Amateur soccer player presented with pain in the posterior left ankle of 4 weeks duration. There was no recent history of acute trauma. On physical examination there was pain anterior to the Achilles tendon and a minor swelling could be palpated on the postero-lateral ankle. The pain was exacerbated by plantar flexion and kicking.
The patient who was an amateur soccer player presented with pain in the posterior left ankle of 4 weeks duration. There was no recent history of acute trauma. On physical examination there was pain anterior to the Achilles tendon and a minor swelling could be palpated on the postero-lateral ankle. The pain was exacerbated by plantar flexion and kicking. Plain films revealed the presence of an os trigonum.
Subsequent MR images demonstrated bone marrow edema within the os trigonum . Associated inflammatory changes were evident in the adjacent soft tissues. A diagnosis of a posterior ankle impingement syndrome due to an os trigonum was made.
Posterior ankle impingement syndrome (PAI) refers to a group of pathologic entities. It is a condition that arises from compression of the posterior talus and the surrounding soft tissues between the tibia and the calcaneus on plantar flexion of the foot, resulting in bone and/or soft tissue lesions. The mechanism of injury has been likened to a nut in a nutcracker [1,2]. If an os trigonum is present, additional bony impingement with these structures can occur. This is called the os trigonum syndrome and can be an important cause of chronic pain, particularly amongst professional athletes [3-5].
The term “os trigonum” is often used inappropriately. Between the ages of 11 and 13 years in boys and 8 and 10 years in girls a separate ossification center forms at the posterolateral aspect of the talus. This ossification center forms within a cartilaginous extension from the posterior portion of the talus. Normally this ossification center fuses with the rest of the talus within 1 year. If there is failure of fusion, an os trigonum is formed, which articulates with the talus via a synchondrosis (frequency 7%-14%) [2-5].
The syndrome can develop after a disruption of the os trigonum (fracture, fragmentation and pseudoarthrosis ) due to a significant acute injury. However, this is relatively rare and the syndrome usually arises insidiously (in predisposed athletes) as a result of repetitive forced plantar flexion of the foot and chronic injury to the posterior osseous and soft tissues [3,4].
Ballet dancers and professional soccer players are especially prone to this injury.
The diagnosis of PAI or os trigonum syndome is based primarily on the patient’s clinical history and physical examination and is supported by findings at radiography, computed tomography (CT), scintigraphy, and MR imaging.
Typically the patient presents with posterior ankle pain exacerbated by plantar flexion of the foot.
Conventional radiographs show the presence of an os trigonum, but further evaluation is required to confirm if this is in fact the source of associated symptoms. On the other hand it is not always possible to differentiate between an os trigonum and a fractured lateral talar tubercle on radiographs. Although an os trigonum is usually round or oval with well-defined corticated margins and a fracture of the lateral tubercle has irregular serrated margins between the ossicle and the posterior talus, a fracture fragment may also have smooth borders[2,5].
CT, with its high spatial resolution, may be helpful in evaluating the osseous structures but is less sensitive for the depiction of the occult fractures or soft tissue involvement. Isotope bone scans have been used in the past with the view that a symptomatic os trigonum will show increased activity, whereas a negative scan excludes this diagnosis.
Both techniques have been superseded by conventional MR imaging with its multiplanar capabilities, exquisite soft tissue and bone marrow contrast and large field of view availability. MR imaging may demonstrate bone marrow edema within the os trigonum, a fracture line, or fluid in the synchondrosis (indicating os trigonum fracture). Additional inflammatory changes in the adjacent soft tissues are well demonstrated and possible associated flexor hallucis longus abnormality can also be assessed [3-5]. Disruption of the os trigonum synchondrosis can be sometimes difficult to define even on MR images. In this situation, fluoroscopically guided arthrography of the synchondrosis will help define its integrity and also allow therapeutic intervention by injecting a steroid or local anesthetic into the area of pain [3,4].
The initial treatment is conservative. A below-the-knee cast is applied for 4-6 weeks or longer if necessary (2). Once the cast is removed, a rehabilitation program is instituted. If conservative treatment fails, then surgical excision of the os trigonum is required and has resulted in good prognoses in classical ballet dancers [2, 5].
Os trigonum syndrome
Based on the provided X-ray and MRI images, a separate small bone fragment (suggesting an "accessory talus" or "os trigonum") can be observed posterior to the left talus. In the MRI sequences, there appears to be mild bone marrow edema or a focal inflammatory signal between this small bone fragment and the posterior margin of the talus, with corresponding inflammatory changes or edema in the surrounding soft tissues. No obvious large fracture displacement is visible; however, minor bone surface irregularities or hairline cracks cannot be ruled out. Mild effusion or swelling is noted in the surrounding soft tissue, especially in the area anterior to the Achilles tendon.
Given the patient’s symptoms and the relatively obvious signal changes in the “accessory talus,” with no clear features of an acute fracture, the most common pathology remains posterior ankle impingement caused by an os trigonum.
Considering the patient’s age, clinical presentation (notably posterior foot pain that worsens with extreme plantarflexion or kicking), and imaging findings of a small bone fragment behind the talus with surrounding soft tissue inflammation:
The most likely final diagnosis: Posterior Ankle Impingement (PAI) combined with Os Trigonum Syndrome.
Rehabilitation training should follow a gradual progression, adhering to the FITT-VP principles (Frequency, Intensity, Time, Type, Progression, and Individualization):
If there is osteoporosis, knee joint vulnerability, or insufficient cardiopulmonary function, the program should be individualized under the guidance of a rehabilitation specialist or physician.
The above analysis and report are for clinical reference only and cannot replace an in-person consultation or professional medical judgment. If you have any questions or if symptoms worsen, please seek medical attention or consult a specialist promptly.
Os trigonum syndrome
