Multiscale vibration response analysis and fatigue damage prediction after idiopathic scoliosis kyphosis surgery

Purpose The multiscale vibratory response of the spine following orthopedic surgery in patients with idiopathic scoliosis and postoperative traumatic fatigue injury remains largely unexplored. Methods This paper analyzes the postoperative macroscopic spine model in the modal, time, and frequency domains to obtain the vibration response of the patient's entire spine. Subsequently, the stresses in the cortical bone mesoscopic bone units around the surgically damaged interface were calculated using submodeling algorithms. The pore stresses and pore flow velocities of the osteocytes were then derived from the stresses of the mesoscopic bone units to predict fatigue damage at the fusion surface. Results The findings indicated that the first three orders of intrinsic frequency exerted the most significant influence on the spine model. The maximum stress of the bone unit was observed at the X3 bone plate on the left side of the fusion surface, and the maximum pore pressure and flow velocity of the bone cells occurred at the X4 on the right side of the fusion surface. The medical implants used in spinal orthopedics, titanium cages and pedicle nails, change the mobility of the adjacent segments and also create a stress shielding effect that impacts the fusion of bone tissues. Conclusions Microscopic bone cell synapses experience greater pore pressures and pore flow velocities in the vibration environment compared to those under the static environment, which may promote cell growth. Vibration at low loads typically does not induce fatigue damage to cancellous bone at the fusion surface of medical implants.