A difficult diagnostic problem from the clinical and radiographic viewpoints is the evaluation of a patient with symptoms following spinal surgery. The causative factors accounting for the failed back surgery syndrome include recurrent disc herniation (12%-16%), lateral (58%) or central (7%-14%) spinal stenosis, arachnoiditis (6%-16%) and epidural fibrosis (6%-8%). Less frequent causes include meningocele formation, mechanical instability, nerve injury, and wrong-level surgery. In regard to chiropractic treatment, many patients will benefit from our care; however, it is only prudent to evaluate the cause of the patient's symptoms before performing any aggressive manipulation. This advice particularly holds true if instability or nerve injury is present; a recurrent disc herniation may also become aggravated by rotatory type manipulation.
In evaluating the postoperative patient, plain radiographs are generally not helpful since they only demonstrate the osseous postoperative changes and disc narrowing or fusion masses. The vertebral canal and soft tissues are not seen on plain radiographs. High-resolution computed tomography (CT) will demonstrate the osseous and some of the soft tissues of the vertebral canal; however with CT it is often impossible to differentiate a recurrent disc herniation from postoperative scar. Magnetic resonance (MR) when not enhanced by contrast agents is slightly better at differentiating scar from recurrent disc material. Presently, the best technique for evaluating the postoperative patient is using enhanced MR studies. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) is a paramagnetic contrast agent used in magnetic resonance imaging (MRI). Gd-DTPA will help differentiate epidural fibrosis from recurrent or persistent disc herniation. Basically, the procedure for a contrast MR is first to perform an unenhanced MR scan of the region of interest, followed by a Gd-DTPA-enhanced MR scan of the same region. Please note the Gd-DTPA is an intravenous injection and is not generally associated with any side effects as with a myelogram where the contrast material is injected into the subarachnoid space in the vertebral canal. In general, the epidural scar will be enhanced (brighten) on the Gd-DTPA MR scan and the recurrent disc will not, as scar tissue is more vascular than the disc, which is generally devoid of vascularity. Generally, Gd-DTPA-enhanced MR studies are very helpful when assessing the postoperative patient with the exception of mechanical instability.
In regard to mechanical instability, plain film motion studies may be helpful. However, if there is a question of a non-union at the fusion mass a bone scan will often answer the question. Minimal mechanical instability may respond to conservative treatment, but if there is frank luxation of a region over 5 mm or a pseudo- arthrosis present, surgical consultation is advisable. The consequences of manipulating a region that is unstable could be nerve or cord injury.
In regard to nerve damage, one of the more sensitive tests that can be performed is a somatosensory evoked potential (SSEP). The test is not uncomfortable to the patient and can assess the patency of the nerve, centrally and peripherally. If there are abnormal reflexes in a postoperative patient and associated sensory and motor deficits, nerve damage should be ruled out. In summary, there are a few reasonable tools that we can use to prevent further injury to the patient and also help avoid any issue that might involve malpractice.
To simplify the possibly confusing options that we have just discussed, all one needs to remember is: to perform a GD-DPTA enhanced MR study to rule out recurrent disc from postoperative scar or to assess soft tissue stenosis; a CT study to evaluate osseous stenosis; motion plain radiographs and/or bone scan to assess mechanical instability; and SSEP study to assess nerve damage.
Deborah Pate, D.C., D.A.C.B.R.
San Diego, California
Editor's Note:
Dr. Pate's book, Case Studies in Chiropractic Radiology is now available through MPI's Preferred Reading and Viewing list. Please see page xx, Part #T123 for further information on how to order your copy.
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