Revisiting the concept of talar shift in ankle fractures.

BACKGROUND

In 1976, Ramsey and Hamilton published a classic experiment investigating the biomechanical effects of talar shift in a simple ankle fracture model. Their finding was that 1 mm of talar shift resulted in a 42% decrease in tibiotalar contact surface area. Based on this conclusion, 1 mm of talar shift became the recognized indication for operative fixation.

METHODS

Twelve cadaver ankles were dissected and the distal tibia coated with carbon powder. A 70-kg load was applied to the distal tibia that resulted in transference of the carbon onto the talus. The contact surface area was determined at 0, 1, 2, 4 and 6 mm of talar shift using spacers fixed in the medial gutter. Tracing paper was used to mark the outline of the contact area and measured using graph paper.

RESULTS

Our results were similar to Ramsey and Hamilton's original experiment. One millimeter of lateral talar shift resulted in 40% loss of contact surface area compared with 42% in the original experiment. A large variance was seen in talar contact surface area depending on the morphology of the ankle joint.

CONCLUSION

Ramsey and Hamilton's original experiment was valid.