Stress in lumbar intervertebral discs during distraction: a cadaveric study.

BACKGROUND CONTEXT The intervertebral disc is a common source of low back pain (LBP). Prospective studies suggest that treatments that intermittently distract the disc might be beneficial for chronic LBP. Although the potential exists for distraction therapies to affect the disc biomechanically, their effect on intradiscal stress is debated. PURPOSE To determine if distraction alone, distraction combined with flexion, or distraction combined with extension can reduce nucleus pulposus pressure and posterior annulus compressive stress in cadaveric lumbar discs compared with simulated standing or lying. STUDY DESIGN Laboratory study using single cadaveric motion segments. OUTCOME MEASURES Strain gauge measures of nucleus pulposus pressure and compressive stress in the anterior and posterior annulus fibrosus. METHODS Intradiscal stress profilometry was performed on 15 motion segments during 5 simulated conditions: standing, lying, and 3 distracted conditions. Disc degeneration was graded by inspection from 1 (normal) to 4 (severe degeneration). RESULTS All distraction conditions markedly reduced nucleus pressure compared with either simulated standing or lying. There was no difference between distraction with flexion and distraction with extension in regard to posterior annulus compressive stress. Discs with little or no degeneration appeared to distribute compressive stress differently than those with moderate or severe degeneration. CONCLUSIONS Distraction appears to predictably reduce nucleus pulposus pressure. The effect of distraction therapy on the distribution of compressive stress may be dependent in part on the health of the disc.