The lateral malleolus is the prominent bony knob on the outside of your ankle, formed by the end of the fibula bone. It is a fundamental part of the ankle joint, contributing to stability and movement. Swelling in this area indicates that underlying tissues, ligaments, tendons, or bone have experienced trauma, inflammation, or a change in fluid balance. The cause can range from a sudden injury to a gradual, chronic condition.
Acute Traumatic Injuries
Acute swelling around the lateral malleolus usually results from an acute injury, typically involving a twisting or rolling motion of the ankle. The most common trauma is an ankle sprain, which occurs when the ankle is forced beyond its normal range of movement, stretching or tearing the outer ligaments. The anterior talofibular ligament (ATFL), the weakest of the lateral ligaments, is most often damaged in an inversion injury where the foot rolls inward.
Sprains are categorized into grades based on the extent of ligament damage, ranging from Grade 1 (a mild stretch) to Grade 3 (a complete tear). Swelling and bruising are immediate and localized around the outer ankle, increasing with the severity of the sprain. Diffuse swelling, however, may suggest a more serious issue, such as a fracture that accompanies a severe sprain.
A fracture of the lateral malleolus involves a break in the fibula bone itself, causing rapid, significant swelling and pain. This fracture is common and often occurs via the same twisting mechanism that causes a sprain. Differentiating a severe sprain from a fracture often requires medical imaging, like an X-ray, because the symptoms are very similar.
Less commonly, the two peroneal tendons running behind the lateral malleolus can be acutely injured, resulting in a tear or subluxation (dislocation). A forceful muscle contraction can cause a tear or a “popping” sensation as the tendons move out of their groove. This injury typically presents with pain and swelling located specifically behind the lateral malleolus.
Inflammatory and Chronic Conditions
Swelling that develops gradually, persists, or recurs without trauma suggests an inflammatory or chronic underlying problem. Tendinopathy, often affecting the peroneal tendons, involves inflammation from repetitive stress or overuse. This condition causes a dull, constant ache and stiffness, often worsened by walking on uneven surfaces, with swelling focused along the tendon’s path.
Arthritis is a source of persistent swelling caused by joint inflammation. Osteoarthritis, the “wear and tear” type, involves cartilage breakdown and causes recurrent swelling and stiffness, especially in older adults or those with prior ankle injuries. Inflammatory types, such as rheumatoid arthritis, are autoimmune conditions that often cause bilateral swelling in the ankle joint.
Gout, a specific inflammatory arthritis, is caused by the buildup of uric acid crystals in the joint, leading to sudden, intense pain, redness, and swelling. Bursitis occurs when the small, fluid-filled sacs (bursae) that cushion the bones become irritated near the lateral malleolus, causing localized, soft swelling.
Systemic edema, or generalized fluid retention, is a non-injury related cause that can manifest as swelling around the lateral malleolus. This swelling is typically bilateral and occurs due to issues with the heart, kidneys, or liver, which affect fluid management. Unlike trauma-related swelling, this edema is often pitting, meaning a temporary depression remains after pressure is applied.
Immediate Care and Medical Triage
Immediate management of acute swelling and pain around the lateral malleolus starts with the R.I.C.E. protocol: Rest, Ice, Compression, and Elevation. Rest involves avoiding weight-bearing to prevent further damage. Applying ice for 15 to 20 minutes several times a day helps reduce swelling by constricting blood vessels and eases discomfort.
Compression, using a snug elastic bandage, minimizes swelling but must not be wrapped so tightly that it causes numbness or tingling. Elevating the ankle above the heart utilizes gravity to help drain excess fluid. These first aid steps control the initial inflammatory response and are beneficial for nearly all causes of swelling.
When to Seek Medical Attention
Several “red flags” indicate the need for professional medical intervention beyond first aid. Seek immediate medical care if you are unable to bear any weight on the ankle or walk more than a few steps, which may signal a fracture. Other concerning symptoms include visible deformity, numbness or coldness in the foot or toes, or signs of infection such as fever, red streaks, or spreading warmth.
A healthcare provider will perform a physical examination and may order diagnostic imaging to confirm the diagnosis. X-rays are typically used first to rule out a fracture. Ultrasound or magnetic resonance imaging (MRI) may then be used to assess the integrity of soft tissues, such as ligaments and tendons. This process determines if the injury is a stable soft tissue issue managed conservatively or a severe problem requiring casting, bracing, or surgical consultation.