Anatomical And Biomechanical Study On Thoracic Extrapedicular Fixation In The Upper And Middle Thoracic Spine

Objective: To evaluate the morphology of Costovertebral joints in the thoracic spine of normal thoracic human spines with particular attention to T1-T8, and to compare the dimensions of the Costovertebral joint with corresponding dimensions of the adjacent pedicles, and to compare the mechanical stability of the extrapedicuar and transpedicular fixation with an aim to provide anatomical and biomechanical evidence for clinical treatment.Methods: 12 adult cadavers were obtained (9 male and 3 female). No history of spine disease was noted, and cause of death was unrelated to spinal disorder or trauma. These cadaveric thoracic spine were divided into two groups at random(six extrapedicular, six intrapedicular) were instrumented with the Kanghui spine system in T4-T5. The diameter 6. 0mm and length 5. 0cm pedicle screws were placed using an extrapedicular approach;the diameter 4.5mm and length 4.0cm pedicle screws were placed using an intrapedicular approach. The screws were placed according to one defined method described later. X-rays images were obtained. The position of each screw was analyzed. The specimens were tested in flexion-extension, axial torsion, bilateral lateral bending loading and recorded load-displacement relationship. Measurements of the transverse diameter, screw path length of the Costovertebral joint , the angle e (the angle between the pedicle rib unit and the processus spinosus) and angle f(the angle between the pedicle rib unit and lamina)were obtained and compared with measurements of the adjacent pedicles.