A newly designed miniplate staple for high tibial osteotomy.

A biomechanical study was made to compare the mechanical performance of the newly designed Miniplate staple to the conventional Coventry staple in high tibial osteotomy (HTO). Using twenty fresh porcine tibiae, the fixational strength of the two different types of staples in HTO was compared. To minimize the error due to the specimen-to-specimen individuality, the bone mineral density of the tibiae was measured with bone densitometry and those with 0.8 to 1.2 gm/cm2 at the proximal tibia were used in the biomechanical test. Testing was performed on a material testing system with aid of a commercial data processor. Using two different loading modes, "pull-out" and "push-out," the maximum resistant force required to release the staple from the substrate bone was recorded. In the pull-out test, ten nonosteotomized specimens were used and the staple was pulled out by subjecting an axial tension on the head of the staple inserted. In the push-out test ten tibiae osteotomized in the usual method of HTO were used and the staple was not directly loaded. In this testing, as a mimic condition of the natural knee, the proximal part of the specimen tibia was pushed horizontally in order for the staple to be pulled out while the distal tibia was fixed. The pull-out strength of Coventry staple and Miniplate staple were found to be 27.88 +/- 5.12 kgf and 182.47 +/- 32.75 kgf, respectively. The push-out strength of Coventry staple and Miniplate staple were 18.40 +/- 4.47 kgf and 119.95 +/- 19.06 kgf, respectively. The result revealed that the Miniplate staple has both a pull-out and push-out strength that is more than six times higher than Coventry staple. Based on the data, it is believed that the Miniplate staple provides better postoperative fixation in HTO. The postoperative application of long leg casting may not be needed after HTO surgery.