Avoiding rotational mismatch of locking distal tibia plates depends on proper plate position.

Abstract

The purpose of this study was to evaluate the most appropriate positioning of anatomical locking plates on the distal tibia. We positioned 4 types of locking plates (3 straight and 1 bayonet) at anterior, middle, and posterior positions on the medial malleolus on both lower limbs of 15 cadavers. We measured the rotational mismatch angle between the tibia and the proximal part of the plate and calculated the plate prominence at each position. The average rotational mismatch angles of a combined group containing all 3 straight plates were 0.3, 16.9, and 29.4 degrees at the anterior, middle, and posterior positions, respectively (P < 0.001). In the group with 1 bayonet plate, the rotational mismatch angles were -10.5, 0, and 16.7 degrees on average, respectively (P < 0.001). The average plate prominence for each of the positions (anterior, middle, and posterior) in the group with 3 straight plates were 3.5, 6.9, and 9.4 mm, respectively (P < 0.001). The average plate prominence in the group with 1 bayonet plate were 5.4, 3.6, and 6.7 mm, respectively (P < 0.001). We confirmed that anterior placement of the 3 straight locking plates in the distal tibia showed the best fit with regard to rotational alignment and that middle placement of the bayonet locking plates showed best fit. Placement of distal end of the locking plates in inappropriate positions results in a greater risk of rotational mismatch and plate impingement.