The reported incidence of symptomatic recurrent disc herniation after lumbar discectomy varies between 3% and 18% in retrospective studies.¹⁴ Subjects with larger anular defects and those in whom a smaller proportion of disc volume was removed during the first surgery were associated with an increased risk of symptomatic recurrent disc herniation. Carragee et al. demonstrated that the reherniation rate varied from 1.1% with small fissure-like anular defects to 27.3% for large open anular defects.¹⁵ Recurrent disc herniation or progressive disc space loss after discectomy often leads to increased pain and disability, which necessitates repeat surgery. Revision surgery, however, does not always improve symptoms.¹⁶ The differentiation of a recurrent disc herniation from an epidural scar presents a dilemma. Characteristics associated with recurrent disc herniation include a nonenhanced or rim-enhanced abnormality surrounding a low-signal-intensity lesion on MRI and extension of contrast into the epidural space and an enhancing abnormality on CT/discography.¹⁷ However, the discovery of a focal mass of scar that is obviously compressing a nerve root may still be an indication for surgery. Diffuse epidural scar without nerve root compression, however, is not.

Reoperation for a recurrent lumbar disc herniation often requires lengthening the surgical incision to expose the normal laminae above and below the interspace and freeing of the scar from the previous laminotomy using sharp dissection with a tool such as a sharp curet or a no. 15 knife. A high-speed drill or angled punch is used to obtain further bony decompression and to allow visualization of normal epidural tissue. Residual ligamentum flavum from previous surgery should be removed and the disc space approached from normal epidural tissue rostrally toward the disc space and nerve root. It is important to completely dissect out the nerve root, with good exposure of the axilla of the nerve root and its entire course in the lateral recess. If the dura mater or the nerve root is firmly attached to a recurrent disc fragment, sharp dissection and magnification should be used to free it so that no dural tear occurs during manipulation of the disc fragment. Utmost care should be taken to visualize the paramedian aspect of the disc, which is frequently the site of residual or persistent compressive disc herniations. Exploration, both above and below the disc space, should be carried out to ensure that at the conclusion of the second procedure, no extruded fragment has migrated over the body of the vertebra above or below the disc space. Using a microinstrument, the surgeon should circumferentially feel around the nerve root as it passes through the lateral recess and along its course in the neural foramen. Any dural tears that occur during the dissection should be repaired, if possible, before further dissection is performed. Repairing the dura mater prevents significant CSF fluid loss, with resultant decompression of the dural sac and increased risk of epidural venous bleeding. Primary closure of the dural defect with microsurgical technique or a dural patch graft gives a better result in preventing postoperative CSF leak. If the dura mater cannot be repaired primarily, it can be covered with absorbable gelatin sponge or muscle with fibrin tissue adhesive. A subcutaneous or epidural fat graft covering the dural defect is an effective alternative seal.

Reoperation for Thoracic Disc Herniation

Between 7% and 15% of patients with thoracic disc herniations are asymptomatic; symptomatic herniation is very rare, accounting for only 0.25% to 0.57% of herniated discs in the whole spine. The true incidence for recurrent thoracic disc herniation is not known. An accurate diagnosis may be difficult to determine and therefore may be delayed, resulting in either progressive or occasionally relapsing and remitting neurologic impairment. Reoperation at the thoracic spine level is usually due to persistent or inadequately removed centrally located calcified discs. Thoracotomy for treatment of centrally located recurrent thoracic disc herniations is associated with improvement in or stabilization of myelopathic symptoms in the majority of patients, with an acceptable rate of complications. Modified transfacet pedicle-sparing decompression and fusion is also an alternative. Other indications for reoperation for thoracic disc herniation are missed level at the first operation, missed intradural herniation, and CSF leaks.

Inadequate Decompression of the Nerve Root in Patients with a Large Foraminal Osteophyte

Vertebral osteophytes are a common radiologic finding, affecting 20% to 30% of the elderly population. A number of factors are responsible for the local osteogenesis, notably mechanical factors.

Reoperation for persistent cervical nerve root compression can usually be undertaken via one of several options. In a patient with a previous ventral cervical discectomy and fusion and with a persistent large osteophyte in the neural foramen, correction may be accomplished by performing a simple cervical foraminotomy from a dorsal approach, with or without drilling off the osteophyte. This procedure is probably easier than reoperating from the ventral approach and drilling out the previous fusion and decompressing the foramen. If, however, the osteophyte is ventral and medial in location and cannot be decompressed adequately from a dorsal approach, a reoperation from the ventral approach should be performed. The soft tissue planes may be scarred, but the tissue plane between the carotid sheath and the esophagus and trachea is usually maintained and easily dissected. If the soft tissue scarring is due to previous infection or radiation therapy, the operation may be simplified by operating from the opposite, or virgin, side. An operation being performed from the ventral approach for inadequate neural decompression requires increased bone resection, at least a minicorpectomy, to remove 7 or 8 mm of each vertebral body rostrally and caudally to the disc space and to allow definitive visualization of both nerve roots with magnification. This is often best accomplished by using a high-speed drill and an operating microscope. If the problem is a persistent central osteophyte or ossification of the posterior longitudinal ligament, corpectomy is the safest ventral approach, allowing complete decompression of the spinal cord. The corpectomy is followed by a ventral interbody fusion.

Inadequate Decompression of the Cauda Equina in Spinal Stenosis

Cauda equina syndrome (CES) is a complex of clinical symptoms and signs most commonly secondary to a massive prolapsed intervertebral disc, accounting for 2% to 6% of all lumbar disc herniations. Less common causes of CES are epidural hematoma, infections, primary and metastatic neoplasms, trauma, and prolapse after manipulation, chemonucleolysis, or spinal anesthesia. Meta-analysis of surgically treated CES suggests benefit if decompression is undertaken within 48 hours from symptom onset ¹⁸ in pooled data from retrospective studies. However, not all studies support this argument, which has raised the notion that the principal determinant of outcome may be not timing, but the extent of the neurologic deficit before surgery.¹⁹

Recurrent symptoms of CES occur not only from inadequate previous decompression but also from progression of the disease. The most common radiographic findings are disc herniation and hypertrophic facet arthritis, whereas other features, such as acquired spondylolisthesis, osteophyte formation, stenosis, and scoliosis, are observed less frequently. The pathophysiology remains unclear but may be related to damage to the nerve roots composing the cauda equina from direct mechanical compression and venous congestion or ischemia. A high index of suspicion is necessary in the postoperative spine patient with back or leg pain refractory to analgesia, especially in the setting of urine retention. Regardless of the setting, when CES is diagnosed, the treatment is urgent surgical decompression of the spinal canal.

Recurrence and Inadequate Decompression of the Spinal Cord in Neoplasia

Spinal cord compression from neoplasms is characterized based on location as intramedullary, intradural extramedullary, and extradural. Reoperation represents a viable option in patients with high-grade epidural spinal cord compression who have recurrent metastatic tumors at previously operated spinal levels. In carefully selected patients, reoperation can prolong ambulation and result in good functional and neurologic outcomes. Treatment is palliative, with the goals of achieving pain control and improving or maintaining neurologic function. Reoperation should be considered as a treatment option in patients with tumor recurrences who are no longer candidates for radiotherapy or those who have high-grade spinal cord compression.

A reoperation for persistent spinal cord compression secondary to epidural tumor usually results from a dorsal decompression that was performed on a ventrally or ventrolaterally situated tumor. A different surgical approach, either a lateral extracavitary or a ventral approach, is required for resection of tumor and decompression of the spinal cord, as well as for appropriate stabilization of the spinal column. Reexposure of the dorsal spine may also be necessary for performing dorsal arthrodesis and segmental instrumentation to supplement the ventral arthrodesis.

Reoperation for intramedullary tumors needs a special mention. With advances in microsurgical technology, management of these tumors has shifted toward aggressive treatment with radical resection. This approach is associated with increased long-term survival and improved quality of life for both intramedullary and extramedullary tumors. Spine deformity, a well-documented complication after intradural spinal tumor resection, has been reported in up to 10% of cases in adults and 22% to 100% of cases in children.^20,²¹ Laminoplasty for the resection of intradural spinal tumors is not associated with a decreased incidence of short-term progressive spinal deformity or improved neurologic function. However, laminoplasty may be associated with a reduction in incisional CSF leak.²²

Reoperation for intradural tumors requires exposing the dura mater. Intraoperative real-time ultrasound is extremely helpful for planning the dural opening and its extent. If a previous dural incision with retained suture material is present, the dura mater should be opened above and below the previous dural closure, and a small blunt dissector should be used to free the underlying spinal cord or arachnoid from the dura mater. When the dura mater has been opened a second time, placing a dural patch graft on the closure is usually prudent, both to reduce the chances of the dura mater adhering to the spinal cord and to provide increased room for the spinal cord.

Dissection of recurrent tumor from nerve roots and the spinal cord needs to be accomplished under high magnification. Great care regarding hemostasis is necessary to allow good visualization. Dissection is obtained best by using sharp dissection with two-point microcoagulation. If no neurologic structures are deep to the tumor, a laser may be used. The laser is particularly effective in removing ventrally based dural tumors.

Instability

Extrusion of a bone graft, failure of fusion, the development of instability, or failure of instrumentation is an indication for reoperation.^12,^13,²³^–³⁵

Extrusion of a Bone Graft

Extrusion of a cervical interbody bone graft with persistent pain, cervical deformity, or swallowing difficulty is an indication for reoperation. The graft extrusion is more common in C2-3, C6-7, and C7-T1 levels due to the anatomic variation in the bony spine. The extrusion of a strut graft associated with a corpectomy may have been caused either by a poorly fitting graft or by fracture of the vertebral body into which the graft is fixed. This allows for the caudal portion of the graft to extrude ventrally. The dislocation of the graft may be associated with collapse of the disc spaces, which, in turn, may cause nerve root irritation and pain. Furthermore, the extruded graft may result in adjacent structure compression, causing symptoms such as dysphagia and hoarseness of voice.

The extruded bone fragment is removed, the graft site is freshened, usually by use of a high-speed drill to accomplish good preparation of the end plates, and a new graft is inserted. A ventral plate-and-screw construct provides further assurance of retention of the bone graft. High reoperation rates for extruded grafts and symptomatic pseudarthrosis have been associated with nonplated two-level anterior discectomy and fusion (ADF) and single-level anterior corpectomy with fusion (ACF) procedures. However, comparison of single-level ACF performed with and without plates showed that plating did not appear to reduce pseudarthrosis or graft extrusion rates.³⁶ If the vertebral body is fractured as well, partial corpectomy of the fractured segment must be performed and the graft refitted. This necessitates a longer graft. Ventral plating with screw fixation may add to the stability of the new construct. A supplement to fixation via a dorsal approach should often be considered.

Failure of Fusion

The ultimate goal of spinal hardware is to provide temporary stability allowing for bony fusion, usually requiring 6 to 9 months. Failure of fusion and the development of pseudarthrosis or fibrous union are the sequelae of ongoing low-grade mobility. Pseudarthrosis is defined as an absence of bridging bone between grafted bone and vertebral bodies and the presence of a radiolucent defect, a halo sign, or a loss of grafted bone. Despite advances in the technologies and instrumentation of spine surgery, pseudarthrosis still occurs in 10% to 15% of all patients.³⁷ Pseudarthrosis itself can be a source of pain, or it may provide a lead point for ongoing mobility leading to increased stress on hardware and inevitable failure, one of the indications for reoperation. Revision spinal arthrodesis for pseudarthrosis and loose instrumentation with widely dilated screw tracts is a difficult clinical problem.

The optimal revision strategy in cases of lumbar pseudarthrosis depends on the specific clinical scenario, and multiple techniques have been described. If stable fixation cannot be achieved in these cases, revision fusion may fail, or adjacent normal levels may need to be fused to gain stable fixation. According to the latest Cochrane review,³⁸ pedicle screw instrumentation produces a higher fusion rate, but any improvement in clinical outcome is probably marginal as compared to fusion without instrumentation.

Single-level anterior cervical discectomy and fusion (ACDF) is a highly successful procedure yielding high reported fusion rates, ranging from 83% to 97% for autograft and 82% to 94% for allograft, respectively. However, in multilevel ACDF, as the number of grafts increases, the cervical spine is predisposed to decreased fusion rates as contact stress increases between the graft–body interface, further contributing to unacceptable micromotion. Pseudarthrosis after ACDF has been recognized as a cause of continued cervical pain and unsatisfactory outcomes. Debate continues as to whether a revision ventral approach or a dorsal fusion procedure is the best treatment for symptomatic cervical pseudarthrosis. Patients with symptomatic cervical pseudarthrosis that develops after ACDF may be managed successfully with dorsal lateral mass screw fixation and fusion. The rationale for the dorsal approach includes the advantages of avoiding the scar tissue and potentially difficult tissue planes encountered in a revision ventral approach, as well as encountering a fresh fusion bed when a dorsal approach is used. Contraindications to the dorsal approach include those problems that can only be addressed through a ventral approach, such as graft migration or kyphosis. Advocates for a revision ventral approach suggest that patients experience more stiffness and pain after a dorsal approach secondary to disruption of the dorsal musculature.³⁹

Since it became clinically available in 2002, bone morphogenetic protein (BMP) has been widely used as an adjunct to promote fusion in lumbar spine surgery, especially in the setting of established pseudarthrosis or a limited availability of autograft. Use of BMP has demonstrated comparable fusion rates and clinical outcomes while avoiding iliac graft harvest site morbidity when compared with iliac bone graft in both interbody and dorsolateral fusions in prospective, randomized clinical studies.

Development of Instability

Kyphosis may develop in up to 21% of patients who have undergone laminectomy for cervical spondylotic myelopathy. Progression of the deformity appears to be more than twice as likely if preoperative radiologic studies demonstrate a straight spine. The incidence of progressive deformity and instability after cervical laminectomy was highest in the pediatric population and in those with a malignant intramedullary lesion, adjuvant radiotherapy, or preoperative findings of kyphosis or instability. Other intraoperative factors, including resection of the C2 lamina, multilevel laminectomies (>3 levels removed), and removal of greater than 25% of the facet joint, have also been correlated with an increased risk for subsequent development of deformity, instability, and neurologic sequelae. Although cervical laminoplasty has been proposed to reduce the risk of postsurgical deformity, recent reports suggest no significant reduction in the incidence of spine deformity, especially in the setting of intradural spinal tumor resection.^22,⁴⁰

Late failures in lumbar spinal stenosis may be due to persistent or acquired instability, recurrence of stenosis at operated levels, new stenosis at adjacent levels, epidural fibrosis, or arachnoiditis. Degenerative discogenic pain and reports of narrowing of the intervertebral disc space, reactive changes in adjacent vertebral bodies, vacuum disc phenomenon, spondylolisthesis (ventral or dorsal), and abnormal motion of 3 mm or more on flexion-extension radiographs are all indicative of lumbar instability.⁴¹ The development of postoperative intraspinal facet cysts has been related to the presence of postoperative segmental spinal instability, including a progression of spondylolisthesis and disc degeneration. Pedicle screw fixation fusion with interbody fusion gives better results in postoperative spinal instability. Dorsal closing wedge osteotomy is suitable to treat kyphosis of less than 40 degrees. Ventral release and dorsal spinal osteotomy is effective, especially in patients with severe kyphotic deformity or with previous surgery.

Failure of Instrumentation

Assessment of spinal hardware often involves a multimodality approach, including nuclear medicine, CT, and MRI, but plain radiographs are an essential component that can provide information other modalities cannot. Changes in component position, bony alignment, hardware fractures, and changes in the implant–bone interface (e.g., screw loosening with haloing) can be first identified and sometimes best appreciated on serial radiographs.⁴² Hardware fracture generally occurs secondary to metal fatigue from repetitive stress. The presence of a fracture is frequently associated with regional motion and instability, which may lead to or result from pseudarthrosis.⁴³ Hardware failure includes hardware fracture, loosening of the screws, and screw pullout leading to junctional failure. Hardware loosening can be caused by osseous resorption surrounding screws and implants. Loosening in turn allows for movement, which causes further osseous resorption, increased mobility, and eventually catastrophic screw pullout or vertebral fractures.^44,⁴⁵ Serial radiographs, starting from the earliest postoperative study, should be evaluated for any evidence of hardware migration or fracture. Identification of a change in sagittal or coronal balance is often a valuable initial step. Set-screw loosening, rod fatigue bending without frank fracture, and sacral screw subsidence are subtle abnormalities that should also be carefully examined in patients with late postoperative loss of sagittal alignment.⁴⁶

A review of the literature noted a 28.1% to 39.9% rate of pedicle screw malposition in clinical studies and a 5.5% to 31.3% malposition rate in cadaver studies. However, meta-analysis shows that only 0.6% to 4.3% of patients need reoperations for device malposition.⁴⁷ The percentage of malpositioned screws may be higher when normal anatomic landmarks have been obscured, as with revision surgery in the setting of a dorsolateral fusion.⁴⁸ Minor violations of the cortex are not uncommon and may be asymptomatic. In these cases, the screw position may be acceptable. Screw malposition with related clinical symptoms needs revision surgery. Pedicle screw loosening has been recorded as being caused mainly by cyclic caudocephalad toggling at the bone–screw interface. To prevent pedicle screw loosening, a meticulous screw insertion technique to prohibit the toggling effect that could be occurring during screw insertion is needed. On reoperation, a larger-diameter screw or augmentation with polymethylmethylacrylate (PMMA) gives a better result.

Reoperation to remove instrumentation that has either failed or has eroded through the skin requires full exposure of the instrumentation and construct, with care taken to not create fracture of the bone grafts or vertebral column when removing the implant. Large metal shears and rod cutters may create enough torque to actually fracture the dorsal elements of the vertebra and should be used with great caution. A high-speed carbide bur may be used to cut the rods, but all exposed soft tissue should be covered to prevent the small metal filings from being spread throughout the wound. Otherwise, these filings cause a great deal of artifactual change on future imaging studies.

Cerebrospinal Fluid Leak

CSF leakage may occur at the dural suture line postoperatively or may be caused by inadvertent dural tears during extradural spinal approaches for disc surgery or decompressive laminectomy. Prior surgery, with subsequent development of scar tissue, altered anatomy, poor dissection planes, and adherence of tissue to the dura, all have been demonstrated to increase the risk of incidental durotomy. Possible sequelae of incidental durotomy include the formation of a pseudomeningocele, a CSF cutaneous fistula, arachnoiditis, meningitis, epidural abscess, or deterioration in neurologic status. A persistent CSF leak may result in a chronic pain disorder associated with radiculopathy or postural headaches. A CSF leak also predisposes the patient to poor wound healing and possible wound dehiscence.

Reoperation for CSF leak requires adequate exposure of the dural defect, which may require further bone removal. Primary closure is attempted whenever possible. A patch of autologous fascia or artificial dura material with fibrin tissue adhesive is useful if primary closure is not possible.⁴⁹^–⁵¹ Black⁵² used a large sheet of fat to cover not only the dural tears but also all of the exposed dura with good results. A randomized, controlled trial concluded that the PEG hydrogel spinal sealant (DuraSeal) is safe and effective for providing watertight closure when used as an adjunct to sutured dural repair during spinal surgery.⁵³ Placement of a CSF drain for 5 days may be used for dural repair if primary dural closure fails. Good muscle and fascia closure will prevent dead space and prevent CSF collection and postoperative pseudomeningocele. In recurrent CSF leak, myocutaneous muscle flaps can be considered an option with good results.

Infection

Surgical site infection in the setting of spine fusion is associated with significant morbidity and medical resource utilization. The reported rate of spinal surgical site infection in the literature ranges from 0.7% to 16 %.^54,⁵⁵ Risk factors include smoking, diabetes, prolonged operative time, large-volume blood loss, previous surgery, use of nonautograft bone graft alternatives, and number of levels affected. Spinal surgical site infections can be challenging to manage and often require prolonged hospitalizations, extended antibiotic therapy, repeated surgery for wound debridement, instrumentation removal, or delayed complications of deep infection. It is often difficult to diagnose postoperative spine infection before clinical symptoms become apparent. In the early stages, plain film radiography is often normal. In this setting, nuclear scintigraphy with either gallium-labeled bone scan or indium-111-labeled white blood cells or MRI can be useful. MRI can help to diagnose the soft tissue change but is expensive to use as a screening tool. Although inflammatory markers, such as C-reactive protein (CRP), white blood cell count, erythrocyte sedimentation rate, and body temperature are easily measured, their specificities are not high. Elevated serum procalcitonin levels of greater than 0.5 ng/mL may serve as a useful tool for evaluating fevers of unknown origin after spine surgery.⁵⁶

Reoperation for wound infection is best handled by reopening the complete length of the incision to the depth of infectious involvement. After all suture material is removed, along with any dead tissue, the wound is debrided to bleeding tissue. The wound should then be irrigated thoroughly with antibiotic solution. If the infection is superficial, the wound is closed in layers, and the patient is given appropriate intravenous antibiotics to which the organism is susceptible. For deep infections and for infections in the presence of instrumentation or bone grafts, a similar procedure is carried out, or staged closure with wound vacuum is helpful. If osteomyelitis or discitis is present, debridement of the involved bone and disc is performed via a retroperitoneal or dorsal-only approach in the lumbar spine, a lateral extracavitary approach in the thoracic spine, and a ventral or dorsal approach in the cervical spine. A fresh autologous cortical bone graft is inserted for ventral stabilization. Unlike in joint arthroplasty, hardware removal is not mandatory to eradicate most infections, although removal of the hardware may be indicated in certain cases in which medical treatment has failed, especially if the infection is delayed and fusion is solid.^42,⁵⁷ The antibiotics are usually continued for 6 weeks or even longer if the CRP level has not returned to normal by that time.