Spinal Fusion – Indications, Types and Complications

Last Updated on August 26, 2023

Spinal fusion is a surgery done to fuse two or more vertebrae. Fusing means two bones are permanently placed together so there is no longer movement between them. The term is technically similar to arthrodesis. Spinal fusion is usually done along with other surgical procedures of the spine.

Other terms for spinal fusion are spondylodesis or spondylosyndesis.

A spinal fusion surgery aims to stop the motion at a painful vertebral segment, which in turn should decrease pain generated from the joint.

In the procedure of spinal fusion, supplementary bone tissue like autograft or allograft is used to aid in fusion. Now, synthetic bone grafts are also used with promising results. The bone grafts or substitutes are used to stimulate and aid in fusion by working in conjunction with the body’s natural osteoblastic processes [New bone formation],  this graft helps in creating a bony bridge across the vertebrae.

Indications for Spinal Fusion

The main aim of spinal fusion is to block movement to alleviate pain or to provide stability by fusing the vertebra. It is indicated in all the diseases where the motion of the vertebrae is contributory to pain occurrence or alleviation of the movement between two or more vertebrae may relieve the pain, Spinal fusion is may be indicated in the following diseases.

• Degenerative disc disease
• Spinal disc herniation
• Spinal surgeries for spinal tumor
• Vertebral fracture
• Scoliosis
• Spondylolisthesis
• Spondylosis
• Spinal Instability

The abnormal mobility of a motion segment in the spine is the commonest cause of chronic low back pain.

The basic indication for spinal fusion is instability in a motion segment of the spine causing low back pain.

The instability may be present from birth like in spondylolisthesis or acquired as in trauma, tuberculosis, metabolic, degenerative or neoplastic disorders of the spine not to forget the iatrogenic causes and failed back syndromes.

Thus, the fusion can be used to

• Correct a spinal deformity
• Relieve pain caused by vertebral motion
• Restore stability when spinal instability is present
• Fuse the broken vertebral segments to restore alignment and stability

Here is a brief discussion of different conditions.

Degenerative Disc Disease

It is a degenerative disease where the intervertebral disc undergoes many age-related changes. It may result in associated changes around such as facet joints. Most of the time the condition is amenable to nonoperative treatment.

Surgery when required involves decompression of the neural structure involved and removal of motion between two vertebrae to decrease the pain by fusion of the involved vertebrae.

Spinal disc herniation

An acute herniation of the disc especially in the cervical region may warrant the need for removal of the disc and bone grafting for spinal fusion as removal of the disc would cause instability between the two involved vertebrae.

In lumbar disc herniation though, just the disc removal is enough in most of the cases. However, addition of spinal fusion may produce better results in some cases.

Spinal surgeries for Spinal Tumor

Spinal tumor surgeries may cause bone loss and warrant spinal fusion to block the movement.

Vertebral Fractures

Vertebral fracture surgery involves fixation of the injury by using the suitable implant, a pedicle screw in most cases. A spinal fusion is needed to create a union between injured vertebrae that would protect the spine after the implant has been removed or fatigued. [Note: the implant has a limited life span, hence fusion is almost always required]

Scoliosis

Correction of the scoliotic curves may require multiple fusions across the length of the corrected curve to stabilize the corrected curve.

Spondylolisthesis

Spondylolisthesis, if progressive, and greater than 30%, needs to be corrected in situ and requires vertebral fusion.

De­compression and fusion have been associated with better outcomes than decompression alone in degenerative spondylolisthesis.

Spondylolysis

Degenerative spondylosis, when advanced may require decompression and/ or fusion of the painful motion segment.

Multilevel spinal stenosis

When decompression involves more than 3 levels, fusion is added to protect the spine from instability.

How is Spinal Fusion Done

The spine may be approached from the front [anterior approach], the back [posterior approach] or the side [lateral]

In the lumbar spine, both anterior and posterior approaches may be used. Cervical spine fusion surgery mostly employs the anterior approach.

The nature and location of the lesion would determine the right approach.

All the primary surgeries are carried out first as required. these may include decompression, fixation, curve correction, etc.

For fusion, bone grafting is done. The procedure includes the insertion of pieces of graft bone between nd across the vertebrae to be fused.

Bone Grafting stimulates the bone healing and results in formation of bone that provides solid union.

Autograft is the most commonly used type of bone graft. It is often harvested from iliac crest of the patient.

Allograft is the term when a graft from other person,s cadever bone is used.

Several substitutes to graft are also available. These are

• Demineralized bone matrices
• Bone morphogenetic proteins
• Synthetic bone grafts

Types of Spinal Fusion

There are several types of spinal fusion surgery options. The most commonly employed surgical techniques for the lumbar spine.

• Posterolateral Gutter Fusion
  • Posterior approach
  • Gutter is created on the posterolateral aspect for the bone graft.
• Posterior Lumbar Interbody Fusion (PLIF)
  • Posterior approach
  • The disc  between two vertebrae removed
  • Graft bone is inserted between the two vertebral bodies
• Anterior Lumbar Interbody Fusion (ALIF)
  • Anterior approach
  • Disc removal and graft between the body
• Anterior/Posterior Spinal Fusion
  • Combined fusion
• Transforaminal Lumbar Interbody Fusion (TLIF)
  • Unilateral access to the disc space through the intervertebral foramen.
  • The spine is approached posteriorly and a graft is used for fusion.
• Extreme Lateral Interbody Fusion (XLIF)
  •  An interbody fusion in which the approach is from the lateral side through the psoas muscle
• Oblique Lateral Lumbar Interbody Fusion (OLLIF)
  • Retroperotineal access
• Multilevel Spinal Fusion
  • >3 or more levels
  • Usually in deformity correction

For the cervical and thoracic spine, the two types of fusion are anterior and posterior. The actual surgical details may vary depending on the additional procedures chosen for decompression. For example, in the cervical spine, it could be just a discectomy or in some cases corpectomy.

Primarily, the fusion is augmented by a fixation device. The aim of using a fixation device is to keep holding the bones in position until the fusion occurs.

Open vs. Minimally Invasive Spinal Fusion

Minimally invasive spinal fusion is the procedure where the surgery is done using very small incisions as compared to the traditional form of surgery which requires a bigger incision and is called open surgery.

MIS fusion may be done endoscopically too.

Complications of Spinal Fusion

With any type of spine fusion, there is a risk of clinical failure. Complications also depend on the type/extent of spinal fusion surgery performed.

• Infection
• Bleeding
• Iatrogenic injury to nerve or vessels
• Adjacent segment disease – Degeneration of vertebrae above/below the fused segments
• Epidural fibrosis
• Failure of Relief
  • 20% cases
  • Called failed back surgery syndrome
• Pseudoarthrosis
  • Failure of vertebrae to fuse
  •  5% to 10% of spine fusion surgeries
  • Occurs more in smokers.
• Hardware Failure
• Graft Migration

Anterior grafts and cages can migrate or subside, which may require repeat spine surgery

Follow Up and Recovery after Spinal Fusion

The fusion process typically takes 6–12 months after surgery. Sometimes spinal fusion fails to occur and surgery may be required.

Recovery from surgical procedures has individual variations. However, a general outline is given.

After the recovery from the effects of a surgical procedure, which includes a few days of hospital stay for wound care and drug administration, as the patient regains independence, she is discharged.

The union across the fusion takes time and the activity level is gradually increased.

Light activity and walking begin within the first week depending on pain tolerance.

From the second week onward patient is generally allowed to sit.

Driving and sedentary work can begin in 3-6 weeks.

Manual work and heavy lifting are not to be done before 12 weeks.

Physical therapy is initiated after 6 weeks to 3 months after surgery

The Success of Spinal Fusion

Spinal fusion is typically an effective procedure but surgery does not always improve pain, and in some cases, can make it worse.

The clinical success following spinal fusion is judged by the relief of pain and a clini­cally stable spine. The stability is dependent on successful arthrodesis.

Techniques of spinal fusion and constitutional factors like age, sex, and osteoporosis affect the outcome.

Degeneration of adjacent segments may lead to back pain issues in future.

References

• Miyazaki M, Tsumura H, Wang JC, Alanay A. An update on bone substitutes for spinal fusion. Eur Spine J. 2009 Jun;18(6):783-99. doi: 10.1007/s00586-009-0924-x.
• Mobbs RJ, Loganathan A, Yeung V, Rao PJ. Indications for anterior lumbar interbody fusion. Orthop Surg. 2013 Aug;5(3):153-63. doi: 10.1111/os.12048.
• ujita T, Kostuik JP, Huckell CB, Sieber AN. Complications of spinal fusion in adult patients more than 60 years of age. Orthop Clin North Am. 1998 Oct;29(4):669-78. doi: 10.1016/s0030-5898(05)70040-7.