Spastic muscle properties are affected by length changes of adjacent structures

Effect of prone trunk-extension on lumbar and lower limb muscle stiffness

This study investigated the effect of the prone trunk extension test (PTE) on lumbar and lower limb muscle stiffness to explore the optimal angle for lumbar muscle training, understand the peripheral muscle force transmission effect, and determine the modulation strategy and interaction mode of different muscles during PTE. Twenty healthy young females were recruited for this study, and the stiffness of the erector spinae (ES), semitendinosus (ST), biceps femoris (BF), medial head of the gastrocnemius (MG), and lateral head of the gastrocnemius (LG) was measured by MyotonPRO under four angular PTE conditions (0° horizontal position, 10°, 20°, and 30°). With the increasing angle, the stiffness of ES decreased gradually, while ST and BF increased first and then decreased. The stiffness of MG and LG increased first, then decreased, then increased. There was a moderate to strong negative correlation between ES stiffness variation and ST (r = -0.819 to -0.728, p < 0.001), BF (r = -0.620 to -0.527, p < 0.05), MG (r = -788 to -0.611, p < 0.01), and LG (r = -0.616 to -0.450, p < 0.05). Horizontal PTE maximizes the activation of ES. There is a tension transfer between the ES, hamstrings, and gastrocnemius, mainly between the ES, ST, and LG. The study provides data to explore the effect of peripheral muscle force transmission and the modulation strategies of different muscles during trunk extension.

Significance of epimuscular myofascial force transmission under passive muscle conditions

In the past 20 yr, force transmission via connective tissue linkages at the muscle belly surface, called epimuscular myofascial force transmission, has been studied extensively. In this article, the effects of epimuscular linkages under passive muscle conditions are reviewed. Several animal studies that included direct (invasive) measurements of force transmission have shown that different connective tissue structures serve as an epimuscular pathway and that these tissues have sufficient stiffness, especially at supraphysiological muscle lengths and relative positions, to transmit substantial passive forces (up to 15% of active optimal force). Exact values of lumped tissue stiffness for different connective tissue structures have not yet been estimated. Experiments using various imaging techniques (ultrasound, MRI, shear wave elastography) have yielded some, but weak, evidence of epimuscular myofascial force transmission for passive muscles in humans. At this point, the functional consequences of epimuscular pathways for muscle and joint mechanics in the intact body are still unknown. Potentially, however, these pathways may affect sensory feedback and, thereby, neuromuscular control. In addition, altered epimuscular force transmission in pathological conditions may also contribute to changes in passive range of joint motion.

Minimal force transmission between human thumb and index finger muscles under passive conditions

It has been hypothesized that force can be transmitted between adjacent muscles. Intermuscle force transmission violates the assumption that muscles act in mechanical isolation, and implies that predictions from biomechanical models are in error due to mechanical interactions between muscles, but the functional relevance of intermuscle force transmission is unclear. To investigate intermuscle force transmission between human flexor pollicis longus and the index finger part of flexor digitorum profundus, we compared finger flexion force produced by passive thumb flexion after one of three conditioning protocols: passive thumb flexion-extension cycling, thumb flexion maximal voluntary contraction (MVC), and thumb extension stretch. Finger flexion force increased after all three conditions. Compared to passive thumb flexion-extension cycling, change in finger flexion force was less after thumb extension stretch (mean difference 0.028 N, 95% CI 0.005 to 0.051 N), but not after thumb flexion MVC (0.007 N, 95% CI -0.020 to 0.033 N). As muscle conditioning changed finger flexion force produced by passive thumb flexion, the change in force is likely due to intermuscle force transmission. Thus, intermuscle force transmission resulting from passive stretch of an adjacent muscle is probably small enough to be ignored.

Altered mechanical interaction between rat plantar flexors due to changes in intermuscular connectivity

Connective tissue formation following muscle injury and remedial surgery may involve changes in the stiffness and configuration of the connective tissues linking adjacent muscles. We investigated changes in mechanical interaction of muscles by implanting either a tissue-integrating mesh (n = 8) or an adhesion barrier (n = 8) to respectively increase or decrease the intermuscular connectivity between soleus muscle (SO) and the lateral gastrocnemius and plantaris complex (LG+PL) of the rat. As a measure of mechanical interaction, changes in SO tendon forces and proximal-distal LG+PL force differences in response to lengthening LG+PL proximally were assessed 1 and 2 weeks post-surgery. The extent of mechanical interaction was doubled 1 week post-implantation of the tissue-integrating mesh compared to an unaffected compartment (n = 8), and was more than four times higher 2 weeks post-surgery. This was found only for maximally activated muscles, but not when passive. Implanting the adhesion barrier did not result in a reduction of the mechanical interaction between these muscles. Our findings indicate that the ratio of force transmitted via myofascial, rather than myotendinous pathways, can increase substantially when the connectivity between muscles is enhanced. This improves our understanding of the consequences of connective tissue formation at the muscle boundary on skeletal muscle function.

Significant mechanical interactions at physiological lengths and relative positions of rat plantar flexors

In situ studies involving supraphysiological muscle lengths and relative positions have shown that connective tissue linkages connecting adjacent muscles can transmit substantial forces, but the physiological significance is still subject to debate. The present study investigates effects of such epimuscular myofascial force transmission in the rat calf muscles. Unlike previous approaches, we quantified the mechanical interaction between the soleus (SO) and the lateral gastrocnemius and plantaris complex (LG+PL) applying a set of muscle lengths and relative positions corresponding to the range of knee and ankle angles occurring during normal movements. In nine deeply anesthetized Wistar rats, the superficial posterior crural compartment was exposed, and distal and proximal tendons of LG+PL and the distal SO tendon were severed and connected to force transducers. The target muscles were excited simultaneously. We found that SO active and passive tendon force was substantially affected by proximally lengthening of LG+PL mimicking knee extension (10% and 0.8% of maximal active SO force, respectively; P < 0.05). Moreover, SO relative position significantly changed the LG+PL length-force relationship, resulting in nonunique values for passive slack-length and optimum-length estimates. We conclude that also, for physiological muscle conditions, isometric force of rat triceps surae muscles is determined by its muscle-tendon unit length as well as by the length and relative position of its synergists. This has implications for understanding the neuromechanics of skeletal muscle in normal and pathological conditions, as well as for studies relying on the assumption that muscles act as independent force actuators.

Is ankle contracture after stroke due to abnormal intermuscular force transmission?

Contracture after stroke could be due to abnormal mechanical interactions between muscles. This study examined if ankle plantarflexor muscle contracture after stroke is due to abnormal force transmission between the gastrocnemius and soleus muscles. Muscle fascicle lengths were measured from ultrasound images of soleus muscles in five subjects with stroke and ankle contracture and six able-bodied subjects. Changes in soleus fascicle length or pennation during passive knee extension at fixed ankle angle were assumed to indicate intermuscular force transmission. Changes in soleus fascicle length or pennation were adjusted for changes in ankle motion. Subjects with stroke had significant ankle contracture. After adjustment for ankle motion, 9 of 11 subjects demonstrated small changes in soleus fascicle length with knee extension, suggestive of intermuscular force transmission. However, the small changes in fascicle length may have been artifacts caused by movement of the ultrasound transducers. There were no systematic differences in change in fascicle length (median between-group difference adjusting for ankle motion = -0.01, 95% CI -0.26-0.08 mm/degree of knee extension) or pennation (-0.05, 95% CI -0.15-0.07 degree/ degree of knee extension). This suggests ankle contractures after stroke were not due to abnormal (systematically increased or decreased) intermuscular force transmission between the gastrocnemius and soleus.

Muscle-specific changes in length-force characteristics of the calf muscles in the spastic Han-Wistar rat

The purpose of the present study was to investigate muscle mechanical properties and mechanical interaction between muscles in the lower hindlimb of the spastic mutant rat. Length-force characteristics of gastrocnemius (GA), soleus (SO), and plantaris (PL) were assessed in anesthetized spastic and normally developed Han-Wistar rats. In addition, the extent of epimuscular myofascial force transmission between synergistic GA, SO, and PL, as well as between the calf muscles and antagonistic tibialis anterior (TA), was investigated. Active length-force curves of spastic GA and PL were narrower with a reduced maximal active force. In contrast, active length-force characteristics of spastic SO were similar to those of controls. In reference position (90° ankle and knee angle), higher resistance to ankle dorsiflexion and increased passive stiffness was found for the spastic calf muscle group. At optimum length, passive stiffness and passive force of spastic GA were decreased, whereas those of spastic SO were increased. No mechanical interaction between the calf muscles and TA was found. As GA was lengthened, force from SO and PL declined despite a constant muscle-tendon unit length of SO and PL. However, the extent of this interaction was not different in spastic rats. In conclusion, the effects of spasticity on length-force characteristics were muscle specific. The changes observed for GA and PL muscles are consistent with the changes in limb mechanics reported for human patients. Our results indicate that altered mechanics in spastic rats cannot be attributed to differences in mechanical interaction, but originate from individual muscular structures.

Intraoperative experiments show relevance of inter-antagonistic mechanical interaction for spastic muscle's contribution to joint movement disorder

BACKGROUND

Recent intra-operative knee angle-muscle force data showed no abnormal muscular mechanics (i.e., a narrow joint range of muscle force exertion and peak muscle force availability at flexed joint positions), if the spastic gracilis muscle was stimulated alone. This can limit inter-muscular mechanical interactions, which have been shown to affect muscular mechanics substantially. We aimed at testing the hypothesis that the knee angle-muscle force curves of the spastic gracilis muscle activated simultaneously with a knee extensor are representative of joint movement disorder.

METHODS

Experiments were performed during remedial surgery of spastic cerebral palsy patients (n=6, 10 limbs tested). Condition-I: muscle forces were measured in flexed knee positions (120° and 90°) after activating the gracilis exclusively. Condition-II: knee angle-muscle force data were measured from 120° to full extension after activating the vastus medialis, simultaneously.

FINDINGS

Condition-II vs. I: Inter-antagonistic interaction did not consistently cause a gracilis force increase. Condition-II: Peak muscle force=mean 47.92 N (SD 22.08 N). Seven limbs showed availability of high muscle force in flexed knee positions (with minimally 84.8% of peak force at 120°). Knee angle-muscle force curves of four of them showed a local minimum followed by an increasing force (explained by an increasing passive force, indicating muscle lengths unfavorable for active force exertion). High active gracilis forces measured at flexed knee positions and narrow operational joint range of force exertion do indicate abnormality. The remainder of the limbs showed no such abnormality.

INTERPRETATION

Our hypothesis is confirmed for most, but not all limbs tested. Therefore, tested inter-antagonistic mechanical interaction can certainly, but not exclusively be a factor for abnormal mechanics of the spastic muscle.

Rationale for using botulinum toxin A as an adjunct to upper limb rehabilitation in children with cerebral palsy

Cerebral palsy describes a group of disorders of movement and posture that result from disturbances in the developing brain. Although the brain lesion is nonprogressive, the secondary physical symptoms change with time and growth. If left untreated, symptoms may result in the development of physical impairment and impede independent performance of daily tasks. Intramuscular injection of botulinum neurotoxin A is a relatively safe and effective adjunct to upper limb therapy. Botulinum neurotoxin A primarily aims to reduce muscle overactivity, thereby reducing the development of increased muscle stiffness that can lead to permanent changes. With a specific focus on the physiological action of botulinum neurotoxin A, this article describes the secondary symptoms of cerebral palsy and their different contributions. To highlight research directions and future implications for clinical practice, this article also documents the recent scientific evidence for upper limb botulinum neurotoxin A and proposes a preventive clinical model that aims to mitigate the effects of increasing upper limb impairment.

Intramuscular connective tissue differences in spastic and control muscle: a mechanical and histological study

Cerebral palsy (CP) of the spastic type is a neurological disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks. Secondary to the spasticity, muscle adaptation is presumed to contribute to limitations in the passive range of joint motion. However, the mechanisms underlying these limitations are unknown. Using biopsies, we compared mechanical as well as histological properties of flexor carpi ulnaris muscle (FCU) from CP patients (n = 29) and healthy controls (n = 10). The sarcomere slack length (mean 2.5 µm, SEM 0.05) and slope of the normalized sarcomere length-tension characteristics of spastic fascicle segments and single myofibre segments were not different from those of control muscle. Fibre type distribution also showed no significant differences. Fibre size was significantly smaller (1933 µm2, SEM 190) in spastic muscle than in controls (2572 µm2, SEM 322). However, our statistical analyses indicate that the latter difference is likely to be explained by age, rather than by the affliction. Quantities of endomysial and perimysial networks within biopsies of control and spastic muscle were unchanged with one exception: a significant thickening of the tertiary perimysium (3-fold), i.e. the connective tissue reinforcement of neurovascular tissues penetrating the muscle. Note that this thickening in tertiary perimysium was shown in the majority of CP patients, however a small number of patients (n = 4 out of 23) did not have this feature. These results are taken as indications that enhanced myofascial loads on FCU is one among several factors contributing in a major way to the aetiology of limitation of movement at the wrist in CP and the characteristic wrist position of such patients.

Human spastic Gracilis muscle isometric forces measured intraoperatively as a function of knee angle show no abnormal muscular mechanics

BACKGROUND

To show whether mechanics of activated spastic muscle are representative of the functional deficiencies clearly apparent in the joints, our goal was to test the following hypotheses: (1) The muscle's joint range of force exertion is narrow, and (2) high muscle forces are available at low muscle length.

METHODS

During remedial surgery, we measured the forces of the Gracilis muscle of spastic cerebral palsy patients (n=7, 10 limbs tested) as a function of knee joint angle from flexion (120°) to full extension (0°).

FINDINGS

The spastic Gracilis exerted non-zero forces for the entire knee angles studied. For four limbs, the peak force was exerted at the highest length. For the remainder limbs, the closest knee angle of peak force exertion to 120° was 66°. Maximally 79.1%, and for most limbs only a much lower percentage (minimally 22.4%) of peak Gracilis force (mean 41.59N (SD 41.76N)) was available at 120° knee flexion. Moreover, a clinical metric was obtained showing that the occurrence of a contracture was not correlated significantly with key determinants of knee angle-Gracilis force characteristics.

INTERPRETATION

Our hypotheses are rejected: the spastic Gracilis has no narrow operational joint range of force exertion and no supreme active resistance capacity to stretch at low length. We conclude that if activated alone, spastic muscle shows no abnormal mechanics representative of joint movement disorder. Simultaneous stimulation of other muscles as in daily activities may change this situation.

Managing lower extremity muscle tone and function in children with cerebral palsy via eight-week repetitive passive knee movement intervention

This study used a repeated measures design to assess the effect of an eight-week repetitive passive movement (RPM) intervention on lower extremity muscle tone and function in children with cerebral palsy (CP). Eighteen children (aged 9.5 ± 2.1 years) with spastic CP were randomly assigned to a knee RPM intervention condition of 3 times a week for 8 weeks or a control condition. The 8 weeks were followed by 4 weeks of washout period, after which the participants were crossed over to the other group. In the RPM condition, each subject's knees were intervened with continuous passive motion device (at a velocity of 15°/s) for 20 min. The subjects were evaluated via variables measuring range-of-motion, muscle tone, and ambulatory function before, after, 1 day after, and 3 days after each intervention. Repeated-measures statistical analyses found significant differences between condition variable on active range-of-motion of the knee (AROM, increased), relaxation index (RI, increased), Modified Ashworth Scale (MAS, decreased), timed up-and-go (TUG, decreased), 6-min walk test (6 MWT, increased); and significant differences among time variable including RI, MAS, and 6 MWT. No difference was found in passive range-of-motion measurements. Repetitive passive movement reduced lower extremity spastic hypertonia in children with cerebral palsy, and it also improved ambulatory function in terms of walking speed. Effects of this treatment protocol on ambulation lasted up to 3 days post intervention. Findings of this study provide clinicians and patients an alternative, effective and efficient strategy for spastic control and ambulatory improvement.

Why is joint range of motion limited in patients with cerebral palsy?

Patients with spastic cerebral palsy of the upper limb typically present with various problems including an impaired range of motion that affects the positioning of the upper extremity. This impaired range of motion often develops into contractures that further limit functioning of the spastic hand and arm. Understanding why these contractures develop in cerebral palsy will affect the selection of patients suitable for surgical treatment as well as the choice for specific surgical procedures. The generally accepted hypothesis in patients with spastic cerebral palsy is that the hyper-excitability of the stretch reflex combined with increased muscle tone result in extreme angles of the involved joints at rest. Ultimately, these extreme joint angles are thought to result in fixed joint postures. There is no consensus in the literature concerning the pathophysiology of this process. Several hypotheses associated with inactivity and overactivity have been tested by examining the secondary changes in spastic muscle and its surrounding tissue. All hypotheses implicate different secondary changes that consequently require different clinical approaches. In this review, the different hypotheses concerning the development of limited joint range of motion in cerebral palsy are discussed in relation to their secondary changes on the musculoskeletal system.

Effects of knee joint angle on global and local strains within human triceps surae muscle: MRI analysis indicating in vivo myofascial force transmission between synergistic muscles

Purpose

Mechanical interactions between muscles have been shown for in situ conditions. In vivo data for humans is unavailable. Global and local length changes of calf muscles were studied to test the hypothesis that local strains may occur also within muscle for which global strain equals zero.

Methods

For determination of globally induced strain in m. gastrocnemius in dissected human cadavers several knee joint angles were imposed, while keeping ankle joint angle constant and measuring its muscle–tendon complex length changes. In vivo local strains in both gastrocnemius and soleus muscles were calculated using MRI techniques in healthy human volunteers comparing images taken at static knee angles of 173° and 150°.

Results

Imposed global strains on gastrocnemius were much smaller than local strains. High distributions of strains were encountered, e.g. overall lengthened muscle contains locally lengthened, as well as shortened areas within it. Substantial strains were not limited to gastrocnemius, but were found also in synergistic soleus muscle, despite the latter muscle–tendon complex length remaining isometric (constant ankle angle: i.e. global strain = 0), as it does not cross the knee. Based on results of animal experiments this effect is ascribed to myofascial connections between these synergistic muscles. The most likely pathway is the neurovascular tract within the anterior crural compartment (i.e. the collagen reinforcements of blood vessels, lymphatics and nerves). However, direct intermuscular transmission of force may also occur via the perimysium shared between the two muscles.

Conclusions

Global strains imposed on muscle (joint movement) are not good estimators of in vivo local strains within it: differing in magnitude, as well as direction of length change. Substantial mechanical interaction occurs between calf muscles, which is mediated by myofascial force transmission between these synergistic muscles. This confirms conclusions of previous in situ studies in experimental animals and human patients, for in vivo conditions in healthy human subjects.

The pathophysiological basis of weakness in children with cerebral palsy

PURPOSE

To examine the evidence concerning the neurologic and muscular pathophysiology that contributes to clinically observed weakness in children and young people with cerebral palsy (CP).

METHOD

Literature concerning the neural or muscular changes in subjects with CP was found by searching 6 databases plus supplementary searching.

RESULTS

A final set of 51 articles was identified by 2 independent reviewers.

SUMMARY OF KEY POINTS

Muscle weakness is due to reduced central drive, possible abnormal neural maturation, insufficient and disorganized motor recruitment, impaired voluntary control, impaired reciprocal inhibition, altered setting of muscle spindles, and reinforcement of abnormal neural circuits. Muscle tissue is altered, with selective atrophy of fast fibers and altered myosin expression, changes in fiber length and cross-sectional area, changes in the length-tension curve, reduced elasticity, and impoverished muscle tissue development.

CONCLUSION

Children with CP are weak because of both neurologic and muscular changes.

The importance of neurorehabilitation to the outcome of neuromodulation in spasticity

The neuromodulation specialist who is involved in the management of spasticity should not be interested only in the technical aspects of the implantation of a device. It is important that (s)he has a sound understanding of all aspects of this serious disability in order to determine appropriately whether an ablative or a neuromodulatory intervention (intrathecal baclofen administration, spinal cord stimulation, peripheral nerve stimulation) is best for the patient. It is also important that s(he) is able to collaborate effectively with the physiatrists, othopaedic surgeons, neurologists, physiotherapists, neuropsychologists, and care counselors. In this article, we review our approach to the neurorehabilitation of patients with spasticity due to multiple sclerosis, spinal cord injury, cerebrovascular disease or head injury and, on the basis of our experience, we highlight the importance of the integrated management that combines both rehabilitation and neuromodulation methods in order to ensure the maximum benefits for the patients.

Thumb and finger forces produced by motor units in the long flexor of the human thumb

The uncommonly good proprioceptive performance of the long flexor of the thumb, flexor pollicis longus (FPL), may add significantly to human manual dexterity. We investigated the forces produced by FPL single motor units during a weak static grip involving all digits by spike-triggered averaging from single motor units, and by averaging from twitches produced by intramuscular stimulation. Nine adult subjects were studied. The forces produced at each digit were used to assess how forces produced in FPL are distributed to the fingers. Most FPL motor units produced very low forces on the thumb and were positively correlated with the muscle force at recruitment. Activity in FPL motor units commonly loaded the index finger (42/55 units), but less commonly the other fingers (P < 0.001). On average, these motor units produced small but significant loading forces on the index finger ( approximately 5.3% of their force on the thumb) with the same time-to-peak force as the thumb ( approximately 50 ms), but had no significant effect on other fingers. However, intramuscular stimulation within FPL did not produce significant forces in any finger. Coherence at 2-10 Hz between the thumb and index finger force was twice that for the other finger forces and the coherence to the non-index fingers was not altered when the index finger did not participate in the grasp. These results indicate that, within the long-term coordinated forces of all digits during grasping, FPL motor units generate forces highly focused on the thumb with minimal peripheral transfer to the fingers and that there is a small but inflexible neural coupling to the flexors of the index finger.

Kinematic Aiming Task

OBJECTIVE

To describe different aspects of a kinematic aiming task (KAT) as a quantitative way to assess changes in arm movements within 2 wks after botulinum toxin-A (BTX-A) injections in children with spastic hemiplegia.

DESIGN

Intervention study randomized clinical trial; follow-up within 4 wks after baseline measurement.

RESULTS

The KAT gave a high intraclass correlation on movement time, spread of end points (END), and index of performance effective (IP-E). After BTX-A, a significant increase of END and IP-E was shown if precision demand in the KAT was high, whereas the inverse occurred when speed was more important. These functional changes coincided with a significant decrease of the maximum voluntary contraction of the flexor muscles of the forearm. Muscle tone measured with the Ashworth scale did show a nonsignificant decrease of muscle tone, as did the stretch restricted angle and the active and passive ranges of motion of the elbow and wrist.

CONCLUSIONS

Muscle force decreased immediately after BTX-A, showing the direct effect of BTX-A. The KAT is an adequate, reproducible way to quantify functional changes after BTX-A in the upper limb. BTX-A has an inverse effect in the precision task when accuracy is important, and it has a positive effect when speed prevails.

Substantial effects of epimuscular myofascial force transmission on muscular mechanics have major implications on spastic muscle and remedial surgery

The specific aim of this paper is to review the effects of epimuscular myofascial force transmission on muscular mechanics and present some new results on finite element modeling of non-isolated aponeurotomized muscle in order to discuss the dependency of mechanics of spastic muscle, as well as surgery for restoration of function on such force transmission. The etiology of the effects of spasticity on muscular mechanics is not fully understood. Clinically, such effects feature typically a limited joint range of motion, which at the muscle level must originate from altered muscle length-force characteristics, in particular a limited muscle length range of force exertion. In studies performed to understand what is different in spastic muscle and what the effects of remedial surgery are, muscle is considered as being independent of its surroundings. Conceivably, this is because the classical approach in muscle mechanics is built on experimenting with dissected muscles. Certainly, such approach allowed improving our understanding of fundamental muscle physiology yet it yielded implicitly a narrow point of view of considering muscle length-force characteristics as a fixed property of the muscle itself. However, within its context of its intact connective tissue surroundings (the in vivo condition) muscle is not an isolated and independent entity. Instead, collagenous linkages between epimysia of adjacent muscles provide direct intermuscular connections, and structures such as the neurovascular tracts provide indirect intermuscular connections. Moreover, compartmental boundaries (e.g., intermuscular septa, interosseal membranes, periost and compartmental fascia) are continuous with neurovascular tracts and connect muscular and non-muscular tissues at several locations additional to the tendon origins and insertions. Epimuscular myofascial force transmission occurring via this integral system of connections has major effects on muscular mechanics including substantial proximo-distal force differences, sizable changes in the determinants of muscle length-force characteristics (e.g. a condition dependent shift in muscle optimum length to a different length or variable muscle optimal force) explained by major serial and parallel distributions of sarcomere lengths. Therefore, due to epimuscular myofascial force transmission, muscle length-force characteristics are variable and muscle length range of force exertion cannot be considered as a fixed property of the muscle. The findings reviewed presently show that acutely, the mechanical mechanisms manipulated in remedial surgery are dominated by epimuscular myofascial force transmission. Conceivably, this is also true for the mechanism of adaptation during and after recovery from surgery. Moreover, stiffened epimuscular connections and therefore a stiffened integral system of intra- and epimuscular myofascial force transmission are indicated to affect the properties of spastic muscle. We suggest that important advancements in our present understanding of such properties, variability in the outcome of surgery and considerable recurrence of the impeded function after recovery cannot be made without taking into account the effects of epimuscular myofascial force transmission.

Myofascial force transmission and tendon transfer for patients suffering from spastic paresis: a review and some new observations

The current rationale of clinical practice in spastic tendon transfer surgery is based on four assumptions: (1) changes in muscle fiber length (serial number of sarcomeres) determine the available length range and joint excursion, (2) muscle cross-sectional area determines the maximal force output, (3) fiber length and muscle force are invariable functions of muscle length, (4) there is an invariable relation between the elastic force and the active force exerted by the sarcomeres. The validity of these assumptions is discussed. Additionally, some new perspectives in muscle research are discussed and myofascial force transmission is introduced as a co-determinant for the outcome of tendon transfer by presenting some exploratory observations.

Adaptation of the properties of spastic muscle with wrist extension deformity

To show that human muscle may adapt to tendon transfer, adaptation of flexor carpi ulnaris (FCU) function was studied by measuring active and passive length-force characteristics at initial operation and at reoperation in a case of extension deformity secondary to FCU tendon transfer. At reoperation, FCU was 20 mm shorter; active force decreased approximately 10%, indicating atrophy; and passive force increased, reflecting increased stiffness. FCU fiber length was unchanged. The presented case shows that human forearm muscle may adapt to a transferred function.