title: Passive mechanical properties of the lumbar multifidus muscle support its role as a stabilizer.
abstract: The purpose of this study was to compare the passive mechanical properties and titin isoform sizes of the multifidus, longissimus, and iliocostalis muscles. Given our knowledge of each muscle's architecture and the multifidus' operating range, we hypothesized that multifidus would have higher elastic modulus with corresponding smaller titin isoforms compared to longissimus or iliocostalis muscles. Single-fiber and fiber-bundle material properties were derived from passive stress-strain tests of excised biopsies (n=47). Titin isoform sizes were quantified via sodium dodecyl sulfate-vertical agarose gel electrophoresis (SDS-VAGE) analysis. We found that, at the single-fiber level, all muscles had similar material properties and titin isoform sizes. At the fiber-bundle level, however, we observed significantly increased stiffness (approximately 45%) in multifidus compared to longissimus and iliocostalis muscles. These data demonstrate that each muscle may have a different scaling relationship between single-fiber and fiber-bundle levels, suggesting that the structures responsible for higher order passive mechanical properties may be muscle specific. Our results suggest that divergent passive material properties are observed at size scales larger than the single cell level, highlighting the importance of the extracellular matrix in these muscles. In addition to architectural data previously reported, these data further support the unique stabilizing function of the multifidus muscle. These data will provide key input variables for biomechanical modeling of normal and pathologic lumbar spine function and direct future work in biomechanical testing in these important muscles.
authors.affiliation: Department of Orthopaedic Surgery, University of California and Veterans Administration Medical Centers, San Diego, USA; Department of Radiology, University of California and Veterans Administration Medical Centers, San Diego, USA; Department of Bioengineering, University of California and Veterans Administration Medical Centers, San Diego, USA.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Ward
authors.affiliation: Department of Orthopaedic Surgery, University of California and Veterans Administration Medical Centers, San Diego, USA.
authors.forename: Akihito
authors.initials: A
authors.lastname: Tomiya
authors.affiliation: Department of Orthopaedic Surgery, University of California and Veterans Administration Medical Centers, San Diego, USA.
authors.forename: Gilad J
authors.initials: GJ
authors.lastname: Regev
authors.affiliation: Department of Bioengineering, University of California and Veterans Administration Medical Centers, San Diego, USA.
authors.forename: Bryan E
authors.initials: BE
authors.lastname: Thacker
authors.affiliation: Department of Orthopaedic Surgery, University of California and Veterans Administration Medical Centers, San Diego, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Benzl
authors.affiliation: Department of Orthopaedic Surgery, University of California and Veterans Administration Medical Centers, San Diego, USA.
authors.forename: Choll W
authors.initials: CW
authors.lastname: Kim
authors.affiliation: Department of Orthopaedic Surgery, University of California and Veterans Administration Medical Centers, San Diego, USA; Department of Bioengineering, University of California and Veterans Administration Medical Centers, San Diego, USA. Electronic address: rlieber@ucsd.edu.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Lieber
mesh_terms: D000328:Adult; D000368:Aged; D001363:Awards and Prizes; D001696:Biomechanical Phenomena; D064211:Connectin; D004548:Elasticity; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008161:Lumbosacral Region; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009124:Muscle Proteins / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D011494:Protein Kinases / Q000502:physiology; D012958:Societies, Scientific
chemical_list: D064211:Connectin; D009124:Muscle Proteins; C577285:TTN protein, human; D011494:Protein Kinases