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SEGMENTAL INSTABILITY AFTER APPARENT SOLID INSTRUMENTED ARTHRODESIS: A CASE REPORT John S. Toohey, M.D. Introduction: Spondylolysis was originally reported in 1854 by Kilian. There are several proposed etiologies of defects in the pars interarticularis. It is unusual to have two adjacent levels of pars interarticularis defects. When conservative measures fail, appropriate treatment would include instrumented posterolateral fusion. Patients generally recover uneventfully and if hardware is symptomatic, it may be removed. While x-ray studies are helpful, the gold standard for determination of a solid posterolateral arthrodesis is exploration of the fusion1, 2, 3. We report on a case of an instrumented posterolateral arthrodesis for two-level spondylolysis, which developed segmental instability following hardware removal and fusion exploration. Case Report: A 40-year-old male presented with lower back pain. X-rays demonstrated bilateral pars interarticularis defects at L3-4 and L4-5 (Figure 1). After multiple attempts at conservative treatment, the patient was offered an instrumented fusion. Two years later, the patient developed recurrent pain, which was thought secondary to the hardware. His pain was improved with local injection. The patient underwent removal of the hardware with exploration of the fusion. The fusion was thought to be solid. Figure 2 shows films taken before the surgical procedure. There appears to be a solid posterolateral arthrodesis. At the time of surgery, the patient was felt to have a solid arthrodesis. The patient recovered and did not return until nearly three years later, when he presented complaining of lower back pain. Flexion and extension x-rays were obtained (Figure 3), demonstrating significant instability at L4-5. Discussion: It is often very difficult to determine whether a fusion is successful by radiographic studies alone. The majority of evidence for this phenomenon comes from the scoliosis literature2. The fusion of facet joints and incorporation of bone into the posterolateral intertransverse processes can be inferred from routine x-rays. CT scans with sagittal reconstruction are often helpful2, 4, 5, 6. However, the gold standard often remains surgical exploration. In spite of studies and a surgical exploration, which found a "solid arthrodesis", this patient clearly had an incomplete fusion with development of segmental instability. Bibliography: 1. Brodsky, A. E., Hendrick, R. L., Khalil, M. A., et al.: Segmental ("floating") lumbar spine fusions. Spine, 14:447-450, 1989. 2. Laasonen, E. M. and Soini, J.: Low-back pain after lumbar fusion: Surgical and computed tomographic analysis. Spine 14:210-213, 1989. 3. Lang, P., Chafetz, N., Genant, H. K., and Morris, J. J.: Lumbar spinal fusion: Assessment of functional stability with magnetic resonance imaging. Spine 15:581-588,1990. 4. Lang, P., Genant, H. K., Chafetz, N., et al.: Three-dimensional computed tomography and multiplanar reformations in the assessment of pseudarthrosis in posterior lumbar fusion patients. Spine 13: 69-75, 1988. 5. Silzofski, W. J., Collier, B. D., Flatley, T. J., et al.: Painful pseudarthrosis following lumbar spinal fusion. Detection by combined SPECT and planar bone scintigraphy. Skeletal Radiol. 16:136-141, 1987. 6. Zinreich, S. J., Long, D. M. Davis, R., et al.: Three-dimensional CT imaging in postsurgical "failed back" syndrome. J. Comput. Assis. Tomogr. 14:574-580, 1990. Back to Papers and Presentations |
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