Influencia del Par de Apriete en las Cargas Axiales de Extracción de Tornillos Quirúrgicos de Cuerpos Vertebrales en Técnicas Vbt

Currently, there are several surgical corrective treatments for scoliosis problems. Most of them are based on anchoring devices that employ surgical screws and allow the fixation and stabilization of the bone structure [1]. Among these treatments, the Vertebral Body Tethering (VBT) technique is specifically applied in cases of pediatric idiopathic scoliosis because it allows adapting to the patient's growth thanks to the use of an anchoring system using screws to the vertebrae and a flexible cord that joins them and allows dynamic stabilization of the anterior thoracic part of the spine [2]. For the improvement of the VBT technique, the study of the main factors that optimize screw fixation to the vertebral body, without causing irreversible damage, is of great interest. One of these factors, studied in this work, is the final tightening torque during the screwing process. The results show that applying a final tightening torque to the surgical screw increases the anchor's resistance. This study reveals that the pullout force (fy) increased by 14.6%, averaging 1,462 kN compared to 1,276 kN without tightening. Similarly, the pullout failure load (fr) increased by 19.5%, reaching an average of 1,728 kN compared to 1,446 kN without tightening. These findings are critical for the design and evaluation of spinal correction treatments for the aforementioned technique, since greater initial stiffness helps reduce deformations under daily loads, improving anchorage stability and safety. The results also highlight that applying the tightening torque showed an increase in initial stiffness, where the average stiffness in the studies with tightening was 1.4 kN/mm, 55.6% higher compared to 0.9 kN/mm in the studies without tightening. The vertebral samples tested are of porcine origin and in all cases the screw has been introduced laterally into the vertebra, typical of VBT, until reaching bicortical support.