Microdiscectomy or Open Discectomy?
abstract & commentary
Source: Hermantin FU, et al. A prospective, randomized study comparing the results of open discectomy with those of video-assisted arthroscopic microdiscectomy. J Bone Joint Surg Am 1999;81:958-965.
Sixty patients with single-level lumbosacral intracanalicular disc herniation at L2-3 or lower were prospectively enrolled in this unblinded study comparing open discectomy (n = 30) with video-assisted arthroscopic microdiscectomy (n = 30). Ages ranged from 15 to 67 years, with a mean age of 39.5, and men outnumbered women by 2:1. All patients demonstrated radicular symptoms including a dermatomal pattern of pain consistent with the disc herniation seen on imaging studies, and positive straight-leg raising (Lasegue sign) with or without neurologic deficit. All had failed conservative measures, administered for a minimum of 14 weeks, including rest, nonsteroidal anti-inflammatory medication, physical therapy, exercise, and oral or epidural steroids. None had previous low back surgery and none was involved in litigation or workers’ compensation. Exclusionary criteria included diffuse disc bulging with spinal stenosis, a sequestered herniation, drug dependency, or psychological abnormality. Both open laminotomy and arthroscopic microdiscectomy were performed using standard technique that required an overnight admission for the former but not the latter. Patients were followed for up to 42 months following surgery (mean 31 months) and end points included pre- and post-surgical patient self-evaluation, plus neurological evaluation including use of pain medication and ability to return to work.
Post-operatively, open discectomy patients required intravenous morphine for 24 hours, followed by oral percocet, for a mean of 25 days and at last follow-up, six patients (20%) used occasional codeine for pain control. A mean of 49 days was lost from work in this group. None of the arthroscopic microdiscectomy patients required parenteral medication. The mean use of oral analgesics was only seven days, and a mean of 27 days were lost from work. One open discectomy patient developed a dural leak but neither group developed infection or neurovascular injury. Overall, 28 (93%) of open discectomy and 29 (97%) of microdiscectomy patients had an excellent (painfree, unremarkable examination, return to normal activity) or good outcome (as above with residual back pain modifying occupation). Despite similar outcomes, arthroscopic microdiscectomy patients suffered lower morbidity, required no hospitalization, and returned to work sooner than open discectomy patients. In properly selected patients, arthroscopic microdiscectomy appears to be the treatment of choice for solitary herniated discs of the lumbosacral spine.
Commentary
Why do some patients experience continued pain following disc surgery? Neurology Alert overlooked a paper by Nygaard and colleagues (J Neurol Neurosurg Psychiatry 1998;64:120-123) that discusses this. The recovery of sensory nerve function was examined in 39 patients following microdiscectomy (25 men and 14 women, mean age 38 years) to determine whether this could be predicted preoperatively. All patients satisfied strict criteria for nerve root compression, including typical radicular pain pattern, positive Lasegue sign, unilateral disc herniation on CT or MRI scan, and surgical confirmation of compression. Exclusionary criteria included previous back surgery, diabetes, other neurological disease, and age older than 60 years. All patients underwent clinical evaluation and quantitative sensory testing (QST) comprising cold, warm, and vibratory detection thresholds prior to and at 6 weeks, 4 months, and 12 months following microdiscectomy. A clinical overall score (COS) encompassing maximum pain, clinical symptoms, and signs was tallied (Haaland AK, et al. Spine 1992; 17:1024-1027) and patients were divided into good and poor outcome based on COS less than 250 or COS more than 250, respectively (maximum score = 1000). Twenty healthy volunteers served as controls, and RANOVA and two-tailed tests were used for statistical analysis.
Cold detection threshold improved to normal at 12 months post-operatively, but not at four months, in the good outcome group (P = 0.005), whereas warm detection thresholds improved within six weeks (P = 0.034). No further significant change followed at 12 months. Vibratory threshold improved at 12 months in the good outcome patients but this was not significant. Retrospectively, the poor outcome group preoperatively had significantly higher warm, but not cold or vibratory, detection thresholds. A simple regression analysis demonstrated an association between preoperative warm detection threshold and COS at 12 months (P = 0.031). The varied time course of improvement for cold and warm sensations, transmitted via small myelinated A delta and unmyelinated C fibers, respectively, and the absence of significant improvement for vibratory threshold, transmitted via large myelinated fibers, indicates a range of nerve injury from compression with larger fibers more affected, axonal injury may affect small fibers leading to longer or lesser recovery. Preoperative evidence of C fiber dysfunction is a negative prognostic factor for recovery following surgery and may be responsible for the surgical failures. —mr
Which of the following statements is correct?
a. Microdiscectomy is not as effective for the surgical treatment of well-selected single-level intracanalicular lumbar disc herniation as is open laminectomy.
b. Residual pain following microdiscectomy may be due to injury to unmyelinated C fibers at the nerve root level.
c. Cold detection threshold may have positive predictive value in the surgical treatment of lumbar disc disease.
d. Vibratory detection threshold may have positive predictive value in the surgical treatment of lumbar disc disease.
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