What are the surface markings for Botox (Botulinum toxin) injection in a patient with conditions affecting the Extensor Hallucis Longus (EHL) and Flexor Digitorum Brevis (FDB) muscles?

Surface Marking for Botulinum Toxin Injection in EHL and FDB

For Extensor Hallucis Longus (EHL) and Flexor Digitorum Brevis (FDB) botulinum toxin injections, use ultrasound guidance rather than surface landmarks alone, as ultrasound significantly improves accuracy and safety compared to surface anatomical techniques. 1

Extensor Hallucis Longus (EHL) Surface Marking

Anatomical Positioning

• EHL is located in the anterior compartment of the leg, between the tibialis anterior medially and extensor digitorum longus laterally. 2
• The muscle belly extends from the middle third of the fibula and interosseous membrane distally toward the great toe. 2

Injection Site Location

• Target the middle to distal third of the leg, approximately 40-60% of the distance from the tibial plateau to the lateral malleolus. 2, 3
• Position the injection site lateral to the tibial crest, in the anterior compartment where EHL muscle belly is most prominent. 2
• Use ultrasound to identify the muscle between tibialis anterior and extensor digitorum longus, targeting zones of intramuscular neural arborization. 2

Clinical Considerations

• EHL spasticity contributes to hallux extension deformities and gait abnormalities. 2
• Dynamic ultrasound assessment during active toe extension helps confirm proper muscle identification before injection. 2

Flexor Digitorum Brevis (FDB) Surface Marking

Anatomical Positioning

• FDB is an intrinsic foot muscle located in the plantar aspect of the foot, superficial to the flexor digitorum longus tendons. 2
• The muscle originates from the medial calcaneal tuberosity and lies in the central compartment of the plantar foot. 2

Injection Site Location

• Target the muscle belly in the medial plantar aspect of the foot, approximately at the junction of the anterior and middle thirds of the foot length. 2
• The optimal injection zone is typically 3-5 cm distal to the medial calcaneal tuberosity. 2
• Ultrasound guidance is essential to avoid the medial plantar nerve and vessels that run alongside FDB. 2

Clinical Considerations

• FDB contributes to claw toe deformities when spastic. 4, 2
• For comprehensive claw toe treatment, consider injecting both FDB and flexor digitorum longus (FDL), as these muscles work in coupling with flexor hallucis longus (FHL). 4

Critical Technical Points

Why Ultrasound is Superior to Surface Landmarks

• Surface landmark techniques show significant discrepancies compared to ultrasound-confirmed locations, particularly for deep flexor muscles. 1
• Ultrasound prevents inadvertent injection into neurovascular structures. 1
• Real-time visualization confirms proper needle placement within the target muscle belly. 2, 1

Dosing Considerations

• Botulinum toxin is effective for reducing spasticity in lower limb muscles with Class IIa, Level A evidence. 5
• Doses should be adjusted based on muscle size, severity of spasticity, and previous response. 5
• For focal spasticity affecting multiple toe flexors, inject both FDL and FHL muscles, as anatomical studies show tendon coupling between these muscles. 4

Common Pitfalls to Avoid

• Do not rely solely on surface landmarks for FDB injection, as the medial plantar neurovascular bundle runs in close proximity. 2
• Avoid injecting too proximally in EHL, as this may affect tibialis anterior function. 2
• For claw toe deformities, injecting FDL alone often produces poor results; include FHL in the treatment plan. 4

Practical Injection Protocol

• Position the patient supine with the leg relaxed for EHL access. 2
• For FDB, position the patient prone or with the foot accessible for plantar approach. 2
• Use a 12-MHz linear ultrasound transducer for real-time guidance during injection. 1
• Confirm muscle identity with dynamic contraction before injection. 2, 1