Comparative Experimental Study of Hook and Pedicle Fixation Systems Used at Surgical Treatment of Spine Deformities

Using human cadaver spines we compared the stiffness of pedicle screws and laminar hooks under cyclic and static pull-out loads. Transpedicular and hook fixation (sub- and supralaminar) of cadaveric thoracic spine segments was performed. Axial pull-out strength was measured using w+b (walter + bai ag) servoelectric testing machine (LFV-10-T50, Switzerland). Static pull-out tests were performed on 7 spine blocks with transpedicular and 7 blocks with hook fixation. The same blocks were tested under cyclic loads. At cyclic pull-out loading 800 N strength with 5 Hz frequency was applied. It was shown that at increasing static load hook implants could bear 1417 N at average. At higher loads the vertebral arch was destroyed. Transpedicular implants could bear 2286 N at average and at higher loads the screw migrated from the arch root. Cyclic tests showed that hooks could bear 2935 cycles at average and at prolonged loading the arch was destroyed. The hooks could bear the full; program of cyclic loads without destruction (18 000 cycles).

experiment, pedicle screw fixation, hook fixation, pull-out