Spinal Instability and Spinal Fusion Surgery Treatment & Management

Indications for spinal fusion

Acute overt instability

Conditions that result in acute overt instability require stabilization, either internally (by fusion) or externally (by reduction and bracing). In traumatic injuries, if instability is due to a fracture rather than ligamentous rupture, if the fracture fragments are (or can be reduced to be) in contact and in near-anatomic alignment, and if there is no significant neural compression, an external brace (eg, halo, collar, or thoracolumbosacral orthosis [TLSO] brace) is tried until the fracture heals. In all other circumstances and in cases where bracing has failed, fusion is indicated.

Tables 2 and 3 summarize treatment algorithms and indication for fusion in cervical, thoracic, and lumbar spine trauma.

Table 2. Treatment of Traumatic Instability of Cervical Spine (Open Table in a new window)

Table 3. Treatment of Traumatic Instability of Thoracic and Lumbar Spine (Open Table in a new window)

When overt instability is produced by a tumor, indications for surgery depend on the patient's life expectancy, physical condition, extent of cord compression, responsiveness to radiation and chemotherapy, number of motion segments involved by tumor, and severity of pain. The ideal candidate for decompression and fusion is a patient with limited systemic and spinal neoplastic disease who presents with an acute pathologic fracture with incomplete cord compromise.

Infections of the spine, if discovered early, may produce no neural compromise or instability and may be treated by antibiotics alone. However, advanced infections of the disks and vertebral bodies are highly destructive and destabilizing, requiring debridement/decompression and fusion, either simultaneously or in separate sessions.

Chronic overt instability

Chronic overt instability is initially managed conservatively (eg, with analgesics, anti-inflammatory drugs, physical therapy, or bracing). If and when the patient fails to respond to conservative management or if significant neurologic compromise exists, fusion is indicated.

Anticipated instability

Surgical removal of two columns of the spine (or removal of one column when another is known to be deficient), radical removal of one facet joint (see the image below), or partial substantial removal of both facet joints in one motion segment would be expected to produce instability. In these cases, it is prudent to consider fusion at the time of the original surgery.

Covert instability

Like chronic overt instability, covert instability is initially managed conservatively, but with a much higher threshold for abandoning conservative treatment in favor of fusion.

Isolated spondylolysis without spondylolisthesis and spondylolisthesis without dynamic instability are typically treated conservatively with physical therapy and epidural steroid injections for at least 3-6 months. If back pain exists without radicular symptoms, greater effort is made to avoid surgery. The patient must quit smoking and demonstrate the ability to limit the intake of narcotics. With appropriate patient selection, good results can be achieved with fusion when conservative treatment has failed.

In symptomatic spinal stenosis without spondylolisthesis, decompression alone is the treatment of choice, but in spinal stenosis with degenerative spondylolisthesis of significance, fusion improves outcome. ^{[20, 40]}

Much more controversial is the treatment of that subcategory of covert instability that is known as microinstability or dysfunctional motion segment. Here, an abnormal disk or facet joint is presumed to be the pain generator. Provocative diskography and facet injections are often used in this setting to "locate" the pain generator. The idea is that fusion, by eliminating motion across the dysfunctional motion segment, may alleviate the pain.

This controversy and the relevant recommendations of the American Association of Neurological Surgeons (AANS)/Congress of Neurological Surgeons (CNS) Joint Section on Disorders of Spine and Peripheral Nerves are explored in greater detail elsewhere (see Prognosis).

Contraindications for spinal fusion

Absolute contraindications for fusion are relatively uncommon and include the following:

• Diffuse multilevel neoplastic disease such that no adjacent normal segments exist for engagement of instrumentation
• Severe osteoporosis such that the bones would not support instrumentation and fusion would not be expected to solidify in absence of instrumentation
• Infection of soft tissues adjacent to spine or epidural infection that has not spread to the vertebral bones or disks, in which case the fusion construct would be at risk for infection (see below for established diskitis/osteomyelitis)

Relative contraindications for spinal fusion include the following:

• Osteoporosis
• Smoking
• Malnutrition
• Systemic infection
• Anemia
• Chronic hypoxemia
• Severe cardiopulmonary disease
• Severe  depression, psychosocial issues, and secondary gain issues

As always, the contraindications for surgery have to be weighed against the risks of not performing the operation in each particular situation. For instance, smoking and severe depression may be contraindications for fusion in a patient with back pain and disk degeneration but should not deter the surgeon from fusing an unstable cervical spine fracture.

It is important to note that an active spine infection (diskitis/osteomyelitis) does not necessarily constitute a contraindication for fusion and instrumentation. To the contrary, advanced spine infections exert severe destabilizing effects on the spine, often necessitating stabilization at the time of debridement and decompression.

In this setting, careful clinical, laboratory, and radiographic follow-up are essential as the patient receives prolonged intravenous (IV) antibiotic treatment (for ≥6 weeks) to confirm eradication of the infection. Worsening pain or neurologic deficit, persistent fever, leukocytosis, or bacteremia and persistently elevated erythrocyte sedimentation rate (ESR) signal the possibility of persistent infection.

Similarly, evidence of loosening of screws on radiography (see the first image below) or evidence of increased bone destruction on computed tomography (CT) or magnetic resonance imaging (MRI) should be further investigated. However, persistent and stable vertebral enhancement on MRI (see the second image below) does not necessarily indicate persistent infection; this finding can lag behind microbiologic cure.

Radionuclide bone scanning lacks specificity in this setting, but a tagged white blood cell (WBC) scan may be more useful. If there is doubt, CT-guided biopsy/aspiration of the region can help confirm the possibility of persistent infection, which would then be treated with reoperation.

In acute overt instability, stabilization of the spine is required in all cases. In this context, medical treatment refers to the use of external bracing for spine stabilization. If instability is due to an osseous fracture, if the fracture fragments can be reduced to near-anatomic alignment, and if there is no significant neural compression after reduction, the patient may be treated nonsurgically with a brace until the fracture heals.

In anticipated instability (eg, extensive diskitis and osteomyelitis treated with debridement, decompression and antibiotics), bracing may be used as a temporary means of stabilization, before fusion is undertaken or until spontaneous fusion occurs.

Many forms of external orthoses and braces are available. In the cervical spine, a halo offers the greatest amount of stabilization. Rigid cervical collars (eg, the Philadelphia collar and the Miami collar) and various cervicothoracic orthoses provide intermediate amounts of stabilization, whereas soft collars provide little stabilizing benefit. For the thoracic and lumbar spine, the only brace that provides significant stabilizing benefit is a rigid TLSO brace. Rigid lumbar braces that do not extend to the chest and soft braces/corsets provide little stabilizing benefit.

In chronic overt instability and covert instability, medical treatment plays a more prominent role. If not at risk for imminent neurologic deterioration, patients with these forms of instability generally undergo conservative (nonsurgical) treatment first. Fusion is reserved for those in whom conservative treatment fails (see Approach Considerations).

Conservative treatment may include some or all of the items below:

• Medications - Analgesics, anti-inflammatories, muscle relaxants, tricyclic antidepressants, antiepileptics
• Physical therapy
• Behavior modification - Smoking cessation, weight loss
• Injection therapy (eg, epidural or facet steroid injections)
• Transcutaneous electrical nerve stimulation (TENS)
• Psychological treatment (especially for depression)
• Alternative treatments (eg, acupuncture, biofeedback)

Once the decision has been made to fuse a particular spine segment, there may be several surgical methods by which this task can be accomplished. After a particular method is selected, the etiology of the instability is no longer relevant, because the technical steps would be the same. The most commonly employed fusion techniques in various regions of the spine are described in subsequent sections.

Preparation for surgery

Routine preoperative tests usually consist of complete blood count (CBC), electrolytes, blood urea nitrogen (BUN), creatinine, glucose, prothrombin time (PT), activated partial thromboplastin time (aPTT), international normalized ratio (INR), chest radiography, and electrocardiography (ECG). Blood is typed and screened. If extensive blood loss is anticipated, one or two units of packed red blood cells (RBCs) are cross-matched or a cell saver is used. Alternatively, if the procedure is scheduled electively, the patient may donate autologous blood several weeks beforehand.

Thigh-high compression stockings (TED hose) and sequential compression devices are applied preoperatively for prophylaxis of deep vein thrombosis (DVT) and are not removed until the patient is mobilized postoperatively.

In patients who are at particular risk for DVT and pulmonary embolism (PE; eg, those who are paraplegic, quadriplegic, or bedbound prior to surgery), subcutaneous injections of low-molecular-weight heparin (LMWH) may begin before the operation, with the individual patient's risk of postoperative epidural hematoma carefully weighed against the risk of PE. Meticulous attention to hemostasis, liberal use of closed wound drainage, and careful postoperative neurologic evaluation are indispensable when heparin is used.

An antibiotic with antistaphylococcal activity, usually a first-generation cephalosporin, is given within 1 hour prior to the skin incision and continued for three doses postoperatively.

The Enhanced Recovery After Surgery (ERAS®) Society has formulated recommendations for the perioperative care of patients undergoing lumbar spinal fusion. ^[41]  

Operative details

The following are general concepts pertaining to intraoperative management of all fusion procedures. Intraoperative details specific to each fusion technique are provided in subsequent sections. 

Positioning

For posterior cervical procedures, a prone position is preferred. Although some surgeons use a sitting position to minimize bleeding from epidural veins, this position puts the patient at risk for intraoperative hypotension and venous air embolism. Meticulous surgical technique, judicious use of bipolar coagulation, and use of an operating microscope when necessary permit all posterior cervical procedures to be performed safely in prone position.

The patient's head may be immobilized by means of three-point skeletal fixation in a Mayfield head holder, which also permits precise control of cervical contour. If the head is positioned over a foam or horseshoe head holder instead, special attention should be given to avoiding compression of the eyes, which could result in raised intraocular pressure and retinal ischemia.

For posterior lumbar and thoracolumbar fusions, the patient is positioned prone over a frame or table that permits the abdomen to hang free. Otherwise, the increased intra-abdominal pressure would interfere with venous return and would increase intraoperative bleeding. The Wilson frame fulfills this requirement and provides the fastest and least cumbersome means for positioning the patient. Certain other spine frames and tables (eg, the Andrews table) allow the patient to be positioned in a knee-to-chest position.

The resultant lumbar flexion facilitates access to the spinal canal and disk spaces by increasing the interlaminar and posterior interbody distances. However, if the patient is fused in this position, the natural lumbar lordosis is lost, resulting in "flat back" syndrome. Other spine tables, such as the Jackson table, which allows the patient to be flipped from supine to prone position and vice versa, are useful for combined anterior-posterior procedures. Regardless of the position or frame used, all pressure points must be carefully padded to prevent compression neuropathy.

Fluoroscopy

Intraoperative fluoroscopy is essential for safe and accurate instrumentation of the spine. A radiolucent frame should be used when applicable to allow for lateral and anteroposterior (AP) fluoroscopy. The C-arm should be draped in sterile fashion and positioned so that it can be readily moved in and out of imaging position. (See the image below.)

Alternatively, fluoroscopy-based stereotactic navigation can be used, wherein a computer with sophisticated stereotactic software permits virtual fluoroscopic navigation throughout the surgery. In this case, AP and lateral fluoroscopic images are taken after the spine is exposed and a bone-mounted stereotactic frame is attached. The C-arm is then removed and the procedure is performed on the basis of computer-assisted navigation of the original fluoroscopic images.

Neurophysiologic monitoring

Intraoperative neurophysiologic monitoring for spine procedures consists of the use of somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), or electromyography (EMG) to detect and correct factors that lead to neurologic compromise during the surgical procedure. During pedicle screw placement, stimulation of the pedicle probe with a nerve stimulator at subthreshold currents would result in EMG activity in the lower extremities if the probe is in contact with the nerve root, prompting its repositioning.

Microdissection under microscopy

Microdissection under an operating microscope allows safer decompression of neural elements, particularly in settings where visualization is limited (eg, anterior cervical diskectomy and osteophyte resection). The microscope can be moved out of position when the more delicate decompression phase of the procedure is completed before proceeding with fusion and instrumentation.

Anesthesia

Anesthetic considerations during fusion surgery include ensuring adequate blood pressure and fine-tuning muscle relaxation during the operation while maintaining the depth of anesthesia. Muscle relaxation facilitates the initial exposure of the spine but must be avoided or reversed if intraoperative MEP or EMG is to be used. When muscle relaxation is not present, it is important to maintain deep anesthesia to prevent patient movement during critical parts of the procedure, such as decompression of the spinal cord.

Adequate blood pressure must be maintained at all timed to avoid neural ischemia, which could exacerbate existing neural injury. In patients with labile blood pressure or cardiopulmonary risk factors, an arterial line may be inserted for continuous monitoring. If adequate peripheral venous access is not available, a central line is inserted. If the procedure is expected to last longer than 2 hours, a bladder catheter is inserted.

Atlantoaxial instability may be caused by a variety of conditions, including the following:

• Odontoid fractures
• Rupture of the transverse ligament
• Ligamentous incompetence due to rheumatoid arthritis
• Congenital instability associated with os odontoideum

C1-2 fusion with cable fixation

Before the advent of screw fixation techniques, wiring of C1-2 posterior elements with an interposed bone graft was the only method of fusion of the atlantoaxial segment. The monofilament wires once commonly used are being abandoned in favor of multistranded braided cables, which offer greater flexibility, strength, and fatigue resistance.

The following three techniques are available:

• Gallie technique
• Brooks technique
• Sonntag technique

In the Gallie technique (see the image below), a cable loop is passed under C1 posterior arch from below, folded over C1, and hooked under the base of the C2 spinous process. The free ends of the cable are then brought together in the midline to secure a unicortical onlay bone graft against the decorticated surfaces of C1 and C2 laminae. Although relatively safe and easy to perform, this technique provides little rotational stability and has a higher pseudarthrosis rate as a consequence of the onlay nature of the graft.

In the Brooks technique (see the image below), one (central) or two (lateral) bicortical bone grafts are wedged between the C1 posterior arch and the C2 lamina. A tension band is constructed by passing two separate cables under both C1 and C2 laminae and attaching their free ends posterior to the graft(s). The cancellous surfaces of the graft are in good contact with the decorticated undersurface of the C1 arch and the top rim of the C2 lamina, placing the graft(s) under compression and thus enhancing fusion rates. In addition, this technique provides greater rotational stability by virtue of bilateral engagement of the C2 lamina. 

The problem with the Brooks technique is that sublaminar passage of the cable under both C1 and C2 substantially increases the technical difficulty and risk of spinal cord injury during the procedure, particularly if the canal diameter is already compromised by the underlying pathology.

The Sonntag technique (see the image below) combines the ease and safety of the Gallie technique with the superior biomechanical features of the Brooks technique. Here, the cable loop is passed only under the C1 lamina and hooked under the C2 spinous process base, as in the Gallie technique. The difference is that the bicortical bone graft is wedged between C1 and C2 posterior elements, as in the Brooks technique, and the free ends of the cables are attached under the C2 spinous process base.

Because the Sonntag technique, unlike the Brooks technique, does not involve the use of a C2 sublaminar wire to protect against anteropulsion of the graft, a notch is made in the inferior portion of the graft, and it is wedged over the superior surface of the C2 spinous process.

Regardless of the technique used for C1-2 cable fixation, a halo is generally applied until fusion occurs (usually 3-6 months). This is a major drawback from the standpoint of patient comfort and rehabilitation.

C1-2 transarticular screw fixation

Screw fixation of the atlantoaxial segment provides immediate rigid fixation of the joint and eliminates the need for a halo. The main consideration is the risk of injury to the vertebral artery. In about 18% of cases, the vertebral artery rides high after emerging from the C2 transverse foramen, positioning itself in the path of the screw. Before surgery, it is imperative to perform high-resolution computed tomography (CT) with sagittal reconstructions to detect this variant anatomy and avoid screw insertion on that side.

The technique is as follows. The patient is placed in a prone position, and the head is carefully flexed under fluoroscopic guidance and fixed in a Mayfield head holder. An incision is made from the skull base to C7. In addition, small stab incisions may be necessary more inferiorly and laterally to permit placement of the drill in the correct trajectory. C1, C2, and C3 are exposed to the lateral margin of the lateral masses.

The ligamentum flavum above C2 is removed to expose the C2 nerve root (greater occipital nerve), which runs posterior to the facet joint, unlike any other location in the spine. The nerve and its surrounding venous plexus are retracted superiorly to expose the facet joint. A 2.5-mm drill is used to establish the crew trajectory, starting at the C2-3 facet edge about 2-3 mm lateral to the medial aspect of the lateral mass.

Drilling is performed in 2-mm increments pointing 10º medially in a cephalad trajectory aimed at the posterior cortex of the anterior arch of C1 under continuous lateral fluoroscopic imaging. As the drill crosses the C1-2 articulation, decreased mobility of C1 is often immediately palpable. To correct any subluxation, C1 may be pushed or pulled in anterior or posterior directions before the drill crosses the facet joint.

The drill hole is then filled with a self-tapping screw of the appropriate length; alternatively, the hole can be tapped before the screw is inserted (see the image below). The procedure is then repeated on the opposite side. The posterior surfaces of the C1 and C2 lateral masses and the posterior aspect of the facet joint are decorticated with a drill and packed with cancellous bone graft.

If vertebral artery injury is encountered on one side, the screw is left in place, and screw placement on the opposite side is avoided in order to prevent bilateral injury. Postoperative vertebral angiography is performed to rule out pseudoaneurysm formation.

C1-2 transarticular screw fixation is best supplemented with C1-2 cable fixation in order to provide a better bone substrate for fusion than what can be packed in the facet joints.

Postoperatively, the patient is placed in a Philadelphia collar.

C1-2 lateral mass/isthmus fixation

When preoperative CT reveals that a high-riding vertebral artery would be in the trajectory of a C1-2 screw, an alternative technique can be employed. A screw is inserted in the C1 lateral mass. A second screw is inserted into the C2 isthmus. The two screws are then connected with a rod or a plate. The procedure is repeated on the opposite side. The technique for exposure is identical to C1-2 transarticular screw placement. After the ligamentum flavum is resected, the medial wall of the C2 isthmus is exposed and palpated with a Penfield 4 instrument.

Although the isthmus is sometimes called the C2 pedicle, this is not strictly correct. The isthmus is a tubular structure that courses medially and superiorly, connecting each C2 lateral mass to the body, and is more correctly identified as the pars equivalent.

The drill and screw are directed along the visualized trajectory of the isthmus. The entry point is at the center of the lateral mass, and the trajectory is angled 25º medially and 25º cephalad. The more medial trajectory of the screw in this technique helps avoid vertebral artery injury. Palpation of the medial wall of the isthmus during screw insertion helps avoid breach of the spinal canal.

Odontoid screw fixation

Odontoid fractures are categorized according to the scheme in Table 4 below and treated according to the algorithm in Table 2 above (see Approach Considerations).

Table 4. Odontoid Fracture Classification (Open Table in a new window)

Odontoid screw fixation is reserved for certain type 2 odontoid fractures—specifically, those that are reducible to less than 3 mm of fracture fragment displacement and are not associated with rupture of transverse ligament or a tumor in C2. The main advantage of this technique is that it directly repairs the odontoid fracture, thus avoiding a C1-2 fusion and maintaining range of motion (ROM). Its shortcoming is the limited circumstances in which it can be employed.

In addition, type 2A fractures, fractures in patients older than 65 years, slanted fracture lines, and old nonhealing fractures may be better treated by means of C1-2 fusion; odontoid screw fixation is less likely to yield a satisfactory outcome in these circumstances.

The technique is as follows. An anterior approach under biplanar fluoroscopy is followed. The neck is slightly extended. A transverse incision is created on the right side of the neck, overlying the C5-6 interspace. Dissection is carried down to the spine, as in anterior cervical fusion (see Surgical Therapy for Subaxial Cervical Instability). A plane is developed cephalad along the anterior aspect of the spine to the C2-3 disk space.

An Apfelbaum retractor specifically designed for this technique is deployed. A Kirschner wire (K-wire) is placed at the anterior-inferior margin of C2, and a shallow pilot hole is drilled under fluoroscopy toward the odontoid tip. The entry point is along the midline if one screw is desired and lateral to the midline if two screws are intended.

A reamer is placed over the K-wire to create a tangential slot along the anterior margin of C3 and the C2-3 disk space. The reamer is removed and replaced with a drill guide. The spikes of the drill guide are tapped into the anterior body of C3 to stabilize it. The K-wire is removed and replaced with a drill through the drill guide.

Drilling is performed toward the odontoid tip. The screw hole is tapped, and a lag screw of appropriate length is screwed in to engage the cortex of the odontoid tip. The lag screw will help compress the fracture fragment against the C2 body. If a second screw is inserted, it does not have to be a lag screw. A Philadelphia collar is applied postoperatively for 3 months.

Anterior cervical fusion

Anterior cervical fusion (see the image below) is one of the most commonly used fusion techniques in spine surgery. The anterior approach is increasingly used in preference to the posterior approach to the cervical spine ^[15]  because it provides distinct advantages with regard to decompression, fusion, and instrumentation.

Most pathologic processes in the cervical spine, especially degenerative and neoplastic disorders, affect structures anterior to the spinal cord. An anterior approach to the cervical spine permits thorough decompression of the spinal canal without manipulation of the spinal cord. Furthermore, such an approach permits placement of the bone graft in an interbody position under compression, which significantly enhances the success of fusion. Finally, the relatively large surface areas and volumes of the vertebral bodies as compared with the posterior cervical elements render them ideal substrates for instrumentation.

The most common indications for anterior cervical fusion are in treatment of degenerative disorders. Large central disk herniations with cord compression and chronic disk-osteophyte complexes at one or more levels cannot be safely removed via a posterior approach. (See the images below.) Cervical spinal stenosis associated with kyphosis is best treated via an anterior approach because a multilevel posterior decompression by laminectomy does not relieve the stretching of spinal cord over disk-osteophytes and may exacerbate the kyphosis in the long run. 

Anterior cervical diskectomy is effective not only for treatment of neural compression (myelopathy and radiculopathy) but also for treatment of chronic axial pain associated with disk degeneration and correction of spinal deformity (kyphosis).

Anterior cervical corpectomy (removal of vertebral body) is employed when the pathology extends behind the vertebral body anterior to the cord (eg, large osteophytes or ossification of the posterior longitudinal ligament) or involves the vertebral body itself (eg, tumor or burst fracture). Traumatic cervical dislocations associated with disk herniation should be treated via an anterior approach.

The technique is as follows. The patient is placed on the operating table in supine position. Rolls are placed under the shoulders and under the hip from which iliac crest graft is to be harvested. The arms are padded and tucked by the patient’s sides. The shoulders are taped to the foot of the bed to permit unencumbered visualization of the spine by fluoroscopy. The fluoroscopic C-arm is positioned in cross-table lateral orientation and draped.

The skin incision is typically made on the right side of the neck for a right-handed surgeon and on the left side for a left-handed surgeon; this significantly facilitates access. If the C7-T1 disk is the target, some surgeons prefer a left-side approach to minimize the risk of recurrent laryngeal nerve (RLN) palsy, though this puts the thoracic duct at risk. If unilateral RLN palsy is present preoperatively, surgery must be performed from the side of the palsy to avoid the risk of bilateral RLN palsy.

A transverse skin incision over a skin crease centered along the anterior border of the sternocleidomastoid muscle provides the best cosmetic result for one- and two-level fusions. With practice, a three-level fusion can also be performed through a transverse incision. An oblique vertical incision along the anterior border of the sternocleidomastoid is used if greater rostrocaudal exposure is required.

The platysma is divided in line with the skin incision. A subplatysmal dissection is carried out. A large external jugular vein is best mobilized and retracted to the side, whereas a smaller one can be ligated and divided.

An avascular plane is developed medial to the sternocleidomastoid and carried medial to the carotid sheath to reach the anterior border of the cervical spine. Gentle medial retraction of the midline structures significantly facilitates this task.

The omohyoid muscle courses obliquely in this region from an inferolateral to a superomedial location. For C3-4, C4-5, and C5-6 disks, the plane of dissection is superior to the omohyoid, whereas for C6-7 and C7-T1 disks, it is below the omohyoid. Occasionally, for an extensive procedure that spans several segments above and below C6, the omohyoid is divided and later reapproximated. 

Small tributaries to the internal jugular vein running transversely across the field of exposure can be coagulated and divided. If the common facial vein is hindering the exposure of the upper cervical spine, it can be ligated and divided. The carotid sheath is never entered. If the ansa cervicalis is encountered, it can be mobilized either medially or laterally.

In very high exposures, care is taken to prevent injury to the hypoglossal nerve deep to the digastric muscle. In very low exposures, care is taken to spare any neural structures that might correspond to a variant crossing of the recurrent laryngeal nerve.

The prevertebral fascia is opened and the esophagus and pharynx are retracted toward the contralateral side. A transverse cervical artery, often accompanied by a vein, is usually identified over the C7 vertebral body in the superior extension of the mediastinal fat pad. This artery and the fat pad can usually be swept inferiorly and preserved. If exposed, this artery should be carefully inspected at the end of the procedure to make sure that it is intact. If damaged by stretching, it must be ligated to avoid the risk of a catastrophic postoperative neck hematoma.

The attachments of longus colli muscles to the anterolateral aspects of the vertebral bodies above and below the target site are divided. Bleeding from muscle edges and bone is controlled with electrocautery and bone wax. Excessive use of the monopolar electrocautery is avoided so as to prevent the risk of thermal damage to the nearby sympathetic chain and resultant Horner syndrome.

If large anterior osteophytes are present, they are resected flush with the anterior surface of the vertebral bodies. An anterior cervical self-retaining retractor is inserted and its lips secured under the mobilized edges of the longus colli muscles. If sufficient dissection of the longus colli muscles is not carried out, the retractors will not remain in place, creating a significant nuisance during the remainder of the case. Many contemporary retractors have blades that distract not only medially and laterally but also superiorly and inferiorly, providing excellent exposure.

Caspar posts are inserted in the midportion of the vertebral bodies above and below the target site under fluoroscopic guidance. The Caspar distractor is then used to distract the disk space(s). The anterior longitudinal ligament and the anterior anulus of the disk are resected. Under the operating microscope, the contents of the disk(s) are thoroughly evacuated to expose the converging posterior lips of the superior and inferior endplates and the intervening posterior anulus of the disk.

The posterior anulus is temporarily left in place as a protective shield while the posterior lips of the endplates and the underlying osteophytes are meticulously drilled with a bur under the operating microscope until they are reduced to thin shells of cortical bone. The posterior anulus of the disk is then completely resected. The herniated disk material is removed.

The residual osteophyte shells are elevated away from the dura with a small hook or a small up-angled curette and removed. The posterior longitudinal ligament is completely resected from side to side to fully expose and decompress the dura. In rare instances, an ossified or thickened posterior longitudinal ligament is fused to the dura and cannot be completely resected without risking dural laceration.

The medial aspects of the uncinate processes are resected to ensure decompression of the symptomatic nerve roots. A nerve hook is passed laterally into the neural foramina to ensure their patency. Bleeding from the lateral epidural veins is readily controlled with Gelfoam.

Care is taken during lateral dissection to avoid injury to the vertebral arteries, which are located lateral and anterior to the uncovertebral joints. A careful review of the axial images from preoperative CT or MRI will provide useful information about the proximity of the vertebral artery to the neural foramina and any aberrant looping of that vessel into the normal course of the exposure.

If a corpectomy is to be performed, the disks above and below the vertebral body are first resected, as described above. The anterior aspect of the vertebral body is readily resected with a large rongeur. The posterior half of the vertebral body is carefully drilled until the posterior wall is thinned down to a shell of bone. Venous bleeding from the lateral walls of the resected vertebral body is controlled with bone wax. The posterior cortex and posterior longitudinal ligament are carefully elevated away from the dura and resected.

After satisfactory decompression is obtained, the endplates are decorticated with a drill, in preparation for fusion. The cartilaginous endplate is removed, but excessive removal of the bony endplate is avoided in order to minimize settling of the graft. Posterior ledges in the endplates are left behind to prevent retropulsion of the graft.

The height of the interspace is measured. An appropriately sized tricortical bone graft is harvested from the anterior iliac crest or fashioned out of cadaveric allograft bone. The graft is inserted into the interspace and tapped in place under fluoroscopic guidance. The distraction is then released and the distraction posts removed. An appropriately sized anterior cervical plate is affixed to the vertebral bodies above and below the fused segment(s) with cancellous screws under optional fluoroscopic guidance. The screws are locked with the locking mechanism specific to the plate. (See the image below.)

The retractors are removed. Hemostasis is secured. The wound is irrigated. The platysma is closed with absorbable sutures. The skin is closed in subcuticular fashion.

Some surgeons do not perform a fusion after an anterior cervical diskectomy. This is only appropriate if the operation consists of a limited central single-level diskectomy for a soft central disk herniation in the absence of spondylosis, wherein comprehensive removal of the posterior longitudinal ligament and uncovertebral joints has not been performed. Even if spontaneous fusion occurs as desired in these cases, the resultant reduction in foraminal height may predispose the patient to future nerve-root compression.

It is acceptable to perform a single-level diskectomy and fusion without plating, relying on the tension band provided by the middle and posterior columns to promote stability and fusion. A plate is employed for all multilevel diskectomies and corpectomies.

No collar may be needed, or a soft collar or rigid cervical collar may be applied for 1-6 weeks postoperatively, depending on the extent of the procedure. After multilevel corpectomies, a halo is considered.

Lateral mass screws

Excellent stabilization of the subaxial cervical spine can be achieved via a posterior approach by using lateral mass screws. Here, screws are inserted into the lateral masses at trajectories designed to avoid the vertebral artery and cervical nerve roots. The adjacent screws are linked by bilateral plates or rods. This procedure can be employed whether or not a previous laminectomy has been performed.

The following two techniques are available:

• Magerl technique
• Roy-Camille technique

In the Magerl technique, the entry point is 2 mm medial and 2 mm superior to the center of lateral mass, and the screw trajectory is 20-25º lateral and parallel to the facet surface in the sagittal plane. In the Roy-Camille technique, the entry point is just above the center of the lateral mass, and the trajectory is only 10º lateral and perpendicular to the lateral mass surface in the sagittal plane. Although the Magerl technique leaves a greater safety zone between the screw tip and the nerve root, achieving the cranial angulation that this technique requires during surgery is not always easy.

Before rods or plates are placed, the facet joints and lateral mass surfaces are decorticated and packed or covered with cancellous bone. If laminae are present, corticocancellous strips of bone graft can be placed over the decorticated laminae and wired in place.

Posterior cervical wiring

Monofilament wires, double-stranded twisted wires, Drummond wires (wire loops passing through a button), and braided multistranded cables can be used for wiring of posterior cervical elements.

Spinous process wiring is the simplest technique but provides no limitation of extension and little rotational stability. In this technique, a wire is passed through the center of one spinous process around the base of a lower spinous process. Multiple wire loops can be used to connect multiple spinous processes in an interlocking chain array. More complicated spinous process wiring patterns (eg, the Bohlman triple-wire technique) allow firm attachment of bone graft strips to the sides of the spinous processes.

Sublaminar wiring involves the use of a loop of wire that is carefully passed under the lamina and then cut in half. Each wire is then brought laterally to each side and tightened around a rod or bone graft. The technique is repeated for two or more laminae.

When a laminectomy has been performed, the only available structure for wiring is the facet joint. Wires passed through the midportion of the inferior articulating facet are tightened around a rod or bone graft strip.

In general, wiring techniques are inferior to anterior or posterior screw/plate/rod fixation methods.

Posterior thoracic and thoracolumbar instrumentation

Since the advent of Harrington rods for posterior thoracolumbar stabilization and deformity correction, ^[42]  posterior instrumentation constructs have evolved substantially. Harrington rods were nonsegmental systems attached to the spine via hooks at proximal and distal ends of long rods and relied primarily on distraction for deformity correction. Modern posterior thoracolumbar instrumentation constructs differ from Harrington rods in several key aspects, as follows:

• They are segmental; that is, they are attached to the spine not only at the proximal and distal ends of rods but also at multiple intervening segments
• They are modular and hybrid, allowing simultaneous use of hooks (laminar hooks, transverse process hooks, pedicle hooks), wires, and pedicle screws
• They rely more on three-point-bending biomechanical principles than on distraction for deformity correction and stabilization

These instrumentation systems can be used for treatment of acute overt instability due to trauma, neoplasms, or infections, in addition to deformity correction. Hooks can be applied above a lamina, facing down, or below a lamina, facing up. When two hooks are placed on the same lamina or adjacent laminae, facing each other, a "claw" construct is formed. Claw constructs help secure the ends of the rods against the spine.

When placement of laminar hooks is not possible (because of laminectomy) or desirable, transverse process hooks can be used. Hooks can also be placed under pedicles (inserted through the thoracic facet joint and screwed to the undersurface of the pedicle).

When the construct relies primarily on hooks, a long section of the spine is instrumented (generally three segments above and two below) to prevent construct failure. The segments receiving bone graft would be shorter than the instrumented segments (the "rod long, fuse short" principle). Pedicle screws are playing an increasingly prominent role in segmental modular constructs in the thoracic and thoracolumbar regions. The greater stability conferred by the screw-based systems allows construction of shorter constructs spanning the unstable motion segment. (See the image below.)

Posterior systems also allow reduction of anterior (vertebral body) fractures by using segmental distraction (see the image below). Above all, use of posterior instrumentation for thoracic and thoracolumbar spinal instability is clearly augmented by the fact that exposure of this portion of the spine is far easier via a posterior approach than via an anterior approach.

Anterior thoracic and thoracolumbar instrumentation

There are instances in which thoracic and thoracolumbar instability cannot be adequately addressed through a posterior approach and for which an anterior approach is therefore preferred. These instances include the following:

• Pathologic fractures of the vertebral bodies due to tumor or infection that produce cord compression
• Some traumatic burst fractures (associated with retropulsion and rupture of posterior longitudinal ligament) that cannot be reduced by means of posterior distraction

The upper thoracic region (T1-3) is approached anteriorly by extending an anterior cervical approach inferiorly to the mediastinum via a partial or complete median sternotomy. The fusion and instrumentation methods here are identical to those employed in anterior cervical procedures.

The midthoracic region (T4-11) is generally approached through a transthoracic approach from the left side. This usually involves a thoracotomy with opening of the pleura and deflation of the ipsilateral lung, which provides excellent exposure of the entire T4-11 region from an anterolateral perspective. Alternatively, an extracavitary (extrapleural) approach can be used, which provides a more limited rostrocaudal and anterior exposure.

The thoracolumbar region (T12-L2) is approached through an anterior thoracolumbar approach, which combines a thoracotomy with a retroperitoneal approach to the upper lumber spine and requires division and mobilization of the diaphragm.

When a thoracic or thoracolumbar corpectomy is performed, the corpectomy gap must be reconstructed in the same fashion as a lumbar corpectomy (see above). For this purpose, expandable cages are available, which are placed in the corpectomy defect and expanded to engage and distract the adjacent vertebral bodies (see the image below). The cages are then filled with bone and supplemented with a plate. The plate is applied to the lateral surface of the vertebral bodies and serves as a tension band construct.

Besides permitting more thorough decompression of anterior pathology, anterior thoracic and thoracolumbar reconstructions enable the surgeon to limit the instrumented fusion to the pathologic motion segment, sparing the adjacent segments. (See the image below.)

Posterior and posterolateral noninstrumented lumbar fusion

Noninstrumented posterior or posterolateral fusion of the lumbar spine is fairly simple to perform and is an acceptable treatment for certain instances of degenerative instability, when the patient is not believed to be a candidate for pedicle screw insertion. Because of its greater susceptibility to pseudarthrosis, it is not recommended for situations in which overt instability is present. The patient is kept in a TLSO brace until the fusion solidifies.

The technique is as follows. The lumbar spine is exposed in a standard fashion through a posterior midline incision. Bilateral exposure of the laminae is extended further laterally to completely expose the facet joints and transverse processes of the vertebrae to be fused.

Usually, a decompressive laminectomy is carried out to treat neural compression. In this process, medial facetectomies may be carried out to fully decompress the lateral recesses, if necessary. The transverse processes, the lateral aspect of the facet joints, and the synovial facet surfaces are decorticated with a high-speed drill.

Corticocancellous strips of bone are harvested from the posterior iliac crest and placed in the "lateral gutters" over the lateral aspect of the facet joints and transverse processes. The space between the articulating surfaces of the facet joints is packed with cancellous bone graft. The fusion mass may be supplemented with cortical bone obtained from the laminectomy.

If the laminar surfaces have not been completely removed (eg, if only a laminotomy has been performed), bone graft can be applied to the decorticated laminae and spinous processes to produce a true posterior fusion. The posterolateral fusion may be supplemented with a posterior lumbar interbody fusion (PLIF).

A randomized double-blind clinical trial from Scandinavia evaluated patient-reported outcomes and intertransverse fusion rates in noninstrumented posterolateral fusion augmented with either 15-amino-acid residue (ABM/P-15) or allograft. ^[43]  The patients in the ABM/P-15 group had a statistically significantly higher fusion rate than those in the allograft group when assessed with postoperative fine-cut (0.9 mm) CT with reconstructions, but this difference did not translate to better clinical outcomes.

Instrumented lumbar fusion with pedicle screws

Pedicle screw fixation is the most commonly used approach for internal stabilization of the lumbar spine. Screws are inserted into the pedicles of the vertebrae to be fused and connected to each other with bilateral rods or plates.

The technique is as follows. The spine is exposed (and decompressed if necessary) as it would be for a noninstrumented fusion. Pedicle screws are inserted into the pedicles above and below the motion segment to be fused. The main concern during screw insertion is to avoid breach of the pedicle wall and injury to the exiting nerve root.

If a laminectomy or upper laminotomy has been carried out, it will be possible to visualize or palpate the medial and inferior surfaces of the pedicle, which are in contact with the nerve root. In this case, only lateral fluoroscopy is necessary to guide the entry and trajectory of the screw in the sagittal plane. (See the image below.) If the pedicle has not been exposed via laminectomy or laminotomy, AP and lateral fluoroscopy are usually used. The inferolateral aspect of the pedicle can also be exposed by subperiosteal dissection via a lateral approach along the base of the transverse process.

The entry point to the pedicle is located at the junction of lines bisecting the transverse process and the superior articulating facet. A starting hole is created at the entry point with an awl or a drill. A pedicle probe is then used to establish the path of the screw under fluoroscopic guidance. The probe may be stimulated with a nerve stimulator to elicit EMG activity from the lower extremities. If EMG is elicited at low stimulation currents, contact between the probe and the nerve root is suspected and the probe is removed and reinserted differently.

The trajectory in the sagittal plane is parallel to the superior endplate for L1-5 and toward the sacral promontory for S1. In the axial plane, the probe is directed slightly medially into the vertebral body. As one descends the lumbar spine, the medial angulation of the pedicles increases. After the probe is removed, the screw path is tapped and the appropriately sized screw inserted. In order to avoid penetration of the anterior cortex of the vertebral body, the screw should not extend beyond 80% of the diameter of the vertebral body on lateral fluoroscopy.

Once all of the screws have been inserted, they are usually linked with rods, though notched plates may also be used for this purpose. (See the image below.) Depending on the instrumentation system used, the screw-rod interface may be fixed, requiring extensive contouring of the rod to fit the screw heads, or variable, requiring minimal contouring.  Before the screw-rod interface is tightened and locked, the pedicle screws can be used to distract or compress the vertebral bodies. 

If reduction of spondylolisthesis is desired, the inferior screw is locked to the rod and the superior screw pulled back toward the rod, with the latter acting as a cantilever beam. If adequate decompression of the spinal canal and nerve roots has been carried out by laminectomy and partial facetectomy, it may not be necessary to reduce the spondylolisthesis, in which case the fusion is said to have been performed in situ. Some surgeons prefer to attempt to reduce all spondylolisthesis in order to restore sagittal balance.

After pedicle screw insertion, a posterolateral bony fusion is performed as previously described. Instrumented posterolateral fusion can be further supplemented by interbody fusion (see below), thus producing a global fusion.

Lumbar interbody fusion

Lumbar interbody fusion refers to replacement of disk space with bone. Because of the substantial surface area of the vertebral endplates and the fact that the bone graft is under compression, interbody fusion enjoys a favorable fusion environment. Ideally, it is supplemented with pedicle screw instrumentation to provide internal fixation ^[44] ; it may or may not be further supplemented with posterolateral fusion. (See the image below.)

Interbody fusion can be performed through the following approaches:

• Posterior approach - PLIF
• Posterolateral approach - Transforaminal lumbar interbody fusion (TLIF)
• Anterior approach - Anterior lumbar interbody fusion (ALIF)
• Far lateral approach - Extreme lateral interbody fusion (XLIF) 

The original PLIF procedure was performed through a routine posterior exposure for lumbar diskectomy. After the disk space was thoroughly evacuated, the endplates were decorticated with large angled curettes and bone rasps. The disk space was then packed with autologous cancellous bone.

In current practice, PLIF, TLIF, and ALIF are usually performed with the aid of interbody implants. The implants (made of a PEEK polymer, machined cortical allograft bone, or metal) are filled with cancellous bone before insertion into the disk space. The remaining disk space around the implant is also packed with cancellous bone. These three techniques differ only in the method of insertion of the interbody implant.

Posterior lumbar interbody fusion

Laminectomy (or bilateral hemilaminectomy), bilateral medial facetectomy, and bilateral diskectomy are carried out at the target segment. The traversing and exiting nerve roots are identified bilaterally, and the intervening epidural veins are coagulated with a bipolar device and divided. The endplates are thoroughly decorticated.

The traversing nerve roots and the dural sac are retracted medially as the interbody implants are inserted bilaterally under fluoroscopic guidance. Depending on the type of the implant, specific instruments are used for preparation of the disk space and insertion of the implant.

Transforaminal lumbar interbody fusion

This technique is usually performed unilaterally and does not require an extensive laminectomy. It lends itself to open or minimally invasive ^{[45, 46]} approaches.

A partial facetectomy is performed to unroof the neural foramen and identify the exiting and traversing nerve roots. A unilateral diskectomy is performed, and the endplates are thoroughly decorticated with long angled curettes and bone rasps.

A banana-shaped interbody implant packed with bone is inserted into the disk space via a transforaminal approach and tapped in place under fluoroscopic guidance. Because of its shape, as the implant is inserted and tapped, it gradually assumes a transverse orientation within the disk space. The disk space posterior to the implant is packed with cancellous bone.

A percutaneous endoscopic robot-assisted approach to TLIF for lumbar spondylolisthesis has been described; this technique has a steep and long learning curve and requires long-term follow-up. ^[47]

Anterior lumbar interbody fusion

The appropriate lumbar or lumbosacral segment is reached through an anterior transperitoneal or extraperitoneal approach. This can be accomplished via either an open or a laparoscopic method.

The L5-S1 disk is always approached between the iliac vessels; this often requires mobilization and lateral retraction of the left iliac vein. For the L4-5 disk space, the level of aortic bifurcation and size of the left iliac vein determine the direction of vessel retraction. The iliolumbar vein is divided for L4-5 disk access. The anterior longitudinal ligament and the anterior anulus of the disk are incised and the disk contents evacuated. The endplates are prepared, and the interbody implants are inserted by using instruments and methods specific to the type of implant used.

ALIF is sometimes combined with pedicle screw instrumentation, necessitating an anterior-posterior approach, which avoids opening the spinal canal. In conditions that require decompression of the spinal canal, PLIF or TLIF can be performed in conjunction with pedicle screw instrumentation; in this way, a global fusion can be performed through a single approach without the need to open the abdomen.

Lumbar corpectomy

A lumbar corpectomy is generally performed for neoplastic disease affecting the vertebral body but may be performed for other indications as well, such as burst fractures with substantial retropulsion that cannot be reduced through a posterior approach or extensive vertebral osteomyelitis with pathologic fracture that cannot be adequately debrided and decompressed through a posterior approach.

The technique is as follows. The L2-5 segments are approached through a left retroperitoneal approach with the patient in a lateral decubitus position. The retroperitoneal approach is usually provided by a general surgeon. The peritoneum is mobilized forward until the psoas muscle is visualized.

The kidney is mobilized forward. The ureter is found over the psoas muscle and mobilized forward with its surrounding fat. The sympathetic chain and the genitofemoral nerve are identified over the psoas muscle and preserved. The psoas muscle attachments to the lateral aspects of the vertebral bodies are mobilized posteriorly with a Cobb periosteal elevator to expose the lateral aspect of the pedicles. The segmental vessels are ligated and divided over the midportion of the vertebral bodies.

The vertebral body bone is removed in a left-to-right approach. The posterior margin of the vertebral body is identified at the level of the pedicle and followed inferiorly. Retropulsed bone fragments or ventral epidural tumor is removed. The disks above and below the level of corpectomy are removed and the endplates decorticated.

Reconstruction across the gap produced by corpectomy requires a large interbody implant. This may be a piece of tibial or femoral allograft, cored out and filled with autologous bone. Alternatively, a Steinman pin wedged between the adjacent vertebral bodies and surrounded by methylmethacrylate may be used in the case of malignant disease, when bony fusion is not realistically expected.

Most commonly, metal cages of fixed height (Harms cage) filled with bone or expandable metal cages are used to reconstruct the vertebral body defect. A plate or plate-rod system is screwed to the lateral aspect of the vertebral bodies above and below the level of corpectomy, the latter providing the advantage of compression across the cage. (See the image below.)

Postoperative pain is controlled aggressively with parenteral opiates for the first 12-36 hours, after which period the patient is converted to oral analgesics. Muscle relaxants and benzodiazepine anxiolytics can help reduce the requirement for opiates. If significant postoperative pain is anticipated, IV patient-controlled analgesia (PCA) with a continuous basal rate is employed.

Prophylactic antibiotics, started preoperatively, are continued for three doses (24 hours) after the procedure. In the absence of infection, further antibiotic administration after this 24-hour period has not been shown to be beneficial and may lead to the emergence of antibiotic-resistant pathogens.

If dexamethasone is used preoperatively and intraoperatively for neuroprotection, it is discontinued after the procedure as quickly as the patient’s neurologic condition permits. Prolonged postoperative use of corticosteroids may increase the risks of wound infection and dehiscence.

IV fluids are administered until the patient can tolerate oral feeding and drinking. In anterior thoracolumbar procedures, nasogastric drainage may be required if paralytic ileus occurs. Routine orders for antiemetics, antacids, and stool softeners are written.

If closed wound drainage is employed, the drain is removed when its output diminishes (usually on postoperative day 1). In transthoracic procedures, the chest tube is removed when the lungs have fully reexpanded and pneumothorax has resolved. If significant blood loss has occurred during or after the operation (through the drain or chest tube), hemoglobin levels are checked. If symptomatic anemia exists, blood transfusion is considered.

Wound hematoma is of particular significance after anterior cervical surgery. Small neck hematomas may cause dysphagia, odynophagia, hoarseness, or sore throat, and are treated conservatively. However, a large neck hematoma can result in upper airway compromise, which constitutes a life-threatening emergency and necessitates immediate surgical evacuation. Although rare, such hematomas develop within the first 24 hours after the operation—hence the general practice of keeping patients in hospital overnight after anterior cervical fusion procedures.

Neurologic deterioration within the first 24-48 hours after surgery should raise clinical suspicions of epidural hematoma, prompting immediate imaging studies or surgical reexploration.

Early mobilization of the patient after fusion surgery not only expedites rehabilitation but also prevents certain complications (eg, DVT, atelectasis, and pneumonia). If fusion is performed without instrumentation, an external orthosis is employed until the fusion has matured. After instrumented fusion, an external orthosis may still be applied to supplement the internal instrumentation, depending on the type and extensiveness of the procedure and the risk of instrumentation failure.

Fever is not uncommon after fusion surgery. A low-grade fever on postoperative day 1 or 2 is usually due to atelectasis and is treated with incentive spirometry and early patient mobilization. A high-grade or protracted fever should be worked up to exclude pneumonia, urinary tract infection (UTI), wound infection, and bacteremia. The incision should be examined daily (by the healthcare staff during the hospitalization and by the patient and family after discharge).

Occasionally, fever occurs in absence of any evidence of infection after an operation that required significant muscle retraction and manipulation. In such cases, the fever may be due to pyrogenic substances released as a result of muscle necrosis.

The patient is usually discharged from the hospital within 24-48 hours after an elective fusion operation. Debilitated and elderly patients and those with neurologic or systemic injuries may require longer hospitalization.

Although initiation of exercise therapy is often delayed until more than 3 months after lumbar fusion, Abbott et al showed that rehabilitation can be conducted during the first 3 postoperative months. ^[48] All patients in this study received a home program focusing on the following:

• Pain-contingent training of functional strength and endurance of back, abdominal, and leg muscles
• Stretching
• Cardiovascular fitness

One group also received three outpatient sessions focusing on modifying maladaptive pain cognitions, behaviors, and motor control. ^[48] Patients who also received psychomotor therapy demonstrated significant improvement with respect to functional disability, self-efficacy, outcome expectancy, and fear of movement/(re)injury.

Specific complications of fusion surgery include injury to nearby structures specific to the particular operation or approach (eg, RLN palsy after anterior cervical surgery).

General complications of fusion surgery include the following:

• Infection of soft tissues, epidural space, bone, disk space, fusion mass, or hardware, which may necessitate removal of instrumentation, prolonged IV antibiotic treatment, or both
• Bleeding, which may necessitate transfusion - Studies from Asia suggested that tranexamic acid and batroxobin may be helpful for reducing blood loss in spinal surgery ^{[49, 50, 51]}
• Wound hematoma, which may necessitate surgical evacuation, particularly if it causes airway compromise after anterior cervical surgery
• Epidural hematoma, necessitating surgical evacuation
• Nerve-root or spinal cord injury
• Cerebrospinal fluid leakage or pseudomeningocele formation, necessitating repair
• Vascular injury (eg, vertebral or carotid artery injury in the cervical spine or iliac vessel injury in the lumbar spine)
• Organ injury (eg, to the esophagus, pharynx, or rectum)
• Nerve injury (eg, to the RLN or the hypoglossal nerve)
• Pseudarthrosis, necessitating redo fusion
• Excessive subsidence, displacement, or breakage of a structural graft
• Hardware failure (eg, loosening, pullout, or breakage), necessitating reoperation
• Discomfort associated with the hardware
• Wound dehiscence

Complications associated with iliac crest bone graft harvest include the following:

• Infection
• Bleeding, hematoma formation, bruising
• Pelvic fracture
• Pain of musculoskeletal or neuralgic origin
• Numbness around or related to the incision
• Sacroiliac joint dysfunction and pain

Systemic complications of fusion surgery include, but are not limited to, the following:

• DVT, PE
• Myocardial infarction, congestive heart failure
• Atelectasis, pneumonia
• UTI
• Peripheral nerve injury related to patient positioning
• Blindness related to intraoperative retinal ischemia

A potential long-term complication of fusion in the cervical or lumbar spine is adjacent segment degeneration, also known as transition level syndrome (see the image below). The intended loss of motion across the fused motion segment or segments increases the biomechanical stress on the adjacent motion segments. Over time, this may result in disk herniation, accelerated disk or facet degeneration, or spinal stenosis at the adjacent segments above or below the level of fusion.

Although some instances of adjacent segment disease are undoubtedly due to the natural history of the underlying degenerative disease, and others are due to unintended injury to the adjacent segment elements (eg, facet joints) during the original fusion operation, the rest are thought to be caused by the biomechanical mechanism described above.

Symptomatic adjacent segment disease is more likely to develop if the adjacent segment is already diseased, albeit asymptomatically, at the time of the original fusion operation. In order to avoid reoperation in this situation, it is common practice to fuse the adjacent degenerated motion segment at the same time that the symptomatic motion segment is fused. If the degenerated adjacent segment is felt to be contributing to the patient’s pain syndrome, its fusion is further justified.

By the same token, if a patient presents with significant multilevel degenerative disease, fusion should be avoided if at all possible, unless sufficient indication exists for fusion of all of the affected motion segments (eg, multilevel cervical spondylosis with myelopathy).

A very rare complication of anterior or posterior decompression and fusion is the "white cord syndrome" of acute hemiparesis, which is believed to be due to acute reperfusion of chronically ischemic areas of the spinal cord. ^[52] The hallmark finding is an intramedullary hyperintense signal on T2-weighted MRI in a patient with unexplained neurologic deficits after spinal cord decompression. Patients with this syndrome have improved with steroid therapy and acute rehabilitation.

Patient follow-up is geared toward assessment of functional recovery (reduced pain and improved neurologic function), radiographic assessment of fusion, and detection of delayed postoperative complications.

The first follow-up visit is scheduled about 7-10 days after the procedure to assess the condition of the wound, remove staples and sutures, and address the patient’s questions and concerns.

Usually, the second and third follow-up visits are scheduled at 6 weeks and 3 months after the operation, though considerable variation exists in practice patterns. The focus of these visits is to ensure that the wound has healed properly, the fusion has progressed well, the patient’s neurologic function has improved as expected, the patient’s preoperative pain syndrome has resolved or diminished, the pain medications are tapered off, the brace is discontinued, and rehabilitation measures are instituted when appropriate.

If all has progressed well, additional follow-up can be performed through telephone calls, mailed questionnaires, or online communications, as dictated by specific practice patterns. Routine radiographic studies are performed at predefined intervals (eg, 6 weeks, 6 months, and 1 year postoperatively) until the fusion is deemed to be solid. Routine CT or MRI is not required after fusion surgery; these imaging methods are indicated only when there is concern regarding a specific problem that requires them for diagnosis.