Accessory Navicular Pain Syndrome – The Clinical Syndrome
Foot and ankle pain secondary to accessory navicular pain syndrome is being seen with increasing frequency in clinical practice because of the increased interest in physical fitness and the use of exercise machines. Accessory navicular pain syndrome is the name given to pain that has as its nidus an accessory ossicle occasionally found in relation to the medial navicular bone and posterior tibial tendon. It is thought that accessory ossicles such as the accessory navicular decrease friction and pressure of tendons as they pass in proximity to a joint. Similar accessory ossicles are found in the elbows, hands, wrists, and feet.
Classification of Accessory Navicular Bone Types
|Type I||Isolated, well-defined accessory ossicle with smooth rounded or oval shape|
|Type Ia||Well-defined accessory ossicle with smooth rounded or oval shape embedded in the substance of the posterior tibial tendon|
|Type IIa||Triangular or heart-shaped accessory ossicle joined by synchondrosis to true tarsal navicular bone and a less acute angle (50–70 degrees), making it susceptible to avulsion injuries|
|Type IIb||Triangular or heart-shaped accessory ossicle joined by synchondrosis to true tarsal navicular bone and a more acute angle (10–35 degrees), making it susceptible to shear force injuries|
|Type III||Cornuate-shaped accessory ossicle joined by bony bridge to true tarsal navicular bone, which is often symptomatic|
Foot and ankle pain secondary to accessory navicular pain syndrome is characterized by tenderness and pain over the medial foot and ankle. Patients often report irritation from a shoe, and patients with accessory navicular pain syndrome may come to the physician’s office wearing a loose slipper on the affected foot. The pain of accessory navicular pain syndrome worsens with activities that require repeated range of motion of the foot and ankle or with high-impact forces on the foot and ankle, as seen with jumping sports and high-impact aerobics routines. Accessory navicular pain syndrome is often associated with loose bodies in the foot and ankle joint and may coexist with bursitis and posterior tibial and Achilles tendinitis.
Signs and Symptoms
On physical examination, pain can be reproduced by pressure on the accessory navicular bone and medial navicular. Some pes planus deformity may be evident if considerable compromise of the posterior tibial tendon is present. In contradistinction to Achilles bursitis, in which the tender area remains posteriorly over the area of the Achilles bursa, with accessory navicular pain syndrome, the area of maximal tenderness is just above the accessory ossicle. A creaking or grating sensation over the posterior tibial tendon may be appreciated by the examiner with range of motion of the ankle if considerable posterior tibial tendinitis is present.
How is Accessory Navicular Pain Syndrome diagnosed?
Plain radiographs are indicated in all patients with accessory navicular pain syndrome to rule out fractures and identify accessory ossicles that may have become inflamed. Plain radiographs also often identify loose bodies or joint mice, which are frequently seen in patients with foot and ankle pain secondary to accessory navicular pain syndrome. Based on the patient’s clinical presentation, additional tests, including complete blood cell count, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated. Magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging of the foot and ankle joint is indicated if joint instability, loose bodies, occult mass, or tumor is suspected and to clarify the diagnosis further. Radionucleotide bone scanning may be useful in identifying stress fractures or tumors of the foot and ankle and distal humerus that may be missed on plain radiographs.
Primary pathology of the foot and ankle, including gout and occult fractures, especially of the navicular tuberosity, may mimic the pain and disability associated with an accessory navicular bone. Entrapment neuropathy of the posterior tibial nerve, bursitis, and tendinitis also may confuse the diagnosis—all of which may coexist with accessory navicular pain syndrome. Köhler bone disease and synovial chondromatosis may mimic the pain associated with accessory navicular pain syndrome. Primary and metastatic tumors of the foot and ankle may present in a manner analogous to foot and ankle pain secondary to accessory navicular pain syndrome.
Initial treatment of the pain and functional disability associated with accessory navicular pain syndrome should include a combination of nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors and physical therapy. Local application of heat and cold may be beneficial. Avoidance of repetitive activities that aggravate the symptoms may provide relief. For patients who do not respond to these treatment modalities, injection of the accessory navicular ossicle with a local anesthetic and steroid may be a reasonable next step. Ultrasound guidance may improve the accuracy of needle placement and decrease the incidence of needle-related complications. For pain that persists, or if the accessory navicular pain syndrome is causing damage to the foot and ankle joint, surgical removal is indicated.
Complications and Pitfalls
The major complication of injection of an accessory navicular ossicle is infection. This complication should be exceedingly rare if strict aseptic technique is followed. Approximately 25% of patients report a transient increase in pain after injection of an accessory navicular ossicle, and patients should be warned of this possibility. Another potential risk of this injection technique is trauma to the extensor tendons from the injection.
Pain emanating from the foot and ankle is a common problem encountered in clinical practice. Accessory navicular pain syndrome must be distinguished from fractures of the foot and ankle, fractures of the accessory navicular bone itself, entrapment neuropathies of the tibial nerves, bursitis, and tendinitis. Less common causes of posterior foot and ankle pain, including Köhler bone disease, should be considered when evaluating patients thought to have accessory navicular pain syndrome.