Immunohistochemical study of muscle biopsy in children with cerebral palsy

Neuromuscular abnormalities associated with spasticity of upper extremity muscles in hemiparetic stroke

Our objective was to assess the mechanical changes associated with spasticity in elbow muscles of chronic hemiparetic stroke survivors and to compare these changes with those recorded in the ankle muscles of a similar cohort. We first characterized elbow dynamic stiffness by applying pseudorandom binary positional perturbations to the joints at different initial angles, over the entire range of motion, with subjects relaxed. We separated this stiffness into intrinsic and reflex components using a novel parallel cascade system identification technique. In addition, for controls, we studied the nonparetic limbs of stroke survivors and limbs of age-matched healthy subjects as primary and secondary controls. We found that both reflex and intrinsic stiffnesses were significantly larger in the stroke than in the nonparetic elbow muscles, and the differences increased as the elbow was extended. Reflex stiffness increased monotonically with the elbow angle in both paretic and nonparetic sides. In contrast, the modulation of intrinsic stiffness with elbow position was different in nonparetic limbs; intrinsic stiffness decreased sharply from full- to mid-flexion in both sides, then it increased continuously with the elbow extension in the paretic side. It remained invariant in the nonparetic side. Surprisingly, reflex stiffness was larger in the nonparetic than in the normal control arm, yet intrinsic stiffness was smaller in the nonparetic arm. Finally, we compare the angular dependence of paretic elbow and ankle muscles and show that the modulation of reflex stiffness with position was strikingly different.

The dependence of spinal cord development on corticospinal input and its significance in understanding and treating spastic cerebral palsy

The final phase of spinal cord development follows the arrival of descending pathways which brings about a reorganisation that allows mature motor behaviours to emerge under the control of higher brain centres. Observations made during typical human development have shown that low threshold stretch reflexes, including excitatory reflexes between agonist and antagonist muscle pairs are a feature of the newborn. However, perinatal lesions of the corticospinal tract can lead to abnormal development of spinal reflexes that includes retention and reinforcement of developmental features that do not emerge in adult stroke victims, even though they also suffer from spasticity. This review describes investigations in animal models into how corticospinal input may drive segmental maturation. It compares their findings with observations made in humans and discusses how therapeutic interventions in cerebral palsy might aim to correct imbalances between descending and segmental inputs, bearing in mind that descending activity may play the crucial role in development.

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.

A review of orthopedic surgeries after selective dorsal rhizotomy

Selective dorsal rhizotomy (SDR) is an evidence-based treatment for cerebral palsy (CP) spasticity. During their lifetime, patients with CP spasticity may require orthopedic surgery for muscles and joints to correct physical deformities and provide a better quality of life. In this review, the authors discuss the timing of such orthopedic surgery, its necessity, and whether it is influenced by the performance of SDR. A review of findings from the authors' 19 years of experience yields the following conclusions: 1) that SDR reduces orthopedic surgery requirements when compared with historical controls; 2) that SDR performed in patients at a young age (2-4 years) can reduce future orthopedic surgery requirements; 3) that independent walkers and diplegic patients will have the smallest amount of orthopedic surgery post-SDR; and 4) that patients who need assistance walking and those with quadriplegia will have the greatest amount, although the frequency of orthopedic surgery for quadriplegic patients is not as high as popularly believed.

Overstretching of sarcomeres may not cause cerebral palsy muscle contracture

To answer the question whether the muscle contracture in patients with cerebral palsy is caused by overstretching of in-series sarcomeres we studied the active and passive force-length relationship of the flexor carpi ulnaris muscle (FCU) in relation to its operating length range in 14 such patients with a flexion deformity of the wrist. Force-length relationship was measured intra-operatively using electrical stimulation, a force transducer, and a data-acquisition system. Muscle length was measured in maximally flexed and maximally extended position of the wrist. The spastic FCU was found to exert over 80% of its maximum active force at maximal extension of the wrist and this indicates abundant overlap of the sarcomeres. At maximal wrist extension, FCU passive force corresponded with only 0.7-18% of maximum active force. Both findings imply that the FCU sarcomeres are not overstretched when the wrist is extended. We conclude that the overstretching of in-series sarcomeres appears not to be the cause of contracture of the spastic FCU.

Structural and functional changes in spastic skeletal muscle

This review summarizes current information regarding the changes in structure or function that occur in skeletal muscle secondary to spasticity. Most published studies have reported an increase in fiber size variability in spastic muscle. There is no general agreement regarding any shift in fiber type distribution secondary to spasticity. Mechanical studies in whole limbs as well as in isolated single cells support the notion of an intrinsic change in the passive mechanical properties of muscle after spasticity in addition to the more widely reported neural changes that occur. Evidence is presented for changes within both the muscle cell and extracellular matrix that contribute to the overall changes in the tissue. Taken together, the literature supports the notion that, although spasticity is multifactorial and neural in origin, significant structural alterations in muscle also occur. An understanding of the specific changes that occur in the muscle and extracellular matrix may facilitate the development of new conservative or surgical therapies for this problem.

Androgen receptor YAC transgenic mice recapitulate SBMA motor neuronopathy and implicate VEGF164 in the motor neuron degeneration

X-linked spinal and bulbar muscular atrophy (SBMA) is an inherited neuromuscular disorder characterized by lower motor neuron degeneration. SBMA is caused by polyglutamine repeat expansions in the androgen receptor (AR). To determine the basis of AR polyglutamine neurotoxicity, we introduced human AR yeast artificial chromosomes carrying either 20 or 100 CAGs into mouse embryonic stem cells. The AR100 transgenic mice developed a late-onset, gradually progressive neuromuscular phenotype accompanied by motor neuron degeneration, indicating striking recapitulation of the human disease. We then tested the hypothesis that polyglutamine-expanded AR interferes with CREB binding protein (CBP)-mediated transcription of vascular endothelial growth factor (VEGF) and observed altered CBP-AR binding and VEGF reduction in AR100 mice. We found that mutant AR-induced death of motor neuron-like cells could be rescued by VEGF. Our results suggest that SBMA motor neuronopathy involves altered expression of VEGF, consistent with a role for VEGF as a neurotrophic/survival factor in motor neuron disease.