The anterior scalene muscle in thoracic outlet compression syndrome. Histochemical and morphometric studies
H. I. Machleder, F. Moll and M. A. Verity
Histochemical studies and morphometric fiber type analysis were done on
biopsy specimens of anterior scalene muscle (ASM) from patients with
thoracic outlet compression syndrome (TOS), without structural abnormality.
Hypertrophy and atrophy factors were determined from muscle fiber
histograms of ASM from controls, patients with TOS, and after scalene
tenotomy. Scalene muscle from patients with TOS showed marked type 1 (tonic
contracting) fiber predominance (85.1% +/- 5.1%) and type 1 fiber
hypertrophy (55.6 +/- 2.7 microns). After tenotomy there is a reduction of
type 1 fiber representation, selective atrophy in the type 1 fiber system
(atrophy factor, 0.66 +/- 0.24), and increase of type 2 fibers. These
distinctive changes indicate that ASM is uniquely structured in fiber
composition to sustain prolonged contraction. The ASM in patients with TOS
demonstrates an extraordinary adaptive transformation and recruitment
response in the type 1 fiber system reflecting chronic increased tone or
motor neuron stimulation. These observations form a basis for clarifying
the structural and pathophysiologic changes in TOS.
