The posterior tibial tendon lies immediately behind the medial malleolus. Degeneration results from long-standing biomechanical problems, such as excessive pronation (often in obese people) or chronic tenosynovitis.
Tenosynovitis of the tendon sheath begins with acute inflammation. The tendon can be involved by primary inflammatory disorders, such as rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is a chronic systemic autoimmune disease that primarily involves the joints. Rheumatoid arthritis causes damage mediated by cytokines, chemokines, and metalloproteases.... read more 
or gout Gout Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more 
.
(See also Overview of Foot and Ankle Disorders Overview of Foot and Ankle Disorders Most foot problems result from anatomic disorders or abnormal function of articular or extra-articular structures (see figure Bones of the foot). Less commonly, foot problems reflect a systemic... read more .)
Symptoms and Signs
Early on, patients experience occasional pain behind the medial malleolus. Over time, the pain becomes severe, with painful swelling behind the medial malleolus. Normal standing, walking, and standing on the toes become difficult. If the tendon ruptures (eg, with chronic tendinosis), the foot may acutely flatten (arch collapse) and pain may extend into the sole.
In tenosynovitis, pain is typically more acute and the tendon may feel thick and swollen as it courses around the medial malleolus.
Diagnosis
MRI
Tibialis posterior tendinosis and tenosynovitis are diagnosed clinically. Palpation of the tendon with the foot in an inverted plantar flexed position with applied resistance is usually painful. Standing on the toes is usually painful and may not be possible if the tendon is ruptured or severely dysfunctional. Pain and swelling with tenderness of the tibialis posterior tendon behind the medial malleolus is suggestive of tenosynovitis. Unilateral arch collapse with medial ankle bulging and forefoot abduction (too many toes sign) is particularly suggestive of advanced tendon pathology and warrants testing for tendon rupture.
MRI or ultrasonography can confirm a fluid collection around the tendon (indicating tenosynovitis) or the extent of chronic degradation or tearing to the tendon with associated tendinosis.
Treatment
Orthotics and braces or surgery
Complete rupture of the tibialis posterior tendon requires surgery if normal function is the goal. Surgery is especially important in young active patients with acute tears. Conservative therapy consists of mechanically off-loading the tendon by using custom-molded ankle braces or orthotics modified with a deepened heel cup and appropriate medial wedging or posting. Corticosteroid injections exacerbate the degenerative process (see Considerations for using corticosteroid injections Considerations for Using Corticosteroid Injections 
).
For tenosynovitis, rest and aggressive anti-inflammatory therapy are warranted.
