Lumbar Spine Fusion

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Lumbar Spine Fusion

Chris Izu, Haideh V. Plock, Jessie Scott and Paul Slosar, Adam Cabalo

In the early 1900s two surgeons began performing lumbar fusions. Dr. Russell Hibbs and Dr. Fred Albee pioneered the posterior approaches for arthrodesis.1,2 Over the subsequent decades, many surgeons improved fusion techniques, with extension of the fusion laterally to incorporate the transverse processes and the sacral ala.36 The patient’s autogenous iliac crest is the standard source of bone graft material.7,8 A rapid evolution has occurred in the development and use of spinal fixation devices. Although tracing the historical evolution of these devices is beyond the scope of this chapter, they can simply be categorized as anterior or posterior fixation devices. The most common and most controversial are the pedicle screw and rod/plate systems. Anterior fixation devices include screw and rod/plate systems, as well as the recently introduced interbody cages. This chapter describes the indications for elective lumbar fusions and discusses the various methods of arthrodesis.

Surgical Indications and Considerations

In the elective patient population, most indications for lumbar arthrodesis are based on the presence of severe, disabling back or leg pain. Posttraumatic cases of segmental instability or potential neurologic injury also may require fusions, but this chapter focuses on patients with degenerative spinal pathology.

Patients with low back pain experience symptoms resulting from tissue aggravation during the degenerative cascade.9 Trauma or overuse causes the disc wall to begin to develop microtears; this eventually results in a loss of disc height that alters the alignment of the facet joints. This may lead to pain, with accompanying spasm and guarding. The joints begin to develop synovitis, articular cartilage degeneration, and adhesions. This alters the spinal motion mechanics at that segment, further stressing the annulus of the disc and accelerating the degenerative process of the facet. Increased wearing of the cartilage and hypermobility of the facet also occur. The superior and inferior facet surfaces begin to enlarge. As the joint becomes more disrupted, normal motion at that segment becomes impossible. The disc begins to undergo greater strain. The disc wall weakens further, begins to bulge, and can eventually herniate. The disc continues to lose fluid and height, causing narrowing of the neural foramen, or foraminal stenosis. This process is outlined in Table 16-1.

Patients with severe back pain that is refractory to conservative care may be candidates for surgical evaluation. Conservative care should include a rigorous attempt at exercise-based dynamic stabilization training, therapeutic injections, and medications. Surgical treatment should only be discussed with the patient after a firm diagnosis has been made.

Diagnostic Tests

Spinal radiographs show osteophytes and segmental disc space narrowing in patients with degenerative spondylosis. A defect in the pars interarticularis is seen in patients with spondylolysis. Anterolisthesis, or a forward slippage of one vertebra on the next, is the hallmark radiographic finding in spondylolisthesis. Flexion and extension films can help to detect hypermobility or excessive motion in degenerative lumbar conditions.

Computed tomography (CT) reliably evaluates the bone or spondylosis compression against the nerves. Computer-enhanced reformatted CT images are as effective in evaluating spinal stenosis as myelography. CT scanning is more sensitive than magnetic resonance imaging (MRI) in the evaluation of bony stenosis, whereas MRI gives useful information about the health of the discs and nerves. Combining the two imaging modalities gives a very accurate, thorough picture of the lumbar spinal pathoanatomy.

Provocative discography can be a useful diagnostic tool in the work-up of patients with painful degenerative lumbar disc disease. The lumbar discs are deep within the abdominal cavity and do not have true dermatomal pain patterns in axial discogenic cases. Overlapping sclerodermal referred pain patterns in the lumbar spine make the localization of the true pain generator difficult. Discography has evolved as a test to examine the lumbar discs morphologically and, most importantly, provocatively. On injection into the disc, the patient must communicate to the discographer if that disc is concordantly painful. Many degenerative discs are either not painful or discordantly painful. This information can be useful for the surgeon and the patient contemplating lumbar arthrodesis. The test is not used as frequently as in the past, as authors have described conflicting results and there is emerging concern that the injection itself may cause eventual disc deterioration.10

Diagnosis

Among patients undergoing elective lumbar arthrodesis, painful degenerative disc disease is the most prevalent diagnosis. Confirmatory diagnostic testing often includes MRI scanning and discography for equivocal cases. Overlap occurs among patients who have had previous surgery and have a diagnosis of “failed back surgery syndrome,” a nonspecific diagnosis. Before surgery is contemplated, every effort must be made to arrive at a diagnosis that specifically isolates the source of pain.

Patients often have numerous diagnoses, each of which may be valid. For example, a 45-year-old man who had a laminotomy performed 5 years ago for a herniated nucleus pulposus comes to his physician complaining of 50% low back pain and 50% right leg pain and numbness. Diagnostic imaging is significant for L4 to L5 segmental degeneration with osteophytes and narrowing of the disc space. A multiplanar CT scan reveals moderate spondylosis (bone spurs) with stenosis along the right neural foramen. Discography is concordant with pain reproduction at the L4 to L5 disc. The appropriate diagnoses include painful degenerative disc disease, lumbar spondylosis with stenosis, and postlaminectomy syndrome.

The absolute requisite for a successful lumbar surgery outcome is matching concordant patient symptoms with the appropriate surgical procedure. Patients who cannot manage their pain with conservative measures and have demonstrable, concordant pathology on diagnostic testing may benefit from lumbar arthrodesis.

Types of Fusions

Instrumentation Versus Noninstrumentation

The goal of a lumbar arthrodesis is the successful union of two or more vertebra. Controversy exists over the most efficient way to achieve this result. Instrumentation can be used to immobilize the moving segments while the fusion becomes solid. One of the original and most popular systems is the Harrington hook/rod construct. Although this distraction type of fixation immobilizes the spine in certain planes, it causes a loss of physiologic lordosis, or a “flat-back syndrome,” in many patients.

Today, most spine surgeons use pedicle screw constructs to immobilize the vertebrae rigidly while preserving the normal lumbar lordosis2 (Fig. 16-1). Typically, external orthosis bracing is not needed in these cases. As well-controlled studies emerge, data support the use of internal fixation for fusion.11 Most studies support the use of pedicle screw fixation to obtain a more reliable bony union, although complication rates tend to be higher with these devices as well.12,13

Some surgeons do not routinely use pedicle screws for arthrodesis. In most of these situations (when pedicle screws are used) the patient must wear a lumbar orthosis for an extended period postoperatively. To immobilize the L5 to S1 motion segment effectively, an orthosis with a thigh-cuff extension must be applied. Patients with noninstrumented fusions may take an extensive amount of time to stabilize and become comfortable in their rehabilitation. Conversely, most patients with internal fixation become mobile and independent more rapidly, making early rehabilitation more predictable.

Posterior Fusion

Posterolateral Lumbar Fusion

Different surgeons use different techniques to perform a lumbar fusion. The traditional approach is through a midline posterior incision. If necessary the surgeon performs a laminectomy/laminotomy to address the pertinent pathology. Most surgeons perform a posterolateral fusion, which means that the transverse processes, pars interarticularis, and, if needed, the sacral alae are decorticated. The patient’s own iliac crest bone graft or a bone graft substitute is then placed on the decorticated surfaces, forming a fusion bed contiguous with all the surfaces to be fused. Pedicle screws and rods or plates may be placed to immobilize the motion segments rigidly and augment the formation of a solid union.

The problems with a posterolateral fusion are both mechanical and physiologic. The fusion is attempting to form at a mechanical disadvantage because of tension. Bone heals more reliably under protected physiologic loads of compression, not tension. Also, the available area for the bone union to occur is limited to the remaining posterolateral bone surfaces. After extensive decompression of the neural elements (laminectomy), the available fusion area is reduced and often poorly vascularized. These local factors reduce the likelihood of a successful arthrodesis. Nicotine use negatively influences the formation of posterolateral lumbar fusions.

Finally, the usual source of pain in these patients is the disc itself, hence the term discogenic. In routine cases of posterolateral fusions the disc is not radically resected. Biomechanical studies have shown that people bear load through the middle and posterior thirds of the disc. Several reports describe a persistently painful disc under a solid posterior fusion.14 As surgeons recognized the biomechanical and physiologic aspects of the discs, they began performing interbody fusions.15

Interbody Fusion

Posterior Lumbar Interbody Fusion.

Interbody fusions evolved to address many of the drawbacks of traditional posterolateral fusions. Radical excision of the disc and anterior column support with rigid bone grafting are performed. The available area for successful bone union is greatly increased by using the interbody space.

Using a posterior lumbar approach, a surgeon performs a posterior lumbar interbody fusion (PLIF). After a wide laminectomy the posterior two thirds of the disc is resected and an interbody graft is placed into the evacuated disc space. This provides anterior interbody stability through a posterior approach. PLIF is a technically demanding procedure associated with a higher incidence of postsurgical nerve injuries.

Transforaminal Lumbar Interbody Fusion.

In an effort to reduce the incidence of nerve injury performed through a PLIF, a transforaminal lumbar interbody fusion (TLIF) technique was developed. Studies have shown the results of TLIF with posterior pedicle screw instrumentation to be equivalent to that of anterior-posterior fusions with an anterior lumbar interbody fusion (ALIF). However, despite the intention of reducing nerve injury through a transforaminal approach, nerve root injury has been reported as a complication of the procedure.16 In addition to nerve root injury, TLIFs can cause a kyphotic alignment in the lumbar spine.

After exposing the spine through either a midline or paramedian posterior approach, the facet joint and pars interarticularis above the proposed fusion level is resected. This allows access to the posterolateral aspect of the disc. Care is taken to avoid injury to both the existing and transversing nerve root. A standard discectomy and insertion of an interbody device is then performed.

Anterior Lumbar Interbody Fusion.

Because the risks associated with PLIF were too great for routine use, many surgeons moved to ALIF. Using the same principles of disc excision and interbody bone grafting, many surgeons achieved excellent results. However, ALIF alone cannot withstand the forces across the grafts, so many collapse or do not fuse. Surgeons who perform ALIF have learned to protect the grafts with posterior instrumentation, leading to a predictable fusion rate and good clinical results.

From a technical standpoint, anterior lumbar surgery is most easily and safely accomplished through a retroperitoneal approach. After the anterior disc is exposed, it is relatively simple to perform a discectomy and insert the bone graft of the surgeon’s choice. Posterior fusion and instrumentation can be placed through a separate posterior approach on either the same day or in a staged procedure. A circumferential fusion is accomplished in this manner (see Fig. 16-1).

Lateral Interbody Fusion.

An alternative to performing an ALIF is through a lateral interbody approach. The use of a lateral approach avoids the need for exposure of the great vessels and therefore has less potential for vascular injury. However, it does not come without inherent risks, the most notable of which is nerve stretch injury. The most common is an L4 nerve root injury.17 The lateral approach cannot be used for the L5-S1 intervertebral disc as the pelvis blocks access.

With a lateral approach, the disc is accessed through the psoas muscle under neuromonitoring to avoid injury to the lumbar plexus. After gaining access to the disc, a procedure similar to an ALIF is carried out including discectomy and insertion of an interbody graft.

Interbody Cages.

Ongoing technologic advances have been made in interbody cages. Essentially, these devices are hollow cylinders made of titanium, carbon, or bone (Fig. 16-2). They are filled with autogenous bone graft or a bone graft substitute and inserted between the vertebral bodies. Newer devices have implemented bone ingrowth surfaces and large footprint areas to aid in the fusion process and decrease rates of subsidence.

Research is moving rapidly to find a reliable substitute for the autogenous bone graft, most likely with the use of bone-morphogenic protein. There are other biologic alternatives available to surgeons that can be used to fill the interbody fusion cages and reduce the need for bone graft harvest.

Surgical Procedure

The basic lumbar fusion is the posterolateral fusion. The patient is placed in a prone position on a Jackson frame, allowing the abdomen to hang free. This decompresses the lumbar epidural veins and minimizes bleeding. A skin incision is made over the operative levels, and the paraspinal muscles are stripped off the posterior elements (spinous process, lamina, and transverse processes). Deep retractors hold back the muscles to allow the surgeons to expose the bone for fusion. Using small curettes or a high-speed burr, the surgeon decorticates the dorsal aspect of the transverse processes and facet joints in preparation for the bone graft placement. Through a separate fascial incision, the surgeon harvests the necessary amount of cortical and cancellous bone graft from the posterior iliac crest. This bone graft material is then carefully placed in the recipient site.

If screws are used to augment the fusion, a pilot hole is made over the entry site of the pedicle with a burr (Fig. 16-3). Usually probes are placed in the pedicles and a radiograph is taken to confirm the position of the pedicle probes. After confirmation, the pedicles are tapped and appropriate length screws are placed into the pedicles. Again, an intraoperative radiograph is taken to confirm the position of the screws. The rods or plates are connected to the screws, and lordosis is preserved in the construct. The wound is usually irrigated with an antibiotic solution to minimize the chance of infection and closed over a deep suction drain. The drain is removed when the postsurgical drainage is minimal. Patients are mobilized out of bed as tolerated on the first or second day after surgery.

Therapy Guidelines for Rehabilitation

Description of Rehabilitation and Rationale for Using Instrumentation

Opinion about the degree of rehabilitation needed after spinal surgery ranges from the optimistic view that no rehabilitation is needed to others who argue for aggressive exercise- and education-based programs. As noted earlier there has also been mounting evidence that failing to address psychosocial factors in this population may also be neglecting an integral part of the rehabilitation and recovery process. This chapter is written from the point of view that the patient who has undergone surgery needs not only a program that will protect the surgical area and create an effective healing environment, but also addresses relevant and contributing changes in motor control dealing with both the active subsystems and neural control subsystems as outlined by Panjabi18,19 (Box 16-1). Although the surgery itself deals with improving the passive subsystem, which include such anatomic structures as the vertebral bodies, facets, and ligaments, capsule, it is our job as specialists in rehabilitation to address these other systems.20 It is also important to realize that those individuals with more chronic pain symptoms will most likely exhibit altered pain processing, which may be addressed through including cognitive-behavioral interventions during the recovery process.

Box 16-1

Spinal Stability System Components

The following guidelines are not intended to substitute for sound clinical reasoning but rather serve as a foundation on which a trained physical therapist (PT) can base the rehabilitation of a patient after spinal fusion. It is assumed that the therapist will know the basics of spine and extremity evaluation in order to monitor the patient for symptoms that require prompt reevaluation, along with addressing relevant contributing factors in other body regions that have a significant impact on the lumbar spine.

Preoperative and Planning Phase

Before an individual elects to undergo lumbar spinal fusion, it is generally assumed that conservative measures have not had a significant impact on the patient’s condition and that they have gone through an extensive therapy program. Hopefully the individual has been taught stabilization-based exercises and has begun to address other relevant physical and cognitive dysfunctions. Once surgery is deemed necessary by the patient and rehabilitation team, preoperative management may be very useful in determining functionally relevant outcomes along with realistic goals.21 This is also the time to start on patient education regarding issues such as:

An effective preoperative program before lumbar fusion surgery should also address any other relevant patient concerns and include other advice from the members from other disciplines included in the rehabilitation team. A tour of the facility and operating room along with meeting with individuals who have already undergone such a procedure may also help to decrease patient anxiety surrounding the surgery and hospital experience.21 For the rehabilitation specialists, an understanding of the specific procedure performed is essential for safe rehabilitation. Before beginning a rehabilitation program, the therapist must know whether the patient has had a fusion with or without instrumentation. Patients who were operated on with instrumentation can generally be progressed more aggressively in the first phase of rehabilitation. Patients who were operated on without instrumentation require more time for the bony fusion to take place. Generally a callus should form within 6 to 8 weeks; the surgeon monitors this by radiograph and usually does not refer to outpatient therapy before a callus has formed. The therapist also must know the surgical approach and the levels fused. After a motion segment is fused, increased stress is placed on the levels above and below the fusion. This creates risk for acceleration of the degenerative cascade at the adjacent levels. Obviously the more levels that have been fused, the greater the stress placed on the remaining segments. When the fusion includes the L5-S1 motion segment, abnormal forces are then translated to the sacroiliac joints. To minimize these forces, the therapist must be sure that normal motion exists at all remaining segments, including the thoracic spine, shoulders, and lower extremities (LEs).

During a posterior fusion, the multifidi are retracted from the spine. This partially tears the dorsal divisions of the spinal nerves, resulting in partial denervation of the multifidi.5,22 If an anterior fusion also has been performed, then a midline skin incision will be apparent and the abdominal muscular incision is lateral. The incision passes through the obliques, also partially denervating them. For this reason the therapist should teach the patient the proper way to recruit the transverse abdominis (TA), multifidi, and pelvic floor muscles and watch for any substitution patterns to promote proper spinal stabilization.

Phase I

TIME: 1 to 5 days after surgery (inpatient) and up to 6 weeks

GOALS: Patient education about daily movements, abdominal stabilization, neural mobilization, and home care principles (Table 16-2)

Inpatient Phase

Most patients remain in the hospital for several days after fusion surgery. Physical therapy management during this phase consists of teaching patients the proper way to get in and out of bed, dress and perform other self-care activities, and walk (perhaps with a walker for the first 1 or 2 days). Strenuous abdominal stabilization exercises are not recommended at this time; however, attempts should be made to perform light TA and pelvic floor contractions to begin to practice them in different positions. The patient may use a large “sigh” or more forceful exhalation such as “blowing out a candle” to start to facilitate other abdominal muscles that assist with bracing. The therapist also can teach basic and simple neural mobilization for the nerves involving the lumbosacral plexus. Because of the sensitivity of the nervous system, more focus should be on activities such as “sliders” versus “tensioners.” These are described well by Bulter.12 Patients and their family should leave the hospital with an understanding of the home care required until they begin their outpatient physical therapy, especially in the absence of home PT during the interim. If the physician requests bracing of any kind, then the patient should understand the way to get in and out of the brace and when to wear it. imagePatients will be given instructions from the physician to avoid driving, prolonged sitting, lifting, bending, and twisting. These, along with any other specific precautions, should be understood by the patient. The PT should reinforce this information and teach patients the proper way to avoid these activities by hip hinging or pivoting. This information should be provided in written and visual form, because many patients may be medicated or overwhelmed by the recent surgery and therefore have difficulty recalling or applying what they have just been taught. Most patients are referred for physical therapy anywhere between 4 to 7 weeks after their discharge from the hospital.

Phase II

TIME: 6 to 10 weeks after surgery

GOALS: Increased activity, tissue remodeling, stabilization, and reconditioning (Table 16-3)

TABLE 16-3

Lumbar Fusion and Laminectomy

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Rehabilitation Phase Criteria to Progress to This Phase Anticipated Impairments and Functional Limitations Intervention Goal Rationale
Phase II
Postoperative 6-10 wk

Independent with the following: