(See also Overview of Foot Problems Overview of Foot Problems Some foot problems start in the foot itself, for example, resulting from a foot injury. Problems can occur in any bone, joint, muscle, tendon, or ligament of the foot. Foot and ankle fractures... read more 
.)
The tibialis posterior tendon helps maintain the normal arch of the foot.
Tibialis posterior tendinosis is usually caused by an excessive ongoing strain caused by a problem with the way the ankle moves. Most often, the person has a low arch, and the foot tends to turn outward when walking, often because the person is overweight. Tendon dysfunction may further contribute to flattening of the arch. The tendon may tear completely, sometimes suddenly in a young person.
Tibialis posterior tenosynovitis begins with sudden inflammation of the tendon sheath. The tendon can be affected by inflammatory disorders, such as rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more 
or gout Gout Gout is a disorder in which deposits of uric acid crystals accumulate in the joints because of high blood levels of uric acid (hyperuricemia). The accumulations of crystals cause flare-ups ... read more 
.
Symptoms
In tibialis posterior tendinosis, early on people have occasional pain behind the inner ankle. In time, the pain becomes severe, and swelling occurs. Normal standing and walking become more difficult. Standing on the toes is usually painful and may be impossible if the tendon is completely torn. If the tendon tears completely, the foot may suddenly flatten (called arch collapse) and pain may be felt in the sole.
In tibialis posterior tenosynovitis, pain typically occurs suddenly and the tendon may feel thick and swollen as it winds around the bump on the inside of the ankle (medial malleolus).
Diagnosis
Doctors can often base the diagnosis on the person’s symptoms and the results of an examination. However, sometimes MRI Computed tomography (CT) and magnetic resonance imaging (MRI) A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more 
is necessary to confirm the diagnosis and to see the extent of tendon damage.
Treatment
For tibialis posterior tendinosis, devices placed in the shoe (orthoses) and ankle braces worn with supportive shoes or boots are usually sufficient. Complete tears are treated surgically so people can function normally again. Surgery is especially important in young active people with tears that develop suddenly.
For tibialis posterior tenosynovitis, rest and nonsteroidal anti-inflammatory drugs Nonsteroidal Anti-Inflammatory Drugs In some cases, treating the underlying disorder eliminates or minimizes the pain. For example, setting a broken bone in a cast or giving antibiotics for an infected joint helps reduce pain.... read more (NSAIDs) are used.
