Model Answer
0 min readIntroduction
The dorsum of the foot receives cutaneous innervation from a complex network of nerves primarily derived from the lumbar and sacral plexuses via the common peroneal (fibular) nerve. Understanding this innervation is vital for diagnosing and managing various clinical conditions affecting the foot, such as peripheral nerve injuries, diabetic neuropathy, and compression syndromes. Accurate knowledge of the cutaneous nerve supply is also crucial for performing regional anesthesia and surgical procedures. This detailed description will outline the specific nerves and their territories responsible for sensation on the dorsum of the foot.
Cutaneous Nerve Supply of Dorsum of Foot
The cutaneous innervation of the dorsum of the foot is primarily provided by branches of the superficial peroneal nerve and the deep peroneal nerve, both originating from the common peroneal nerve. The common peroneal nerve itself is a branch of the sciatic nerve (L4-S3).
1. Superficial Peroneal Nerve (Musculocutaneous Nerve)
The superficial peroneal nerve descends along the lateral aspect of the leg and divides into two main branches at the ankle:
- Intermediate Dorsal Cutaneous Nerve: This is the primary nerve supplying the dorsum of the foot. It travels dorsally between the extensor digitorum longus and extensor hallucis longus tendons. It provides cutaneous innervation to the skin on the dorsum of the foot, extending to the base of the first, second, and third metatarsals.
- Lateral Dorsal Cutaneous Nerve: This nerve travels more laterally and supplies the skin over the lateral aspect of the dorsum of the foot, extending towards the base of the fifth metatarsal.
2. Deep Peroneal Nerve
The deep peroneal nerve travels deep to the extensor retinaculum and provides innervation to the muscles of the anterior compartment of the leg and the foot. It also contributes to the cutaneous innervation of the dorsum of the foot via its branches:
- Dorsal Digital Cutaneous Nerve: This nerve arises near the tarsometatarsal joints and runs dorsally between the first and second toes. It provides cutaneous innervation to the dorsal aspect of the first, second, and third toes, extending to the distal interphalangeal joints.
3. Sural Nerve (Contribution)
While primarily supplying the lateral aspect of the leg and ankle, the sural nerve (formed by branches of the tibial and common peroneal nerves) can contribute to the cutaneous innervation of the posterolateral aspect of the dorsum of the foot, particularly near the lateral malleolus.
4. Dermatomal Distribution
The dermatomal distribution on the dorsum of the foot is not strictly defined, but generally follows these patterns:
- L5 Dermatome: Primarily covers the dorsum of the foot and the base of the first metatarsal.
- S1 Dermatome: Covers the lateral aspect of the dorsum of the foot and the base of the fifth metatarsal.
- S2 Dermatome: Contributes to the medial aspect of the dorsum of the foot.
5. Clinical Correlation - Common Peroneal Nerve Palsy
Damage to the common peroneal nerve, often due to fracture of the fibula or compression at the fibular head, results in foot drop and loss of sensation over the dorsum of the foot and lateral leg. This highlights the importance of understanding the nerve’s course and cutaneous distribution.
The following table summarizes the key cutaneous nerves and their territories:
| Nerve | Territory |
|---|---|
| Intermediate Dorsal Cutaneous Nerve | Central dorsum of foot, base of 1st-3rd metatarsals |
| Lateral Dorsal Cutaneous Nerve | Lateral dorsum of foot, base of 5th metatarsal |
| Dorsal Digital Cutaneous Nerve | Dorsal aspect of 1st-3rd toes |
| Sural Nerve | Posterolateral dorsum of foot (variable) |
Conclusion
In conclusion, the cutaneous innervation of the dorsum of the foot is a complex interplay between the superficial and deep peroneal nerves, with contributions from the sural nerve. A thorough understanding of these nerve pathways and their respective territories is essential for accurate clinical assessment and management of conditions affecting the foot and ankle. Recognizing the dermatomal patterns can aid in localizing nerve lesions and guiding diagnostic and therapeutic interventions.
Answer Length
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