Spinal Disorders: Fundamentals of Diagnosis and Treatment Part 54 doc

Table 1. Etiology-based classification Congenital stenosis Acquired stenosis idiopathic degenerative achondroplastic congenital with secondary degenerative changes isthmic spondylolisthesis metabolic iatrogenic (postlaminectomy) post-traumatic eralized disorders such as achondroplasia. Identification is usually in infancy or childhood. Stenosis may develop at several levels of the vertebral column and may often lead to serious neurologic deficits. The vast majority of patients pre- sent with acquired lumbar canal stenosis. It may occur due to degenerative pro- cesses of the lumbar spine during aging [65, 99] or less frequently is caused by general metabolic disorders, postsurgical or post-traumatic conditions. An anatomic classification differentiates ( Fig. 3): central stenosis lateral recess stenosis foraminal stenosis a b c Figure 3. Classification of spinal stenosis a Central spinal stenosis with severe compression of the cauda equina (arrows). b Lateral recess stenosis with compression of the exiting nerve roots. c Lateral stenosis with compression of the nerve root (*) as a result of enlargement of the superior process of the facet joint (arrowhead) and a foraminal disc herniation (arrow). 518 Section Degenerative Disorders A pathomorphological classification considers the underlying pathology such as: hypertrophy of the ligamentum flavum hypertrophy of the facet joints osteophyte formations (spurs) disc herniation synovial facet joint cysts vertebral displacements (anterior/lateral) Clinical Presentation History The symptom onset of spinal stenosis is usually insidious Lumbar spinal stenosis is usually a chronic condition, sometimes but not typi- cally with a long history of low-back pain. Occasionally, the stenosis may become symptomatic after a minor trauma or unusual physical stress but usually the onset is insidious. Patients with a congenitally narrow canal may acutely present with major neurologic deficit due to the occurrence of an additional disc protru- sion. In patients with severe congenital stenosis, symptoms may occur in their twenties to thirties, whereas symptom onset in the sixth and seventh decades is common for acquired degenerative stenosis. The cardinal symptom of spinal stenosis is neurogenic claudication,which presents as: numbness, weakness and discomfort in the legs while walking or prolonged standing regression of symptoms during sitting and rest Leg symptoms usually improve or disappear during sitting The characteristic finding in neurogenic claudication is that the symptoms regress during sitting and rest. During sitting (forward bending) the spinal canal is widened, which decreases the compression of the cauda equina. Patients may be asymptomatic while riding a bicycle because they are in a forward bend position. The painfree walking distance can vary from day to day The p ainfree walking distance mayvaryfromdaytoday.Typicallysymptoms will occur at a smaller distance if walking downhill due to the increased lumbar lordosis with consecutive narrowing of the spinal canal. Patients may provoke symptoms after a certain walking distance but be able to continue further before having to bend forward or sitting for pain relief. Furthermore, the distance required to develop these symptoms will decrease with increasing severity of the degenerative changes. At rest, the patients usually complain of few or no symp- toms at all. The leg symptoms may also be described as paresthesia, cramps, burning pain, or weakness. Some patients only report heaviness or deadness of the limbs and a sense that their legs are giving way. Nerve root claudication is characterized by radicular pain on walking Patients with lateral canal stenosis may present with a radicular claudication. Similarly to neurogenic claudication, the symptoms can be provoked during walk- ing and prolonged standing but are localized to a nerve root dermatome. The symp- toms are not so clear in cases of a multilevel foraminal stenosis. These patients, however, often report signs of a mild radiculopathy during rest which worsens on activity. However, some patients present with a radicular pain syndrome during rest and particularly during the night. It is assumed that in those cases the postural change results in a narrowing of the foramen, which results in the pain provocation. Additional but less frequent symptoms may be: mechanical low-back pain (worse on activity) atypical leg pain (non-radicular distribution) cauda equina syndrome (very rare) Lumbar Spinal Stenosis Chapter 19 519 Walking-related back and buttock pain is not uncommon In patients suffering from lumbar spinal stenosis, pain in the lower spine, but- tocks or posterior legs is not uncommon. Often this back pain becomes worse on activity. This finding can be due to the stenosis itself and can be explained by an involvement of the posterior rami of the nerve roots. It may also be related to a segmental instability, e.g. degenerative spondylolisthesis ( Case Introduc- tion ). Rarely, the patients present with an acute or subacute onset of a cauda equina syndrome. Nevertheless, it is important to explore the urinary function and ask for bowel incontinence because many patients do not see the correla- Always explore for bowel and bladder dysfunction tion with their main symptoms and tend not to report bowel and bladder dys- function. Physical Findings The physical exam most frequently is normal Clinical examination in spinal stenosis most often is remarkably normal. As in any spinal disorder, a thorough neurological examination (see Chapter 11 )is mandatory. The most frequent physical findings are [50]: limited lumbar extension 66–100% sensory deficit 32–58% muscle weakness 18–52% straight leg raising 10–90% absent knee reflexes 10–50% absent ankle reflexes 50–68% Consider peripheral neuropathy in cases of absent ankle jerks and sensory deficits However, these symptoms are obviously non-specific. Pain with extension or a voluntary decrease in the range of lumbar extensions is often seen. Dermatomal sensory loss and muscle weakness are uncommon at rest, although they may appear if the patient is reexamined after walking to their tolerance limit. Loss of ankle jerks and distal vibration sense may be present, but are common in the older age group. Straight-leg raising is usually normal. Assess the peripheral pulses to detect vascular stenosis Diminished peripheral pulses or limitation of hip movement may increase suspicion for the most frequent differential diagnosis, i.e. vascular claudication and osteoarthritis of the hip joint. Sometimes signs of a cervical myelopathy may be seen, because lumbar stenosis is associated with cervical canal narrowing in 5%of cases [21]. A reliable assessment of the walking distance is an important parameter for determining the outcome of surgical treatment. The so-called shuttle walking test has been evaluated for spinal stenosis and can be recommended for this pur- pose [93]. Diagnostic Work-up The diagnosis of spinal stenosis is mainly based on the patient’s clinical symp- toms and signs. However, the confirmation of a clinical diagnosis is only made by imaging studies [3, 12, 14, 52, 90]. Neurophysiologic studies can be helpful to fur- ther confirm the diagnosis and allow for a differential diagnosis. Imaging Studies Standard Radiographs Standard anteroposterior and lateral radiographs do not permit a final diag- nosis. Nevertheless, findings ( Fig. 4 ) often associated with spinal stenosis are: 520 Section Degenerative Disorders degenerative spondylolisthesis degenerative scoliosis congenitally narrow spinal canal Degenerative spondylolisthesis is indicative of a spinal stenosis Degenerative spondylolisthesis particularly at the L4/5 level in females is fre- quently associated with spinal stenosis ( Fig. 4a). Isthmic spondylolisthesis is most common at the L5/S1 level and will produce nerve root impingement at the level of the defect while degenerative spondylolisthesis is more likely to produce constriction of the entire cauda equina. In patients with degenerative scoliosis, the stenosis is often found at the apex of the curve (L2/3 and L3/4) ( Fig. 4b). On the anteroposterior view, the interpedicular distance should be identified. In healthy individuals it increases progressively from the L1 to the L5 level. If the interpedicular distance is narrow ( Fig. 4c), it indicates a narrow spinal canal. Radiological signs for congenital or developmental stenosis inthe lateral view are short pedicles indicating a decreased sagittal canal diameter ( Fig. 4d). Less reliable findings implying lateral recess or foraminal stenosis are: disc space narrowing isthmic spondylolisthesis severe facet osteoarthritis a b c d Figure 4. Radiographic findings a Degenerative spondylolisthesis at the L4/5 level. b Degenerative scoliosis with lateral shifting of the L2 and L3 vertebrae indicating central and lateral recess stenosis. c, d Congenitally narrow spinal canal with a narrow interpedicular dis- tance and short pedicles. Lumbar Spinal Stenosis Chapter 19 521 The spinous processes and laminae should be identified to diagnose any previous surgical decompressive procedure. Scalloping of the posterior aspect of the verte- bral body may suggest a congenital process such as achondroplasia, acromegaly, neurofibromatosis, mucopolysaccharidosis, or a tumor. Magnetic Resonance Imaging MRI is the imaging study of choice Magnetic resonance imaging (MRI) is excellent in demonstrating potential causes of nerve root compression, including spinal stenosis. Compared to com- puted tomography (CT), MRI has a significant advantage because of its better soft tissue resolution. Encroachment on the spinal canal with inward bulging of discs and yellow ligaments usually plays a significant role in narrowing of the bony spinal canal and can be depicted excellently by MRI. MRI studies usually encompass a T1- and T2-weighted sagittal and a T2- weighted axial scan. Characterist ic findings of spinal stenosis include: thickened ligamentum flavum ( Fig. 5a) facet joint hypertrophy ( Fig. 5b) hourglass appearance of spinal canal on sagittal images ( Fig. 5c) facet joint synovial cysts ( Fig. 5d, e) trefoil appearance of the thecal sac (indicative of spinal lipomatosis) obliterated perineural fat in neural foramina ( Fig. 5f) short pedicles vertebral endplate osteophytes Parasagittal T1-weighted images define the integrity of the foramen. The normal nerve root has a low signal and is surrounded by the higher intensity signal of fat. Obliteration of the fat is indicative of a foraminal stenosis ( Fig. 5f). The extent of stenosis and clinical symptoms are not closely correlated Stenosis is not a pathological entity per se as it appears in up to 21% of asymp- tomatic subjects over 60 years of age on MR images [13]. In addition, a poor cor- relation between radiological stenosis and symptoms is well established [33]. Debate arises about the value of a funct ional examination of the spinal canal. A simple assessment of the postural influence, e.g. on a degenerative spondylolisthe- sis, can be made by comparing the standard radiograph with the prone MRI. Often a partial reduction during the prone position is seen which indicates the mobility of the slip. Upright MRI has been reported to be helpful in the diagnostic assess- Functional examinations rarely change treatment strategy ment [88, 102], but the chance of detecting a pathology not seen on conventional MRI which would change the therapeutic approach is minimal [101]. So far, no sin- gle study has proven the added diagnostic value in terms of treatment decisions. Computed Tomography and CT Myelography CT is rarely needed in the presence of an MRI scan. The benefits of CT over plain films are that it can provide greater resolution in terms of an increased ability to appreciate density differences. A second advantage of CT is its ability to image in differentplanes,eitherdirectlyorbymultiplanarreconstruction.OnCT,midsag- ittal lumbar canal diameters less than 10 mm are regarded as an absolute stenosis and midsagittal lumbar canal diameters less than 13 mm represent a relative ste- nosis [98]. CT myelography is an alternative in case of MRI contraindications Compared to MR imaging, the disadvantage of CT is that it does not allow good visualization of the nerve roots and exposes patients to radiation. If MRI is not indicated (e.g. pacemaker, metallic artifacts), CT myelography provides the best alternative to confirm nerve root involvement. However, CT myelography may not display foraminal stenosis because the dural root sheath ends at the entrance of the foramen. 522 Section Degenerative Disorders a bc def Figure 5. MRI characteristics of spinal stenosis a Hypertrophy of the yellow ligament (arrowheads)onaT2Waxialscan.b Facet joint hypertrophy with joint effusion (arrowheads) on a T2W axial image. c Hourglass appearance of the spinal canal (arrowheads) on a sagittal T2W image. d Large facet joint synovial cysts on the right side (arrowheads) and a small cyst on the left side (arrow). e Alargefacet joint cyst is compressing the thecal sac shown on a T2W sagittal image. f Fat in the foramen appears with a bright signal on T1W image (arrows). Obliterated perineural fat (arrowheads) in neural foramina indicating foraminal stenosis which is aggravated by a small disc protrusion. Neurophysiologic Studies Neurophysiologic studies are helpful in the diagnostic work-up of equivocal cases Neurophysiologic studies are a reasonable supplement to the clinical and radio- logical assessments. Somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) investigate the central nervous system pathways while EMG and nerve conduction velocity (H-reflex, F-wave) are especially useful for investigating peripheral sensorimotor pathways (see Chapter 12 ). Neurophysiologic studies allow the affection of the cauda equina to be confirmed in the majority of patients and provide a differential diagnosis from peripheral neuropathy, musculoskeletal and vascular disorders, which are especially frequent in the older population. In a study population of patients undergoing lumbar decompression, the neurological examination was normal in 70% of patients or showed only minor and non-specific motor and/or sensory deficits. However, 87% of patients showed pathological electrophysiological recordings. The tibial SSEP was delayed in 79% and the H-reflex in 56% of patients. A diminished compound motoractionpotential(CMAP)wasfoundin39%ofpatients[20]. Lumbar Spinal Stenosis Chapter 19 523 Neurophysiologic assessment is indicated: to confirm the clinical relevance of imaging findings in equivocal cases to identify a peripheral neuropathy to differentiate radiculopathy and mononeuropathy to differentiate non-specific neurological complaints Differential Diagnosis The most common differential diagnosis of neurogenic claudication is intermit- tent ischemic claudication due to peripheral vascular disease ( Table 2): Table 2. Differentiation of vascular and neurogenic claudication Signs and symptoms Vascular Neurogenic walking distance fixed variable type of pain cramps, tightness dull ache, numbness relief at cessation of activity immediate delayed back pain rarely occasionally pain relief standing flexion and sitting posture provocation uncommon common walking up hill pain no pain bicycle riding pain no pain pulses absent normal trophic changes likely absent muscle atrophy rarely occasionally In equivocal cases, ultrasound screening for the presence of pulses and subse- quently angiography is indicated for differential diagnosis. The bicycle test of von Gelderen can be used to distinguish neurogenic from vascular claudication syndromes [19]. Neurogenic claudication has been described as a result of spinal arteriovenous malformations, but such a presentation is extremely rare. Tumors of the cauda equina usually do not produce claudication symptoms. Other differ- ential diagnoses are less frequent. Low-back pain and referred pain associated with non-stenotic lumbar degenerative disease may sometimes mimic neuro- genic claudication. Peripheral neuropathy is a frequent concomitant finding or differential diagnosis Peripheral neuropathy is often found as an independent additional pathology in elderly patients presenting with spinal stenosis. A preoperative diagnosis is important for a proper consultation of the patient about the future treatment result because the neuropathy will remain unaddressed and may result in patient dissatisfaction. Non-operative Treatment The prevailing symptom of patients with lumbar spinal stenosis is neurogenic claudication while back and radicular leg pain is less frequently a predominant complaint. Neurogenic claudication results from a narrowing of the spinal canal, nerve root canals, or intervertebral foramina which cannot be addressed by any form of non-operative treatment. However, it is anecdotally well known that the course of patients with spinal stenosis is sometimes very stable over time and many patients report intermittent improvement. 524 Section Degenerative Disorders Natural History Natural course of spinal stenosis is generally benign Little is known about the natural history of spinal stenosis. Some authors reported that the natural course is benign and that the subjective and physical manifestations can be remarkably stable [43]. After a mean follow-up period of 59 months, symptoms were unchanged in 70%, improved in 15%, and worsened in 15% of patients [43]. Since no proof of deterioration was found, it was con- cluded that expectant observation could be an alternative to surgery [43]. Despite a benign natural history, the long term course is characterized by a slow deterio- ration because the motion segment degeneration ( Fig. 2)progressivelyleadstoa worsening of the stenosis. The end stage of the disease can be described in terms of a completely immobilized patient in whom the stenosis severely impacts on the remaining quality of life. Non-operative Options Conservative measures may be indicated to relieve symptoms in patients with only mild and intermittent symptoms or only minimal interference with lifestyle ( Table 3): Table 3. Favorable indications for non-operative treatment mild claudication symptoms concomitant back pain mild to moderate radiculopathy minimal interference with lifestyle absence of motor deficits Conservative therapy may be the first choice if surgery is associated with a poten- tially high perioperative risk for general medical reasons. Conservative treatment options may consist of: medication (analgetics, NSAIDs, muscle relaxants) administration of calcitonin (nasal spray, subcutaneous, intramuscular) postural education therapeutic exercise with avoidance of extension epidural infiltration of corticosteroids (see Chapter 10 ) The scientific evidence for the effectiveness of conser- vative measures is limited Various types of oral medication are available to control pain in patients with spi- nal stenosis and help to control the symptoms. However, there is no evidence in the literature on the clinical effectiveness. The administration of calcitonin has been reported to improve the symptoms of neurogenic claudication [22, 75]. However,arecentwell-conductedrandomizedcontrolledstudy[73]didnotfind evidence that nasal application of calcitonin is more effective than placebo treat- ment. Some patients may improve their function as a result of postural education and instructions for a home exercise program. As extension worsens the symp- toms by reducing the size of the spinal canal, it is obvious that extension exercises must be avoided. Epidural injec tions anecdotally have a temporary beneficial effect and may be considered as a treatment in elderly patients in whom surgery would be too risky or who refused surgery. However, the therapeutic value of epi- dural injections in all lumbar spinal disorders and particularly in spinal stenosis (see Chapter 10 ) remains controversial [26, 60, 84]. Well conducted studies comparing conservative with surgical treatment are few in number and difficult to compare because of the heterogeneity of the study population. However, studies comparing non-operative and surgical treatment demonstrated better overall results of surgery [4, 7, 8, 44]. Moreover, only one Lumbar Spinal Stenosis Chapter 19 525 single randomized study compared short- and long-term results of medical and surgical therapy. Amundsen et al. [4] concluded that an initial conservative approach is advisable for oligosymptomatic patients because those with an unsatisfactory result can be treated surgically later without impairment of the prognosis. Operative Treatment General Principles Surgery for lumbar spinal stenosis is generally accepted when conservative treat- ment has failed or if the stenosis substantially impacts on the patients’ lifestyle. The general goals of the operative treatment are to improve quality of life by reducing symptoms such as those in Table 4: Table 4. Indications for surgery moderate to severe claudication symptoms significant interference with lifestyle progressive neurological deficits (rare) caudaequinasyndrome(veryrare) With the exception of a cauda equina syndrome or progressive neurologic defi- cits, the indication for surgery remains relative and is dominated by the subjec- tive interference with the patients’ quality of life. Surgical Techniques The surgical technique is largely dependent on the type of stenosis (i.e. central, lateral recess, or foraminal) and the presence of concomitant back pain. The principal surgical options for decompression of central and/or lateral spinal ste- nosis are: decompression (uni-/bilateral laminotomy or laminectomy) decompression with non-instrumented fusion decompression with instrumented fusion Laminotomy and Laminectomy Laminectomy may increase or create segmental instability Theobjectiveofdecompressionistocreatemorespaceforthecaudaequinaand nerve roots by liberating the neural structures from compressing soft tissues (disc herniation, hypertrophied flavum, thickened facet joint capsules) and osse- ous structures (hypertrophied facet joints, osteophytes). Until the last decade, total laminectomy was the standard method of decompression in central spinal stenosis. However, the recognition that total laminectomy may increase or cause segmental instability [31, 35] has led to a more conservative approach, preserv- ing the lamina and only removing those parts which actually cause the stenosis [91]. Selective decompression is the surgical technique of choice in patients pre- senting with neurogenic claudication without relevant back pain ( Case Study 1). Favorable indications include: central stenosis predominantly due to flavum hypertrophy nerve root claudication due to lateral recess stenosis absence of degenerative spondylolisthesis and scoliosis absence of osseous foraminal stenosis 526 Section Degenerative Disorders abc d Case Study 1 A 26-year-old male complained of severe bilateral leg pain which was worse on walking. He did not report any significant back pain. Physiotherapy was not helpful and the patient was severely incapacitated by the pain. NSAIDs had only little effect. A lateral radiograph ( a) revealed evidence for a congenitally narrow spinal canal with short pedicles (arrows). T1W ( b)andT2W(c)sagittal images demonstrated a narrow spinal canal with secondary degenerative changes. Disc protrusions (arrowheads) and hypertrophied flavum (arrows)at the level of L4/5 and L5/S1 worsened the preexisting narrow spinal canal. The axial T2W image ( b) showed a severe stenosis at the level of L4/5. Note the rather advanced degenerative changes of the facet joint (arrowheads) already in young age. The patient was treated by a selective bilateral decompression with preservation of the interspinous ligaments and undercutting of the lami- nae. At 6 weeks postoperatively the patient was completely pain free and resumed normal activities. Decompression alone is indicated in patients without deformity This procedure (Fig. 6) can be performed with the assistance of loops or the microscope althoughthereisnoevidenceforthesuperiorityofamicrosurgical approach. A technical detail is related to the preservation of the facet joint cap- sules when an undercutting medial facetectomy is required to decompress the thecal sac. In selected cases, a unilateral approach suffices to bilaterally decompress the thecal sac (over-the-top technique) by undercutting of the laminae, preserving the interspinous ligaments and the contralateral muscles [53]. Total laminectomy is still indicated in cases in which the thecal sac cannot be sufficiently decompressed or the access to the foramen is obliterated (foraminal stenosis). In rare cases of cauda equina syndrome, total laminectomy is indicated to ensure adequate neural decompression. Laminectomy alone should be avoided in cases with preexisting instability such as: degenerative spondylolisthesis isthmic spondylolisthesis with secondary degenerative changes degenerative scoliosis Clinical outcomes of laminectomy and laminotomy are similar Clinical results of decompressive laminectomy are favorable with appropriate indications accounting for preexisting instability. Patient satisfaction varies from 57% to 81% with regard to excellent to good results [1, 38, 39, 41, 45, 46, 48, 49, 78, 79, 83, 89]. While the postoperative outcome of decompressive laminectomy is well maintained for several years after surgery, the condition is known to dete- Lumbar Spinal Stenosis Chapter 19 527 . symptom of spinal stenosis is neurogenic claudication,which presents as: numbness, weakness and discomfort in the legs while walking or prolonged standing regression of symptoms during sitting and. evaluated for spinal stenosis and can be recommended for this pur- pose [93]. Diagnostic Work-up The diagnosis of spinal stenosis is mainly based on the patient’s clinical symp- toms and signs shifting of the L2 and L3 vertebrae indicating central and lateral recess stenosis. c, d Congenitally narrow spinal canal with a narrow interpedicular dis- tance and short pedicles. Lumbar Spinal