Passive knee muscle moment arms measured in vivo with MRI

Objective. To determine moment arm lengths from seven knee muscles and the patellar tendon. The knee muscles were the biceps femoris, semitendinosus, semimembranosus, gracilis, sartorius, and the lateral and medial gastrocnemius muscles.

Design. The moment arms were calculated based on MRI measurements.

Background. Moment arm lengths of different muscles with respect to the joint centre of rotation (CR) or the centre of the contact point between joint surfaces are necessary basic data for biomechanical models predicting joint load.

Methods. Ten male and seven female subjects participated. Using a 1.5 Tesla magnetic resonance imaging system, 3-dimensional coordinates of relevant points were recorded from a 3-D volume reconstruction of the right knee at knee flexion angles of 0, 30 and 60 °. Muscular moment arms were calculated in both the sagittal and frontal planes. The recordings were all made during passive mode, which means that no muscular contraction was performed.

Results. All muscles except the lateral gastrocnemius showed statistically significant differences (P < 0.05) of moment arm lengths between gender in the frontal plane. All muscles except biceps femoris and sartorius showed significant differences (P < 0.05) of moment arm lengths between gender in the sagittal plane. Most muscles also showed a linear or quadratic trend of changing moment arms with varying knee angle.

Conclusions. Our results indicate that for most biomechanical analyses involving knee muscles, gender- and angle-specific moment arms should be used.     

Passive insufficiency of two-joint shoulder muscles

This preliminary study examined the effects of full elbow flexion and full elbow extension on the end-point of active range of motion of shoulder flexion and shoulder extension respectively. The end-points were measured from lateral photographs of the right upper limbs of 30 men after they flexed and extended their shoulders with their elbows held in full flexion and full extension. Angular measurements showed that full elbow flexion limited shoulder flexion range of motion and that full elbow extension limited shoulder extension range of motion.

The results indicated that passive muscle insufficiency of active shoulder flexion and extension was probably brought about by lengthening the triceps brachii and the biceps brachii muscles respectively. Clinicians are encouraged to considerthis passive insufficiency when measuring range of motion of shoulderflexion and extension and when implementing therapeutic interventions.     

Relation between knee motion and ligament length patterns

Fifteen knee specimens were tested in a 6°-of-freedom test machine using quadriceps force to drive continuous flexion-extension motion. Ten of the knees were again tested following isolated transaction of the anterior cruciate ligament. From transducer outputs, three-dimensional motion was determined. Using biplanar radiography and bone sectioning, ligament insertion coordinates and joint surface geometry were determined and used to calculate ligament length ratios as a function of knee flexion. Consistent motion patterns were seen in all knees. The prominent aspects of motion were a 15° internal rotation and an 8.6 mm anterior displacement of the tibia with flexion from 0 to 120°. Anterior cruciate transaction resulted in abnormal and excessive anterior-posterior displacement in early flexion, but a return to normal in late flexion. The results indicated that under our test conditions the boundaries of anterior-posterior motion were determined primarily by the cruciate ligaments, but tibial rotation was not guided by the cruciate ligaments.     

Experimental determination of force—length relations of intact human gastrocnemius muscles

The purpose of this study was to determine force—length relations of intact human gastrocnemius muscles experimentally. Changes in maximal active isometric forces of the gastrocnemius muscle were calculated from resultant ankle joint moments of carefully executed maximal effort contractions at systematically changing knee and ankle joint configurations. Changes in muscle lengths were obtained using second-order polynomial regression equations that relate the length of the gastrocnemius muscle—tendon unit to knee and ankle joint angles. From these changes in muscle lengths, changes in muscle fibre lengths were estimated based on assumptions about fibre structure and series elastic properties. The results indicate that intact human gastrocnemius muscles operate on the ascending limb of the force—length relation, and that passive forces are minimal within a normal range of ankle and knee joint configurations.     

Comparison of the mechanical performance of three types of external fixators: linear, circular and hybrid

Different configurations of the Monticelli-Spinelli and Ilizarov external fixation systems were tested to define their mechanical properties. In five configurations the external fixator consisted of rings with tensioned wires (circular), while in one configuration two pairs of the tensioned wires and their correspondent ring were replaced by threaded pins (hybrid). Testing was performed in axial compression, bending and torsion. The results were compared to the characteristics of a selected linear fixator group. Both the circular and the hybrid configurations were non-linear in compression. In bending, circular fixators had a similar pattern in both anteroposterior and oblique loading directions. The bending load-displacement pattern for the hybrid fixators was similar to the linear fixators, higher stiffness in the plane of the pins. Torsion was linear for both circular and hybrid fixators, as for the linear fixators. By combination of wires and pins (hybrid configuration), the mechanical behaviour had characteristics from both linear and circular fixators. It is concluded that the three studied groups own different mechanical performance and can be considered as different types of fixators. While it has been demonstrated that osteogenesis can be achieved independently of the mechanical behaviour of the fixator, this study supports the suggestion that some complications can be related to the mechanical behaviour of the fixator.     

Ribcage compressibility in living subjects

The purpose of this study was to examine the responses of normal living subjects to the application of anteroposterior forces to the ribcage. Seventeen subjects aged between 25 and 37 years were tested during slow oscillatory loading while breath-holding at the end of a normal expiration. The mean stiffness coefficient was found to be 9.4 N mm⁻¹ ( 2.9) and the mean gradient of the force-strain relation was 1888 N ( 646). Comparison with previously published cadaver data indicates that the embalmed cadaver ribcage stiffness is in the order of three times stiffer than living subjects, while fresh cadavers showed comparable stiffness to living subjects.

A number of studies have used models to predict and understand the behaviour of the thoracic spine. Validation of the behaviour of models which include the thoracic spine and ribcage depends on comparison of model response predictions with observed responses of human subjects. The present study provides data on the anteroposterior compressibility of the ribcage of living subjects which may be suitable for use in model validation studies.     

Effect of directional symmetry on the torsion testing of paired long bones

Paired long bones (canine humeri) demonstrated no significant biomechanical difference between left and right limbs torsioned tested symmetrically (a) both internal: (b) both external or asymmetrically, (c) right internal/left external.     

Traumatic dislocation of the knee

Traumatic dislocation of the knee is an uncommon orthopedic injury affecting primarily young males who have been subjected to major trauma. The presentation may be subtle and the diagnosis is frequently overlooked. The high frequency of associated limb-threatening vascular injury mandates careful search for and aggressive treatment of this entity, as misdiagnosis of the knee injury or failure to pursue evaluation of the vascular status of the limb will result in a large number of potentially avoidable amputations.     

Annular bulge contours from an axial photogrammetric method

Objective. To determine the characteristic contour of annular bulge in the lumbar spine under compression using a non-contacting technique.

Design. Transverse bulge of the annulus in lumbar motion segments was measured from photographs taken through an acrylic load plate.

Background. Annular bulge is considered a potential factor in nerve root impingement. However, consensus is lacking regarding which annular region bulges most. Previous studies have relied on markers in discrete locations or on contacting techniques, both of which limit the accuracy of bulge measurements. Reporting of continuous contours around the periphery of the disc has been limited to individual cases; characteristic behavior derived from a statistical treatment of the data is unknown.

Methods. Sixteen lumbar discal motion segments were loaded to 2500 N in compression. Axial photographs were taken in the pre-loaded and loaded states and digitized with an effective accuracy of 0.05 mm at 5 ° intervals. The bulge was averaged over the sample of specimens at each interval to provide a mean-value plot in the transverse plane. Regional variations were evaluated statistically.

Results. It was found that the bulge was greatest posterolaterally (0.93 mm, SD 0.52 mm), and smallest anteriorly (0.37mm, SD 0.26 mm; corrected p < 0.05), with an average of all data points of 0.67 mm, SD 0.42 mm. The restraining influence of the posterior longitudinal ligament, while not statistically significant, was evident in magnified view of the bulge contour. These regional differences were greater in the lower than in the upper lumbar segments.

Conclusions. Herniation posterolaterally may be associated with relatively large annular bulge in that region, although normal bulge is only of the order of 1/100th the diameter of the disc.     

Quantifying the magnitude of torque physiotherapists apply when stretching the hamstring muscles of people with spinal cord injury

OBJECTIVE: To quantify the magnitude of stretch that physiotherapists apply to the hamstring muscles of people with spinal cord injury (SCI). DESIGN: Repeated-measures design. SETTING: SCI unit in Australia. PARTICIPANTS: Fifteen individuals with motor complete paraplegia or tetraplegia. INTERVENTION: Twelve physiotherapists manually administered a stretch to the hamstring muscles of each subject. The stretch was applied by flexing the hip with the knee extended.Main Outcome Measure: Applied hip flexor torque. RESULTS: Therapists applied median hip flexor torques of between 30 and 68Nm, although some torques were as large as 121Nm. The stretch applied by different therapists to any 1 subject varied as much as 40-fold. CONCLUSION: There is a large range of stretch torques provided by physiotherapists to patients with SCI. Some therapists provide stretch torques well in excess of those tolerated by individuals with intact sensation.     

Effect of elongation rate on the failure properties of the rabbit anterior cruciate ligament

The effect of elongation rate on the failure properties of the rabbit femuranterior crucicate ligament-tibia were investigated. Paired limbs were elongated to failure at rates of 0.0001 m s⁻¹ and 0.92 m s⁻¹. Two distinct types of tibial avulsion injury reflecting rate-dependent areas of weakness were noted. ‘Bony avulsions’ formed by the junction between cortical and trabecular bone comprised the predominant injury observed at the faster elongation rate. ‘Fibrous avulsions’ between the zones of mineralized fibrocartilage and bone occurred predominantly at the slower elongation rate. The faster rate significantly increased ultimate load (74%) and stiffness (615%) on average, relative to the slow rate. In contrast to what has been previously described, there was a significant decrease in failure deformation (79%) at the faster rate.     

Role of tectorial membrane in the stability of the upper cervical spine

The purpose of this in vitro experimental study was to determine the role of the tectorial membrane in providing stability to the upper cervical spine. Five fresh human cadaveric specimens from the occiput to C₃ were studied with a flexibility protocol: we applied the physiological moments of flexion, extension, right/left axial torques, and right/left lateral bendings (up to 1.5 N m), and recorded the ensuing three-dimensional intervertebral motions. Tests were performed in the intact state and then after transection of the tectorial membrane. This injury resulted in significant increases in flexion (6.7°, 28.4%) and axial rotation (5.9°, 7.8%) of C₀---C₁---C₂ complex. Flexion increased at both C₀---C₁ and C₀---C₂ joints, while axial rotation increased mainly at C₀---C₁ joint. There were minimal changes in lateral bending (2.3°, 8.0%) and no changes in extension (0.7°, 3.5%).     

Effect of torso position on arthrometric assessment of anterior knee laxity

The purpose of the study was to examine the effect of changes in torso position on arthrometric assessment of knee laxity. Anterior tibial translation (ATT) of 12 control and 12 ACL deficient subjects was assessed using a Dynamic Cruciate Tester during five maximal isometric knee extensions and five passive tests (240 N load) on the right and left knee in each of three torso positions: vertical, reclined, and supine. Electromyographic activity of rectus femoris, vastus lateralis, biceps femoris, and semimembranosus were sampled during arthrometric assessment. Results indicated there was no significant difference in mean ATT as a function of torso position. However, subjects demonstrated significantly greater hamstring activity when seated vertically compared to reclined or supine and significantly greater hamstring activity when reclined compared to supine.     

Effect of stretch positions on hamstring muscle length,lumbar flexion range of motion,and lumbar curvature in healthy adults

Hamstring stretching is a common practice in physical therapy to change not only hamstring muscle length (HML), but also lumbar flexion range of motion (LROM) or lumbar curvature (LC). Yet limited published research compares the effectiveness of two commonly used hamstring stretch positions, sitting and standing. The purposes of this study were to determine the effect of (1) stretch position on HML; and 2) HML on LROM and LC. Thirty-six participants (M=44.8 years, SD=17.1) with short HML (i.e., with shortness for men ≥45° and for women ≥24° of active knee flexion with 90° hip flexion) were measured for HML, LROM, and LC; randomly allocated to one of three groups: (1) hamstring stretching in sitting (SI); (2) standing (ST); or (3) no stretching (control); and remeasured after 4 weeks. Participants in the stretching groups performed two 30-second static stretches 4 days per week for 4 weeks. Multivariate analysis of covariance (MANCOVA) showed significance between the stretching groups and nonstretching group for HML only. Nonsignificance was shown for HML between the stretch positions (i.e., SI–active knee extension (AKE) and ST-AKE), indicating that both were equally effective for increasing HML. However, there was no change in LROM or in LC even though HML increased.     

Biomechanical changes in the low back following reduction mammaplasty surgery

Objective. To give evidence of the mechanical consequences of reduction mammaplasty (RM) on the low back.

Design. A repeated-measures analysis was implemented to test the effect of RM on the external loads and angular velocity of the back during both static and dynamic lifting tasks.

Background. Patient follow-up surveys have documented a decrease in the frequency of low back pain following RM, but there is no quantitative data regarding biomechanical changes following surgery.

Methods. Patients were evaluated before and 4–8 weeks following RM. Flexion moment, compression and shear forces at L3-L4 were quantified for isometric flexion angles between 0 and 40 °. External loads and angular velocities of the back were studied during rapid dynamic lifting tasks.

Results. Isometric external flexion moments at L3-L4 decreased following RM. RM did not effect the applied flexion moment in the lumbar spine, but a trend suggested that RM resulted in increased lifting velocity.

Conclusions. RM does act to reduce the loads on the lumbar spine during simple isometric tasks. During dynamic tasks, subjects may be able to lift faster without generating larger loads.     

Computed tomography-osteoaboorptiometry: a method of assessing the mechanical condition of the major joints in a living subject

A method of making a visual display of subchondral mineralization in the major synovial joints is described. Unlike existing procedures, it can be used on the living subject. A modified application of computed tomography-densitometry, computed tomography-osteoabsorptiometry makes it possible to explore the mechanical adaptability to the prevailing mechanical force. This claim is based upon the comparison of information obtained from 20 anatomical specimens with CT-osteoabsorptiometry and x-ray densitometry of sections; both methods yielding virtually identical results. The distribution of the subchondral density was then expressed as a map of the articular surface with the aid of an image analyser. This method can make a useful contribution to basic clinical research, as well as providing a diagnostic technique which can also be used for observing progress after a corrective osteotomy or any other procedure causing a change in mechanical function. Examples of its use on living patients are given.     

Box tilt and knee motions in manual lifting: two differential factors in expert and novice workers

Objective. It was the objective of this study to investigate the kinematic and kinetic effects of two specific handling factors that differentiate expert and novice workers, namely the level of knee flexion and box tilt.

Design. Seven inexperienced subjects were required to lift a 12-kg box in the sagittal plane using three different strategies: (1) reduced knee flexion and a backward box tilt (more typical of experts); (2) large knee flexion and a backward box tilt; (3) large knee flexion and no box tilt (more typical of novices).

Background. The lifting techniques of highly skilled workers differ substantially from those of novices but only limited information is available to compare their biomechanical differences.

Methods. The methods included dynamic segmental analyses to calculate the net moments at all body joints and a planar single-muscle equivalent to estimate compression loadings at L5/S1; total work and joint work distribution were calculated using the integration of joint power. The 3-D kinematic data were acquired with three video cameras and force data were obtained with one AMTI force platform which were synchronized with the film data.

Results. Box tilt reduced the load trajectory and loadings on the lower back and shoulders; a reduced knee flexion affected body posture and reduced mechanical work and loadings on all body joints. The combination of these two factors, box tilt and reduced knee flexion, showed added effects for almost all variables.

Conclusions. These two factors proper to experts were, in this context, biomechanically more advantageous.     

Adaptations in gait resulting from unilateral ischaemic block of the leg

The purpose of this study was to develop a major temporary perturbation to the peripheral neuromuscular system and to quantify the motor adaptations on the first gait strides taken after the perturbation becomes effective. A unilateral ischaemic block to the leg was induced by a cuff inflated to 200 mmHg; sensory block was evident after 15–20 min and total motor block after about 30 min. Electromyographs from seven muscles on each limb were recorded for the first 16s after walking commenced and were compared with electromyographs from cadence-matched strides recorded 30 min after the cuff was removed. Ensemble-averaged profiles of the ischaemic and control trials from six subjects showed that almost half of the non-ischaemic muscles (4 on the ischaemic limb and 7 on the intact limb) had significantly different profiles. Only two muscles showed consistent changes for all six subjects (gastrocnemius and rectus femoris of the intact limb).     

Comparison of cyclic loading and hold relax technique in increasing resting length of hamstring muscles

To evaluate and compare the effects of hold-relax technique and cyclic loading technique on increasing the resting length of hamstring muscles.

Design and Setting

This was a randomised intervention trial. The setting was an academic rehabilitation centre, which provided physical therapist assistant programs under the supervision of a biomechanics expert. Thirty-six healthy male subjects who exhibited bilateral hamstring muscle tightness (18–30 years of age) volunteered to participate in this study. For each subject, one leg was randomised to receive the hold-relax technique, whereas the other side received the cyclic loading technique. The treatment was applied every alternate day for 3 consecutive weeks. Stretching sessions were supervised by the biomechanics specialist. Measurements were taken before and after the 3-week treatment period by the same investigator, who was blindfolded to the allocation of treatment. The popliteal angle and stretch pain (measured by the visual analogue scale) were the two parameters considered. The analysis was done using the paired t tests. The results showed that both the hold relax and cyclic loading stretch produced significant difference in the popliteal angle and stretch pain (p < 0.001). In conclusion the hold relax and cyclic loading hamstring stretches have comparable effectiveness in improving flexibility. Both produced similar and significant results.     

Acute transverse myelitis in the emergency department: A case report and review of the literature

Acute transverse myelitis (ATM) is a neurologic condition that presents with bilateral lower extremity weakness and sensory loss associated with bowel and bladder dysfunction. Whereas the time of onset may be hours to days, the time to either partial or complete recovery may require months. The etiology is varied and may be idiopathic. Laboratory and radiographic evaluation may be nonrevealing. Corticosteriods have been used for treatment, but their efficacy is controversial. As illustrated by this case report, the essential aspect of the initial management of ATM is the elimination of potentially treatable causes.