Findings: Comminuted fracture of the lateral process of the talus with approximately 8 mm of displacement.

Diagnosis: Fractured talar lateral process.

Discussion: Although fractures of the lateral process of the talus represent slightly less than 1% of all ankle injuries, they are the second most common fracture of the talus. The initial symptoms and physical findings are quite similar to those of simple inversion ankle sprain, and are frequently overlooked both clinically and radiographically. Fractures of the lateral process have approximately a 25% incidence of osteonecrosis. Malunion and osteoarthritis are also frequent sequaelae and with improper or delayed treatment and healing, persistent symptoms which can be severe and debilitating are seen. It is generally agreed that the mechanism of injury is inversion in dorsiflexion which causes a compression force on the lateral process. They also occur in severe direct crush injuries. Recently, this fracture is being noted more commonly in the snowboarding population which is rapidly growing.

Of particular importance to the radiologist is the fact that several studies show fractures of the lateral process of the talus are missed 40 - 50% of the time on initial radiographic examination. In addition, plain radiographs frequently underestimate the full extent of the injury and degree of fracture fragment displacement. Evaluation of the size and displacement of fracture fragments is extremely helpful in determining if surgical treatment is necessary, and, if so, which approach is most beneficial. CT examination is the most accurate in evaluating these parameters and in many cases identifies fractures which were not apparent on the plain films. Therefore, CT should probably be obtained in all patients with talar fractures, or highly suspicious sprains. Displacement of greater than 2 mm is associated with a much higher rate of nonunion.

Hawkins describes three types of lateral process fractures: a) nonarticular chip fracture, b) single large fragment involving the talofibular and subtalar joints, and c) comminuted fracture involving both joints.

The most effective radiographs are of good quality and are taken with the ankle at 0 degree and the leg rotated inward 10 - 20 degrees.

There are case reports of stress fractures of the lateral process of the talus. In these cases also, CT offered the definitive diagnosis. Bone scintigraphy was nonspecific. These fractures can occur in conjunction with abnormal mechanics of the foot. CT also offers evaluation of the calcaneonavicular and talonavicular joints for coalition.

References:
Hawkins LG. Fractures Of The Lateral Process Of The Talus. The Journal
of Bone and Joint Surgery. Vol. 47-A, No.6, September 1965.

Mukherjee SK, Pringle RM, Baxter AD. Fractures of the Lateral Process of the Talus.
The Journal of Bone and Joint Surgery. Vol. 56-B, No. 2, May 1974.

Heckman JD, McLean, MR. Fractures of the Lateral Process of the Talus.
Clinical Orthopedics and Related Research. October 1985;199.

Mills HJ, Horne G. Fractures of the Lateral Process of the Talus.
New Zealand Journal of Surgery. 1987;57:643-646.

Motto SJ. Stress Fracture of the Lateral Process of the Talus - a Case Report.
British Journal of Sports Medicine. 1993;27(4):275-276.

Hadley NR, Paul C. Snowboarder’s Fracture. Journal of the American Board
of Family Practice. 1994;2:130-133. Mar-Apr.

Black KP, Ehlert KJ. A Stress Fracture of the Lateral Process of the Talus in a Runner.
The Journal of Bone and Joint Surgery, Vol. 76-A, No. 3, March 1994.

Ebraheim NA, Skie MC, Podeszwa DA, Jackson WT. Evaluation of Process Fractures
of the Talus Using Computed Tomography. Journal of Orthopedic Trauma. Vol. 8, No. 4, pp 332-337.

Whitby EH, Barrington NA. Fractures of the Lateral Process of the Talus - The Value of
Lateral Tomography. The British Journal of Radiology. 1995;68-583-586.

McCrory P, Bladin C. Fractures of the Lateral Process of the Talus: A Clinical Review:
Snowboarder’s Ankle. Clinical Journal of Sport Medicine. 6:124-128.

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