Tibialis posterior tendon is a solitary tendon that provides tendinous insertion in the navicular bone, which lays between the flexor digitorum longus and flexor hallucis longus muscles within the deep compartment of the leg. It converses from its broad surface on the superior aspect into a long tendon and crosses the flexor digitorum longus muscle medially at the inferior third of the leg. The posterior tibialis tendon (PTT) is located behind the medial malleolus, over the deltoid ligaments, within an osseous-fibrous groove. PTT is divided into three components at the navicular tuberosity, which is the anterior, middle, and posterior division. The anterior component is considered as the continuation of the primary tendon because it has the largest segment. It attaches to the navicular tuberosity, the inferior capsule of the medial cuneonavicular joint, and also the inferior aspect of the medial cuneiform bone. The middle component mainly inserts into the inferior aspect of cuboid, middle cuneiform, and lateral cuneiform bones, but it also extended into the bases of the second to fifth metatarsal bones as metatarsal extensions. The posterior component gives attachment to the sustentaculum tali of the calcaneus. It performs as the main dynamic stabilizer of the rearfoot, the tibialis posterior tendon maintains the structure of the longitudinal arch of the foot. Dysfunctions of this tendon alter the biomechanics of the foot in a static and dynamic state. This problem often results in the lengthening or rupture of the spring ligament and eventually leads to the loss of the medial longitudinal arch of the foot, a condition called adult-acquired flat-foot deformity (AAFD).[17][18][19]

Accessory Navicular Bone

The accessory navicular bone is a condition where a supernumerary ossicle presents adjacent to the navicular tuberosity on the medial side, as a result of irregular embryogenic development. Bauhin, in 1605, described it as an anatomic variant that occurs in 4 to 21% of the population. Women are more often to have this condition than men, and 50 to 90% of the cases are bilateral. It is generally visible in the radiographic examination from the age of 9 years. Most of the time, this condition was asymptomatic and occasionally diagnosed during a radiological study of the foot, however in particular circumstance, people with accessory of the navicular could experience medial foot pain caused by injury of the fibrous connection between the navicular and its accessory, that aggravated by weight-bearing activities, walking, and running. Friction against footwear could also produce medial foot pain, especially if there is a large medial protrusion present.[20][21][22]

Accessory navicular bones got classified into three groups in 1978, according to its morphology, position, and also its connection to the navicular bone. Type I- also called os tibiale externum or os naviculare secundarium; it represents 30% of the total accessory type. It considers as a 2 to 3 mm sesamoid bone with ovoid morphology, embedded within the distal part of the posterior tibial tendon. Type II - also known as prehallux or bifurcate hallux. This type of accessory navicular represented 50 to 60% of all types and formed due to a secondary ossification center within the navicular bone in the embryonic state. It has a triangular or heart-shaped morphology with a 12 mm length of its major axis and connected to the navicular bone by fibrocartilage or hyaline cartilage forming a synchondrosis joint. Type III - known as a cornuated navicular; it has a prominent navicular tuberosity and considered as a result of a fusion of type II.[20][23][20]

Conservative treatment, such as immobilization and anti-inflammatory medication, often been adequate since it is commonly asymptomatic and only produces a mild grade of pain. However, in some cases of recurrent symptomatic issues and failure of conservative treatment, then a bony excision with an anatomic repair of the posterior tibial tendon might be necessary.[24][25]

Adult Acquired Flatfoot Deformity (AAFD)

When conservative treatments failed to improve AAFD, various surgical interventions merit consideration. Medial displacement osteotomy of the calcaneus with posterior tibial tendon replacement using the flexor digitorum longus tendon, spring ligament reconstruction, subtalar arthrodesis, and triple arthrodesis are alternatives of surgical procedures to correct the flatfoot deformity.[26][27]

Navicular Fracture

Navicular fracture typically requires surgical intervention if it is an acute traumatic injury or a stress fracture that happens in high functional demand such as athletes. The common operative procedure is an open reduction with internal fixation with the primary goal to achieve anatomical reduction and also to restore the medial column length. Surgical management often results in a satisfactory prognosis; in a case study of ten patients who underwent surgical management after suffering from a comminuted navicular fracture, achieve union with none requiring an arthrodesis. Several potential complications are avascular necrosis, malunion, nonunion, and persistent stiffness. Osteonecrosis is commonly treated with a fusion of the talonavicular or naviculocuneiform joints to restore its length and alignment.[2][15]

Adult Acquired Flatfoot Deformity

Adult acquired flatfoot deformity (AAFD) most commonly results from a posterior tibial tendon dysfunction. This failure of the posterior tibial tendon leads to an inversion of the rearfoot that blocks the Chopart joint during the middle and late phases of the gait. Therefore, the triceps surae force of contraction inserts mainly on the talonavicular joint instead of the metatarsal heads. This condition causes the head of the talus to repeatedly acts on the spring ligament that results in the lengthening of the ligament, and eventually generates the AAFD. Several potential causes that lead to a dysfunction of the posterior tibial tendon include acute trauma, impingement, compression by flexor retinaculum, an accessory of the navicular bone, hypovascularization of the tendon, arthritis, chronic mechanical load, and corticosteroid injection.[26][28]

Navicular Fracture

While midfoot fracture considered an uncommon injury, navicular stress fracture represents one-third of all stress fracture in the human body. Navicular fracture commonly happens as a consequence of either an acute traumatic injury or chronic overuse, due to high functional demands. It has a higher incidence in young individuals and athletes due to their repetitive high-force activities that make them susceptible to high energy trauma and also musculoskeletal overuse. The Sangeorzan classification has been in wide use since its publication in 1989, for a grading system of navicular fracture. Patients with navicular fractures typically experienced pain in the midfoot area that could be associated with an inflammatory process. The navicular stress fracture could mostly be managed nonsurgically by immobilization and protected weight-bearing for six to eight weeks period. However, in an athlete with a high functioning demand, operative intervention to repair by open reduction and internal fixation become a beneficial option. On the other hand, traumatic navicular fracture typically requires surgical intervention, especially if displaced navicular body fracture occurred. Conservative treatment using short leg cast could become an option if the traumatic fracture is undisplaced or in the form of a small avulsion fracture.[15] 

Kohler Disease

Kohler disease is avascular necrosis (osteonecrosis) of the navicular bone that occurs in young children most commonly within 4 to 7 years old. This condition occurs more commonly in boys and can appear bilaterally. The navicular bone ossified within the third year of life; therefore, the increasing weight of the child makes the navicular bone susceptible to compression by the talus and cuneiform bones during activity. The lack of vascularization in the central third portion of the navicular increases the vulnerability to this disease. Radiology examination often shows sclerosis, fragmentation, or flattening of the navicular bone. Since Kohler disease is a self-limiting condition, surgical intervention is rarely necessary. Anti-inflammatory medication and immobilization with a short leg walking cast often bring satisfying clinical outcomes.[29][30]

Mueller-Weiss Syndrome

Mueller-Weiss syndrome (MWS), also known as Brailsford disease, is a rare disease that refers to a multifactorial spontaneous tarsal navicular osteonecrosis. Differ from Kohler disease pathology, MWS occurs in adults with the highest prevalence between 40 to 60 years of age. It is more common in women and frequently bilateral. Despite being idiopathic, some theories support the pathogenesis of MWS, including osteochondrosis, trauma, biomechanic alteration, migration of the accessory cuboid, dysplasia, and also congenital causes. The pathogenesis of MWS is considered multifactorial and related to a chronic overload to the lateral aspect of the navicular bone that suboptimal ossified. Plain radiograph examination shows a comma-shaped deformity of the navicular bone, caused by the collapse on the lateral aspect. Non-operative treatment such as anti-inflammatory medications, orthotics, and immobilization by short-leg cast, should be attempted before considering surgical intervention. If symptoms persist after conservative treatment, then surgery may be indicated to relieve pain and to restore the plantar and medial longitudinal arch. Talonaviculocuneiform arthrodesis with bone grafting often gives a satisfying result. Other surgical procedures include the percutaneous core decompression of the navicular bone, isolated talonavicular arthrodesis, and also the triple arthrodesis (fusion of the subtalar, talonavicular, and calcaneocuboid joints).[31][32][33]

Talonavicular Ligament Injury

Acute ankle injury is one of the leading causes of emergency department attendance; however, talonavicular ligament (TNL) injuries often remain unnoticed compared to the other ligament causing ankle injury (lateral ligamentous complex, anterior talofibular ligament, and calcaneofibular ligament). In 2016, a study conducted by Dea showed that TNL injury is surprisingly common, with a prevalence of 21% when someone experienced an acute ankle sprain. To date, the proven consequences of TNL injury remain unknown, but the suspicion is that the damage could alter the biomechanics of the foot and eventually leads to degenerative changes that most likely require surgical interventions.[34]

Tarsal Coalition

Tarsal coalition is a condition of fused tarsal bones that leads to a rigid flat foot and foot pain. This condition resulted from embryology anomaly caused by the failure of mesenchymal segmentation and development of fibrous, cartilage, or bone, forming coalitions of the tarsal bones. 50% of the case happens bilaterally, and 20% are multiple coalitions. Calcaneonavicular coalition is the most common type, while talocalcaneal and talonavicular types are much less common. The talonavicular coalition only represents 1% of all tarsal coalition. Non-operative management includes anti-inflammatories, activity modification, and immobilization by a cast. Surgical intervention could be an option if conservative treatments did not meet a satisfying outcome. Coalition resection with interposition graft relieves the pain in most of the tarsal coalition cases. Subtalar arthrodesis and triple arthrodesis are indicated in more severe cases.[35][36][37]