A Comparison of the Torsional Stiffness of the Lumbar Spine in Flexion and Extension

Garges, Kim J.; Nourbakhsh, Ali; Morris, Randall; Yang, Jinping; Mody, Milan; Patterson, Rita

doi:10.1016/j.jmpt.2008.09.002

« Previous Next »Journal of Manipulative and Physiological Therapeutics
Volume 31, Issue 8 , Pages 563-569, October 2008

A Comparison of the Torsional Stiffness of the Lumbar Spine in Flexion and Extension

Kim J. Garges, MD
- Associate Professor and Chief, Division of Spine Surgery, Department of Orthopaedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, Texas
- Submit requests for reprints to: Kim Garges, MD, Associate Professor and Chief, Division of Spine Surgery, Department of Orthopaedic Surgery and Rehabilitation, The University of Texas Medical Branch, Galveston, TX 77555-0165.
Ali Nourbakhsh, MD
- Research Fellow, Division of Spine Surgery, Department of Orthopaedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, Texas
Randall Morris, BS
- Biomechanics Engineering Specialist, Division of Spine Surgery, Department of Orthopaedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, Texas
Jinping Yang, PhD
- Research Fellow, Division of Spine Surgery, Department of Orthopaedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, Texas
Milan Mody, MD
- Resident, Division of Spine Surgery, Department of Orthopaedic Surgery and Rehabilitation, University of Texas Medical Branch, Galveston, Texas; Willis Knighton Orthopaedic Clinic, Shreveport, Louisiana
Rita Patterson, PhD
- Professor and Director, Osteopathic Heritage Foundation, Physical Medicine Core Research Facility, University of North Texas Health Science Center, Fort Worth, Texas

Received 17 March 2008; received in revised form 26 March 2008; accepted 20 May 2008.

Abstract

Objective

The main mechanism of injury to the spine is torsion especially when coupled with compression. In this study, the in vitro torsional stiffness of the lumbar spine segments is compared in flexion and extension positions by cyclic and failure testing.

Methods

Fifteen lumbar spines were sectioned from fresh cadavers into 15 L2/3 and 15 L45 motion segments. Each vertebral segment was then potted superiorly and inferiorly in polymethylmethacrylate, effectively creating a bone-disk-bone construct. The potted spinal segments were mounted in a mechanical testing system, preloaded in compression to 300 N, and axially rotated to 3° in both directions at a load rate of 1°/s. This was done over 3 cycles for each motion segment in the flexion and extension positions. Each specimen was then tested to torsional failure in either flexion or extension. Stiffness, torque, and energy were determined from cyclic and failure testing.

Results

The results showed that in all cases of cyclic testing, the higher segment extension resulted in higher torsional stiffness. In relative extension, the lumbar specimens were stiffer, generated higher torque values, and generally absorbed more energy than the relative flexion condition. There were no differences found in loading direction or failure testing.

Conclusions

Increasing the effective torsional stiffness of the lumbar spine in extension could provide a protective mechanism against interverbral disk injury. Restoration of segmental extension through increasing the lumbar lordosis may decrease the strain and reinjury of the joints, which can help reduce the extent of pain in the lumbar spine.

Key Indexing Terms: Lumbar Region, Lordosis, Torsion, Mechanical