Why is my foot numb or weak after an injury to the outside of my knee?

Why the nerve gets involved

The common peroneal nerve runs just behind the outer knee and curves around the neck of the fibula, very close to where the LCL and the biceps tendon attach. When the knee is forced outward hard enough to tear these structures, the nerve can be stretched, bruised or, rarely, torn. Nerve symptoms are a sign that the injury was forceful and that several ligaments may be involved.

Symptoms to look for

• Numbness or tingling on the top of the foot or the outer side of the lower leg
• Weakness lifting the foot or toes upward
• The foot slapping on the floor or the toes catching when walking, known as foot drop
• Weakness turning the foot outward

Why it is urgent

A nerve injury after a knee injury can be a marker of a knee dislocation that has gone back into place by itself. Knee dislocations can also injure the main artery behind the knee, and that is a limb-threatening emergency. Anyone with new foot numbness or weakness after a significant knee injury should go to an emergency department the same day, or call 999 in Qatar if the leg is cold, pale or very painful.

Once blood flow is confirmed to be normal, the nerve function is documented carefully, as it guides surgical planning and follow-up.

What happens next

Many stretched nerves recover gradually over months, although recovery is not always complete. A foot-up splint helps walking while the nerve recovers, and nerve tests may be used to follow progress. At Aman Hospital in Doha, Dr. Gelber treats the ligament injury and, when the knee is operated on, the nerve is identified and protected. If nerve recovery stalls, referral for specialist nerve surgery may be discussed.