In 1970, Crock first used the term internal disc disruption (IDD) as a pathological condition expressed as a result of changes in the structure and metabolic capacity of the intervertebral disc that are progressed by general injury [1]. He described IDD in patients with lower back and lower extremity pain that worsened after surgical treatment for herniated disc [2]. Rupture of the annulus appears to be the main form of IDD. In general, the diagnosis of discogenic pain due to IDD must meet the following criteria: (1) confirmed as IDD on CT discography, (2) reproducible pain identical or similar to evoked injection with contrast medium, (3) negative findings from stimulation of at least one other disc as a control [3].

Intervertebral disc pain is clinically expressed as chronic low back pain of a deep, throbbing nature, which is not completely relieved by rest and is sometimes accompanied by radiating pain to one or both limbs [4]. Treating disc pain is considered challenging for doctors. In recent years, several minimally invasive treatment modalities have been studied, such as intradiscal steroid injection, intradiscal thermotherapy (IDET), radiofrequency coblation, and epidural steroid injection [5].

These methods have aroused great interest among doctors who lead spinal interventions and provide new alternatives to patients with chronic spinal pain [6]. The main advantages of minimally invasive therapy include relative simplicity, low cost, fast recovery time, and fewer side effects when compared to conventional surgery, but many people question its efficacy. The aim of this report is to discuss the rationale for the use of intradiscal steroids injection and to review the literature on efficacy.

When there are degenerative changes in the nucleus pulposus, part of the axial load between the vertebral endplates is applied directly to the annulus fibrosus. Degeneration of some central fibers appears first, followed by cracking. In the early stages, these changes are microscopic but cause an inflammatory response around the sensitive longitudinal ligaments of the spine, creating a clinical picture of acute low back pain. Inflammation due to direct chemical stimulation or secondary inflammation due to an autoimmune response to the nucleus pulposus is considered to be the main cause of pain [7]. Both steroids and nonsteroidal antiinflammatory drugs are partially effective in treating inflammation-related pain [8]. Given that the symptoms of pain are due to inflammation, anti-inflammatory drugs may be useful in treatment. Therefore, the reason for using intradiscal steroids is to relieve the symptoms of patients by suppressing inflammation within the intervertebral disc [9].

Structurally, there is a study result that steroids in the intervertebral disc promote the stabilization of the spinal segment through additional degeneration of the intervertebral disc. Yong-Hing and Kirkaldy-Willis proposed a 'continuous response of degeneration' of intervertebral disc disease [10]. This continuous response is divided into three stages according to the degree of damage to the intervertebral disc and the zygapophyseal joint at a given time point, and is considered to be a continuous change. The first and second stages, the dysfunctional and unstable stages, are characterized by cracks or lacerations of the outer annulus fibrosus and a decrease in proteoglycan composition in the nucleus pulposus, and the patient complains of intense pain [11]. The third stage, stabilization, is characterized by end-stage tissue damage and attempts to repair. At this stage, nucleus pulposus resorption occurs, exacerbating intervertebral disc space stenosis, fibrosis, endplate irregularities, and bone tissue formation. The spinal segment is stabilized and the patient experiences pain reduction [10].

In 1993, Kato et al. concluded that intradiscal steroid injection resulted in gradual degeneration of the intervertebral disc, and at the same time reported that this eventually resulted in clinical improvement (ie, pain reduction) [12]. This was suggested because the steroid induced tissue contraction and stabilization of the surrounding vertebral segments.

According to this study in 1997, Aoki et al. evaluated histological changes after intradiscal injection of corticosteroids in rabbits [13]. After 24 hours, they found degenerated tissue inside the nucleus pulposus and annulus fibrosus in rabbits that received methylprednisolone acetate injections. They concluded that methylprednisolone caused degeneration and calcification of the intervertebral disc. This was proposed as a basis for clinical improvement in patients who used intra-disc steroids for the treatment of low back pain and sciatica.

Another practical reason for using intra-disc steroids is that steroid administration can be performed concurrently with diagnostic discography without additional time or significant expense (Fig. 1 and 2).

Figure 1. Intradiscal injection at the L5-S1 level, right-sided. (A) Fluoroscopic anteroposterior (AP) view. (B) Fluoroscopic lateral (Lat) view. In the AP and Lat views, the spinal needle tip is positioned at the center of the disc.

Figure 2. (A, B) CT discography saggital and axial images of L3/4 disc. Based on the contrast pattern, it corresponds to Modified Dallas discogram grade 4. (C, D) MRI T2 sagittal and axial images at the same level. Central protrusion and annular tear were confirmed on MRI images. (E, F) CT discography of L4/5 disc, corresponding to modified Dallas discogram grade 4. (G, H) MRI T2 sagittal and axial images at the same level. A central extrusion and annular tear were observed. (I, J) CT discograpy of L5/S1 disc, corresponding to modified Dallas discogram grade 5. (K, L) MRI T2 sagittal and axial images at the same level. Posterior annular tera was observed.

Whether intradiscal steroids pose a serious risk to patients remains controversial. Ito et al. reported the risk of spinal canal ossification and calcification in patients followed up for 5 years after discography and betamethasone injection [14]. There have been several cases of steroid-related necrotizing granulomatous lesions in the intervertebral disc [15].

RESULTS OF CLINICAL TRIALSIn 1954, Feffer et al. injected hydrocortisone into the intervertebral discs of 244 patients and followed them for 4-10 years [6]. The authors found that 114 of 244 patients (46.7%) achieved permanent remission with hydrocortisone injections. 100 patients (53.3%) initially did not respond to injection or relapsed. Although no single factor was particularly favorable in this study, old age, patients with predominantly non-radial back pain, and patients with limited degenerative changes had the best prognosis. Also, the patient's response could not be predicted by the nature or duration of the pain. Two-year follow-up radiographs found that 'there was no abnormal acceleration of the degenerative process.

Wilkinson et al. performed 45 intradiscal injections in 29 patients with lumbar disc disease [16]. Of the patients, 10 had radiating back pain in the legs and 19 had non-radiative pain. All patients complained of symptoms for at least 6 months despite aggressive non-invasive treatment. Patients were not candidates for surgery because they had no objective neurological deficits and many patients had atypical pain patterns. All patients underwent discography for intradiscal injection, and almost all patients were abnormal. This abnormality was usually confined to a single lesion and was closely related to the degenerative changes seen on general radiographs. Initially, subjects received 8 injections using 30-40 mg of Depomedrol. After that, all intradiscal injections were done with 60-80 mg of Depomedrol. All patients were followed for at least 1 year and the mean follow-up period was 2.4 years. The authors found that 54% of patients with intervertebral pain did not respond well and only 31% had good results lasting more than 3 months.

In 1960, Leao et al. studied 32 patients aged 18-70 years, suffering from low back pain and sciatica that failed conservative treatment (rest, lumbosacral corset, analgesic) [17]. Sixteen patients received intradiscal hydrocortisone and the rest received prednisolone. The steroid dose varied between 20-50 mg, but the ideal dose was 25 mg. The authors measured patient response after 24 and 72 hours in both groups and 1 year in the hydrocortisone group. They found that intradiscal steroids produced beneficial outcomes in more than half of the patients and that there were no significant differences between hydrocortisone and prednisolone.

In 1975, Graham reported a double-blind study comparing chemical nuclear degradation by chymopapain and hydrocortisone in 40 patients with chronic low back and sciatica who had failed conservative treatment for several years. [18]. Twenty patients received intradiscal chymopapain injections and 20 patients received hydrocortisone. Patients were followed for 7 months and then evaluated. Of the 20 patients who received chymopapain injections, 12 (60%) had better-than-average outcomes after 7 months, and 10 of the 19 patients (53%) who received hydrocortisone had similar results. They found that chymopapain was not significantly superior to intradiscal injection of hydrocortisone. Although the above study shows that intradiscal steroids injection can be beneficial when used in a selected patient population, it is simply a listing of remission cases and no appropriate control group. Also, due to the small sample size, only limited conclusions could be drawn.

In 1992, Simmons et al. conducted a randomized, double-blind study to evaluate the efficacy of intradiscal steroid injections compared to placebo (bupivacaine) [19]. All selected patients had a positive pain response from a single disc injection, with or without sciatica. All of them failed 6 weeks of conservative treatment. Exclusion criteria were multiple site disc pain, spinal canal or intervertebral foramen stenosis, previous lumbar spine surgery, or medical conditions requiring steroids. A total of 25 patients were randomized to receive 80 mg/ml of depomedrol or 1.5 ml of Bupivacaine and were reevaluated 10-14 days after injection. Of the 25 patients studied, 14 received depomedrol and 11 received marcaine. In the depomedrol group, 21% showed subjective improvement and 79% did not. In the marcaine group, 9% showed clinical improvement and 91% did not. They concluded that there was no statistically significant benefit to intradiscal steroid use.

Khot et al. performed a prospective randomized trial comparing intra-disc steroids with placebo in patients with lumbar disc pain [4]. A total of 120 patients with chronic disc herniation, who failed conservative treatment for at least 6 weeks, were randomized to receive intradiscal saline or methylprednisolone injection. Patients were followed for 12 months and pain was reported according to the Visual Event Scale (VAS) and Oswestry Disability Index (ODI). They found that there was no significant difference in the results between the two groups, as the steroid group showed a change in mean disability index of 2.28% and the saline group showed a change of 3.42%. Also, there was no significant difference in pain score.

Until a few years ago, surgical intervention was the only treatment option for disc pain in patients who did not respond to conservative treatment [24]. Surgical treatment includes discectomy using laminectomy, open discectomy, micro discectomy, spinal fusion, and artificial disc replacement [25]. Altered bladder function and progressive muscle weakness are considered absolute indications for surgery but are rare [26]. The reported effects and complication rates differ depending on the surgical procedure [27,28] and the postoperative complication rate was reported to be about 17-18% [29,30].

Recently, minimally invasive intradiscal procedure has been considered as an alternative treatment for chronic low back pain. The reported complication rate is low, the annulus fibrosus structure is preserved, and the surrounding tissue is less affected by these procedures [34]. The main objective of the minimally invasive procedure is to avoid major disadvantages such as extensive tissue damage, high complications, and reoperation [35].

1. Thermal annular procedures

Thermal annular procedure (TAP) is an alternative option between drug treatment and surgical treatment for patients suffering from discogenic pain [6]. Heat is transferred to the damaged annulus fibrosis by this procedure, leading to denervation and pain relief [38]. Thermal degeneration of collagen fibers is thought to stabilize the intervertebral disc and potentially seal the annulus fissure [39,40]. The effectiveness of TAP is based on rigorous and careful patient selection [37]. Indications are those who have had back pain for at least 6 months, have lower back pain worse than leg pain, and do not respond to conservative treatment [41]. Back pain worsens when sitting or standing and relieves when lying down. Positive prognostic factors are the presence of a radial tear, a residual disc height of at least 50% and a protrusion of less than 5 mm [37]. Compressive radiculopathy and abnormal neurological examination are considered contraindications for TAP.

2. Intradiscal electrothermal therapy (IDET)

IDET uses a radiographically guided, navigable intradiscal catheter to the annulus fibrosus and transfers heat to the annulus fibrosus [42,43]. Heat causes local degeneration of collagen fibrils, cauterization of granulation tissue, and coagulation of nerve fibers [44-46]. Correct patient selection can yield favorable outcomes in pain and disability [42,43].

A meta-analysis evaluating the efficacy of the IDET procedure was performed by Freeman and Appleby et al. [47,48]. They reported an average improvement of 3.4 points and 2.9 points on the visual analogue scale for back pain, respectively. Improvements on the Oswestry disability index were 5.2 and 7, respectively. In the study of Appleby et al., the average decrease in on the short form 36 (SF-36) physical functioning was 21.1 points, and the average decrease in SF-36 bodily pain was 18 points, which was statistically significant [48]. The estimated complication rate was 0.8%. Freeman evaluated five retrospective studies of a total of 379 patients, in which 13-23% of patients underwent surgery for persistent low back pain after an IDET procedure. He concluded that the evidence for the efficacy of IDET was limited [47]. However, contrary to Freeman's conclusion, Appleby et al. reported that the efficacy and safety of the procedure were confirmed.

Two randomized controlled trials of IDET procedures have conflicting results. In a double-controlled trial, a total of 57 patients were randomized in a 2:1 ratio, 38 were included in the IDET group and 19 were included in the control group [49]. The low back pain score of the IDET group was 39.51 at baseline, 38.31 at 6 months, and the average score of the control group was 36.71 and 37.45, respectively. The mean ODI of the IDET group was 41.42 at baseline and 39.77 at 6 months, and the mean ODI of the control group was 40.74 and 41.58, respectively. Results did not improve significantly after IDET or control procedures. In contrast to these results, Pauza et al. [41] showed better outcomes in patients treated with IDET. Of the 64 patients, 37 underwent IDET and 27 underwent control procedures. They reported that both groups of patients improved on the SF-36 score, whereas pain relief and ODI were significantly improved in the IDET group than in the control group. They found that IDET was significantly more effective in a group of patients limited to VAS < 7, SF-36 < 55, or ODI > 40. In addition, pain relief greater than 50% was only seen in 40% of patients treated with IDET and 33% of controls.

Both studies have been criticized. While a wide range of placebo effects were reported in a study by Pauza et al., it was uncertain whether it would be clinically applicable if strict criteria for patient selection were applied [41]. On average, the patients selected for the study were free of disabilities and scored high on most subscales of the SF-36. Freeman’s survey was criticized for not having a placebo effect. Contrary to the literature, Freeman’s study did not show any beneficial results for IDET or controls.

Clinical outcomes of the IDET procedure were compared with those of spinal fusion in a systematic review by Andersson et al. [50]. The overall median improvement after spinal fusion was 50% for VAS for pain, 42% for ODI, and 46% for SF-36. Improvements after IDET were 51%, 14%, and 43%, respectively. The authors conclude that perioperative complications are usually associated with surgical intervention and IDET can be used prior to spinal fusion among eligible patients.

3. Radiofrequency annuloplasty (RFA)

Radiated frequency energy can be transmitted to the intervertebral disc by the procedure [43]. An alternating current (frequency 250-500 kHz) is generated by a high-frequency generator through the electrode, causing an ionic reaction in the tissue directly surrounding the active tip [51]. Molecular friction and tissue heating occur within a limited distance of the electrode [52]. Cosman and Kline reported that the efficacy of RFA was to inactivate the pain nerve, the applied current coagulates the sensory nerve, and prevents the conduction of nociceptive stimuli [52,53].

The clinical effect of RFA was reported in a prospective controlled study by Finch et al. [54]. Thirty-one participants underwent RFA for a radial rupture of a single intervertebral disc, and 15 patients continued conservative treatment. VAS and ODI were significantly decreased in the treatment group, whereas both outcome measures did not change in the control group during 12 months of follow-up.

Two randomized controlled trials of RFA were performed and did not yield beneficial results. In a study by Kvarstein et al., 20 patients were assigned to treatment and control groups in a 1:1 ratio [55]. Pain intensity scores and secondary outcomes did not show significant differences between groups at 6 and 12 months follow-up. Five patients treated with RFA reported greater than 50% pain relief at 12 months compared to one patient in the control group. However, 4 patients in the RFA group reported worse or no change in pain intensity at final follow-up, whereas 7 patients in the control group reported worsening. In Barendse’s study, 13 patients were assigned to the treatment group and 15 patients were assigned to the control group [56]. After 8 weeks of treatment, no differences in pain and disability indices were reported between the two groups.

In contrast to the results of Kvarstein et al., Barendse et al. and Oh et al. conducted a randomized control study and demonstrated clinical improvement after the procedure [57]. In this study, 49 patients complained of back pain for more than 1 year and pain after IDET procedure. Control patients each received lidocaine injections without RFA. After 4 months of follow-up, pain, the VAS score for body pain and SF-36 physical functioning subscales were significantly improved in the treatment group compared to the control group. No significant difference was found in these outcome measures in the control group.

IDET and RFA procedures were compared in a prospective controlled study by Kapural et al. [58]. Twenty-one patients were assigned to two groups. No statistically significant difference was found in VAS or pain disability index between the two groups before treatment. From 3 to 12 months after the procedure, participants in the IDET group improved significantly in VAS and disability index compared to patients in the RFA group.

4. Intradiscal biacuplasty (IDB)

In the IDB, two RF electrodes included in the bipolar system are applied to the posterior annulus fibrosus [24]. The proposed process with respect to IDB is the coagulation of nociceptors within the posterior aspect of the intervertebral disc. The generated temperature causes nerve ablation while maintaining a safe environment for the surrounding tissue. The safety of the procedure and the absence of complications before and after the procedure were reported in many studies in the literature [60-63].

The effect of the IDB procedure was compared with that of a placebo intervention in a double-blind randomized controlled study by Kapular et al. [60]. At 6-month follow-up, there were significant improvements in physical function, pain and disability in the experimental group (n = 27) compared to the control group (n = 28). In the IDB group, there was a significant improvement in body function and pain at 12-month follow-up. Patients with single-level disc pain had better outcomes after treatment compared to patients with disc pain at two sites. At 6-month follow-up, patients in the control group were given IDB, and at final follow-up, improvements in body function, pain, disability, and opioid use were similar to those who initially received IDB. The authors provided evidence that IDB could be a minimally invasive treatment option in carefully selected patients and helped validate efficacy outcomes shown in previous uncontrolled studies [24,64,65].

The safety and clinical effect of IDB was demonstrated in a prospective randomized study by Desai et al. [63]. The authors compared IDB and conservative therapy (n = 29) with conservative therapy alone (n = 34). After 6 months, 89% of conservative alone participants chose to receive IDB in addition to conservative therapy. At 6- and 12-month follow-up, patients in the original IDB and conservative therapy groups showed statistically significant pain relief, of which 55% showed improvement of more than 2 points in VAS. A 50% or greater decrease in VAS was reported in 41% of patients, whereas physical function, ODI, and quality of life were significantly improved. At 6 months, the mean outcome score of the conservative treatment alone group did not improve significantly.

5. Percutaneous disc decompression (PDD)

Disc herniation in patients without abnormal neurological findings can be treated with PDD [71]. Open discectomy has been the primary treatment for many years [72]. Hakkinen et al. reported that the reoperation rate for lumbar disc herniation was 10% at 5-year follow-up [73], whereas Atlas et al. and Osterman et al. reported a reoperation rate of 25% at 10-year follow-up [31,74].

In PDD procedure, the intravertebral disc pressure is relieved to improve pain and maintain the integrity of surrounding tissues [80]. As a result of the decrease in intra-disc pressure, the release of inflammatory mediators is limited, while the disc size decreases and the healing process begins [81]. An important predictor of the success of PDD is determining whether the disc herniation is still contained in the intact fibers of the external annulus fibrosus and posterior longitudinal ligament [25]. Techniques involved in PDD are chemical nucleolysis of chymopapain that produces enzymatic cleavage of the nucleus pulposus, PDD (nucleoplasty), percutaneous laser disc decompression (PLDD), and automated percutaneous lumbar discectomy (APLD) [25,43,82]. Chymopapain is deprecated due to increased risk of fatal anaphylaxis, cartilaginous endplate injury, and bleeding. The effectiveness of PDD is based on rigorous and careful patient selection.

6. Percutaneous disc decompression (nucleoplasty)

Disc nucleoplasty (RF coblation or plasma discectomy) is a PDD method using a coblation technique. Radiated frequency energy is generated through a 1 mm diameter bipolar instrument. By removing about 1 cm or more of the nucleus pulposus, the pressure within the intervertebral disc is reduced, and the removal of the intervertebral disc protrusion and decompression of the nerve root have a good effect on pain relief [43,86,87]. This technique preserves the integrity of the surrounding tissue without direct mechanical or thermal damage [80]. As a result, the risks associated with open surgery such as fibrosis and infection were minimized [88,89], and the most important side effect is temporary pain at the needle insertion point [90].

The beneficial results of nucleoplasty were reported in a prospective study by Al-Zain et al. Participants (n = 69) had VAS scores of 6.59 points before the procedure and 3.36 points one year after the procedure, while back pain was 5.68 and 2.5, respectively. These results were statistically significant. Pain relief of at least 50% was reported in 58% of participants. Similarly, clinical improvement after nucleoplasty was reported in a systematic review by Nedeljkovic [80]. This study included 14 studies. 53% of patients reported pain relief greater than 50%. The median improvement in VAS over baseline was 38.5% and ranged from 11 to 72%. Improvements in VAS were reported in all studies, but improvements were statistically significant in 9 studies. Three studies evaluated functional improvement in patients and found that more than 50% of participants improved at the final follow-up.

A comprehensive meta-analysis was performed to analyze the efficacy and safety of the procedure in the treatment of lumbar and cervical disc herniation. Eichen et al. evaluated 27 studies with a total of 3211 patients and concluded that the procedure reduced pain and increased functional mobility of patients in the long term [91]. In 17 studies, VAS was used as an outcome measure and nucleoplasty resulted in statistically significant pain reduction compared to baseline at all measurement time points. Four studies had a control group and found that nucleoplasty was more effective than conservative treatment after 6 weeks and 3 months. ODI was significantly reduced relative to baseline at all time points.

It has been mentioned that nucleoplasty and PDD technology are necessary for patients with disc herniation [89]. The assumption that patients with greater prolapse would have less favorable outcomes from nucleoplasty was evaluated in a prospective, nonrandomized cohort study [87]. Three groups of patients were evaluated. In the first group, 24 patients had disc herniation of less than 5 mm. The second group included patients with disc herniation size of 6-9 mm, and in the third group, 27 patients were assigned disc herniation. All of them were treated with nucleoplasty. Sixty-five patients with disc herniation were assigned to the fourth and treated with micro resection. Both the first and the second were found to be identical in terms of pain severity and disability index after 1 year of follow-up. In the third group, statistically significant worsening of pain severity and disability index was reported during the first 3 months, and stabilization of the patient’s condition was found at the next follow-up. In the fourth group, pain intensity and disability index significantly decreased during the first 6 months. The authors concluded that in the case of disc herniation, the annulus fibrosus injury had poor outcomes and less pain relief when treated with nucleoplasty. Conversely, nucleoplasty has been shown to have beneficial results for disc herniations up to 9 mm.

7. Percutaneous laser disc decompression (PLDD)

PLDD has been approved by the US Food and Drug Administration since 1991 as one of the minimally invasive treatment methods for lumbar disc herniation [34]. In PLDD, laser energy is delivered by a laser fiber placed in the nucleus pulposus through a percutaneous approach under local anesthesia [92]. The water content of the nucleus pulposus is evaporated by laser energy, resulting in a decrease in the volume in the intervertebral disc and a decrease in the pressure in the intervertebral disc [93-96]. In Hellinger’s survey, 3377 patients were evaluated. A complication rate of 0.5% was reported [97]. Among 377 PLDD procedures, one case of infectious intervertebral discitis was reported [96], and according to a study by Quigley, three cases of abdominal perforation and one case of partial horsehair syndrome due to PLDD occurred [98].

Limited evidence of short- and long-term effects of PLDD has been reported in systematic reviews [34,92]. In a study by Singh et al., 75% of 3171 patients experienced clinical improvement [34]. A review by Schenk et al. included 16 clinical trials with a total of 1579 patients [92]. Schenk et al., and Singh et al. concluded that PLDD could be effective in appropriately selected patients, citing the lack of randomized controlled trials.

The first randomized study to compare the effects of PLDD with conventional surgery in patients with lumbosacral neuromuscular syndrome was conducted by Brouwer et al. [99]. 57 patients were included in the PLDD group and 58 patients were assigned to the surgical group. There were no statistically significant differences in outcome measures between the two groups, except for the rapid recovery of patients who underwent surgery. In the PLDD group, 24 patients (44%) underwent additional surgery during 1 year, while 9 of the patients (16%) underwent surgery and required revision surgery. The surgical group had more complications (11%) than the PLDD group (5%), where complications were less common. The authors concluded that PLDD with additional surgery when needed could be a treatment option with effects similar to surgical intervention.

Tassi reached the same conclusion [35] and compared microdiscectomy and PLDD with a follow-up period of 2 years. In the micro resection group (n = 500), clinical improvement was seen in 85.7% of patients, and the remaining patients (14.3%) worsened or did not improve. In the PLDD group (n = 500), the percentages were 83.8% and 16.2%, respectively. Clinical improvement was faster in the surgical group, and the recovery time was significantly shorter in the PLDD group. Complications were 2.2% in the micro resection group, but no complications occurred in the PLDD group.

8. Automated percutaneous lumbar discectomy (APLD)

A pneumatic aspiration ablation probe is used in APLD and applied to the affected disc through a cannula with an outer diameter of 2.8 mm. 3 g of disc tissue is removed 1 cm anterior to the prolapse, reducing intra-disc pressure and decompression of the nerve root [100].

In a prospective multicenter study, the results of 1582 APLD procedures were evaluated from 1992 to 1994 [101]. The reported success rate was 83% at 1 year. Similarly, a review by Manchikanti et al showed positive results in 80% of patients. In a comparative study by Liu et al., 104 patients were treated with APLD and 82 patients were treated with microendoscopic discectomy with a mean follow-up period of 6 years [103]. According to MacNab criteria, a success rate of 75.96% in the APLD group and 84.15% in the surgical group was reported. Surgically treated patients improved significantly in the social function and body pain areas of ODI and SF-36 scores compared to the APLD group. Eight patients (7.69%) in the APLD group and 2 patients (2.44%) in the surgical group underwent open surgery. Long-term postoperative satisfaction was higher in patients who underwent surgery, but complications, length of hospitalization, and cost were lower in patients in the APLD group.

Two randomized trials were conducted to evaluate the effectiveness of APLD, but were criticized for their quality and outcome. Chatterjee et al. conducted a randomized study comparing APLD and micro resection [104]. Beneficial results were obtained in 29% of APLD patients and 80% of micro resection patients. The authors have been criticized for incorrect selection criteria, the unreasonably low success rate of APLD, may be significantly less than placebo, and not using CT disc angiography. The absence of a control group limits the quality of randomized studies. A second randomized study was conducted by Haines et al. [105]. The effect of APLD was compared with that of conventional discectomy. According to Macnab criteria, the success rate of APLD was 41% for percutaneous discectomy patients and 40% for conventional discectomy. Haines et al failed to recruit a sufficient number of participants, and only 34 patients were included in the study [105].

According to a literature review, intra-disc steroids did not show significant clinical improvement in pain or function in patients with disc herniation. Early studies without controls showed encouraging results, but more recent controlled trials had little benefit. Recent literature has shown significant improvement with intradiscal steroid injection in patients with signs of MRI modic changes and end-plate inflammatory changes.

Patients who underwent IDET improved their VAS score by 51%, ODI by 14%, and SF-36 by 46%, while complications were about 0.8% [47,50] RFA-related results were not very beneficial [55] . IDB in combination with conservative therapy showed 55% pain relief [63]. PLDD outcomes were reported to be beneficial in 75% of patients [34].

In a 2-year follow-up of the Swedish Lumbar Study [27], the mean reduction in back pain was 33% in the surgical group and 7% in the non-surgical group. In a Norwegian study, there was no difference in the improvement of low back pain between the lumbar fusion group and the control group at 1-year follow-up [106]. In the UK Medical Research Council trial, spinal fusion was compared to an intensive program of training using exercise therapy, spinal stabilization exercises and cognitive behavioral principles. At 2-year follow-up, pain, ODI, quality of life, or SF-36 physical or mental components were not statistically different between the two treatment modalities. European guidelines reported that fusion cannot be recommended unless two years of conservative treatment or minimally invasive procedures have failed [110].

Therefore, short-term indications for drugs, increased complications, and various surgical success rates increase interest in minimally invasive procedures. IDET procedures have been performed since 1998, and the reported incidence of complications is low. The need for surgical intervention can be eliminated or delayed for a long time in appropriately selected patients with internal disc disorders who underwent IDET. The American Society of Interventional Pain Physicians in their 2007 Evidence-Based Practice Guidelines for the Management of Chronic Low Back Pain concluded that the evidence for IDET was adequate for short- and longterm pain relief [108]. The North American Spine Society also suggested that IDET would be a reasonable first-line treatment option for patients with less disability, with radial lacerations or prolapses less than 3-4 mm and with relatively well-preserved intervertebral disc height [44].

Unlike IDET, there is much less literature on RFA and IDB procedures. There are few data on the effectiveness of RFA and IDB and, according to Helm et al., there is limited evidence on whether both procedures are effective in relieving disc pain [111]. One prospective study compared IDET with RFA and concluded that IDET should be the preferred treatment option for disc pain [58]. Further studies are needed to evaluate the effectiveness of RFA and IDB and provide efficient evidence for use in the management of chronic low back pain.

Nucleoplasty is considered a potentially effective treatment option for patients with disc pain according to many studies. Significant success rates were reported, and the procedure was safe and adherence was not bad. A prospective randomized controlled study is needed to confirm the efficacy of the procedure. Similarly, significant success rates have been reported in observational studies and systematic reviews of PLDD. This finding was verified by a randomized study by Brouwer et al. [99]. The authors noted the efficacy of the procedure and the need for surgical intervention if symptoms persist. APLD has been approved by the American Academy of Orthopedic Surgeons as a treatment option for patients with lumbar disc herniation [109]. Favorable clinical outcomes have been reported in prospective studies, and the importance of rigorous patient selection is acknowledged.

This work was supported by Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korea government (MSIT) (No.2022000218, Development of XR twin-based training content technology for rehabilitation), and also by the Assistive Technology R&D Project for People with Disabilities and the Elderly, funded by the Ministry of Health & Welfare, Republic of Korea (# HJ20C0058).

No potential conflict of interest relevant to this article was reported.