Degenerative Spine Diseases. Ankylosing Spondylitis (Bechterew’s Disease).

Introduction

Degenerative diseases of the spine are among the commonest reasons for orthopedic and neurosurgical consultation in adults. The pathological processes — disc degeneration, facet joint arthropathy, ligamentous hypertrophy, spinal stenosis, spondylolisthesis — produce a spectrum of clinical syndromes ranging from mechanical low back pain to radiculopathy and to severe central or foraminal stenosis with myelopathy or neurogenic claudication. The chapter, synthesizing content principally from Rothman-Simeone The Spine, with supplementary content from Apley & Solomon’s, Miller’s Review, and Dutton’s Orthopaedic Examination, addresses the natural history of disc degeneration, the principal clinical syndromes (mechanical low back pain, radiculopathy, central stenosis with claudication, cervical and thoracic myelopathy), the imaging approach, and the principles of non- operative and surgical management. The chapter concludes with a focused discussion of ankylosing spondylitis as the principal seronegative spondyloarthropathy of the spine.

The Aging Spine: Pathophysiology

The intervertebral disc undergoes characteristic age-related changes that underlie most degenerative spine disease. The nucleus pulposus loses water content progressively (from approximately 85% in youth to less than 70% by middle age), with concurrent reduction of proteoglycan content and increase in collagen content. The annulus fibrosus develops radial and circumferential tears, particularly at the posterolateral aspect where the annulus is thinnest. Loss of disc height transfers load to the facet joints, which undergo their own degenerative changes with cartilage loss and osteophyte formation. The ligamentum flavum hypertrophies in response to mechanical demands and ages with loss of elastin and increase in collagen. The combination of disc height loss, facet arthropathy, and ligamentum flavum hypertrophy produces narrowing of both the central canal (central stenosis) and the foramina (foraminal stenosis). Disc herniation typically affects younger adults (third to fifth decade) before the disc has lost so much water that it cannot herniate; central and foraminal stenosis affects older adults (fifth decade and beyond) after the disc has substantially desiccated. The “Kirkaldy- Willis cascade” describes the progressive stages of segmental degeneration: dysfunction, instability, and finally restabilization with ankylotic bone formation.

Mechanical Low Back Pain

Mechanical low back pain — the commonest form of back pain — affects approximately 80% of adults at some point in life. The pain is typically diffuse, worse with activity, relieved by rest, and not associated with neurological symptoms. The pathological substrate is variable and includes disc-related pain (discogenic low back pain), facet- related pain, muscular pain, and ligamentous pain. The classical clinical features include the absence of radicular symptoms, the absence of red flags (constitutional symptoms,

history of malignancy, recent significant trauma, neurological deficit, age over 50 or under 18, prolonged corticosteroid use, intravenous drug use), and a benign physical examination apart from muscle tenderness and limited range of motion. The natural history of mechanical low back pain is favorable: approximately 50% of patients improve within 1-2 weeks of onset, 90% improve within 3 months, and only 5- 10% develop chronic disabling pain. Treatment is principally conservative: brief activity modification (with avoidance of prolonged bed rest, which is harmful), early return to normal activities, NSAIDs and other analgesics for symptom control, physical therapy directed at core stabilization and gradual progression to normal activity, and patient education about the benign natural history. Imaging is not routinely required for typical mechanical low back pain without red flags; the high rate of incidental findings on MRI (asymptomatic disc bulges, facet arthropathy, mild stenosis) can produce misleading attribution of pain to abnormal but clinically irrelevant findings.

Lumbar Disc Herniation and Radiculopathy

Pathophysiology Lumbar disc herniation is the displacement of disc material (typically the nucleus pulposus, sometimes the annulus) beyond the confines of the disc space. The classical mechanism is repeated loading of a degenerating disc with eventual annular failure and posterior or posterolateral herniation. The herniation may produce mechanical compression of the adjacent nerve root, chemical irritation of the nerve from inflammatory mediators released by the disc material, or both. Disc herniations are classified by morphology (bulging — generalized circumferential extension of the disc; protrusion — focal extension of the disc with intact outer annulus; extrusion — disc material extending beyond the annulus but with continued connection to the parent disc; sequestration — free fragment separated from the parent disc), by location (central, paracentral, foraminal/lateral, far lateral), and by level. The most common herniation pattern is paracentral at L4-L5 or L5-S1, producing characteristic radiculopathy of the L5 or S1 nerve root respectively. Clinical Features The classical presentation is of acute back pain followed by radicular leg pain, often in association with a specific event (lifting, bending, twisting). The radicular pain follows the dermatomal distribution of the affected nerve root: L4 radiculopathy produces pain in the anterior thigh, medial knee, and medial lower leg; L5 produces pain in the posterolateral thigh, lateral lower leg, and dorsal foot to the great toe; S1 produces pain in the posterior thigh, posterior leg, and lateral foot. The pain is typically worse with sitting, bending forward, Valsalva maneuvers (cough, sneeze, defecation), and is improved by lying down with hips flexed. Examination findings include: positive straight leg raise (SLR) test (reproduction of leg pain with passive elevation of the straight leg to 30-70°, indicating nerve root tension; “crossed SLR” — pain in the symptomatic leg reproduced by elevation of the asymptomatic

leg — is highly specific); positive Lasègue test (the same as SLR); sensory findings in the affected dermatome; motor weakness in the affected myotome (L4 — quadriceps and tibialis anterior; L5 — extensor hallucis longus, tibialis anterior; S1 — gastrocnemius); reflex changes (L4 — patellar reflex; S1 — Achilles reflex; L5 — no good reflex marker). The femoral nerve stretch test (reverse SLR) assesses upper lumbar nerve root tension and is positive in L2, L3, or L4 radiculopathy. Cauda Equina Syndrome Cauda equina syndrome — compression of the lumbosacral nerve roots in the spinal canal — is a surgical emergency. The classical features include severe bilateral leg pain, saddle anesthesia (perineal and perianal sensory loss), urinary retention with overflow incontinence, fecal incontinence or loss of rectal tone, and progressive motor weakness. The condition most commonly results from massive central disc herniation. Urgent MRI and surgical decompression within 24-48 hours of symptom onset is essential; outcomes are critically dependent on time to decompression. Imaging MRI is the imaging modality of choice for lumbar disc herniation, demonstrating the location, size, and morphology of the herniation as well as nerve root impingement. Plain radiographs are obtained for assessment of alignment, disc height, and exclusion of other diagnoses but do not demonstrate the herniation itself. CT myelography is an alternative when MRI is contraindicated.

Treatment The natural history of acute lumbar disc herniation with radiculopathy is favorable: approximately 70-80% of patients improve with conservative management over 6-12 weeks. Conservative management includes: brief activity modification; NSAIDs; oral or epidural corticosteroids; physical therapy; and time. Epidural steroid injection provides short-term pain relief in most patients but does not change the long-term outcome. Surgical management — typically lumbar discectomy through a small posterior incision — is indicated for: progressive neurological deficit; cauda equina syndrome (emergency); persistent severe radiculopathy after 6-12 weeks of conservative management; and intolerable pain. The SPORT (Spine Patient Outcomes Research Trial) study and other randomized trials have demonstrated that surgical discectomy produces faster relief of pain and better functional outcomes at 1-2 years compared with conservative management, with the long-term outcomes (4-10 years) being similar between treatments. The decision for surgery balances the desire for faster relief against the risks of surgery. Microdiscectomy (small-incision discectomy with microscopic or loupe visualization) is the standard technique. Minimally invasive tubular approaches and endoscopic discectomy provide alternatives with potentially less soft-tissue disruption.

Lumbar Spinal Stenosis

Pathophysiology and Clinical Features Lumbar spinal stenosis is the narrowing of the central canal, lateral recess, or neural foramen producing compression of the spinal nerve roots. Central canal stenosis produces the classical syndrome of neurogenic claudication: bilateral or unilateral leg pain, fatigue, heaviness, or paresthesia provoked by walking or prolonged standing and relieved by sitting or by spinal flexion (which opens the canal). The “shopping cart sign” — relief of symptoms with forward flexion as when leaning on a shopping cart — is characteristic. Patients can typically walk a longer distance uphill (which produces spinal flexion) than downhill (which produces spinal extension). The natural history is one of gradual progression over years, with periods of relative stability and exacerbation. Foraminal and lateral recess stenosis produce more focal radicular symptoms in the distribution of the compressed root, often combined with the central claudication symptoms. The differential diagnosis includes vascular claudication (which is provoked by activity regardless of posture and is relieved by stopping; pulses are absent or reduced), peripheral neuropathy (typically with bilateral burning pain not related to position), and various other conditions. Imaging MRI demonstrates the central canal narrowing, lateral recess narrowing, and foraminal narrowing, with quantitative assessment by the cross-sectional area of the canal and other measures. CT myelography is an alternative when MRI is contraindicated. Treatment Conservative management includes physical therapy directed at flexion-based exercises, postural training, walking aids, weight loss, and analgesics. Epidural steroid injection provides modest short-term symptom relief in some patients. Surgical management is indicated for persistent symptoms refractory to conservative care. The standard procedure is decompression by laminectomy with or without fusion. The decision to fuse is based on the presence of spondylolisthesis, segmental instability, scoliosis, or extensive decompression that destabilizes the segment. The SPORT trial demonstrated that surgical decompression for symptomatic stenosis without instability produces substantially better outcomes than conservative management, with sustained improvement at 4-year follow-up.

Lumbar Spondylolisthesis

Classification Spondylolisthesis is the anterior translation of one vertebra relative to the vertebra below. The Wiltse classification recognizes five types:

Type I — Dysplastic: Congenital deficiency of the L5-S1 facet joints allows progressive slippage in childhood and adolescence. Type II — Isthmic: Defect in the pars interarticularis (spondylolysis) allows the vertebral body to translate forward. Type IIA — lytic defect from stress fracture; Type IIB — elongated but intact pars; Type IIC — acute fracture. The L5-S1 level is the most common, typically in athletes engaged in hyperextension activities (gymnastics, football lineman, weightlifting). Type III — Degenerative: Degenerative changes at the facet joints and disc allow progressive slippage in middle-aged and older adults. The L4-L5 level is the most common. Type IV — Traumatic: Acute fracture of the posterior elements with translation. Type V — Pathological: Tumor, infection, or metabolic disease producing the slippage. The Meyerding grading system quantifies the severity: Grade I (<25% slip), Grade II (25- 50%), Grade III (50-75%), Grade IV (75-100%), Grade V (spondyloptosis, complete translation). Clinical Features and Treatment Presentation varies by type. Isthmic spondylolisthesis in adolescents and young adults presents with mechanical low back pain and sometimes hamstring tightness; advanced slips may produce neurological symptoms. Degenerative spondylolisthesis in older adults typically presents with central stenosis and neurogenic claudication. Treatment of low-grade slip with mechanical pain is conservative: activity modification, physical therapy, analgesics. Bracing may be useful in adolescent isthmic disease. Surgical management — typically decompression with instrumented fusion — is indicated for progressive slip, progressive neurological symptoms, or intractable pain. The fusion construct typically uses pedicle screws with intervertebral spacers; reduction of the slip is debated, with current practice favoring in-situ fusion for most cases of grade I-II disease.

Cervical Spondylotic Myelopathy

Cervical spondylotic myelopathy (CSM) is the chronic compression of the cervical spinal cord by degenerative changes (disc, facet, ligamentum flavum, osteophytes, ossified posterior longitudinal ligament). The condition typically affects middle-aged and older adults and presents with insidious onset of gait disturbance, balance problems, hand clumsiness, and loss of fine motor control. Examination reveals hyperreflexia, Hoffmann’s sign (flicking of the middle finger produces flexion of the thumb), Babinski sign, gait abnormality, and reduced manual dexterity (the “myelopathy hand” with loss of intrinsic muscle function). MRI is the imaging modality of choice and demonstrates the cord compression, T2 signal change in the cord (which has prognostic significance), and the extent of stenosis. The Nurick scale and modified Japanese Orthopaedic Association (mJOA) score are used to assess severity and to track changes with treatment.

Treatment is principally surgical for progressive disease, with options including anterior cervical decompression and fusion (ACDF), corpectomy with fusion, posterior laminectomy with or without fusion, and laminoplasty. The choice depends on the levels involved, the alignment of the cervical spine (cervical kyphosis is a relative contraindication to posterior-only approaches), and surgeon preference. The natural history of CSM is variable but most often progressive, justifying surgical intervention in most cases of moderate-to- severe disease.

Cervical Radiculopathy

Cervical radiculopathy is the compression of a cervical nerve root, producing pain in the appropriate dermatome (C5 — lateral arm; C6 — radial forearm, thumb, index; C7 — middle finger, dorsal forearm; C8 — ulnar forearm, ring and little fingers) and weakness in the corresponding myotome. The Spurling test — extension and rotation of the head toward the symptomatic side, reproducing the radicular symptoms — is the classical clinical sign. Treatment is principally conservative initially (NSAIDs, physical therapy, oral corticosteroids in selected cases); cervical epidural steroid injection may provide additional relief. Surgical management is indicated for progressive neurological deficit or persistent radiculopathy refractory to conservative care, typically by ACDF (anterior cervical decompression and fusion) or posterior foraminotomy.

Other Degenerative Spine Conditions

Diffuse idiopathic skeletal hyperostosis (DISH): Characterized by flowing ossification of the anterior longitudinal ligament involving four or more contiguous vertebral levels, with relative preservation of the disc spaces. Often asymptomatic; can produce dysphagia from cervical osteophytes, restricted spine motion, and increased fracture risk in the ankylosed spine. Differentiated from ankylosing spondylitis by the absence of sacroiliitis and the asymmetric (anterior-only) ossification. Adult degenerative scoliosis: New-onset scoliosis in skeletally mature patients from asymmetric degenerative changes, often producing both deformity and stenosis-related symptoms. Ossification of the posterior longitudinal ligament (OPLL): Particularly common in East Asian populations, producing cervical or thoracic myelopathy from progressive cord compression.

Ankylosing Spondylitis (Bechterew’s Disease)

The clinical features and management of ankylosing spondylitis have been addressed in the chapter on RA and arthropathies. The principal orthopedic considerations are summarized here: • AS is the prototype seronegative spondyloarthropathy with bilateral sacroiliitis, progressive ankylosis of the spine, and HLA-B27 association.

• The progressive ankylosis produces the characteristic “bamboo spine” on radiographs. • The ankylosed spine is mechanically fragile and prone to fracture from low-energy trauma (the “carrot stick” fracture), with high morbidity and mortality. • These fractures are often missed on initial imaging because of the diffuse spine changes obscuring the fracture line; CT and MRI should be obtained with low threshold in any AS patient with new back pain after even minor trauma. • The kyphotic deformity of advanced AS may require corrective spinal osteotomy (typically pedicle subtraction osteotomy at the lumbar level) to restore sagittal balance and forward-looking gaze. • Total hip arthroplasty for hip involvement is technically demanding but produces good functional outcomes.

Summary and Take-Home Points

Degenerative spine disease encompasses a spectrum of conditions from mechanical low back pain to cervical myelopathy. The aging spine produces predictable patterns of disc degeneration, facet arthropathy, ligamentous hypertrophy, and stenosis that underlie the principal clinical syndromes. Mechanical low back pain affects most adults at some point and has a favorable natural history with conservative management. Lumbar disc herniation with radiculopathy is managed conservatively for most patients, with surgical discectomy reserved for refractory or progressive cases; cauda equina syndrome is a surgical emergency. Lumbar spinal stenosis produces neurogenic claudication relieved by spinal flexion and is treated by decompression with or without fusion when symptoms are refractory. Spondylolisthesis is classified by Wiltse type and Meyerding grade and treated by decompression and fusion when symptomatic. Cervical spondylotic myelopathy demands surgical management for most progressive cases. Ankylosing spondylitis produces progressive spinal ankylosis with fracture vulnerability and kyphotic deformity, and may require corrective spinal osteotomy in advanced disease. Across all degenerative spine conditions, the principles of careful clinical assessment, appropriate imaging, stepwise conservative management, and surgical intervention for refractory or progressive disease produce successful outcomes.