Inferior mechanical properties of spastic muscle bundles due to hypertrophic but compromised extracellular matrix material

Abstract

The passive mechanical properties of small muscle fiber bundles obtained from surgical patients with spasticity (n = 9) and patients without neuromuscular disorders (n = 21) were measured in order to determine the relative influence of intracellular and extracellular components. For both types of patient, tangent modulus was significantly greater in bundles compared to identical tests performed on isolated single cells (P < 0.05). However, the relative difference between bundles and single cells was much greater in normal tissue than spastic tissue. The tangent modulus of normal bundles (462.5 +/- 99.6 MPa) was 16 times greater than normal single cells (28.2 +/- 3.3 MPa), whereas the tangent modulus of spastic bundles (111.2 +/- 35.5 MPa) was only twice that of spastic muscle cells (55.0 +/- 6.6 MPa). This relatively small influence of the extracellular matrix (ECM) in spastic muscle was even more surprising because spastic muscle cells occupied a significantly smaller fraction of the total specimen area (38.5 +/- 13.6%) compared to normal muscle (95.0 +/- 8.8%). Based on these data, normal muscle ECM is calculated to have a modulus of 8.7 GPa, and the ECM from spastic muscle of only 0.20 GPa. These data indicate that spastic muscle, although composed of cells that are stiffer compared to normal muscle, contains an ECM of inferior mechanical strength. The present findings illustrate some of the profound changes that occur in skeletal muscle secondary to spasticity. The surgical implications of these results are discussed.

Architectural Analysis and Intraoperative Measurements Demonstrate the Unique Design of the Multifidus Muscle for Lumbar Spine Stability

“…From a biomechanical and structural standpoint, multifidus fibers are similar to other muscle fibers in terms of slack sarcomere lengths, elastic modulus, and whether fibers express the fast or slow myosin heavy chain isoform 6,36 . Compared with upper extremity muscles 41 and more recent data on the quadriceps muscle 36 , the multifidus yields slack sarcomere lengths of about 2.2 mm and elastic moduli of about 35 kPa. This indicates that the fibers themselves have biomechanical properties comparable with those of other muscles in the body.…”

Extramuscular myofascial force transmission alters substantially the acute effects of surgical aponeurotomy: assessment by finite element modeling

“…Spastic muscles (e.g., Tardieu et al 1982;Sinkjaer and Magnussen 1994) and isolated single muscle fiber segments were reported to be stiffer than normal. In contrast, Lieber et al (2003) showed for passive bundles muscle fibers that despite being hypertropic the collagen reinforced extracellular matrix of spastic muscle tissue was less stiff. Conceivably, if the intramuscular connective tissues are stiffer than presently modeled, more resistance to sarcomere shortening is expected.…”

Rehabilitation after Stroke

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