Working within the frame-work of the Spine Research Laboratory (SRL), our research group is employing a three-pronged attack to discover the causes and the cure of degenerative spinal disease. The SRL is jointly sponsored by the Departments of Orthopaedic and Neurosurgery of the Cleveland Clinic Foundation. As such, the SRL enjoys a unique position among academic spine research entities, and capitalizes on the special contributions of each clinical discipline, while creating intellectual synergies otherwise not possible. Our research group takes full advantage of the multidisciplinary opportunities this structure presents.
Basic anatomical and neurophysiological studies are underway to define the pathological changes that occur as the spine ages and the soft tissue structures that support it degenerate. Traditional biomechanical studies have provided important information on how current treatment methods effect the spinal motion segment, and how future treatments might be altered to improve spinal mechanics and eliminate failures of bone, implants, or adjacent spinal segments. Innovative techniques are being applied and validated in studies of the trabecular micro-environment that may ultimately determine the success or failure of treatments for osteoporosis, disc degeneration, and back pain.
In the United States alone, low back pain costs the health care system, industry, and the government 52 billion dollars annually.Most current forms of treatment involve removal or immobilization of the intervertebral disc, the most common generator of back pain symptoms. These discs absorb and distribute loads applied to the spine, and serve as shock absorbers when the spine is exposed to sudden impacts or loading. Disc degeneration is an age-related deterioration of structure and protein composition that leads to mechanical instability, loss of disc height, and restriction of normal spine motion.
We have shown that changes in the disc cause changes in the surrounding bone and in the way that vertebral bone responds to loads. We have also characterized the distribution of pain-related nerve endings within the spinal tissues, and demonstrated that chronic vibration can alter the function of the spinal nerves and increase the release of pain-related neurotransmitters. These responses have been linked to clinical back pain and degenerative changes in human workers.
Success in current treatment of disc-related back pain typically hinges on success of the fusion procedure. Failure of current spinal implants to hold the bone or to withstand cyclical loading can result in clinical failure requiring re-operation and further disability. Through a series of innovative biomechanical studies, our group has revealed flaws in traditional assumptions about pedicle screw fixation, and has generated mechanically sound principles for screw design and implantation. Ongoing work is assessing newer screw and thread designs, and establishing criteria for future implant and instrument development. Using our unique micro-CT testing configuration, we are now exploring the micro-environment of the vertebral body and pedicle to determine the impact of thread and material design variables on trabecular bone. Changes in trabecular strain and elastic deformation may prove the ultimate determinant of screw and end-plate failure in both normal and osteoporotic patients. Similarly, trabecular mechanics may also reveal the most subtle and clinically important changes of osteoporosis treatment.
More recently, surgeons and researchers have begun to focus on efforts to retain spinal motion following surgical treatment. One appealing alternative, designed as a minimally invasive approach, is to replace the damaged or removed nucleus pulposus with a bio-compatible material that can simulate the function of the nucleus. Preliminary work, carried out in collaboration with the University of Akron, has identified promising new materials and structural designs that may allow us to develop just such a device. Biomechanical testing is underway to establish the optimum material properties this new implant will have to have to survive the constant loading and motion faced within the intervertebral disc. These new prosthetic strategies, combined with rapidly developing minimally invasive surgical techniques, hold great promise for improved clinical satisfaction and reduce cost in the treatment of these common and very disabling lumbar spinal disorders.
