Historically, a variety of terms including osteochondritis dessicans, transchondral talus fracture, and osteochondral talus fracture have been used to describe what are now universally referred to as osteochondral lesions of the talus (OLTs). OLTs have been reported to represent approximately 4% of all cases of osteochondral lesions. The incidence of bilateral lesions is approximately 10%.
The talus is the second largest tarsal bone and is comprised of three major parts including the head, neck, and body. Two thirds of the talar surface is covered with articular cartilage that includes five articular surfaces. Neither tendons nor muscles insert on or originate from the talus. The body includes the dome of the talus at the ankle joint and the posterior facet at the subtalar joint. Recent studies have shown that most osteochondral lesions are not the traditionally described anterolateral and posteromedial lesions, but rather central medial and central lateral lesions. Medial osteochondral lesions are more common than lateral osteochondral lesions. Medial lesions have been described as deeper and larger, extending into subchondral bone and often developing into cystic lesions. Lateral lesions are more commonly associated with a traumatic injury and are described as shallow with a greater tendency to become displaced.
In the normal anatomic relationship between the distal ends of the tibia and fibula, a certain amount of motion is allowed in all three planes. When the ankle joint is loaded in dorsiflexion, the articular geometry contributes to translational stability and to a lesser degree, rotational stability. The ligaments surrounding the ankle take over a more dominant role in the unloaded ankle, particularly when the ankle is in plantar flexion.
The etiology of an OLT can be divided into nontraumatic and traumatic defects. It is hypothesized that traumatic defects represent the chronic phase of a talar dome compression fracture. A single event of macrotrauma or repetitive microtrauma may initiate progression of the lesion in an individual already predisposed to talar dome ischemia. Nontraumatic defects include endocrine or metabolic abnormalities, vasculopathies, and avascular necrosis, but there is no clear consensus regarding these elements. Subchondral cysts with overlying chondromalacia, osteochondral fragments and loose bodies all represent various stages in the progression of osteochondral lesions of the talus.
The primary mechanism is damage and insufficient repair of the subchondral bone plate. The associated pain is believed to be a result of stimulation of the highly innervated subchondral bone underneath the cartilage defect. The precise natural history of an OLT is unclear but osteoarthritis of the ankle has been shown to be an uncommon final outcome.
In most cases it is associated with chronic ankle pain that develops after a traumatic incident, commonly an inversion injury to the lateral ligamentous complex. Patients presenting with an OLT often describe prolonged pain, recurrent ankle swelling, weakness and subjective instability. The pain is commonly described as deep in the ankle. Patients may also report mechanical symptoms including catching, clicking, and locking. A high index of suspicion for an OLT must be maintained when evaluating patients with chronic ankle pain.
Non-operative treatment options include rest, cast immobilization for approximately 6 weeks and the use of nonsteroidal anti-inflammatory drugs (NSAIDs). Weight-bearing exercises and physical therapy are also recommended. The treatment aim is to unload the damaged cartilage, so edema can resolve and necrosis is prevented.
Surgical intervention is indicated for acute displaced osteochondral lesions and for those refractory to conservative care. The primary traditional approach includes open ankle arthrotomy. Numerous exposure methods have been described including several variations of medial malleolar osteotomies, distal tibial osteotomies along with combined anterior and posterior arthrotomies. Open approaches require significant tissue trauma and as a result may be associated with postoperative stiffness, prolonged rehabilitation time and poor cosmetic appearance. Additionally, nonunion or malunion of the malleoli is a risk with approaches involving a malleolar osteotomy. Inadequate visualization of the talar dome lesion, particularly the posterior aspect, remains a primary limitation of many open approaches. Ankle arthroscopy has established itself as a useful tool in both the diagnosis and treatment of osteochondral lesions of the talus. A wide variety of procedures that vary in complexity have been described for the treatment of OLTs. Treatment strategies generally are categorized as primary repair, reparative techniques, or restorative techniques. Future directions in restorative techniques for OLTs include matrix/membrane ACI (MACI), collagen-covered ACI, arthroscopic allograft/autograft with platelet-rich plasma (PRP) implantation, stem cell– mediated cartilage implants, and scaffolds.
Written by Erik Freeland, DO Reviewed by Thomas Dowd, MD Last reviewed June 2015