An intern was doing saphenous cannulation for a burn patient. Then the patient developed sudden onset of pain along the medial border of the corresponding foot. Which nerve must have beenaccidentally ligated?
**Core Concept**
The question tests the knowledge of the saphenous nerve, a branch of the femoral nerve that provides sensory innervation to the medial aspect of the lower limb. The saphenous nerve is particularly susceptible to injury during procedures involving the saphenous vein, such as cannulation.
**Why the Correct Answer is Right**
The saphenous nerve arises from the femoral nerve, a branch of the lumbar plexus. It descends through the adductor canal, passes behind the saphenous opening, and traverses the medial aspect of the leg, providing sensory innervation to the skin and subcutaneous tissue. Accidental ligation of this nerve during saphenous cannulation can lead to sudden onset of pain along the medial border of the foot due to nerve compression or transection.
**Why Each Wrong Option is Incorrect**
**Option A:** The sural nerve, a branch of the common peroneal nerve, provides sensory innervation to the lateral aspect of the leg and foot, making it an unlikely candidate for the nerve accidentally ligated in this scenario.
**Option B:** The saphenous nerve is not a branch of the sciatic nerve, which is a larger nerve that provides motor and sensory innervation to the lower limb. This distractor is incorrect because the saphenous nerve originates from the femoral nerve, not the sciatic nerve.
**Option C:** The femoral nerve itself is a larger nerve that provides motor innervation to the anterior compartment of the thigh and some sensory innervation to the medial aspect of the leg. While it is related to the saphenous nerve, it is not the correct answer because the question specifically asks about the nerve that was accidentally ligated.
**Clinical Pearl / High-Yield Fact**
Remember that the saphenous nerve is particularly susceptible to injury during procedures involving the saphenous vein, such as cannulation. This is because the saphenous nerve descends through the adductor canal and passes behind the saphenous opening, making it vulnerable to compression or transection.
**Correct Answer:** B. The common peroneal nerve.