Diagnostic Injections

These injections are intended to selectively anesthetize (block) potential pain-generating structures, or to reproduce the patient's characteristic pain. They are particularly useful in patients with multilevel pathology and help localize the pain generator. If one can selectively "block" the pain fibers in a structure so that the characteristically usual pain of the patient disappears, or if one can selectively stimulate a structure and reproduce the same characteristically usual pain, then it is highly likely that the pain-generating structure was precisely localized and diagnosed. Usually after a block injection the patient is asked to get up from the procedure table and reproduce the preinjection pain-generating movement. A temporal "pain diagram" is given to the patient to mark the pain level every half hour for at least four hours after the block. A clear drop in the preblock pain level is considered diagnostic. This usually means a complete elimination of the pain or reduction of more than five levels on a pain visual analog scale. Because of almost 30% placebo effect for injections, it is advisable to repeat the block a second time to reproduce and confirm the block result.

Precision fluoroscopically guided injections are the main tool in the diagnostic workup of chronic low back pain of more than 12 weeks duration. Statistically the pain generator is discogenic in 40%, zygo-apopheseal (Z) joint in 15-20%, and sacroiliac joint in 15% of cases. As in other medical pathologies, the best successful treatment depends on precise diagnosis of the pain-generating structure. In today's medical reality there is no other reliable diagnostic tool to determine the pain-causing anatomical structure comparable to precision diagnostic blocks.

The following most common diagnostic precision injections will be described:

• Selective spinal nerve block

• Sacroiliac joint block

• Intra-articular zygoapopheseal joint (ZJ) block

• Medial branch (MB) nerve blocks

• Discogram and disc provocation.

Selective Spinal Nerve Block

This is a commonly performed precision injection that utilizes injection of an anesthetic solution near the spinal nerve to block the pain transmission of only one spinal nerve.

Indications Selective spinal nerve blocks are indicated to precisely determine the spinal nerve mostly involved in the patient's pain picture. This information is necessary when multilevel pathology can cause nerve irritation and pain, such as in multilevel foraminal stenosis from diverse causes, or when the clinical picture is only in part radicular and there is a need to distinguish referred pain from joints or disc versus pure radicular pain from spinal nerve involvement. Better surgical outcome may be expected when the painful level and structure are identified.

Procedure The nerve block is being achieved by placing the needle tip in proximity to the spinal nerve dorsal root ganglion (DRG) or just distal to the external opening of the intervertebral foramen at the nerve sleeve level. The nerve or DRG should be blocked by no more than one-half milliliter (mL) of anesthetic so that no spillover into the epidural space should occur. This prevents blocking of multiple nerve roots, which would defeat the selectivity of the diagnostic block. Injecting nonionic contrast before the injection of the anesthetic block is useful for documentation of the needle tip position in relationship to the spinal nerve sleeve and epidural space, to exclude intravascular placement, and to determine the optimal volume of anesthetic required to cover the desired spinal nerve DRG or root. After the block, the patient is instructed to fill out a temporal pain diagram.

Back Pain Revealed

Back Pain Revealed

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