Chapter 30 Adult Lumbar Spinal Fusion

Charlene Hannon, PT, MBA

More than 200,000 spinal fusions are performed each year in the United States. Controversy exists as to whether spinal fusion is the treatment of choice for patients with various types of low back pain. Some of the reasons for this controversy are that there is a 10% to 40% pseudarthrosis (failure of fusion) rate; improved function, particularly return to work, does not always occur; and many patients experience continued postoperative pain. Furthermore, in some cases, additional surgery is necessary and adds to health care costs. In the United States alone, total health care expenditures incurred by individuals with back pain reached an estimated 90.7 billion dollars, and, on average, individuals with back pain incurred 60% higher expenditures than individuals without back pain. Careful patient selection and choice of the appropriate surgical procedure seem to generate the best surgical outcomes.

Fusions can be classified into two categories: instrumented and noninstrumented. Noninstrumented fusions do not use any hardware. They are much less commonly performed and are usually done for single-level fusions only. The two most common instrumented lumbar spinal fusion procedures are posterior lumbar interbody fusion (PLIF) and circumferential fusion. Both procedures have a very good rate of fusion. Bono and Lee showed that PLIF has a fusion rate of 85%, and circumferential yielded 91% fusion. For the purpose of this guideline, only the PLIF will be described. It is important, however, that the physical therapist be aware that there are many spinal fusion techniques. The principles of rehabilitation following lumbar spinal fusion remain the same, regardless of the procedure.

One of the most important concepts for the physical therapist to understand is the concept that the hardware is merely a temporary scaffold until biological healing is complete. Biological healing can be affected by many factors including smoking, poor surgical technique, and mechanical stress across the fusion mass (movement during the phases of healing). It is the mechanical stress with which the physical therapist is to be most concerned when developing a rehabilitation program. Careful consideration must be made of the forces generated by lever arms, such as the upper and lower extremities and their effects on the lumbar spine. Although there is a paucity of research examining the in vivo forces generated across a healing fusion site, Rohlmann et al. did show that lifting both legs in the supine position generated the highest loads on the fixation devices as compared to most other lumbar stabilization exercises.

Osteoporosis is a relative precaution and does not preclude complete healing from occurring. Additional precautions, such as bracing, may be required in patients with osteoporosis.

In summary, the following are generally accepted indications for spinal fusion:

• When decompression (laminectomy) is warranted because of spinal stenosis, spondylosis or degenerative disc disease, and more than half of the lamina is removed, creating an unstable segment.

• Without decompression to stabilize a motion segment that is unstable (defined as >4 mm excursion on bending X rays).

• To stabilize a motion segment with spondylolisthesis and thus prevent further slippage or possibly correct for slippage.

• After the surgical removal of various types of bony sarcomas (this will not be addressed in this guideline).

• Intractable pain.

• Neurological signs.

• Failed conservative management.

Surgical Overview

• PLIF describes a technique that is indicated to treat various spinal pathologies, as listed previously.

• The primary goal of the technique is to provide a solid interbody fusion with decompression of the surrounding neural structures and restoration of vertebral alignment.

• In addition, the procedure should provide global spinal balance that protects adjacent normal segments. Global spinal balance is the concept that when alignment is corrected at a given intervertebral segment, total spinal alignment is preserved. In other words, a new misalignment is not created.

• The PLIF is a four-stage procedure, as follows:

Stage 1: Exposure and decompression

Stage 2: Spinal instrumentation and preliminary fixation

Stage 3: Anterior column reconstruction and interbody fusion

Stage 4: Internal stabilization and completion of surgery

• Stage 1: The area is decompressed, taking care to preserve normal tissues and structures at adjacent levels, particularly the posterior spinous processes and the interspinous ligaments, as well as the facet joints to prevent late adjacent segment instability. Also, care is taken so as not to denervate the paraspinal muscles.

• Stage 2: The instrument system is also referred to as “hardware” and is essentially internal spinal fixation. The components may consist of rods, plates, hooks, wires, and/or screws and are available in both stainless steel and titanium (the main advantage of titanium is its magnetic resonance imaging compatibility). Instrumentation is placed in the pedicles to prepare for stage 3.

• Stage 3: Numerous distraction techniques may be used to restore normal disc height. Care is taken so as not to place the neural structures under excessive tension. Once the ideal height is attained, the screws on the plates are tightened to maintain the gains. Next, the disc space is prepared. A complete discectomy is performed, and the end plate is scraped to create bleeding. If bleeding becomes excessive, it must be controlled. The ultimate goal is to ensure a good bone graft to vertebral bone contact, a large surface area of bleeding bone, and no interposition of soft tissue. The bone graft is then placed. Graft material may be the bone chipped away from the decompression procedure, iliac crest bone graft, or allograft material.

• Stage 4: The working hardware is replaced with the final implants, and the incision is closed. The procedure described can be repeated for multiple segments, as necessary.

Rehabilitation Overview

• The rehabilitation program begins postoperatively at the bedside and is progressed to achieve short-term goals for discharge to the home.

• Patients continue a basic home exercise program for the first 4 to 6 weeks and then begin outpatient therapy.

1 Careful consideration is given to provide a protective environment for the healing fusion.

2 Outpatient therapy is typically provided from 6 weeks to as long as 6 months, depending on the individual and the surgeon.

3 Generally, for a one-level procedure, fusion should occur within 4 months of the surgery. For more complex, multilevel spinal fusions biological healing of the fusion reaches a peak at 1 year but continues to mature from 1 to 2 years.

• Goals are set individually and are functionally based, targeting return to full activities of daily living (ADL) and return to full-time employment.

Preoperative Phase

GOALS

• Patient education: pain management, logrolling, concept of bending from the hips, and importance of avoiding lumbar movement

• Maximize strength/functional capabilities: Upper body strength becomes important for bed mobility, hamstring flexibility in the absence of neural tension signs

• General conditioning: Improvements in preoperative endurance will benefit patients in the postoperative phase

PRECAUTIONS

• Avoid movements that increase pain (patient may be flexion, neutral, or extension-biased)

• Avoid loaded positions if load-sensitive

• Avoid exercises that aggravate neural tissue in the presence of neural tension signs

TREATMENT STRATEGIES

• Neutral-biased lumbar stabilization

• Functional tests—squatting, lunging, transitions to/from floor

• Gait training (educate in progression from walker to cane)

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