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Abstract

Objective:

The study objective was to quantify the changes in intradiscal pressure (IDP) during the application of a chiropractic procedure known as the Cox flexion-distraction technique.

Materials and Methods:

Pressure sensors were inserted into lumbar intervertebral discs of eight unembalmed cadavers (five male and three female, age range 43–75 years). Five 4-second cycles of flexion distraction were performed for a 20-sec period. Pressure data were collected while the discs were in an unpressurized state as well as a pressurized state (with water). The pressure data were collected during three separate applications of the flexion-distraction procedure with transducers inserted into the L2-L3, L3-L4, and L4-L5 intervertebral discs. The mean pressure values were documented before, during (in the distracted position), and after the treatment procedure (calculated). Pressure differences were compared using the paired t-test for significance in pressure changes from initial prone position to distracted treatment position.

Results:

The IDPs significantly decreased in both pressurized and unpressurized discs at all studied disc levels. The average IDP decreases in unpressurized discs were as follows: 5.6 kPa at L2-L3, 20.6 kPa at L3-L4, and 22.0 kPa at L4-L5. The IDP decrease range in pressurized-in-the-initial-prone-position discs were as follows: 17.8 kPa at L2-L3, 35.2 kPa at L3-L4, and 122.0 kPa at L4-L5.

Conclusions:

IDP was found to decrease during the flexion-distraction procedure, which is consistent with the hypothesis that this procedure may be able to draw a protruded nucleus pulposus back toward the intervertebral disc's center and allow for the nutrients flow into the disc.

Introduction

Lower back and treatment options

Among musculoskeletal disorders, low back pain (LBP) is one of the most common and costly.^1,2 Prevalence of LBP is reported to be about 7.5% of the population.³ Despite extensive research efforts, the causes of LBP are still unknown.⁴

Chiropractic treatment options

Manipulative procedures have been instituted for the treatment of LBP and are recommended in the treatment of patients with LBP.⁵ Several types of chiropractic manipulative procedures are available for treating LBP, including high-velocity low-amplitude spinal manipulations, traction-based procedures, and instrument-assisted very high-velocity low-amplitude techniques.⁶ One technique known as Cox flexion-distraction technique is recorded as being used by 64% of the chiropractors in treating LBP.⁷ Several studies have demonstrated its clinical effectiveness for treating LBP patients.^8–11

Traction and intradiscal pressure measurements

In the biomechanical functioning of the spine, the pressure of the nucleus pulposus is central, particularly as it reduces compressive stress gradients in the annulus fibrosus¹² and affects segmental stability more than ligamentous or bony structure.¹³ Researchers studied the various intradiscal pressure (IDP) characteristics in vitro (cadaveric), computer modeling,¹⁴ and in vivo on human volunteers, initially with Nachemson as he reported the IDP in human lumbar spine.^15,16

Measurements of IDP were determined in vitro by variety of researchers to better understand the influence of various physiological loading conditions.^17–22

Additional reports noted IDP measurements during in vivo loading conditions during a variety of daily activities.^23–26 In a meta analysis, Li et al reported on the in vivo IDPs during sitting and standing scenarios.²⁷

Multiple studies highlighted the pressure measurements, including compressive forces due to loads in daily living activities. Only a few studies focused on IDP measurements during traction-type loading by Ramos and Martin in the lumbar spine, Gay et al on cadaveric lumbar segments, and Gudavalli et al on cervical spine.^28–30

Objective of this study

The objective of this study was to quantitatively report pressure changes in the nucleus of lumbar discs during the application of a chiropractic procedure known as Cox flexion-distraction technique simulated using whole unembalmed cadavers.

Materials and Methods

This study only involves cadavers and as such this study is exempt from Institutional Review Board (IRB) review and approval.

Unembalmed cadavers

For experimentation purposes, eight unembalmed whole cadavers (three female and five male; age range 43–87 years) were freshly frozen at −20°C promptly upon death, and each was brought to room temperature before the study. The causes of death varied from heart failure to stroke.

IDP measurements

To measure IDPs, mini pressure transducers (Model # SPR-524; Millar Instruments, Houston, TX) were utilized. A calibration device that created both an increase in air pressure or a vacuum pressure was used and was used to calibrate the transducers and the calibration data were reported by Gudavalli and Cox.^31,32 The transducers were calibrated in the range of −64 to 141 kPa. The calibration data demonstrated a linear relationship between pressure and voltage signal with a high correlation coefficient greater than 0.9.³¹ Results reported are an extension of the preliminary results reported in the book chapter.³¹

Paraspinal musculature was dissected by a specialist in anatomy to allow the precise insertion of a pressure transducer assembly and a Touhy epidural needle with 17-gauge stylette. The needle and stylette were implanted into the nucleus of the disc to be studied: L2-L3, L3-L4, and L4-L5. Figure 1 shows a photograph of the cadaver with the pressure transducers inserted into the nucleus of disc between vertebra. The stylette was removed and in its place the miniature pressure transducer was inserted exposing the sensing element of the transducer to the nucleus of the respective disc. The pressure transducer was connected to an analog-to-digital converter and amplifier and to a computer for monitoring the pressure data.

FIG. 1.

Cadaver in a prone position showing the dissection and insertion of the sensors to monitor IDP. IDP, intradiscal pressure.

Similar to the placement of an LBP patient on a chiropractic table, the cadaver was placed in a prone position on the table. With hand contact superior to the segment of interest, the application of the chiropractic treatment procedure involved five 4-second sets of downward table movement for close to 20 sec.^32,33 The IDPs of L2-L3, L3-L4, and L4-L5 were observed and recorded in an unpressurized state as well as pressurized state using a Cornwall pipetting system and flexible tube through a second needle into the disc (Fig. 1).

A research assistant operated the computer to collect the pressure data during the chiropractic procedure, which was administered by an experienced licensed Doctor of Chiropractic. Pressure data were collected during two experimental conditions: (1) unpressurized discs and (2) pressurized (with water) discs. The pressure data were collected during three separate applications of the flexion-distraction chiropractic procedure. Between each trial session, there was a 30-min break. Pressures computed for all 15 cycles of the three trials included mean values of pretreatment pressures, mean values during distraction, and the changes in pressures. From these the average values for all eight cadavers were utilized, and the paired t-test was used for statistical significance using SPSS (version 27, IBM Corp., Armonk, NY) software.

Results

IDP measurements

Figure 2 depicts a common plot of IDP change in an L4-L5 disc in the course of the chiropractic procedure (five 4-second flexion-distraction sets). The bottom part of the graph shows the table procedure. In the same time phase, changes in IDP and guided descending motions of the table downward were found to occur synchronously. The pressures returned to respective initial values as the table was brought back to its initial prone position.

FIG. 2.

A typical graph showing table movement and changes in IDPs during the chiropractic procedure.

Standard and mean deviation values of the eight cadavers' IDPs in initial prone position as well as the final distracted position are recorded in Tables 1 and 2. Table 1 data represent IDP data without pressurization of the discs. Table 2 data represent the data while the discs were pressurized with water. The chiropractic procedure utilizing the flexion-distraction maneuver significantly reduced the IDP in both the unpressurized and pressurized discs. The disc pressures in the unpressurized discs fell into the negative range at the final distracted position, paralleling the downward motion of the table.

Table 1.

Changes in Intradiscal Pressure in Kilopascal During a Chiropractic Procedure (Discs not Pressurized)

Segment	N	Initial prone, mean (SD)	Final distracted, mean (SD)	Change in IDP, mean (SD)	95% CI		Significance, p
Segment	N	Initial prone, mean (SD)	Final distracted, mean (SD)	Change in IDP, mean (SD)	Lower	Upper	Significance, p
L2-L3	8	3.7 (0.9)	−1.96 (0.4)	5.6 (0.8)	5.0	6.3	<0.001
L3-L4	8	1.2 (2.9)	−19.4 (8.1)	20.6 (8.6)	13.4	27.7	<0.001
L4-L5	8	2.4 (2.8)	−19.5 (1.6)	22.0 (4.0)	18.6	25.4	<0.001

CI, confidence intervals; IDP, intradiscal pressure; SD, standard deviation.

Table 2.

Changes in Intradiscal Pressure in Kilopascal During a Chiropractic Procedure (Discs Pressurized)

Segment	N	Initial prone, mean (SD)	Final distracted, mean (SD)	Change in IDP, mean (SD)	95%CI		Significance, p
Segment	N	Initial prone, mean (SD)	Final distracted, mean (SD)	Change in IDP, mean (SD)	Lower	Upper	Significance, p
L2-L3	8	36.9 (6.8)	19.1 (2.0)	17.8 (8.3)	10.8	24.7	<0.001
L3-L4	8	58.6 (7.2)	23.4 (3.3)	35.2 (6.6)	29.1	41.3	<0.001
L4-L5	8	138.8 (58.0)	16.8 (7.3)	122.0 (53.4)	77.4	166.7	<0.001

Average decreases in IDP differed from 5.6 kPa at L2-L3, 20.6 kPa at L3-L4, and 22.0 kPa at L4-L5 in unpressurized mode. The decrease in IDP was statistically significant (p < 0.001) in all the three segments. Injecting water into the disc raised the initial disc pressure to a mean value of 36.9 kPa at L2-L3, 58.6 kPa at L3-L4, and 138.8 kPa at L4-L5 in the face down (prone) position. The decrease in pressure ranged from 17.8 kPa at L2-L3, 35.2 kPa at L3-L4, and 122.0 kPa at L4-L5 during the distracted position of the procedure, which was statistically significant (p < 0.001).

IDP measurements were directly correlated with descending table movement. Table motions were monitored. Mean and standard deviation values of table angles were 10.3 (0.53) degrees for nonpressurized discs and 10.75 (0.46) degrees for pressurized discs. The table motions were very similar for nonpressurized discs as well as pressurized discs.

A radiologist reviewed radiographic films of the degenerated discs and graded their status based on disc height and osteophyte presence. The degeneration level of the study's discs were mostly degeneration grade 3 (one specimen: grade 1, two specimens: grade 2, and five specimens: grade 3). Age and degeneration grade may be a factor for low initial pressure in this study.

Discussion and Conclusions

IDP changes in cadaveric lumbar spines during the flexion-distraction procedure were quantified. Based on the hypothesis of IDP reduction may afford an opportunity for disc bulge reduction and/or nutrient flow in and out of the disc, the flexion-distraction procedure is used to treat LBP. No data validating the reduction of disc bulge and change in the nutrients exist at this time. Future in vivo studies should be designed to address these hypotheses. The decrease in the pressure is transient as disc pressures return to pretreatment pressure when the table is returned to its starting point.

A substantial reduction in IDP throughout the chiropractic treatment procedure was noted. Nonpressurized discs in the prone position produced pressures that dropped below 0 kPa. Pressurized discs produced much greater IDP decreases suggesting that in patients with greater IDPs decreases in pressure may be much greater during the distraction treatment. When unloaded and returned to the initial prone position, IDPs returned to their original values suggesting that IDP decreases were transient, yet could be contributive to the fluid in-flow and out-flow of the nucleus and to nutrient flow into the disc.

Cyriax, Quillette, and Kramer proposed a theory that a negative pressure develops in the disc that potentially draws a disc protrusion back toward the center of the disc when the spinal vertebrae are subjected to traction or distraction.^34–36 Nachemson and Elfstrom developed in vivo IDP measurements during daily activities.³⁷ Ramos and Martin described three patient cases' intraoperative IDP reductions throughout a vertebral axial decompression procedure.²⁸ The IDPs dropped to as low as −21 kPa (−160 mmHg). In general, the IDP drops documented in this study's eight cadavers generally agree with Ramos and Martin.²⁸

In both extended and flexed positions while applying traction loads to isolated cadaver segments, Gay et al reported negative IDP reductions with 90 N of traction force.²⁹ Findings in a four volunteer study by Andersson et al, the IDPs at L3-L4 were recorded while each was lying, standing, undergoing active traction as well as passive traction.³⁸ Increases in disc pressure were noted in the study reported by Andersson et al. This study findings on eight cadavers did not concur possibly due to the in vivo subjects' muscles under traction force, which could have been actively contracting. Future study needs to focus on the changes during in vivo states while simultaneously monitoring electromyographic response of the lumbar muscles.

This study's baseline observed pressures were less than those in other studies. Liebsch et al 2021 reported in a summary of the initial pressures of L3-L4 through L4-L5 discs in a prone position reported to be 90–380 kPa.³⁹ The average age in their study was 28–45 years. The age range in this study was 43–87 years, and the pressures in the initial prone position ranged from 1.2 to 3.7 kPa in nonpressurized discs. Initial prone pressures in pressurized discs were in the range of 36.9–138.8 kPa. Current study spine degeneration levels were mostly grade 3 (one specimen: grade 1, two specimens: grade 2, and five specimens: grade 3). Age and degeneration grade could be a factor for low initial pressure in our study. The age of the deceased specimens and their higher degenerated disc conditions could contribute to the lower pressures found in the prone position compared with the other in vivo studies.

The following limitations should be noted. The study was conducted on cadavers, and some of the musculature was dissected to place the sensors. This study's sample size is small, and studies with larger sample sizes need to be undertaken to validate the study. The cadavers were mostly from deceased individuals with elderly and degenerated spinal conditions. In vivo conditions could influence the results of the study. Future studies should address this concern.

The pressure changes were transient and the decreases are not permanent. However, the transient decreases could potentially allow the flow of nutrients into the disc.

Conclusions

IDP was found to decrease during the chiropractic procedure, which could potentially allow nutrients to flow in and out of the intervertebral discs.

Data Availability Statement

All data sets presented in this study are available upon request.

Ethics Statement

The materials were acquired from the donor organizations such as Anatomy Gifts Registry program (AGR, Chicago, IL) and Science Care (Science Care, Inc., Phoenix, AZ), which declared that written informed consent of the donors was obtained before decease.

Footnotes

Authors' Contributions

Seeking grant funds, design of the study, and article preparation by M.R.G. Study design, specimen preparation, experimental testing, discussion, and article preparation and review by G.D.C. Seeking grant funds, discussion, and article preparation and review by A.G.P. All authors contributed to the article and approved the submitted version.

Author Disclosure Statement

No competing financial interests exist.

Funding Information

The investigators acknowledge Health Resources and Services Administration (HRSA) support through a grant no. 1R18 AH10001-01A1, monetary donations from numerous chiropractic physicians, and Williams Healthcare Systems Incorporated who donated the chiropractic table.

Abbreviations Used

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Changes in Intradiscal Pressure During Flexion-Distraction Type of Chiropractic Procedure: A Pilot Cadaveric Study

Abstract

Objective:

Materials and Methods:

Results:

Conclusions:

Introduction

Lower back and treatment options

Chiropractic treatment options

Traction and intradiscal pressure measurements

Objective of this study

Materials and Methods

Unembalmed cadavers

IDP measurements

Results

IDP measurements

Discussion and Conclusions

Conclusions

Data Availability Statement

Ethics Statement

Footnotes

Authors' Contributions

Author Disclosure Statement

Funding Information

Abbreviations Used

References