Regev GJ, Kim CW, Thacker BE, Tomiya A, Garfin SR, Ward SR, Lieber RL.
Cross-sectional study with repeated measures design.
To compare the myosin heavy-chain isoform distribution within and
between paraspinal muscles and to test the theory that fiber-type gradients exist
as a function of paraspinal muscle depth.
SUMMARY OF BACKGROUND DATA:
There is still uncertainty regarding the fiber-type
distributions within different paraspinal muscles. It has been previously
proposed that deep fibers of the multifidus muscle may contain a higher ratio of
type I to type II fibers, because, unlike superficial fibers, they primarily
stabilize the spine, and may therefore have relatively higher endurance. Using a
minimally invasive surgical approach, using tubular retractors that are placed
within anatomic intermuscular planes, it was feasible to obtain biopsies from the
multifidus, longissimus, iliocostalis, and psoas muscles at specific predefined
Under an institutional review board-approved protocol, muscle biopsies
were obtained from 15 patients who underwent minimally invasive spinal surgery,
using the posterior paramedian (Wiltse) approach or the minimally invasive
lateral approach. Myosin heavy chain (MyHC) isoform distribution was analyzed
using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis)
electrophoresis. Because multiple biopsies were obtained from each patient, MyHC
distribution was compared using both within- and between-muscle repeated measures
The fiber-type distribution was similar among the posterior paraspinal
muscles and was composed of relatively high percentage of type I (63%), compared
to type IIA (19%) and type IIX (18%) fibers. In contrast, the psoas muscle was
found to contain a lower percentage of type I fibers (42%) and a higher
percentage of type IIA (33%) and IIX fibers (26%; P<0.05). No significant
difference was found for fiber-type distribution among 3 different depths of
themultifidus and psoas muscles.
Fiber-type distribution between the posterior paraspinal muscles is
consistent and is composed of relatively high percentage of type I fibers,
consistent with a postural function. The psoas muscle, on the other hand, is
composed of a higher percentage of type II fibers such as in the appendicular
muscles. Our data do not support the idea of a fiber-type gradient as a function
of depth for any muscle studied.
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