Abstract: BACKGROUND: Delayed post-traumatic vertebral osteonecrosis (Kummell’s disease) is a special type of osteoporotic vertebral fracture, which was first reported by the German doctor Kummell in 1891. At present, there is a high probability of complications such as bone cement loosening and displacement after treatment with bone cement filling.  
OBJECTIVE: To analyze the biomechanical effect of new bone cement screw combined with vertebroplacty in the treatment of thoracolumbar Kummell’s disease.
METHODS:  Fifty sheep spine specimens were selected and scanned using computed tomography to ensure that the specimens had no vertebral deformity. All sheep spine segments from T12 to L2 were selected, and a Kummell’s disease intravertebral vacuum cleft model was made at the L1 segment, followed by treatment with bone cement augmentation. According to the ways of bone cement filling, the specimens were randomly divided into a vertebroplasty group, a vertebroplasty with unilateral pediculoplasty group, a vertebroplasty with bilateral pediculoplasty group, a unilateral bone cement screw with vertebroplasty group, and a bilateral bone cement screw with vertebroplasty group. There were five groups in each of the following experiments: three-dimensional stability biomechanics test and maximum axial compression test. All the specimens underwent postoperative computed tomography examination to determine whether the screw position was ideal and whether the vertebral body was damaged or not. In the three-dimensional stability biomechanics test, we measured the activity of bone cement in specimens under six motion states, including anteflexion, posterior extension, left flexion, right flexion, and left and right axial rotations. In the maximum axial pressure test, we detected the maximum axial pressure that the bone cement could withstand when it was under pressure until the bone cement was displaced.  
RESULTS AND CONCLUSION: Postoperative imaging examination of all specimens showed that all the screws were positioned normally, and there were no undesirable phenomena such as poor stability and inserting new bone cement screw into the spinal canal. The unilateral or bilateral bone cement screw with vertebroplasty groups had the smallest degree of mobility under the motion states of anteflexion, posterior extension, left and right flexion, and had better biomechanical stability, with a significant difference from the other three groups (P < 0.05). However, there was no significant difference between the unilateral and bilateral novel bone cement screw with vertebroplasty groups (P > 0.05). Therefore, unilateral and bilateral new cement screws could achieve similar cement stabilization effects. Compared with the other three groups, the unilateral and bilateral new bone cement screw with vertebroplasty groups had better compressive capacity of bone cement, in which the bone cement could withstand greater axial pressure and had better stability (P < 0.05). The bilateral new bone cement screw with vertebroplasty group could bear the largest pressure under vertical force, followed by unilateral novel bone cement screw with vertebroplasty group. To conclude, the novel bone cement screw can increase the stability of bone cement and avoid the loosening and displacement of bone cement in the treatment of Kummell’s disease of the thoracolumbar spine.

Key words: Kummell’s disease, novel bone cement screw, internal fixation, biomechanics, sheep, injury, repair, intravertebral vacuum cleft