Intramuscular Connective Tissue Differences in Spastic and Control Muscle: A Mechanical and Histological Study

Abstract

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.

The mechanics of activated semitendinosus are not representative of the pathological knee joint condition of children with cerebral palsy

“…This agrees with the observation of Smith et al (2011). However, de Bruin et al (2014) suggest that the remainder of sarcomeres remain at lower lengths. Finite element modeling has shown that such distribution in sarcomere strain along fascicles is plausible theoretically Yucesoy, 2016, Turkoglu et al, 2014;Yucesoy and Huijing, 2012;Yucesoy et al, 2002).…”

“…In a recent study de Bruin et al (2014) compared mechanical as well as histological properties of flexor carpi ulnaris muscle (FCU) using biopsies from CP patients and healthy controls. They showed that tertiary perimysial structures inside the muscle, which are continuations of branches of the main neurovascular tracts, are thickened in spastic FCU.…”

“…With altered length and relative position of the muscle, myofascial loads act on the muscle belly due to stretching of those structures (Yucesoy, 2010). De Bruin et al (2014) considered enhanced stiffness of tertiary perimysial structures as well as epimuscular connective tissues in CP patients and hence elevated proximally and distally directed myofascial loads occurring simultaneously on the proximal and distal parts of the muscle, respectively. Two notable consequences for such adaptation are implied: (1) stretch of the muscle in opposite directions can cause a fraction of the sarcomeres within muscle fibers to attain higher length.…”

“…(2) Ascribed to thickened tertiary perimysial structures and as a special effect of oppositely directed myofascial loads acting on spastic FCU, de Bruin et al (2014) proposed that force can be transmitted locally through the muscle without being exerted at its origin and insertion. Therefore, without necessarily affecting the active state mechanics of the muscle and being apparent in muscle's morphology, changes to specific intramuscular, as well as epimuscular connective tissue structures in CP may cause loads acting on the joint.…”

Urine hydroxyproline correlates with progression of spasticity in cerebral palsy

“…Collagen that accumulates in the spastic muscle endomysium is thick and fibrotic, especially in severe cases, which suggests that collagen may increase the muscle stiffness in spasticity (2). De Bruin et al questioned the belief that the endomysium is affected in CP muscle (PLOS one 2014) instead highlighting the role of thickening of the tertiary perimysium (4). A study conducted in children with spastic diplegia noted a predominance of type 1 fiber in their spastic muscles (5).…”