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Biomedical subjects

X H Deng

Publications and source records attributed to X H Deng.

18 recordsLinked to original sources
PubMed2001

Rapid magnetic reconnection in the Earth's magnetosphere mediated by whistler waves.

Magnetic reconnection has a crucial role in a variety of plasma environments in providing a mechanism for the fast release of stored magnetic energy. During reconnection the plasma forms a 'magnetic nozzle', like the nozzle of a hose, and the rate is controlled by how fast plasma can flow out of the nozzle. But the traditional picture of reconnection has been unable to explain satisfactorily the short timescales associated with the energy release, because the flow is mediated by heavy ions with a slow resultant velocity. Recent theoretical work has suggested that the energy release is instead mediated by electrons in waves called 'whistlers', which move much faster for a given perturbation of the magnetic field because of their smaller mass. Moreover, the whistler velocity and associated plasma velocity both increase as the 'nozzle' becomes narrower. A narrower nozzle therefore no longer reduces the total plasma flow-the outflow is independent of the size of the nozzle. Here we report observations demonstrating that reconnection in the magnetosphere is driven by whistlers, in good agreement with the theoretical predictions.

Journal Article↗
PubMed1998

Effects of exercise on Achilles tendon healing in a rat model.

The effects of motion, or lack of it, on Achilles tendon healing are not well defined. We have recently shown that immobilization has a detrimental effect on tendon healing in a rat model. The aim of this experiment was to determine whether enforced exercise had an additional beneficial effect on the mechanical and functional recovery of divided Achilles tendons in rats. Male Sprague-Dawley rats were randomly allocated into a nonexercise and an exercise group (N = 10 for each group). In both groups the right Achilles tendon was surgically transected. The left, uninjured lower limb served as an internal control. Both groups of animals were housed under identical conditions with the exception that the exercise group swam for 15 minutes per day. Functional performance was determined from the measurement of hindpaw prints of walking rats preoperatively and on alternate postoperative days. On day 15, the animals were killed and weighed, and biomechanical evaluations were performed on both the injured and uninjured Achilles tendon constructs. There were no differences in weight at time of death. All animals had an initial functional deficit that returned to near-normal by day 15. There were significant differences in the morphological and the mechanical properties of the healing Achilles tendon constructs at day 15 when comparing the injured with the uninjured Achilles tendon constructs. Supplemental exercise, however, had no effect on the functional or mechanical recovery of injured or uninjured Achilles tendons in the rat model.

Achilles Tendon↗
PubMed1998

Hamstring and patellar tendon graft response to cyclical loading.

This study evaluates the effect of submaximal cyclical loads on the tendinous portion of the central 10 mm of the patellar tendon compared with doubled semitendinosus and gracilis tendons. Six fresh-frozen cadaveric knee specimens were used for the study. There was no significant difference between the cross-sectional areas of a 10-mm patellar tendon and four strands of hamstring tendon (looped semitendinosus and gracilis) from the same specimen. The mean cross-sectional area was 44.4 mm2 for the patellar tendon and 47.5 mm2 for the four strands of hamstring. The specimens were cyclically loaded for 1000 cycles from 0 to 300 N at a rate of 1 Hz; the materials testing machine was set on load control. There were no significant differences in the strain, stress, or modulus between the 10-mm patellar tendon and four strands of hamstring tendon after 1000 cycles of loading to 300 N. These data substantiate the excellent clinical results obtained with either graft source and support the use of either graft source for ACL reconstruction.

Aged↗
PubMed1997

Modulation of tendon healing by nitric oxide.

Nitric oxide (NO) is a small, diffusible free radical that is generated from L-arginine by a family of enzymes, collectively termed the nitric oxide synthases. We investigated the role of NO in tendon healing. NO synthase activity and immunoreactivity was absent in un-injured rat Achilles tendon. After surgical division there was a five-fold increase in NO synthase activity and immunoreactivity within the healing tendon at day 7, with a return to near baseline levels at day 14. Inhibition of NO synthase activity with oral administration of N omega-nitro-L-arginine methyl ester (L-NAME) resulted in a significant reduction in cross-sectional area (30% at day 7, p < 0.01, 50% at day 15, p < 0.001) and failure load (24% at day 7, p < 0.01) of the healing Achilles tendon constructs. Rats fed the same regimen of the enantiomer of L-NAME, (D-NAME) had normal tendon healing. These results indicate that nitric oxide synthase is induced during tendon healing and inhibition of nitric oxide synthase inhibits this tendon healing.

Achilles Tendon↗
PubMed1997

Biomechanical evaluation of the medial collateral ligament of the elbow.

UNLABELLED: Anatomical dissection and biomechanical testing were used to study twenty-eight cadaveric elbows in order to determine the role of the medial collateral ligament under valgus loading. The medial collateral ligament was composed of anterior, posterior, and occasionally transverse bundles. The anterior bundle was, in turn, composed of anterior and posterior bands that tightened in reciprocal fashion as the elbow was flexed and extended. Sequential cutting of the ligament was performed while rotation caused by valgus torque was measured. The anterior band of the anterior bundle was the primary restraint to valgus rotation at 30, 60, and 90 degrees of flexion and was a co-primary restraint at 120 degrees of flexion. The posterior band of the anterior bundle was a co-primary restraint at 120 degrees of flexion and a secondary restraint at 30 and 90 degrees of flexion. The posterior bundle was a secondary restraint at 30 degrees only. The reciprocal anterior and posterior bands have distinct biomechanical roles and theoretically may be injured separately. The anterior band was more vulnerable to valgus overload when the elbow was extended, whereas the posterior band was more vulnerable when the elbow was flexed. The posterior bundle was not vulnerable to valgus overload unless the anterior bundle was completely disrupted. The intact elbows rotated a mean of 3.6 degrees between the neutral position and the two-newton-meter valgus torque position. Cutting of the entire anterior bundle caused an additional 3.2 degrees of rotation at 90 degrees of flexion, where the effect was greatest. CLINICAL RELEVANCE: Physical findings in a patient who has an injury of the anterior bundle may be subtle, and an examination should be performed with the elbow in 90 degrees of flexion for greatest sensitivity. As the anterior bundle is the major restraint to valgus rotation, reconstructive procedures should focus on anatomical reproduction of that structure. Parallel limbs of tendon graft placed from the inferior aspect of the medial epicondyle to the area of the sublimis tubercle will simulate the reciprocal bands of the anterior bundle. Temporary immobilization with the elbow in flexion may relax the critically important anterior band of the reconstruction during healing.

Biomechanical Phenomena↗
PubMed1997

[Myotrophic factors].

A variety of substances have been found to show myotrophic effect and are named myotrophic factors. Myotrophic factors provided a new means to the research and treatment of motor neuron diseases and muscle degenerating diseases. In this article, we reviewed the studies of various myotrophic factors, and indicated the clinical significance and direction of their studies.

Amyotrophic Lateral Sclerosis↗
PubMed1995

Effect of lesions of the superior portion of the glenoid labrum on glenohumeral translation.

Lesions of the superior portion of the glenoid labrum were created in seven cadaveric shoulders. The shoulders were mounted on a special apparatus attached to a servocontrolled hydraulic materials-testing device. Sequential fifty-newton anterior, posterior, superior, and inferior forces and a twenty-two-newton joint compressive load were applied to the shoulders. In addition, a fifty-five-newton force was applied to the tendon of the long head of the biceps brachii. The shoulders were tested in seven positions of glenohumeral elevation and rotation. An isolated lesion of the anterosuperior portion of the labrum, which did not involve the supraglenoid insertion of the biceps brachii, had no significant effect on anteroposterior or superoinferior glenohumeral translation, either with or without application of the fifty-five-newton force to the biceps brachii tendon. In contrast, a complete lesion of the superior portion of the labrum that destabilized the insertion of the biceps resulted in significant increases in anteroposterior and superoinferior glenohumeral translations. At 45 degrees of glenohumeral elevation, the complete lesion led to a 6.0-millimeter increase in anterior translation when the arm was in neutral rotation and to a 6.3-millimeter increase when the arm was in internal rotation; inferior translation also increased, by 1.9 to 2.5 millimeters. The increases in translation persisted despite application of a fifty-five-newton force to the long head of the biceps.

Biomechanical Phenomena↗
PubMedDate not supplied

Role of the long head of the biceps brachii in glenohumeral stability: a biomechanical study in cadavera.

Ten cadaveric shoulders were tested to evaluate the effect of simulated contraction of the long head of the biceps brachii on glenohumeral translation. The shoulders were mounted on a special apparatus attached to a servo-controlled hydraulic testing device. Sequential 50 N anterior, posterior, superior, and inferior forces and a 22 N joint compressive load were applied to the shoulders. An air cylinder applied a constant force to the tendon of the long head of the biceps brachii. The shoulders were tested in seven positions of glenohumeral elevation and rotation. Application of a force to the long head of the biceps brachii resulted in statistically significant decreases in humeral head translation. The influence of the long head of the biceps was more pronounced at middle and lower elevation angles. When the shoulder was placed in 45 degrees of elevation and neutral rotation, application of a 55 N force to the biceps tendon reduced anterior translation by 10.4 mm (p = 0.001), inferior translation by 5.3 mm (p = 0.01), and superior translation by 1.2 mm (p = 0.004).

Analysis of Variance↗
PubMedDate not supplied

Articular contact patterns of the normal glenohumeral joint.

The purpose of this study was to determine the articular contact patterns of the normal glenohumeral joint, and to correlate these findings with cartilage and subchondral bone architecture. We studied 10 normal shoulders of cadavers. We removed all soft tissues except the joint capsule and rotator cuff and then placed the shoulders on a testing apparatus that allowed freedom of translation in three planes. After the humerus was placed in a neutral position of rotation, articular contact patterns were measured with specially prepared prescale Fuji film so that it could be inserted between the joint surfaces. Articular contact was analyzed with 222 and 444 N of joint compressive load, and the humerus was positioned in scapular plane abduction of 0 degree, 45 degrees, and 90 degrees. The contact patterns were then digitized to determine percentage contact of the humeral head on the glenoid. We studied 12 additional cadaver shoulders with fine microradiographs and histologic techniques after we sectioned the glenoids in the anterior-posterior and superior-inferior planes. We then analyzed articular and subchondral architecture. We found that when the shoulder was adducted the contact area of the humeral head on the glenoid was limited to the anatomic region of the central glenoid known as the "bare area." This was histologically and radiographically an area of cartilage thinning and increased subchondral bone density. As the shoulder was abducted the articular congruity and percentage contact area increased. We concluded that there was a slight articular mismatch with the shoulder adducted in the normal shoulder. Histologic and radiographic studies suggested that the central bare area region of the glenoid was a region of increased compressive loading. As the shoulder was abducted the joint became more congruent and thus the contact area of the humeral head on the glenoid increased.

Aged↗
PubMedDate not supplied

Thermal modification of collagen.

Shoulder capsular shrinkage has recently been proposed as a therapeutic modality in a select group of patients with instability. Basic science research studying the mechanism of collagen shrinkage and the effect of shrinkage on the tissue's mechanical properties is essential to define the ideal process by which to achieve optimal tissue shrinkage. Tissue shrinkage is a function of both time and temperature. This relationship was studied, and a model was derived to describe the relationship mathematically. Tissue shrinkage rate was extremely sensitive to temperature changes. The purpose of this study, was to shrink collagenous tissue thermally and then to measure the mechanical property changes as a function of tissue shrinkage. Uniaxial tensile testing of normal and heat-shrunken bovine tendon was carried out, and a model was developed to express the relationship between shrinkage and mechanical properties. We found that the mechanical properties decreased with increasing shrinkage, and that the maximal allowable shrinkage before significant material property changes occurred was between 15% to 20%. Ultrastructural analysis with transmission electron microscopy showed denaturation of the collagen fibrillar structure and provided direct support for the observed material changes.

Animals↗
PubMedDate not supplied

Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint.

The purpose of this study was to determine the contributions of specific capsuloligamentous structures to restraining superior-inferior translation of the glenohumeral joint. Eleven cadaveric shoulders were tested using a four degrees-of-freedom test apparatus. The humerus was free to translate in three planes and free to flex and extend when a superior and inferior force of 50 N was applied. Testing was performed in three positions of abduction (0 degree, 45 degrees, and 90 degrees) and three positions of rotation (neutral, maximum internal, and external). Shoulders were tested intact, vented, and after division of specific capsuloligamentous structures. The primary restraint to inferior translation of the adducted shoulder was the superior glenohumeral ligament. The coracohumeral ligament appeared to have no significant suspensory role. With progressive abduction, the anterior and posterior portions of the glenohumeral ligament become the main static stabilizers resisting inferior translation: the anterior portion was the primary capsular restraint at 45 degrees of abduction, while the posterior portion was the primary restraint at 90 degrees of abduction, neutral rotation. Our results indicate that clinical assessment of glenohumeral translation in the superior-inferior plane should be performed in multiple positions of abduction and rotation.

Biomechanical Phenomena↗
PubMedDate not supplied

The strength of the central third patellar tendon graft. A biomechanical study.

Thirty-seven bone-patellar tendon-bone composite grafts from the knees of 21 human cadavers were tested to failure. Average donor age was 28 years. The composites were divided into 4 groups: 3 groups with 10 grafts (5 pairs) and 1 group with 7 grafts from 6 donors. In Group 1 we tested 10- versus 15-mm wide grafts that were used without twisting; Group II, 10-mm wide grafts without twisting versus 10-mm wide grafts that were twisted 90 degrees; Group III, 10-mm wide grafts twisted 90 degrees versus 10-mm wide grafts twisted 180 degrees; and Group IV, 10- versus 7-mm wide grafts that were not twisted. The tests were performed using a newly described potting technique and clamp system and a servohydraulic testing machine with an elongation rate of 5 cm/sec. The results of this study suggest that the central third of the patellar tendon is stronger than previously reported. The mean ultimate load of a 15-mm bone-patellar tendon-bone composite was 4389 N (+/- 708); of the 10-mm wide composites, 2977 N (+/- 516); and of the 7-mm composites, 2238 N (+/- 316). Twisting the graft 90 degrees increased the strength (P < 0.05). Further twisting to 180 degrees had no significant effect compared with twisting 90 degrees. This study supports the practice of using smaller (10 mm) bone-patellar tendon-bone grafts to avoid the potential complications of patellar fracture and graft impingement in the notch.

Adult↗
PubMedDate not supplied

The role of the cruciate and posterolateral ligaments in stability of the knee. A biomechanical study.

The role of the posterolateral and cruciate ligaments in restraining knee motion was studied in 11 human cadaveric knees. The posterolateral ligaments sectioned included the lateral collateral and arcuate ligaments, the popliteofibular ligament, and the popliteal tendon attachment to the tibia. Combined sectioning of the anterior cruciate and posterolateral ligaments resulted in maximal increases in primary anterior and posterior translations at 30 degrees of knee flexion. Primary varus, primary internal, and coupled external rotation also increased and were maximal at 30 degrees of knee flexion. Combined sectioning of the posterior cruciate and posterolateral ligaments resulted in increased primary posterior translation, primary varus and external rotation, and coupled external rotation at all angles of knee flexion. Examination of the knee at 30 degrees and 90 degrees of knee flexion can discriminate between combined posterior cruciate ligament and posterolateral injury and isolated posterolateral injury. The standard external rotation test performed at 30 degrees of knee flexion may not be routinely reliable for detecting combined anterior cruciate and posterolateral ligament injury. However, measurements of primary anterior-posterior translation, primary varus rotation, and coupled external rotation may be used to detect combined anterior cruciate and posterolateral ligament injury.

Aged↗
PubMedDate not supplied

The role of the popliteofibular ligament in stability of the human knee. A biomechanical study.

The popliteal tendon has a significant attachment to the fibula, the popliteofibular ligament. The role of this ligament in knee stability has not been determined. In this study we used selective cutting techniques to measure the static contribution of the popliteal tendon attachments to the tibia and the popliteofibular ligament for stability of the knee. Sectioning of all the posterolateral structures except the popliteal tendon attachments to the tibia or the popliteofibular ligament resulted in increased primary posterior translation, varus rotation, external rotation, and coupled external rotation. Although statistically significant, these increases were small. Sectioning of all the posterolateral structures resulted in larger increases in primary posterior translation, varus rotation, external rotation, and coupled external rotation. Our data indicate that the popliteal tendon attachments to the tibia and the popliteofibular ligament are important in resisting posterior translation and varus and external rotation. If an isolated injury to the posterolateral structures occurs, anatomic reconstruction of the major ligaments that restrain posterior translation and varus and external rotation may provide the best functional result. Reconstruction for isolated posterolateral instability should include anatomic attachment of the popliteal tendon to the tibia and the popliteofibular ligament.

Aged↗
PubMedDate not supplied

The combined dynamic and static contributions to subacromial impingement. A biomechanical analysis.

Ten human cadaveric shoulders were tested with a dynamic shoulder model simulating physiologic rotator cuff, deltoid, and biceps muscle forces. The combined effect of the muscle forces and acromial structure on subacromial impingement was measured with minimally invasive, miniature pressure transducers. Shoulders with large acromial spurs had significantly greater impingement pressures at the anterolateral acromion in neutral, internal, and external rotation compared with those with flatter acromia. Application of a biceps muscle force reduced anterolateral acromial pressures by 10%. Failure to simulate a supraspinatus force decreased acromial pressure 52% in shoulders with type III acromia in neutral rotation. Without rotator cuff forces applied, the maximum deltoid muscle force required to elevate the arm increased by 17%. Acromial pressures were increased when no rotator cuff forces were applied, but the increases were not significant. After an anterior acromioplasty, pressures decreased by 99% anteriorly. However, failure to achieve a flat surface posteriorly increased pressures in this location, especially with the shoulder in external rotation. Modeling the rotator cuff and deltoid muscle forces demonstrated the importance of the muscular force couple to center the humeral head during elevation of the arm. The inferior forces of the infraspinatus, teres minor, and subscapularis muscles were necessary to neutralize the superior shear force produced by the deltoid and supraspinatus muscles.

Acromioclavicular Joint↗
PubMedDate not supplied

Use of recombinant human bone morphogenetic protein-2 to enhance tendon healing in a bone tunnel.

This study examines the hypothesis that recombinant human bone morphogenetic protein-2 can enhance bone ingrowth into a tendon graft placed into a bone tunnel. We transplanted the long digital extensor tendon into a drill hole in the proximal tibia in 65 adult mongrel dogs. We applied two different doses of the bone morphogenetic protein to the tendon-bone interface in one limb using an absorbable type I collagen sponge carrier and only the collagen sponge to the contralateral (control) limb. The healed tendon-bone attachment was evaluated at serial times between 3 days and 8 weeks using radiography, histologic examination, and biomechanical testing. At all time points, histologic and radiographic examination demonstrated more extensive bone formation around the tendon with closer apposition of new bone to the tendon in the protein-treated limb than in the paired control limb. Biomechanical testing demonstrated higher tendon pull-out strength in the protein-treated side at all time points, with a statistically significant difference between the low-dose-treated side and the control side at 2 weeks. The histologic and biomechanical data suggested superior healing at the lower protein dose. This study demonstrated that bone morphogenetic protein can accelerate the healing process when a tendon graft is transplanted into a bone tunnel.

Animals↗
PubMedDate not supplied

Relapses in leprosy patients treated with rifampicin plus dapsone after varying periods of dapsone monotherapy.

Leprosy patients treated formerly with dapsone monotherapy followed by combined therapy with rifampicin plus dapsone were surveyed for relapse and rifampicin resistance. The relapse rate was significantly low for the 482 multibacillary (MB) patients receiving > 12 months combined therapy compared with the 49 MB cases receiving < 12 months of combined therapy. The relapse rate was related to the duration of dapsone monotherapy prior to combined therapy. The difference in relapse rate in 247 paucibacillary (PB) patients following > 12 months combined therapy was also of significance, compared with the 66 PB cases who had received < 12 months combined therapy. Five strains of M. leprae isolated from relapsed patients were sensitive to rifampicin by mouse foot-pad test and all relapsed patients responded favourably to fixed duration MDT regimen for MB cases.

Animals↗