Hole preparation techniques for transpedicle screws. Effect on pull-out strength from human cadaveric vertebrae.

In each of eight thoracolumbar human cadaveric vertebrae, a hole was made through one pedicle into the vertebral body with a drill bit and through the contralateral pedicle with a probe. Identical metal screws were implanted into the holes to equal depths, and maximum pull-out force was determined for each screw. Using a paired Student t test, no significant difference (P = 0.87) was found in pull-out strength between the screws implanted into drilled holes and those implanted into probed holes. In fact, the average pull-out strengths for the two groups differed by less than 2%. The pedicular cortex was broken through during hole preparation in 5 of the 16 pedicles: 3 as a result of drilling and 2 secondary to probing. The average pull-out strength of the screws in these five pedicles was 11.0% less than the average pull-out strength of the screws implanted into the contralateral intact pedicles. Although this does not represent a statistically significant difference (P = 0.15), it suggests that damaging the pedicular cortex may weaken pedicle screw fixation.

Placement of transpedicular vertebral screws close to anterior vertebral cortex. Description of methods.

Strengthening of the screw-vertebra interface has been shown to occur with implantation of longer transpedicular screws, the tips of which are placed closer to the anterior cortex of the vertebral body. Such implantation probably results in increased risk for anterior cortex penetration and associated vascular or pulmonary damage. Typically recommended lateral and posterior-anterior radiography is shown here to provide potentially misleading visualization during implantation. To reduce the risk of anterior cortical penetration, presented here are 1) a radiographic method ("near approach view") that avoids this problem and allows direct visualization of the relationship between drill bit or screw tip and anterior vertebral cortex, and 2) a surgical technique ("mallet method") that provides both an audible and a palpable change when the drill bit contacts the anterior cortex.

Stress fractures of the great toe sesamoids.

Stress fractures of the great toe sesamoids have not been previously confirmed as a clinical entity. In this report, we present four such cases, and document the diagnosis by histological sections. All of the patients had experienced the insidious onset of activity-related forefoot pain, and had radiographs that demonstrated a sesamoid fracture. None of the fractures healed with 6 weeks of immobilization and prolonged (4-6 months) inactivity. In all cases, the fractured sesamoid was excised, and the hematoxylin and eosin sections of the fracture segments documented the prefracture stress and incomplete repair characteristic of a stress fracture.