Flexible Disc Implant Eases Chronic Back Pain

Flexible Disc Implant Eases Chronic Back Pain

In between the vertebrae of the human spine are 23 Oreo-sized, cartilage-filled discs that hold the vertebrae together and allow for spine movement.

While the discs are critical for movement, they can become the source of back pain when they degenerate or herniate – a major health problem that affects 85% of Americans and drains the U.S. economy to the tune of $100 billion every year.

A new biomedical device to surgically treat chronic back pain – an artificial spinal disc that duplicates the natural motion of the spine – has been licensed from Brigham Young University to a Utah-based company.

The artificial disc was conceived by engineering professors Anton Bowden and Larry Howell and BYU alum Peter Halverson. It will be developed to market by Crocker Spinal Technologies, a company founded by BYU President’s Leadership Council member Gary Crocker and headed by BYU MBA graduate David Hawkes.

The BYU researchers report on the mechanism’s ability to facilitate natural spine movement in a study published in a forthcoming issue of the International Journal of Spine Surgery.

“Low back pain has been described as the most severe pain you can experience that won’t kill you,” said Bowden, a BYU biomechanics and spine expert. “This device has the potential to alleviate that pain and restore the natural motion of the spine – something current procedures can’t replicate.”

Currently, the most common surgical treatment for chronic low back pain is spinal fusion surgery. Fusion replaces the degenerative disc with bone in order to fuse the adjacent segments to prevent motion-generated pain.

Unfortunately, patient satisfaction with fusion surgery is less than 50 percent.

The solution researched by the BYU team, and now being developed by Crocker Spinal Technologies, consists of a compliant mechanism that facilitates natural spine movement and is aimed at restoring the function of a healthy spinal disc.

Compliant mechanisms are jointless, elastic structures that use flexibility to create movement. Examples include tweezers, fingernail clippers or a bow-and-arrow. Howell is a leading expert in compliant mechanism research.

“To mimic the response of the spine is very difficult because of the constrained space and the sophistication of the spine and its parts,” Howell said. “A compliant mechanism is more human-like, more natural, and the one we’ve created behaves like a healthy disc.”

Under Howell’s and Bowden’s tutelage, BYU student-engineers built prototypes, machine tested the disc and then tested the device in cadaveric spines. The test results show the artificial replacement disc behaves similarly to a healthy human disc.

“Putting it in a cadaver and having it do what we engineered it do was really rewarding,” Howell said. “It has a lot of promise for eventually making a difference in a lot of people’s lives.”

Halverson, who was lead author on the International Journal of Spine Surgery study, has since earned his Ph.D. from BYU and taken a position at Crocker Spinal Technologies, which will likely begin international sales distribution as early as next year.

“Fusion, which is the current standard of care for back pain, leaves a lot to be desired,” said Hawkes, president of Crocker Spinal Technologies. “Disc replacement is an emerging alternative to fusion that has the potential to make a significant difference in the lives of millions.

“BYU’s innovation is a radical step forward in the advancement of disc replacement technology. It is exciting to be a part of this effort and a delight to work with such talented, wonderful people,” he said.

Background

The current generation of total disc replacements achieves excellent short- and medium-term results by focusing on restoring the quantity of motion. Recent studies indicate that additional concerns (helical axes of motion, segmental torque-rotation behavior) may have important implications in the health of adjacent segments as well as the health of the surrounding tissue of the operative level. The objective of this article is to outline the development, validation, and biomechanical performance of a novel, compliant-mechanism total disc replacement that addresses these concerns by including them as essential design criteria.

Methods

Compliant-mechanism design techniques were used to design a total disc replacement capable of replicating the moment-rotation response and the location and path of the helical axis of motion. A prototype was evaluated with the use of bench-top testing and single-level cadaveric experiments in flexion-extension, lateral bending, and axial torsion.

Results

Bench-top testing confirmed that the moment-rotation response of the disc replacement matched the intended design behavior. Cadaveric testing confirmed that the moment-rotation and displacement response of the implanted segment mimicked those of the healthy spinal segment.

Conclusions

Incorporation of segmental quality of motion into the foundational stages of the design process resulted in a total disc replacement design that provides torque-rotation and helical axis–of–motion characteristics to the adjacent segments and the operative-level facets that are similar to those observed in healthy spinal segments.

Source : http://www.journals.elsevierhealth.com/periodicals/ijsp/article/S2211-4599%2812%2900012-4/abstract

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