Sciatic nerve, paralysis of common peroneal nerve

Sciatic Nerve Journey:

The sciatic nerve:

• Slips into the gluteal region through the greater sciatic foramen, just below the piriformis, and makes its way inferolaterally.
• Glides posteriorly over the superior gemellus, obturator externus, inferior gemellus, and quadratus femoris, sneaking into the posterior thigh beneath the long head of the biceps femoris.
• When it arrives at the apex of the popliteal fossa, it splits into the tibial and common fibular nerves.

Nerve Roots: L4, L5, S1, S2

The sciatic nerve is like the grandmaster of leg nerves,it splits into the tibial and common fibular nerves.

Tibial nerve

This nerve is quite the multitasker. It gives off a cutaneous branch known as the sural nerve, which takes care of the sensation in the lateral part of your leg and foot.

Then it dives deep between the soleus and the foot flexors, innervating some key players like the soleus, gastrocnemius, tibialis posterior, flexor hallucis longus, and flexor digitorum longus.

From there, it splits into three branches:

• Lateral plantar and medial plantar: Handling motor duties for the foot.
• Medial calcaneal: The cutaneous branch that takes care of the skin.

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Common Fibular Nerve

This nerve knows how to share responsibilities. It branches into:

Superficial Fibular Nerve:

This nerve takes a scenic route along the lateral side of your foreleg, nestled between the fibularis muscles. It's got a dual role:

• Motor Innervation: It powers up the fibularis longus and brevis muscles.
• Sensory Innervation: The rest of the nerve is all about sensation, giving rise to terminal branches that provide feeling to the dorsal aspect of the foot. Specifically, it branches into the medial dorsal cutaneous and intermediate dorsal cutaneous nerves.

Deep Fibular Nerve:

This nerve takes the high road towards the front of the foreleg and dives into some serious muscle work:

• Motor Innervation: It activates the tibialis anterior, extensor digitorum longus and brevis, and extensor hallucis longus and brevis—basically, all the extensor muscles.
• Sensory Innervation: Its terminal branch handles the delicate task of providing sensation to the skin between the big toe (hallux) and the second digit on the dorsum of the foot.

Note : at the lateral margin of the popliteal fossa, common fibular nerve gives off 2 branches:

• Lateral Sural Cutaneous Nerve: This branch is responsible for supplying the skin on the lateral aspect of the foreleg, ensuring you can feel that area.
• Fibular Communicating Branch: A bit further down, this branch comes into play. It doesn't work alone, though. It teams up with the medial sural cutaneous branch from the tibial nerve to form the sural nerve, which is your go-to for sensation in the back of the leg and the lateral side of the foot.

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Paralysis of the Common Fibular Nerve (aka common peroneal nerve):

In this case of palsy, there wont be any control over the extensor muscles and lateral muscles.

• The common fibular nerve often damages when the fibula fractures, since it wraps snugly around the neck of the fibula.
• If this nerve is damaged, patients lose the ability to dorsiflex the foot at the ankle joint. This means the foot stays permanently plantarflexed, leading to what's known as 'foot-drop.'
• Additionally, the patient will experience a loss of sensation over the top of the foot and along the outer side of the leg.

The most common palsy in the lower limb due to the superficial location and the proximity to the knee joint.

Can also happen because of over-extension of the knee joint.

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Reference:

• Salvador notes ( final notes )
• "Answers for final exam" notes