The bony prominence on the inner side of your ankle is called the medial malleolus. It is the lower end of the tibia (your shinbone), which flares out to form that hard bump you can feel just under the skin. The medial malleolus is not just a landmark you occasionally bang against a table leg; it anchors a network of ligaments, tendons, and nerves that keep your foot stable and moving properly. Problems in this area range from sprains to stress fractures to nerve compression, and they are often underdiagnosed because inner-ankle pain gets less attention than the outer side.
What Exactly Is the Medial Malleolus
The medial malleolus is the portion of the tibia that extends downward and slightly inward at the ankle joint. If you run your fingers along the inside of your ankle, the hard ridge you feel is the medial malleolus. Its counterpart on the outer ankle, the lateral malleolus, is the bottom of the fibula. Together, these two bony projections form a mortise that grips the talus, the bone sitting on top of your heel bone, and creates the main hinge of the ankle joint.
Between the medial malleolus and the talus, the joint capsule is reinforced by dense fibrous tissue that holds these bones tightly together. The tibial side of this attachment sits in a groove-like depression, and the talar side forms an elliptical depressed area, creating a snug mechanical fit that resists the ankle from shifting inward or outward during movement.1PubMed Central. Anatomic study of the medial side of the ankle base on the joint capsule: an alternative description of the deltoid and spring ligament The medial malleolus is also the starting point for the deltoid ligament, the strongest ligament complex on the inner ankle, and it serves as a passageway for several tendons and nerves that run behind it on their way to the foot.
The Deltoid Ligament Complex
The deltoid ligament is the primary stabilizer of the inner ankle. It fans out from the medial malleolus in a roughly triangular shape, connecting the tibia to several bones below: the talus, the calcaneus (heel bone), and the navicular. Anatomists divide it into a superficial layer and a deep layer, though in practice these layers blend into a single continuous band of tissue rather than separating neatly into independent cords.2PubMed. The deltoid ligament: an in-depth review of anatomy, function, and treatment strategies
Cadaver studies have identified as many as six distinct ligamentous bands within the deltoid complex, including two superficial components and four deep ones.3PubMed Central. Defining the Components of the Deltoid Ligament (DL): A Cadaveric Study The deep portion attaches directly from the tibia to the talus and is the main restraint against the talus tilting or rotating outward within the ankle mortise. The superficial portion covers a wider area and helps resist the foot from rolling into excessive eversion, that outward-tilting motion you might experience when stepping awkwardly on an uneven surface. The reason this matters to you in everyday life is that the deltoid ligament’s strength is a big part of why inner-ankle sprains are far less common than outer-ankle sprains. It takes considerably more force to overcome this ligament than the thinner ligaments on the lateral side.
Tendons Running Behind the Medial Malleolus
Several important tendons pass through a groove just behind the medial malleolus on their way from the calf muscles to the foot. The largest and most forward of these is the posterior tibial tendon, which plays a central role in pointing your foot downward and turning the sole inward. Crucially, it is the primary dynamic support for your foot’s arch.4PubMed. Tibialis posterior: a review of anatomy and biomechanics in relation to support of the medial longitudinal arch Behind it run the tendons of the flexor digitorum longus (which curls the lesser toes) and the flexor hallucis longus (which curls the big toe).5PubMed Central. Tarsal Tunnel Syndrome – A Comprehensive Review
These tendons travel through a fibrous channel called the tarsal tunnel, which also houses the posterior tibial artery and the tibial nerve. Think of the space behind your medial malleolus as a packed corridor: bones form the floor and walls, and a thick band of connective tissue called the flexor retinaculum forms the roof. When everything fits well, the structures glide past each other smoothly. When something swells, shifts, or degenerates, problems follow quickly because there is very little room to spare.
Medial Ankle Sprains
Most people associate ankle sprains with the outside of the ankle, and with good reason: lateral sprains are far more common. But medial sprains do happen, and they tend to be more serious when they do. The injury mechanism involves the foot being forced into pronation, abduction, and dorsiflexion, essentially twisting outward and upward at the same time. The rapid change in ankle orientation strains the deltoid ligament first, and if the force is large enough, damage can extend to ligaments on the outer side as well.6Asia-Pacific Journal of Sports Medicine, Arthroscopy, Rehabilitation and Technology. Kinematic analysis of a televised medial ankle sprain
In contact sports, the most common cause is direct impact. A study of ankle sprains in the NFL found that about four out of five eversion-mechanism injuries resulted from direct contact to the foot, ankle, or leg from a large external force such as an opponent’s body during a tackle. Only about 15% of the reviewed injuries came from forces transmitted solely through the shoe’s interaction with the playing surface.7PubMed. Injury Scenarios of Ankle Sprains in the National Football League: External Rotation and Eversion Mechanisms This helps explain why medial sprains are more often seen in collision sports than in, say, trail running, where lateral sprains dominate.
Diagnosing a medial sprain can be tricky. The standard clinical test is the eversion stress test, where a clinician stabilizes your lower leg and applies an outward-tilting force to the heel while comparing the amount of movement to the uninjured side. However, this test lacks strong evidence for its sensitivity and specificity, and data supporting its diagnostic accuracy are essentially absent from the literature.8Archives of Rehabilitation Research and Clinical Translation. Physical Examination of the Ankle: A Review of the Original Orthopedic Special Test Description and Scientific Validity of Common Tests for Ankle Examination – Section: Orthopedic tests for examining sprains of the medial collateral ligaments of the ankle Imaging usually picks up the slack. Ultrasound combined with standard X-rays can grade deltoid ligament injuries with results that closely match MRI findings, offering a faster and cheaper initial assessment.9WFUMB Ultrasound Open. Added clinical advantage of combining ultrasound with radiograph in assessing ankle injuries: Comparison with MRI
Posterior Tibial Tendon Dysfunction
If there is one condition on the inner ankle that flies under the radar, it is posterior tibial tendon dysfunction. This is the most common cause of adult-acquired flatfoot, and it develops gradually, often over years.10PubMed Central. Posterior Tibial Tendon Dysfunction: An Overview Because the posterior tibial tendon is the main muscular support for your arch, when it weakens or tears, the arch slowly collapses and the foot begins to roll inward more than it should.
Early on, the main symptom is pain and swelling along the inner ankle, particularly during walking or standing for long periods. If left untreated, the tendon degeneration progresses and can lead to visible foot deformity and degenerative changes in surrounding joints.11PubMed Central. Posterior tibial tendon dysfunction: an overlooked cause of foot deformity The classic profile of someone who develops this condition is an overweight woman over 50 with pre-existing flat feet, but it can affect younger and more active people as well, especially runners who log high mileage.
What makes this condition particularly frustrating is its progressive nature. Research on how the hindfoot responds to loss of posterior tibial tendon function shows that the remaining ligaments and bones can initially compensate and maintain normal alignment. But once those soft tissues start to stretch and weaken under the repeated abnormal loading, the tendon alone cannot correct the position of the foot, and the deformity becomes self-reinforcing.12PubMed. The effect of posterior tibial tendon dysfunction on hindfoot kinematics Early intervention, usually with supportive bracing, physical therapy, and shoe inserts, is far more effective than trying to reverse a deformity that has already set in. Insoles with medial arch and heel support have been shown to reduce excessive ankle eversion during walking by a few degrees, which sounds modest but can meaningfully reduce strain on the tendon over thousands of daily steps.13PubMed Central. Effect of medial arch-heel support in inserts on reducing ankle eversion: a biomechanics study
Tarsal Tunnel Syndrome
The tarsal tunnel, that crowded corridor behind the medial malleolus, is where the tibial nerve can get pinched. Tarsal tunnel syndrome is essentially the ankle’s version of carpal tunnel syndrome in the wrist. Compression of the tibial nerve within this space causes pain, numbness, tingling, and sometimes weakness along the bottom of the foot and heel.5PubMed Central. Tarsal Tunnel Syndrome – A Comprehensive Review
The symptoms can come on gradually over months or years, or start suddenly after an injury. Almost anything that physically reduces the volume of the tarsal tunnel can trigger it: swelling from a sprain, a ganglion cyst, varicose veins in the area, scar tissue from a prior injury, or even systemic conditions like diabetes that make nerves more vulnerable to compression.14PubMed Central. An Update on Posterior Tarsal Tunnel Syndrome The clinical picture varies a lot from person to person because the tibial nerve branches within the tunnel, and exactly where the compression occurs determines which part of the foot is affected. Some people feel burning pain across the entire sole, while others have numbness isolated to just the heel or just the toes.
Tarsal tunnel syndrome is one of several nerve entrapment conditions that can affect the foot and ankle, and distinguishing it from other causes of foot pain, like plantar fasciitis, can be challenging. Repetitive strain and anatomical variations both play a role in who develops it.15PubMed Central. Overview of nerve entrapment syndromes in the foot and ankle If you have persistent burning or tingling along the inner ankle and sole of the foot, especially if tapping the area behind the medial malleolus reproduces the symptoms, it is worth having the nerve evaluated rather than assuming the pain is purely muscular or skeletal.
Stress Fractures of the Medial Malleolus
The medial malleolus itself can develop stress fractures, particularly in athletes involved in running and jumping sports. These are overuse injuries rather than sudden breaks: repetitive loading gradually weakens the bone until a crack forms. Soccer is the sport most commonly associated with medial malleolar stress fractures.16PubMed Central. Medial Malleolar Stress Fracture Treatment and Return to Activity: A Systematic Review
Symptoms tend to be vague at first: generalized ankle pain, mild swelling, and tenderness when pressing directly over the medial malleolus. Pain worsens with weight-bearing or high-impact activity and is often provoked by dorsiflexion, bending the ankle upward. Some athletes push through the discomfort for weeks or months before seeking help, with symptom duration before clinical presentation ranging from as few as five days to as long as a year.17PubMed Central. The Treatment and Outcomes of Medial Malleolar Stress Fractures: A Systematic Review of the Literature The danger of ignoring a stress fracture here is that it can progress to a complete fracture, which is a much bigger problem requiring surgery and a longer recovery.
Impingement and Osteochondral Lesions
Two related conditions can cause deep, nagging pain near the medial malleolus: ankle impingement and osteochondral lesions of the talus.
Medial ankle impingement occurs when bony spurs develop on the leading edge of the medial talar facet and on the tibia just in front of the medial malleolus. These “kissing” osteophytes bump against each other during dorsiflexion, causing pain and limiting how far you can bend your ankle upward. The condition is especially common in athletes who run and jump repeatedly, and it may be associated with subtle foot-shape variations, prior ankle instability, or previous talar injuries.18PubMed Central. Medial impingement of the ankle in athletes
Osteochondral lesions of the talus are areas where the cartilage and underlying bone on the talus become damaged, often after ankle injuries. Symptoms are nonspecific and overlap with many other inner-ankle problems: pain, swelling, stiffness, and sometimes mechanical catching or locking of the joint.19PubMed Central. Management of Osteochondral Lesions of the Talar Dome Medial lesions on the talus are frequently linked to a history of trauma, with about 80% of medial dome lesions traceable to a prior injury.20PubMed. Osteochondritis dissecans of the talus (transchondral fractures of the talus): review of the literature and new surgical approach for medial dome lesions Chronic cases or those with displaced cartilage fragments often end up requiring surgical treatment, so persistent deep ankle pain after a previous sprain warrants imaging rather than a wait-and-see approach.
The Accessory Navicular Bone
Not everyone’s inner ankle anatomy follows the textbook. One of the more common variations is the accessory navicular bone, an extra piece of bone embedded near the navicular, which sits just below and slightly forward of the medial malleolus. Estimates of how many people have one vary, but studies place the prevalence somewhere between about 4% and 23% of the general population, depending on the study group and imaging method used.21The Egyptian Rheumatologist. Symptomatic accessory navicular bone: A case series22PubMed Central. Prevalence and classification of accessory navicular bone: a medical record review A large radiographic review found accessory navicular bones in roughly one in five patients presenting with ankle pain, with middle-aged adults being the most commonly affected group.23PubMed. Accessory navicular bone incidence in Chinese patients: a retrospective analysis of X-rays following trauma or progressive pain onset
Many people live their entire lives with an accessory navicular and never know it is there. The bone becomes a problem when it is irritated by shoe pressure, repetitive activity, or trauma. It can cause pain and swelling on the medial side of the foot, sometimes contributing to flat-footedness because the posterior tibial tendon, which attaches to the navicular, may not pull as effectively when the bone’s anatomy is altered. The condition is worth knowing about because it is a surprisingly common source of inner-ankle and midfoot pain that is easy to miss if nobody thinks to look for it on an X-ray. When conservative treatments like padding, orthotics, and activity modification fail, surgical removal of the extra bone is an option with generally good outcomes.
When to Pay Attention to Inner Ankle Pain
Inner-ankle pain is easy to dismiss as a minor strain, but the anatomy packed behind the medial malleolus means the cause is not always obvious. A few patterns are worth knowing. Pain that worsens specifically with dorsiflexion, bending your ankle upward toward the shin, can point toward impingement or a stress fracture. Burning or tingling that radiates to the sole of your foot suggests nerve involvement and possible tarsal tunnel syndrome. A gradually flattening arch combined with inner-ankle pain is a red flag for posterior tibial tendon dysfunction, and earlier treatment yields much better results than waiting. Pain that appeared after an ankle sprain and never fully resolved may indicate an osteochondral lesion on the talus rather than simple ligament healing.
A standard X-ray will catch fractures and bony spurs but will miss soft-tissue injuries. Ultrasound is increasingly used as a first-line tool alongside X-rays for evaluating the inner ankle because it can assess ligaments, tendons, and fluid collections in real time and at relatively low cost. When ultrasound and X-ray findings are combined, bone fracture detection improves significantly compared to using either modality alone.9WFUMB Ultrasound Open. Added clinical advantage of combining ultrasound with radiograph in assessing ankle injuries: Comparison with MRI MRI remains the gold standard for detailed evaluation of cartilage, deep ligaments, and tendons, but it is not always necessary as a first step.