A patient underwent a coronary bypass graft with the great saphenous vein. The patient now complains of paresthesia and sensory loss over the medial aspect of the leg and foot. Which of the following nerves is most likely to be involved?

Correct Answer: C. Saphenous nerve

The saphenous nerve is the terminal sensory branch of the femoral nerve, arising from the femoral nerve in the femoral triangle. It descends medially along the thigh, accompanying the saphenous vein (the great saphenous vein—GSV), and provides cutaneous innervation to the medial aspect of the leg and foot. During coronary artery bypass grafting (CABG), the GSV is harvested as a conduit for the graft. The saphenous nerve runs in close anatomical proximity to the GSV throughout its course, particularly in the medial thigh and leg. Iatrogenic injury to the saphenous nerve is a well-recognized complication of GSV harvesting, occurring in 10–30% of CABG patients in Indian and international series. The nerve can be stretched, ligated, or divided during vein stripping or dissection. Patients present with paresthesia, numbness, or dysesthesia over the medial leg and foot—exactly as described. This is a common postoperative morbidity in cardiac surgery units across India. The sensory deficit is typically permanent but non-disabling, though it can cause significant patient distress. Recognition of this complication is critical for informed consent and surgical technique refinement.

Why the other options are wrong

A. Femoral nerve — The femoral nerve is the parent nerve of the saphenous nerve and innervates the anterior thigh and knee joint. Femoral nerve injury would cause motor loss (quadriceps weakness, loss of knee extension) and sensory loss over the anterior and medial thigh—a much broader distribution than isolated medial leg/foot paresthesia. GSV harvesting does not injure the femoral nerve trunk itself, only its terminal sensory branch. B. Superficial peroneal nerve — The superficial peroneal nerve (branch of common peroneal) innervates the lateral compartment of the leg and provides sensation to the lateral leg and dorsum of the foot. Injury causes foot drop and sensory loss over the lateral leg—not the medial aspect. This nerve is not at risk during GSV harvesting, which occurs along the medial thigh and leg. D. Sural nerve — The sural nerve is formed from branches of the tibial and common peroneal nerves and innervates the lateral border of the foot and heel. While it can be injured during saphenous vein harvesting in some cases, it is not the primary nerve at risk. Medial leg and foot sensory loss is characteristic of saphenous nerve injury, not sural nerve injury, which would affect the lateral foot.

High-Yield Facts

Mnemonics

GSV Harvest Nerve Injury Great Saphenous Vein → Saphenous nerve injury. The vein and nerve travel together medially; harvest the vein, risk the nerve. Saphenous = Medial Saphenous → Sensory Medial leg/foot. Remember: Saphenous = Sensory + Medial distribution.

NBE Trap

NBE may lure students who confuse the femoral nerve (parent nerve) with the saphenous nerve (terminal sensory branch), or who incorrectly associate lateral leg symptoms with GSV harvesting. The key discriminator is the medial distribution of sensory loss and the sensory-only (no motor) deficit.

Clinical Pearl

In Indian cardiac surgery units, saphenous nerve injury is so common after CABG that it is now considered an expected complication rather than a surgical error. Patients undergoing GSV harvesting should be counseled preoperatively about the risk of medial leg numbness, which helps manage expectations and reduces postoperative dissatisfaction. Minimally invasive vein harvesting techniques are increasingly used to reduce this complication.

_Reference: Bailey & Love Ch. 52 (Cardiac Surgery); Robbins Ch. 27 (Peripheral Nerve Injury); Harrison Ch. 379 (Coronary Artery Disease)_