Numbness, medically known as paresthesia, is a common symptom described as a sensation of tingling, “pins and needles,” or a complete loss of feeling. When this occurs around the kneecap (patella), it typically indicates that the small sensory nerves supplying that area have been irritated, compressed, or damaged. This altered sensation is usually an isolated issue affecting only the skin, not the larger nerves that control muscle movement.
The Nerves Responsible for Sensation
Sensation in the skin below and around the kneecap is primarily managed by the infrapatellar branch of the saphenous nerve. The saphenous nerve is the longest purely sensory nerve in the leg, originating as a branch of the femoral nerve high in the groin. It travels down the inner side of the thigh and knee, providing feeling to the skin along its path.
The infrapatellar branch is particularly vulnerable because it separates from the main nerve trunk and must pierce through connective tissue layers, such as the sartorius muscle fascia, near the joint line. This branch forms part of a small network of nerves over the kneecap called the plexus patellae. Damage or irritation to this specific branch is the most frequent cause of isolated numbness in the anterior knee area.
Mechanical Injury and Compression
Knee numbness often relates to direct physical forces acting on the sensory nerves. Acute trauma, such as a direct blow to the knee during a fall or sports injury, can cause localized swelling and bruising. This inflammation puts temporary pressure on the infrapatellar nerve branch, interrupting signal transmission and resulting in numbness.
External compression is another frequent mechanical cause, often stemming from everyday activities or medical devices. Wearing an overly tight knee brace, compression garment, or restrictive clothing can squeeze superficial nerves against underlying structures. Prolonged positions, such as extended kneeling on hard surfaces, can also directly compress the nerve, leading to transient numbness.
The healing process following an injury can also lead to nerve entrapment when scar tissue or persistent swelling compresses the nerve. For example, a major ligament injury like an anterior cruciate ligament (ACL) tear can cause internal swelling that pinches nearby nerves. This nerve irritation is often temporary, resolving as the acute injury heals and the swelling subsides.
Underlying Medical Conditions and Surgery
Numbness not linked to mechanical injury may stem from a systemic medical problem affecting nerve health. Peripheral neuropathy, which involves damage to nerves outside the brain and spinal cord, is a common culprit. This disorder results from various systemic diseases, with diabetes being the most frequent cause due to high blood sugar levels damaging nerve fibers.
Diabetic neuropathy typically affects the longest nerves first, causing tingling and numbness that begins in the feet and gradually progresses upward, sometimes reaching the knee area. Other metabolic disorders, vitamin deficiencies, or autoimmune diseases can also contribute to this generalized nerve damage. Chronic joint conditions like severe osteoarthritis can also cause bony spurs or inflammation that irritates sensory nerves within the knee joint.
Surgical Causes
Intentional medical interventions, particularly surgery, are a common and expected cause of numbness around the kneecap. Procedures like total knee arthroplasty (TKA), or total knee replacement, require a significant incision that unavoidably disrupts superficial sensory nerve branches. A high percentage of patients experience some degree of objective numbness around the incision site following TKA.
Less invasive procedures like arthroscopy also carry a risk of nerve injury, particularly to the infrapatellar branch. Surgical numbness is usually localized to a patch of skin on the outer or lower aspect of the kneecap. While this loss of sensation can be long-lasting or permanent, it rarely causes functional problems, and the area of numbness often shrinks over the first six to twelve months as the nerve attempts to regenerate.
Diagnosis and Treatment Options
A healthcare professional will begin the diagnostic process by performing a thorough physical examination and taking a detailed medical history to pinpoint the cause of the numbness. The physical exam includes testing sensation with light touch and pinprick in the affected area, which helps map the specific nerve distribution involved. The doctor will also check for localized tenderness, which is a common sign of a nerve entrapment issue.
In some cases, further testing may be necessary to confirm the diagnosis and rule out more serious conditions. Nerve conduction studies and electromyography (NCS/EMG) can measure the speed and strength of electrical signals passing through the nerves, helping to assess the extent of nerve damage. Imaging, such as Magnetic Resonance Imaging (MRI), can visualize soft tissues to identify tumors, cysts, or severe swelling that may be compressing a nerve.
Treatment for knee numbness is entirely dependent on the underlying cause. If the numbness is due to external compression or a mild injury, conservative measures are usually effective, including rest, activity modification, and avoiding tight garments. For inflammatory causes, non-steroidal anti-inflammatory drugs (NSAIDs) can help reduce swelling that is irritating the nerve.
For more persistent symptoms, physical therapy can be beneficial, employing techniques such as nerve gliding exercises to help the nerve move freely within its surrounding tissues. A diagnostic nerve block, involving an injection of a local anesthetic near the suspected nerve, can confirm the source of the sensation change and may also provide temporary relief. If the numbness is severe, persistent, and caused by a clear point of entrapment, a surgical procedure to decompress the nerve may be considered. Persistent numbness, especially if it spreads, is accompanied by muscle weakness, or causes changes in walking, should prompt a medical evaluation.