Pseudoarthrosis ankylosing spondylitis · Spinal pseudarthrosis in ankylosing spondylitis. Clinicopathological correlation andtheresults ofanterior spinal fusion. _7 Bone Joint Surg1988;

Annals of the Rheumatic Diseases 1994; 53: 206-210

CASE STUDIES IN DIAGNOSTIC IMAGING Series Editor: V C Cassar-Pullicino*

Pseudoarthrosis in ankylosing spondylitis

Wilfred C G Peh, Keith D K Luk

Clinical historyA 32 year old Chinese man presented with arecent severe exacerbation of spinal pain at thethoraco-lumbar junction. He had a history of

Figure 1 Pelvic radiograph shows fusion of both sacro-iliac joints. Whiskering is present atboth ischial tuberosities and rami (arrowheads). Irregularity and sclerosis of the lessertrochanters are arrowed. Hipjoints are concentrically narrowed.

chronic low back pain and stiffness, of gradualonset, for 10 years. He was living in Chinapreviously, receiving herbal applications andpain killers without relief. There were noperipheral joint symptoms. On examination,the patient had loss of normal lumbar lordosis.The thoracic and lumbar spine werecompletely stiff, with tenderness on percussionof the thoraco-lumbar junction. Chestexpansion was reduced but the shoulders, hipsand other peripheral joints showed satisfactoryranges of movement.

Plain radiographic findingsPelvic radiograph showed complete fusion ofboth sacro-iliac joints, consistent with grade IVsacro-iliitis (fig 1). Enthesopathic changes weremanifested as whisker-like new bone formationat the ischial tuberosities as well as irregularityand sclerosis at both lesser trochanters. Hipjoints showed concentric joint space narrowing.

Antero-posterior (AP) and lateral radio-graphs of the thoraco-lumbar spine demon-strated a widened disc space at T12/LI level,with irregular sclerotic margins. There was alinear fracture line, with sclerotic rims, throughthe fused posterior elements at the same level.This lesion produced mild kyphotic angulationof an otherwise straight spine (fig 2A,B). The

Departments ofDiagnostic Radiology,and OrthopaedicSurgery,-University ofHong Kong,Queen Mary Hospitaland Duchess ofKentHospital,Hong KongW C G PehK D K Lukt*Department ofRadiodiagnosis,The Robert Jones andAgnes Hunt OrthopaedicHospital,Oswestry,Shropshire SY10 7AG,United KingdomCorrespondence to:DrW C G Peh,Department of DiagnosticRadiology,University of Hong Kong,Queen Mary Hospital,Hong Kong.

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Figure 2 (A) AP and (B) lateral radiographs show T12/LI pseudoarthrosis. There is destructive change at theintervertebral space with surrounding sclerosis (arrows). A transverse linear break continues through the fused posteriorelements at the same level (small arrows). Syndesmophytes are present above and below this level (arrowheads).

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Figure 3 Reformatted (A) posterior coronal and (B) midline sagittal CT images showtransverse linear breaks through the posterior elements bilaterally (arrows). The facetjointsare fused, hypertrophied and sclerotic. Discovertebral lesion with adjacent sclerosis is welldemonstrated (arrowheads).

adjacent vertebral bodies above and below thisunfused level had a 'squared' appearance, andwere linked together by extensive syndes-mophytes. The thoracic and lumbar facetjoints were fused.

Differential diagnosisThis patient had all the characteristic radio-graphic features of advanced ankylosingspondylitis. The clinical picture was consistentwith this diagnosis although the recent severeonset of pain together with the presence ofthe T12/L1 disco-vertebral lesion stronglysuggested the development of a stress fracture,with non-union and a pseudoarthrosis. Aninfective process was the only alternative

diagnosis of the intervertebral disc changes.Conventional tomograms or computerisedtomograms (CT) with reconstructions weretherefore valuable in demonstrating posteriorelement defects typically seen in pseudo-arthrosis (fig 3A,B), and excluding theparavertebral soft tissue mass of a pyogenic ortuberculous lesion.

Diagnosis: pseudoarthrosis in ankylosingspondylitisThe patient continued to have persistentthoraco-lumbar junction pain, and did notrespond to conservative treatment. A T12/JL1anterior spinal fusion with resection of thepseudoarthrosis was performed (fig 4A,B). Thepatient's symptoms improved considerablyafter the operation. At follow up five years later,he was free of pain with no thoraco-lumbarspine tenderness. A repeat radiograph showedgood healing of the previous site ofpseudoarthrosis (fig 5).

DiscussionSpinal pseudoarthrosis is an importantcomplication in patients with long-standingankylosing spondylitis as it may result in severedisabling back pain, deformity and neuro-logical deficit. It is a state of mobile non-unionwhich occurs transversely through the discspace or less commonly, the vertebral body ofa spinal segment. The classification of pseudo-arthrosis as a 'non-inflammatory' type ofdestructive disco-vertebral (or Andersson)lesion is generally accepted (fig 6). 1 Thepresence of a posterior element defect fromeither a fracture or unfused facet joint is anessential component in the development of theanterior vertebral lesion.2 3 A recent paper hasintroduced the term 'pseudopseudarthrosis' todescribe extensive discovertebral destructionwithout fracture or posterior element pseudo-arthrosis but having abnormal motion betweentwo fused spinal segments.4 Recent authorsare, however, in agreement with the'mechanical' hypothesis for development ofpseudoarthrosis.'-8

Clinically, pseudoarthrosis should besuspected in patients who develop localisedback pain in previously quiescent disease asspinal symptoms tend to diminish withprogression of intervertebral ossification.There may or may not be a history of recentminor trauma. The thoraco-lumbar junction,being a site of stress concentration in anankylosed spine, is the commonest site ofpseudoarthrosis.3 The presence and degree ofneurological deficit depends on the severity ofpseudoarthrosis, with the possibility ofquadriplegia and death occurring in cervicalspine involvement.

Plain radiographic appearances of disco-vertebral destruction are often mistakenlydiagnosed as an infective lesion, especially inAsian or Oriental patients in whom tuber-culosis is not uncommon. Absence ofosteophytes, presence of surrounding sclerosisand posterior element defect are useful

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Figure 4 (A) AP and (B) lateral radiograph three weeks after anterior spinalfusion show satisfactory position ofbone graft at the T12/LI space (arrows).

Figure 5 Radiograph taken three years post-surgery showscomplete fusion of anterior and posterior elements at theT12/LI junction (arrowheads).

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A B C

Figure 6 Types of disco-vertebral lesions in ankylosing spondylitis. (A) Romanus lesion isseen as a superficial anterior or antero-lateral corner erosion in very early disease, with healingand bony repair resulting in syndesmophyte formation. (B) 'Inflammatory' type ofAnderssonlesion occurs at a relatively early stage of disease as a circumscribed defect in the vertebral endplate, often with disc space narrowing, angular kyphosis and reactive sclerosis. (C)Pseudoarthrosis (or 'non-inflammatory'Andersson lesion) is characterised by prominentosteolytic destruction ofadjacent vertebral bodies, variable subjacent sclerosis, an associatedposterior element defect and occurs in advanced disease.

Figure 7 Technetium 99m bone scan (three hour image)shows two horizontally orientated areas offocal uptake atLl and L2 vertebrae in a 25year old man with ankylosingspondylitis (arrows). Pseudoarthrosis at this site wassubsequently confirmed radiographically.

distinguishing features. Where pseudoarthrosisis suspected clinically, but is not apparentradiographically, isotope bone scans are verysensitive in demonstrating the lesion as areas offocal increased uptake on either side of atransverse spinal defect (fig 7). Isotope bonescans may also reveal a second clinically occultpseudoarthrotic segment.9 CT with 2D-recon-structions is superior to conventional tomo-graphy in differentiating posterior elementfractures from mobile facet joints, demon-stration of detailed features of pseudoarthrosisand associated spinal canal stenosis. 0Utilisation ofMRI has recently been described

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Figure 8 MRI of30year old man with ankylosing spondylitis. Tl weighted (A) mid sagittal and (B) parasagittal images demonstrate thepseudoarthrotic site as a band of intermediate intensity running obliquely through the Tll/T12 disc space (arrowheads) andfused Tl 1 posterior elements(arrows). There is loss of normal signal in the adjacent vertebral bodies. Corresponding T2 weighted images, figures (C) and (D), show linear high signalintensity (long arrows) consistent with vascularisedfibrous tissue and organising exudatefound in pseudoarthrosis.

and may be useful in the early detection ofpseudoarthrosis (fig 8)."As well as the initial diagnosis and assessment

of pseudoarthrosis, imaging plays an importantrole in determining progression or healing oflesions in patients undergoing conservativetreatment. Plain radiographs, supplemented byCT, form the main modalities in assessingdeformity, progressive osteolysis, or spinal canalcompromise. In patients not responding toconservative management, surgical fusion of thepainful unstable spinal segment may benecessary. Excision of pseudoarthrosis and

spinal fusion through an anterior approach isrecommended.'2 Postoperatively, bony healingis also assessed radiologically. It is important tobe able to detect refracture or non-healing of aposterior element defect, as an additionalposterior surgical fusion may be required tostabilise the spine and prevent redevelopment ofan anterior lesion.'2 Persistent postoperativeback pain may signal recurrent pseudoarthrosisat a different site, also known as migratingpseudoarthrosis. These lesions are difficult totreat, the options being repeat surgery orexternal bracing.'3

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1 Dihlmann W, Delling G. Disco-vertebral destructive lesions(so-called Andersson lesions) associated with ankylosingspondylitis. Skeletal Radiol 1978; 3: 10-6.

2 Rivelis M, Freiberger R H. Vertebral destruction at unfusedsegments in late ankylosing spondylitis. Radiology 1969;93: 251-6.

3 Chan F L, Ho E K W, Fang D, Hsu L C S, Leong J C Y,Ngan H. Spinal pseudoarthrosis in ankylosing spondylitis.Acta Radiol 1987; 28: 383-8.

4 Furst S R, Kindynis P, Gundry C, Haghighi P, Sartoris DJ, Resnick D. Pseudopseudarthrosis in a patient withankylosing spondylitis. _7 Rheumatol 1990; 17: 258-62.

5 Cawley M I D, Chalmers T M, Kellgren J H, Ball J.Destructive lesions of vertebral bodies in ankylosingspondylitis. Ann Rheum Dis 1972; 31: 345-58.

6 Pastershank S P, Resnick D. Pseudoarthrosis in ankylosingspondylitis. _7 Can Assoc Radiol 1980; 31: 234-5.

7 Hunter T, Dubo H I C. Spinal fractures complicatingankylosing spondylitis. Arthritis Rheum 1983; 26: 751-9.

8 Wu P C, Fang D, Ho E K W, Leong J C Y. The pathogenesis

of extensive discovertebral destruction in ankylosingspondylitis. Clin Orthop 1988; 230: 154-61.

9 Park W M, Spencer D G, McCall I W, Ward D J, WatsonBuchanan W, Stephens W H. The detection of spinalpseudoarthrosis in ankylosing spondylitis. Br _J Radiol1981; 54: 467-72.

10 Chan F L, Ho E K W, Chau E M T. Spinal pseudarthrosiscomplicating ankylosing spondylitis: comparison of CTand conventional tomography. A7R 1988; 150: 611-4.

11 Peh W C G, Ho T K, Chan F L. Pseudoarthrosiscomplicating ankylosing spondylitis - appearances onmagnetic resonance imaging. Clin Radiol 1993; 47:359-61.

12 Fang D, Leong J C Y, Ho E K W, Chan F L, Chow S P.Spinal pseudarthrosis in ankylosing spondylitis.Clinicopathological correlation and the results of anteriorspinal fusion. _7 Bone Joint Surg 1988; 70B: 443-7.

13 Ho E K W, Chan F L, Leong J C Y. Postsurgical recurrentstress fracture in the spine affected by ankylosingspondylitis. Clin Orthop 1989; 247: 87-9.

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Documents

Pseudoarthrosis ankylosing spondylitis · Spinal pseudarthrosis in ankylosing spondylitis. Clinicopathological correlation andtheresults ofanterior spinal fusion. _7 Bone Joint Surg1988;