Introduction

The role of intervertebral Disc (IVD) in producing spinal pain was first described in 1934 by Mixter and Barr [1]. Later in 1940, Roofe [2] described the presence of nerve supply to the lumbar disc annulus raising the possibility of IVD being a source of spinal pain. Injection of procaine into the disc in 1948 by Hirsch [3] provided pain relief confirming the role of disc pathology in axial back pain. Lindblom [4] in the same year reported the clinical application of disc injection to identify the responsible disc for spinal pain and used the term “discography”. Additionally, in 1958, cervical discography was reported in two separate publications [5, 6] and then, in 1975, the first report on thoracic discography was published [7].

Provocation discography is a diagnostic test designed to confirm the role of IVD in producing painful symptoms in patients with internal disc derangement (IDD). This unique and mostly objective test combines the clinical and imaging findings to confirm or rule out the symptomatic role of each IVD in producing discogenic axial back pain. In other words, it’s an extension of physical exam and imaging, coined by some as a “disc stress test”.

One of the limitations of the current diagnostic imaging of symptomatic spine is due to it being performed in a non-weight-bearing position while the most painful position generated by pressure on IVD is during weight-bearing. Therefore, provocation discography provides the means to better assess IVD by raising intradiscal pressure in a non-weight-bearing position. Each disc is accessed separately and injected with a limited amount of contrast medium and by monitoring intradiscal pressure (discography). The clinical finding is based on provocation and reproduction of pain concordant with the patient’s usual pain, following the pressurization of IVD. The reproduced pain needs to be concordant with the patient’s usual pain and distinguished from discordant pain. Fluoroscopy imaging is observed in real time during the injection of contrast and pressurization, while monitoring the patient for reproduction of concordant pain. In most cases, a CT scan is performed at the conclusion of procedure and within one to three hours, which enhances diagnostic accuracy to 93.8–99.55% [8]. It also provides valuable information to complement the findings on plain film, in order to further assess the disc pathology and plan for surgical or interventional pain treatment.

The final assessment is made by combining both the clinical and imaging data.

Anatomy

An intervertebral disc consists of an outer annulus made of fibrocartilaginous lamellae and a central gelatinous nucleus pulposus (Figure 36.1).

The cartilaginous end plates are hyaline-like cartilages that separate the vertebral bone from the outer layers of IVD. Of note, end plates do not completely cover the annulus and superficial lamellae insert into the vertebral body. The posterior annulus has 50% incomplete lamellae and is thinner, while the rest of annulus has only 40% incomplete layers. This could partly explain the higher incidence of annular tears in the posterior disc.

• In a normal disc, 90% of the load distribution is anterior in a sitting and 80% in a standing position. In a degenerated disc, there is equal distribution throughout the disc. Also, in a normal disc, 72% of load bearing is on the nucleus [9].
  
• The disc is largely avascular and the metabolism is mainly load dependent, anerobic and nutrients enter by diffusion through the end plates. Diffusion distance may be as great as 8 mm. A physiologic level (0.33 MPa) of hydrostatic pressure acts in an anabolic fashion, stimulating proteoglycan synthesis [10].
  
• The nerve supply to the anterior annulus is provided by branches of ventral rami and gray rami communicantes (Figure 36.2).

Sinuvertebral nerves provide innervation to the posterior annulus [11, 12]. Nerve fibers extend 3 mm into the annulus. No nerve fibers or neuropeptides are present in a normal nucleus pulposus but in abnormal discs nerve endings may reach the nucleus [13].

Pathophysiology

Discogenic axial back pain is the symptom of internal disc derangement (IDD) generated by a damaged annulus, commonly caused by injury resulting from compressive or torsional strain by a single trauma or multiple micro-traumas. Changes in the nucleus pulposus matrix cause loss of hydrostatic pressure and buckling of annular layers. Increased mobility and sheer stress lead to fissuring and inflammation leads to further tissue breakdown. Proteoglycans’ destruction leads to radial tears and back pain. Damage to the annulus or end plate results in dense ingrowth of nociceptors, vasculature, and granulation tissue. Fissured annulus increases the strain on the remaining healthy lamellae and increased strain results in nociception [14].

Indications

• To determine if a disc is contributing to spinal pain especially when other diagnostic modalities have not been able to determine the source of spinal pain.
  
• Planning for surgical procedures such as fusion or artificial disc replacement and deciding on the extent of intervention and levels involved.
  
• The following are the recommendations by the North American Spine Society [15]:
  
  
  
  • Further evaluation of radiographically abnormal discs to help assess the extent of abnormality or correlation of the image abnormality with clinical symptoms (in the case of recurrent pain from a previously operated disc and a lateral disc herniation).
    
  • Patients with persistent, severe symptoms in whom other diagnostic tests have failed to reveal clear confirmation of a suspected disc as the source of pain.
    
  • Assessment of patients who have failed to respond to surgical procedures to determine if there is painful pseudoarthrosis or a symptomatic disc in a posteriorly fused segment, or to evaluate possible recurrent disc herniation.
    
  • Assessment of discs before fusion to determine if the discs within the proposed fusion segment are symptomatic and to determine if discs adjacent to this segment are normal.
    
  • Assessment of minimally invasive surgical candidates to confirm a contained disc herniation or to investigate contrast distribution pattern before intradiscal procedures.

Contraindications

Technique

• The use of fluoroscopy and/or CT scan is a requirement for the safe performance of discography. All those present in the operating suite need to adhere to complete sterile techniques.
  
• Lumbar discography is performed in prone position.
  
• In order to have a more objective test, in addition to the target disc, it is recommended to test one or two adjacent discs as controls.
  
• If the patients’ symptoms are more dominant on one side, in order to reduce the chance of confusing the pain of needle placement with the provoked pain, it is prudent to place the needles on the contralateral side.
  
• Safe and effective IV sedation while monitoring the vital signs (BP, HR, EKG, O₂Sat and ETCO₂
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