Intramuscular injection of collagenase clostridium histolyticum may decrease spastic muscle contracture for children with cerebral palsy.

In cerebral palsy (CP), the spastic motor type is most common, associated with a velocity-dependent increase in muscle stiffness that precedes the development of fixed muscle contracture - a permanent shortening of the muscle tendon unit even when relaxed. Intra-muscular injections of botulinum toxin type A (BTX-A) have become popular for the treatment of spastic muscle contractures but unfortunately its use has not resulted in long-term functional benefits and, paradoxically, has been associated with a persistent loss of contractile material. Recent biomechanical work has shown that the stiffness of the CP muscle increases in proportion to total collagen content within the perimysial extra-cellular matrix. Thus, rather than the use of tone-reducing agents, we hypothesize that the focal use of a selective collagenase, injected into spastic muscle at an appropriate dilution and concentration, may serve to reduce the extent of muscle contracture, improving clinical range of motion and perhaps sarcomere length.