The inner ankle (medial side) is supported by a complex network of tendons, ligaments, and nerves that stabilize the foot’s arch. While outer ankle injuries are more common, inner ankle pain often suggests a specific underlying condition. The causes of this medial pain generally fall into three categories: chronic issues from overuse, acute trauma, or problems involving nerve compression and structural anomalies. Understanding the source of the discomfort is the first step toward effective diagnosis and recovery.
Overuse and Chronic Tendon Problems
The most frequent cause of chronic inner ankle pain is Posterior Tibial Tendon Dysfunction (PTTD), sometimes referred to as adult-acquired flatfoot. This tendon is a major supporting structure running along the inner ankle, attaching to the midfoot and maintaining the arch. Overuse (e.g., high-impact activities or prolonged standing) causes inflammation (tendinitis) or degenerative changes (tendinosis).
As the condition progresses, the tendon weakens and can no longer effectively support the medial arch of the foot, leading to a gradual flattening. This loss of arch support causes the heel to tilt outward, which is often visible as a collapsing foot structure. Initially, pain and swelling are localized to the bony prominence on the inner ankle, but as the foot flattens, the pain may shift to the outer side of the ankle due to impingement.
A less common chronic issue is tendinitis of the flexor hallucis longus tendon, which controls the big toe. This tendon passes behind the inner ankle bone and is irritated by repetitive push-off motions, common in runners or dancers. Both PTTD and flexor hallucis longus issues are overuse injuries that strain the structures responsible for arch stability.
Sudden Injuries and Ligament Damage
Acute inner ankle pain is typically the result of a traumatic event, most commonly involving a sprain of the Deltoid ligament complex. This exceptionally strong, fan-shaped structure on the medial side resists the foot rolling outward (eversion). Because of its strength, isolated Deltoid ligament sprains are relatively rare, accounting for less than 15% of all ankle sprains.
These injuries usually occur from a powerful external force that causes the foot to roll severely outward, an action known as forced eversion and external rotation. When significant force is involved, the Deltoid ligament injury is often accompanied by a fracture of the outer ankle bone (lateral malleolus). In some cases, the trauma can also result in a fracture of the inner ankle bone itself, known as a medial malleolus fracture.
A fracture to the medial malleolus is a break in the large bony prominence on the inside of the ankle joint. This type of injury requires substantial impact and results in immediate, severe pain, swelling, and often an inability to bear weight. The presence of a fracture or a Deltoid ligament tear signifies an acute destabilization of the ankle joint.
Nerve and Structural Contributors
A distinct source of medial ankle discomfort is Tarsal Tunnel Syndrome (TTS), which involves the compression of the posterior tibial nerve. This nerve passes through the narrow tarsal tunnel on the inner ankle, alongside several tendons and blood vessels. Swelling, a bone spur, or a varicose vein can reduce the space within this tunnel and pinch the nerve.
The symptoms of TTS are characteristic of nerve irritation, including burning, tingling, or an electrical shock sensation radiating into the arch and sole of the foot. This nerve compression causes pain that worsens with activity or prolonged standing, differentiating it from mechanical tendon pain. TTS is sometimes overlooked because its symptoms can be mistaken for other common foot conditions.
Another structural cause is Accessory Navicular Syndrome, a condition present from birth where an extra piece of bone or cartilage exists next to the navicular bone in the arch. This extra bone, found in approximately 4% to 14% of the population, is usually asymptomatic until adolescence or adulthood. Pain arises when the extra bone is irritated by trauma, shoe friction, or strain on the posterior tibial tendon, which attaches directly to the area.
When to Consult a Specialist
While many mild ankle discomforts resolve with rest, certain symptoms warrant a professional medical evaluation. If you experience an immediate inability to place weight on the foot following an injury, or if there is a visible deformity (such as a sudden flattening of the arch), seek prompt attention. These signs indicate an acute fracture or a severe ligament tear.
Persistent symptoms, like pain that does not improve after a week of home care, or swelling that continues to worsen, suggest a condition that requires intervention. The presence of neurological symptoms, such as numbness, tingling, or shooting pain that radiates into the foot, is a red flag for potential nerve entrapment like Tarsal Tunnel Syndrome. Early diagnosis of conditions like PTTD is beneficial, as treatment is more effective before the arch fully collapses.