Posterior tibial tendon dysfunction is a disorder in which nomenclature remains confusing, with current nomenclature including: posterior tibial tendon dysfunction, posterior tibial tendon syndrome, posterior tibial muscle insufficiency, and adult acquired flatfoot. The posterior tibial muscle is located between the long toe flexors and the long bunion flexors and starts behind the interosseous membrane of the tibia, fibula and calf, and the long tendon runs behind the medial ankle to the medial plantar aspect of the foot, ending at the navicular ramus and the medial, middle and lateral cuneiform bones, and its function is to plantarflex the ankle joint (to bring the foot down) and to turn the ankle inward (to turn the plantar aspect of the foot inward). When the posterior tibial tendon is dysfunctional due to various etiologies, it can cause secondary flattening of the arch, followed by hindfoot valgus, midfoot abduction, and forefoot rotation forward. The occurrence of various deformities is related to the degree of loss of function of the posterior tibial tendon and is most pronounced during standing. Diagnosis: Depending on the etiology and the duration of the dysfunction, the patient may present with different symptoms. If the etiology is recurrent tenosynovitis, the main manifestation is pain in the medial ankle and hindfoot. If tenosynovitis continues to progress unchecked, the ability of the tendon to glide may be lost, either due to mechanical blockage of the flexor support band, which prevents movement of the inflamed, edematous tendon and tendon sheath, or due to the inability of the muscle to actively contract due to pain. As the disease progresses, a range of foot deformities may develop, including loss of the medial longitudinal arch, hindfoot valgus, midfoot abduction, and forefoot rotation forward. X-rays can reveal foot deformities, and ultrasound and MRI examinations can detect posterior tibial tendon lesions. Treatment: In the early stage of posterior tibial tendon tenosynovitis, treatment may include rest, NSAIDs and bracing. Physical therapy and massage can also be used, with arch pads on the soles of the shoes and attention to exercising the posterior tibial muscles. Local hormone injections can also be used to suppress the inflammatory response, but may lead to tendon rupture. If conservative treatment is not effective, tenosynovectomy may be considered. If partial and full tears of the posterior tibial tendon are present, surgical treatment with tendon suturing or transposition is considered. If significant foot deformity is present, arthrofusion needs to be considered.