Os Trigonum Syndrome

Os Trigonum Syndrome: Understanding the Condition and Its Treatment Options

Os Trigonum Syndrome (OTS) is a condition that affects the posterior ankle, often causing pain and discomfort in the lower leg. This syndrome occurs when a small, extra bone—called the os trigonum—fails to fuse with the talus during development. Although the os trigonum is present in a small percentage of the population, it does not typically cause symptoms. However, under certain conditions, this extra bone can lead to significant discomfort, particularly in individuals who engage in activities involving repetitive ankle movements, such as athletes, dancers, and certain laborers.

Introduction to Os Trigonum

The os trigonum is an accessory ossicle that forms on the posterior talar process, located at the back of the ankle joint. Rosenmuller first described this structure in 1804, identifying it as a secondary ossification center. In most individuals, the os trigonum fuses with the talus in childhood, but in a percentage of the population, this fusion does not occur, resulting in a small extra bone. This unfused bone can sometimes lead to posterior ankle impingement, especially in athletes who perform repetitive plantar flexion movements like ballet dancers, swimmers, and soccer players .

Pathophysiology and Causes

Os trigonum syndrome, or posterior ankle impingement syndrome (PAIS), develops when this accessory bone causes friction or compression against surrounding structures during ankle movement. The syndrome is most commonly triggered by repetitive plantar flexion, where the foot is pointed downward, causing the os trigonum to impinge against the tibia or calcaneus. This condition can also result from an acute injury to the ankle, such as a fracture of the Stieda process, which is the bony prominence that extends from the posterior talus .

Os trigonum syndrome is also associated with tendon issues, especially involving the flexor hallucis longus (FHL) tendon, which runs along the posterior side of the ankle. When the FHL tendon rubs against the os trigonum, it can become inflamed, leading to additional pain and discomfort. This can exacerbate symptoms, as the tendon becomes irritated during movements that involve pushing off, like running or dancing.

Symptoms and Diagnosis

The main symptom of os trigonum syndrome is pain at the back of the ankle, which worsens with plantar flexion or activities that require forceful ankle movements. Other symptoms may include swelling, tenderness, and stiffness in the ankle. The pain is often deep and can be aggravated by activities such as jumping, running, or pushing off during a dance routine.

Diagnosing os trigonum syndrome requires a comprehensive evaluation, including a thorough patient history and physical examination. During the examination, the physician will assess the range of motion in the ankle and may perform specific tests, such as the heel thrust test, which involves compressing the talus between the tibia and calcaneus to reproduce the pain. Imaging tests, such as X-rays and MRI scans, are essential to confirm the diagnosis. X-rays can reveal the presence of the os trigonum, and MRI scans can assess any soft tissue damage or inflammation, particularly in the FHL tendon .

Treatment Options

Treatment for os trigonum syndrome generally begins with conservative measures aimed at reducing inflammation and alleviating pain. These may include:

  • Rest and Activity Modification: Avoiding activities that exacerbate symptoms, such as excessive plantar flexion, can help manage the condition.
  • RICE Protocol: Rest, ice, compression, and elevation can reduce swelling and provide temporary relief.
  • Anti-Inflammatory Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) can help control pain and inflammation.
  • Physical Therapy: Targeted exercises to strengthen the ankle muscles and improve flexibility can reduce strain on the affected area.
  • Corticosteroid Injections: In cases where pain persists, corticosteroid injections may provide relief by reducing inflammation around the os trigonum or the FHL tendon .

If conservative treatments fail to improve symptoms after 3 to 6 months, or if the patient is an athlete or dancer who requires quicker recovery, surgical intervention may be necessary. Surgery typically involves excising the os trigonum to relieve impingement and restore normal movement in the ankle.

Surgical Approaches

There are several surgical techniques to treat os trigonum syndrome, depending on the severity of the condition and the patient’s specific needs. The most common approaches include:

  • Endoscopic Surgery: This minimally invasive technique uses a small camera and instruments to remove the os trigonum. Studies have shown that endoscopic excision results in faster recovery times and fewer complications than open surgery. It is particularly beneficial for athletes and dancers who wish to return to activity quickly .
  • Arthroscopic Surgery: This method involves using a small camera to guide the surgeon in removing the os trigonum through tiny incisions. This technique is suitable for more complicated cases where additional joint pathologies, such as arthritis or tendon damage, are present.
  • Open Surgery: In some cases, a larger incision may be necessary, particularly if the os trigonum is large or if there are associated issues that need to be addressed. Open surgery may be required in more complex cases where other structures around the ankle joint are involved.

Each surgical technique has its pros and cons. Endoscopic and arthroscopic approaches offer quicker recovery times and less risk of complications, while open surgery may be required for more extensive cases.

Postoperative Care

After surgery, patients are typically placed in a bulky dressing and a boot to protect the ankle. Weight-bearing may be limited initially, but most patients can begin gentle range-of-motion exercises within a few days. Full return to activity typically occurs between 3 and 6 months, depending on the type of surgery performed.

Conclusion

Os trigonum syndrome is a condition that can significantly affect an individual’s ability to perform daily activities or engage in sports. While conservative treatment is often effective, surgical intervention may be necessary for those who do not respond to initial therapies or who are involved in high-demand activities. The choice of treatment depends on the severity of the condition, the patient’s activity level, and the specific symptoms present. With appropriate diagnosis and management, individuals with os trigonum syndrome can achieve significant pain relief and return to their normal activities.