Intramuscular nerve distribution pattern of the adductor longus and gracilis muscles demonstrated with Sihler staining: guidance for botulinum toxin injection

Abstract

INTRODUCTION: The aims of this study were to clarify the intramuscular branching patterns and arborizing area of hip adductor muscles with reference to surface landmarks on the thigh and to thus suggest effective and safe injection points for botulinum neurotoxin (BoNT).

METHODS: Ten gracilis and 10 adductor longus specimens were subjected to Sihler staining to reveal intramuscular nerve arborization patterns, and findings were matched with and referred to surface landmarks. Using these results, we determined the optimal location for BoNT injection in hip adductors in relation to the long axis of the femur.

RESULTS: The corrected, most dense areas of innervation in adductor longus and gracilis were typically 30-50% and 40-50% from the anterior superior iliac spine (ASIS) along the vertical line of the femur, respectively.

CONCLUSIONS: The most effective and safest point for BoNT injection into adductor muscles appears to be between 35% and 50% from ASIS, where neuromuscular junctions are most densely distributed.