Chopart
An avulsion fracture occurs when a small piece of bone attached to a tendon or ligament is pulled away from the main bone mass, usually by a forceful, sudden contraction or stretch. In the midfoot, specific avulsion fractures are often associated with Chopart's joint injuries (mid-tarsal joint) or the Os Peroneum.
Avulsion Fractures of Chopart's Joint
The Chopart's joint, also known as the mid-tarsal joint, is a critical complex that separates the hindfoot from the midfoot. It consists of two articulations: the talonavicular (TN) joint and the calcaneocuboid (CC) joint. Injuries here, often resulting from low-energy inversion sprains (like an ankle twist), can cause avulsion fractures where strong ligaments attach.
| Location | Associated Ligament & Mechanism | Clinical Significance |
| Anterior Process of the Calcaneus | Avulsion by the bifurcate ligament during a forced inversion and plantar flexion of the foot. | This is one of the most common midfoot avulsion fractures. It can involve the articular surface of the calcaneocuboid joint, potentially leading to chronic pain or osteoarthritis if displaced or left untreated. It may be misdiagnosed as an ankle sprain. |
| Dorsal Navicular | Avulsion of the dorsal talonavicular ligament. | Part of a mid-tarsal sprain, this injury is often subtle. The dorsal talonavicular ligament is a key stabilizer, so this fracture indicates a significant force transmitted across the TN joint, contributing to midfoot instability or pain. |
| Cuboid (CC Joint) | Avulsion by the calcaneocuboid component of the bifurcate ligament or the dorsal calcaneocuboid ligament. | Similar to the calcaneus anterior process fracture, this is a sign of injury to the lateral column. It's often associated with inversion injuries. |
Diagnosis and Management
Diagnosis: Initial X-rays (three views of the foot) are essential, but small avulsion fragments are often missed. A CT scan provides superior detail for assessing displacement and articular involvement, while MRI is best for evaluating associated ligamentous injuries, bone marrow edema, and surrounding soft tissues.
Treatment:
Non-operative: Most small, non-displaced fractures (especially Type I and II anterior process calcaneus fractures) are treated conservatively with immobilization (e.g., in a walking boot or cast) and non-weight bearing for several weeks, followed by physical therapy.
Surgical: Displaced fragments, those involving the joint surface (Type III anterior process calcaneus fractures), or fragments causing persistent, chronic symptoms may require open reduction and internal fixation (ORIF) with screws or, in some cases of chronic non-union, excision of the fragment.
Os Peroneum Avulsion Fracture
The Os Peroneum is a small accessory bone (a normal variant present in up to 26% of people) embedded within the sheath of the Peroneus Longus tendon as it passes beneath the cuboid bone.
| Pathology | Mechanism & Context | Clinical Significance |
| Os Peroneum Fracture/Diastasis | An avulsion fracture (or a separation of a naturally bipartite os peroneum) typically results from a sudden, forceful contraction of the peroneus longus muscle or acute inversion/supination injury. | The fracture often causes the fragments to separate (diastasis), which is highly suggestive of a Peroneus Longus tendon tear (partial or complete). This is a hallmark of the condition known as Painful Os Peroneum Syndrome (POPS). |
Diagnosis and Management
Presentation: Patients report pain localized to the lateral midfoot, over the cuboid area. Pain is often worse with activities that involve resisted plantarflexion and eversion of the foot (activating the peroneus longus).
Diagnosis: Oblique view X-rays are best for visualizing the os peroneum. A fracture is typically distinguished from a normal bipartite ossicle by its irregular, sharp margins (vs. the smooth, well-corticated margins of a normal variant). Ultrasound and MRI are crucial for confirming an associated peroneus longus tendon tear or evaluating for surrounding tendinopathy. A fragment gap of >6 mm strongly suggests a complete tendon rupture.
Treatment:
Non-operative: Rest, immobilization, and anti-inflammatory medication are used for non-displaced fractures without significant tendon injury.
Surgical: Surgery is often indicated for acute, displaced fractures, especially those with a confirmed or suspected associated peroneus longus tendon tear (large fragment diastasis). Surgical options include excision of the os peroneum (ossicle removal) combined with tendon repair or tenodesis if the tear is extensive. This aims to restore tendon function and alleviate chronic pain.