Pseudarthrosis in Ankylosing Spondylitis

• (a, b - All India Institute of Medical Sciences)

Introduction: Lytic lesions in an ankylosed spine occasionally seen in clinical practice has been mentioned earlier in literature as Romanus / Anderson lesion or 'pseudoarthrosis'. Using description in the literature and using CT / radiographs a new classification is suggested for this lesion.

Methodology: A total of 215 patients of ankylosing spondylitis presented between 1983 and 2001 were reviewed. A total of 21 patients presented with backache with or without neurological deficit. Routine anteroposterior and lateral views were taken in all the patients along with greater/extension lateral views wherever indicated. There were involvement of D9 - D10, D10 - D11 level were D12-L1 in 4 patients each D5-6, D9-10 and L2-L3 level were involved in 3 patients each. D3 - D4 in 2 patient, D5-6, L2 - L3 level in 3 patients. CT scan at the level of the lesion was done in all case lesions were classified as following:Type I : Romanus sign or lytic defect on anterior and anterolateral aspect of the vertebral rim. Majority of the time asymptomatic.Type II : Spondylodiscitis type : Irregular lytic area in central and peripheral part of disc-bone border with sclerosis of adjacent area. May be symptomatic or asymptomatic, posterior column is spared.Type III : Extensive lesion : True pseudoarthrosis involving single motion segment and all the three columns. Unstable on flexion /extension views : may be associated with neurological complications. Lesions were further subclassified according to symptoms and treatment plan was formulated.6 patients had type I lesion, 10 patients type II and 5 patients type III lesions. All the patients with type I lesion were treated by analgesics, 6 type II lesions were treated by PVC brace for a period of 5 months, 3 patients with persistent pain and one patient with the neurological deficit was treated by anterior fusion. All the five type III lesions were treated by combined anterior and posterior fusion using instrumentation.

Results: All the 6 type I lesions healed completely by ossification, 6 lesions treated by PVC brace showed good evidence of bony union at 6 months, while the patients treated by surgery showed a evidence of good fusion four months postoperatively.

Discussion: Spinal pseudoarthrosis in ankylosing spondylosis is an intriguing lesion and its etiopathology is far from understood. Non-ossification of a short segment, stress fracture through ankylosed disc space, or repeated minor traumas have been suggested as aetiological factors. CT scan help in delineation of the exact extent of the lesion especially those involving posterior column which may not be visible on plain radiography. Absence of soft tissue mass around the vertebrae further differentiating this condition from tuberculosis which is very common in our part of world. Majority of the patients respond to conservative treatment by NSAIDS or PVC bracing for four to six months. Those patients with persistent pain or neurological deficit respond very well to operative treatment in the form of posterior spinal instrumentation with Interbodyfusion of the "lytic" site . The three types mentioned are perhaps the same lesion at various stages of their extent, hither too thought to be of different aetiologies by different workers in literature.

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