Purpose: Since the human intervertebral disc (IVD) is loaded in compression for approximately 16h per day, we investigated the effect of 16h compression loading on the magnetic resonance imaging (MRI) parameters, biochemical contents, and mechanical properties, of IVDs.

Method: Bovine caudal discs (2–3 years-old; non-degenerated) from 3-disc motion segments were injected in the NP with either 5 mg of trypsin in 40 μl Tris buffer or with Tris buffer only. The motion segments were placed in bags containing saline solution and antibiotics and were kept at 37°C throughout the experiment. The motion segments were subjected to either 16h of cyclic compression loading or were left unloaded for 16h. The motion segments were then paraffin embedded for MRI examinations, which were carried out in a 1.5T machine. The IVDs were dissected and the NP and AF were separated for biochemical and mechanical analyses. The NP and AF tissues were analyzed for contents of water, glycosaminoglycan (GAG), total collagen, and denatured collagen. Swelling pressure, compressive modulus HA, and hydraulic permeability were also measured.

Results: Loading had a significant effect on the MRI parameters (T1, T2, T1rho, MTR, ADC) of both the NP and AF tissues. Loading had a greater effect on the MR parameters and biochemical composition of the NP than trypsin. In contrast, trypsin had a larger effect on the mechanical properties. Localized trypsin injection predominantly affected the NP. T1rho was sensitive to loading and correlated with the water content of the NP and AF but not with their proteoglycan content.

Conclusion: Few studies have been directed towards developing an objective and accurate diagnostic tool in the detection and quantification of matrix and mechanical changes in early IVD degeneration. In this report, we demonstrated that MR parameters were influenced by compression loading. We also show showed specific correlations between T1rho and the structural and compositional changes in the disc. Further studies are required to determine the potential of the T1rho technique to be used as a non-invasive diagnostic tool of the biochemical and mechanical changes occurring in disc degeneration.

Despite a relentless search for adequate and effective treatment, low back pain is one of the most prevalent and costly illness in today’s society. While disc degeneration has been implicated as a major etiologic component of low back pain, there has been relatively little study in developing an objective, accurate, non-invasive diagnostic tool in the detection and quantification of matrix changes in early disc degeneration. The aim of the present study was to establish the correlations between magnetic resonance (MR) parameters and the biochemical and mechanical properties of the nucleus pulposus (NP) undergoing targeted trypsin digestion and axial compression.

Three-disc segments from bovine tails were either unloaded or loaded (cyclic compression: 50N-300N-50N at 1 Hz for 16h) to evaluate the effect of compression loading and the interactive effects of trypsin treatment and mechanical loading. The MR examinations were carried out in a 1.5-Tesla whole-body Siemens Avanto System (Siemens AG, Germany). The frozen NP and annulus fibrosus (AF) tissue sections reserved for mechanical analysis were tested under confined compression; swelling pressure was calculated based on the increase in measured force throughout the initial dwell period. Total water, proteoglycan, collagen, and denatured collagen contents were also measured.

Results showed that loading had a significant effect on the MR properties (T1, T2, T1ñ, MTR, ADC) of both disc tissues. Loading had a greater effect on the MR parameters and biochemical composition of the NP than trypsin. In contrast, trypsin had a larger effect on the mechanical properties. Results also indicated that localised trypsin injection predominantly affected the NP. T1ñ was sensitive to loading and correlated with the water content of the NP and AF but not with their proteoglycan content.

Results support the concept that physiologic loading is an important confounder and that T1ñ is an essential parameter in efforts to develop quantitative MRI as a non-invasive diagnostic tool to detect and quantify matrix and material changes in early disc degeneration. Further studies are required to determine the potential of the T1ñ technique to be used as a non-invasive diagnostic tool of the biochemical and mechanical changes occurring in disc degeneration.

Purpose: Quantitative MRI is currently being tested as an early and non-invasive diagnostic tool of disc problems prior to the appearance of symptoms. The aim of the present study was to determine the effects of cyclic loading and enzymatic digestion on quantitative MRI, biochemical composition, and mechanical properties of intervertebral disc tissue.

Methods: Bovine tail segments consisting of three discs were subjected to 16h of cyclic compression loading (50N–300N–50N at 1Hz) or left unloaded for 16h while in saline solution at 37°C. Prior to loading, the nucleus pulposus were injected with either a trypsin or buffer solution. MR examinations were carried out in a 1.5T Siemens` Avanto system to measure T1 and T2 relaxation times, magnetization transfer ratio (MTR), and trace of the apparent diffusion coefficient (TrD). The nucleus pulposus and annulus fibrosus were dissected and analyzed for contents of water, glycosaminoglycan, total collagen, and denatured collagen. Cylindrical nucleus pulposus and annulus fibrosus tissue plugs were harvested, prepared, and tested under confined compression to measure compressive modulus (HA) and hydraulic permeability (k). ANOVA and linear regression analyses were performed (p< 0.05).

Results: Loading decreased the T1, T2, and TrD of NP while it increased MTR. Only water content in the nucleus pulposus was significantly influenced by loading. T1, water content, and k of the annulus fibrosus tissue were significantly reduced with loading.|Enzymatic treatment of the nucleus pulposus had no effect on its MR properties, but increased the percent of denatured collagen and thus decreased HA. None of the biochemical, mechanical, and MR parameters of the annulus fibrosus changed with trypsin treatment.

Conclusions: Dynamic loading of the disc segments for 16h decreased the permeability of both disc tissues. This was consistent with the measured drop in tissue hydration and was observed as a decrease in T1. Targeted trypsin digestion of the nucleus pulposus was confirmed with no detectable changes in the biochemical, biomechanical, or MR properties of the annulus fibrosus. Future studies will address additional quantitative MR parameters such as T1-rho, a higher strength magnet, and different enzymatic treatments. Funding: Other Education Grant Funding Parties: Canadian Institutes of Health Research, McGill William Dawson Scholar Award, and Whitaker Foundation