Swelling on the inside of the ankle, known medically as medial ankle edema, is a common symptom. This complex anatomical area houses the medial malleolus (inner ankle bone), a strong network of ligaments, and several important tendons that stabilize the foot’s arch. Swelling indicates a localized problem, such as an injury or inflammation, or a generalized issue causing fluid to pool due to gravity. Understanding this structure is the first step toward discerning the cause of the swelling.
Specific Injuries to the Inner Ankle
The most frequent source of pain and swelling localized to the inner ankle is Posterior Tibial Tendon Dysfunction (PTTD). This tendon runs along the inside of the ankle, acting as the primary support structure for the foot’s arch during walking and standing. When the tendon is overworked, acutely injured, or subjected to chronic strain, it begins to degenerate, leading to tenosynovitis and noticeable swelling just behind the medial malleolus.
The resulting failure of this tendon can cause the arch to slowly collapse, a condition often termed acquired adult flatfoot deformity. People with PTTD often experience pain that is worse with activity and may notice the swelling is accompanied by a change in foot shape over time. Early diagnosis is beneficial because the progression of the dysfunction can alter the biomechanics of the lower leg.
While most ankle sprains affect the outside (lateral) ligaments, a medial ankle sprain involves damage to the robust deltoid ligament complex. This injury typically requires a high-force eversion mechanism, where the foot is forcefully turned outward. Because the deltoid ligament is one of the strongest in the body, these sprains are less common, but they cause immediate pain and swelling directly over the ligament attachment points.
Another mechanical cause is a stress fracture, which can involve the lower end of the tibia (shin bone) or the talus (ankle bone). These are not acute breaks but rather tiny cracks that develop from repetitive, high-impact activities like running or jumping. The constant microtrauma leads to a localized inflammatory response, resulting in a persistent, bony-feeling swelling and pain that intensifies during weight-bearing activities.
Swelling Caused by Circulation and Foot Structure
Swelling in the inner ankle may also be a manifestation of generalized fluid retention, known as edema, which is gravity-dependent. Conditions affecting the body’s fluid balance, such as chronic venous insufficiency, can cause blood to pool in the lower extremities due to weakened or damaged vein valves. This pooling forces fluid out of the capillaries and into the surrounding tissues, resulting in soft, often bilateral, pitting swelling that is most noticeable around the ankles.
Issues with the heart or kidneys can also impair fluid management, leading to widespread edema that settles in the ankles and feet due to gravity. Separately, the inherent structure of the foot itself contributes significantly to the risk of localized swelling. Feet with excessive pronation, commonly called “flat feet,” place chronic undue strain on the medial ankle structures.
During gait, overpronation causes the arch to roll inward and downward, stretching the posterior tibial tendon and irritating soft tissues. This repetitive biomechanical stress can lead to chronic inflammation or bursitis around the inner ankle, mimicking a direct injury. The resulting localized irritation is a reaction to the mechanical misalignment.
Conditions Involving Inflammation or Infection
Swelling that arises rapidly and is accompanied by intense heat and pain often points toward an inflammatory disease like gout. This condition occurs when high levels of uric acid in the blood lead to the formation of sharp, needle-like crystals that deposit within a joint space. Although it classically affects the big toe, gout frequently targets the ankle joint and surrounding soft tissues, causing an acute flare-up that can be debilitating.
Other forms of inflammatory arthritis, such as rheumatoid arthritis or psoriatic arthritis, can also manifest as inner ankle swelling. These are autoimmune disorders where the body’s immune system mistakenly attacks the lining of the joints, causing chronic synovitis. The resulting accumulation of inflammatory fluid can cause persistent, painful swelling of the ankle joint, often affecting both ankles simultaneously.
A serious cause of inflammatory swelling is cellulitis, a bacterial infection of the skin and underlying tissues. Cellulitis presents with rapidly spreading, diffuse redness and swelling that is warm and tender to the touch, often without a specific focal point of injury. The presence of a fever or chills alongside this localized swelling suggests a systemic infection requiring immediate antibiotic treatment.
When to Seek Immediate Medical Attention
While many causes of inner ankle swelling can be managed with rest and observation, certain symptoms necessitate prompt medical evaluation. The inability to place any weight on the affected foot, or a sudden, sharp increase in pain, may indicate a severe ligament tear, an acute tendon rupture, or a bone fracture. Such mechanical instability requires immediate diagnostic imaging to prevent long-term damage or chronic instability.
Swelling accompanied by systemic signs of illness, such as a fever, chills, or generalized body aches, suggests a serious infection like cellulitis or a widespread inflammatory process. Unilateral swelling that appears suddenly and is accompanied by calf pain or tenderness could indicate a deep vein thrombosis (DVT), a potentially life-threatening blood clot that requires emergency intervention.
If the ankle swelling is bilateral and occurs alongside chest pain, shortness of breath, or palpitations, these are signs that a serious cardiovascular or pulmonary issue may be contributing to the fluid retention. Any swelling that persists for more than three to five days without improvement, despite conservative measures like elevation, ice, and rest, warrants professional diagnosis.