Study Design. A descriptive case review.
Objectives. To assess the outcomes of anterior lumbar interbody fusion for painful discs within a solid posterolateral spinal fusion.
Summary of Background Data. Some patients continue to have pain after posterolateral spinal fusion despite apparently solid arthrodesis. One potential etiology is pain that arises from a disc within the fused levels.
Method. Retrospective review of 176 patients with anterior interbody fusion, which located 20 who had anterior interbody fusion levels of prior posterolateral spinal fusion. All had low back pain, solid posterolateral spinal fusion, and painful disc(s) at the posterolateral spinal fusion level(s) but not elsewhere. Pain was measured by the Numerical Rating Scale, function by Oswestry Disability Questionnaire, and patient satisfaction by the North American Spine Society Outcome Questionnaire.
Results. Follow-up data were available for 18 patients (90%). Mean follow-up was 58 months (25 to 102). There were 10 men and 8 women. Mean age was 45 years (26 to 72). Diagnoses were degenerative discs, herniated nucleus pulposus, spondylolisthesis, and spinal stenosis. Eight patients had injuries after the previous posterolateral spinal fusion that precipitated new symptoms. Two patients had one level fusion, 14 had two levels, and 1 each had three and four levels. Four patients had one prior surgery, 5 had two, and 9 had three or more. All patients had solid anterior interbody fusion by radiograph. Mean Numerical Rating Scale improved from 7.9 before surgery to 4.7 after (P < 0.001). Mean Oswestry Disability Questionnaire improved from 56.3 before surgery to 47.9 after (P = 0.04). Of 15 patients unable to work before anterior interbody fusion, 5 returned to work. Sixteen patients (89%) were satisfied with their results.
Conclusion. Low back pain that continues or recurs after apparently solid posterolateral spinal fusion may be caused by painful disc(s) at motion segment(s) within the fusion. A solid posterolateral spinal fusion may not protect the residual disc(s) from injury. Anterior interbody fusion can provide significant improvements in pain and function and a high degree of patient satisfaction in this clinical setting.
Some patients continue to have pain after a posterolateral lumbar fusion (PLF). The potential causes for failed back surgery syndrome in general and continued pain after PLF in particular are well known. 4,7,10,18 Some of the causes for pain after PLF include pseudarthrosis, recurrent or residual disc herniation, residual foraminal stenosis, psychological disorders, neuropathic pain, occult infection, and discogenic pain. 4,12,18,32 In some patients, the cause of the pain can be identified with routine testing, but in others, the diagnosis remains elusive. One of the most difficult diagnostic and therapeutic challenges is continued pain despite a PLF that appears solid, with no readily identifiable structural or psychologic pathology. 12,19,20,33
One explanation for continued pain despite an apparently solid fusion is an occult pseudarthrosis not apparent on plain radiograph or computed tomography (CT) scan. 2,3,13 There is only fair correlation between the appearance of fusion on radiograph or CT scan and the findings at surgical exploration. 2,3,13 Persistent or recurrent pain also may originate from pathology at another motion segment. In some patients, pain may originate from disc(s) within the fused motion segments. 32,33
Many spine specialists agree that discs can cause pain without impinging on neural structures. 6,7,34 Pain is thought to be caused by stimulation of nociceptors in the outer anulus. In painful discs, nociceptors may grow inward to the inner anulus and nucleus. 11,17 Crock 6,7 hypothesized that these nociceptors are activated by mechanical or biochemical stimuli to cause pain. Many surgeons use discography to establish whether a disc is painful, 5–7,27,33,34 but others question whether discography is useful for diagnosis or treatment planning. 25,26
Weatherly et al 33 performed anterior interbody fusion (AIF) to treat painful discs within a solid fusion. However, he reported only five patients and used outcome measures that were not quantified. To evaluate whether AIF is helpful for discogenic pain in the presence of a solid PLF, the current authors reviewed their experience with 18 patients and used established outcome measures.