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Chapter: Clinical Anesthesiology: Regional Anesthesia & Pain Management: Chronic Pain Management

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Low Back Pain & Related Syndromes

Back pain is an extremely common complaint and a major cause of work disability worldwide.

LOW BACK PAIN & RELATED SYNDROMES

 

Back pain is an extremely common complaint and a major cause of work disability worldwide. Lum-bosacral strain, degenerative disc disease, and myo-fascial syndromes are the most common causes. Low back pain, with or without associated leg pain, may also have congenital, traumatic, degenerative, inflammatory, infectious, metabolic, psychologi-cal, and neoplastic causes. Moreover, back pain can be due to disease processes in the abdomen andpelvis, particularly those affecting retroperitoneal structures (pancreas, kidneys, ureters, and aorta), the uterus and adnexa, the prostate, and the recto-sigmoid colon. Disorders of the hip can also mimic back disorders. A positive Patrick’s sign (or Patrick’s test)—ie, the elicitation of pain in the hip or sacro-iliac joint when the examiner places the ipsilateral heel of the supine patient on the contralateral knee and presses down on the ipsilateral knee—helps identify back pain due to hip or sacroiliac joint dis-orders. This sign is also referred to by an acronym, FABERE (sign), because the movement of the leg involves flexion, abduction, external rotation, and extension.

 

1. Applied Anatomy of the Back

 

The back can be described in terms of anterior and posterior elements. The anterior elements consist ofcylindrical vertebral bodies interconnected by inter-vertebral discs and supported by anterior and poste-rior longitudinal ligaments. The posterior elements are bony arches extending from each vertebral body, consisting of two pedicles, two transverse processes, two laminae, and a spinous process. The transverse and spinous processes provide points of attachment for the muscles that move and protect the spinal col-umn. Adjacent vertebrae also articulate posteriorly by two gliding facet joints.

Spinal structures are innervated by the sinu-vertebral branches and posterior rami of spinal nerves. The sinuvertebral nerve arises before each spinal nerve divides into anterior and posterior rami, and reenters the intervertebral foramen to innervate the posterior longitudinal ligament, the posterior annulus fibrosus, periosteum, dura, and epidural vessels. Paraspinal structures are supplied by the posterior primary ramus. Each facet joint is innervated by the medial branch of the posterior primary rami of the spinal nerves above and below the joint.

 

As lumbar spinal nerve roots exit the dural sac, they travel down 1–2 cm laterally before exit-ing through their respective intervertebral foramina; thus, for example, the L5 nerve root leaves the dural sac at the level of the L4–L5 disc (where it is more likely to be compressed) but leaves the spinal canal beneath the L5 pedicle opposite the L5–S1 disc.

2.Paravertebral Muscle & Lumbosacral Joint Sprain/Strain

 

Approximately 80–90% of low back pain is due to sprain or strain associated with lifting heavy objects, falls, or sudden abnormal movements of the spine. The term sprain is generally used when the pain is related to a well-defined acute injury, whereas strain is used when the pain is more chronic and is likely related to repetitive minor injuries.

Injury to paravertebral muscles and ligaments results in reflex muscle spasm, which may or may not be associated with trigger points. The pain is usually dull and aching, and occasionally radiates down the buttocks or hips. Sprain is a self-limited benign pro-cess that resolves in 1–2 weeks. Symptomatic treat-ment consists of rest and oral analgesics.

 

The sacroiliac joint is particularly vulnerable to rotational injuries. It is one of the largest joints in the body and functions to transfer weight from the upper body to the lower extremities. Acute or chronic injury can cause slippage, or subluxation, of the joint. Pain originating from this joint is char-acteristically located along the posterior ilium and radiates down the hips and posterior thigh to the knees. The diagnosis is suggested by tenderness on palpation, particularly on the medial aspect of the posterior superior iliac spine, and by compression of the joints. Pain relief following injection of the joint with local anesthetic (3 mL) is diagnostic and may also be therapeutic. Injection of intraarticular steroid medication may be considered. For poten-tially longer duration of analgesia, radiofrequency ablation may be performed at the dorsal ramus of L5 as well as the lateral branches of the S1, S2, and S3 nerves if the patient responded well to local anes-thetic injections of the sacroiliac joint or to diagnos-tic injections of these nerves.

3. Buttock Pain

 

Buttock pain may be due to several different fac-tors, and can be quite debilitating. Coccydynia (or, coccygodynia) may the result of trauma to the coc-cyx or surrounding ligaments. It may resolve by means of physical therapy, coccygeal nerve blocks to the lateral aspects of the coccyx, or ablative or neuromodulatory techniques. Piriformis syndromepresents as pain in the buttock, which can be accom-panied by numbness and tingling in distribution of the sciatic nerve. The nerve may or may not be entrapped. Injection of local anesthetic into the belly of this muscle or into trigger points located at the origin and insertion of the muscle may help relieve the pain.

 

4. Degenerative Disc Disease

 

Intervertebral discs bear at least one third of the weight of the spinal column. Their central portion, the nucleus pulposus, is composed of gelatinous material early in life. This material degenerates and becomes fibrotic with advancing age and follow-ing trauma. The nucleus pulposus is ringed by the annulus fibrosus, which is thinnest posteriorly and bounded superiorly and inferiorly by cartilaginous plates. Disc (discogenic) pain may be due to one of two major mechanisms: (1) protrusion or extru-sion of the nucleus pulposus posteriorly or (2) loss of disc height, resulting in the reactive formation of bony spurs (osteophytes) from the rims of the ver-tebral bodies above and below the disc. Degenera-tive disc disease most commonly affects the lumbar spine because it is subjected to the greatest motion and because the posterior longitudinal ligament is thinnest at L2–L5. Factors such as increased body weight and cigarette smoking may play a role in the development of lumbar disc disease. The role of the disc in producing chronic back pain is not clearly understood. In patients with persistent axial low back pain, the history and physical examination may provide clues. If the patient has pain when sitting or standing, or maintaining a certain position for an extended period of time, there may be an element of discogenic pain.

 

Discography is a procedure that is often used to try to provide some objective evidence of the role of a given disc in producing a patient’s back pain. After a needle is inserted into the disc, the opening pressure can be assessed; a subsequent injection of radiocontrast material produces increased pressure that may reproduce the patient’s pain and may pro-vide radiographic identification of anatomic abnor-malities within the disc (eg, a rent or tear). It the pain produced with injection is similar to that which the patient experiences on a daily basis, it is deemed concordant pain. If not, it is deemed discordant. Insome circumstances, the pressure in the disc fol-lowing injection is not significantly higher than the opening pressure. This may be due to the presence of a fissure in the disc that tracks to the epidural space. Risks of discography include infection and discitis, which may be difficult to treat because the disc is relatively avascular.

 

Treatment options for discogenic pain include conservative therapy, steroid injections into the disc, intradiscal biacplasty, involving heating the poste-rior annulus of the disc by way of radiofrequency ablation, and surgical fusion with bone graft or hardware placement; each has shown mixed degrees of success. The evaluation and treatment of disco-genic pain is an area of significant controversy and ongoing research.

 

Herniated (Prolapsed) Intervertebral Disc

 

Weakness and degeneration of the annulus fibrosus and posterior longitudinal ligament can cause her-niation of the nucleus pulposus posteriorly into the spinal canal. Ninety percent of disc hernia-tions occur at L5–S1 or L4–L5. Symptoms usually develop following flexion injuries or heavy lifting and may be associated with bulging, protru-sion, or extrusion of the disc. Disc herniations usu-ally occur posterolaterally and often result in compression of adjacent nerve roots, producing pain that radiates along that dermatome (radiculopathy). Sciatica describes pain along the sciatic nerve due tocompression of the lower lumbar nerve roots. When disc material is extruded through the annulus fibro-sus and posterior longitudinal ligament, free frag-ments can become wedged in the spinal canal or the intervertebral foramina. Less commonly a large disc bulges or large fragments extrude posteriorly, compressing the cauda equina in the dural sac; in these instances patients can experience bilateral pain, urinary retention, or, less commonly, fecal incontinence.

Pain associated with disc disease is aggravated by bending, lifting, prolonged sitting, or anything that increases intraabdominal pressure, such as sneezing, coughing, or straining. It is usually relieved by lying down. Numbness or weakness is indicative


of radiculopathy (Table 47–9). Bulging of the disc through the posterior longitudinal ligament can also produce low back pain that radiates to the hips or buttocks. Straight leg-raising tests may be used to assess nerve root compression. With the patient supine and the knee fully extended, the leg on the affected side is raised and the angle at which the pain develops is noted; dorsiflexion of the ankle with the leg raised typically exacerbates the pain by further stretching the lumbosacral plexus. Pain while raising the contralateral leg is an even more reliable sign of nerve compression.

 

The use of MRI has increased dramatically in the past decade in association with a two- to three-fold increase in back surgeries, although this has not correlated with improved patient outcome. The American Pain Society’s clinical practice guidelines for low back pain do not recommend routine imag-ing or other diagnostic tests for patients with nonspe-cific low back pain. Up to 30–40% of asymptomatic persons have abnormalities of spinal structures on CT or MRI. In addition, the patient’s awareness of his or her imaging abnormalities may influence self-perception of health and functional ability.

 

Imaging studies and further tests should be acquired when severe or progressive neurological deficits are present, or when serious underlying con-ditions are suspected. CT myelography is the most sensitive test for evaluating subtle neural compres-sion. Discography may be considered when the pain pattern does not match the clinical findings. A centrally herniated disc will usually cause pain at the lower level, and a laterally protruded disc will cause pain at the same level as the disc. For example, a centrally located disc herniation at L4–L5 may compress the L5 nerve root whereas a laterally located disc herniation at this level may compress the L4 nerve root.

 

The natural course of herniated disc disor-ders is generally benign and the duration of pain is usually less than 2 months. Over 75% of patients treated nonsurgically, even those with radiculopa-thy, have complete or near-complete pain relief. The goals of treatment should therefore be to allevi-ate the pain and rehabilitate the patient to return to a functional quality of life. Acute back pain due to a herniated disc can be initially managed with modification of activity and with medications such as NSAIDs and acetaminophen. A short course of opioids may be considered for patients with severe pain. After the acute symptoms subside, the patient can be referred to a physical therapist for instruc-tion on exercises to improve lower back health. Patients who smoke tobacco should be advised to stop smoking, not only for the obvious health ben-efits but also because nicotine further compromises blood flow to the relatively avascular intervertebral disc. Percutaneous disc decompression involving extraction of a small amount of nucleus pulposus may help to decompress the nerve root. For patients with acute-onset weakness correlating with the level of the disc herniation, surgical management should be considered.

When symptoms persist beyond 3 months, the pain may be considered chronic and may require a multidisciplinary approach. Physical therapy continues to be a very important component of rehabilitation. NSAIDs and antidepressants are also helpful, and percutaneous interventions may be con-sidered. Of note, back supports should be discour-aged because they may weaken paraspinal muscles.

Spinal Stenosis

 

Spinal stenosis is a disease of advancing age. Degen-eration of the nucleus pulposus reduces disc height and leads to osteophyte formation (spondylosis) at the endplates of adjoining vertebral bodies. In con-junction with facet joint hypertrophy and with liga-mentum flavum hypertrophy and calcification, this process leads to progressive narrowing of the neural foramina and spinal canal. Neural compression may cause radiculopathy that mimics a herniated disc. Extensive osteophyte formation may compress multiple nerve roots and cause bilateral pain. The back pain usually radiates into the buttocks,thighs, and legs. It is characteristically worse with exercise and relieved by rest, particularly sitting with the spine flexed (the “shopping cart sign”). The terms pseudoclaudication and neurogenic claudication areused to describe such pain that develops with pro-longed standing or ambulation. The diagnosis is sug-gested by the clinical presentation and is confirmed by MRI, CT, or myelography. Electromyography and nerve conduction studies may be useful in evaluat-ing neurological compromise.

 

Patients with mild to moderate stenosis and radicular symptoms may obtain benefit from epi-dural steroid injections via a transforaminal, inter-laminar, or caudal approach. This may help these individuals tolerate physical therapy. Those with moderate to severe stenosis may be amenable to more recently developed procedures, such as the minimally invasive lumbar decompression (MILD) procedure, which involves percutaneously sculpting the lamina and ligamentum flavum to reduce central canal compression. Severe multilevel symptoms may warrant surgical decompression.

5. Facet Syndrome

 

Degenerative changes in the facet (zygapophyseal) joints may also produce back pain. Pain may be near the midline; may radiate to the gluteal region, thigh,and knee; and may be associated with muscle spasm. Hyperextension and lateral rotation of the spine usually exacerbate the pain. The diagnosis may be confirmed if pain relief is obtained following intraar-ticular injection of local anesthetic solution into affected joints or by blockade of the medial branch of the posterior division (ramus) of the spinal nerves that innervate them. Long-term studies suggest that medial branch nerve blocks are more effective than facet joint injections. Medial branch rhizotomy may provide long-term analgesia for patients with facet joint disease.

6. Cervical Pain

 

Although most spine-related pain due to disc dis-ease, spinal stenosis, or degenerative changes in the zygapophyseal joints is felt in the low back and lower extremities, patients may have cervical pain attrib-uted to these processes. A key anatomic difference is that the cervical nerve roots, unlike those in the thoracic and lumbar spine, exit the foramina above the vertebral bodies for which they are named. This occurs until the level of C7, where the extra cervi-cal nerve roots, C8, exit below the pedicles of C7, thus transitioning to the nomenclature of the tho-racic- and lumbar-level vertebral bodies and nerve root denominations. The clinical examination may help to identify the nerve root that is affected with confirmation by a selective nerve root block. Risks inherent with percutaneous cervical procedures include accidental intravascular injection of local anesthetic or steroid. Particulate steroid injections in the neck have been associated with devastating outcomes such as spinal cord injury and death and should be avoided.

 

For primarily axial pain in the neck with extension into the head or to the shoulders, cervi-cal medial branch blocks may clarify the diagnosis. Long-term analgesia may be obtained with radiofre-quency ablation of the medial branches innervating the zygapophyseal joints.

7. Congenital Abnormalities

 

Congenital abnormalities of the back are often asymptomatic and remain occult for many years. Abnormal spinal mechanics can make the patient prone to back pain, and in some instances, pro-gressive deformities. Relatively common anomalies include sacralization of L5 (the vertebral body is fused to the sacrum), lumbarization of S1 (it func-tions as a sixth lumbar vertebra), spondylolysis (a disruption of the pars interarticularis), spondylolis-thesis (displacement anteriorly of one vertebral body on the next due to disruption of the posterior ele-ments, usually the pars), and spondyloptosis (sub-luxation of one vertebral body on another resulting in one body in front of the next). The diagnosis is made radiographically. Spinal fusion may be nec-essary in patients with progressive symptoms and spinal instability.

8. Tumors

 

Benign primary tumors of the spine include hem-angiomas, osteomas, aneurysmal bone cysts, and eosinophilic granulomas. Malignant spine tumors include osteosarcomas, Ewing’s sarcoma, and giant cell tumors. In addition, breast, lung, prostate, renal, gastrointestinal, and thyroid carcinomas, lympho-mas, and multiple myelomas frequently metasta-size to the lumbar spine. Pain is usually constant and may be associated with localized tenderness over involved vertebrae. Bony destruction, with or without neural or vascular compression, produces the pain. Intradural tumors such as meningiomas, schwannomas, ependymomas, and gliomas can present with a radiculopathy and may rapidly prog-ress to flaccid paralysis. The primary site may be asymptomatic or difficult to localize, thus requiring imaging studies for diagnosis. Treatment options usually involve surgical decompression, chemo-therapy, radiation therapy, and palliative symptom relief.

9. Infection

 

Bacterial infections of the spine usually begin as dis-citis before progressing to osteomyelitis, and can be due to pyogenic as well as tuberculous organisms. Patients may present with chronic back pain with-out fever or leukocytosis (eg, spinal tuberculosis). Those with acute discitis, osteomyelitis, or epidural abscess present with acute pain, fever, leukocytosis, elevated sedimentation rate, and elevated C-reactive protein, warranting immediate initiation of antibiot-ics. Urgent surgical intervention is indicated when the patient also suffers from acute weakness.

10. Arthritides

 

Ankylosing spondylitis is a familial disorder that is associated with histocompatibility antigen HLA-B27. It typically presents as low back pain associated with early morning stiffness in a young patient, usu-ally male. The pain has an insidious onset and may initially improve with activity. After a few months to years, the pain gradually intensifies and is associated with progressively restricted movement of the spine. Diagnosis may be difficult early in the disease, but radiographic evidence of sacroiliitis is usually pres-ent. As the disease progresses, the spine develops a characteristic “bamboo-like” radiographic appear-ance. Some patients develop arthritis of the hips and shoulders, as well as extraarticular inflamma-tory manifestations. Treatment is primarily directed at functional preservation of posture. NSAIDs, particularly indomethacin, are effective analge-sics that reduce the early morning stiffness. Anti– tumor necrosis factor-α agents have been shown to decrease the progression of ankylosing spondylitis when administered early in the course of therapy. These agents include infliximab (Remicaid), etan-ercept (Enbrel), adalimumab (Humira), and golim-umab (Simponi). Although this treatment approach shows promise, patients may be at an increased risk for infection and the development of lymphoma.

 

Patients with Reiter’s syndrome, psoriatic arthritis, or inflammatory bowel disease may also present with low back pain, but extraspinal mani-festations are usually more prominent. Rheumatoid arthritis usually spares the spine except for the zyg-apophyseal joints of the cervical spine.

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