Thoracic and lumbar pedicle morphometry in achondroplasia

For safe pedicle screw insertion, knowing pedicle anatomy is essential. Pedicle morphometry in achondroplasia has not been quantitatively described. Therefore, we analyzed 302 thoracic and lumbar pedicles in 11 patients using computed tomography. Transverse endosteal diameter, screw path length, transverse angle, sagittal diameter, and sagittal angle were calculated. We analyzed for safe screw length, size, and trajectory. The data were compared with that on healthy people of different races. In patients with achondroplasia, the maximum endosteal diameter was at L5 and the minimum was at T5. Screw path length was longest at L2 and shortest at T2. Most dimensions were smaller compared with those of healthy people. Abnormal anteromedial transverse angulations were observed between T11 to L2. The maximum transverse angulations were at T2. Sagittal diameter was largest at T12 and smallest at T5. The maximum sagittal angle was seen at T2, and at L5 it was caudal. At all levels except L5, the transverse diameter is the limiting factor for screw size. Six-millimeter screws can be used at L5. Screws that are 35 mm or less are safe to use between T7 to L5. There are surgically important differences in the different angles and diameters of thoracic and lumbar pedicles of patients with achondroplasia and those of healthy people.