Introduction

Low back pain (LBP) is the commonest condition affecting the lumbar spine. Around 80% of the population experience at least once LBP in their lifetime. The most frequent cause of LBP with sciatica is the disc herniation. The natural history of herniated disc is characterized by disappearance of symptoms in up to 50% of patients, with shrinkage of the disc herniation revealed by MRI within 8 to 9 months after the onset of pain. However, not all patients can wait so long before symptoms improve. ^1-6 An initial period of nonoperative management is recommended in such cases. After six weeks of nonoperative management, some patients will have persistent pain and will require additional treatment. Surgeries available do not offer clear, safe options free of complications in all cases. Moreover, some reported postoperative complications are more difficult to treat than the original illness.^7-9

Epidural injections, described by Evans in 1930, have been used in the treatment of disc disease for over 80 years and epidural steroids for over 50 years. The procedure has been traditionally performed using a blind technique without fluoroscopic guidance, as described by Barry and Kendal. ^10,11 Because of many favourable reports, epidurals have been increasingly used. The results obtained from many published studies, suggest a more rational use of that treatment. Several large epidemiologic studies have demonstrated safety and efficacy of this root of therapy in properly selected cases. Safety of epidural route has been well documented and enhanced by avoidance of accidental injection of large doses intravascularly, by continuous monitoring of blood pressure and respiration, and by avoidance of this technique in the presence of anti-coagulation. However, epidural root of drug administration has been remarkably stagnant over at least 25 years, with no new drugs developed for epidural administration. Existing agents used include local anesthetics, analgesics, and steroids. ^10-19

I am introducing a new modification of that type of therapy, named (catheter virtual discectomy – CVD). Presenting our experience with this new modified procedure in which epidural catheter is used to deliver epidural cocktail of drugs into the desired target (the prolapsed disc and its surroundings), describe the technique of this relatively painless outpatient procedure, and present the complications we encountered. Delivering a unique drug cocktail to deal with the pathology of lumbar disc disease is finally evaluated.

Materials And Methods

Patient Selection

Patient Population

The Procedure

The skin is prepped in a sterile fashion using povidone-iodine (Betadine) followed by an alcohol rinse, after which a fenestrated drape is applied. Local anesthetic (1% lidocaine) is generally not needed and is only rarely injected subcutaneously, in sensitive patients. A stainless steel 18-gauge Tuohy epidural needle is advanced into the epidural space via a posterior approach. The puncture site is typically 2 to 3 cm caudal to the intended point of entry into the dorsal epidural space (Fig 1). An interlaminar technique at L3, L4, or L5 was used for most patients. The primary target for injection was at the L4–L5 level, unless any technical problems pushed the operator to the L3–L4 level. A total volume of 10–20 ml was separately injected per injection. The patient was trained to change his or her position every ten minutes after injection for better access of the drug to the diseased area. However, patients are kept in bed, in 45 degree position for at least 2 hours post-injection, and to have absolute bed rest for a week after the last injection.

Fig.1: CT axial cuts at the level of CVD placement showing the epidural catheter (A) entering the epidural space (B) through the interlaminar window. The space is well demonstrated around the dural sac; with the catheter appearing as a signal void (C). The catheter can also be visualized (D) on plain fluoroscopy.

Figure 1

Insertion Technique

The Injected Cocktail

Outcome Assessment

Results

Of the 60 patients studied, there were 35 male (58.3%) and 25 female (41.7%) patients with ages ranging from 17 to 52 years, with a mean age of 32 years. The duration of pain to epidural injections ranged from 6 weeks to 36 months.

Clinical Outcome

Access Failures

Complications

Radiological Outcome

(Fig.2 to Fig.6)

Reviewing the radiological follow up images of all the study cases at different follow up visits, clinical improvements was associated with definite radiological improvement in the form of definite volume decrease of the bulged, or prolapsed disc material, as shown clearly in figures 2 to 6. On the other hand, the absence of clinical improvement was associated with no radiological changes. Cases with recurrence of symptoms had either no radiological changes or mild volume changes, not enough to result in definite clinical change.

Figure 2

Fig.2: A pre-injection MRI showing L4,5 disc bulge, in a 35 years old male. Notice the post-injection difference in MRI image, with gradual decrease in size at I month post-injection (A) and as if the bulge was cut by a knife, 3 months later (B).

Figure 3

Figure 4

Fig.3: A pre-injection MRI showing L5-S1 disc protrusion. Notice the post-injection difference in MRI image, the protrusion volume grossly decreased, 3 months later.

Figure 5

Fig.4: (A) Saggital MRI images showing multilevel disc lesions, which are shown to change in size in relation to a 2 month post-injection images. (B) Axial images of the same patient.

Figure 6

Figure 7

Fig.5: Axial MRI images showing unilateral foraminal severe stenosis which apparently decreased 40 days post-injection, accompanied with marked clinical improvement.

Figure 8

Fig.6: Axial MRI images showing postero-lateral L5-S1 disc protrusion which apparently decreased 6m post-injection, accompanied with partial clinical improvement.

Discussion

Lumbar discogenic pain (LDP) could be related to mechanical and inflammatory causes. The inflammatory causes include immune response to the protruded disc material in the form of cell-mediated, biohumoral factors and inflammatory enhancers. Thus, logically speaking, anti-inflammatory medications are the corner stones in the treatment of that type of pain.

Regarding the mechanical causes of LDP, they are both direct (compression of the nerve roots, deformation of the ligaments and annulus, and stimulation of the nociceptors of Luschka’s nerve of the posterior root of the spinal nerve), and indirect (ischaemia due to arterial compression, and venous stasis). To counteract these mechanical effects, the unique microstructure of the intervertebral disc (IVD) should be understood. The IVD has a heterogeneous structure made of two different regions, namely the annulus fibrosus (AF), and the nucleus pulposus (NP). The nucleus appears macroscopically cloudy and jelly-like and is composed mostly of water, collagen and proteoglycans. The annulus is similar in composition to the nucleus, with less water and a greater amount of collagen. The annulus has a laminar structure that is regular on the outer most regions of the IVD with thick lamellae, but begins to lose some laminar structure closer to the nucleus. The IVD is populated by chondrocyte-like or fibrochondrocyte-like cells of mesenchymal origin in all zones as well as larger, highly vacuolated notochordal cells present only in the NP. These cells are responsible for the synthesis of the IVD matrix during development and maintenance of the extracellular matrix throughout life. ^{1, 2, 5, 20-25}

The idea of the present study is to have a new drugs mixture by which we can alter, virtually, without any invasive or even minimally invasive structural intervention, the lumbar disc disease scenario, and manage the presenting clinical and radiological pictures. We took into consideration important findings of previous studies, namely, successful epidural steroid injection (ESI) alone, and volume changes in response to osmotic stresses.

Regarding ESI, some studies reported lumbar disc herniation regression after successful EPI alone. Patients who were successfully treated conservatively and whose pain decreased significantly within the first six weeks were found to have a larger number of resorbed extruded and sequestered disc herniations on follow-up magnetic resonance imaging (MRI). ^26-28 Carette et al showed a slightly better improvement in leg pain over six weeks in a randomised controlled trial of ESI in patients with sciatica due to herniated discs. ²⁹

Regarding disc volume changes, normally, the IVD under dynamic compressive loads shows diurnal variations in disc height and water content. The biophysical mechanisms involved are not fully understood, but are believed to involve changes in the interstitial osmolality or pH secondary to exudation of interstitial water. As the cell membrane is relatively permeable to water, increasing the extracellular osmolality leads to a decrease in cell volume. The mechanism by which IVD cells are able to transduce the applied osmotic stress is unclear. The response is triggered not only by the presence of an osmotic gradient, but rather by some downstream cellular response to the osmotic stress (cellular volume change, membrane stretch, and membrane depolarization). Within the IVD, zonal variations in the cellular volumetric response to hyperosmotic stress were also observed. The volume adaptation characteristics of NP differed markedly from those of AF. ^30-41

Given these findings of volume changes in response to osmotic changes, our idea suggests that the addition of hyperosmotic media to the antioedema and anti-inflammatory media have a good chance of decreasing the volume of the prolapsed disc material. This hypothesis is supported by our findings of definite clinical and radiological improvement in properly selected cases. Reducing intervertebral disc size by chemical aspiration of water of the HIZ or partially shrinking the herniation by drying reduces the pressure on the torn annulus and creates a space for bulge regression whenever the tension of the annular fibres regain capacity to contain the disc. The proposed suggestion is that a small change in volume produces large change in pressure, and later allows healing of the annular cracks.

Widely differing results have been published by various authors using epidural injections, and various combinations of saline, local anaesthetic and steroid injections have been used and the results differ significantly even in series using the same medication. Revising these series, it was obvious that the precise selection of the cases is of importance in determining the results and indeed a look at published work shows that very little attempt has been made to relate the results of treatment to the precise cause of the symptoms and this almost certainly accounts for the differences in the results. ^42-54

It is reasonable to assume that the earlier a CVD is given the more effective it will be, and that the more chronic the case is, the more the failure rate will be. Chronicity may indicate a tight mechanical compression, a nerve root infiltrated with chronic inflammatory cells, ischaemic root, or neuropathic type of pain that may need different treatment methodologies. This concept is borne out by the observations from the present series, i.e., a 60-80% success in all patients having CVDs within 6 months of the onset of symptoms, with only a 40% success in “chronic” patients, having had symptoms for longer than 6 months when given their CVD.

As most minimally invasive procedures, CVD needs only a short hospital stay, or even nonhospital, outpatient protocol. It also eliminates the risks of post-operative scarring linked to surgery which is responsible for recurrence of pain in many cases. CVD can also be repeated in the same patient leaving the anatomical corridors intact and normal if they should fail. The success rates reported in our study vary from 50 to 80% of excellent or good results, according to the selection criteria.

White and coworkers found that inaccurate needle placement occurred in 25% to 30% of blinded techniques, even in skilled and experienced hands. ⁵⁵ Based on the high rate of erroneous needle placement described in the literature and the potentially devastating effects of intrathecal drug injection, we used to perform epidurography in conjunction with CVD in image-guided group of patients unless there is either a history or reasonable suspicion of allergy to iodinated contrast agents. It is a safe outpatient procedure that can assure correct needle placement and demonstrate anatomic features. ^56,57 The use of 5 mL of water-soluble contrast material in order to adequately draw the epidural space is usually enough. However, in the present study, no significant difference was noted between the two groups in expert hands. Only early in the study the difference was significant. In the literature, the argument between the two insertion techniques holds true and this is especially important in our multi-session CVD technique. However, after doing a lot of these techniques and after evaluation of both interventionists and aneasthetists, it would be fair enough to say that if one masters the technique, either blind or image-guided, erroneous needle placement would be minimized. In skilled hands, our procedure ensures delivery of the therapeutic materials into the epidural space and prevents complications due to intrathecal or intravascular injections. ^58-62

It is our practice to perform at least three consecutive epidural instillations. If there is any doubt, injectate delivery was shown to be accurate with epidurography. Another CVD can be repeated for nonresponders, if indicated. We have reviewed the efficacy of CVD in our daily practice and have confirmed a high rate of success of a non-invasive procedure on outpatient bases with low morbidity. Moreover, using CVD is justified by the patients. Before CVD, discussing the technique with the patient make them keen to try. After CVD, most of our patients have commented on the relatively painless nature of the procedure as compared with any other intervention. This is important as no patient was sedated before the procedure. So, cardiac monitoring is not required for CVD when performed under these circumstances. Thus, CVD is extremely safe and causes minimal patient discomfort, making the procedure ideally suited to outpatient settings. Performing CVD in an awake and fully alert patient virtually eliminates the potential for serious complications when done by skilled, experienced spine surgeon.

Conclusion

Despite the supposed argue, this series confirms the value of Catheter virtual discectomy (CVD) in the treatment of lumbar disc protrusions. The current study provides evidence that immediate pain relief and increase in function can be provided by CVD with a very low rate of morbidity. It is a safe & effective treatment for symptomatic lumbar disc herniations in nearly one-half, if not more, of the patients treated, with reported resolution of symptoms at the follow-up evaluations. The follow-up images showed, in addition to the clinical improvement, definite structural decrease of the disc bulges in a way as if discectomy was done without any surgical or interventional intervention. That is why the name catheter virtual discectomy (CVD) was introduced. Failures are largely due to continued mechanical pressure on the nerve root, especially with hard disc protrusions, in chronic cases. The significant increase in the success rate in acute cases (those who have an epidural within 6 months of the onset of symptoms) warrants the role of CVD in decreasing the volume of the compressing disc and decreasing its inflammatory effects. Importantly, this study also demonstrated that even for those in whom treatment with CVD failed, there did not appear to be any deleterious consequences due to the delay in operative intervention. The current study adds further credence to our belief that most patients with lumbar radicular pain without a profound neurologic deficit should first be offered CVD injection trial, especially in young patients.