A Biomechanical Comparison of Two Novel Vertebral Augmentation Implants to a Traditional Vertebroplasty Technique in Stabilizing Vertebral Compression Fractures

Presented at SMISS Annual Forum 2014
By Eeric Truumees MD
With Brandon Bucklen PhD, Noelle Klocke MS, Jonathan Harris MS, Suresh Chinthakunta MS,

Disclosures: Eeric Truumees MD A; Pfizer, Stryker. F; Stryker. Brandon Bucklen PhD E; Globus Medical Inc., Noelle Klocke MS E; Globus Medical, Inc., Jonathan Harris MS E; Globus Medical, Inc., Suresh Chinthakunta MS E; Globus Medical, Inc.,

Introduction:
After conservative management fails, several cement augmentation procedures are available to treat vertebral compression fractures. Percutaneous vertebroplasty is associated with cement embolism following leakage. Minimizing this risk using implants to encompass the cement, while maintaining fracture stability, might be advantageous for improved patient outcomes.

Aims/Objectives:
To biomechanically assess the fracture stabilization of unipedicular, minimally invasive cement augmentation methods (traditional vertebroplasty, a nitinol implant used in vertebroplasty, and a deployable polymeric implant used following balloon kyphoplasty) through measurement of anterior vertebral height and load-to-failure values.

Methods:
Cadaveric vertebral bodies (T11-L4) were assigned to a vertebroplasty group (TV) and two balloon kyphoplasty variants (n=6 each). The first utilized a rigid, non-inflatable, nitinol sheath which directed cement anteriorly though ventrally-placed holes (RV, Audubon, PA). The second variant resembled a kyphoplasty balloon, but was deployable and enveloped all cement (CK, Audubon, PA). Posterior elements (except pedicles) were removed, and endplate impressions made (Bondo, Bondo Corp, Atlanta, GA). Anterior burst fractures were created (5mm/min axial compression until height was reduced by 40%) using a MTS 858 Mini Bionix (MTS Corporation, Minneapolis, MN). Under continuous, physiological axial loading (111N), a bone tamp was placed, and lateral fluoroscopic images captured each procedural phase: after fracture creation, balloon inflation (only CK), and after cement injection. After curing, the augmented bodies were compressed axially. Anterior vertebral height measurements were made using ImageJ (NIH, USA). A one-way ANOVA with Tukey’s post hoc (p<0.05) was used for comparisons to intact.

Results:
Normalized anterior height of the vertebral bodies were statistically equivalent (p>0.05) following cement augmentation (TV=85.7±14.7%, RV=77.8±4.9%, CK=79.9±6.8%). The initial TV raw load-to-failure value was statistically lower (p<0.05), which subsequently made the normalized augmented load-to-failure value (463.91±124.2%) higher than the other groups’ (RV=250.6±51.2%, CK=166.8±105.7%). However, raw post-augmentation load-to-failure values for TV were either equivalent (p=0.67, TV vs. CK) or nearing significance (p=0.046, TV vs. RV).

Conclusions:
Both of the more cement-containing procedures (RV and CK) produced equivalent fracture stabilization results compared to traditional vertebroplasty, as measured by anterior vertebral body height. A lower BMD score may proffer the TV group's lower initial load-to-failure; yet unknown BMD scores remain a study limitation. Each group's raw post-augmentation values far exceed the natural bone’s observed failure points, thus demonstrating each procedure's efficacy in fracture stabilization and resistance against refracture. However, the procedures using the two deployable implants may permit fewer incidences of cement leakage and reduce the clinically-associated risks than traditional vertebroplasty alone.