A blood clot, or thrombosis, forms when blood cells clump together, a process necessary to stop bleeding. When this clotting happens inappropriately inside a vein, it can obstruct blood flow. The most common site for a serious clot, known as Deep Vein Thrombosis (DVT), is the larger veins of the calf and thigh. Clots in the heel area are rare but can occur in the deep veins of the foot, sometimes called Plantar Vein Thrombosis (PVT), or in the superficial veins near the skin’s surface. Understanding the difference between these types of clots and other causes of heel pain is important for seeking timely medical attention.
Blood Clot Formation in the Foot and Ankle
The venous system in the lower extremity is divided into deep and superficial veins, and clots in each system carry different levels of risk. Deep Vein Thrombosis (DVT) involves the deep veins, which are surrounded by muscle that helps pump blood back toward the heart. DVT typically originates in the larger veins of the calf or thigh because slower blood flow makes clot formation more likely there.
The deep veins running through the sole of the foot are called plantar veins. A clot forming here is termed Plantar Vein Thrombosis (PVT), a form of distal DVT. PVT can interfere with circulation and cause pain, though it is less common than clots higher up. When a clot forms beneath the skin, it is called Superficial Venous Thrombosis (SVT) or superficial thrombophlebitis. SVT is less dangerous than DVT because these clots are unlikely to travel to the lungs, though they cause localized pain, redness, and inflammation.
SVT is characterized by inflammation and a clot that is often visible or palpable near the skin, sometimes presenting as a hardened cord. The smaller, superficial veins in the foot and ankle are more prone to this localized clotting, especially in people with varicose veins. Any clot in the lower leg requires careful evaluation because a superficial clot can sometimes spread into the deep venous system, increasing the risk of DVT.
Identifying Serious Clot Symptoms
Recognizing the signs of a serious vascular issue is necessary because DVT symptoms can sometimes be subtle or absent. Classic DVT symptoms involve localized physical changes that often manifest quickly. These signs include sudden, unexplained swelling in one leg, ankle, or foot, which is typically unilateral.
The affected area may feel warmer than the surrounding skin, and the skin may appear reddish, pale, or bluish. DVT pain is often described as a deep, aching, or cramping sensation that does not improve with rest or elevation. Concern for a clot increases when these symptoms occur alongside risk factors, such as recent surgery, prolonged immobility, pregnancy, or estrogen-containing medications.
The most serious complication of DVT is a Pulmonary Embolism (PE), which occurs if a piece of the clot breaks off and travels to the lungs. PE symptoms require immediate emergency medical attention. These symptoms include sudden shortness of breath, sharp chest pain that worsens with a deep breath, and a rapid heartbeat. Since DVT can present with non-specific pain in the foot or ankle, any sudden, unexplained combination of swelling, warmth, and deep pain should prompt a medical evaluation.
Other Reasons for Acute Heel Pain
While a blood clot can cause heel pain, most acute cases are due to musculoskeletal issues rather than vascular problems. The most common cause of pain under the heel is Plantar Fasciitis, which involves inflammation of the thick tissue band across the bottom of the foot. This pain is typically sharp and most severe with the first few steps in the morning or after periods of rest.
Pain located just above the heel is often related to Achilles Tendinopathy, characterized by stiffness and tenderness in the tendon connecting the calf muscle to the heel bone. This pain often increases with activities like running or jumping. Stress fractures, which are tiny cracks in the heel bone (calcaneus) from overuse, present as pain that progressively worsens with weight-bearing activities.
A bone bruise, or contusion, can cause deep, localized tenderness in the middle of the heel following trauma, such as landing hard on the foot. Musculoskeletal causes of pain are usually distinguished from a deep vein clot because they are often related to physical activity or impact. They rarely present with the sudden, unilateral, and non-improving swelling characteristic of DVT.
Medical Evaluation and Next Steps
If you experience sudden, unexplained swelling, deep pain, or warmth in your heel or lower leg, seek prompt medical evaluation. Healthcare providers assess the likelihood of a clot using a clinical probability score based on symptoms and risk factors. If DVT is suspected, the initial diagnostic process often involves a blood test called a D-dimer assay, which measures a protein fragment typically elevated when a clot is present.
If the D-dimer test is positive or suspicion is high, the definitive diagnostic tool is usually a duplex ultrasound. This non-invasive test uses sound waves to visualize blood flow and vein compressibility. If the ultrasound probe cannot compress a vein, it indicates the presence of a clot, confirming the diagnosis. Consult a physician for any persistent or worsening heel pain to ensure an accurate diagnosis, regardless of whether the cause is vascular or musculoskeletal.