The Elias University Hospital Approach: A Visual Guide to Ultrasound-Guided Botulinum Toxin Injection in Spasticity, Part IV-Distal Lower Limb Muscles

Abstract

Spasticity of the distal lower limb substantially impairs stance, gait, and quality of life in patients with upper motor neuron lesions. Although ultrasound-guided botulinum toxin A (BoNT-A) injections are increasingly employed, structured, muscle-specific visual guidance for the distal lower limb remains limited. This study provides a comprehensive guide for ultrasound-guided BoNT-A injections across ten key distal lower limb muscles: gastrocnemius, soleus, tibialis posterior, flexor hallucis longus, flexor digitorum longus, tibialis anterior, extensor hallucis longus, flexor digitorum brevis, flexor hallucis brevis, and extensor digitorum longus. For each muscle, we present (1) Anatomical positioning relative to osseous landmarks; (2) Sonographic identification cues and dynamic features; (3) Zones of intramuscular neural arborization optimal for injection; (4) Practical injection protocols derived from literature and clinical experience. High-resolution ultrasound images and dynamic videos illustrate real-life muscle behavior and guide injection site selection. This guide facilitates precise targeting by correlating sonographic signs with optimal injection zones, addresses common spastic patterns-including equinus, varus, claw toe, and hallux deformities-and integrates fascial anatomy with motor-point mapping. This article completes the Elias University Hospital visual series, providing clinicians with a unified framework for effective spasticity management to improve gait, posture, and patient autonomy.

Keywords: botulinum toxin-A injections; distal lower limb muscles; musculoskeletal ultrasound; post-stroke spasticity; ultrasound-guided therapy.

Figure 1

Ultrasound anatomy of the lateral head of gastrocnemius with key landmarks: LG—lateral head of gastrocnemius; SOL—soleus; FIB—fibula.

Figure 2

Ultrasound anatomy of the medial head of gastrocnemius with key landmarks: TIB—tibia; MG—medial head of gastrocnemius; SOL—soleus.

Figure 3

Ultrasound anatomy of the soleus: MG—medial head of the gastrocnemius; MSCN—medial sural cutaneous nerve; LG—medial head of gastrocnemius; SOL—soleus; TIB—tibia.

Figure 4

Ultrasound anatomy of the tibialis posterior—anterior window: ATV—anterior tibial vein; ATA—anterior tibial artery; FIB—fibula; DFN—deep fibular nerve; EDL—extensor digitorum longus; TA—tibialis anterior; IOM—interosseous membrane; TP—tibialis posterior; TIB—tibia.

Figure 5

Ultrasound anatomy of the tibialis posterior—medial window: TIB—tibia; FDL—flexor digitorum longus; TP—tibialis posterior; PTA—posterior tibial artery; PTV—posterior tibial vein; TN—tibial nerve; FHL—flexor hallucis longus; IOM—interosseous membrane; SOL—soleus.

Figure 6

Ultrasound anatomy of the tibialis posterior—posterior window: FDL—flexor digitorum longus; PTA—posterior tibial artery; PTV—posterior tibial vein; TN—tibial nerve; TIB—tibia; TP—tibialis posterior; SOL—soleus; FHL—flexor hallucis longus; FA—fibular artery; FV—fibular vein; IOM—interosseous membrane; FIB—fibula.

Figure 7

Ultrasound anatomy of the flexor hallucis longus: FIB—fibula; FHL—flexor hallucis longus; TP—tibialis posterior; IOM—interosseous membrane; PTA—posterior tibial artery; PTV—posterior tibial vein; TN—tibial nerve; SOL—soleus; FDL—flexor digitorum longus.

Figure 8

Ultrasound anatomy of the flexor digitorum longus: TIB—tibia; FDL—flexor digitorum longus; TP—tibialis posterior; IOM—interosseous membrane; PTA—posterior tibial artery; PTV—posterior tibial nerve; FHL—flexor hallucis longus; SOL—soleus; TN—tibial nerve.

Figure 9

Ultrasound anatomy of the tibialis anterior: TIB—tibia; TA—tibialis anterior; IOM—interosseous membrane; TP—tibialis posterior; EDL—extensor digitorum longus.

Figure 10

Ultrasound anatomy of the extensor hallucis longus: EDL—extensor digitorum longus; FIB—fibula; EHL—extensor hallucis longus; IOM—interosseous membrane; TP—tibialis posterior; TAt—tibialis anterior tendon; TIB—tibia.

Figure 11

Ultrasound anatomy of the flexor digitorum brevis: NAV—navicular; AbH—abductor hallucis; FDB—flexor digitorum brevis; QP—quadratus plantae; CUB—cuboid.

Figure 12

Ultrasound anatomy of the flexor hallucis brevis: AbH—abductor hallucis; AbHt—abductor hallucis tendon; FHB-MH—flexor hallucis brevis medial head; FHB-LH—flexor hallucis brevis—lateral head; FHLt—flexor hallucis longus tendon; I—first metatarsophalangeal joint; II—second metatarsal joint, AH—adductor hallucis.

Figure 13

Ultrasound anatomy of the extensor digitorum longus: FIB—fibula; FL—fibularis longus; SFN—superficial fibular nerve; ATA—anterior tibial artery; DFN—deep fibular nerve; EDL—extensor digitorum longus; IOM—interosseous membrane; TP—tibialis posterior; TA—tibialis anterior; TIB—tibia.