Evaluation of the mechanical environment during distraction osteogenesis

Physical forces have been hypothesized to direct the process of bone regeneration during distraction osteogenesis. However, despite significant clinical experience, relatively little is known about how the mechanics of distraction influence bone formation. This study investigated net fixator forces and strains in the distraction callus during bilateral lengthening of tibiae in New Zealand White rabbits. Distractions yielded a classic viscoelastic response with a sharp increase in fixator force, followed immediately by significant relaxation. Tension acting on mesenchymal gap tissue caused by distraction was estimated to reach more than 30 N by the time full lengthening was achieved. Average maximum cyclic strains within the distraction zone during ambulation were estimated to be 14% to 15% and supported by the results of fluoroscopic imaging. Paradigms for fracture healing have hypothesized that such strains are incompatible with new bone formation. The documented clinical success of distraction osteogenesis at stimulating large volumes of new bone suggests that other mechanisms that warrant additional investigation may be at work during distraction.     

Blood transfusion practices in Mwanza Region, Tanzania. Bugando Medical Centre

Uncertainty exists about the forces applied by dentists during dental crown cementation. A measuring system was developed based around a commercially available miniature (3.8 mm high and 12.7 mm diameter) load cell. The load cell was mounted in a finger stall and the applied force measured. Experimental results suggest that dentists typically apply a force to metal crowns of about 60 N for a few seconds, followed by the application of a steady force of about 20 to 30 N. Lower forces are applied to porcelain crowns.     

Functional evaluation of the ligaments at the acromioclavicular joint during anteroposterior and superoinferior translation

We examined the anatomy and measured the in situ force in ligaments at the acromioclavicular joint using a universal force-moment sensor. The in situ force in the coracoacromial, conoid, trapezoid, superior acromioclavicular capsular, and inferior acromioclavicular capsular ligaments of 10 fresh-frozen cadaveric shoulders was determined for a load of 70 N applied to the clavicle in anteroposterior and superoinferior directions. The lengths of the conoid and trapezoid ligaments were found to be 15.1 +/- 4.1 and 11.5 +/- 2.2 mm, respectively; the widths of the conoid and trapezoid ligaments were 10.7 +/- 1.5 and 11.0 +/- 2.8 mm, respectively. The in situ force of the trapezoid (42.9 +/- 15.4 N) was significantly greater than that for the other ligaments during posterior displacement. Otherwise, no statistically significant differences could be found between any of the in situ forces in each ligament during all other motions examined. During anterior displacement, the inferior acromioclavicular capsular ligament appeared to be the major restraint. The trapezoid ligament was the primary restraint during posterior displacement and provided 55.8% +/- 20.0% of the resisting force. Our results suggest that the coracoclavicular and other acromioclavicular joint capsular ligaments should be considered for reconstruction to restore normal joint function, especially in the anterior, posterior, and superior directions.     

A biomechanical evaluation of graft loading characteristics for anterior cervical discectomy and fusion. A comparison of traditional and reverse grafting techniques

STUDY DESIGN: A biomechanical study of graft loading characteristics for anterior cervical discectomy and fusion comparing the amount and location of transmitted forces. OBJECTIVES: To evaluate the difference between traditional iliac grafting and reverse iliac grafting used for anterior cervical discectomy and fusion in the amount and location of forces applied to the grafts. SUMMARY OF BACKGROUND DATA: Traditional fusion after anterior cervical discectomy involves placing a tricortical iliac crest strut into the disc space with the cortical portion facing anteriorly and the cancellous portion posteriorly. Recently, reverse iliac grafting has been introduced in which the cortical portion is placed in the posterior disc space and the cancellous portion in the anterior disc space. There is no biomechanical or clinical study showing an advantage of using one technique over the other. This study is the first to produce data supporting one technique as biomechanically superior. METHODS: Five fresh cadaveric cervical spines were tested using pressure-sensitive film placed between the bone graft and the vertebral endplate after an anterior discectomy was performed. A 10-pound load was applied to the cervical spine at predetermined sagittal positions. Recordings were made at neutral, 10 degrees of flexion, and 10 degrees and 20 degrees of extension after traditional and reverse iliac grafting. RESULTS: Graft forces were identical in both traditional and reverse grafting in the location and amount of force applied. Total force increased to the maximum in flexion and gradually decreased in more extended positions. The location of the forces was completely anterior with flexion, moving to the posterior portion of the graft with positions of extension. With 10 degrees of flexion, the load applied to the grafts was 20.4 N. In the neutral position, the load was 12 N. The loads decreased further with extension with forces of 11 N in 10 degrees extension, and 4 N in 20 degrees of extension. CONCLUSIONS: The optimal position of the tricortical iliac graft for an anterior cervical fusion is with the stronger cortical portion placed in the anterior disc space and the weaker cancellous portion placed in the posterior disc space. In this traditional position, the graft will best resist the loads applied to the cervical spine, preventing graft collapse.     

Sequence analysis of 18S-28S rRNA spacer regions from Saccharomyces kunashirensis, S. martiniae, S. rosinii, and S. transvaalensis

Although bone response can be evaluated by radiography, there have been no reports in human confirming formation of new soft tissue in limb lengthening. This study evaluated the tensile force between pin clamps in 14 lower limb lengthenings. Legs were lengthened 0.5 mm every 12 hours and the tensile was measured continuously. The tensile force increased simultaneously with each lengthening and decreased gradually. However, the reduction rate of tensile force during the nighttime (120+/-22%) was significantly higher than that during the daytime (72+/-10%). This differed from the stress relaxation phenomenon shown by viscoelastic material and suggested the presence of other phenomena such as histogenesis.     

Transfer of loads between lumbar tissues during the flexion-relaxation phenomenon

STUDY DESIGN AND METHODS: This study used an anatomically detailed model of the lumbar tissues, driven from biologic signals of vertebral displacement and myoelectric signals, to estimate individual muscle and passive tissue force-time histories during the performance of the "flexion-relaxation" maneuver. Eight male university students performed three trials each of the "flexion-relaxation" maneuver with six pairs of surface myoelectric electrodes monitoring the right side of the trunk musculature, an electromagnetic device to record lumbar flexion, and videotape to record body segment displacement. OBJECTIVES: To examine the loads on individual tissues during the transfer of moment support responsibility from predominantly active muscle to predominantly passive tissue. SUMMARY OF BACKGROUND DATA: No previous studies, to the authors' knowledge, have examined individual tissue loading during the flexion-relaxation maneuver. RESULTS: Although most subjects were able to "relax" their lumbar extensors in full flexion, activity remained in the thoracic extensors and abdominals. Tissue load predictions suggested that while the lumbar extensor muscles were neurally "relaxed" (i.e., myoelectric silence), substantial elastic forces would assist the passive tissues in extensor moment support. On average, subjects sustained almost 3 kN in compressive load on the lumbar spine and about 755 N of anterior shear during full flexion with only 8 kg held in the hands. CONCLUSIONS: The "relaxation" of lumbar extensor muscles appeared to occur only in an electrical sense because they generated substantial force elastically through stretching. Loading of the interspinous and supraspinous ligaments, in particular, was high relative to their failure tolerance.     

A simple technique for correction of complicated tibial deformity including rotational deformity

Although the simplest way to correct bone deformity is one-stage correction, the problem associated with that method is overstretching of the soft tissues, which limits the correction and leads to complications such as compartment syndrome or peripheral nerve palsy. If an adequate amount of tissue necessary for correction is formed in advance, the deformity can be corrected safely at one stage without overstretching of the tissues. A leg lengthening technique was employed to form the necessary tissues. After leg lengthening with an unilateral external fixator (Hifixator), deformities were corrected manually at one stage without anesthesia, and the corrected positions were again secured with the fixator. To correct rotational deformity, two sets of pins were inserted into the proximal bone fragment of the tibia at the time of the operation, and after lengthening the proximal pin clamp of the fixator was disconnected from one pin set and reconnected to the other set. We applied this method to four tibias of three patients without any complications. The tension of the tissues was monitored using a pressure sensor built into a Hifixator to prevent the tissues from overstretching. During and after the correction, the tension of the tissue was maintained at less than before the correction.     

Role of endothelin-1 in repeated electrical stimulation-induced microcirculatory disturbance and mucosal damage in rat stomach

Ollier's disease is a chondromatosis of the long bones that occurs rarely but that is highly disabling because it causes severe dysmetria and deformity of the lower limbs. Surgical correction of these skeletal changes is obstructed by poor mechanical resistance of the bone tissue affected and by the amount of lengthening required to even the lower limbs. It is the purpose of this study to indicate the surgery of choice for the treatment of this disease, comparing the two most recent methods used: Wagner's technique and the Ilizarov method. The latter is more reliable in terms of mechanical hold and the possibility of correcting severe deformities, producing bone regenerate of excellent quality even in major lengthening procedures. These results were obtained by adapting the Ilizarov method to the features of the chondromatous bone, thanks to the extreme malleability of the circular external fixator.     

Comparison of plasma lidocaine concentrations after injection of a fixed small volume in the stellate ganglion, the lumbar epidural space, or a single intercostal nerve

Carpal tunnel syndrome may be caused by repeated or sustained elevated carpal tunnel pressure. This study examined the relationship between carpal tunnel pressure, posture, and fingertip load. In 20 healthy individuals, carpal tunnel pressure was measured with a catheter inserted into the carpal tunnel of the dominant hand and connected to a pressure transducer. With the wrist in a pressure-neutral position, the subjects pressed on a force transducer with the index finger to levels of 0, 5, 10, and 15 N. They then pinched the transducer at the same levels of force. For both fingertip-loading postures, the carpal tunnel pressure increased with increasing fingertip load. Carpal tunnel pressures were significantly greater (p < 0.015) for the pinching task (14.2, 29.9, 41.9, and 49.7 mm Hg [1.89, 3.99, 5.59, and 6.63 kPa] for 0, 5, 10, and 15 N force levels, respectively) than for simple finger pressing (7.8, 14.1, 20.0, and 33.8 mm Hg [1.04, 1.88, 2.67, and 4.51 kPa]). This study indicates that although the external load on the finger remained constant between the two tasks, the internal loading, as measured by carpal tunnel pressure, experienced a near 2-fold increase by using a pinch grip. These findings should be given consideration in designing work tasks and tools because relatively low fingertip forces, especially in a pinch grip, elevate carpal tunnel pressures to levels that, if prolonged, may lead to the development or exacerbation of carpal tunnel syndrome.     

底部两层框架——抗震墙砖房抗震设计探讨

根据《建筑抗震设计规范》（GBJ11－89）中有关底层框架－抗震墙砖房的规定,从工程实用的角度出发,探讨了度部两层框架－抗震墙砖房的设计要点,并从过渡层楼板,构造柱的设置、抗震墙的设置、结构形式、抗震墙的构造、钢筋混凝土圈梁、过渡层外纵墙、上部承重砖墙等的构造设计方面提出了抗震构造措施。     

Stresses at the meniscofemoral joint: elastostatic investigations on the applicability of interface elements

Stress distributions at the meniscofemoral joint were analysed and the applicability of nonlinear interface elements in a finite element model (FEM) were tested. Centred and 70% off-centre load cases with a complete, a partially removed or a totally removed medial meniscus were evaluated in two dimensions. Interface width was assumed to increase linearly from almost zero to 1 mm at the inner and outer border of the femoral condyles. Maximum interface forces were found at the centre of the condyles, decreasing to zero at the peripherical and intercondylar femoral border. Simulation data concerning a removed medial meniscus or medial 70% off-centre load with complete meniscus indicated higher medial contact forces in the first case. A decrease in the elastic modulus of the articular surface tissues caused two small force transfer peaks (femoral centre and intercondylar border), which were strongly influenced by the predefined gap width.     

Inherent stability of proximal first metatarsal osteotomies: a comparative analysis

Proximal first metatarsal osteotomies have been criticized for their instability leading to the dorsal displacement of the first metatarsal head. The purpose of this study was to compare inherent stability of fixated proximal oblique wedge and crescentic first metatarsal osteotomies against simulated vertical ground reactive forces. The authors evaluated four groups of 10 models each with various proximal osteotomy and fixation configurations. Group I was a control group of bone models without osteotomies; group II had oblique closing wedge osteotomies with one 2.7-mm, fully threaded, cortical screw fixation; group III had oblique closing wedge osteotomies with two 2.7-mm, fully threaded, cortical screw fixation; and group IV had proximal crescentic osteotomies with one 4.0-mm, partially threaded, cancellous screw fixation. All 40 bone models were stressed with simulated vertical ground reactive forces. Maximum load to achieve catastrophic failure was higher in the crescentic group (67.7 N, SD 15.1 N, p < or = .005), but the energy required to displace the osteotomy during the stressing sequence was higher in the two-screw oblique closing wedge osteotomy (390.6 N.mm, SD 153.4 N.mm, p < or = .01). The single-screw oblique closing wedge osteotomies showed the least ability to resist simulated vertical ground reactive forces (39.6 N, SD 19.1 N, p < or = .005).     

Oral health assessment of an adult rural community

A pneumatic indentation system using a copper bellows has been developed for physiological studies where a controlled uniaxial compressive force is required to be applied to the surface of the skin. Such a system is useful for studies where the physiological response of the tissues is to be monitored following a known loading history. The indentation system is driven by a vacuum/compression pneumatic pump through solenoid valves under closed-loop computer control. A load cell placed between the indentor and bellows monitors the applied force providing a feedback signal to the computer. The signal from the computer activates the valves supplying air pressure to the bellows, and the applied force is controlled using a digital closed-loop protocol. This system can be used to provide a controlled loading sequence to the skin without utilizing gravitational forces, which allows the subject to keep a more natural position during the experiment.     

Experimental evaluation of various anchoring techniques for synthetic ligaments

One of the weak points of augmentation or replacement of cruciate ligaments by synthetic material is the fixation of these artificial ligaments to the bone. The present investigation examines the mechanical properties of a newly developed anchoring technique (ligament fixation device = LFD) in regard to linear and maximum load, stiffness, creep, and long-term durability compared to single staples, double staples in belt buckle technique, and passing the ligament through an additional bone tunnel. The tests are carried out on cadaver knees and plastic bones under standardized conditions with the same artificial ligament in all experiments (Trevira hochfest). The LFD shows a linear load of 1866 N in cadaver knees and 1874 N in plastic bones. The stiffness is 68.3 N/mm respectively 51.9 N/mm, the elongation at 500 N load 12.7 mm respectively 10.9 mm. In the hysteresis tests with submaximum loads the ligament/LFD-unit lasts 8515 cycles in the plastic bone and 4431 cycles in the cadaver knee. These results are significantly superior to all other fixation techniques concerning linear load, stiffness and long-term durability. They permit aggressive functional treatment and immediate postoperative weight bearing of the operated knee.     

Rapid-staged strategy for concomitant critical carotid and left main coronary disease with left ventricular dysfunction: IABP use

Fascicle length, pennation angle, and tendon elongation of the human tibialis anterior were measured in vivo by ultrasonography. Subjects (n = 9) were requested to develop isometric dorsiflexion torque gradually up to maximal at the ankle joint angle of 20 degrees plantarflexion from the anatomic position. Fascicle length shortened from 90 +/- 7 to 76 +/- 7 (SE) mm, pennation angle increased from 10 +/- 1 to 12 +/- 1 degrees, and tendon elongation increased up to 15 +/- 2 mm with graded force development up to maximum. The tendon stiffness increased with increasing tendon force from 10 N/mm at 0-20 N to 32 N/mm at 240-260 N. Young's modulus increased from 157 MPa at 0-20 N to 530 MPa at 240-260 N. It can be concluded that, in isometric contractions of a human muscle, mechanical work, some of which is absorbed by the tendinous tissue, is generated by the shortening of muscle fibers and that ultrasonography can be used to determine the stiffness and Young's modulus for human tendons.     

Melatonin in palate tonsils with recurrent acute tonsillitis and tonsillar hypertrophy

In this study we present a method of monitoring the forces under the knees of preterm infants lying in the prone position. Dual force sensing resistor transducers, connected to optically-isolated amplifiers, were used to monitor the forces. A thermistor airflow sensor was used for the parallel monitoring of the respiratory signal. The measurements were made on ten preterm infants. The average forces were 0.51 and 0.50 N for the left and right knees, respectively. In the frequency domain, the basic harmonic of the force traces was 1.27 Hz approximately, corresponding to the respiratory rhythm. Additional, smaller harmonics, were detected in the force traces at 2.54 and 3.81 Hz. A rather notable power signal could also be seen around 0.1 Hz. The results obtained indicate that the system developed is highly sensitive for providing data on the amplitudes, periods and sequences of oscillations and symmetry of load bearing in preterm infants. Knowledge of the normal and abnormal reaction force patterns may assist in the early diagnosis of abnormal neurodevelopment.     

In situ calibration of miniature sensors implanted into the anterior cruciate ligament part I: strain measurements

The goals of this study were to (a) evaluate the differential variable reluctance transducer as an instrument for measuring tissue strain in the anteromedial band of the anterior cruciate ligament, (b) develop a series of calibration curves (for simple states of knee loading) from which resultant force in the ligament could be estimated from measured strain levels in the anteromedial band of the ligament, and (c) study the effects of knee flexion angle and mode of applied loading on output from the transducer. Thirteen fresh-frozen cadaveric knee specimens underwent mechanical isolation of a bone cap containing the tibial insertion of the anterior cruciate ligament and attachment of a load cell to measure resultant force in the ligament. The transducer (with barbed prongs) was inserted into the anteromedial band of the anterior cruciate ligament to record local elongation of the instrumented fibers as resultant force was generated in the ligament. A series of calibration curves (anteromedial bundle strain versus resultant force in the anterior cruciate ligament) were determined at selected knee flexion angles as external loads were applied to the knee. During passive knee extension, strain readings did not always follow the pattern of resultant force in the ligament; erratic strain readings were often measured beyond 20 degrees of flexion, where the anteromedial band was slack. For anterior tibial loading, the anteromedial band was a more active contributor to resultant ligament force beyond 45 degrees of flexion and was less active near full extension; mean resultant forces in the range of 150-200 N produced strain levels on the order of 3-4%. The anteromedial band was also active during application of internal tibial torque; mean resultant forces on the order of 180-220 N produced strains on the order of 2%. Resultant forces generated by varus moment were relatively low, and the anteromedial band was not always strained. Mean coefficients of variation for resultant force in the ligament (five repeated measurements) ranged between 0.038 and 0.111. Mean coefficients of variation for five repeated placements of the strain transducer in the same site ranged from 0.209 to 0.342. Insertion and removal of this transducer at the anteromedial band produced observable damage to the ligament. In our study, repeatable measurements were possible only if both prongs of the transducer were sutured to the ligament fibers.     

Effects of group discussion and guided patient care experience on nurses'' attitudes towards care of patients with AIDS

An in vivo study was carried out to determine if capacitive coupled electrical stimulation increased the rate of recovery of strength of regenerate bone produced as a result of lengthening by the Ilizarov technique. Thirty-four adult male beagles underwent a right tibial mid-diaphyseal corticotomy, followed by a 5-day delay, and then 21 days of lengthening (1 mm/day). At the start of the post-distraction period (day 27), stimulation (3-6.3 V peak to peak, 5-10 mA root-mean-square at 60 kHz) was applied for 28 days to one group. The nonstimulated group (n = 17) underwent a 28-day period with no stimulation. From each group, four tibiae were prepared for histology; both ends of the remaining bones were embedded in polymethylmethacrylate and tested in torsion (internal rotation at 4.7 degrees/sec) until failure. Statistically significant changes included a 37% lower maximum torque capacity and a 40% decrease in strain energy to failure in the stimulated group compared with the nonstimulated group. The findings are supported by measured trends to a lower modulus of rigidity (37% decrease) and a smaller percentage of active osteoid perimeter (20% decrease) for the stimulated group. The experimental data suggest that when this dose of capacitive coupled electrical stimulation is applied to the regenerating bone created during distraction osteogenesis, it delays the recovery of bone strength compared with an untreated control.     

Method for establishing and measuring in vivo forces in an anterior cruciate ligament composite graft: response to differing levels of load sharing in a goat model

In order to determine the appropriate load history for optimal remodeling of an anterior cruciate ligament graft, methods for establishing and measuring the graft force due to an external load could be set to a preselected value in in vivo are required. Our objectives with this study were to (a) develop a method in which the graft force due to an external load could be set to a preselected value in a living animal, (b) show that this force could be maintained after fixation, and (c) determine what happens to the forces after the animal has functioned for as long as 2 weeks postoperatively, when differing levels of load sharing between the segments had been set at surgery. The anterior cruciate ligament was reconstructed in 12 goats with use of a bone-patellar tendon-bone graft and a synthetic augmentation device. The forces in the graft segments were established, at the time of surgical fixation, with use of a force-setting technique. In five animals, the tendon segment was set to carry 90% of the total graft force; in the remaining seven animals, the augmentation segment was set to share 90% of the total graft force. Graft forces were measured, with the use of buckle transducers mounted extra-articularly over the anterior tibia, under a 67 N anterior tibial load at 60 degrees of knee flexion before and after fixation and at 2 weeks postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)