Osteotomy distal to apex for thoracolumbar kyphosis secondary to ankylosing spondylitis

English Keywords:Ankylosing spondylitis  Thoracolumbar kyphosis  Pedicle subtraction osteotomy  Distal to apex

English Abstract:

  【Abstract】 Objectives: To investigate the indications and efficacy of performing pedicle subtraction osteotomy (PSO) distal to the apex for thoracolumbar kyphosis caused by ankylosing spondylitis(AS). Methods: Between January 2001 and August 2017, 39 AS patients(35 males and 4 females) treated with osteotomy distal to apical region were retrospectively reviewed. The mean age was 38.2±10.5 years(range, 20 to 59 years). The location of apex ranged from T9 to L1. Preoperative pseudarthrosis was found in 9 cases, involving 4 cases with pseudarthrosis located at apex but without neurologic deficit and 5 cases with the lesions located below apex with neurologic deficit. Bilateral total hip replacement(THR) was performed for 2 patients. Besides, 37 cases presented with unilateral or bilateral hip dysfunction before surgery. The mean BASRI-hip scores were 2.56±0.77 for the left side and 2.42±0.65 for the right side. Severe narrowing of unilateral or bilateral hip joint space(BASRI≥3) was found in 24 out of 39 cases. Hypolordotic lumbar spine was found in 22 cases while kyphotic lumbar spine was identified in 1 case. Preoperative CBVA and VAS were 23.00°±17.08° and 4.83±2.63, respectively. The osteotomy level, complications were assessed. Also, the radiographic parameters including global kyphosis(GK), sagittal vertical axis(SVA), lumbar lordosis(LL), angle of fused segments(AFS), and chin-brow vertical angle(CBVA) were evaluated. Results: All the 39 patients underwent correction surgery. The osteotomy level varied from T12 to L5(T12 2 cases, L1 8 cases, L2 16 cases, L3 12 cases and L5 1 case). Surgical complications included one case of intraoperative vertebral subluxation and one case of screw malposition. Intraoperative dural tears with cerebrospinal fluid leakage was observed in one case and was resolved at discharge. Also, no vascular complication, infection or postoperative nonunion was found. Kyphotic deformity, persistent back pain and impaired horizontal gaze were all resolved postoperatively. The average follow-up was 40.26±28.52 months, ranging from 14 to 144 months. One patient underwent revision surgery for rod breakage and achieved solid bone union at 3-month follow-up. On the contrary, conservative treatment was performed for another case with stable fused region. The preoperative GK, LL, SVA and CBVA were 69.47°±14.37°, 19.32°±19.19°, 120.77±48.34mm and 23.00°±17.08°, respectively. The above-mentioned parameters were changed to 28.76°±12.83°, 51.62°±16.08°, 26.56±41.12mm and 4.19°±6.58° after operation, respectively, and there was significant difference with that of preoperation(P<0.05). At the final follow-up, the above-mentioned parameters were 30.53°±13.95°, 49.32°±16.64°, 32.56±35.14mm, 4.78°±6.22°, and there was no significant difference with that of postoperation(P>0.05). AFS was 22.77°±10.86° of postoperation, and 24.29°±10.99° at the final follow-up(P>0.05). VAS was 1.82±1.64 at the final follow-up, and there was significantly difference with that of preperation(P<0.05). Conclusions: PSO distal to apex was a feasible and effective method to restore sagittal balance in AS-related kyphosis. Osteotomy distal to apex can be considered with the following criteria including primary surgical goal was to correct the SVA instead of GK, pseudarthrosis located at apex without neurologic deficit, pseudarthrosis located below apex with neurologic deficit, preoperative restricted hip function, apex located at middle thoracic spine, and flattening of the lumbar spine with apex at thoracolumbar junction.