A study of in vivo intradiscal pressure in subjects with and without lower back pain (LBP) sought to find out how disc degeneration affects intradiscal pressure, measure the loading capacity of the L4/L5 IVD segment, and determine any relationship between movement in that disc segment and the spinal loading capacity. The researchers found that there was a significant relationship between spinal loading and the angle of the motion segment in healthy discs in vivo. In degenerated discs, the intradiscal pressure was much lower than that measured in healthy discs. Further study with wider parameters is suggested to fully understand the phenomenon and the problems associated with it.
Study Motivation and Design
The only way to directly measure spinal loading in humans is via the measurement of intradiscal pressure—a complex in vivo task. Most current knowledge about loading capacities were derived from pioneering studies in the 1960’s and 1970’s by Nachemson, but little corroborating evidence has been published on the topic since. These early studies utilized an inefficient means of evaluating intradiscal pressure—the polyethylene coated disc pressure needle until 1965, and after that, another needle designed specifically for intradiscal pressure measurements. This new needle was not without its deficits and required special handling and was prone to destroying structural defects on insertion. The current study’s authors utilized a newly designed silicone-based needle to measure the pressure and spinal load in 28 patients suffering from LBP, sciatica, or both at the L4/L5 segment, and in eight healthy volunteers with an average age of 25 years-old.
Magnetic resonance imaging (MRI) was performed on the healthy subjects prior to the beginning of the study to ensure no disc degeneration in the volunteers. The 28 LBP patients (10 women and 18 men with a mean age 45 years) were also imaged prior to pressure measurements being taken to visualize the amount of water content in their discs. These patients were diagnosed with disc herniation (16 patients) or spondylosis (12 patients).
The subjects were measured while in the prone position, without sedation but with a “local” dose of anesthesia. A guiding needle was used to position the pressure sensor needle into the nucleus pulposus of the L4/L5 IVD discs. Fluoroscopy was used to confirm correct placement of the needle had been achieved. The subjects were measured in eight positions: prone, upright standing, lateral decubitus, flexion and extension standing, and upright, flexion, and extension sitting positions. Radiograms of the lateral view were also taken of each of the subjects during their testing.
Pressure measurements in this study indicate that respiration creates a fluctuation in intradiscal pressure even when subjects are in the prone position and utilizing no other muscle activities. An IVD that is healthy is also elastic, with an intradiscal pressure that fluctuates in correspondence to muscle activities and respiration. It is possible that the normal pressure changes involved with respiration could be associated with the maintenance of the nutritional content inside the nucleus pulposus. There was a slight difference between horizontal and vertical pressures in healthy and degenerated discs and in the silicon gel, which may indicate that the nucleus pulposus has a similar pressure tropism to silicon gel. Normal discs had high water content, which explains the small difference between the horizontal and vertical pressure measurements. There was, however, a significant difference between the pressures of the total value (horizontal and vertical and whole posture) of healthy and degenerated discs. These values may not have been significant enough to measure in previous studies utilizing the less efficient needle-types. The information obtained in this study through the use of the sensitive silicone pressure needle will help in developing a better understanding of degenerative disc disease.
KEYWORDS: Link Between Lower Back Pain, Disc Degeneration and Intradiscal Pressure, relationship between spinal loading and the angle of the motion segment in healthy discs, respiration creates a fluctuation in intradiscal pressure, degenerative disc disease