Biomechanical analysis of range of motion and failure characteristics of osteoporotic spinal compression fractures in human cadaver

Background: Vertebroplasty is a treatment for osteoporotic vertebral compression fractures. The optimal location of needle placement for cement injection remains a topic of debate. As such, the authors assessed the effects of location of two types of cement instillations. In addition, the motion and failure modes at the index and adjacent segments were measured. Materials and Methods: Seven human osteoporotic cadaver spines (T1-L4), cut into four consecutive vertebral segments, were utilized. Of these, following the exclusion of four specimens not suitable to utilize for analysis, a total of 24 specimens were evaluable. Segments were randomly assigned into four treatment groups: unipedicular and bipedicular injections into the superior quartile or the anatomic center of the vertebra using confidence (Confidence Spinal Cement System^®, DePuy Spine, Raynham, MA, USA) or polymethyl methacrylate. The specimens were subjected to nondestructive pure moments of 5 Nm, in 2.5 Nm increments, using pulleys and weights to simulate six degrees of physiological motion. A follower preload of 200 N was applied in flexion extension. Testing sequence: range of motion (ROM) of intact specimen, fracture creation, cement injection, ROM after cement, and compression testing until failure. Nonconstrained motion was measured at the index and adjacent levels. Results: At the index level, no significant differences were observed in ROM in all treatment groups (P > 0.05). There was a significant increase in adjacent level motion only for the treatment group that received a unipedicular cement injection at the anatomic center. Conclusion: The location of the needle (superior or central) and treatment type (unipedicular or bipedicular) had no significant effect on the ROM at the index site. At the adjacent levels, a significant increase occurred with therapy through a unipedicular approach into the centrum of the vertebra at the treated segment.