The process of patient selection involves identification and exclusion of patients who would be unlikely to ben-
efit from the IDET procedure. Patients with mild to moderate degenerative disc disease, absent radicular symptoms, and a positive disco-gram are the best candidates for IDET. Patients with discogenic pain following previous discectomy may also be good candidates. Patients with severe radicular symptoms due to a frankly herniated disc are not candidates for the procedure. Careful patient evaluation allows for appropriate exclusion of patients with multifactorial back complaints who would be unlikely to benefit from IDET. The inclusion criteria for IDET include function-limiting low back pain of at least 3-6 mo duration, lack of satisfactory improvement with a comprehensive nonoperative care program, a normal neurological examination, negative straight leg raise maneuver, magnetic resonance imaging (MRI) without neural compressive lesion, and concordant pain on a provocative discogram.
The findings of disc desiccation and the presence of a high-intensity zone have been shown to have a high correlation with an annular tear in most patients (25,26) (Fig. 4). The high-intensity zone is, however, present in only
20-30% of patients with annular tears; therefore, discog-raphy is an essential diagnostic criterion (Fig. 5). Patients may have a painful annular tear without concomitant MRI findings. Disc bulging is always associated with annular degeneration and fissures; however, the presence of disc bulging does not necessarily produce clinically significant discogenic pain (27) (Fig. 6). Discography is performed at all abnormal and possibly symptomatic disc levels demonstrated on MRI as well as at a normal MRI disc control level. Multiple regression analyses have established that radial fissures are not a feature of degeneration and that degenerative changes do not correlate with pain, but that radial fissures correlate strongly with the reproduction of pain when the disc is stressed during discography (28). If concordant pain, that is, pain representing the patient's typical symptoms, is reproduced at discography, the patient is a candidate for the IDET procedure. If the pain at discography is not concordant, the IDET procedure is not offered. The patient is usually then further counseled on what to expect from the IDET procedure and the postprocedural course. The IDET procedure may then be performed, at least 1 wk following discography. The physiologic rationale for the delay is that the liquid contrast within the disc could potentially cool the IDET catheter and prevent the even distribution of thermal energy into the posterior annular wall. Patients who usually respond most favorably are young, nonsmok-ers, highly motivated individuals, and those who have an annular tear.
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