What is Medicine – Accessory Navicular
This is an anatomical condition due to the present of an accessory ossicle located at the medial edge of the navicular. It is also known as Os tibiale, os tibiale externum, prehallux and naviculare secundum.
Accessory ossicle derives from the unfused ossification centers. Patients remain asymptomatic and the finding is incidental on radiograph.
The incidence of accessory navicular is 4-21% with 90% of the cases are bilateral. Less than 1% of patients are symptomatic. It is commonly seen over the medial pole of the navicular bone in adolescent patient. It is the common accessory ossicles in the foot.
Accessory navicular is common in adolescent patients or young adults with arch pain or flat foot deformity . It appears more frequent in females compared to males. May also appears in older adults as incidental finding or appears symptomatic together with degenerative changes in the synchondrosis, posterior tibialis tendinosis and bursitis.
It can only be symptomatic due to overuse or any forms of trauma in children and adult which is known as ‘accessory navicular syndrome’.
Accessory navicular is associated with flatfoot deformity and secondary Achilles tendon contracture.
There are three major types of accessory navicular adjacent to the posteromedial navicular tuberosity. There are type I, II and III.
Type I (30%) also known as ‘os tibiale externum’ is presented as small, 2-3 mm sesamoid bone in the posterior tibial tendon. There is no cartilaginous connection to the navicular tuberosity .
Type II of Accessory Navicular can be divided into type IIa and type IIb.It is divided based on the location. It is most commonly symptomatic. There will be a larger ossicle than type I. the cause is due to the secondary ossification center of the navicular bone. There is a heart shaped or triangular ossicle which forms a synchondrosis with the navicular.
Type III may present with enlarged navicular tuberosity. Type III of Accessory Navicular is considered as a fused variant of a type II with a pointed shape.
Accessory navicular is a variant of normal anatomy. The symptom appears due to the impingement of the bony prominence against the shoe wear. The patient may present with diffuse medial and plantar arch pain. Accessory navicular cause problem by destabilizing the insertion and diminishing the pull of the posterior tibial tendon. Lateral pain may occur secondary to impingement of the calcaneus against the fibula mostly in patient with associated severe flatfoot deformity.
Any traumatic event may lead to the injury to the fibrocartilaginous synchondrosis which attaches the ossicle to the main navicular.
The signs and symptoms of accessory navicular are pain which is localized to the medial aspect of the navicular. The pain may begin after wearing ill-fitting shoes, with weight bearing activities or athletics or after trauma to the foot. The pain or weakness when the patient attempts to run, rise on toes or jump. The pain and tenderness along the medial aspect of the foot in the region of accessory navicular. In young athletes, symptomatic accessory tarsal navicular may develop. Swelling and redness may present on the bony prominence. The pain is often relieved by rest.
On physical examination, tenderness is localized to the medial pole of the navicular. This tenderness might be exacerbated by abducting and adducting the foot.
It is important to assess the insole of the shoe. As it may exacerbate the symptoms. Identify any contracture of the Achilles tendon and assess the motion of the ankle and subtalar joint. The strength of the posterior tibialis tendon, is assessed by manual resistance testing against plantarflexion-inversion or by determining ability to perform multiple single limb heel rises.
Differential diagnosis of accessory navicular include posterior tibial tendinitis, acute avulsion fracture of the tuberosity of the navicular, stress fracture of navicular,
Pathologically, there is osteoblastic or osteoclastic activity in the tissue between the main body of the navicular and the ossicle. In type II accessory navicular there is proliferation of cartilage and vascular mesenchymal tissue.
The important imaging technique include the X-Ray and MRI. X-Ray include standing AP, external oblique and lateral radiographs of the foot. The image produced by X Ray in Type II accessory ossicle, include smooth borders and triangular or heart shaped. The base is 1-2mm from the medial and posterior aspect of the navicular bone. The accessory ossicle is best visualized on the internal oblique view. It may resemblance the characteristic of acute fracture. The differences between acute fracture and accessory navicular is the present of smooth margins with well-formed cortex in accessory navicular.
MRI has the higher sensitivity and specificity. MRI may show an alteration in signal intensity and bone marrow edema which are the signs suggesting In type II accessory navicular, the MRI shows soft tissue edema consistent with a synchondrosis sprain or tear. MRI may show posterior tibialis tendon degeneration.
The complications of accessory navicular are continued deformity, incomplete pain relief and weaknesses.
General treatment may include prescription of anti -inflammatory medication, patient need to rest and avoid any aggravating activities such as athletics. Use of a softer and wider shoe. A medial arch support may be useful in flatfoot cases. However, the patient may not tolerate due to the direct pressure on the ossicle. For persistent symptoms consider below the knee walking case or removable fracture boot for 3-6 weeks. Physical therapy, cryotherapy or strengthening exercises may be considered.
Surgical excision may be considered if pain is progressive or does not remit with non operative treatment. Excision of accessory navicular and naviculoplasty is considered. Naviculoplasty is a partial resection of medial edge of navicular bone.
The contemporary surgical treatment may include the excision of the ossicle and reattachment of the posterior tibial tendon insertion to the navicular with suture anchors or sutures passed through drill holes.
In the kidner procedure, the accessory navicular is excised and the posterior tibial tendon is re routed into a more plantar position.
Concomitant osteotomy of the calcaneus or medial column of the foot is considered in severe flatfoot deformity with lateral impingement symptoms. Hoping to improve the alignment and decrease mechanical stress of the posterior tibial tendon insertion.
Percutaneous drilling of the synchondrosis of accessory navicular for bone union is acceptable in adolescent athletes with immature basal phalanx of the great toe.
Kembara's Health Solutions
Discovering the world of health and medicine.