Biomechanical properties of the triceps surae muscle after limb lengthening

The hindlimb of New Zealand white rabbit was osteotomized and then slowly lengthened at a rate of 1 mm/day until a 2.0-cm gain in length was reached. The triceps surae muscle-tendon unit was then tested either with or without 2 months fixation for bony consolidation. After limb lengthening, the strain at peak load was decreased and the axial rigidity was increased significantly; but other biomechanical parameters such as peak load, maximal deformation at peak load, stiffness, and energy absorption before peak load did not show any significant difference. We conclude that healthy triceps surae muscle has a great potential to be lengthened despite the changes in intrinsic structural properties of the muscle. The change in the biomechanical properties occurred during the time of distraction and was not affected by the time of bony consolidation. RELEVANCE: As noted in this study, many biomechanical parameters of the triceps surae muscle were not affected after prolonged distraction. This fact suggested that the healthy muscle-tendon unit is not a main causative factor of joint contracture after limb lengthening. However, there were intrinsic changes in the structural properties of the triceps surae muscle. Equinus contracture after limb lengthening may be caused by the aggravated intrinsic structural changes of the injured or denervated scarred muscular tissue.     

Failure of stimulated skeletal muscle mainly contributed by passive force: an in vivo rabbit model

OBJECTIVE: To evaluate the role of active and passive muscle forces in the failure mechanism of stimulated muscle. DESIGN: An in vivo rabbit model. BACKGROUND: Eccentric contractions can result in a greater incidence of muscle injury. However, the relative role of the active and passive muscle force in the failure mechanism of the activated muscle is not well elucidated. METHODS: After anaesthesia, New Zealand white rabbits were fixed in a frame on a materials testing machine. The triceps surae muscle-tendon units were passively stretched to rupture with our without continuous nerve stimulation. The force and muscle length were simultaneously recorded. Active muscle force, passive muscle force, and ratio of the active to passive muscle were calculated and depicted against strain. RESULTS: The results showed that the mean maximal passive force of triceps surae muscle was 293.1 N at a strain of 38%. The mean peak active muscle force was 21.5 N at a strain of 21%. The ratio of active to passive muscle force reached its peak first, followed by the active muscle force, and then the passive muscle force. The ratio of active to passive muscle force at the peak total force was only 3.3%. CONCLUSIONS: The stimulated muscle can exert its maximal response at extreme physiological extension. Injury of the stimulated muscle is caused mainly by passive muscle force.     

The effect of cooling on muscle co-ordination in spasticity: assessment with the repetitive movement test

Purpose: Cooling muscles might produce a temporary reduction of spasticity. This study investigated muscle coordination in spasticity under the influence of cooling. Methods: A repetitive movement (RM-) test of the ankle was used, while measuring the angle and surface-electromyography (EMG) of the m. tibialis anterior and m. triceps surae. Ensemble averaging provided quantified measures of muscle activation. Sixteen patients with spasticity in their lower extremity due to stroke or spinal cord injury participated in the study. Physical examination and the RM-test was done before and after cooling the m. triceps surae for 20 minutes by coldpacks. Results: The results show that Achilles hyperreflexia and clonus were abolished in all, and all but one patient, respectively. The EMG of the m. triceps surae, acting as a prime mover, was increased (p 0.028). However, this improved muscle coordination resulted in just a slightly increased active range of motion (less than 2 degrees at p 0.049). Conclusion: Apparently, the increase in excitability of the alpha motoneuron pool in voluntary movements of patients with spasticity is not followed by an improvement in the ability to move.     

超声剪切波弹性成像在脑卒中患者小腿康复评定中的应用

目的 探讨超声剪切波弹性成像对脑卒中下肢运动障碍患者小腿三头肌和跟腱进行康复评定的价值。方法 2018年至2019年,脑卒中后单侧下肢运动障碍住院患者32例,于康复治疗前后,对患者双侧小腿三头肌和跟腱行超声二维测量和剪切波弹性成像检查,记录剪切波速度(SWV)以及跟腱(比目鱼肌肌腱)长度和厚度。结果 治疗前,患侧跟腱和小腿三头肌SWV较健侧增高(t > 2.426, P < 0.05);患侧跟腱长度较健侧显著增加( t = 11.801, P < 0.001);治疗后,患侧小腿三头肌SWV减低( t > 2.447, P < 0.05);患侧跟腱长度显著缩短( t = 8.577, P < 0.001)。 结论 康复治疗可降低脑卒中下肢运动障碍患者小腿三头肌肌张力。超声剪切波弹性成像可用于评价跟腱和小腿三头肌弹性特征,指导脑卒中康复。     

Biomechanical properties of muscle-tendon unit under high-speed passive stretch.

OBJECTIVE: The purpose of this study was to investigate the strain injury mechanisms of the Achilles muscle-tendon unit during high-speed passive stretch.DESIGN: The high-speed traction device consisted of an impactor which dropped freely to hit one end of a lever, transferring the impact energy to traction energy at the other end. A muscle-tendon unit was attached to the other end of the lever via a force link, and the elongation was recorded with a high-speed camera.BACKGROUND: The muscle-tendon unit is thought to act viscoelastically. It is generally strain rate dependent, exhibiting higher tensile stress at faster strain rates. However, previous studies of passive stretch in muscle-tendon units usually employed low strain rates.METHODS: 16 fresh Achilles muscle-tendon units were subjected to passive stretch at a test speed of 310 cm s(-1). The history of elongation and the traction force of the muscle-tendon unit during the elongation process were analyzed. RESULTS: The muscle-tendon units exhibited highly nonlinear mechanical behavior. Most of the elongation occurred in muscle and resulted in structural failure. Failure was not found in the tendon or muscle-tendon junction. Muscle fibers during stretching reached their maximum mechanical strength and then progressively ruptured. CONCLUSION: The strain rate is an important factor in strain injuries of the muscle-tendon unit due to passive stretch. The muscle is a good energy absorber; the rupture process can absorb a great deal of external energy and prevent complete failure of the muscle, while also protecting bone and joints.RELEVANCE: The study of muscle-tendon unit under high-speed stretch could help us to understand the mechanism of strain injuries over passive stretch in real-life situations.     

Triceps surae muscle-tendon unit mechanical property changes during 10 minutes of streching

ObjectiveTo verify the effect of 10-min static stretching on the triceps surae mechanical properties. Design: Quasi-experimental one-group pre test-post test study compared the time points of before, after, and minute by minute of one session of triceps surae passive static stretching.Methods15 participants performed a 10-min plantar flexor passive static stretching on the isokinetic dynamometer. We evaluated passive torque and myotendinous junction (MTJ) displacement before, minute by minute, and after the intervention. In contrast, we evaluated the range of motion (ROM), passive torque, MTJ displacement, and hysteresis before and after the intervention. Paired t-test compared pre and post-intervention time points. Passive torque and MTJ displacement in the minute-by-minute evaluations were compared by repeated measures one-way ANOVA with a Bonferroni post-hoc test.ResultsROM increased (effect size d = 0.56) and passive torque and muscle-tendon unit stiffness decreased (effect size d = 0.65 and d = 0.73, respectively) post-stretching. There was a reduction only in passive torque in the minute-by-minute evaluation, mainly at minutes five and seven.Conclusionspassive torque decreased over a 10-min static stretching session of the ankle plantar flexors, followed by a ROM increase and muscle-tendon unit, a stiffness decrease.     

Evaluation of triceps surae muscle length and resistance to passive lengthening in patients with acquired brain injury

OBJECTIVE: To examine changes in muscle length and resistance to passive lengthening in the triceps surae muscles in patients with recently acquired brain injury. BACKGROUND: Increased passive resistance in the triceps surae muscles is common following acquired brain injury. Adaptive shortening secondary to relative immobility, and increased stiffness due to rheologic changes within the musculo-tendinous unit, may be exacerbated by plantarflexor muscle overactivity related to the brain injury itself. DESIGN: Three variables representing resistance to passive lengthening and soleus muscle length were compared between subjects with recent brain injury and age matched normal controls. Comparison between limbs was made for subjects with unilateral neurological impairment. METHODS: Slow passive dorsiflexion stretches were performed using a computer controlled dynamometer. Muscle stiffness in the initial and latter portion of the range, and the angles achieved at torques of 5 and 10 N m were determined from torque-angle curves. Maximal ankle dorsiflexion with the knee flexed was considered to reflect soleus muscle length. RESULTS: Significant differences were demonstrated for all variables, except passive stiffness near the end of available range. The limb ipsilateral to unilateral brain injury differed from control limbs in that significantly less passive range of dorsiflexion was available and initial resistance to passive stretch was significantly less. CONCLUSIONS: The reduction in soleus muscle length evident in subjects with recent acquired brain injury, even in neurologically unaffected limbs, may reflect the influence of relative immobility. Although plantarflexor muscle overactivity was found to be associated with increased resistance to slow passive stretch, the mechanism was unable to be elucidated from these data. The limb ipsilateral to unilateral neurological impairment cannot be considered to be a 'normal' control for comparative purposes. RELEVANCE: Adaptive shortening and increased resistance to passive lengthening limit active ankle dorsiflexion, and alter ankle biomechanics. Tonic muscle overactivity has the potential to exacerbate these changes. Prophylactic management of inappropriate muscle activity and maintenance of muscle length may facilitate the achievement of rehabilitation goals and reduce subsequent disability following acquired brain injury.     

Preliminary comparison of the rupture of human and rabbit anterior cruciate ligaments

Objective. This study was aimed at examining ruptures of the human anterior cruciate ligaments by scanning electron microscopy and video imaging and comparing the appearance of the rupture surfaces with those from rabbit anterior cruciate ligaments.

Design. The specimens were tested to failure as femur-anterior cruciate ligament–tibia complexes using an Instron 8511 materials testing machine.

Background. Rupture of the anterior cruciate ligament is a major clinical problem, leading to instability of the knee joint. Due to the frequency and potential severity of the injuries, a need still exists for information on the biomechanical properties of ligaments under loading conditions, which occur at the time of trauma.

Methods. Four human femur-anterior cruciate ligament–tibia complexes were loaded to failure at a displacement rate of 0.008 m/s. Video recordings of the tests were used to study the progress of the ruptures and to compare the modes of failure of the ligaments. Scanning electron microscopy was employed to study the appearance of collagen fibres at the rupture surfaces.

Results. The modes of failure of the rabbit anterior cruciate ligament and appearance of the rupture surfaces were similar to those of the human anterior cruciate ligaments.

Conclusion. The rabbit anterior cruciate ligament provides a model for investigating failure of the human ligament during trauma.Relevance

The results will be of significance since most studies on ligaments are carried out on animal models with the intention of applying the deductions from the results to human ligaments. Examining the appearance of collagen fibres at these surfaces may help us to understand more about what actually happens during and after ligament rupture.     

Reflex and non-reflex elements of hypertonia in triceps surae muscles following acquired brain injury: implications for rehabilitation

Background : Following adult onset acquired brain injury, the triceps surae muscles tend to become shortened and exhibit increased resistance to passive lengthening; a phenomenon that has been termed 'hypertonia'. Spasticity (velocity dependent tonic reflex hyper-excitability) has traditionally been considered a major component of hypertonia. In addition, unmodulated descending excitatory influences on the alpha motorneurone pool may result in inappropriate or excessive muscle activity (dystonia). Non-reflex changes, secondary to the brain injury, and as a consequence of subsequent immobility, also take place in the passive and active elements of the muscle. These non-reflex changes affect the stiffness and extensibility of the musculo-tendinous unit. Atrophy of muscle fibres combines with collagen proliferation to produce increased muscle stiffness. This may be compounded by increased actin-myosin cross-bridge linkages, which are thought to be associated with reduced rates of cross-bridge detachment. Prolonged immobilization in a shortened position results in a loss of sarcomeres in series. Arthrogenic changes associated with disuse include remodelling of dense connective tissue and intra-articular adhesions. Conclusion : Decreased muscle extensibility may be exacerbated by muscle overactivity. Consideration of all of the potential factors contributing to hypertonia of the triceps surae muscle will assist clinicians to identify appropriate intervention strategies, which may facilitate better treatment outcomes.     

Influence of calcaneus angle and muscle forces on strain distribution in the human Achilles tendon

Background

Heterogeneous distribution of tendon strain is considered to contribute to the development of the Achilles tendon overuse injuries. Force distribution between the three portions of the triceps surae muscle and position of the calcaneus might affect the extent of strain differences within the Achilles tendon. Purpose of this study was to determine the effect of changes in force distribution within the triceps muscle and changes in calcaneus position on intratendinous strain distribution of the Achilles tendon.

Methods

Five cadaveric Achilles tendons including complete triceps surae and calcaneus were dissected. Specimens were mounted in a loading simulator allowing independent force application for the three parts of triceps muscle and changes calcaneus eversion and inversion position. Strain was determined in different aspects of the Achilles tendon.

Findings

Changes of calcaneus position resulted in intratendinous strain differences up to 15%, changes in force distribution within the triceps muscle resulted in strain differences up to 2.5%. Calcaneal eversion was connected to a higher degree of strain in medial tendon portions, while inversion increased strain in lateral tendon portions.

Interpretation

Medio-lateral, proximo-distal and dorsal–ventral distribution of tendon strain is rather influenced by kinematics of the subtalar joint than by muscular imbalances within the triceps muscle. Clinical movement analyses should focus on motion pattern combining rearfoot eversion with high Achilles tendon load. The results indicate that twist of the Achilles tendon fascicles seems of paramount importance in balancing tendon strain. To get more insight into the Achilles tendon injuries pathogenesis future research should focus on methods monitoring heterogeneous distribution of strain in vivo.