Safe zones of pin insertion in thoracic spine: a ‘cadaveric study’

Abstract

Purpose This experimental study was conducted to identify the safe zones and angles of half pin insertion in thoracic vertebrae.Materials and methods Simple tools were used, power drill, 4, 5, and 6 mm half pins, goniometer, and portable radiographic apparatus. There were two bony specimens comprising complete lumbar thoracic and cervical spine with ribs and sternum attached, and three cadaveric specimens preserved in formalin, comprising the thorax and abdomen with the back muscle dissected to show the thoracic pedicle. The methodology comprised insertion of the Schanz screw in the thoracic pedicle from T1 to T12 using the free-hand technique in bony skeleton, and then this was repeated on the cadaveric specimens to evaluate the correct angle of insertion, checking the site of half pin insertion using radiography for the cadaveric specimen.Results The suggested safe angulation of half pins was 20°–30° at T1, 15°–25° at T2, 10°–15° at T3, 10°–15° at T4, and from T5 to T9 the safe angle was from 5° to 15°. In T11 and T12, the safe angle was between 0° and 5°. The safe angle of half pin insertion in the pedicle of the thoracic spine in the sagittal plane in all vertebrae from T1 to T12 was between 10° and 15°.Conclusion It was concluded that the application of the external fixator in the thoracic spine is safe, provided there is a better understanding of the anatomical properties of the thoracic spine.