Spinal instability in ankylosing spondylitis

Abstract

Background: Unstable spinal lesions in patients with ankylosing spondylitis are common and have a high incidence of associated neurological deficit. The evolution and presentation of these lesions is unclear and the management strategies can be confusing. We present retrospective analysis of the cases of ankylosing spondylitis developing spinal instability either due to spondylodiscitis or fractures for mechanisms of injury, presentations, management strategies and outcome.

Materials and methods: In a retrospective analysis of 16 cases of ankylosing spondylitis, treated surgically for unstable spinal lesions over a period of 12 years (1995-2007); 87.5% (n=14) patients had low energy (no obvious/trivial) trauma while 12.5% (n=2) patients sustained high energy trauma. The most common presentation was pain associated with neurological deficit. The surgical indications included neurological deficit, chronic pain due to instability and progressive deformity. All patients were treated surgically with anterior surgery in 18.8% (n=3) patients, posterior in 56.2% (n=9) patients and combined approach in 25% (n=4) patients. Instrumented fusion was carried out in 87.5% (n=14) patients. Average surgical duration was 3.84 (Range 2-7.5) hours, blood loss 765.6 (+/- 472.5) ml and follow-up 54.5 (Range 18-54) months. The patients were evaluated for pain score, Frankel neurological grading, deformity progression and radiological fusion. One patient died of medical complications a week following surgery.

Results: Intra-operative adverse events like dural tears and inadequate deformity correction occurred in 18.7% (n=3) patients (Cases 6, 7 and 8) which could be managed conservatively. There was a significant improvement in the Visual analogue score for pain from a pre-surgical median of 8 to post-surgical median of 2 (P=0.001), while the neurological status improved in 90% (n=9) patients among those with preoperative neurological deficit who could be followed-up (n =10). Frankel grading improved from C to E in 31.25% (n=5) patients, D to E in 12.5% (n=2) and B to D in 12.5% (n=2), while it remained unchanged in the remaining - E in 31.25% (n=5), B in 6.25% (n=1) and D in 6.25% (n=1). Fusion occurred in 11 (68.7%) patients, while 12.5% (n=2) had pseudoarthrosis and 12.5% (n=2) patients had evidence of inadequate fusion. 68.7% (n=11) patients regained their pre-injury functional status, with no spine related complaints and 25% (n=4) patients had complaints like chronic back pain and deformity progression. In one patient (6.2%) who died of medical complications a week following surgery, the neurological function remained unchanged (Frankel grade D). Persistent back pain attributed to inadequate fusion/ pseudoarthrosis could be managed conservatively in 12.5% (n=2) patients. Progression of deformity and pain secondary to pseudoarthrosis, requiring revision surgery was noted in one patient (6.2%). One patient (6.2%) had no neurological recovery following the surgery and continued to have nonfunctional neurological status.

Conclusion: In ankylosing spondylitis, the diagnosis of unstable spinal lesions needs high index of suspicion and extensive radiological evaluation Surgery is indicated if neurological deficit, two/three column injury, significant pain and progressive deformity are present. Long segment instrumentation and fusion is ideal.

Keywords: Ankylosing spondylitis; low energy fracture; spinal instability.

Figure 1

Case no. 11: (a) A pre-operative radiograph of D11-12 Andersson’s lesion in a male patient of 36 years age presenting with back pain due to spinal instability and neurological deficit. (b) A radiograph two years following D11-12 anterior decompression, bone grafting and D9-L3 posterior instrumented fusion. Patient had complete neurological recovery and pain relief after the surgery. (c) Three dimensional reconstruction CT scan image 2 years post surgery showing a sound D11-12 anterior fusion

Figure 2

Case no. 7: (a) A pre-operative mid sagittal T2 weighted MR image of lumbar spine demonstrating a L1-2 Andersson’s lesion with significant anterior and posterior neural compression in a male patient of 60 years age presenting with cervical and lumbar spine injury, back pain due to spinal instability and neurological deficit. (b) A post-operative radiograph three years following L1-2 posterior decompression and D10-L5 posterior stabilization and instrumented fusion. Patient had relief of pain and complete improvement in the neurological status following the surgery

Figure 3

(a) Case no 10: A pre-operative radiograph of D12-L1 Andersson’s lesion in a male patient of 32 years age presenting with back pain due to instability. (b) A pre-operative mid sagittal CT scan reconstructed image demonstrating a D12-L1 Andersson’s lesion. (c) Case no. 10: Lateral radiograph at three years following D12-L1 anterior decompression, bone grafting, instrumented fusion and D10-L3 posterior stabilization and instrumented fusion. Patient had excellent pain relief following the surgery