Changes of muscular fibre types in erector spinae and multifidus muscles in the unstable lumbar spine

Abstract

In a prospective study conducted between the years 1999 and 2002 we harvested 26 valuable muscle samples from patients with an unstable lumbar spine from the multifidus muscle and erector spinae muscle at the level of the L4/L5/S1 segments and evaluated them using histochemical methods. Control samples were taken from six patients with a acute fracture of the low lumbar spine. A statistical difference was evident between the experimental and control group in type I fibres from the erector muscle. There was a percentage increase in type I fibres and a decrease in type IIA fibres from the erector muscle compared to the control group. The percentage of IIX and IIC fibres in the musculus erector spinae was the same in both groups. The investigated multifidus muscle underwent significant changes in type IIA fibres, where the percentage decreased and the percentage of type IIX fibres was almost double in comparison to the control group. Fibres of types I and IIC were not statistically changed. Type IIX fibres react to the exceeding of normal ranges of movement in the functional spinal unit to prevent an abnormal shift and thus stabilize the segment. These changes in the multifidus muscle are the premise of its mostly local stabilizing function, whereas the erector muscle has predominantly postural, long-term stabilisation features because of the increase of type I fibres.