Background
Lower back pain is a very common symptom, with a reported lifetime prevalence of 84% [
1]. Previously, non-specific lower back pain accounted for 85% of cases; however, improvements in diagnostic approaches have led to more than 75% of cases being diagnosed pathologically and anatomically, with non-specific lower back pain now accounting for only approximately 22% of cases [
2]. Identifying the specific causes of lower back pain enables practitioners to treat each cause with an appropriate method.
Research suggests that discogenic lumbar pain accounts for 13% of all cases of lower back pain [
2]. Discogenic lumbar pain is typically diagnosed based on physical manifestations, such as lumbar pain at anterior bending and deep pain, as well as magnetic resonance imaging (MRI) findings. However, a definitive diagnosis is difficult to make when images suggest abnormal findings in multiple discs, thus requiring discography and discoblock procedures to confirm a diagnosis [
2‐
4].
Recent advancements in ultrasound have led to improvements in the diagnosis of orthopaedic diseases, including those affecting the spine [
5,
6]. Among them, palpation combined with ultrasonography (i.e., sonopalpation) allows for accurate palpation even at deeper structures [
7,
8]. Our group has developed a novel ultrasound-guided disc pain induction test that relies on sonopalpation to detect discogenic lumbar pain. In this test, manual pressure is applied to each disc during real-time ultrasound monitoring at the disc level from the ventral side. In the present study, we aimed to examine the usefulness of this method for the simple and accurate diagnosis of culprit lesion(s) in patients with discogenic lumbar pain.
Results
Pain was confirmed in 44 patients based on the results of an ultrasound-guided disc pain induction test. Three patients were excluded, and the remaining 41 patients were included for further analysis. Demographic data and examination findings for the 41 included patients (11 men and 30 women) are summarized in Table
1. The median age was 43.5 (range 28.0–60.5) years. Pain during anterior bending was the most common symptom, affecting 25 patients (61%). Anterior–posterior bending did not increase pain in five patients (12%). Pain only during posterior bending was observed in six patients (15%). Pain during both anterior and posterior bending was observed in five patients (12%). XP and MRI findings showed disc herniation in 17 patients (41%), high-intensity zone in 17 patients (41%), degenerative spondylolisthesis in one patient (2%), and spondylolytic spondylolisthesis in one patient (2%).
Table 1
Demographic data and findings of examination
Demographic data | |
Number of patients (M:F) | 41 (11:30) |
Age (years) | 43.5 (28.0–60.5) |
Pain at anterior–posterior bending of the trunk (n = 41) | |
Anterior bending | 25 |
Posterior bending | 6 |
Both of anterior and posterior bending | 5 |
None | 5 |
MRI findings | |
Disc herniation | 17 |
High intensity zone | 17 |
Degenerative spondylolisthesis | 1 |
Spondylolytic spondylolisthesis | 1 |
Table
2 summarizes the results of the ultrasound-guided disc pain induction test, which identified pain in a total of 65 discs. Disc tenderness was most common at L4/5, affecting 31 patients (48%), and tenderness in a single disc was the most common (23 patients, 56%).
Table 2
Results of ultrasonographic-guided disc pain induction test
Location of tender disc (n = 65) | |
L1/2 | 0 |
L2/3 | 3 |
L3/4 | 13 |
L4/5 | 31 |
L5/S1 | 18 |
Number of tender disc (n = 41) | |
1 | 23 |
2 | 12 |
3 | 6 |
Table
3 summarizes the comparison between painless and painful discs based on MRI findings. All painful discs had Pfirrmann classifications of grade 1 or higher and showed signs of more advanced degeneration compared with painless discs (
p < 0.05). There was no clear association between the presence or absence of induced pain and Modic type (
V = 0.18).
Table 3
Comparison between painless disc and induced pain disc about MRI findings
0 | 108 | 0 | p < 0.05 |
1 | 0 | 5 | |
2 | 1 | 5 | |
3 | 9 | 19 | |
4 | 19 | 33 | |
5 | 3 | 3 | |
0 | 132 | 56 | V = 0.18 |
1 | 1 | 4 | |
2 | 6 | 4 | |
3 | 1 | 1 | |
Table
4 summarizes comparisons among painful, painless, and other painful discs based on MRI findings. Discogenic pain was associated with more advanced signs of degeneration compared with painless discs (
p < 0.05). However, there was no significant difference in the degree of disc degeneration between the most painful disc and other painful discs. There was no clear association between the Modic type and any of the three types of discs (
V = 0.23).
Table 4
Comparison between most painful disc, other pain disc, and painless disc about MRI findings
0 | 108 | 0 | 0 | p < 0.05 |
1 | 0 | 4 | 1 | |
2 | 1 | 0 | 5 | |
3 | 9 | 9 | 10 | |
4 | 19 | 11 | 22 | |
5 | 3 | 0 | 3 | |
0 | 132 | 23 | 33 | V = 0.23 |
1 | 1 | 1 | 3 | |
2 | 6 | 0 | 4 | |
3 | 1 | 0 | 1 | |
Seventeen patients who required injection due to severe pain underwent discoblock procedures for the most painful disc. VAS scores improved by three or more points in 16 out of 17 patients. Overall, significant improvements in pain levels were observed, with the pre-procedure and post-procedure VAS scores being 9.5 ± 0.9 and 2.5 ± 2.7, respectively. Based on these results, the positive predictive value of the ultrasound-guided disc pain induction test was 94%.
Discussion
The current results suggest that our ultrasound-guided disc pain induction test can be used for simple, non-invasive identification of the culprit lesion(s) in patients with discogenic lumbar pain. Painful discs exhibited significant disc degeneration compared with painless discs. These findings are in accordance with those of previous studies reporting associations of disc protrusion and disc degeneration on MRI with lumbar pain [
3,
12]. However, we observed no association between tenderness and Modic type. Although studies have suggested that Modic type is associated with disc degeneration [
10], which is often observed in patients with lower back pain [
3], Modic changes in the vertebral body occur due to spinal degeneration and are not directly associated with discogenic lumbar pain.
A high-intensity zone on MRI is a characteristic finding in patients with discogenic lumbar pain; however, this finding was not observed in more than half of the patients in the current study. Some reports suggest that the presence of a high-intensity zone is not sufficient for the accurate identification of the cause or level of pain [
12], as high-intensity zones can be observed even in asymptomatic patients [
13]. Therefore, concurrent sonopalpation may be ideal for improving diagnostic accuracy.
In this study, discoblock procedures at the disc with the most intense pain were effective, indicating that the disc in which the most intense pain is induced during the ultrasound-guided disc pain induction test is likely the cause of discogenic lumbar pain. This result supports the value of our method for improving diagnostic accuracy for discogenic lumbar pain. The discography and discoblock procedure are useful for the definitive diagnosis of discogenic pain in the lumbar spine. A previous report described that pain relief following an injection of a small amount of local anaesthetic agent into the painful disc was a useful tool for the diagnosis of discogenic low back pain compared with discography [
4]. A review into the indication for discography has revealed the following [
14]:
1.
Further evaluation of demonstrable abnormal discs to help assess the extent of abnormality or correlation of the abnormality with the clinical symptoms. Such symptoms may include recurrent pain from a previously operated disc or due to lateral disc herniation.
2.
Patients with persistent, severe symptoms where other diagnostic tests have failed to reveal clear confirmation of a suspected disc as the source of pain.
3.
Assessment of patients who have failed to respond to surgical intervention to determine if there is painful pseudarthrosis or a symptomatic disc in a posteriorly fused segment. The aim is to evaluate the risk of recurrent disc herniation.
4.
Assessment of discs before fusion to determine if the discs within the proposed fusion segment are symptomatic and to determine if the discs adjacent to this segment are normal.
5.
Assessment of candidates for minimally invasive surgical intervention to confirm a contained disc herniation or to investigate the dye distribution pattern prior to chemonucleolysis or percutaneous procedures.
The review also discussed the complications of discography such as spinal headaches, discitis, meningitis, intrathecal haemorrhage, arachnoiditis, reaction to accidental intradural injection and damage to the disc itself. However, these complications were mainly reported from the late 1940s to the mid-1960s. The most frequent and severe complication now reported from discography is discitis, and the overall incidence calculated by adding all the occurrences together was less than 0.25% by patient and less than 0.14% by disc. The review described that the improvement of radiographic equipment, improved technique and smaller needles have made the procedure increasingly safer. However, it is still important to avoid unnecessary testing. Given that our ultrasound-guided disc pain induction test is simple and non-invasive, it may aid in the early diagnosis of the culprit lesion in patients with discogenic lumbar pain, thereby reducing unnecessary discography procedures.
In the present study, disc pain was most common at L4/5, and however, we could not identify past reports that have described the distribution of discogenic low back pain. Since a past population-based cohort study in our country showed the prevalence of lumbar disc degeneration was highest at L4/5 [
15], this is considered to be consistent with our research results. However, there are reports that low back pain that presents in a similar manner to discogenic low back pain is associated not only with disc degeneration but also with endplate signal changes and Schmorl nodules. Therefore, it is difficult to diagnose discogenic low back pain based solely on the presence of disc degeneration [
16]. We believe that clinical symptoms along with imaging finding are important in the diagnosis of discogenic low back pain.
In the present study, characteristic pain during anterior bending of the trunk was observed in 61% of patients, while 12% of patients experienced no increase in pain intensity during anterior–posterior bending of the trunk. A previous report has described that in discogenic low back pain patients, sensitivity was 0.650 and specificity was 0.311 for the restriction of lumbar flexion range of motion, whereas sensitivity was 0.175 and specificity was 0.636 for the restriction of lumbar extension range of motion [
2]. The report suggests that several examinations should be conducted to confirm the final diagnosis in low back pain. The axis of rotation in the spine during anterior–posterior bending of the trunk is reportedly located in the posterior disc region [
17‐
20], suggesting that disc pressure increases during posterior bending. Many patients do not experience such characteristic mechanical pain, resulting in a diagnosis of non-specific lumbar pain.
Previous studies have indicated that discogenic lumbar pain results from vascular ingrowth into the inner lining of the cartilage endplates and annulus fibrosus, along with nerve ingrowth into the inner annulus fibrosus and nucleus pulposus of the injured disc [
21,
22]. Discogenic pain may, therefore, occur due to increases in disc pressure during anterior bending, which stimulates the ingrown nerve. Effective sonopalpation methods for diagnosing discogenic pain in the cervical spine have been documented [
7]. Furthermore, as pressure is applied to the discs at each level in real-time, the ultrasound-guided disc pain induction test may help to identify the culprit lesion(s) by increasing the internal pressure in the individual discs. Diagnosis based on provocative testing under ultrasound guidance is primarily advantageous given the ability to avoid the use of iodine-based contrast agents in patients with allergies, as well as the exposure of both patients and examiners to ionizing radiation.
This study had some limitations, including possible selection bias, as well as unclear sensitivity and specificity of the test. Furthermore, not all patients underwent discoblock procedures, and we did not examine the influence of patient physique or disc level on the ability to ensure proper application of pressure.
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