Comparison of ultrasound-guided anterior and posterior approaches for needle insertion into the tibialis posterior in hemiplegic children with spastic cerebral palsy.

OBJECTIVE Although the tibialis posterior is a potentially difficult muscle to locate for botulinum toxin injection because of its deep location, needle insertion is usually performed using anatomic landmarks for guidance. Accordingly, the ultrasonographic anatomy of the lower leg was investigated in hemiplegic children with spastic cerebral palsy to improve the safety and the accuracy of needle placement into the tibialis posterior. DESIGN Twenty-five subjects (2 yrs 2 mos to 5 yrs 11 mos; 12 boys, 13 girls; Gross Motor Function Classification System levels I-II) were recruited. B-mode, real-time ultrasonography was performed using a 5- to 12-MHz linear array transducer. During anterior and posterior approaches, safety window width (tibia to the neurovascular bundle) and depth (skin to the midpoint of the tibialis posterior) were measured at the upper third and at the midpoint of the tibia. RESULTS For the anterior approach, the safety window width at the upper third of the tibia (mean [SD], 0.63 [0.12] cm, range, 0.44-0.93 cm) was significantly larger than that at the midpoint (0.38 [0.09] cm, range from 0.22 to 0.59 cm, P < 0.05) of the affected leg. However, for the posterior approach, the safety window width at the midpoint (0.74 [0.23] cm, range from 0.21 to 1.18 cm) was significantly larger than that at the upper third of the tibia (0.48 [0.23] cm, range from 0.10 to 0.97 cm, P < 0.05) on the affected leg. CONCLUSIONS Ultrasonographic guidance is a useful, safe, and accurate tool for needle insertion into the tibialis posterior. Considering the safety window width, this study suggests needle placement at the upper third point of the tibia for the anterior approach and at the midpoint for the posterior approach.