Os Trigonum Syndrome: Symptoms, Types, Causes and Treatment

Os Trigonum Syndrome is a condition that, while often overlooked, can be the source of persistent ankle pain, especially in athletes and dancers. Understanding its symptoms, types, causes, and treatment options is crucial for timely diagnosis and management. This comprehensive guide will walk you through every essential aspect of Os Trigonum Syndrome, supported by up-to-date research and clinical evidence.

Symptoms of Os Trigonum Syndrome

Recognizing the symptoms of Os Trigonum Syndrome is the critical first step toward effective management. While many people with an os trigonum remain symptom-free, others—especially those engaged in repetitive ankle activities—may experience significant discomfort. Early identification of symptoms can help prevent chronic pain and long-term mobility issues.

Symptom	Description	Typical Contexts	Sources
Posterior Pain	Aching or sharp pain at the back of the ankle	During/after plantar flexion	1, 2, 3, 4
Swelling	Localized swelling at the back of the ankle	After activity or trauma	4, 8
Stiffness	Reduced range of motion, especially with flexion	Dancers, athletes	2, 13
Impingement	Sensation of blockage or pinching in ankle	Ballet, sports	13, 2
Clicking	Audible or palpable click in the posterior ankle	With movement	6, 1

Table 1: Key Symptoms of Os Trigonum Syndrome

Posterior Ankle Pain

The hallmark symptom of Os Trigonum Syndrome is pain at the back of the ankle, particularly during activities involving repeated or forceful plantar flexion—such as dancing en pointe, jumping, or pushing off during running or soccer. The pain can be sharp or aching and may become chronic if not addressed 1 2 3 4.

Swelling and Stiffness

Swelling often accompanies pain, especially after intense activity or acute trauma. Some individuals notice visible puffiness or tenderness at the posterior ankle. Stiffness may follow, particularly making plantar flexion (pointing the toes) or dorsiflexion (lifting the foot) uncomfortable 4 8.

Mechanical Impingement and Clicking

A sensation of "blockage" or impingement—where the patient feels as though something is physically obstructing ankle movement—is another classic sign. This is particularly common in ballet dancers and athletes who force the foot into extreme positions 13 2. Some may also report a clicking or popping sensation, especially if the flexor hallucis longus tendon is involved 6 1.

Activity-Related Symptoms

Symptoms typically worsen with activity and improve with rest or activity modification. This pattern is especially evident in sports or dance activities that demand repeated plantar flexion 2 13. Nighttime pain is less common but can occur in severe or chronic cases.

Types of Os Trigonum Syndrome

Os Trigonum is not a one-size-fits-all condition. The anatomical variations of the os trigonum and its relationship to surrounding structures can influence both the likelihood of developing symptoms and the severity of the syndrome.

Type	Description	Prevalence/Size	Sources
Type I	Small, oval, unfused os trigonum	Least common (1.9%)	5, 7
Type II	Larger os trigonum, separate from talus	Moderate (10.5%); largest volume	5, 7
Type III	Elongated posterolateral tubercle (Stieda’s process)	Most common (14.7%); intermediate	5, 7

Table 2: Anatomical Types of Os Trigonum

Type I: Small, Unfused Os Trigonum

Type I is characterized by a small, oval-shaped accessory bone that remains unfused behind the talus. This type is the least commonly seen on imaging but can still cause symptoms in susceptible individuals 5.

Type II: Large, Separate Os Trigonum

Type II features a larger os trigonum, distinctly separated from the talus. This form has the largest volume and can be more prone to impingement or mechanical symptoms due to its size 5. Athletes and dancers are particularly at risk if they have this anatomical variation.

Type III: Elongated Posterolateral Tubercle (Stieda’s Process)

Type III, also known as Stieda’s process, is an elongated bony prominence at the back of the talus. It is the most common variant and can mimic or coexist with a true os trigonum 5 7. Its prominence makes it susceptible to similar impingement syndromes.

Clinical Implications of Variants

• Prevalence: Studies indicate os trigonum variants are present in up to 20% of individuals, with slight differences between sexes—higher rates of Stieda’s process in males and os trigonum in females 7.
• Symptomatic vs. Asymptomatic: Not all anatomical variants cause symptoms. Clinical context and imaging help distinguish problematic cases.

Causes of Os Trigonum Syndrome

Understanding what triggers Os Trigonum Syndrome is vital for both prevention and targeted therapy. While the presence of an os trigonum is often congenital, the syndrome itself results from a combination of anatomical predisposition and mechanical stressors.

Cause	Mechanism/Description	At-Risk Groups	Sources
Repetitive Microtrauma	Chronic plantar flexion leads to inflammation/disruption	Ballet, soccer, runners	1, 2, 4, 8, 13
Acute Injury	Forced plantar flexion or ankle sprain	Athletes, dancers	8, 4
Flexor Hallucis Longus Dysfunction	Tenosynovitis due to impingement	Active individuals	1, 6, 2
Anatomical Predisposition	Larger or prominent os trigonum/Stieda’s process	General population	5, 7
Chronic Ankle Instability	Increases risk of surgery for symptomatic cases	Athletes with instability	9

Table 3: Main Causes and Risk Factors for Os Trigonum Syndrome

Overuse and Repetitive Microtrauma

The most common cause of Os Trigonum Syndrome is repetitive microtrauma from activities involving extreme or repeated plantar flexion. This is particularly prominent in ballet dancers (especially those working en pointe or demi-pointe), soccer players, and runners 2 4 13. Over time, the constant motion leads to inflammation and sometimes disruption at the synchondrosis (cartilaginous joint) between the os trigonum and talus 1.

Acute Injury

A sudden hyper-plantarflexion injury—such as landing awkwardly from a jump or an ankle sprain—can also precipitate the syndrome. In these cases, symptoms may appear suddenly and may persist if not properly managed 8 4.

Flexor Hallucis Longus Involvement

The flexor hallucis longus (FHL) tendon runs close to the os trigonum. Repetitive impingement can cause FHL tenosynovitis, leading to pain, swelling, and sometimes a clicking sensation 1 6 2. This tendon involvement is often seen in conjunction with os trigonum pathology, especially in athletes.

Anatomical Predisposition

Some individuals are simply more likely to develop symptoms due to the shape or size of their os trigonum or posterolateral talar process. Larger or more prominent ossicles are more prone to causing mechanical impingement 5 7.

Chronic Instability

In athletes, chronic lateral ankle instability significantly increases the likelihood of developing symptomatic Os Trigonum Syndrome and the need for surgical intervention 9.

Treatment of Os Trigonum Syndrome

Treatment for Os Trigonum Syndrome ranges from conservative approaches to surgical intervention, depending on the severity and persistence of symptoms. A patient-centered approach, guided by the latest evidence, ensures optimal outcomes.

Treatment	Approach/Description	Indications	Sources
Rest & Activity Modification	Avoid aggravating movements, temporary rest	First-line, mild cases	2, 8, 4
Physical Therapy	Stretching, strengthening, mobilization	Conservative management	2, 6
Medication	NSAIDs for pain/inflammation	Symptom relief	8, 2
Injections	Corticosteroid or anesthetic injections	Persistent or severe cases	8
Surgery (Open/Endoscopic)	Excision of os trigonum, FHL retinaculum release	Failure of conservative therapy	2, 10, 11, 12, 13, 14

Table 4: Overview of Treatment Options

Conservative Management

The majority of cases start with conservative treatments:

• Rest and Activity Modification: Avoidance of activities that worsen symptoms is the first step. Many patients experience symptom relief with temporary rest 2 8 4.
• Physical Therapy: Therapy focuses on stretching, strengthening, and improving ankle mechanics. This can help reduce impingement and inflammation 2 6.
• Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) are often prescribed for pain and swelling 8 2.
• Injections: Corticosteroid or local anesthetic injections may be used for severe or persistent symptoms. These can provide significant relief and help confirm the diagnosis 8.

Surgical Intervention

Surgery is considered when conservative measures fail—especially for athletes or performers who need a rapid return to full activity.

• Open Excision: Traditional surgical removal through a posterolateral approach. Effective, but associated with longer recovery and higher complication rates (e.g., sural nerve injury) 10 12.
• Endoscopic/Arthroscopic Excision: Minimally invasive techniques have gained favor due to faster recovery, less pain, and lower risk of complications 11 12 14.
  • Studies show that endoscopic excision allows athletes and dancers to return to sport more quickly (typically 4–8 weeks post-op) compared to open surgery (9–12 weeks) and with fewer complications 12 13 14.
  • Both procedures are highly effective, but the endoscopic approach is preferable for most patients requiring early return to high-level activity 12 14.
• Flexor Hallucis Longus Retinaculum Release: If the FHL tendon is involved, releasing its sheath may be performed alongside os trigonum excision 6.

Prognosis and Return to Activity

Most patients who undergo surgical excision—especially via endoscopic or arthroscopic methods—experience excellent outcomes, high rates of satisfaction, and early return to their previous activity levels 12 13 14. Complications are uncommon but may include nerve injury, infection, or persistent symptoms, particularly if surgery is delayed 10.

Conclusion

Os Trigonum Syndrome is a complex but manageable cause of posterior ankle pain, especially in athletes and dancers. Here are the key takeaways:

• Symptoms: Posterior ankle pain, swelling, stiffness, mechanical impingement, and activity-related discomfort are common warning signs.
• Types: Os trigonum varies anatomically (Type I, II, III), influencing the likelihood and severity of symptoms.
• Causes: Repetitive plantar flexion, acute injury, tendon involvement, anatomical predisposition, and ankle instability are key contributors.
• Treatment: Most cases respond well to conservative treatment; surgery (endoscopic preferred) is highly effective for persistent cases.

Early recognition and appropriately tailored treatment can ensure rapid recovery and return to activity, minimizing the risk of chronic pain or disability. If you or someone you know has persistent posterior ankle pain—especially with a history of high-level athletic or dance activity—consider consulting a specialist familiar with Os Trigonum Syndrome for proper evaluation and care.