The saphenous nerve is a purely sensory nerve, carrying information about touch, temperature, and pain back to the spinal cord and brain. It is the largest and longest terminal branch of the femoral nerve, originating from the lumbar plexus in the lower back. Since it lacks motor function, injury to the saphenous nerve results only in changes to sensation, such as numbness or pain, and not muscle weakness.
Anatomical Origin and Path
The saphenous nerve begins in the upper thigh as a branch of the femoral nerve, with fibers derived primarily from the L3 and L4 spinal nerve roots. It descends through the thigh, initially traveling through the deep, muscular adductor canal (Hunter’s canal). This canal also contains the femoral artery and vein, and the nerve maintains an intimate relationship with these major blood vessels.
The nerve then separates from the vessels and exits the adductor canal near the inner side of the knee. It becomes superficial by piercing the fascia between the sartorius and gracilis muscles, continuing its path down the medial side of the leg alongside the great saphenous vein.
Sensory Distribution in the Knee and Thigh
The saphenous nerve provides sensory innervation to the skin on the medial side of the distal thigh before reaching the knee. It also contributes to the sensation of the knee joint itself, supplying parts of the fibrous capsule that surrounds the joint.
A major branch, the infrapatellar branch, separates from the main nerve trunk near the knee. This branch curves toward the front of the joint to supply sensation to the skin anterior and medial to the kneecap (patella). Because of its superficial location, the infrapatellar branch is particularly vulnerable to injury during surgical procedures around the knee. The main nerve trunk continues past the knee, providing a continuous strip of sensation down the inner leg.
Sensory Distribution in the Leg and Foot
The saphenous nerve is the primary source of sensation for the entire medial side of the lower limb below the knee. It runs along the inner side of the calf, supplying the skin that covers the shin bone (tibia) down to the ankle. This extensive coverage is provided by its terminal branches, which travel with the great saphenous vein.
As the nerve descends, it provides numerous medial crural cutaneous branches covering the skin of the inner calf. At the ankle, the nerve continues to supply the skin over the medial malleolus, which is the bony prominence on the inside of the ankle. The nerve extends its reach into the foot, typically supplying the skin over the medial arch and sometimes as far forward as the base of the great toe. The long, continuous sensory strip provided by the saphenous nerve is distinct from the sensory areas supplied by other nerves in the lower leg, such as the sural or superficial peroneal nerves.
Clinical Significance of Nerve Injury
The long, superficial course of the saphenous nerve makes it susceptible to injury, often causing chronic pain and numbness in the lower leg. The nerve can be damaged during various surgical procedures, including total knee replacement, meniscus repair, or operations to harvest veins for bypass surgery. Due to its close proximity to the great saphenous vein, it is also at risk during varicose vein stripping or endovenous ablation procedures.
The nerve can also become compressed or entrapped, a condition known as saphenous nerve neuropathy. This typically occurs where the nerve passes through the adductor canal or where it becomes superficial near the knee. Symptoms often include a burning sensation, tingling (paresthesia), or numbness along the medial side of the knee, leg, and ankle.
Since the nerve is purely sensory, a diagnosis of saphenous nerve injury will not include motor weakness, which helps doctors distinguish it from more serious conditions like femoral nerve damage or nerve root compression in the spine.