Twisted Ankle with Edema and Tenderness - Patient Case of the Week

Educational Objective:

Recognize appropriate treatment for osteochondral fractures.

Key Point:

The patient has an osteochondral talar dome fracture, a subtle radiological diagnosis that is easily missed, leading to insufficient immobilization. This patient's treatment plan should involve a cast for 6 weeks

Explanation:

Osteochondral fractures of the talar dome (also known as transchondral fracture, dome fracture of the talus, and chip or flake fractures) involve both the cartilage and subchondral bone (see Figure 2).

Figure 2.

They account for 1% of talar fractures and are usually missed initially and diagnosed late in the clinical course after ankle trauma.

Mechanisms identical to those causing ankle sprains are the most common cause, but a significant number of these injuries cannot be ascribed to an acute traumatic event. An osteochondral fracture should be considered in any patient with ligamentous ankle injury accompanied by gross edema and an effusion on plain radiographs.

The diagnosis often is missed initially and only made when the patient returns with long-term ankle discomfort. Physical examination findings are usually nonspecific, although localized tenderness over the posteromedial aspect of the talus and increasing pain with exertion, weight-bearing, or passive plantar flexion may be noted.

When an osteochondral fracture is diagnosed or suspected, outpatient orthopedic referral is advised, because long-term ankle discomfort and osteoarthritis are potential sequelae. After inadequate treatment or failure to treat an osteochondral fracture, a subacute or long-term talar dome defect called osteochondritis dissecans may develop.

With appropriate treatment, either by cast immobilization for 6 weeks or by excision, the prognosis in patients like this one is good, particularly if treatment begins ≤ 12 months of symptom onset.

This patient required x-rays by the Ottawa Ankle rules because she was unable to bear weight. She did not meet the criterion of bony tenderness of the malleoli during palpation. It is important to note the importance of the non–weight-bearing rule of the Ottawa Ankle rules to avoid missing more obscure ankle fractures. The rules also state that an ankle radiographic series is required if there is pain in the malleolar region (present in this patient) with any of the following findings:

• Bone tenderness at the posterior edge of the distal 6 cm or the tip of the lateral malleolus (not present in this patient)
• Bone tenderness at the posterior edge of the distal 6 cm or the tip of the medial malleolus (not present in this patient)
• Inability to bear weight for ≥ 4 steps both immediately after the injury and at the time of evaluation (present in this patient)