Height restoration and sustainability using bilateral vertebral augmentation systems for vertebral compression fractures: a cadaveric study

BACKGROUND CONTEXT: The treatment of vertebral compression fractures using percutaneous augmentation is an effective method to reduce pain and decrease mortality rates. Surgical methods include vertebroplasty, kyphoplasty, and vertebral augmentation with implants. A previous study suggested that a titanium implantable vertebral augmentation device (TIVAD) produced superior height restoration compared to balloon kyphoplasty (BKP) but was based on a less clinically relevant biomechanical model. Moreover, the introduction of high pressure balloons and directional instruments may further aid in restoring height. PURPOSE: The objective was to evaluate three procedures (BKP, BKP w/ Kyphon Assist (KA; directional instruments), and TIVAD) used for percutaneous augmentation of vertebral fractures with respect to height restoration and sustainability post-operatively. STUDY DESIGN/SETTING: This is an in vitro cadaver study performed in a laboratory setting. METHODS: Five osteoporotic female human cadaver thoracolumbar spines (age: 63–77 years, T-score: -2.5 to -3.5, levels: T7–S1) were scanned using computed tomography and dissected into 30 two-functional spine units (2FSUs). Vertebral wedge compression fractures were created by reducing the anterior height of the vertebrae by 25% and holding the maximum displacement for 15 minutes. Post-fracture, surgery was performed on each 2FSU with a constant 100 N load. Surgeries included BKP, BKP w/ KA, or TIVAD (n=10 per treatment group). Post-surgery, cyclic loading was performed on each 2FSU for 10,000 cycles at 600 N (walking), followed by 5,000 cycles at 850 N (standing up/sitting down), and 5,000 cycles at 1250 N (lifting a 5-10kg weight from the floor). Fluoroscopic images were taken and analyzed at the initial, post-fracture, post-surgery, and post-loading timepoints. Anterior, central, and posterior heights, Beck Index, and angle between endplates were assessed. RESULTS: No difference in height restoration was observed among treatment groups (p=.72). Compared to the initial height, post-surgery anterior height was 96.3±8.7% for BKP, 94.0±10.0% for BKP w/ KA, and 95.3±5.8% for TIVAD. No difference in height sustainability in response to 600 N (p=.76) and 850 N (p=.20) load levels was observed among treatment groups. However, after 1250 N loading, anterior height decreased to 93.8±6.8% of the post-surgery height for BKP, 95.9±6.4% for BKP w/ KA, and 86.0±6.6% for TIVAD (p=.02). Specifically, the mean anterior height reduction between post-surgery and post-1250 N loading timepoints was lower for BKP w/ KA compared to TIVAD (p=.02), but not when comparing BKP to TIVAD (p=.07). No difference in Beck Index or angle between endplates was observed at any timepoint among the treatment groups. CONCLUSIONS: The present study, utilizing a clinically relevant biomechanical model, demonstrated equivalent height restoration post-surgery and at relatively lower-level cyclic loading using BKP, BKP w/ KA, and TIVAD, contrary to results from a previous study. Less anterior height reduction in response to high-level cyclic loading was observed in the BKP w/ KA group compared to TIVAD. CLINICAL SIGNIFICANCE: All three treatments can restore height similarly after a vertebral compression fracture, which may lead to pain reduction and decreased mortality. BKP w/ KA may exhibit less height loss in higher-demand patients who engage in physical activities that involve increased weight resistance.