Os Trigonum Pain Syndrome

Os Trigonum Pain Syndrome – The Clinical Syndrome

Foot and ankle pain secondary to os trigonum 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. Os trigonum pain syndrome, also known as posterior ankle impingement 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 os trigonum decrease friction and pressure of tendons as they pass in proximity to a joint. Similar accessory ossicles are found in the elbows, knees, hands, wrists, and feet. Foot and ankle pain secondary to os trigonum pain syndrome is characterized by tenderness and pain over the medial foot and ankle. The patient often reports irritation from a shoe, and often patients with os trigonum pain syndrome come to the physician’s office wearing a loose slipper on the affected foot. The pain of os trigonum 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. Os trigonum 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.

What are the Symptoms of Os Trigonum Pain Syndrome

On physical examination, pain can be reproduced by pressure on the os trigonum bone and medial navicular. Some pes planus deformity may be evident if serious compromise of the posterior tibial tendon has occurred. In contradistinction to Achilles bursitis, in which the tender area remains posteriorly over the area of the Achilles bursa, with os trigonum pain syndrome, the area of maximal tenderness is just above the accessory ossicle itself. A creaking or grating sensation over the posterior tibial tendon may be appreciated by the examiner with range of motion of the ankle if serious posterior tibial tendinitis is present.

How is Os Trigonum Pain Syndrome diagnosed?

Plain radiographs are indicated in all patients with os trigonum 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 that are frequently seen in patients with foot and ankle pain secondary to os trigonum 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) and computed tomography (CT) of the foot and ankle joint is indicated if joint instability, loose bodies, fracture, occult mass, or tumor is suspected and to further clarify the diagnosis. Ultrasound imaging may provide additional useful information as to the etiology of the patient’s pain symptomatology and functional disability. 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.

Differential Diagnosis

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 os trigonum bone. Entrapment neuropathy of the posterior tibial nerve, bursitis, and tendinitis also may confuse the diagnosis—all of which may coexist with os trigonum pain syndrome. Köhler bone disease and synovial chondromatosis may mimic the pain associated with os trigonum pain syndrome. Primary and metastatic tumors of the foot and ankle also may manifest in a manner analogous to foot and ankle pain secondary to os trigonum pain syndrome.


Initial treatment of the pain and functional disability associated with os trigonum 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 also may provide relief. For patients who do not respond to these treatment modalities, injection of the os trigonum 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 os trigonum 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 os trigonum 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 os trigonum 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.

Clinical Pearls

Pain emanating from the foot and ankle is a common problem encountered in clinical practice. Os trigonum pain syndrome must be distinguished from fractures of the foot and ankle, fractures of the os trigonum bone itself, entrapment neuropathies of the tibial nerves, bursitis, and tendinitis, and less common causes of posterior foot and ankle pain, including Köhler bone disease, should be considered when evaluating patients thought to have os trigonum pain syndrome.


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