Intramuscular distribution of nerves in the human triceps surae muscle: anatomical bases for treatment of spastic drop foot with botulinum toxin.

Recent progress has been made in selective functional treatment of hypertonia of spastic origin by local injection of botulinum toxin into the muscles responsible for equinus foot dynamic deformation. The technical aspect of the intervention requires a strategy adapted to the individual patient. Good practice is founded on precise knowledge of the intramuscular nerve distribution of end plate zones, since the target organ of the toxin is the motor end plate. Knowledge about the location of motor end plates, which differs according to the structure of the muscle in question, remains rather poor. Through macroscopic and stereoscopic microscopic dissection of the nerve courses in the triceps surae muscular group in 40 legs, we have ascertained in more detail the distribution of motor end plates, which appear to be more numerous in certain zones of the muscle bellies. These zones were measured morphometrically and divided into segments which are expressed in percentages of a standard leg length. We maintain that these zones are the injection sites most likely to guarantee the best treatment efficacy.