General Session: Innovative Technologies II - Hall F

Presented by: K. Tillinghast

Author(s):

K. Tillinghast(1,2), J.V. Chen(2), K. Lee(1), B. Halloran(3), A.B. Dang(1,2)

(1) University of California, San Francisco, Department of Orthopaedic Surgery, San Francisco, CA, United States
(2) San Francisco VA Health Center, Orthopaedic Translational Research Lab, San Francisco, CA, United States
(3) University of California, San Francisco, Department of Medicine, Endocrinology, San Francisco, CA, United States

Abstract

Pseudarthrosis and non-union are harmful complications that have serious personal and financial penalties. Over $3 billion is lost each year in direct and indirect costs due to failures to heal or form bone such as the case with spinal fusion or the treatment of tibial fractures. Bone graft extenders or substitutes have increased the rate of fusion but not without consequences such as increased cancer risk and cost. Costing only 15 cents per gram, ascorbic acid has been shown to differentiate bone marrow stromal cells and maintain collagen synthesis. We hypothesized that locally delivered ascorbic acid will increase the volume of fusion mass when used as an allograft extender in a murine lumbar spinal fusion model. One and half month old male C5BL/6 mice underwent posterolateral L3-5 lumbar fusion (n=22). After induction of inhaled isoflurane anesthesia, vertebrae were exposed and decorticated similar to clinical spine surgery. Fresh allograft consisted of 1 cc of morselized murine femur obtained from donor mice. The control group (AG) received allograft only. A second control group (GF), received a combination of allograft and 1cc of a collagen sponge ("Gelfoam"). The experimental group (VC) received fresh allograft and 1cc of collagen sponge that had specifically been prepared with ascorbic acid. Micro CT imaging was used to assess the fusion 3 months post-operatively. The volume was calculated by analyzing the dorsal-half and ventral-half of the vertebrae separately. To remove the potential for error, the ventral volume was used as a correction factor for the potential size of the lamina dorsally. The ratio between the dorsal and ventral halves generate BV, the total volume of bone corrected for host lamina size. To analyze bone density, pixel intensity data was extracted from dorsal volume to generate BD values. Statistical analysis was performed using Student's T-Test and an analysis of variance with Turkey post-test. The 24 vertebrae receiving ascorbic acid had a statistically significant increase in bone formation compared to AG vertebra with a 56.3% increase in BV (p< 0.0001). Compared to GF vertebrae, the 24 vertebrae receiving ascorbic acid had a statistically significant increase in bone formation with a BV increase of 25.4% (p = 0.03). Comparing GF group to AG, GF animals had non-significant increase and bone formation (p = 0.7). There was no statistically significant difference between AG, GF, or VC groups in BD (p = 0.09). The addition of ascorbic acid and Gelfoam to allograft resulted in a statistically significant increase in new bone formation. Considering the multiple order of magnitude difference in cost between ascorbic acid and BMP2 further investigation on the use of surgically delivered ascorbic acid to enhance bone formation is clearly warranted.

Bone Volume and Bridging in VC, GF, and AG