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PubMed2006

Mechanomyographic and electromyographic responses to eccentric muscle contractions.

Little is known regarding the modulation of torque during eccentric muscle actions. Mechanomyographic (MMG) and electromyographic (EMG) signals have been used to examine motor control strategies. The purpose of this study was to examine the MMG and EMG amplitude and frequency in relation to torque during eccentric muscle contractions. Eight women performed eccentric leg extension muscle contractions at 10-100% of peak torque (PT). A piezoelectric crystal contact sensor and bipolar surface electrodes were placed on the vastus medialis to detect the MMG and EMG signals. Polynomial regression analyses indicated that EMG amplitude (r(2)=0.994) and MMG wavelet center frequency (CF) (r(2)=0.846) increased linearly to 100% eccentric PT, whereas there were no significant relationships for EMG wavelet CF or MMG amplitude and eccentric torque. These results suggested that eccentric torque is primarily modulated through changes in motor unit firing rate.

Adult↗
PubMed1997

Identification of time-varying stiffness dynamics of the human ankle joint during an imposed movement.

The time-varying stiffness dynamics of the human ankle joint were identified during a large stretch imposed upon the active triceps surae muscles. Small stochastic position perturbations were superimposed upon many repetitions of the larger movement and an ensemble time-varying identification technique was then used to characterize the relationship between the small perturbation and the torque it evoked at each sample in time throughout the movement. This technique was found to provide an excellent description of the ankle stiffness dynamics throughout this movement, with the identified stiffness impulse response functions accounting for more than 80% of the torque variance at all times. The average low-frequency stiffness values (K(low)) derived from the stiffness impulse responses at each sample in time are believed to reflect primarily the instantaneous elastic properties of active crossbridges. These properties, which reflect the contractile state of the muscles more directly than force or torque measurements, have not been obtained previously from an intact muscle-joint system. We found that stiffness actually increased during the later portion of the large imposed stretch, indicating the triceps surae muscles did not yield significantly, and that the post-stretch steady-state stiffness level was approximately 60% higher than prior to the stretch. Reflex activity evoked by the large stretch did not produce a detectable change in K(low), even though this activity did produce a clear twitch-like response in joint torque beginning approximately 60 ms following stretch onset. A second-order mechanical model was found to provide an adequate characterization of stiffness dynamics for steady-state periods before and well after the imposed movement, but it could not adequately describe the observed changes in stiffness dynamics during the movement itself. However, the variation of model parameters indicated that the torque evoked by the stochastic displacement was predominantly elastic in nature. The stiffness behavior during stretch observed here for the intact human ankle joint is largely consistent with previous studies performed in isolated muscle preparations.

Adult↗
PubMed1997

Anticipatory postural adjustments in stance and grip.

The reactive forces and torques associated with moving a hand-held object between two points are potentially destabilising, both for the object's position in the hand and for body posture. Previous work has demonstrated that there are increases in grip force ahead of arm motion that contribute to object stability in the hand. Other studies have shown that early postural adjustments in the legs and trunk minimise the potential perturbing effects on body posture of rapid voluntary arm movement. This paper documents the concurrent evolution of grip force and postural adjustments in anticipation of dynamic and static loads. Subjects held a manipulandum in precision grasp between thumb and index finger and pulled or pushed either a dynamic or a fixed load horizontally towards or away from the body (the grasp axis was orthogonal to the line of the load force). A force plate measured ground reaction torques, and force transducers in the manipulandum measured the load (tangential) and grip (normal) forces acting on the thumb and finger. In all conditions, increases in grip force and ground reaction torque preceded any detectable rise in load force. Rates of change of grip force and ground reaction torque were correlated, even after partialling out a common dependence on load force rate. Moreover, grip force and ground reaction torque rates at the onset of load force were correlated. These results imply the operation of motor planning processes that include anticipation of the dynamic consequences of voluntary action.

Adult↗
PubMed2001

A method to reduce the number of measured parameters when using isokinetic muscle strength as a clinical indicator in rheumatoid arthritis patients.

The aim of the study was to present a method enabling a reduction of the number of measurements when quantifying isokinetic muscle strength (IMS), and to describe an expression for IMS which is independent of measuring conditions. IMS is a measure of muscle strength used to categorise patients and to assess changes over time. IMS measurements involve one or several measures of peak torque at different chosen angular velocities. Comparisons between studies are difficult and an expression of IMS independent of measuring conditions is needed. Thirty-six women with rheumatoid arthritis were followed for 1 year. IMS was measured on five occasions on both knees at seven angular velocities, giving 10 sets of peak-torque data for each patient. The log[peak-torque]-angular-velocity diagram showed a linear relationship. From this, the peak-torque value at the chosen angular velocity of 30 degrees/s (IMS30) was estimated for each test and the uncertainties involved were quantified. IMS30 is a reliable parameter when comparing effort between knees, visits and patients, and may be based on three sets of data only. IMS may be expressed by a single value, IMS30, representing the fitted line in a log[peak-torque]-angular-velocity diagram. The regression line may be fitted by three or more angular velocities. In principle, IMS30 is independent of the chosen angular velocity, which makes it possible to use an estimated value as IMS30 to compare results, studies and centres in between.

Arthritis, Rheumatoid↗
PubMed2000

Different effects of strenuous eccentric exercise on the accumulation of neutrophils in muscle in women and men.

The purpose of this study was to evaluate the sex differences in delayed onset muscle soreness (DOMS), torque, and accumulation of technetium-99m (Tc-99m) neutrophils in eccentric-exercised muscle. A group of 10 female and 12 male subjects took part in this study. The subjects completed a pre-test using the descriptor differential scale (DDS) to describe DOMS, and tests of concentric and eccentric torque of the right quadriceps. A volume of 100 ml of blood was taken by venipuncture for neutrophil labelling in the early morning of the exercise day. The Tc-99m neutrophils were re-infused intravenously before the eccentric exercise. The exercise stimulus consisted of 300 eccentric repetitions of the right quadriceps muscles. Radionuclide images of both quadriceps muscles (lateral views) were taken at 2 and 4 h. The DDS, and concentric and eccentric torques of the quadriceps were subsequently evaluated at 0 h, 2, 4, 20 and 24 h post-exercise. The presence of Tc-99m neutrophils was greater in the exercised leg than the non-exercised leg at 2 and 4 h post-exercise (P </= 0.013) and greater in the exercised leg of the women compared to the men at 2 h (P = 0.03). The DOMS had increased post-exercise (P < 0.001) and torque had decreased post-exercise (P </= 0.002) but the patterns were different between the sexes. We concluded that the sex influences the presence of Tc-99m neutrophils in the exercised muscle following eccentric exercise. In addition, different patterns of DOMS and torque were observed between the sexes after eccentric exercise, and require further investigation.

Adult↗
PubMed2004

Target-dependent differences between free and constrained arm movements in chronic hemiparesis.

This study compares the kinematic and kinetic characteristics of constrained and free upper limb movements in eight subjects with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in five control subjects. Rapid movements were performed in the horizontal plane from a central starting point to five targets located to require various combinations of flexion/extension rotations at the elbow and shoulder. Support of the upper limb against gravity loading was provided either by a low-friction air-bearing apparatus (constrained condition) or by voluntary generation of abduction and external rotation torques at the shoulder (free condition). Data analysis focused on the peak joint torques generated during the acceleratory phase of movement, and on the net change in joint angles at the elbow and shoulder. We found that movement parameters were broadly invariant with support condition for either limb of control subjects, as well as for the nonparetic limb of hemiparetic subjects. In contrast, support condition had a target-dependent effect on movements of the paretic limb. Relative to the constrained condition, peak torques for free arm movements were significantly reduced for distal targets requiring elbow extension and/or shoulder flexion torques. However, peak elbow flexion and shoulder extension joint torques for proximal targets were relatively unaffected by support condition. Of perhaps more functional importance, free movements were characterized by a target-dependent restriction in the hand's work area that reflected a reduced range of active elbow extension, relative to constrained movements. The target-dependent effects of support condition on movements of the paretic limb are consistent with the existence of abnormal constraints on muscle activation patterns in subjects with chronic hemiparesis, namely an abnormal linkage between activation of the elbow flexors and shoulder extensors, abductors, and external rotators.

Acceleration↗
PubMed2001

The development of balance control in children: comparisons of EMG and kinetic variables and chronological and developmental groupings.

This cross-sectional study examined electromyographic (EMG) and kinetic variables during reactive balance responses in children grouped according to developmental level as compared with chronological age. Purposes were to explore relationships between the two types of variables and the effectiveness of the two grouping methods. Forty-four children between 9 months and 10 years old were tested for reactive balance control on a moveable platform. Surface electrodes measured EMG activity in the gastrocnemius (GA), hamstrings (HA), paraspinals (PS), tibialis anterior (TA), quadriceps (QA), and abdominal (AB) muscles. Timing and distance of center-of-pressure (COP) movements and peak muscle torques at the ankle, knee, and hip were also examined. Significant relationships and group differences were found between postural muscle activity and both the torque generated in the lower limbs and the timing and distance of COP adjustments employed to restabilize balance. As postural muscle activity increased and became more coordinated in timing, peak torque at the ankle and hip also increased, while the distance of and time to complete COP readjustments decreased. Children in younger/developmentally lower groups had smaller-magnitude and less-synergic muscle activity, lower peak torques, longer times to restabilize the COP, and greater COP paths than older/higher developmental groupings. Grouping by developmental level produced more statistical differences than did grouping by age. The correspondence of GA, HA, and PS muscle activity with COP measures and joint peak torques confirms that these muscles are key contributors to the balance synergy correcting for induced forward sway. Additionally, developmental level appears to be a much better predictor of balance improvement than chronological age.

Age Factors↗
PubMed2001

The effect of muscle length on motor-unit recruitment during isometric plantar flexion in humans.

The triceps surae muscle group, consisting of the mono-articular soleus (SOL) and bi-articular gastrocnemius (GAS) muscles, primarily generates plantar flexor torque. Since the GAS muscle crosses the knee joint, flexion of the knee reduces the length of this muscle, thus limiting its contribution to torque output. However, it is not clearly understood how the central nervous system activates muscles that are at inefficient or non-optimal force-producing lengths. Therefore, the present study was designed to determine the effect of muscle length on motor-unit recruitment in the medial GAS muscle. Single motor-unit activity was recorded from the medial GAS muscle while electromyographic (EMG) activity was recorded from the SOL muscle in nine male subjects. With the ankle angle held constant at 90 degrees, the knee angle was changed from 180 degrees to 90 degrees, corresponding to a long and short GAS muscle length, respectively. Levels of voluntary plantar flexor torque were produced at a rate of 2 Nm.s-1 until motor-unit activity was detected. A total of 229 motor units were recorded, of which 121 and 108 were obtained at the long and short muscle lengths, respectively. At the short length, onset of motor-unit activity occurred at significantly higher levels of plantar flexor torque and SOL EMG. Onset of motor-unit activity occurred at 2.97 +/- 7.78 Nm and 32.14 +/- 10.25 Nm, corresponding to 0.045 +/- 0.075 mV and 0.231 +/- 0.129 mV of SOL EMG in the long and short positions, respectively. No individual GAS motor unit could be recorded at both muscle lengths. Motor units in the shortened GAS muscle may be influenced by peripheral afferents capable of reducing the excitability of the motoneurone pool. This may also reflect a specific inhibition of motor units having shortened, non-optimal fascicle lengths, and they are thereby incapable of contributing to plantar flexor torque.

Action Potentials↗
PubMed1998

Hierarchical control of different elbow-wrist coordination patterns.

The present paper focused on the role of mechanical factors arising from the multijoint structure of the musculoskeletal system and their use in the control of different patterns of cyclical elbow-wrist movements. Across five levels of cycling frequency (from 0.45 Hz up to 3.05 Hz), three movement patterns were analyzed: (1) unidirectional, including rotations at the elbow and wrist in the same direction; (2) bidirectional, with rotation at the joints in opposite directions, and (3) free-wrist pattern, which is characterized by alternating flexions and extensions at the elbow with the wrist relaxed. Angular position of both joints and electromyographic activity of biceps, triceps, the wrist flexor, and the wrist extensor were recorded. It was demonstrated that control at the elbow was principally different from control at the wrist. Elbow control in all three patterns was similar to that typically observed during single-joint movements: elbow accelerations-decelerations resulted from alternating activity of the elbow flexor and extensor and were largely independent of wrist motion at all frequency plateaus. The elbow muscles were responsible not only for the elbow movement, but also for the generation of interactive torques that played an important role in wrist control. There were two types of interactive torques exerted at the wrist: inertial torque arising from elbow motion and restraining torque arising from physical limits imposed on wrist rotation. These interactive torques were the primary source of wrist motion, whereas the main function of wrist-muscle activity was to intervene with the interactive effects and to adjust the wrist movement to comply with the required coordination pattern. The unidirectional pattern was more in agreement with interactive effects than the bidirectional pattern, thus causing their differential difficulty at moderate cycle frequencies. When cycling frequency was further increased, both the unidirectional and bidirectional movements lost their individual features and acquired features of the free-wrist pattern. The deterioration of the controlled patterns at high cycling frequencies suggests a crucial role for proprioceptive information in wrist control. These results are supportive of a hierarchical organization of control with respect to elbow-wrist coordination, during which the functions of control at the elbow and wrist are principally different: the elbow muscles generate movement of the whole linkage and the wrist muscles produce corrections of the movement necessary to fulfill the task.

Elbow Joint↗
PubMed1999

Forearm postural control during unloading: anticipatory changes in elbow stiffness.

In this study, the equilibrium-point hypothesis of muscle-torque generation is used to evaluate the changes in central control parameters in the process of postural-maintenance learning. Muscle torque is described by a linear spring equation with modifiable stiffness, viscosity, and equilibrium angle. The stiffness is considered to be the estimation of the central command for antagonist-muscle coactivation and the equilibrium angle to be the estimation of the reciprocal command for a shift of invariant characteristics of the joint. In the experiments, a load applied to the forearm was released. The subjects were instructed to maintain their forearm in the initial horizontal position. Five sessions of approximately twenty trials each were carried out by eight subjects. During two "control" series, the load release was triggered by the experimenter. During three "learning" series, the load supported by one forearm was released by the subject's other hand. The elbow-joint angle, the angular acceleration, and the external load on the postural forearm were recorded. These recordings as well as anthropometric forearm characteristics were used to calculate the elbow-joint torque (which we called "experimental"). Linear regression analysis was performed to evaluate the equilibrium angle, joint stiffness, and viscosity at each trial. The "theoretical" torque was calculated using a linear spring equation with the found parameters. The good agreement observed between experimental and theoretical joint-torque time courses, apart from the very early period following unloading, argues in favor of the idea that the movement was mainly performed under a constant central command presetting the joint stiffness and the equilibrium angle. An overall increase in the stiffness occurred simultaneously with a decrease in the equilibrium angle during the "learning" series in all the subjects. This suggests that subjects learn to compensate for the disturbing effects of unloading by increasing the joint stiffness. The mechanism possibly responsible for the presetting of the central control parameters is discussed.

Cognition↗
PubMed2004

Functional recovery of the plantarflexor muscle group after hindlimb unloading in the rat.

Research into skeletal muscle's response to hindlimb unloading (HU) of the rodent has focused on that of the markedly affected slow-twitch anti-gravity muscles (e.g., soleus). However, the ability of the animal to locomote following HU should be best determined by the in vivo functional properties of the muscle groups involved and, to our knowledge, this has not been investigated. Our objective was to determine how the in vivo functional properties of the rat ankle plantarflexor group change after 28 days of HU and during a subsequent 28-day recovery. Rats ( n=48) were unloaded for 28 days after which they were either tested immediately or allowed to recover for 7, 14, or 28 days before being tested. Control rats ( n=61) were tested at comparable times. In vivo functional properties of the ankle plantarflexors were assessed under anesthesia using an isokinetic dynamometer and included determination of the isometric torque-frequency relationship, the concentric torque-ankle angular velocity relationship, and fatigability. Immediately after HU, plantarflexor muscle weight was reduced by 24% but isometric torque production was reduced by 7-9% only at > or =100 Hz and concentric torque production was not significantly affected. However, after 7 days of recovery, in vivo function was more adversely affected; isometric and concentric torques were reduced by 12-33% and 16-36%, respectively, relative to control levels. In vivo plantarflexor function was recovered by 14 days. In conclusion, 28 days of HU has minor adverse effects on the in vivo function of the rat ankle plantarflexors. During the first week of recovery from HU, injury apparently occurs to the plantarflexors resulting in a transient impairment of functional capacity.

Animals↗
PubMed2005

Morning to evening changes in the electrical and mechanical properties of human soleus motor units activated by H reflex and M wave.

The aim of the present study was to compare the relative contribution of the soleus motor units (MUs) activated by H and M waves to the plantar-flexion torque in the morning and in the evening. Twelve healthy male subjects (physical education students) took part in this investigation. The electromechanical properties of the plantar flexor muscles were recorded at two different times of day: between 06:00 and 08:00 h and between 17:00 and 19:00 h. Plantar-flexion torque and concomitant electromyographic activity of soleus muscle were assessed under voluntary and evoked conditions. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae and associated soleus EMG in the evening as compared with the morning. The mean values of MVC ranged from 131.6+/-9.6 N m in the morning to 125.1+/-9.0 N m in the evening. Peak-to-peak values of soleus H (max) and M (max) potentials were comparable in the morning and in the evening (2.97 vs 3.18 mV and 7.95 vs 7.44 mV for H (max) and M (max), respectively). The H (max)/M (max) ratio was not modified between the two experimental test sessions (34.8 vs 41.3%). The peak amplitude of the twitch produced by the H (max) wave (Pt (H max)) decreased significantly. When estimating the mechanical contribution to (Pt (H max)) of the slowest and fastest-twitch MUs reflexively and directly activated, we observed that the contribution of the slowest MUs did not change while those of the fastest decreased significantly in the evening. To conclude, a weaker reflex twitch torque caused by higher fatigue state of the MUs directly activated by the M wave which accompanied H (max) in the evening may be regarded as a possible explanation of the weaker plantar-flexion torque production in the evening.

Adult↗
PubMed2006

Effects of neuromuscular electrical stimulation parameters on specific tension.

This study examined the effects of altering surface neuromuscular electrical stimulation (SNMES) parameters on the specific tension of the quadriceps femoris muscle. Seven able-bodied subjects had magnetic resonance images taken of both thighs prior to and immediately after four SNMES protocols to determine the activated muscle cross-sectional area (CSA). The four protocols were: (1) research (RES, 100 Hz, 450 micros, and amplitude set to evoke 75% of maximal voluntary isometric torque, MVIT); (2) pulse duration (PD, 100 Hz, 150 micros, same current as in RES); (3) frequency (FREQ, 25 Hz, 450 micros, and same current as in RES); (4) amplitude (AMP, 100 Hz, 450 mus, and current set to evoke the average of the initial torques of PD and FREQ, 45 +/- 9% of MVIT). Reducing the amplitude of the current from 75 to 45% of MVIT did not alter specific tension, 25 +/- 8 N/cm2, suggesting that the amplitude probably affects torque and the area of activated muscle proportionally. Shortening the pulse duration from 450 to 150 micros caused specific tension to drop from 25 +/- 6 to 20 +/- 6 N/cm2 (P < 0.05), indicating that pulse duration increased torque and the activated CSA disproportionally. Alternatively, reducing the frequency from 100 to 25 Hz decreased specific tension from 25 +/- 6 to 17 +/- 4 N/cm2 (P < 0.05), suggesting that the frequency increased torque without affecting the activated CSA. Clinicians who administer SNMES should be aware of the magnitude of adaptations to a given amplitude, pulse duration, and frequency.

Adult↗
PubMed2001

Is passive stiffness in human muscles related to the elasticity of tendon structures?

The purpose of this study was to examine in vivo whether passive stiffness in human muscles was related to the elasticity of tendon structures and to performance during stretch-shortening cycle exercise. Passive torque of plantar flexor muscles was measured during passive stretch from 90 degrees (anatomical position) to 65 degrees of dorsiflexion at a constant velocity of 5 degrees.s-1. The slope of the linear portion of the passive torque-angle curve during stretching was defined as the passive stiffness of the muscle. The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured using ultrasonography during ramp isometric plantar flexion up to the voluntary maximum. The relationship between the estimated muscle force of MG and tendon elongation was fitted to a linear regression, the slope of which was defined as the stiffness of the tendon. In addition, the dynamic torques during maximal voluntary concentric plantar flexion with and without prior eccentric contraction were determined at a constant velocity of 120 degrees.s-1. There were no significant correlations between passive stiffness and either the tendon stiffness (r = 0.19, P > 0.05) or the relative increase in torque with prior eccentric contraction (r = -0.19, P > 0.05). However, tendon stiffness was negatively correlated to the relative increase in torque output (r = -0.42, P < 0.05). The present results suggested that passive stiffness was independent of the elasticity of tendon structures, and had no favourable effect on the muscle performance during stretch-shortening cycle exercise.

Adult↗
PubMed2001

Motor impairment in the human hand following eccentric exercise.

Motor impairment was induced by having subjects perform two sets of 50 maximal contractions, using the first dorsal interosseus (FDI) muscle to abduct the index finger, while the muscle was being stretched. Tests were conducted prior to the exercise (pre-exercise) and 24 h following the exercise (post-exercise). There were declines of 19% in maximal abduction torque and 15% in maximal flexion torque at the metacarpaphalangeal joint, during isometric contraction post-exercise compared to pre-exercise. The ability to stabilize the metacarpophalangeal joint about the abduction/adduction axis was reduced by 14% post-exercise, and the variability in tracking an isometric torque target increased by 30%. There was a decrement of 7%-10% in the median frequency of the power density spectrum of FDI electromyogram (EMG) throughout a 60 s maintained abduction at 50% maximal voluntary contraction. The mean rectified EMG, on the other hand, increased by 100%-175% for torque levels below 40% of maximal voluntary contraction, post-exercise. The results were consistent with preferential injury of type II muscle fibres in FDI. Although non-exercised synergist muscles appeared to be inhibited during maximal voluntary flexion, there was evidence that they compensated for injured FDI muscle fibres during maintained contraction at sub-maximal flexion torque.

Adult↗
PubMed2000

Accurate assessment of in situ isometric contractile properties of hindlimb plantar and dorsal flexor muscle complex of intact mice.

An isometric torque sensor for measuring in situ contractions of plantar or dorsal flexors of intact mouse hindlimb has been developed and evaluated. With this device, muscle torque can be accurately measured within the range of -14 mN.m to +14 mN.m. Special attention was paid to fixation of the mouse hindlimb to the measurement device. Halothane-anaesthetized Swiss wild-type mice were positioned on the thermostatic measurement platform, and fixated with a hip and foot fixation system. The novel fixation unit was evaluated by measuring knee and ankle displacements during a contraction. A mathematical muscle model was used to quantify the effects of these displacements on the contractile parameters. Measured ankle and knee displacement, due to non-absolute fixation. resulted in a calculated muscle fibre shortening of 2.5%. Simulations of a contraction with this degree of fibre shortening, using the mathematical muscle model, showed only minor effects on maximal torque generation and the temporal parameters (half-relaxation time and 10-50% rise time). Furthermore, we showed that muscle torque in our set-up is hardly affected by eccentricity between ankle and measurement axis. Measured tetanic muscle torques of intact dorsal and plantar flexors were 3.2+/-0.4 mN.m and 11.8+/-1.6 mN.m, respectively. The half-relaxation time of plantar flexors was significantly higher than that of dorsal flexors (12.9+/-2.7 ms versus 8.8+/-1.2 ms), whereas the 10-50% rise time was longer in plantar (14.9+/-0.6 ms) than in dorsal (11.8+/-2.0 ms) flexors.

Animals↗
PubMed2002

Coordination of the anterior and posterior cruciate ligaments in constraining the varus-valgus and internal-external rotatory instability of the knee.

Tension along both cruciate ligaments was measured simultaneously under various loading conditions, and the interaction of these ligaments as constraints on knee instability was analyzed. Six fresh cadaveric knees were used. The attachments for both cruciate ligaments were detached from the femur and reattached to their original positions using metal plates equipped with 12 strain gauges. Each knee was moved under various loading conditions, and changes in tension along the cruciate ligaments were recorded simultaneously using the output of the strain gauges. Under varus torque, tension along the anterior cruciate ligament increased near full extension whereas that along the posterior cruciate ligament increased near 90 degrees of flexion. Similar results were obtained under valgus torque. Under internal rotatory torque, a pattern similar to that under varus torque was also observed. Under external rotatory torque, no remarkable changes in tension were observed along either cruciate ligament. Thus, we conclude that both the anterior cruciate ligament and the posterior cruciate ligament cooperate to control varus-valgus and internal rotatory instabilities of the knee, and that the constraining function is transferred from the anterior cruciate ligament to the posterior cruciate ligament as the knee joint is flexed.

Adult↗
PubMed2005

Dental fracture risk of metal vs plastic laryngoscope blades in dental models.

BACKGROUND: Dental fracture is a complication of laryngoscopy and endotracheal intubation. PURPOSE: The purpose of this study is to compare the potential fracture rates in dental models using metal laryngoscope blades with those using plastic laryngoscope blades. METHODS: Size 3 Macintosh plastic and metal laryngoscope blades were applied against 4 different dental model materials at varying torques to determine when the dental model material would fracture. RESULTS: The plastic blade did not fracture any of the dental model materials. The metal blade fractured the glass dental model material even at the lowest torque setting. At a moderate torque setting, the plastic blade showed evidence of structural failure, whereas the metal blade did not fail at any torque setting. Fracture of wooden dowel and ceramic teeth model materials occurred with the metal blade but only at torque settings higher than what the plastic blade could achieve. CONCLUSION: Based on the dental fracture models studied, plastic laryngoscope blades have a lower potential for dental fracture compared with metal blades. Plastic laryngoscope blades would be best suited for trainees performing routine intubations under direct supervision. Metal blades would be more advantageous in difficult intubations preferably done by experienced intubators.

Equipment Design↗