The ulnar nerve is not located in the knee; it is one of the major nerves of the upper limb, responsible for sensation and motor function in the forearm and hand. The common confusion about its location likely stems from the specific, sharp sensation people experience when the nerve is struck, commonly referred to as hitting the “funny bone.” It originates from the brachial plexus in the neck and shoulder and descends down the arm.
The Ulnar Nerve’s Actual Path
The ulnar nerve begins high in the arm and continues its descent along the inner side toward the elbow. It passes through a narrow space behind the medial epicondyle, the bony prominence on the inner side of the elbow joint. This passage, known as the cubital tunnel, leaves the nerve relatively exposed and close to the skin surface.
The characteristic tingling, electrical shock sensation of the “funny bone” occurs when this exposed section of the nerve is compressed or bumped. After passing the elbow, the nerve travels into the forearm and extends into the hand, providing sensory input to the pinky finger and the adjacent half of the ring finger. It also controls small muscles in the hand responsible for fine motor movements, such as gripping and pinching.
The Nerve Often Mistaken for the Ulnar Nerve
The nerve in the knee area prone to similar compression-related symptoms is the Common Fibular Nerve, also known as the Common Peroneal Nerve. This nerve is a major branch of the sciatic nerve, which runs down the back of the thigh and splits near the knee.
The Common Fibular Nerve is particularly vulnerable to injury and compression where it wraps around the head of the fibula, just below the knee joint. Consistent pressure from activities like prolonged squatting, wearing tight casts, or habitually crossing one’s legs can compress this nerve at this superficial point.
Compression of the Common Fibular Nerve can cause symptoms that mimic the ulnar nerve’s electric shock feeling, including numbness and tingling in the outer lower leg and the top of the foot. Unlike the ulnar nerve, damage to this nerve can lead to a condition called “foot drop,” which is the inability to lift the front part of the foot, causing the toes to drag while walking.
When to Seek Medical Guidance
While mild tingling or numbness from temporary pressure often resolves quickly with rest, persistent or worsening nerve symptoms require medical evaluation. If the tingling, pain, or numbness from a compressed nerve lasts for more than a few days, or if it does not improve with simple self-care measures, consult a healthcare provider.
Specific warning signs that warrant immediate attention include a sudden onset of severe weakness in the affected limb, such as the inability to grip objects or the inability to lift the foot (foot drop). Timely diagnosis and treatment are important, as unrelieved pressure on a peripheral nerve can lead to long-term or permanent damage.