, and measurements of fiber length, muscle length, and muscle volume obtained using calipers and water displacement technique. The physiologic cross-sectional area, fiber/muscle length ratio, muscle mass fraction, and tension fraction were then calculated. RESULTS: Intrinsic muscle length was related to foot size. The mean fiber length ranged from 13.6 mm (first plantar interosseous) to 28.0 mm (second extensor digitorum brevis). The mean muscle length ranged from 24.8 mm (adductor hallucis transverse) to 115.8 mm (abductor hallucis). The mean muscle volume ranged from 0.4 cc (fifth lumbrical) to 15.2 cc (abductor hallucis). The physiologic cross-sectional area ranged from 0.28 cm2 (second and third lumbrical) to 6.68 cm2 (abductor hallucis). The fiber/ muscle ratio ranged from 0.20 (abductor hallucis) to 0.82 (adductor hallucis transverse). The mass fraction ranged from 0.33% (fifth lumbrical) to 16.59% (abductor hallucis). The tension fraction ranged from 0.34% (fifth lumbrical) to 15.37% (abductor hallucis). CONCLUSIONS: The abductor hallucis and adductor hallucis oblique had much greater physiologic cross-sectional areas compared to those of the other intrinsic muscles. The lumbrical muscles had relatively low physiologic cross-sectional areas. These observations illustrate the underlying structural basis for the functional capacities of the intrinsic muscles of the foot.

Cadaver↗

PubMed1997

Reproducibility of the kinematics and kinetics of the lower extremity during normal stair-climbing.

The purpose of this study was to examine the intrasubject reproducibility of the kinematic and kinetic measures of the lower extremity during normal stair-climbing. Three-dimensional video and force-plate data were collected for three trials per subject during each of three conditions: ascending, descending, and level walking. Three-dimensional angles and moments of the ankle, knee, and hip joints were calculated. The coefficient of multiple correlation was used to determine the intrasubject reproducibility of joint angles and resultant moments. Analysis of variance with repeated measures was conducted to compare the magnitudes of the coefficients between different steps, different joints, and different joint functions. The results showed that (a) generally, the kinematic and kinetic measures of normal subjects climbing stairs were reproducible; (b) the kinetic measures during the transition steps from level walking to ascending and from descending to level walking were significantly less reproducible than those during the other steps; (c) the data from the sagittal plane were more reproducible than those from the other two planes; and (d) the kinetic measures were more reproducible than the kinematic measures, especially for abduction-adduction and internal-external rotation.

Adult↗

PubMed1997

Monte Carlo simulation of a planar shoulder model.

Although variability of anthropometric measures within a population is a well established phenomenon, most biomechanical models are based on average parameter values. For example, optimisation models for predicting muscle forces from net joint reaction moments typically use average muscle moment arms. However, understanding the distribution of musculoskeletal morbidity within a population requires information about the variation of tissue loads within the population. This study investigated the use of Monte Carlo simulation techniques to predict the statistical distribution of deltoid and rotator cuff muscle forces during static arm elevation. Muscle moment arms were modelled either as independent random variables or jointly distributed random variables. Moment arm data was collected on 22 cadaver specimens. The results demonstrated the use of Monte Carlo techniques to describe the statistical distribution of muscle forces. Although assuming statistically independent moment arms did affect the statistical distribution shape, that assumption did not affect the median predicted forces. The standard deviations of muscle forces predicted using Monte Carlo techniques were similar to the standard deviation of muscle force predictions using the whole sample of specimens. It is concluded that Monte Carlo simulation techniques are a useful tool to analyse the interindividual variability of rotator cuff muscle forces.

Biomechanical Phenomena↗

PubMed1997

Reversal of antagonists: effect of elbow extension strength and endurance.

OBJECTIVE: To evaluate the reversal of elbow antagonists designed to facilitate the extensors relative to agonist-only contractions of the extensors, while using a protocol previously demonstrated to result in an increase in strength through motor learning. DESIGN: Two-group convenience sample composed of healthy subjects. SETTING: Clinic research laboratory. SUBJECTS: Twenty-eight healthy women without a history of upper extremity injury or neurologic disorder. MEASUREMENTS: Elbow extension strength and endurance were measured during maximal effort isometric reversal of the elbow antagonists (experimental group) and elbow extension only (control group) resistance exercise. Biceps brachii short head (BBS), triceps brachii lateral head (TLAT), and triceps brachii long head (TLNG) electromyographic (EMG) activity was measured concurrently. RESULTS: There were no significant differences between groups for either elbow extension strength, BBS, TLAT, or TLNG EMG activity. The experimental and control groups exhibited a significant linear (p < .01) and quadratic (p < .01) increase in baseline strength of 5.2N.m (30.5%). EMG activity from each muscle group increased linearly (p < .01) across all test sessions. Similar results were observed for elbow extension strength and biceps and triceps EMG activity during fatigue testing. CONCLUSIONS: The reversal of antagonists technique was not superior to agonist-only resistance exercise, nor did it interfere with the acquisition of muscular strength or endurance through motor learning.

Adult↗