Biomechanical Comparison of Unipedicular Versus Bipedicular Kyphoplasty

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Abstract
A cadaveric study comparing the biomechanics of unipedicular versus bipedicular kyphoplasty in the treatment of osteoporotic vertebral compression fractures. The objectives of this study were to compare unipedicular kyphoplasty to bipedicular kyphoplasty in restoring strength, stiffness, and height to osteoporotic vertebral compression fractures and to study the degree of unilateral wedging when using a unipedicular versus bipedicular approach to kyphoplasty. Osteoporotic vertebral compression fractures are a common ailment of the elderly that can lead to chronic pain and deformity. Recently developed treatments known as vertebroplasty and kyphoplasty provide pain relief by percutaneously augmenting the fractured vertebral body with polymethyl methacrylate via a transpedicular approach. Vertebroplasty via a unipedicular approach has been shown to provide comparable restoration of vertebral body stiffness when compared to a bipedicular approach. The anticipated benefits of a unipedicular approach include reduction in patient risk, operative time, radiation exposure, and cost. No studies have evaluated the efficacy of unipedicular kyphoplasty. Two fresh-frozen human cadaveric spines (T3–L5) were disarticulated, and the vertebral bodies (n = 30) were compressed using an Instron 8521 machine, recording load versus displacement. The fractured vertebral bodies then underwent kyphoplasty via either a unipedicular or bipedicular approach. The augmented vertebral bodies were then recompressed. The strength, stiffness, and height restoration of the groups were compared. Following recompression, the risk for lateral wedging was evaluated by comparing lateral height measurements. Following fracture and subsequent kyphoplasty augmentation, the mean strength of the bipedicular group was 1.40 kN (± 0.38) versus 1.57 kN (± 0.55) in the unipedicular group. Average stiffness in the bipedicular group was 0.4387 kN/mm (± 0.2095) compared to 0.6880 kN/mm (± 0.3179) in the unipedicular group. Postcompression vertebral body height was restored to 96% of prefracture height in the bipedicular group and 94% of prefracture height in the unipedicular group. The mean absolute value of the difference in height between right and left side of the vertebral bodies was 1.06 mm (± 1.01) in the bipedicular group, whereas the unipedicular group had a mean of 1.78 mm (± 1.84). Statistical analysis using 1-way analysis of variance revealed no significant difference in any of the outcome measurements between the unipedicular and bipedicular groups (P < 0.05). Unipedicular kyphoplasty is comparable to bipedicular kyphoplasty in the restoration of vertebral body strength, stiffness, and height in experimentally induced vertebral compression fractures. There was no greater risk for lateral wedging in the unipedicular group compared to the bipedicular group. Given the advantages of a unipedicular approach with respect to vertebral pedicle cannulation risk, operative time, radiation exposure, and cost, this study would support the use of a unipedicular approach to kyphoplasty in the treatment of vertebral compression fractures.