Effective botulinum neurotoxin injection in treating iliopsoas spasticity.

[INTRODUCTION] To detect ideal locations for botulinum toxin (BoNT) injection by exploring the intramuscular nerve arborization of the psoas major and iliacus muscles.

[METHOD] A modified Sihler's method was performed on the psoas major and iliacus muscles (16 specimens each). Intramuscular nerve arborization was recorded according to the most prominent point of the anterior superior iliac spine (ASIS), the posterior superior iliac spine (PSIS), the lesser trochanter (LT), and the transverse process of the 12th thoracic vertebra.

[RESULTS] Intramuscular nerve arborization of the psoas major muscle was the largest from 1/5 to 3/5 the distance from the transverse process of the 12th thoracic vertebra to the PSIS, and the tendinous portion of the muscle occupied from 3/5 to 5/5 this distance. In terms of the plane of the ASIS, the PSIS, and the LT, the arborization of the iliacus muscle was the largest from 1/5 to 3/5 the horizontal distance and 0 to 1/3, the distance longitudinally, and from 1/5 to 2/5, the horizontal distance and 1/3 to 2/3, the longitudinal distance.

[DISCUSSION] These results suggest that an injection of BoNT to the psoas major and iliacus muscle should be applied in specific areas. Additionally, the posterior approach is an ideal method for targeting only the psoas major because the injection point is above the PSIS. However, when treating both the psoas major and iliacus muscles, the proximal anterior approach is an ideal method according to the arborization patterns.