Vertebroplasty with high-viscosity polymethylmethacrylate cement facilitates vertebral body restoration in vitro.

STUDY
DESIGN: In vitro biomechanical study on 6 fresh frozen human thoracolumbar spine specimens.
OBJECTIVE: Using a novel high viscosity polymethylmethacrylate (PMMA) cement and vertebroplasty kit to correct the kyphosis angle of wedge compression fractures (AO/ASIF 1.2). SUMMARY OF BACKGROUND DATA: Vertebroplasty is typically used to stabilize vertebral compression fractures in situ without correcting kyphosis, with the main target to reduce pain and disability. The vertebroplasty system investigated in this study comprises a high viscosity PMMA cement and uses a hydrostatic pressure hand piece for enhanced cement allocation and flow control. A recent clinical trial demonstrated a significantly reduced incidence of cement leakage with this system.
METHODS: Six spinal segments (Th11-L1 and Th12-L2) were loaded in a spine tester with pure moments of 7.5 Nm in lateral bending, flexion/extension and axial rotation. The segmental range of motion (ROM) was continuously recorded. The tested states of the specimens were: intact (a), fractured (b), treated with vertebroplasty (c), after loading with 50 to 250 N (d), 50 to 450 N (e) and 50 to 650 N (f) of 1000 cycles each. In each state (a-f), the kyphosis angle was documented fluoroscopically.
RESULTS: Kyphosis angle was significantly reduced between intact and fractured states (P<0.02). Between treated and fractured states, we found highly significant difference (P<0.001), indicating full correction. During 3000 loading cycles (50-250, 50-450, and 50-650 N), the kyphosis angle remained constant compared to the treated state (P=1.0). We noted a logistic relationship between injected cement volume and extent of kyphosis correction (R=0.89, P<0.001). In the fractured state, the ROM in flexion/extension increased to 252% of the intact state (P<0.001). The vertebroplasty treatment decreased ROM to 72% of fractured state in flexion/extension (P<0.001). Macroscopic inspection of the vertebrae after testing showed an intact interface and tight mechanical interlocking of cement filling and trabecular bone.
CONCLUSION: High viscosity vertebroplasty effectively reduced and stabilized thoracolumbar wedge compression fractures and may represent a one-step solution for restoring vertebral body dimensions following thoracolumbar compression fractures, while minimizing the risk of cement leakage and associated complications in vivo.