Failed Back Surgery

Etiology of failed back surgery syndrome

Patient factors

• Psychological- anxiety, depression, poor coping strategies
• Social- litigation, worker compensation

Surgical factors

• Poor technique
• Incorrect level of surgery
• Revision surgery
• Poor candidate selection

Post operative factors

• Progressive disease (recurrent disc herniation, spondylolisthesis)
• Epidural fibrosis
• Surgical complications (nerve injury, infection, hematoma)
• Myofascial pain development

Assessment of patients with FBSS

Detailed history from the patient is important, with focus on pain characteristics. It is useful to determine whether the pain is predominantly in the lower back (axial) or the leg (radicular). If the pain is mainly radicular, it is more likely to be due to inadequate decompression, foraminal stenosis, epidural fibrosis, or recurrent disc herniation or residual disc fragments. Leg pain,different in character and appearing shortly after surgery, is more suggestive of an iatrogenic cause, such as a pedicle screw compressing an exiting nerve root.

Pain that is predominantly in the lower back is more suggestive of facet joint, sacroiliac joint, myofascial, or discogenic causes.

Red flags should be identified, if present. Other causes of back pain including pelvic inflammatory disease and abdominal causes should be ruled out. ‘Yellow flags’ (significant psychosocial stressors) are now known to play an important role in patients with FBSS. Specific inquiry should be made into the possibility of anxiety, depression, active or passive coping mechanisms, ongoing litigation, and worker’s compensation.

Investigations

The choice of investigations is dictated to an extent by findings on history and examination. Laboratory tests measuring markers of infection (white cell count, ESR, C reactive protein) are indicated in the presence of systemic symptoms. Plain radiographs including flexion/extension view may show the presence of instability, pars defect, and deformity. Plain radiographs may detect spondylolisthesis on flexion–extension views that may not be apparent on MRI scans. However, plain radiographs will miss spinal stenosis and will not give any information to the clinician on soft
tissue conditions including neural impingement.

MRI provides very useful information in investigating the cause of symptoms. Gadolinium-enhanced MRI helps with the differentiation of scar tissue (postoperative epidural fibrosis) from recurrent or residual disc herniation. The formation of fibrosis and adhesions within the epidural space is a normal response to spine surgery and will be observed on MRI in the majority of postoperative patients. However the severity of scar tissue correlates with recurrent radicular and activity-related pain. Nerve root enhancement on postoperative MRI correlates with recurrent or residual symptoms. MRI may also reveal stenosis in the lateral recess and neural foramen, discitis, and pseudomeningocele. The presence of gadolinium enhancement in the intervertebral disc and vertebral bodies may indicate presence of postoperative infection.

MRI is contraindicated in patients with pacemakers and cerebral aneurysm clips. Furthermore, the presence of metal instrumentation or hardware from previous spinal surgery can produce significant artifact on scanning. In these cases, CT scanning or a CT myelogram is recommended. CT with myelography is useful in demonstrating compression of neural structures by bony elements.

Specialized interventional diagnostic investigations

Lumbar medial branch blocks

Predominantly axial lumbar spine pain may arise from the lumbar facet joints. The medial branches of the lumbar dorsal rami supply the articular branches of the facet joints. Lumbar medial branch blocks performed under fluoroscopic guidance are target-specific and valid for diagnosing facet joint pain.

Sacroiliac joint injections

The sacroiliac joint may be susceptible to altered biomechanics following lumbar spine operations producing persistent low back pain. The diagnosis of sacroiliac pain is made by performing controlled sacroiliac joint blockade.

Selective nerve root blocks

For predominantly radicular pain, the transforaminal injection of local anesthetic and corticosteroids may greatly assist in diagnosing a specific spinal level as the source of pain and provides possibility of long-lasting analgesia. Compared with interlaminar or caudal routes, the nerve root blocks have the added advantage of delivering the drug in maximal concentration closer to the suspected site of pathology. These injections must be performed under imaging guidance to ensure accurate level and placement of medication and to avoid inadvertent intravascular or intrathecal injection. The response to transforaminal epidural steroid injections may also help determine whether surgery might be beneficial for pain associated with a herniated disc.

Management of FBSS

Pharmacological

While prescribed to reduce pain, medications should facilitate exercise therapy and enable improvements in functional status. Antineuropathic agents such as the gabapentinoids are frequently prescribed if there is a radicular or neuropathic component to chronic pain.

Exercise Therapy

FBSS causes muscle deconditioning, leading to weakness of the musculature (e.g., transverses abdominis, paraspinal muscles) responsible for maintaining spinal stability. Though different approaches exist, the general aim of exercise therapy is to decrease pain, improve posture, stabilize the hypermobile segments, improve fitness, and reduce mechanical stress on spinal structures. An additional benefit is that patients are taught active coping mechanisms with pain, giving them a sense of control over their predicament. Exercise programmes that are individualised and supervised and composed of stretching and strengthening are associated with superior outcomes. More recent evidence suggests benefits of core muscle strengthening to improve stability of the spine and reduce pain.

Cognitive and behavioural therapy (CBT)

Considering the influence of psychological factors on chronic low back pain, it is not surprising that psychological therapy is an important component of treatment for failed back surgery syndrome. CBT is broadly defined as interventions that apply psychological principles to change the overt behavior, thoughts, or feelings of persons with chronic pain to help them experience less distress and enjoy more satisfying and productive daily lives. The common components of CBT include teaching and maintenance of relaxation skills, behavioural activation such as goal setting and pacing strategies, interventions to change perception such as visual imagery, desensitization, or hypnosis, and promotion of self-management perspective.

Interventional Management Options

Medial branch blocks and radio frequency denervation

In chronic low back pain, pain may originate from the facet joints. Reliable diagnosis may be drawn from the response to medial branch blocks with local anaesthetic. Radio frequency denervation may produce more sustained analgesia.

Epidural injections

Epidural steroids are effective for epidural fibrosis, disc disruption, disc herniation, and spinal stenosis and hence may address several of the pathologies associated with the development of FBSS.

Spinal cord stimulator

Spinal cord stimulator involves the placement of electrodes in the epidural space and production of an electrical current by means of a pulse generator, which is buried subcutaneously. The analgesia produced by SCS is believed to work by the gate control mechanism and modulation of excitatory and inhibitory neurotransmitter release in the dorsal horn.