Failed Back Surgery Syndrome
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Failed Back Surgery Syndrome (FBSS) is the presence of persistent, severe pain in the lower back, hip and leg of a patient who has undergone previous spine surgery. Some degree of FBSS is found in approximately 15% of such patients. Patients with this condition typically have multiple sites of pain and the exact source of the pain generator may be difficult to identify. Both somatic (nociceptive) and neuropathic pain components can be identified in these patients.
Somatic pain is due to the normal function of pain-sensitive peripheral neurons, and is typically a response to tissue injury. Neuropathic pain is due to abnormal function of the nervous system and is characterized by burning pain accompanied by tingling and other annoying paresthesias. In the patient with a "failed back" there may be an additional element of pain that is not directly related to tissue damage, but rather to a change in the state of the nervous system. In animal models in which nociceptive stimuli are applied continuously, the neuron firing threshold decreases and signal frequency increases. This suggests a mechanism for why the pain threshold may be decreased when tissue injury is chronic.
Etiology of Pain in FBSS
There are typically two components to the syndrome: 1) low back pain that is worsened with activity and movement, and 2) radiating leg pain that may be accompanied by neurologic changes. We consider these symptoms as separate entities with different causes. Low back pain may be caused by structural changes to the spine following surgery. Stresses may be redirected laterally into the facet and sacroiliac joints. Arthritis in these areas may cause radicular symptoms into the buttocks and legs and it is important to differentiate these symptoms from true radiculopathy produced from nerve root irritation. Other causes of low back pain include muscle spasm, discogenic pain and paraspinous muscle atrophy caused by injury to the dorsal ramus during the operative procedure.
The second chief complaint in FBSS is radicular symptoms. Patients may complain of pain, or may also describe neurologic symptoms such as tingling, weakness or numbness. As opposed to the pseudo-radicular symptoms with facet or SI joint disease, these symptoms usually carry all the way to the foot. Causes of radicular symptoms include recurrent disc prolapse, post-operative epidural scarring and fibrosis, and arachnoiditis. Differentiation of the precise etiology is important since re-operation may be appropriate in selected cases. In a patient with epidural scarring the dura and nerve roots are bound by post-surgical fibrosis, with resultant traction on the nerve roots and dura, and resultant inflammation.
Treatment
Usually, surgery is indicated only for defined nerve root compression or recurrent disc prolapse. Further surgery on an exploratory basis in a patient with FBSS is not warranted. This emphasizes the importance of accurately localizing and identifying the etiology of the patient's symptoms.
Spinal injections may be appropriate for diagnostic and therapeutic indications. If epidural medications are thought appropriate, the lumbar approach is not used due to the presence of scar tissue and disruption of normal anatomy. An epidural catheter is placed through the sacral hiatus and advanced with radiologic guidance to the level of surgery. Contrast medium may be injected to delineate the extent and location of fibrosis. Medications injected include steroids, local anesthetics and hyaluronidase. (an enzyme that disrupts epidural scar tissue.)
Injection therapy may be particularly helpful for the patient with low back pain following surgery. Most of these patients have arthropathy in the facet joints or the sacroiliac joints. A careful history and physical examination usually can identify the source of pain. Injections of these areas are always done with fluoroscopic guidance in order to ensure proper placement of medications. After receiving the injections, patients are asked to reproduce maneuvers that cause pain and the success of the blocks usually can be determined at this point.
For many patients, oral medications may provide the mainstay of their therapy. Prior to prescribing these medications, it is helpful to define the precise neuropathic and somatic contribution to the pain syndrome. Different types of medications are used depending on the type of pain being treated. If side-effects can be avoided, anti-inflammatory medications usually provide significant relief. For a small set of patients, chronic opioid therapy may be useful, but these patients need to be monitored closely for dependence, tolerance and side effects. Still, this is a useful class of medications that can significantly decrease a patient's pain level and improve functional ability.
Neuropathic pain is much more difficult to treat. Neurontin has recently been approved by the FDA for treatment of seizures, but has shown great effect for certain neuropathies. Other medications used include the tricyclic anti-depressants and clonidine.
Physical therapy is an important component in the rehabilitation of these patients. Pain and deconditioning lead to a progressively downward cycle of further impairment and disability. Breaking this chronic pain cycle improves outcome and may provide faster rehabilitation.
Psychological support is an important component during treatment. Chronic pain is a well-defined source of stress, anxiety and depression. For serious disruptions of personal or professional lives, psychologic support is appropriate.
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