Commonly targeted forearm muscles for upper extremity spasticity are wrist flexors, finger flexors, and pronators. The wrist flexors include the flexor carpi radialis and flexor carpi ulnaris. The finger flexors include the flexor digitorum superficialis which flexes the proximal interphalanges and the flexor digitorum profundus, which flexes the distal interphalanges. The flexor pollicis longus flexes the interphalangeal joint of the thumb. Pronator teres and pronator quadratus are responsible for forearm pronation.

Henzel et al. compared the ultrasound localization of forearm flexor muscles to anatomical landmarks described by Delagi for the flexor carpi radialis, pronator teres, and flexor pollicis longus, and the landmark mapping technique for the flexor digitorum superficialis developed by Bickerton [11, 13]. This study showed that ultrasound localization of the muscle bellies of certain forearm muscles, in particular the pronator teres, the flexor pollicis longus, the flexor carpi radialis, and the flexor digitorum superficialis to the 3rd or ring finger, was distinctly different from the points localized via surface landmarks or mapping. In a study by Munin, the mapping technique for the flexor digitorum superficialis muscle described by Bickerton was demonstrated to be feasible and effective to accurately target this muscle’s individual muscle bellies [14]. The mapping technique is time intensive, however taking 10 min in this study. The use of ultrasound would allow the identification of the muscle within several seconds to a few minutes, depending on the operator’s experience. Also, limitation in limb range of motion and positioning, as well as muscle atrophy and fibrosis, may interfere with anatomical mapping. Ultrasound identification of target muscles would likely be beneficial in these situations (Table9.4).

The iliopsoas muscle is the primary hip flexor. It originates from the lateral vertebral bodies of T12 to L5 and inserts on the lesser trochanter of the femur. Spasticity of this muscle typically presents as hip and knee flexion, and internal rotation and adduction of the hip, known as “crouched gait.”

Two techniques for ultrasound-guided injections of the iliopsoas muscle have been described. The first technique described uses an anterolateral approach angled 45° medially from the anterior superior iliac spine and swept through a 30° arc proximally and medially [15]. This approach carries a high risk of perforation of the bowel, external iliac vasculature, ureters, and femoral nerve compared to alternative approaches. This approach also appears to be more challenging and have more risk of perforation in larger adults compared to the pediatric population in this study. Westhoff describes the injection of the muscle via an anterior approach under the ilioinguinal ligament [16]. All 13 pediatric patients were noted to experience improvement in tone or range of motion, and no complications from the procedure were observed. However, this approach delivers botulinum toxin primarily to the iliacus portion of the iliopsoas, and not the psoas muscle. The anterior approach to the iliopsoas muscle using EMG localization is typically accurate, and the use of ultrasound does not confer additional benefit.

When reviewing studies on motor end plate locations, the anterior injection approach to the iliopsoas delivers botulinum toxin into a region of the muscle distal to the primary motor end plate zone. Van Campenhout found that the proximal and distal limits of the motor end plate zone for the psoas muscle were located 30–70 % of the distance between the twelfth thoracic vertebrae and the inguinal ligament [17, 18]. Therefore, the dorsal approach is suggested to be an effective injection approach to deliver the botulinum toxin close to the primary motor end plates.

Ward described a blind technique using a dorsal approach to target the psoas by inserting the needle through the erector spinae at L2, L3, and L4 with a slight lateral approach to move just past the lateral border of the transverse processes. The needle is then advanced 1–1.5 cm to reach the psoas muscle [19]. The concern with a blind or EMG-guided technique using this approach is that there is little certainty that the needle has been inserted the correct depth to assure its placement in the psoas muscle. In order for a safe injection via the dorsal approach, visual guidance with ultrasound combined with auditory guidance from EMG is preferred. Takai found ultrasound to be reliable for determining the thickness and the cross-sectional area of the psoas muscle using a dorsal approach [20].

Spinner, Khan, and Kirschner recently demonstrated that ultrasound guidance combined with EMG guidance to inject the psoas muscle via a dorsal approach is feasible (in publication). In this approach, the psoas muscle is visualized in cross section adjacent to the L3 vertebra, and an in-plane technique is used to guide the needle into the muscle. The accuracy was confirmed by EMG. The combined ultrasound and EMG-guided dorsal approach to chemodenervation of the psoas muscle may prove useful as an alternative for the treatment of hip flexion spasticity for patients in which the traditional anterior approach to the injection has shown suboptimal results.

The tibialis posterior originates from the interosseus membrane, proximal tibia, and fibula, and inserts on the navicular, cuneiform, cuboid, and second to fourth metatarsal bones of the foot. Activation of this muscle causes plantar flexion and inversion of the foot. Spasticity of the tibialis posterior muscle may result in an equinovarus deformity. Its location deep in the posterior lower leg makes this a more challenging muscle to target for electrodiagnosis and chemodenervation injections. The accuracy of using anatomical landmarks and palpation to target this muscle has been shown to be about 11 % [5].

Two techniques have been described for a tibialis posterior injection. For the posterior-medial approach is, the practitioner inserts the needle just posterior to the medial tibia at the midpoint of the lower leg, about halfway between the tibial tuberosity and the medial malleolus. Using ultrasound, Won et al. [21] assessed the safety window and depth for EMG needle insertion into the tibialis posterior muscle using a posterior-medial approach into the upper 1/3 distal border compared to the midpoint of the distance between the tibial tubercle and the bimalleolar line. The safety window was defined as the distance between the tibia and neurovascular bundle, and the depth was defined as the distance between the skin and tibialis posterior muscle. Compression of the medial calf was used to decrease the depth necessary to reach the desired muscle. The safety window was significantly greater at the midpoint compared to the upper 1/3 (1.47 cm vs. 1.16 cm, respectively), and the depth was significantly less at the midpoint in relation to the upper 1/3 (2.31 cm vs. 2.52 cm, respectively). Needle insertion in the posterior-medial approach is medial to the tibia and the neurovascular bundle (which is located just posterior to the tibialis posterior muscle). The needle is inserted through the medial gastrocnemius and flexor digitorum longus to reach the tibialis posterior. Compression widens the flexor digitorum longus and displaces the neurovascular border laterally, improving the safety window and decreasing needle depth. An anatomical study of cadavers performed by Oddy et al. determined that the motor point of the tibialis posterior is located in an area 22 % of the distance of a reference line from the fibular head and proximal medial tibia to the intermalleolar line [22]. Therefore, chemodenervation to the distal limit of the upper 1/3 of the tibialis posterior may theoretically provide better results due to proximity to the motor points.

The anterior approach between the tibia and fibula traverses through the tibialis anterior muscle and the interosseous membrane to reach the tibialis posterior muscle in the upper 1/3 segment, with the tibial neurovascular bundle located lateral to the targeted muscle. The safety window in the posterior-medial approach with compression is greater, and the depth is less than the anterior approach. Studies involving MRI and ultrasound of the tibialis posterior examining the posterior and anterior approach have shown that the safety window for needle insertion is greatest using an anterior approach in the proximal 1/3 of the tibia [23, 24].