Injections

“Necessity’s sharp pinch!”

—W. Shakespeare, King Lear

Injection procedures, both diagnostic and therapeutic, have become an established tool in the evaluation and treatment of spinal pathology.

Discography

The most controversial diagnostic injection is the discogram (Fig. 15-1). Since first introduced by Lindblom (18) in the late 1940s the discogram has been a constant source of debate. Touted as an indicator of discogenic back pain, the procedure has been dogged with questions about its specificity and reliability. Attitudes toward discography have swung back and forth over the years. Dye injection can fairly definitively outline annular defects, leaks, and disc herniations. However, uncertainty has persisted on the ability of intradiscal injection to activate concordant pain reproduction. Physician perspectives have been influenced on the one hand by papers suggesting a relatively high incidence of positive discography in normal subjects (15) or those with minor back pain (6) versus more positive articles indicating refined methodology and improved specificity (8,9). Technique modifications have included routine monitoring for pain hypersensitivity by including a control level injection, differential intradiscal pressure manometry, gauging a postinjection anesthetic effect on pain, use of minimal sedation, and alternating levels of injection all may help better scrutinize a patient’s pain response. Psychologic factors may invalidate the discogram as a reliable test (7). Serious complications such as postinjection discitis have been described (11). The “two needle” technique has been used to reduce the incidence of infection by avoiding having a skin plug from the initial puncture of the dermis carried into the injection site.

A 2003 Contemporary Concepts Review from the North American Spine Society (14) suggested that the use of discography was reasonable for the following situations:

Further evaluation of demonstrably abnormal discs to help assess the extent of abnormality or correlation of the abnormality with the clinical symptoms. Such may include recurrent pain from a previously operated disc and 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 pseudarthrosis 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 dye distribution pattern before chemonucleolysis or other intradiscal procedures.

FIGURE 15-1 AP x-ray of a three-level lumbar discogram. Normal “cookie” appearance at L3-L4. Mild fissuring of the annulus at L4-L5. Note the double-needle technique.

Facet Blocks/Medial Branch Blocks

Facet blocks serve a diagnostic and therapeutic purpose but do not appear completely reliable in diagnostic accuracy. The diagnostic aspect of facet injections can be accomplished using intra-articular injection of anesthetic agents (Fig. 15-2) or medial branch blocks (3). However, false-positive rates as high as 38% are reported (24). In an effort to be more reliable, complimentary procedures have evolved. Differential blocks have been touted as a method to improve dependability. In this approach, a positive response depends not only on the amount of pain relief (generally more than 50%), but must also correlate with the expected time frame for anesthetic effect from a short-versus long-acting analgesic injection. This has been termed the double-block technique (2,24). A triple-block method has also been described (2

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