Introduction

In the absence of intra-articular ankle pathology, posteromedial ankle pain is most often caused by disorders of the posterior tibial tendon. 
These disorders can be divided in two groups: the younger group of patients with dysfunction of the tendon, caused by some form of systemic inflammatory disease (e.g. rheumatoid arthritis); and an older group of patients whose tendon dysfunction is mostly caused by chronic overuse.

Following trauma, surgery, and fractures, adhesions and irregularity of the posterior aspect of the tibia can be responsible for symptoms in this region. 
Mostly a dysfunctioning posterior tibial tendon evolves in a painful tenosynovitis. Tenosynovitis is also a common extra-articular manifestation of rheumatoid arthritis, where hindfoot problems are a significant cause of disability. Tenosynovitis in rheumatoid patients eventually leads to a ruptured tendon.
Although the precise aetiology is unknown, the condition is classified on the basis of clinical and radiographic findings.

Anatomy

The posterior tibial muscle arises from the interosseous membrane and the proximal adjacent surfaces of the tibia and fibula and is part of the deep posterior compartment of the calf. The tendon forms in the distal third of the calf and passes behind the medial malleolus where it changes direction. The posterior tibial tendon is the most superficial structure coursing behind the medial malleolus. 
Pain complaints are often located in the relative hypovascular zone immediately distal to the medial malleolus, beginning 4 cm proximal to the insertion of the tendon. This hypovascular zone may contribute to the development of degenerative changes and consequently ruptures. 
The posterior tibial tendon is held in the retromalleolar groove by a strong fibro-osseous tunnel and the flexor retinaculum originating from the tip of the medial malleolus inserting into the calcaneus. Distally, the retinaculum blends with the sheath of the tendon and the superficial deltoid ligament. The anterior, major slip of the tendon inserts primarily into the tuberosity of the navicular, the inferior capsule of the medial naviculocuneiform joint and the inferior surface of the medial cuneiform. A second slip extends to the plantar surfaces of the cuneiforms and the bases of the 2nd, 3rd and 4th metatarsals. 
A tendon sheath surrounds the posterior tibial tendon, and both structures are connected by a vincula, which carries part of the blood supply to the tendon. A vincula can become symptomatic when damaged, causing thickening, shortening and scarring of the distal free edge. In these patients, a painful local thickening can be palpated posterior and just proximal to the tip of the medial malleolus. 
Coursing posterolaterally through the tarsal tunnel, the flexor digitorum longus- and flexor hallucis longus tendons can be found respectively. Between the flexor digitorum longus- and flexor hallucis longus tendon the posterior tibial nerve, - artery and - veins are situated.

History & Physical Examination

History

In the early stage of dysfunction, patients complain of persisting ankle pain medially along the course of the tendon, in addition to fatigue and aching on the plantar medial aspect of the ankle. When a tenosynovitis is present, swelling is common. A typical observation is abnormal wear of the medial sides of the shoes. Walking increases pain and participation in sports activities becomes difficult.

Physical Examination

Careful clinical examination is important and both feet should be examined. Valgus angulation of the hindfoot is frequently seen with accompanying abduction of the forefoot, which is named the "too-many-toes" sign. This sign is positive when inspecting the patient's foot from behind: in case of significant forefoot abduction, 3 or more toes are visible lateral to the calcaneus, where normally only 1 or 2 toes are seen. 
With the patient seated, the strength of the tendon and location of pain are evaluated by asking the patient to invert the foot against resistance.

Differential Diagnosis

Intra-articular lesions such as a posteromedial impingement syndrome, subtalar pathology, calcifications in the dorsal capsule of the ankle joint, loose bodies or osteochondral defects should be excluded. Entrapment of the posterior tibial nerve in the tarsal canal is commonly known as a tarsal tunnel syndrome. Clinical examination is normally sufficient to adequately differentiate these disorders from an isolated posterior tibial tendon disorder.

Diagnostic Imaging

After initial history taking and physical examination, diagnosis can be confirmed or rejected using radiography. Conventional radiographs may show abnormal alignment like flattening of the plantar arch or bony changes such as bony irregularity and hypertrophic change at the navicular attachment, providing an important clue to the presence of longstanding problems with the posterior tibial tendon. However, for the diagnosis of pathology to this soft tissue structure is easier to identify using ultrasound or magnetic resonance imaging (MRI). 

Ultrasound imaging is known as a cost-effective and accurate to evaluate disorders of the posterior tibial tendon.Thickening of the tendon and/ or peritendinous soft tissue, hypoechoic texture, ill-definition of the fibrillar pattern, associated hypervascularity on colour Doppler, thinning, splitting or rupture may be useful clues. In our practise, MRI is the method of choice since the images can be interpreted by the orthopaedist in contrast to ultrasound images and therefore are more helpful for pre-operative planning. It is also considered the gold standard of assessing tibialis posterior dysfunction and related soft tissue injuries. Findings can be fluid or synovitis around the tendon, hypertrophy of the tendon, intrasubstance tears showing increased signal, longitudinal tears and complete tendon tears.

Post-operative rehabilitation

The patient can be discharged the same day of surgery and weightbearing is allowed as tolerated. The patient is instructed to perform active dorsiflexion of the ankle to the neutral position (knee slightly bent). This exercise should be performed 2 or 3 days times per hour for the first days after surgery. The patient is instructed to elevate the foot when not walking to prevent edema. The dressing is removed 3 days post-operative. Normal walking without crutches at 4 - 5 days post surgery. Patients with limited range of motion are directed to a physiotherapist. Running can be started when range of motion is normal and in absence of swelling. This can on avarage be expected at 3 weeks post surgery. Sport resumption can on average be expected at 6 weeks post surgery. 

Recommended Literature

Van Dijk CN, Kort N, Scholten PE.Tendoscopy of the posterior tibial tendon. Arthroscopy. 1997 Dec;13(6):692-8.

Van Sterkenburg MN, Haverkamp D, van Dijk CN, Kerkhoffs GM.A posterior tibial tendon skipping rope. Knee Surg Sports Traumatol Arthrosc. 2010 Dec;18(12):1664-6.