The Role of Spinal Fusion and the Aging Spine: Stenosis without Deformity

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50 The Role of Spinal Fusion and the Aging Spine

Stenosis without Deformity

Nelson S. Saldua, Chukwuka Okafor, Eric B. Harris, Alexander R. Vaccaro

KEY POINTS

• The incidence of spinal stenosis is increasing secondary to the growing size of the elderly patient population.

• Because these patients lead more physically demanding lives and participate more in physical leisure activities than was common for the elderly in the past, demand for aggressive treatment of stenosis symptoms is likely.

• Most of these patients can be managed nonoperatively and, of those that require decompressive surgery, only a minority will also require fusion.

• Instability is the primary indication for including fusion in operative treatment of stenosis; it may be subtle and present prior to surgery or may be expected secondary to the extent of decompression required.

• Careful patient selection and limited use of fusion in appropriate cases results in excellent long-term results for patients with spinal stenosis.

Introduction

Spinal stenosis is defined as any condition that results in a narrowing of the spinal canal, nerve root canal, or intervertebral foramina. This narrowing can occur at several locations at the same spinal level, or it can affect multiple levels at similar locations at each level. Spinal stenosis may be due to soft tissue impingement from a herniated intervertebral disc or an infolded ligamentum flavum, from bony processes such as osteophytes or hypertrophied facet joints, or from a combination of these.

Spinal stenosis usually involves the lumbar spine and tends to affect patients in the sixth or seventh decade of life. With an increase in the average age of the patient population, the incidence of patients seeking medical care for symptomatic spinal stenosis is also increasing. Not only are patients living longer, but also they are remaining more active in their older years, thereby making symptoms of neurogenic claudication more apparent. Additionally, surgeries such as total hip and knee arthroplasties are helping patients remain very active further into their lives. Patients with lumbar spinal stenosis often complain of symptoms consistent with neurogenic claudication, including pain, numbness, and paresthesias in the posterolateral portions of the legs and thighs. These symptoms are improved by activities in which the lumbar spine is held in flexion, such as leaning over a walker or shopping cart or riding a bicycle. Spinal stenosis also occurs in the cervical and thoracic spine. The clinical presentations are different, as is the decision-making process for treatment options.

The initial treatment for symptomatic spinal stenosis is nonoperative and consists of activity modification, oral medications, epidural steroid injections, and physical therapy. For those cases recalcitrant to nonoperative treatment, surgery is considered. Surgical options include decompression alone, decompression with a noninstrumented fusion, decompression with an instrumented fusion, and, recently, decompression followed by posterior pedicle-based dynamic stabilization. Newer technologies involving minimally-invasive approaches to the spine have been developed that indirectly improve the dimensions of the spinal canal and neuroforamina in select cases of moderate spinal canal stenosis (interspinous process spacers). Minimally invasive surgical (MIS) techniques have also been developed for spinal decompression as well as fusion.

Fusion in the aging spine can be problematic, due to poor bone quality. Spinal arthrodesis should be incorporated in the surgical treatment of spinal stenosis, either when potentially significant instability is present preoperatively, or if postoperative instability is expected secondary to the extent of decompression performed. The indications for spinal arthrodesis for spinal stenosis will be discussed in this chapter, as well as the arguments both for and against fusion. Outcomes and potential complications of spinal arthrodesis for stenosis will also be discussed.

Basic Science

As with other segments of the spine, the etiology and specific location of the narrowing is important when treating cervical spinal stenosis. Cervical spinal stenosis can occur from a herniated cervical disc, an ossified posterior longitudinal ligament, a redundant ligamentum flavum, an ossified ligamentum flavum, a hypertrophied facet joint, or from any combination of these potentially compressive pathologies.

Stenosis in the cervical spine is of particular importance, due to the relatively small canal diameter as compared to the caliber of the spinal cord. Some surgeons now recommend surgical treatment for severe asymptomatic cervical spinal stenosis for prophylaxis against paralysis, while others recommend observation.

The clinical presentation of stenosis in the cervical spine can be that of myelopathy, radiculopathy, or both. Patients with compressive pathology secondary to a herniated disc pressing on the spinal cord may report symptoms of myelopathy, including loss of hand dexterity and gait abnormalities. Physical exam will show signs of upper motor neuron pathology, which can be manifested as hyperactive deep tendon reflexes, a positive Hoffmann sign, or as a Babinski sign. If, instead, this herniated disc places pressure on an exiting nerve root, or if the loss of intervertebral disc height causes a loss of cross-sectional area of the neuroforamen, then the patient may exhibit signs and symptoms of a particular nerve root radiculopathy. This will result in motor weakness, paresthesias, and loss of deep tendon reflexes (if applicable) for that particular cervical nerve root.

Radiographically, cervical stenosis is often diagnosed using a radiographic measurement called the Pavlov ratio. This ratio is defined as the ratio between the sagittal diameter of the spinal canal and the sagittal diameter of the vertebral body, as measured on a lateral radiograph. A ratio of greater than 1 is considered normal, while a ratio of less than 0.8 is considered to be diagnostic for spinal stenosis. A cervical MRI can help determine the etiology of the compression if the source is a herniated disc or a redundant ligamentum flavum. Additionally, an MRI can show any evidence of spinal cord compression, such as a lack of cerebrospinal fluid around the spinal cord and/or myelomalacia within the cord itself. A CT scan can be used to diagnose bony abnormalities such as osteophytes or hypertrophied facet joints.

Stenosis in the Cervical Spine

Case 1

A 63-year-old female presented to clinic with an 8-year history of worsening neck pain radiating to her bilateral shoulders and scapulae. The pain radiated primarily down her bilateral biceps and radial forearms into the thumb and index fingers of both hands. Additionally, she had noted a gradually worsening weakness in her legs, with loss of balance, worsening handwriting, and difficulty buttoning buttons and manipulating small objects with her hands. She had no bowel or bladder dysfunction. Despite nonoperative management that included activity modification, physical therapy, and nerve root and trigger point injections, her symptoms persisted and seemed to be worsening.

Physical examination revealed tenderness to palpation in the cervical paraspinal musculature as well as in the midline. She had an unsteady gait with a positive Romberg sign. Range of motion was limited by pain, and neck extension reproduced the pain, numbness, and tingling in her arms. She had weakness in her right greater than left biceps, wrist extensors, and hand intrinsics, but intact sensation throughout all dermatomes. Reflex testing was significant for global hyperreflexia and a positive Hoffmann sign bilaterally.

Radiographs, seen in Figure 50-1A and B, demonstrate loss of normal cervical lordosis, severe spondylosis, and a spondylolisthesis of C4 on C5. Sagittal and coronal MRI cuts, seen in Figure 50-2A and B, demonstrate significant spinal stenosis, loss of normal disc height, and severe spinal cord compression with myelomalacia.

FIGURE 50-1 A and B. AP and lateral radiographs demonstrating severe spondylotic changes and a 4 mm anterolisthesis of C4 on C5.

FIGURE 50-2 A and B. MRI showing severe stenosis from C3 to C7 with cord compression at multiple levels and signal change within the spinal cord.

The patient was taken to the operating room for a combined anterior and posterior cervical decompression and fusion. Discectomies and interbody fusion were performed with allograft spacers and an anterior plate at C4-5, C5-6, and C6-7. This portion of the procedure restored normal lordosis and addressed the anterior pathology, including reduction of the spondylolisthesis at C4-5. The posterior procedure included laminectomy from C3 to C7 with screw and rod fixation from C3 to C7 as well (Figure 50-3A and B).

FIGURE 50-3 A and B. AP and lateral postoperative radiographs. Note the restoration of natural cervical lordosis accomplished through multiple anterior discectomies. Posterior decompression and fusion creates additional space for the spinal cord and provides increased stability for fusion.

Postoperatively, the patient did well, with complete resolution of her arm pain. At last visit, her gait and balance were steadily improving, with overall improved function compared to preoperatively.

Clinical Practice Guidlines

Cervical radiculopathy can be successfully treated nonoperatively with activity modification, oral medications, and selective nerve root block injections. Operative indications include symptoms that are recalcitrant to nonoperative treatment as well as development of myelopathy. The natural history of cervical myelopathy is that of a stepwise progression of symptoms alternating with periods of nonprogressive neurological symptoms.

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