Os Trigonum: Should You Treat It Surgically?

Christopher Corwin, DPM, MS and John Sekel, DPM

Yes. Christopher Corwin, DPM says surgical excision, when properly indicated, addresses the cause of os trigonum pain, offers a lower risk of recurrence and facilitates a quick recovery and return to activity.

   The os trigonum is the second most common accessory bone in the foot. Asymptomatic os trigonum rarely requires treatment. However, in the case of symptomatic os trigonum, especially when the pain arises from an ankle injury, it can be difficult sometimes to discern between os trigonum and a fracture of the posterolateral process of the talus (Stieda’s process).

   Injuries to the posterolateral process of the talus are relatively common in athletes who participate in football, soccer, basketball, gymnastics and dance. These injuries can be debilitating to the athlete.

   Symptoms with os trigonum injuries typically involve pain in the deep posterior aspect of the ankle when the athlete places the foot in extreme plantarflexion. Football punters and soccer players may state they have no pain when running but extreme pain when kicking the ball. Dancers may have pain going on pointe.

Keys To The Diagnostic Workup

   The mechanism of os trigonum injury varies but it is commonly associated with plantarflexion type ankle injuries. The posterior process of the talus gets pinched between the posterior aspect of the distal tibia and the posterosuperior aspect of the calcaneus. This leads to a fracture. Inversion ankle sprains that affect the posterior talofibular ligament can also cause avulsion fractures as the posterior talofibular ligament inserts into the lateral tubercle of the talus.

   Physicians often diagnose these fractures after the resolution of anterolateral ankle pain. With these injuries, patients often note an ache in the deep posterior or posterolateral ankle that has not gotten better.

   Physical examination reveals pain with palpation on the deep posterolateral aspect of the ankle. Forced plantarflexion to end range of motion often reproduces the symptoms as the posterior process of the talus is impinged between the tibia and calcaneus. This is a relatively reliable diagnostic tool.

   Much less useful is the classically described test of dorsiflexion and plantarflexion of the hallux in an attempt to elicit pain in the deep posterior ankle via movement of the flexor hallucis longus tendon against the Stieda’s process. We have found this test to be positive less than 10 percent of the time.

   Radiographs may show an avulsion of the posterior process or an os trigonum to be present. Magnetic resonance imaging (MRI) evaluation clearly demonstrates injury with inflammatory fluid surrounding the os trigonum and stress related changes in the bone that show an increased signal in the lateral posterior process on T2 weighted images.

Pertinent Pearls On Surgical Management And Post-Op Protocol

   One should attempt conservative therapy first. This includes immobilization, activity modification, athletic taping to prevent end range of plantarflexion and possible steroid injection. Should these options fail, surgical intervention is warranted in the active, symptomatic individual or in athletes competing in sports that require plantarflexion type of movement. Surgical management of the symptomatic os trigonum and the fractured posterolateral process of the talus involves the same surgical procedure.

   One would perform surgery with the patient under the anesthesia of choice. Surgery often involves general or spinal anesthesia. Ensure the patient is in a full lateral position with a beanbag and use a thigh tourniquet to achieve hemostasis. Make a 3 to 4 cm curved incision on the posterior aspect of the peroneal tendons and center the incision at the level of the posterosuperior aspect of the calcaneus. Pay careful attention to avoid the sural nerve, which runs in the area and is often protected posteriorly in the subcutaneous fat.

   Perform deep blunt dissection, following the superior aspect of the calcaneus as a guide. Moving anteriorly along the calcaneus, it is relatively easy to find the os trigonum or avulsion of the posterolateral process of the talus. Remove the fracture fragment with careful dissection, which one can usually perform by pushing osteotomes by hand. Take great care on the medial side of the fragment as the flexor hallucis longus (FHL) tendon lies just medial to the fragment. The tibial nerve is also located on the medial aspect of the FHL tendon. Be aware that moving too medially with the dissection may inadvertently injure the tibial nerve.

   After removing the fragment, one can easily examine the FHL tendon by putting the hallux through range of motion. The surgeon can repair defects in the tendon and one can also examine the tendon for a low lying muscle belly, which may also cause posterior ankle impingement. Intraoperative imaging is valuable in determining that one has removed the proper amount of bone. Physicians should also assess the ankle’s range of motion in order to evaluate for any remaining bony impingement.

   Using a rasp, smooth the rough edges of the posterior aspect. Irrigate the area and then close the subcutaneous tissue with an absorbable suture followed by a running subcuticular absorbable suture to close the skin.

   Apply dressings and a posterior splint with ice. Our protocol includes five to seven days of non-weightbearing followed by 10 to 14 days of full weightbearing in a cast. This allows for adequate healing of the incision curving around the posterior aspect of the ankle. Then progress the patient to a removable walking boot for another seven to 10 days. He or she can remove the boot to do range of motion exercises and aggressive physical therapy. Most athletes resume running four to six weeks after the surgery.

Examining The Advantages Of Surgical Excision

   There are many benefits to surgical intervention. Recovery is relatively quick with a full return to activity. By removing the painful bone via surgical excision, there is a low risk of regrowth or recurrence. Removal of the offending bone addresses the cause of the pain as opposed to just treating the symptoms. Surgeons can also perform the procedure successfully across a wide age range of patients.

   One can minimize the risk of possible complications with careful dissection and appropriate incision placement. Protection of the sural nerve in the subcutaneous fat and avoidance of the FHL tendon help decrease the risk of the most common postoperative complications.

   Active individuals benefit from the surgery as they are able to return to pre-injury activity without pain. Athletes have had no trouble returning to play at high levels of competition. The removal of the excess bone reduces the risk of additional injury or re-injury to the posterior ankle. Patients will be able to perform kicking, dancing, gymnastics and any other activity that requires plantarflexion of the ankle without discomfort.

In Conclusion

   Surgical excision of the fractured posterolateral process of the talus or the symptomatic os trigonum is a safe, effective option for patients with pain and limitations of activities. The relatively quick healing time frame, the limited surgical exposure required, the ability to treat the cause of the problem and the high success rate of the procedure make surgical excision an effective alternative to conservative treatments.

Dr. Corwin is an Associate of the American College of Foot and Ankle Surgeons. He is in private practice specializing in sports medicine in Media and Phoenixville, Pa.
For related articles, please visit the archives at www.podiatrytoday.com

No. John Sekel, DPM, says surgery is a last resort as the majority of patients can attain relief from symptoms with conservative therapy such as offloading and orthoses.

   Os trigonum syndrome has been described as posterior ankle pain caused by the entrapment of an accessory ossicle between the talus and calcaneus when the ankle is forced into plantarflexion. This usually occurs with a single traumatic event or via repetitive microtrauma to the posterior talus.

   The literature has widely reported the occurrence rate of an accessory os trigonum as ranging between 1 and 20 percent with most authors agreeing to the prevalence of 7 to 8 percent.1 This wide variation is likely due to the different terminology physicians have used to describe this condition. Some of the other terms physicians have used to describe this condition include posterior ankle impingement, talar compression syndrome and posterior ankle block. In many cases, physicians misuse the term os trigonum.2

   It is important to realize that a true os trigonum is a secondary ossification center that has not fully fused with the talus and is connected by fibrous or cartilaginous tissue. Often, physicians incorrectly describe a fracture of Stieda’s process as an os trigonum.

   The complex nature of this condition is better understood by the biomechanics of the injury. As the ankle plantarflexes, the talus adducts and places tension along the posterior talocalcaneal and tibiotalar ligaments. As plantarflexion increases, the flexor hallucis longus (FHL) tendon will tighten and apply pressure along the os trigonum or Stieda’s process.

   The pulling of these ligaments and tension from the FHL tendon can cause a fracture of Stieda’s process or injury to the os trigonum.2,3 Placing the foot and ankle in this position will reproduce the initial injury and elicit pain in the posterior ankle joint. This injury often occurs with those who participate in soccer and ballet.

Key Pointers On Diagnostic Imaging

   Standard anteroposterior and lateral ankle radiographs can rule out fracture and one should take contralateral views for comparison. Observation of a large talar process on one foot and a sharp demarcated fracture fragment on the other foot is useful to aid in the diagnosis of a fracture of the lateral process of the talus.3 When lateral radiographs demonstrate a smooth round ossicle, then one can rule out a fracture of the process and make the diagnosis of os trigonum syndrome.

   Physicians can often perform a diagnostic injection of 1 mL of 1 to 2% plain lidocaine into the area of maximal tenderness to help confirm the diagnosis.

   Further imaging studies that are useful include a Tc-99m bone scan or magnetic resonance imaging (MRI). The MRI may be a more beneficial study with its ability to also diagnose fracture of Stieda’s process, injury to the fibrous bridge connecting the os trigonum or an injury to the FHL tendon.4 Individuals with recurrent os trigonum syndrome often have stenosing tenosynovitis of the FHL tendon and MRI would be useful in diagnosing FHL pathology.

Pertinent Insights On Conservative Treatment

   After performing a thorough history and physical, and making the diagnosis of os trigonum syndrome, one should initiate conservative treatment. The goal of conservative treatment is reducing inflammation and it is essential to initiate treatment immediately after injury.

   Treatment includes immobilization through the use of a below knee cast, a controlled ankle motion (CAM) walker or ankle brace. Immobilization prevents further impingement of the ossicle by the calcaneus and talus.

   In my practice, patients usually present three to four days after injury with pain and swelling of the posterior ankle joint. A majority of these patients are under the age of 40. After a thorough history and physical, I will attempt to recreate the position of the foot and ankle at the time of injury. This produces pain along the posterior ankle joint. I take three views of the ankle to rule out a fracture and confirm the presence of an os trigonum. I also take contralateral views for comparison.

   After diagnosing os trigonum syndrome, I place the patient into a CAM walker and crutches if needed. I will start the patient immediately on a standard nonsteroidal anti-inflammatory (NSAID) medication. The patient may remove the CAM walker for bathing and applying ice to the ankle. However, I instruct the patient to wear it at all times while weightbearing. Patients wear the CAM walker for four to six weeks.

   At that time, if they continue to have residual pain and swelling of the posterior ankle joint, then I will recommend a cortisone injection. I use 1 cc of 10 mg/mL of triamcinolone (Kenalog, Bristol Myers-Squibb) with 1 cc of 0.25% marcaine plain injected posterior lateral behind the fibula and peroneal tendons into the posterolateral aspect of the joint. Patients wear the CAM walker for an additional two to three weeks after the injection.

   Once symptoms have resolved, I have the patient initiate a physical therapy program for strengthening and range of motion exercises. At this time, patients have returned to regular sneakers without any assistance.

   In order to prevent further injury and reoccurrence, patients wear an ankle brace for walking and athletic activities. It is important to identify and address biomechanical faults of the foot and ankle that may contribute to patient symptoms. I will usually prescribe a rigid orthotic with rearfoot extrinsic posting to vertical and neutral forefoot posting.

   I find that most patients are asymptomatic with conservative treatment in six to eight weeks. Preventing re-injury decreases the possible need for surgical excision.

When Is Surgery Recommended?

   It is difficult to find studies that document the success of conservative treatment versus surgical excision. There is a general consensus and agreement to start with conservative treatment for an undefined length of time. This eventually proceeds to surgical excision once conservative treatment has failed.

   However, a vast majority of patients who present with an initial injury respond well with conservative treatment. These patients rarely require surgical excision since their symptoms are due to a single traumatic event.

   If patients continue to have reoccurrence of injury or fail to respond to conservative treatment, then surgical excision is recommended.

   Like all surgical procedures, surgical excision of the os trigonum has associated risks and complications. Incision approaches for removal of the os trigonum include a posterior medial or posterior lateral ankle incision. Podiatric surgeons most commonly employ the posterior lateral incision in order to avoid injury to the neurovascular structures of the tarsal tunnel.

   The main complication with this approach is injury to the sural nerve, which can result in sural neuritis, reflex sympathetic dystrophy syndrome, and sensory loss of the lateral ankle joint.5 While these complications are rare, they may cause permanent disability to the patient if they occur.

In Conclusion

   Patients who present with an initial injury and first time occurrence of os trigonum syndrome respond well to conservative treatment. One would only consider surgical excision if these conservative measures fail to alleviate symptoms or if the symptoms reoccur. Correcting the faulty biomechanics with a custom orthosis is imperative to prevent further injury and reoccurrence.

Dr. Sekel is board qualified in forefoot and rearfoot surgery by the American Board of Podiatric Surgery. He practices in Chambersburg, Pa. and Hagerstown, Md.

Editor’s note: For further reading, see “Treating Foot And Ankle Injuries In Ballet Dancers” in the June 2003 issue of Podiatry Today, “Essential Tips For Tackling Football Injuries” in the September 2002 issue, “Mastering Ankle Impingement Syndromes” in the August 2007 issue or “What You Should Know About Dance Injuries” in the January 2005 issue.

To access the archives or get reprint information, visit www.podiatrytoday.com.


1. Blake RL, Lallas PJ, Ferguson HB. The os trigonum syndrome. JAPMA 1992; 82(3):154-161.

2. Wenig JA. Os trigonum syndrome. JAPMA 1990; 80(5):278-282.

3. Hedrick MR, McBryde AM. Posterior ankle impingement. Foot Ankle Int 1994; 15(1):2-8.

4. Karasick D, Schweitzer ME. The os trigonum syndrome: imaging features. Am J Radiology 1996; 166(1):125-129.

5. Abramowitz Y, Wollstein R, Barzilay Y, London E, Matan Y, Shabat S, Nyska M. Outcome of resection of a symptomatic os trigonum. J Bone Joint Surg 2003; 85-A(6):1051-1057.


I have a patient that I am treating for Os Trigonum Syndrome except the Os Trigonum appears to be fused to the calcaneus just posterior to the lateral process of the talus, is this still considered an Os Trigonum? B/L views show a similar presentation on the opposite foot. This patient also has significant peroneal subluxation with audible popping and there is Talo-navicular joint spurring and DJD are these findings linked to the chronic effects of a lack of plantarflextion secondary to the Os Trigonum?

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