Spine Fusion Surgery

Overview

Spinal fusion is a surgical procedure that permanently unites two or more vertebrae in your spine to increase stability, repair a deformity, or relieve discomfort. Spinal fusion may be recommended by your doctor to correct spinal deformities such as scoliosis, spinal weakness or instability, and herniated disk.

Spinal fusion procedures are intended to mirror the natural healing process of damaged bones. During spinal fusion, the surgeon inserts bone or a bone-like substance between two spinal vertebrae. Metal plates, screws, and rods may be used to hold the vertebrae together until they heal into an one solid unit.

Spinal fusion is a relatively risk-free treatment. However, as with any surgery, there is a risk of problems such as infection, poor wound healing, bleeding, blood clots, injury to blood vessels or nerves in and around the spine, and pain at the location where the bone transplant is extracted.

Even if spinal fusion relieves your symptoms, it does not prevent you from getting new back pain in the future. The majority of degenerative spine disorders are caused by arthritis, and surgery will not cure your body of that disease.

Immobilizing a segment of the spine adds stress and pressure to the areas around the fused section. This may hasten the degeneration of specific parts of the spine, necessitating more spinal surgery in the future.

Demographic Facts About Spine Fusion Surgery

According to the Agency for Healthcare Research and Quality (AHRQ), roughly 488,000 spinal fusions were performed during hospital stays in the United States (at a rate of 15.7 stays per 10,000 population), accounting for 3.1 percent of all operating room procedures. This is a 70% increase in procedures since 2001. Lumbar fusions are the most common type of fusion, with 210,000 performed each year. Every year, 24,000 thoracic fusions and 157,000 cervical fusions are performed.

A recent analysis of spinal fusions in the United States reported the following characteristics:

• Average age for someone undergoing a spinal fusion was 54.2 years – 53.3 years for primary cervical fusions, 42.7 years for primary thoracic fusions, and 56.3 years for primary lumbar fusions.
• 5% of all spinal fusions were on men.
• 8% were white, 7.5% black, 5.1% Hispanic, 1.6% Asian or Pacific Islander, 0.4% Native American.
• Average length of hospital stay was 3.7 days – 2.7 days for primary cervical fusion, 8.5 days for primary thoracic fusion, and 3.9 days for primary lumbar fusion.
• In-hospital mortality was 0.25%.

Why Spine Fusion Surgery Is Done?

Spinal fusion can be utilized to treat a wide range of disorders affecting the spine at any level (e.g. lumbar, cervical and thoracic). Spinal fusion is typically used to decompress and stabilize the spine. The greatest effect appears to be in spondylolisthesis, while evidence for spinal stenosis is less promising.

Degenerative disc disease is the most prevalent source of pressure on the spinal cord/nerves. Disc herniation, spinal stenosis, trauma, and spinal malignancies are also prevalent causes. Spinal stenosis is caused by bone growths (osteophytes) or thickened ligaments that cause the spinal canal to narrow over time. This results in leg pain with increased activity, which is known as neurogenic claudication.

Radiculopathy, or pressure on the nerves as they exit the spinal cord, causes discomfort in the location where the nerves originated (leg for lumbar pathology, arm for cervical pathology). This pressure can produce neurologic impairments such as numbness, tingling, bowel/bladder malfunction, and paralysis in severe cases.

Thoracic spinal fusions are less common than lumbar and cervical fusions. Because of increased motion and stress, degeneration occurs more frequently at higher levels. Because the thoracic spine is more immovable, most fusions are done as a result of trauma or abnormalities such as scoliosis, kyphosis, and lordosis.

Conditions where spinal fusion may be considered include the following:

• Degenerative disc disease.
• Spinal disc herniation.
• Discogenic pain.
• Spinal tumor.
• Vertebral fracture.
• Scoliosis.
• Kyphosis (e. g., Scheuermann's disease).
• Lordosis.
• Spondylolisthesis.
• Spondylosis.
• Posterior rami syndrome.
• Other degenerative spinal conditions.
• Any condition that causes instability of the spine.

Is There Any Contraindication For Spine Fusion Surgery?

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

1. Diffuse multilevel neoplastic disease such that no adjacent normal segments exist for engagement of instrumentation.
2. Severe osteoporosis such that the bones would not support instrumentation and fusion would not be expected to solidify in absence of instrumentation.
3. 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:

1. Osteoporosis.
2. Smoking.
3. Malnutrition.
4. Systemic infection.
5. Anemia.
6. Chronic hypoxemia.
7. Severe cardiopulmonary disease.
8. Severe depression, psychosocial issues, and secondary gain issues.

In each case, the risks of not doing the procedure must be evaluated against the dangers of performing the operation. For example, while smoking and severe depression may be contraindications for fusion in a patient with back discomfort and disk degeneration, the surgeon should not be discouraged from fusing an unstable cervical spine fracture.

It is crucial to remember that an active spine infection (diskitis/osteomyelitis) does not always exclude fusion and instrumentation. On the contrary, advanced spine infections cause substantial destabilization of the spine, frequently necessitating stability during debridement and decompression.

Careful clinical, laboratory, and radiographic monitoring are required in this context, since the patient gets prolonged intravenous (IV) antibiotic treatment (for 6 weeks) to confirm infection eradication. A persistent infection is indicated by worsening pain or neurologic deficit, persistent fever, leukocytosis, or bacteremia, and persistently high erythrocyte sedimentation rate (ESR).

Effectiveness of Spine Fusion Surgery

Although spinal fusion surgery is commonly used, there is insufficient proof that it is useful for a variety of common medical disorders. In a randomized controlled trial of patients with spinal stenosis, for example, there were no significant therapeutic benefits of lumbar fusion in combination with decompression surgery compared to decompression surgery alone after 2 and 5 years. This Swedish study, which included 247 patients enrolled from 2006 to 2012, discovered that those who got fusion surgery had higher medical costs as a result of increased operation time, hospital stay duration, and implant cost.

Furthermore, a 2009 systematic review on surgery for lower back pain discovered that there was no benefit in health outcomes (improvement in pain or function) of performing fusion surgery versus intensive rehabilitation including cognitive-behavioral treatment for nonradicular low back pain with degenerative disk disease.  Similarly, researchers in Washington State believed that lumbar fusion surgery provided uncertain medical value, higher expenses, and increased risks when compared to intense pain regimens for chronic low back pain with degenerative disk disease.

How To Prepare Yourself For The Surgery?

Once the decision to fuse a specific spine section has been taken, there may be numerous surgical approaches available to achieve this process. When a specific approach is chosen, the etiology of instability becomes irrelevant because the technical processes are the same. Following sections discuss the most commonly used fusion procedures in various locations of the spine.

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 are common preoperative tests (ECG). Blood is examined and typed. If there is going to be a lot of blood loss, one or two units of packed red blood cells (RBCs) are cross-matched or a cell saver is utilized. Alternatively, if the procedure is arranged on a voluntary basis, the patient may donate autologous blood several weeks in advance.

Thigh-high compression stockings (TED hose) and sequential compression devices are used to prevent deep vein thrombosis (DVT) before surgery and are not removed until the patient is mobile.

Subcutaneous injections of low-molecular-weight heparin (LMWH) may begin before surgery in patients who are at high risk for DVT and pulmonary embolism (PE; for example, those who are paraplegic, quadriplegic, or bedbound prior to surgery), with the individual patient's risk of postoperative epidural hematoma carefully weighed against the risk of PE. When heparin is given, meticulous hemostasis, liberal use of closed wound drainage, and thorough postoperative neurologic assessment are required.

An antistaphylococcal antibiotic, commonly a first-generation cephalosporin, is administered one hour before the skin incision and is continued for three doses postoperatively.

What Happens Before Spine Fusion Surgery?

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.

1. Positioning:

A prone position is ideal for posterior cervical surgeries. Although some surgeons utilize a sitting position to prevent epidural vein hemorrhage, this position puts the patient at risk for intraoperative hypotension and venous air embolism. All posterior cervical operations can be performed safely in the prone position with careful surgical technique, judicious use of bipolar coagulation, and the use of an operating microscope as appropriate.

Three-point skeletal fixation in a Mayfield head holder can immobilize the patient's head while also allowing precise control of neck shape. If the head is placed on a foam or horseshoe head holder, special care should be taken to minimize eye compression, which could result in increased intraocular pressure and retinal ischemia.

The patient is positioned prone over a frame or table that allows the abdomen to hang freely for posterior lumbar and thoracolumbar fusions. Otherwise, the increased intra-abdominal pressure might obstruct venous return and worsen intraoperative bleeding. This criteria is met by the Wilson frame, which provides the quickest and least laborious method of placing the patient. Other spine frames and tables, such as the Andrews table, allow the patient to be positioned knee-to-chest.

The increased interlaminar and posterior interbody distances provide for easier access to the spinal canal and disk areas as a result of the lumbar flexion. If the patient is fused in this posture, the patient's natural lumbar lordosis is lost, resulting in "flat back" syndrome. For combined anterior-posterior surgeries, other spine tables, such as the Jackson table, which allows the patient to be switched from supine to prone and vice versa, are beneficial. To prevent compression neuropathy, all pressure areas must be carefully padded regardless of the position or frame employed.

2. Fluoroscopy:

Intraoperative fluoroscopy is required for safe and accurate spine instrumentation. When possible, a radiolucent frame should be used to allow for lateral and anteroposterior fluoroscopy. The C-arm should be draped sterilely and placed in such a way that it may be easily manipulated into and out of imaging position.

Alternatively, fluoroscopy-based stereotactic navigation, which uses a computer with advanced stereotactic software to provide virtual fluoroscopic navigation throughout the surgery, can be used. After the spine is exposed and a bone-mounted stereotactic frame is installed, AP and lateral fluoroscopic images are acquired. After that, the C-arm is withdrawn, and the surgery is carried out using computer-assisted navigation of the original fluoroscopic pictures.

3. Neurophysiologic monitoring:

Intraoperative neurophysiologic monitoring for spine surgeries includes the use of somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), or electromyography (EMG) to detect and rectify factors that contribute to neurologic impairment during the surgical procedure. Stimulation of the pedicle probe with a nerve stimulator at subthreshold currents during pedicle screw placement would result in EMG activity in the lower extremities if the probe came into contact with the nerve root, urging its repositioning.

4. Microdissection under microscopy:

Microdissection under an operating microscope allows for safer decompression of neural components, which is especially useful in situations where visibility is limited (eg, anterior cervical diskectomy and osteophyte resection). When the more delicate decompression part of the surgery is completed, the microscope can be taken out of place before proceeding with fusion and instrumentation.

5. Anesthesia:

Anesthetic issues during fusion surgery include maintaining adequate blood pressure and fine-tuning muscular relaxation while preserving anesthetic depth. Muscle relaxation helps with initial spine exposure, but it must be avoided or reversed if intraoperative MEP or EMG is to be employed. When there is no muscular relaxation, it is crucial to maintain deep anesthesia to prevent patient movement during critical phases of the surgery, such as spinal cord decompression.

To avoid neural ischemia, which could exacerbate existing neurological injury, adequate blood pressure must be maintained at all times. An arterial line may be placed for continuous monitoring in patients with labile blood pressure or cardiopulmonary risk factors. A central line is placed if appropriate peripheral venous access is not available. A bladder catheter is implanted if the treatment is likely to last more than 2 hours.

What Happens During Spine Fusion Surgery?

There are numerous spinal fusion procedures. Depending on the level of the spine and the location of the compressed spinal cord/nerves, each technique varies. Following decompression of the spine, bone graft or artificial bone replacement is put between the vertebrae to aid in their healing. Fusions are typically performed on the anterior (stomach), posterior (back), or both sides of the spine.

Most fusions are now accompanied with hardware (screws, plates, and rods) because it has been demonstrated that they have higher union rates than non-instrumented fusions. Minimally invasive procedures are also getting popular. These procedures employ modern image guidance systems to put rods/screws into the spine through smaller incisions, resulting in reduced muscle injury, blood loss, infections, pain, and hospital stay.

The following list gives examples of common types of fusion techniques performed at each level of the spine:

Cervical spine:

1. Anterior cervical discectomy and fusion (ACDF): Anterior cervical discectomy and fusion (ACDF) is a neck procedure that removes a herniated or degenerative disc. To reach and remove the disc, an incision is made in the throat. A graft is used to join the bones above and below the disc. If physical therapy and medications fail to relieve your neck or arm pain caused by pinched nerves, ACDF surgery may be an option. Patients are usually discharged on the same day.

2. Anterior cervical corpectomy and fusion: When the cervical disease encompasses more than just the disc space, the spine surgeon may recommend removal of the vertebral body as well as the disc spaces at either end to completely decompress the cervical canal.This procedure, a cervical corpectomy, is often done for multi-level cervical stenosis with spinal cord compression caused by bone spur (osteophytes) growth.

3. Posterior cervical decompression and fusion: The principal advantage of the posterior approach is that a spine fusion does not need to be done after removing the disc.The principal disadvantage is that the disc space cannot be jacked open with a bone graft to give more space to the nerve root as it exits the spine. Also, since the posterior approach leaves most of the disc in place, there is a small chance (3% to 5%) that a disc herniation may recur in the future.

Thoracic spine:

1. Anterior decompression and fusion.

2. Posterior instrumentation and fusion: many different types of hardware can be used to help fuse the thoracic spine including sublaminar wiring, pedicle and transverse process hooks, pedicle screw-rod systems, vertebral body plate systems.

Lumbar spine:

• Posterolateral fusion is a bone transplant between the transverse processes at the rear of the spine. These vertebrae are then secured in place with screws or wire threaded through the pedicles of each vertebra and attached to a metal rod on each side of the vertebrae.

• Interbody fusion is a graft in which the entire intervertebral disc between the vertebrae is removed and a bone graft is implanted in the gap between the vertebrae. To preserve spine alignment and disc height, a plastic or titanium device can be implanted between the vertebrae.The types of interbody fusion are:

1. Anterior lumbar interbody fusion (ALIF) – the disc is accessed from an anterior abdominal incision.
2. Posterior lumbar interbody fusion (PLIF) – the disc is accessed from a posterior incision.
3. Transforaminal lumbar interbody fusion (TLIF) – the disc is accessed from a posterior incision on one side of the spine.
4. Transpsoas interbody fusion (DLIF or XLIF) – the disc is accessed from an incision through the psoas muscle on one side of the spine.
5. Oblique lateral lumbar interbody fusion (OLLIF) – the disc is accessed from an incision through the psoas muscle obliquely.

Post-operative Complications of Spine Fusion Surgery

Spinal fusion is generally a safe procedure. But as with any surgery, spinal fusion carries the potential risk of complications.

Potential complications include:

• Infection.
• Poor wound healing.
• Bleeding.
• Blood clots.
• Injury to blood vessels or nerves in and around the spine.
• Pain at the site from which the bone graft is taken.

Conclusion

Spinal fusion, is a neurosurgical or orthopedic surgical technique that joins two or more vertebrae. This procedure can be performed at any level in the spine (cervical, thoracic, or lumbar) and prevents any movement between the fused vertebrae. There are many types of spinal fusion and each technique involves using bone grafting—either from the patient (autograft), donor (allograft), or artificial bone substitutes—to help the bones heal together. Additional hardware (screws, plates, or cages) is often used to hold the bones in place while the graft fuses the two vertebrae together. The placement of hardware can be guided by fluoroscopy, navigation systems, or robotics.

Spinal fusion is most commonly performed to relieve the pain and pressure from mechanical pain of the vertebrae or on the spinal cord that results when a disc (cartilage between two vertebrae) wears out (degenerative disc disease). Other common pathological conditions that are treated by spinal fusion include spinal stenosis, spondylolisthesis, spondylosis, spinal fractures, scoliosis, and kyphosis.

Like any surgery, complications may include infection, blood loss, and nerve damage. Fusion also changes the normal motion of the spine and results in more stress on the vertebrae above and below the fused segments. As a result, long-term complications include degeneration at these adjacent spine segments.