The Clinical Validity of Disc Degeneration on

a Magnetic Resonance Imaging for the

Lumbar Related Symptoms

Masahiko KANAMORI 1,2,3)

Taketoshi YASUDA 3)

Kayo SUZUKI 3)

Kazuo OHMORI 4)

1) Department of Human Science, University of Toyama, Toyama, Japan

2) Department of Orthopaedics, Hida Municipal Hospital, Gifu, Japan

3) Department of Orthopaedics, University of Toyama, Toyama, Japan

4) Department of Orthopaedics, Nippon-Kokan Hospital, Kawasaki, Japan

ABSTRACT Objective: To assess the clinical validity of a new grading system based on T2-

weighted magnetic resonance imaging (MRI) for lumbar disc degeneration

Study Design: Retrospective study

Overview of the Literature: Various MRI classification criteria have been widely used

for evaluation of intervertebral disc pathology. However, there is still considerable

controversy regarding the MRI factors that allow accurate diagnosis.

Materials and Methods: Data were collected from 570 lumbar discs in 114 patients

and evaluated. The new grading system based on T2-weighted MRI was developed

for lumbar disc degeneration, and its clinical validity was assessed. Symptoms were

categorized according to the Japanese Orthopaedic Association’s low back pain

score (JOA score; 15-point-method).

Results: The shape of nucleus pulposus and signal intensity could be evaluated in

the new grading system. Leg symptoms and walking ability graded by JOA score

correlated with a new grading system (p<0.05). The rate of intraobserver

reproducibility of the new grading system showed a little higher agreement (85.0%)

compared with Schneiderman’s criteria (81.5%). The rate of interobserver reliability

was similar.

Conclusion: The new T2-weighted MRI grading system for disc degeneration was

primarily useful for assessing leg symptoms and walking ability. Intraobserver

reproducibility of the new grading system was higher than those of Schneiderman’s

criteria.

INTRODUCTION Magnetic resonance imaging (MRI) is the most important and widely used

technique for the clinical assessment of intervertebral disc pathology. The signal

characteristics of the disc in T2-weighted MRI scans reflect pathological changes

caused by aging or degeneration. A number of morphological grading systems for

lumbar disc degeneration have been proposed. However, considerable controversy

still exists regarding the factors affecting accurate diagnosis. We investigated the

clinical validity of a new grading system, which assesses the correlation between

lumbar disc degeneration features on MRI and symptoms such as low back pain or

sciatica.

Most previous grading systems and reliability studies of lumbar disc

abnormalities on MRI have focused on the differences in signal intensity of the

nucleus pulposus or the posterior aspect of the disc structure that allow

distinguishing between bulging, protrusion, and extrusion. However, grading

systems that simultaneously focus on both signal intensity and disc structure have

been rare. Reliability and reproducibility studies for the assessment of intervertebral

disc degeneration are critical for evaluating the validity of data. Nevertheless, there

have been few comparative studies that have investigated the reliability of the

correlations between MRI findings and patient symptoms.

Therefore, the purpose of this study is to develop a new grading system

for lumbar disc degeneration based on T2-weighted MRI and to assess its clinical

validity.

PATIENTS AND METHODS Patient Demographics

The study involved lumbar MRI scans of 114 patients (57 men and 57 women) with

a mean age of 52.0 years (range, 12-88). All patients included in this study initially

presented to the orthopaedic outpatient clinic of Hida Municipal Hospital, Gifu,

Japan, and were then referred for lumbar MRI because of low back pain or sciatica.

One hundred and fourteen routine MRI scans of the lumbar spine were

consecutively collected from the medical records. Postoperative scans, repeated

scans of the same patient, and scans of patients with systemic disease such as

tumor metastasis, rheumatoid arthritis, and spinal infection were excluded.

Clinical Assessment

Clinical findings of patients were obtained from their medical records. Symptoms

were categorized according to the 6 items of the Japanese Orthopaedic

Association’s low back pain score (JOA score; 15-point method; Table 1).

Imaging Technique

MRI scans of the lumbar spine were performed with a 1.0-Tesla scanner (Siemens

Medical Systems, Erlangen, Germany) equipped with a spine coil. The basic

imaging parameters included a sagittal T1-weighted spin-echo repetition time (TR)

and echo time (TE) of 700 and 12msec, respectively; and T2-weighted fast spin-

echo TR and TE of 5000 and 130msec, respectively. In this study, T2-weighted mid-

sagittal MRI scans were collected, and analyzed.

TABLE 1. The Japanese Orthopaedic Association’s (JOA) score (15-point-method)

Subjective symptoms Low-back pain

0. Continuous severe pain 1. Occasional severe pain 2. Occasional mild pain 3. None

Leg pain, tingling, or both 0. Continuous severe pain 1. Occasional severe pain 2. Occasional mild pain 3. None

Walking ability 0. Able to walk less than 10 m 1. Able to walk more than 100 m but less than 500 m 2. Able to walk more than 500 m, but with some leg pain or tingling 3. Normal

Clinical signs Straight-leg raising test (including tight hamstrings) 0. Less than 30º 1. More than 30º, but less than 70º 2. Normal Sensory

0. Marked disturbance 1. Slight disturbance (not subjective) 2. Normal

Motor 0. Marked disturbance (MMT, 3 to 0) 1. Slight disturbance (MMT, 4) 2. Normal

MMT: manual muscle testing

New Grading System for Lumbar Intervertebral Discs

A new comprehensive grading system for lumbar disc degeneration was developed

(Fig. 1). The system comprised 4 grades by the evaluation of the shape and signal

intensity of the nucleus pulposus, and offered a reasonable method for assessing the

morphology and quality of lumbar discs on T2-weighted MRI.

Imaging, Clinical Assessment

The imaging assessment was conducted

using the Schneiderman’s criteria and the

new grading system. In the Schneiderman’s

criteria, the only signal intensity on T2-

weighted MRI is classified. The 4 grades

used were normal, intermediate loss, marked

loss, or absent signal. Two orthopaedic

surgeons were used as blinded observers to

grade each of the 570 lumbar intervertebral

discs on the midline sagittal T2-weighted

images.

All MRI scans were analyzed by the

same method again on a separate occasion,

with a minimum interval of 1 month. Each

observer reviewed only 20 scans (100 discs)

per day to avoid rater fatigue. Moreover, we

applied the clinical assessment based on the

JOA score (15-point-method).

RESULTS Disc degeneration could be reliably and reproducibly graded by the 2 blinded

observers using the 2 grading systems on the basis of routine T2-weighted MRI

results. With the new grading system, 197 Grade I, 103 Grade II, 234 Grade III,

and 36 Grade IV discs were identified by the first author (Observer A), and 192

Grade I, 137 Grade II, 212 Grade III, and 29 Grade IV discs were identified by

another author (Obserever B) during the first evaluation session. All other data

are presented in Table 2.

Intraobserver reproducibility

Each MRI has being reviewed by the 2 blinded observers on 2 different

occasions with at least 1-month interval between the assessments (Table 2).

Both of the evaluation systems were used to independently review all of the MRI

scans by the 2 observers. The mean rate of complete agreement was 81.5% for

the evaluations using the Schneiderman’s criteria. But the new grading system

showed a little higher agreement (85.0%) (Table 3).

Interobserver reliability

Interobserver reliability rate was relatively high (60%) according to the new

system. But the Schneiderman’s criteria showed the similar agreement (58.5%)

(Table 3). For grades II and III, the mean difference in the assessments

between the 2 raters using the Schneiderman’s criteria and the new grading

system was ≧10% and 4-6%, respectively.

Correlation between MRI findings and JOA score

The severity of the symptom was divided into four groups based on total JOA

score, such as very severe: 0-3 points; severe: 4-7 points; moderate: 8-11;

mild: 12-15). The severity of the symptom corresponded to the findings

determined using the new MRI grading system (Fig. 2).

Moreover, we analyzed the relationship between the each item of the

JOA score and the severity of the symptom. The item of the total best score 3,

or 2 was divided into 4 groups (0, 1, 2, 3-points), or 3 groups (0, 1, 2-points),

respectively. These factor analyses showed that the new grading system could

assess leg pain (p<0.05) and walking ability (p<0.05). But the MRI findings did

not reflect the low back pain, SLR test, sensory disturbances, or muscle

weakness (Fig. 3).

Non of the authors has any potential conflict of interest.

DISCUSSION Evaluation of disc degeneration and herniation should depend not only on

the signal intensity of the nucleus pulposus but also on its morphology. Pfirrmann

has already classified disc degeneration and herniation by structure, distinction,

signal intensity of the nucleus pulposus, and height of the intervertebral discs. This

classification is detailed and reliable, but it was too complicated to be used widely.

In this study, we proposed a 4-grade system for evaluating lumbar

intervertebral disc degeneration and herniation on MRI. With new grading system,

lumbar-related symptoms were not always reflected on MRI, but the system gave

useful assessments of leg pain and walking ability. The symptom of low back pain

is not correlated the disc change on MRI, because the pain is originated from the

existence of the inflammation, or not. We can’t detect the inflammation on routine

MRI. But the leg pain is generated from the compression to the nerve roots. The

nerve root compression is visible on MRI.

Therefore, the evaluation of the shape of the disc material might be

concomitant to the leg pain and walking ability.