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Orthopaedic Management of Ankylosing Spondylitis Erik N. Kubiak, MD, Ronald Moskovich, MD, Thomas J. Errico, MD, and Paul E. Di Cesare, MD Abstract Ankylosing spondylosis (AS) is a se- ronegative inflammatory disease of unknown etiology characterized by inflammation in the axial skeleton. The sacroiliac joints are often involved initially, followed by enthesopathy in the paravertebral zygapophyseal joints and disk spaces. Enthesopathy is inflammation at the site of tendon insertions that predis- poses to the development of fibrosis and calcification; left untreated, it leads to fusion of the zygapophyseal joints and intervertebral disk space. This fusion in turn can lead to a fixed, hyperkyphotic posture and compromised sagittal balance. Hip and knee flexion contractures occur when patients compensate for loss of sagittal balance by assuming a crouched position. Degeneration and ankylosis of peripheral joints, such as the hip, knee, and shoulder, may ensue. Deformity resulting from inflammation and fusion of the sacroiliac joints, spine, and hips leads to severe functional impairment in approximately 30% of patients. 1 Several diagnostic and treatment strategies are available for early and late manifestations of AS. Epidemiology AS typically affects young adults, most commonly males (M:F = 3:1) in their second through fourth decades. The incidence of AS in North America is reported to be 1 to 2 per 1,000. 2 Worldwide prevalence is up to 0.9%. 3 Fifteen percent to 20% of patients with AS have a positive family history of the disease. AS is linked to HLA-B27; 80% to 95% of patients with AS are HLA- B27–positive. 2 Carriers of this gene have a 16% to 50% increased risk of developing AS, but other genetic factors are likely involved as well. 4 HLA-B27 is present among the in- habitants of Eurasia, North Africa, and North America; it is virtually absent among the aboriginal pop- ulations of Australia and South America. 2 Although both HLA- B27–negative and HLA-B27–positive AS patients have similar artic- ular manifestations, the former usually develop the disease at an older age and lack a positive family history. AS tends to occur at a later age in females than in males, and diagnosis is often delayed. 2 Dr. Kubiak is Resident, Musculoskeletal Research Center, NYU–Hospital for Joint Diseases Depart- ment of Orthopaedic Surgery, New York, NY. Dr. Moskovich is Associate Chief, Spine Service, Mus- culoskeletal Research Center, NYU–Hospital for Joint Diseases Department of Orthopaedic Sur- gery. Dr. Errico is Chief, Spine Service, Muscu- loskeletal Research Center, NYU–Hospital for Joint Diseases Department of Orthopaedic Sur- gery. Dr. Di Cesare is Chief, Adult Reconstruc- tive Service, Musculoskeletal Research Center, NYU–Hospital for Joint Diseases Department of Orthopaedic Surgery. None of the following authors or the departments with which they are affiliated has received anything of value from or owns stock in a commercial com- pany or institution related directly or indirectly to the subject of this article: Dr. Kubiak, Dr. Mos- kovich, Dr. Errico, and Dr. Di Cesare. Reprint requests: Dr. Di Cesare, Musculoskele- tal Research Center, NYU–Hospital for Joint Dis- eases, 301 E 17th Street, New York, NY 10003. Copyright 2005 by the American Academy of Orthopaedic Surgeons. Ankylosing spondylitis is an inflammatory disease of unknown etiology that affects an estimated 350,000 persons in the United States and 600,000 in Europe, primarily Caucasian males in the second through fourth decades of life. Worldwide, the prevalence is 0.9%. Genetic linkage to HLA-B27 has been established. Ankylosing spondylitis primarily affects the axial skeleton and is characterized by inflammation and fusion of the sacroiliac joints, spine, and hips. The resultant deformity leads to severe functional impairment in approximately 30% of patients. Orthopaedic management primarily involves correction of hip deformity through total hip arthroplasty and, less frequently, correction of spinal deformity with spine osteotomy. Closing wedge osteotomies have the lowest incidence of complications. Whether patients with ankylosing spondylitis are at increased risk for heterotopic ossification remains controversial, but comparison with age- and sex-matched counterparts suggests no dramatically higher risk. Because of the high rate of missed fractures and complications after minor trauma in patients with ankylosing spondylitis, plain radiographs are usually not sufficient for evaluation. Thorough patient assessment should include a comprehensive history, physical examination, and laboratory studies. J Am Acad Orthop Surg 2005;13:267-278 Vol 13, No 4, July/August 2005 267 Etiology Not everyone who is HLA-B27– positive develops AS; it is likely that other genetic and/or environmental factors play a role in the etiology. 5 One recent theory is that AS is an autoimmune disorder that occurs subsequent to a Klebsiella pneumoniae infection in HLA-B27–positive individuals, with molecular mimicry between HLA-B27 and K pneumoniae bacterial antigens. 6 Elevated levels of antibodies to K pneumoniae have been noted in AS patients. Elevated IgA levels in AS patients may reflect mucosal immunity to a persistent bacterial infection and may be the autoimmune trigger for AS, idiopathic bowel disease, and other reactive arthritides. No causal relationship has been established between AS and other autoimmune diseases, but the incidence of AS in patients with idiopathic bowel disease is approximately 3.7%. 7 Pathophysiology The pathognomonic feature of AS is a combination of inflammation and bony destruction at the site of tendon insertion (ie, enthesopathy). Pannus or fibroblastoid tissue and inflammatory cell infiltrates invade the bone adjacent to entheseal at- tachments; new bone formation in response to inflammation leads to ankylosis of affected joints. Preferen- tial involvement of the zygapophyseal joints has been noted on magnetic resonance imaging (MRI). Ankylosis and subsequent loss of motion of the zygapophyseal joints leads to syndesmophyte formation, resulting in the characteristic “bamboo spine” of individuals with AS (Fig. 1). Enthesopathy also can occur in peripheral joints, leading to sy- novitis-like symptoms and joint degeneration. 8 Other manifestations of AS include inflammatory bowel disease, psoriasis, uveitis/iritis (25%), 9 pulmonary fibrosis, aortitis, and genitourinary problems, with prevalence up to 40%. 10,11 Clinical History Patients usually present with symptoms and physical findings consistent with the nonmechanical and inflammatory nature of AS. Onset is often insidious; patients typically cannot give the precise time of onset or even pinpoint the initially affected site. These individuals frequently present in the second through fourth decades of life with low back pain and stiffness, particularly in the morning, at night, or after prolonged periods of sitting and/or recumbency. Chest wall pain is a frequent complaint, particularly with deep inhalation. Back pain not relieved by recumbency and the persistent discomfort may com- pel the individual to leave the bed at night. 12 Patients also may have but- tock pain that radiates down the posterior thigh. Enthesopathy involving the Achilles and plantar tendon insertions with associated symptoms also is common. Some patients experience no pain but present with increasing stiffness in the hips and spine. As with other inflammatory diseases, symptoms often improve with exercise. Physical Examination A systematic examination of the en- tire patient is imperative. Ocular pain, scleral redness, and photophobia are often indicativeofacuteanterior uveitis and may be clinically apparent before other symptoms or signs of AS appear. Chest expansion measured at the fourth intercostal space typically is limited to <2.5 cm after fusion of the costovertebral joints; the patient then becomes an obligate diaphrag- matic breather. Total lung volume and vital capacity usually are preserved; the diaphragm excursion is affected only in the patient with severe thoracic kyphosis. Patients become tachypneic when the degree of kyphosis compresses the abdominal cavity, thereby limiting diaphragmat- ic excursion. Pulmonary function test- ing should be performed before surgery on all patients with AS. Aortic and mitral regurgitation murmurs can occur as a consequence of aortitis in patients with long-standing disease. Right bundle branch block and varying degrees of atrioventricular block occur in up to 30% of patients as a result of fibrosis extending from the aorta to the intraventricular sep- tum. 13 Early in the disease, examination of the sacroiliac joints may reveal ten- derness to palpation, which can be ex- Figure 1 Lateral radiograph of the lumbar spine in a 46-year-old man demonstrating the flowing syndesmophytes and posterior element fusion consistent with bamboo spine. Disk spaces are often maintained, especially in the lumbar spine. Anteriorly, osteophytes are often oriented vertically rather than hor- izontally, which is common in spondylitis and diffuse idiopathic skeletal hyperostosis. Orthopaedic Management of Ankylosing Spondylitis 268 Journal of the American Academy of Orthopaedic Surgeons acerbated by hyperextension of the hips. Patients with hip involvement develop hip flexion contractures. Some patients exhibit loss of lordot- ic curvature of the lumbar spine and loss of spine movement in all planes. Patients with decreased mobility of the thoracolumbar spine have an ab- normal Schober sign—that is, lack of at least a 5-cm increase in distance from a midline point 5 cm below and 10 cm above the posterior superior iliac spine, measured in both the erect standing position and full forward flexion. Late in the disease, the cervical spine can become rigid, with loss of flexion and extension. Chin- brow angle, occiput-to-wall distance, and gaze angle are used to evaluate functional deformity involving the cervical spine (Fig. 2). Most patients are neurologically normal, with pres- ervation of deep tendon reflexes. A slow, progressive cauda equina syn- drome may appear late in the course of the disease. Assessment of Deformity Correction of deformity most often is performed to improve the patient’s visual field, respiratory function, 14 balance, sitting position, swallowing function, or ambulation. Determining the site of deformity is critical before surgically treating the deformity. Flexion contracture of the hips, loss of lumbar lordosis, and progressive thoracic and cervical kyphosis all may contribute to the functionally disabling stooped posture of patients with AS. Deformity must be assessed both clinically and radiographically as part of preoperative planning. The level of deformity will aid in determining the benefit of total hip arthroplasty (THA) and/or the level of corrective spine osteotomy and degree of correction necessary. The chin-brow angle is the angle formed by the vertical line drawn from the chin to the brow with the patient’s hips and knees fully extended (Fig. 2). Occiput-to-wall distance is measured to grossly determine the patient’s sagittal balance. The horizontal distance from the occiput to the wall is measured with the patient’s buttocks and heels against the wall, with hips and knees extended. Clin- ically, occiput-to-wall distance should be 0 to 2 cm. The degree of hip flexion contracture is determined by placing the patient supine with the lumbar spine pressed flat to the ex- amining table, then measuring the angle that each femur makes with the horizontal. Normal sagittal balance places the center of mass just in front of the S1 vertebral body. Radiographically, a plumb line drawn from the center of the C7 vertebral body should just touch the anterior edge of the body of S1 on the lateral radiograph. Nor- mal individuals are able to compensate for small changes in sagittal balance through changes in sacral inclination; hip, knee, and ankle flexion; or extension. In patients with AS, these normal compensatory changes are ameliorated by loss of motion in these areas. 15 Laboratory Evaluation Baseline laboratory investigation in patients suspected of having AS should include a basic metabolic panel, complete blood count, erythrocyte sedi- mentation rate (ESR), C-reactive pro- tein (CRP) level, and rheumatoid factor. Although routine HLA-B27 status is not required to make a diagnosis of AS, it is helpful in the differential diagnosis. The clinician should be suspicious of a diagnosis ofAS in patients who are HLA-B27–negative. Patients in the active phase of the disease have mildly elevated ESR, CRP level, and white blood cell count. In most cases, rheumatoid factor is negative and HLA-B27 is positive. Patients with chronic AS may have a normocytic, normochromic anemia. Imaging Studies The sacroiliac joints usually are the first joints affected in patients with AS. Sacroiliitis initially presents as a widening of the sacroiliac joints with progressive sclerosis of the joint margins, leading to eventual bony fusion across the joints with subsequent loss of sclerosis. Care must be taken to disregard congen- ital deformities and degenerative changes as well as osteitis conden- sans ilii (symmetric sclerosis on the iliac sides of both sacroiliac joints without erosions, seen in women who have borne children). Standard anteroposterior radiographs of the pelvis are inadequate to fully evaluate the sacroiliac joints. For accurate diagnosis, a Ferguson view of the pelvis (anteroposterior with the x-ray tube tilted 30° cephalad) and oblique radiographs are required. Hip involvement presents as ossification of the ligamentous origins and insertions about the trochanters, iliac crests, and ischial tuberosities. Late findings include loss of joint Figure 2 Measurement of occiput-to-wall distance, gaze angle, and chin-brow angle. Erik N. Kubiak, MD, et al Vol 13, No 4, July/August 2005 269 space, sclerosis, and fusion with loss of sclerosis at the hips. The ascending osseous changes of the cervical, thoracic, and lumbar spine lead to the characteristic bamboo spine in advanced stages of the disease. The erosive sclerotic process- es that occur in the spine are differ- ent from those that occur in diffuse idiopathic skeletal hyperostosis (DISH, also known as Forestier’s disease). AS can be erroneously diag- nosed in patients who have ankylosis of the spine for other reasons. Spine lesions in AS are the result of wedging of vertebral bodies and ossification of disk spaces leading to a rigid kyphotic spine. Enthesopathy of the zygapophyseal joints leads to fusion of the posterior elements. The bone loss and reabsorption that lead to these deformities occur early in young persons with active disease. 16 Erosions at the discovertebral junctions are called Romanus lesions; sclerosis in this region gives rise to so- called “shining corners.” In AS, the syndesmophytes are bilateral and have their insertions at the upper and lower margins of adjacent vertebrae; in DISH, the syndesmophytes are larger and asymmetric, with nonmar- ginal vertebral insertions consistent with their status as ligamentous os- sifications. Additionally, DISH spares the sacroiliac joints and is not associated with HLA-B27. In patients with AS, the zygapophyseal joints are pre- dominantly involved and frequently obliterated by fusion. Four other spondyloarthropathies—psoriatic arthritis, reactive arthritis, arthritis associated with inflammatory bowel disease, and undif ferentiated spondy- loarthropathy—can have radiographic changes similar to those of AS. Both computed tomography (CT) and MRI are more sensitive than plain radiographs for detecting early disease. In a review of imaging techniques for sacroiliitis, Braun et al 17 advocated the use of CT for evaluation of erosions and regional ankylosis. MRI is the most sensitive instrument for detecting early disease, with a sensitivity of 95% and a specificity of 100%. 18 Early detection may be important in determining which patients would likely benefit from immune-modulating medication reg- imens when radiographic evidence is lacking. Bone scans are unreliable, although a negative bone scan should create suspicion of an AS diagnosis in a patient with sacroiliitis or low back pain. Diagnostic Criteria The Rome criteria for AS, established in 1961, were modified by the Amer- ican Academy of Rheumatology in 1966 and renamed the New York clas- sification. The New York criteria were modified in 1984 by van der Linden et al 19 to improve sensitivity and re- tain specificity (Table 1). The modified New York criteria combine clinical and radiographic findings for the diagnosis of AS. Radiographic evaluation (eg, Ferguson’s view, oblique views) of the sacroiliac joints is used to determine the degree of the sacroiliitis, which is graded 0 (normal), 1 (suspicious), 2 (minimal sacroiliitis), 3 (moderate sacroiliitis), and 4 (ankylosis). Limitations of this system are an inability to detect all sacroiliac and/or spinal involvement on plain radiographs, failure to include patients with other forms of spondyloar- thropathy, and an assumption that the duration of inflammatory back pain has exceeded 3 months. The presence of HLA-B27 is not necessary to make the diagnosis. Nonsurgical Management Nonsteroidal anti-inflammatory drugs (NSAIDs)—specifically, in- domethacin—remain the mainstay of medical therapy. Cyclooxygenase-2 inhibitors offer the potential benefits of decr eased gastrointestinal morbidity, but their efficacy in the treatment of AS remains to be proved. Sulfasala- zine, methotr exate, thalidomide, and anti–tumor necrosis factor (TNF)-α agents (infliximab, etanercept, adal- imumab) ar e frequently used in long- term AS management. 20 Indometha- cin and radiation therapy have been employed to manage ankylosis and myositis ossificans. In 2003, the As- sessment in Ankylosing Spondylitis Working Group recommended that anti–TNF-α be used to treat patients with AS when any of the following exists: (1) a definitive diagnosis of AS; (2) presence of the disease for at least 4 weeks; (3) presence of refractory disease (defined by the failure of two types of NSAIDs during a single 3-month period); (4) failure of local corticosteroid injection into inflamed sacroiliac joints; (5) failure of sul- fasalazine in patients with peripher- Table 1 The Modified New York Criteria for Diagnosing Ankylosing Spondylitis 19 Clinical Criteria 1. Low back pain of at least 3 months’ duration improved by exercise and not relieved by rest 2. Limitation of lumbar spine motion in sagittal and frontal planes 3. Chest expansion decreased relative to normal values for age and sex Radiographic Criteria 4. Bilateral sacroiliitis, grade 2-4 5. Unilateral sacroiliitis, grade 3-4 Orthopaedic Management of Ankylosing Spondylitis 270 Journal of the American Academy of Orthopaedic Surgeons al disease; and (6) no medical con- traindications to the initiation of treatment. 21 Braun et al 22 summarized the results of anti–TNF-α medications in more than 300 patients enrolled in clinical trials, which indicated significant (P < 0.0001) short-term improvement in disease activity, function, and quality of life. Long-term efficacy of these medications is being studied in ongoing clinical trials. Early medical intervention may improve patient function, lessen pain, and delay disease progression. The physician is responsible for educating the patient about the disease and its natural history. An activity program of physical exercise, including stretching and postural alignment, should be consistently followed. A medium-firm mattress is recommended, and the patient may benefit from sleeping supine with one pillow to maintain a more normal sagittal spinal alignment and pr event hip flexion contractures. Ultimate ankylosis of the spine in an anatomic position, an achievable outcome for patients who receive early diagnosis and counseling, is far preferable to progressive kyphosis. Surgical Management Indications for surgical treatment of patients with AS are to lessen pain and to improve function. Addition- ally, the psychosocial effects of severe deformity are devastating, and correction may help the patient recover vital social skills and possibly accept having the disease. THA is the most common surgical intervention in AS patients, followed by spinal osteotomies for correction of cervical deformity and thoracolumbar sagittal balance. Few patients require surgical intervention for correction of peripheral joint abnormalities. Hip Deformity Thirty percent to 50% of patients with AS exhibit involvement of the hips; of those, 90% present bilateral- ly. 23 Hip involvement ranges from flexion contractures to complete ankylosis, often in a disabling flexed position. THA consistently improves both range of motion (ROM) and function; it also decreases pain in patients with AS. Patients with AS onset at an early age are more likely to require THA. Sweeney et al 24 reported the mean age of AS onset in patients undergoing THA to be 19.5 years, an average of 3.5 years younger than matched con- trols with AS who had not undergone THA. In addition, 16% ofAS patients with onset before age 16 years required THA within 20 years. Indications for THA are correction of hip flexion contractures and reduction of pain caused by degeneration, with the goal of improved function. Patients with AS typically undergo THA at a younger age than do patients having THA for osteoarthritis. THA implant survival in AS patients is similar to that in other young patients with THA. It was previously thought that patients with AS were at a significantly greater risk of developing disabling heterotopic ossification (HO) than other patients undergoing THA; however, careful review of the literature reveals that there may not be dramatically higher rates of HO for age- and sex- matched counterparts. 25,26 Correction of hip flexion contracture with THAcan restore sagittal balance in patients with AS. Tang and Chiu 27 noted that, because of the presence of relative hyper extension of the hips after THA, AS patients are more prone to anterior dislocation when acetabular components are placed in their normal position relative to the pelvis. When positioning the acetabular component in a patient with AS, one must account for the relationship of the pelvis to the lumbar spine in the sagittal plane in order to avoid an excessively hyperextended hip once the patient resumes an upright position. In patients with severe spinal deformity, corrective spinal osteotomies should be performed before THA to prevent future acetabular component malposition. However, many surgeons still concur with Lee, 28 who as early as 1963 stated that THA should be performed before considering spinal osteotomy because improvement in hip ROM and pain relief may ob- viate the need for spinal osteotomy in patients with severe hip flexion deformity. Determining surgical se- quence should be based on patient circumstances. Several studies indicate that THA is beneficial in AS patients (Table 2). The studies listed in Table 2 evaluated a total of 524 THAs performed in 320 patients with AS. Ambulatory status improved in all patients. Sixty percent to 97% of patients reported no pain after THA. 23,25,27,29-31 Fifteen-year survival (ie, time to THA failure) ranged from 66% to 81.4%. 23,27,31 Av- erage age at time of surgery was 38 years. 23,25,27,29-31 Thirty patients had Brooker 33 class 3 or 4 HO. 27,29,32 Eighty-six revision THAs were performed. 23,27,29-32 Sweeney et al 24 re- viewed charts and questionnaires of 340 patients with AS who were treated with THA. Survival rates of pri- mary THA were 90%, 78%, and 64% at 10, 15, and 20 years, respectively. Survival rates of revisions were 73%, 55%, and 55% at 10, 15, and 20 years, respectively. These THA survival rates and those listed in Table 2 are not dissimilar to survival rates in other young patients requiring THA. 34-40 The majority of revisions in the studies listed in Table 2 were performed for aseptic loosening of both the femoral and acetabular components. 27,30 Tang and Chiu 27 used both uncemented and cemented implants in their series of THA in patients with AS; they reported loosening rates of 5% and 28% in uncemented and cemented implants, respectively. The short duration of follow-up in patients r eceiving uncemented implants prevented Tang and Chiu from fully Erik N. Kubiak, MD, et al Vol 13, No 4, July/August 2005 271 advocating their use. However, more recent preliminary clinical data 39,40 support the use of uncemented acetabular and femoral components in young, active patients, including those with AS. The level of risk for heterotopic bone formation after THA in patients with AS remains controversial. Previous reports have resulted in the impression that the rates of postoperative HO are unacceptably high after THA in AS patients. How- ever, careful review of the previously reported high rates of HO after THA in patients with AS shows rates not unlike those seen in other young patients undergoing THA. Additionally, patients with preoperative ankylosis often experience significant improvement in function after THA. 23,30,41 The proportion of AS patients with functional ankylosis secondary to HO following THA is likely substantially lower than previously thought. Patients with class 3 HO, nevertheless, experienced significant (P < 0.01) improvement in ROM, pain relief, and independent ambulation after THA. 41 Higher rates of HO after THA have been reported in AS patients who have undergone repeat operations, who have experienced postoperative infection, who were treated with a transtrochanteric approach, and/or who had an active disease (reflected by elevated ESR or CRP level). Brinker et al 25 found similar rates of HO in 12 patients with AS and in an age-matched control group without AS who underwent THA. High-risk patients with preoperative ankylosis, with previous hip surgery, with previous infection, and/or in whom a transtrochanteric approach to the hip was used should be considered for HO prophylaxis with indo- methacin or low-dose radiation. The benefits of HO prophylaxis in other patients with AS has not been defin- itively determined. Other Peripheral Joint Involvement The rate of shoulder and knee involvement in AS ranges from 25% to 70%. 42 Although little has been reported on managing the shoulder and knee in patients with AS, Finsterbush et al 32 noted marked improvement in walking, function, and pain in 21 of 23 patients with severe hip, knee, and ankle involvement who were treated with sur gery and rehabilitation. They did not address survivorship or the treatment of knee or ankle involvement. Parvizi et al 43 recently reported on 30 total knee arthroplasties in 20 patients (mean age, 55 years) who were followed for a mean of 11.2 years. Knee Society pain scores improved significantly (P < 0.0001), from a mean of 14 preoperatively to a mean of 76.3 at final follow-up. Knee Soci- ety function scores improved from 16.3 to 58.7. There was essentially no improvement in ROM (84.8° to 86.7°). In both series, 32,43 severe preoperative Table 2 Review of Total Hip Arthroplasty in Patients With Ankylosing Spondylitis Study Patients/ Hips (N) Ce- mented/ Unce- mented Preop- erative Anky- losis (N) Mean Age at Surgery (yrs) Mean Follow-up (yrs [range]) HO: Brooker Class 1-2/3-4 Mean Survival at 10/15/20 yr (%) Revi- sions (N) Patients With- out Pain (%) Ambu- lation Status Finster- bush et al 32 23/35 — 13 — — 0/4 — 4 — I Shih et al 29 46/74 — 25 36 10 (3-15) 48/6 78/—/— 23 97 I Brinker et al 25 12/20 U — 35 6 (2-10) 6/0 — — 60 I Sochart and Porter 30 24/43 C — 29 23 (1 mo- 30 yr) 6/0 91/—/73 12 88 I Tang and Chiu 27 58/95 46 C; 49 U — 39 11.3 (2-28) 70/20 96.8/66.3/— 19 79 I Lehti- mäki et al 31 54/76 C — 40 — — 80/66/62 3 83 — Joshi et al 23 103/181 C 42 47 10 (2-27) 40/0 87.3/81.4/— 25 95 I — = no data, C = cemented, HO = heterotopic ossification, I = improved, U = uncemented Orthopaedic Management of Ankylosing Spondylitis 272 Journal of the American Academy of Orthopaedic Surgeons morbidity justified total knee arthroplasty as a reliable means of provid- ing durable pain relief and modest improvement in function, regardless of the high incidence of postoperative stiffness. In their review of 158 patients with AS, Emery et al 44 identified 52 with shoulder involvement, 6 of whom had acute inflammatory arthropathy of the sternoclavicular or acromio- clavicular joints. Most symptoms re- sponded to NSAIDs. Forty-one of the 52 patients with shoulder involvement experienced restriction of scapulothoracic motion, which was always bilateral; of these, 34 patients had involvement of the scapulothoracic joint with loss of ROM (forward flexion, abduction, and external rota- tion), and 7 patients had asymmetric scapulothoracic and glenohumeral involvement. Most shoulder involvement was minimally disabling and re- sponded to nonsurgical management. Destructive glenohumeral involvement, although rare, was the most disabling. The presence of limited scapulothoracic ROM may compli- cate treatment of AS patients, similar to the difficulties encountered during treatment of other patients with destructive glenohumeral arthropathy. Spine In AS, chr onic inflammation of the zygapophyseal joints leads to progressive fusion of the spine, typically in a caudal to cranial fashion. As spinal segments become progressive- ly fused, pain often disappears. Os- teopenia is common in patients with AS. Rigid fused sections of the spine concentrate and convert compressive stresses to shear stresses at the atlanto-occipital, cervicothoracic, and thoracolumbar junctions. This can lead to fracture, pseudarthrosis, and spondylodiscitis. Additionally, progressive increases in cervical and thoracic kyphosis, combined with loss of lumbar lordosis and of motion at the hip joints, can result in loss of sagittal balance. The resultant stooped posture can lead to significant functional deficits and a deformed ap- pearance. Incapacitating symptoms include the inability to lie in bed or to look straight ahead. Patients with cervical ankylosis may have difficulty with horizontal gaze even after correction of lumbar alignment. Sur- gical intervention also may be indicated for management of deformity, pseudarthrosis, fracture, and spondylodiscitis. Cervical Deformity Correction of deformity at the level of the cervical spine is indicated for patients in whom sagittal balance has been maintained or regained surgically, but whose kyphotic chin-brow angle has significantly impaired the visual field or interfered with either hygiene or swallowing. These patients may exhibit chin-on-chest deformity. Patients with evidence of fracture, hypermobility of the cervical spine, and subluxation of C1-C2 leading to kyphotic deformity should be treated with gradual halo traction to restore accurate alignment of the spinal canal and chin-brow angle. Pa- tients with C1-C2 instability should be treated initially with cervical traction in a halo, followed by posterior arthrodesis. Osteotomy of the cervical spine should be limited to patients with rigid deformities. Evidence of recent fracture, characterized by an overt fractur e or by new onset of pain in the cervical spine of a person previously without pain, is a contrain- dication to osteotomy. Urist 45 first described extension osteotomy of the cervical spine for correction of cervical deformity. This operation is performed under local anesthesia with the patient awake to facilitate neurologic monitoring during the reduction. The level of correction is centered at C7-T1 because the canal is relatively wide at this level and the cervical cord and nerve roots are relatively mobile. In addition, the vertebral vessels do not enter the lateral masses at this level. In 1998, Liew and Simmons 46 recommended resec- tion extension osteotomy followed by posterior fusion and immobilization, with either halo or collar postoperatively, depending on the fixation method. In 1997, McMaster 47 reported the results of extension osteotomy at the C7-T1 level in AS patients with severe flexion deformity of the cervical spine. All 15 patients (mean age, 48 years) had a mean correction of 54°. One patient became quadriparet- ic, two had unilateral C8 palsies, and four experienced subluxations. Neu- rologic problems were attributed to dural traction (ectasia), posterior element impingement of C8 roots, and subluxation. Rigid fixation using plates and rod-and-screw constructs may decrease neurologic complications by maintaining stability during and after osteotomy. Thoracolumbar Deformity Corrective osteotomy of the lumbar spine is indicated to correct sagittal balance when correction of hip flexion contractures does not restore sagittal balance and the patient is markedly disabled. For patients with pseudarthrosis, Simmons 48 advocated correction of kyphotic deformity by spine osteotomy to convert trans- lational forces to compressive forces at the site of pseudarthrosis. Van Royen et al 15 devised an equa- tion correlating sagittal balance and physiological end plate angle. Nomo- grams constructed from this informa- tion allow the surgeon to correlate the correction angle, horizontal position of the C7 plumb line, and the level of the spinal osteotomy, predicting the optimum level and degree of correction. Most authors advocate general anesthesia and fiberoptic intubation for thoracic and lumbar deformity correction. In a review of 66 spinal osteotomies, Bridwell et al 49 stressed the importance of the “wake-up test” for intraoperative patient evaluation. Five neurological sequelae were missed by somatosensory evoked po- Erik N. Kubiak, MD, et al Vol 13, No 4, July/August 2005 273 tentials but were detected by the wake-up test. The osteotomies can be performed in either the lateral decubitus or prone position. Initially plaster thoracolumbosacral orthosis with one leg includ- ed was used for postoperative immobilization. Since the advent of segmental pedicle screw fixation, many surgeons immobilize patients in custom rigid thoracolumbosacral orthoses with a hip extension or fore- go postoperative immobilization al- together. Recommended periods of immobilization vary from 2 to 4 months for closing wedge osteotomies and 6 to 15 months for opening wedge and polysegmental osteotomies. The opening wedge, polysegmental wedge, and closing wedge osteotomies (Fig. 3) are the three surgical techniques used for correcting lumbar kyphosis. In 1945, Smith-Petersen et al 50 first described an opening wedge osteotomy for correction of lumbar kyphosis in six patients. Hehne et al 51 advocated polysegmental wedge osteotomy (Fig. 4), which was first described by Wilson and Turkell 52 in 1949. In 1985, Thomas- en 53 subsequently described a mono- segmental closing wedge osteotomy of the lumbar spine, in which the posterior elements, pedicles, and a por- tion of the vertebral body are resect- ed to accomplish the correction (the so-called pedicle subtraction osteotomy). In their meta-analysis of articles published between 1945 and 1998, Van Royen and De Gast 14 reported on 856 patients with AS who underwent correction of fixed kyphotic thoracolumbar deformity. There were 451 opening wedge osteotomies, 249 polysegmental wedge osteotomies, and 156 closing wedge osteotomies. Mean patient age was 41 years at the time of operation; mean correction obtained was 40.3° for opening wedge osteotomies, 40.3° for polysegmental wedge osteotomies, and 36.5° for closing wedge osteotomies. Of the 856 patients who underwent surgery, 34 (4%) died from intraoperative or postoperative complications. The authors noted a tendency toward less severe complications with closing wedge osteotomy. Jaffray et al 54 reported that closing wedge osteotomy Figure 4 Preoperative (A) and postoperative (B) weight-bearing lateral radiographs of a 41-year-old man who underwent polysegmental closing wedge osteotomy of the lumbar spine for correction of severe kyphotic deformity and loss of sagittal balance. Lumbar lordosis was corrected from 37° preoperatively to 60° postoperatively, which resulted in a 16-cm correction of the patient’s sagittal balance to neutral. Figure 3 Bone removed for opening wedge osteotomy (A), polysegmental closing wedge osteotomy (B), and closing wedge osteotomy (C). Orthopaedic Management of Ankylosing Spondylitis 274 Journal of the American Academy of Orthopaedic Surgeons can be performed even when the anterior longitudinal ligament is com- pletely ossified. The anterior column is not forcibly extended in this tech- nique, ther eby minimizing the risk of abdominal aortic injury. In their series of 45 patients undergoing pedicle subtraction closing wedge osteotomy, Kim et al 55 demonstrated an ability to effect sagittal and coronal balance correction with one- and two- level closing wedge osteotomies with no long-term neurologic sequelae. Berven et al 56 also r eported correction of sagittal balance with closing wedge osteotomy. Pedicle subtraction osteotomy avoids intraoperative nerve r oot compression resulting from closing down the neural foramina as the spine is extended. Halm et al 57 collected functional outcome data from 148 of 175 patients who had spinal deformity correction surgery between 1979 and 1988. Im- provement was noted in 47 of the 60 items of the modified Arthritis Impact Measurement Scales at a mean follow-up of 4.8 years. Eighty-eight percent of patients were very satisfied with the results of surgery, and 60.9% were able to return to work. In a series of 83 patients (5 with AS) undergoing spinal osteotomy to correct fixed sagittal and/or coronal plane deformity, Ahn et al 58 demonstrated a statistically significant correlation between patient functional outcome and satisfaction with sagittal lordosis >25° (P = 0.034) and coronal plumb alignment <2.5 cm (P = 0.041). Suk et al 59 prospectively evaluated 34 patients with AS after they underwent pedicle subtraction extension osteotomy for correction of sagittal plane deformity. Correction of chin-brow angle fr om −10° to 10° resulted in significantly (P = 0.000) better horizontal gaze. Additionally, the functional scores of items r elated to the horizontal gaze were higher than the overall mean score. Because of the neck stiffness of AS patients, correcting the chin-brow angle is better for them than absolute correction of coronal and sagittal balance would be, because correcting the chin-brow angle improves these patients’ visual field. The importance of planning deformity correction so as to correct visual fields is essential in AS patients. It is unclear which type of spinal osteotomy is most appropriate for the treatment of severe kyphotic deformity, although closing wedge osteotomies appear to have a lower incidence of complications. Deformity correction surgery in AS patients is associated with dural tears secondary to dural ectasia, transient nerve root compression, loss of correction, implant failur e, postoperative spinal instability, and aortic injury. Fortunate- ly, the number of patients with severe kyphotic deformity is decreasing because of improved medical management and earlier detection. 60 Fracture Generalized spinal osteopenia is common in patients with AS. Spinal fracture often is caused by minor trauma and can be missed on spine radiographs because of distortion of the normal spinal anatomy by ectop- ic bone formation, erosions, sclerosis, disk ossification, vertebral wedging, or difficulty with patient positioning. Onset of pain after even minor trauma should suggest a fracture, which may not be visible on plain radiographs. 61 Fractures frequently occur at the C7-T1 junction and are difficult to visualize radiographically. Bone scan, MRI, or fine-cut CT can be used to evaluate AS patients who present with cervical pain (Fig. 5). The rigid, unsupported, osteo- porotic cervical spine is most suscep- tible to hyperextension injuries, and the cervical spine is the most common site of fracture in patients with AS. The drastic increase in stiffness at the cervicothoracic junction, combined with the lever arm of the fused cervical spine and weight of the head, makes fractures at the C6-C7 and C7-T1 levels most common. The lumbar and thoracic spines are more resistant to fracture because the anterior and posterior longitudinal ligaments are more thoroughly ossified than in the cervical spine. Spinal fractures typically occur through the ossified disk and vertebral body; vertebral body fractures are more common and have a higher risk of neural compromise, partly as a consequence of a higher incidence of epidural hematoma and the possibility of the newly mobile fracture severely translating, resulting in neural injury. 61 AS patients who sustain spinal fractures typically have high rates of neurologic injury. 62 Missed fractures are frequent and often present as rapidly progressing cervical kyphosis. Surgi- cal treatment is more commonly used, especially in patients with neurologic compromise, obscured visual fields, pseudarthrosis, or recurrent fracture. When traction or internal fixation are Figure 5 T2-weighted sagittal reconstruction magnetic resonance image of a 46-year-old man with a C7-T1 disk space fracture with subluxation and cord compression. Fast spin- echo sequences may show edema, thereby al- lowing fracture localization, even without fracture displacement. Erik N. Kubiak, MD, et al Vol 13, No 4, July/August 2005 275 used to manage these injuries, the neck should be aligned to prefracture position, not necessarily to a normal position (Fig. 6). Minor findings in patients with AS may be associated with substantial instability in the cervical spine, secondary to the altered bio- mechanics of the fused spine in addition to osteopenia and the concen- tration of forces at the cervico-occipital and cervicothoracic junctions. Preoperative evaluation of the cervical spine is essential when ma- nipulating the neck during intubation and patient positioning. Physi- cians also must be aware that, because the atlanto-occipital joint is last to fuse, atlantoaxial instability may occur. Instability is usually demonstrated on lateral flexion-extension views of the neck, where the atlantodens and posterior atlantodens intervals are measured. An atlantodens interval >3.5 mm is in- dicative of instability. A difference of 7 mm indicates disruption of the alar ligaments, and a difference >9 to 10 mm or a posterior atlantodens interval >14 mm is associated with an increased risk of neurologic injury and usually requires surgical intervention. Spondylodiscitis Spondylodiscitis has been reported to occur in 5% to 23% of patients with AS; 50% of these patients are asymptomatic. 63,64 Spondylodiscitis, which presents as an erosive sclerotic pr ocess, characteristically involves the intervertebral disk and adjacent bone. It can be confused radiographically with diskitis and pseudarthrosis. Unlike diskitis, biopsies of these lesions demonstrate chronic inflammatory changes with no infective or- ganisms. 63,64 Spondylodiscitis lesions occur at the level of the intervertebral disk rather than through the vertebral body, as in pseudarthrosis. Pseudar- throsis often presents as new back pain in a previously asymptomatic individual and often arises after minor trauma. Most cases of spondylodiscitis and pseudarthrosis resolve with nonsurgical management. Surgical stabilization may be required in patients with intractable pain, associated posterior element disruption, and fracture. It is important to assess kyphotic deformity before stabilization because deformity can create shear stresses at the site of spondylodiscitis or pseudarthrosis. These transla- tional for ces can be converted to compressive forces at the time of stabilization, leading to higher rates of fusion. Summary AS, which affects approximately 350,000 people in North America and 600,000 in Europe (worldwide prevalence, 0.9%), belongs to a larger group of spondyloarthropathies and is characterized predomi- nantly by involvement of the sacroiliac joints in young men who present with inflammatory low back pain in their third or fourth decade. The disease primarily affects the axial skeleton and is characterized by enthesopathy, which leads to fusion of the sacroiliac joints, hips, and spine. Young men presenting with inflammatory back pain and evidence of sacroiliitis should be screened for AS; most patients are HLA-B27–positive. Management of AS remains pal- liative, with NSAIDs continuing to be the mainstay of treatment. How- ever, new anti–TNF-α drugs offer the promise of arresting the progression of AS. AS patients presenting with back or neck pain after minor trauma should be considered to have spinal fractures until defini- tively proven otherwise with CT or MRI. THA can significantly improve function, pain, and deformity in AS patients with severe hip involvement. Results are comparable to those in other young patients with severe hip pathology. Because the incidence of HO in AS patients undergoing THA may not be significantly more than that of similar non-AS patients undergoing THA, the routine use of HO prophylaxis in AS patients should be reserved for Figure 6 Preoperative (A) and postoperative (B) lateral radiographs of a 31-year-old man who sustained a C5-C6 fracture through the disk space. Posterolateral fusion was done with lateral mass plates and posterior element wiring. Orthopaedic Management of Ankylosing Spondylitis 276 Journal of the American Academy of Orthopaedic Surgeons