The Experimental And Clinical Studies About Absorbable Balloon Vertebroplasty For The Treatment Of Thoracolumbar Burst Fractures

[Objective]To study the feasibility of absorbable balloon vertebroplasty for the treatment of thoracolumbar burst fractures.[Methods]Six fresh adult thoracolumbar spinal specimens were collected, and 10 segmental specimens (T₁1-L₁, L_2-4 , L_1-3 ) were processed. Burst fractures were created by free-drop test. The intracorporeal porosity of the injuried vertebrae were measured using spiral CT after the fractures were reduced with APR On these data, absorbable balloon was produced which diameter was 1.9cm, using absorbable high polymer materials PDLLA-CL made from the homoconjugate DL-lactic acid and e-caprolactone with the ratio 70:30.The in vitro degradation and animal tests were done for the sake of observing the healing results of the tibial upper end bone returned-graft and degradation of the ballon. Then the defects in the vertebral body were enlarged through rasing the upper end plate transpedicularly with the self-made instrument after the fracture was reduced and fixed with APF. And absorbable balloon vertebroplasty was performed with the absorbable balloon put into the vertebral body transpedicularly and calcicum phosphate cement (CPC) was injected into the ballon. The intracorporeal porosity of the injured vertebrae were measured after absorbable balloon vertebroplasty and the biomechanical effects before fracture and after absorbable balloon vertebroplasty treatment were tested. In clinical application, Eight patients with fresh thoracolumbar burst fracture were treated with absorbable balloon vertebroplasty.[Results]1. There was no evident intracorporeal gap before fracture, which appered evident gap after reduction with APF with average volume of 5.43cm³ (14.5% of total corporeal volume).2. The initial split strength of absorbable ballon was 8.5Mpa, and 4.2Mpa 2 weeks later. It degraded absolutely in vitro 24 weeks later. In animal test, the absorbable balloon, loaded with calcicum phosphate cement, was absorbed partly 16 weeks later. And the healing results of the tibial upper end bone returned-graft was perfect, without periosteum reaction and rejection.3. The intracorporeal porosity decreasd significantly (P<0.01) after absorbable balloon vertebroplasty, approaching the level before fracture.4. The stress, strain and crushing strength in traumatic vertebrae after absorbable balloon vertebroplasty increased somewhat, which did 8% under flexion, 15% under extension and 9.8% under lateral flexion, but was significant under extension (P<0.05) . Axial stiffness got more generally after absorbable balloon vertebroplasty treatment, but wasn't significant (P>0.05 ) . The stiffness of disc decreasd significantly under flexion and extension stress(P<0.05), but not significantly under lateral flexion stress (P>0.05) after absorbable balloon vertebroplasty. The stiffness under torsion stress after absorbable balloon vertebroplasty was smaller than before Fracture, but the difference was no significant between them (P > 0.05) . The ultimate strength against compression increased but not significantly (P>0.05) .5. The fractures were reduced satisfactorily in the 8 patients. The calcicum phosphate cement in the ballon develops clearly ,without leakage, general and local reaction .And all cuts were healed primarily after operation.[Conclusion]1. The absorbable balloon made from PDLLA—CL not only has perfect biological compatibility—no harmful effects on the surrounding normal organisms and structures, butalso has good mechanical function — effectively preventing leakage of the calcicum phosphate cement through as well as forming good protective screen between the calcicum phosphate cement and the local organisms.2. The intracorporeal porosity decreasd significantly after absorbable balloon vertebropiasty with pedicle screw system and the stiffness and the strength of the traumatic vertebre may be increased satisfactorily.3. Absorbable balloon vertebropiasty for the treatment of thoracolumbar burst fracture based on the premise that avoid the potential danger induced by leakage of bone cement, can reestablish intact corporeal structure of traumatic vertebrae and restore their height essentially, so that spinal physiologic curve can be gained to restore and maintain, tardive lumbodorsal pain and spinal cord injury and nerve injury caused by secondary kyphosis can be prevented, which can fundamentally solve complications left over by thoracolumbar burst fracture treated merely using pedicle screw system. So it provides a new method for clinical treatment of thoracolumbar burst fractures.