Swelling below the knee occurs when excess fluid accumulates in the lower leg tissues. This fluid buildup can be temporary and harmless, or it may signal an underlying health issue. Understanding the causes of fluid retention in the lower extremities helps determine when medical attention is needed. This article explores common everyday causes and more serious medical conditions that can lead to this symptom.
Everyday Factors and Minor Issues
Many common, non-medical situations can lead to temporary swelling below the knee. Prolonged periods of standing or sitting, such as during long flights or desk-bound work, can cause fluid to pool in the lower extremities due to gravity. Minor injuries like an ankle sprain or a calf muscle strain can also result in localized swelling, as the body’s inflammatory response sends fluid to the injured area to aid in healing.
Warm weather and high humidity can contribute to leg swelling by causing blood vessels to dilate, allowing more fluid to leak from capillaries into surrounding tissues. Dietary choices play a role, with high sodium intake leading the body to retain water in an effort to balance electrolyte levels. For some individuals, particularly women, hormonal fluctuations associated with the menstrual cycle can induce temporary fluid retention throughout the body, including the legs. These factors often resolve with rest, elevation, or simple lifestyle adjustments.
Underlying Medical Conditions
Swelling below the knee can also be a symptom of various medical conditions. These conditions often affect the circulatory, lymphatic, or organ systems.
Vascular Issues
Vascular issues are a frequent cause of leg swelling. Deep Vein Thrombosis (DVT) involves a blood clot forming in a deep vein, often in the calf, which obstructs blood flow and causes pressure to build up, leading to fluid leakage into surrounding tissues. This type of swelling typically affects only one leg and may be accompanied by pain, redness, or warmth. Chronic venous insufficiency (CVI) occurs when valves in the leg veins are damaged, preventing blood from flowing efficiently back to the heart. This causes blood to pool in the lower legs, increasing pressure within the capillaries and forcing fluid into the tissues, often resulting in swelling that can be unilateral or bilateral.
Systemic Conditions
Systemic conditions affecting major organs can also manifest as leg swelling. Congestive heart failure (CHF) means the heart cannot pump blood effectively, leading to blood backing up in the veins and increasing pressure, which causes fluid to leak into the legs, often in both lower limbs. Kidney disease impairs the kidneys’ ability to filter waste and excess fluid from the blood, resulting in widespread fluid retention that can be noticeable in the legs and around the eyes. Liver disease, particularly cirrhosis, can lead to swelling because the damaged liver produces less albumin, a protein that helps keep fluid within blood vessels, and can also cause increased pressure in the veins supplying the liver.
Lymphatic Issues and Infections
Problems with the lymphatic system can cause a specific type of swelling called lymphedema. This condition arises when the lymphatic vessels are damaged or blocked, preventing the proper drainage of lymph fluid, which then accumulates in the tissues and causes swelling. Infections, such as cellulitis, a bacterial infection of the skin and underlying tissues, trigger a localized inflammatory response that results in redness, warmth, and swelling in the affected area.
Medications and Inflammatory Conditions
Certain medications are known to cause fluid retention as a side effect. Calcium channel blockers, commonly prescribed for high blood pressure, can cause swelling by widening blood vessels and increasing pressure within capillaries, leading to fluid leakage. Nonsteroidal anti-inflammatory drugs (NSAIDs) can lead to fluid retention by affecting kidney function and the body’s sodium and water balance, especially with prolonged use or in individuals with pre-existing heart or kidney conditions. Corticosteroids and some diabetes medications can also alter fluid and salt balance, contributing to leg swelling. Inflammatory conditions like various forms of arthritis can cause localized swelling around affected joints in the leg.
Important Warning Signs
While leg swelling can stem from benign causes, certain signs indicate a serious underlying condition that warrants medical attention. A sudden onset of swelling, particularly if it occurs only in one leg, is a significant concern. This is especially concerning if accompanied by pain, tenderness, redness, or warmth in the calf or leg, as these symptoms can point to a deep vein thrombosis (DVT). If leg swelling is accompanied by a fever, it may suggest an infection like cellulitis. Shortness of breath or chest pain alongside leg swelling is a serious concern, as these symptoms could indicate heart issues or a pulmonary embolism, a potentially serious complication of DVT. Any leg swelling that does not improve with elevation or rest, or if there are noticeable skin changes like blistering or ulceration, should prompt a medical evaluation.