Abstracts

INTRODUCTION

Magnetic resonance is the method most often used to specifically assess intervertebral disc degeneration. Based on proton density, water content, and chemical environment, it portrays the morphology and hydration of the intervertebral disc.¹1 Tertti M, Paajanen H, Laato M, Aho H, Komu M, Kormano M. Disc degeneration in magnetic resonance imaging. A comparative biochemical, histologic, and radiologic study in cadaver spines. Spine (Phila Pa 1976). 1991;16(6):629-34. ^{, 2}2 Viikari-Juntura E, Raininko R, Videman T, Porkka L. Evaluation of cervical disc degeneration with ultralow field MRI and discography. An experimental study on cadavers. Spine (Phila Pa 1976). 1989;14(6):616-9. The Modic and Pfirrmann classifications are two known methods used to evaluate degenerative lumbar disease.³3 Griffith JF, Wang YX, Antonio GE, Choi KC, Yu A, Ahuja AT, et al. Modified Pfirrmann grading system for lumbar intervertebral disc degeneration. Spine (Phila Pa 1976). 2007;32(24):E708-12. ^{, 4}4 Hutton MJ, Bayer JH, Powell JM. Modic vertebral body changes: the natural history as assessed by consecutive magnetic resonance imaging. Spine (Phila Pa 1976). 2011;36(26):2304-7.

Dehydration of the nucleus pulposus and changes in the molecular structures of its components start to occur in the third decade of life, at the onset of the disc degeneration process.⁵5 Nguyen AM, Johannessen W, Yoder JH, Wheaton AJ, Vresilovic EJ, Borthakur A, et al. Noninvasive quantification of human nucleus pulposus pressure with use of T1rho-weighted magnetic resonance imaging. J Bone Joint Surg Am. 2008;90(4):796-802. ^{, 6}6 Gruber HE, Hanley EN Jr. Analysis of aging and degeneration of the human intervertebral disc. Comparison of surgical specimens with normal controls. Spine (Phila Pa 1976). 1998;23(7):751-7.

Pfirrmann established his classification in 2001, basing it on criteria of changes in disc morphology in patient MRIs (intensity of the signal, structure of the disc, distinction between the nucleus and the annulus, and disc height).⁷7 Pfirrmann CW, Metzdorf A, Zanetti M, Hodler J, Boos N. Magnetic resonance classification of lumbar intervertebral disc degeneration. Spine (Phila Pa 1976). 2001;26(17):1873-8.

This classification has good applicability in differentiating between the degrees of disc degeneration.⁸8 Ueno FH, Rodrigues LM, Valesin Filho ES, Puertas EB. Reprodutibilidade intra e inter-observadores da classificação de Pfirrmann para degeneração discal por meio da ressonância magnética.Coluna/Columna. 2008;7(4):330-3. Changes in the end plate were described by Modic⁹9 Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166:193-9. ^{, 10}10 Modic MT, Masaryk TJ, Ross JS, Carter JR. Imaging of degenerative disk disease. Radiology. 1988;168(1):177-86. in 1988. The studies suggest that changes can progress from one type to another; however, there is limited knowledge about the natural course of the changes reported by Modic.¹¹11 Braithwaite I, White J, Saifuddin A, Renton P, Taylor BA. Vertebral end-plate (Modic) changes on lumbar spine MRI: correlation with pain reproduction at lumbar discography. Eur Spine J. 1998;7(5):363-8.

Despite the structural changes observed in disc degeneration, there is no defined association between the Pfirrmann classification and the changes observed in the vertebral plate used by the Modic classification.

However, both are easy to apply and have high intraobserver agreement.¹²12 Jones A, Clarke A, Freeman BJ, Lam KS, Grevitt MP. The Modic classification: inter- and intraobserver error in clinical practice. Spine (Phila Pa 1976). 2005;30(16):1867-9. The objective of this study is to better understand degenerative disc disease and its evolution by establishing a parallel between the two classification systems.

METHODS

We analyzed the MRIs of 300 patients treated between January and December 2011 at the Clinic of Spinal Pathologies of the Hospital Estadual Mario Covas (HEMC), Santo André, SP, Brazil, which is linked to the discipline of Orthopedics and Traumatology of the Faculdade de Medicina do ABC (FMABC). With the patient's consent, a second copy of the MRI exams of the lumbar spine was requested from the Radiology Sector of the HEMC for the study.

The lumbar images (intervertebral discs and end plates from L1 to S1) were analyzed and classified by two doctors of the FMABC Spine Group according to the classifications of Modic and Pfirrmann using the Osirix Image Software ((c)Antoine Rosset, 2003-2011) program. When there were disagreements, they reevaluated the images until they reached consensus.

To meet the objectives of the study, the variables of sex and age group, and the Modic and Pfirrmann measurements were described for each group of patients using absolute and relative frequencies, and the totals of the classifications of the evaluated levels were presented.

The Pfirrmann and Modic measurements at each vertebral level were described according to sex, then compared between the sexes using Mann-Whitney tests. The scales were also described by age group and compared between the groups using Kruskal-Wallis tests. The Pfirrmann and Modic measurements were described at each vertebral level and the existence of a relationship between the two scales was verified using Spearman correlations. The tests were performed with a significance level of 5%. All the analyses were performed using SPSS for Windows version 15.0.

RESULTS

Table 1 shows that most of the patients evaluated are female (59%) and are in the 40-60 years of age group (53%).

It is observed that Pfirrmann Type III is the most common across all the levels evaluated. (Table 2)

Table 3 shows that the Modic signal is absent in most of the discs evaluated and that Type 2 is more common in discs L3-L4, L4-L5, and L5-S1. There was no Type 3 found.

It was observed that in discs L2-L3 and L3-L4 the Pfirrmann grade is statistically higher in female patients. (Table 4)

It was found that the Modic grade is statistically higher in females and in disc L3-L4. (Table 5)

Table 6 shows that the Pfirrmann grade increases statistically with age group in all discs evaluated (p < 0.05), with the exception of disc L5-S1 where the Pfirrmann grade is statistically equal in the three patient age groups (p = 0.127).

It was observed that the Modic grade increases statistically with age group in discs L3-L4 and L5-S1. (Table 7)

It was found that the higher the Pfirrmann grade, the higher the Modic grade, and vice-versa, in all the intervertebral discs evaluated. (Table 8)

DISCUSSION

This study proposes a correlation between the classifications presented based on analyses of magnetic resonance images, the exam of choice for the visualization of changes in soft tissue (intervertebral disc, ligament, and musculature).

The average age of the patients in this study is between 40 and 60 years, compatible with earlier studies in which the onset of symptoms can be associated with degenerative pathologies, given that disc degeneration is an inevitable consequence of the human aging process. During the evolution of degeneration, the disc becomes more vulnerable to inflammatory processes.¹³13 Boos N, Weissbach S, Rohrbach H, Weiler C, Spratt KF, Nerlich AG. Classification of age-related changes in lumbar intervertebral discs: 2002 Volvo Award in basic science. Spine (Phila Pa 1976). 2002;27(23):2631-44.

14 Miller JA, Schmatz C, Schultz AB. Lumbar disc degeneration: correlation with age, sex, and spine level in 600 autopsy specimens. Spine (Phila Pa 1976). 1988;13(2):173-8. ^{- 15}15 Siemionow K, An H, Masuda K, Andersson G, Cs-Szabo G. The effects of age, sex, ethnicity, and spinal level on the rate of intervertebral disc degeneration: a review of 1712 intervertebral discs. Spine (Phila Pa 1976). 2011;36(17):1333-9.

Zuo et al ¹⁶16 Zuo J, Saadat E, Romero A, Loo K, Li X, Link TM, et al. Assessment of intervertebral disc degeneration with magnetic resonance single-voxel spectroscopy. Magn Reson Med. 2009;62(5):1140-6. considered discs with a Pfirrmann grade lower than or equal to type II to be normal, and those with a Pfirrmann grade higher than type II to be degenerated. They also observed greater degeneration in disc L4-L5 compared with the other intervertebral segments, similar to the results of our study.¹⁶16 Zuo J, Saadat E, Romero A, Loo K, Li X, Link TM, et al. Assessment of intervertebral disc degeneration with magnetic resonance single-voxel spectroscopy. Magn Reson Med. 2009;62(5):1140-6. According to the literature, the fact that level L4-L5 has greater mobility may result in greater disc degeneration as compared to the other intervertebral segments.¹⁷17 Fujiwara A, An HS, Lim TH, Haughton VM. Morphologic changes in the lumbar intervertebral foramen due to flexion-extension, lateral bending, and axial rotation: an in vitro anatomic and biomechanical study. Spine (Phila Pa 1976). 2001;26(8):876-82. ^{, 18}18 Koeller W, Meier W, Hartmann F. Biomechanical properties of human intervertebral discs subjected to axial dynamic compression. A comparison of lumbar and thoracic discs. Spine (Phila Pa 1976). 1984;9(7):725-33.

There was also a smaller number of discs classified as type I, due to the patients' age and the fact that they had histories of low back problems.

In relation to the Modic scale, there were no changes at the higher levels (L12 and L23). Where present, changes were observed mainly at the lower levels (L4-L5 and L5-S1), with type 2 being most prevalent, a phenomenon similar to that encountered by Modic et al.⁴4 Hutton MJ, Bayer JH, Powell JM. Modic vertebral body changes: the natural history as assessed by consecutive magnetic resonance imaging. Spine (Phila Pa 1976). 2011;36(26):2304-7. ^{, 9}9 Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166:193-9. ^{, 19}19 Ohtori S, Yamashita M, Yamauchi K, Inoue G, Koshi T, Suzuki M, et al. Change in Modic type 1 and 2 signals after posterolateral fusion surgery. Spine (Phila Pa 1976). 2010;35(12):1231-5. This is probably because the lower levels are exposed to higher biomechanical stress loads, resulting in changes in the end plates.²⁰20 de Schepper EI, Damen J, van Meurs JB, Ginai AZ, Popham M, Hofman A, et al. The association between lumbar disc degeneration and low back pain: the influence of age, gender, and individual radiographic features. Spine (Phila Pa 1976). 2010;35(5):531-6. In the study, most patients did not present Modic type changes (88.7%). In accordance with the findings of Leite et al (88.3%)²¹21 Leite MS, Luciano RP, Martins DE, Wajchenberg M, Puertas EB. Correlação entre as classificações de Pfirrmann e Modic na degeneração do disco intervertebral lombar. Coluna/Columna. 2010;9(4):401-6., no Modic type 3 changes were observed, a situation that is uncommon.⁹9 Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166:193-9. ^{, 22}22 Zhao JG, Zhang P, Zhang SF, Qi F, Huang WJ, Xia YZ, et al. Modic type III lesions and Schmorl's nodes are the same pathological changes? Med Hypotheses. 2010 Mar;74(3):524-6. ^{, 23}23 Zhang YH, Zhao CQ, Jiang LS, Chen XD, Dai LY. Modic changes: a systematic review of the literature. Eur Spine J. 2008;17(10):1289-99.

Previous studies demonstrated similar relationships in terms of the frequency and location of Modic changes in the intervertebral discs studied. Kuisma et al²⁴24 Kuisma M, Karppinen J, Niinimäki J, Ojala R, Haapea M, Heliövaara M, et al. Modic changes in endplates of lumbar vertebral bodies: prevalence and association with low back and sciatic pain among middle-aged male workers. Spine (Phila Pa 1976). 2007;32(10):1116-22., studying MRI changes in middle-aged manual laborers, showed that 85% of the discs at the lower lumbar levels (L5S1) were affected by some change to the end plate (Modic 1 or 2). They did not find any type 3 changes.⁹9 Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166:193-9. Takatalo et al ²⁵25 Takatalo J, Karppinen J, Niinimäki J, Taimela S, Näyhä S, Järvelin MR, et al. Prevalence of degenerative imaging findings in lumbar magnetic resonance imaging among young adults. Spine (Phila Pa 1976). 2009;34(16):1716-21., who studied changes in the MRIs of young adults, found a low incidence of the appearance of changes, similar to the findings of our study, with higher prevalence in men, and they also noted a higher incidence in the lower discs. The study by Schenk et al ²⁶26 Schenk P, Läubli T, Hodler J, Klipstein A. Magnetic resonance imaging of the lumbar spine: findings in female subjects from administrative and nursing professions. Spine (Phila Pa 1976). 2006;31(23):2701-6. showed similar results, with an incidence of around 85% of end plates without any changes and a low incidence of Modic type 3 changes in a group of health care workers whose jobs required, or did not require physical labor.

In this study, changes in the end plate were more prevalent in females, and even though there was some disagreement about whether gradation between the different Modic types exists,⁴4 Hutton MJ, Bayer JH, Powell JM. Modic vertebral body changes: the natural history as assessed by consecutive magnetic resonance imaging. Spine (Phila Pa 1976). 2011;36(26):2304-7. ^{, 9}9 Modic MT, Steinberg PM, Ross JS, Masaryk TJ, Carter JR. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology. 1988;166:193-9. there was a higher prevalence of type 2 changes among females.

In a comparison of the changes in relation to age, it was observed that increasing age coincides with more serious Modic and Pfirrmann type changes. When the two classifications were correlated, the data showed a strong association, showing that the higher the Pfirrmann grade, the higher the Modic changes.

The study was designed to evaluate only the images, without correlating them with the patient's clinical history, symptoms, or social aspects involved. Prior studies suggest a correlation between symptoms and more advanced grades of the classifications studied.¹⁴14 Miller JA, Schmatz C, Schultz AB. Lumbar disc degeneration: correlation with age, sex, and spine level in 600 autopsy specimens. Spine (Phila Pa 1976). 1988;13(2):173-8. Studies correlating the radiographic findings and symptoms could be topics for further research.

CONCLUSION

The ideal classification system for degenerative disc disease should be simple, easily applicable, and highly reproducible. There is a strong correlation between changes in the end plates and the intervertebral discs, as evidenced by changes in the MRI. The greater the level of disc degeneration, the closer the relationship between the Pfirrmann and Modic classification systems.

REFERENCES

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