Effective botulinum neurotoxin injection in treating iliopsoas spasticity

Area of Science:

• Anatomy
• Medical Imaging
• Neurology

Background:

• Understanding the precise intramuscular nerve distribution of the psoas major and iliacus muscles is crucial for targeted therapeutic interventions.
• Botulinum toxin (BoNT) injections require accurate anatomical localization for efficacy and safety.

Purpose of the Study:

• To identify optimal injection sites for botulinum toxin (BoNT) in the psoas major and iliacus muscles by analyzing their intramuscular nerve arborization.
• To provide anatomical guidance for clinicians performing BoNT injections in the hip flexor muscles.

Main Methods:

• A modified Sihler's staining technique was employed on 16 specimens each of the psoas major and iliacus muscles.
• Intramuscular nerve arborization patterns were meticulously documented relative to anatomical landmarks: anterior superior iliac spine (ASIS), posterior superior iliac spine (PSIS), lesser trochanter (LT), and the 12th thoracic vertebra transverse process.

Main Results:

• The psoas major muscle exhibited its largest nerve arborization density between 1/5 and 3/5 the distance from the 12th thoracic vertebra's transverse process to the PSIS.
• The iliacus muscle's nerve arborization was most prominent within specific horizontal and longitudinal planes relative to the ASIS, PSIS, and LT, with distinct zones identified.

Conclusions:

• The findings indicate that botulinum toxin (BoNT) injections into the psoas major and iliacus muscles should be administered at precisely identified locations based on nerve distribution.
• A posterior approach is recommended for targeting the psoas major muscle specifically, utilizing an injection point superior to the PSIS.
• For comprehensive treatment of both the psoas major and iliacus muscles, a proximal anterior approach is suggested as the ideal method, guided by the observed nerve arborization patterns.