RADIOGRAPHIC ASSESSMENT OF PEDICLE HOOK PLACEMENT

Study Design. A cadaveric study of the changes in the radiographic mor phology of the thoracic pedicle with vertebral rotation. Objective, To study the effect of vertebral rotation on the assessment of pedicle h ook placement by determining the radiographic anatomy of the pedicle a nd its relation to the pedicle hook, Summary of Background Data. It is commonly assumed that the oval pedicle shadow seen on spine radiograp hs is formed by the waist of the pedicle. The postoperative assessment of pedicle hook position is based on this assumption. Methods, Thorac ic cadaveric vertebrae between T5 and T8 were studied, with wire marke rs placed at the waist, the pedicle-facet junction, and the pedicle-bo dy junction. Thoracic pedicle hooks were placed in the correct positio n and offset to one side. Radiographs of the vertebral body were taken from 0 degrees to 30 degrees of rotation with reference to the sagitt al plane. Results, The radiographic morphology of the pedicle changes with vertebral rotation; it also differs between the concave and:he co nvex side of a scoliotic spine. With rotation of less than 20 degrees, the pedicle shadow is formed by the waist on both sides. With 30 degr ees of rotation, the concave pedicle shadow is formed by the pedicle-f acet junction, whereas on the convex side, it is overlapped by the tra nsverse process shadow. A laterally misplaced hook on the convex side and a medially misplaced hook on the concave side can appear correctly located with vertebral rotation. Conclusion, The oval pedicle shadow is not simply represented by the waist of the pedicle. An understandin g of the changes in radiographic morphology with rotation is necessary for the assessment of thoracic pedicle hook location after surgery.