Am Fam Physician. 2003 Apr 1;67(7):1438.
to the editor: I enjoyed the article, “Foot Fractures Frequently Misdiagnosed as Ankle Sprains,”1 in American Family Physician. The article provides an excellent discussion of subtle fractures of the tarsal bones that can be easily missed on examination. However, the article does not discuss one type of fracture that is commonly misdiagnosed as an ankle sprain: an avulsion fracture of the proximal fifth metatarsal.
The article1 only addresses this fracture indirectly through a description of the Ottawa ankle rules in Figure 10. When evaluating a patient with a potential ankle injury, this fracture merits focused attention. In my experience, it is the most common fracture misdiagnosed as a sprain by primary care physicians. Its mechanism of injury is similar to that of a lateral ankle sprain. Indeed, patients with this fracture often complain of a “twisted ankle.”2 Furthermore, the area of pain and swelling seen with this fracture may overlap that seen with an ankle sprain. If ankle radiographs are obtained, the fifth metatarsal fracture is often not visible; even if it is visible, it may be overlooked if the physician's attention is focused on the malleoli.
The key to recognizing a proximal fifth metatarsal fracture is to maintain a high index of suspicion for this injury and to apply the Ottawa ankle rules3 when evaluating patients with acute ankle injuries. These rules call for palpation of the proximal fifth metatarsal and navicular in patients with acute ankle injuries and midfoot pain. Radiographs of the foot are recommended if there is tenderness over either of these areas or the patient is unable to bear weight on the foot. Dissemination of these guidelines has helped raise physicians' index of suspicion for this injury. However, many physicians still do not routinely consider this fracture when assessing ankle injuries.
Nondisplaced avulsion fractures of the proximal fifth metatarsal generally heal very well with minimal, conservative treatment. As such, they lend themselves to management by primary care physicians. However, before initiating management, it is important to differentiate this fracture from two other types of proximal fifth metatarsal fractures: a stress fracture of the diaphysis and the so-called “Jones fracture.” The latter fractures require different management and are much more prone to complications. Eiff and colleagues2 provide a discussion of the diagnosis, referral guidelines, and management of proximal fifth metatarsal fractures.
1. Judd DB, Kim DH. Foot fractures frequently misdiagnosed as ankle sprains. Am Fam Physician. 2002;66:785–94.
2. Eiff MP, Hatch RL, Calmbach WL. Fracture management for primary care. 2d ed. Philadelphia, Pa.: W.B. Saunders; 2003:345.
3. Stiell IG, Greenberg GH, McKnight RD, Nair RC, McDowell I, Reardon M, et al. Decision rules for the use of radiography in acute ankle injuries. Refinement and prospective validation. JAMA. 1993;269:1127–32.
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