A modified posterior wedge osteotomy with interbody fusion for the treatment of thoracolumbar kyphosis with Andersson lesions in ankylosing spondylitis: a 5-year follow-up study

Background: Andersson lesions (ALs), also known as spondylodiscities, destructive vertebral lesions and spinal pseudarthrosis, usually occur in patients with ankylosing spondylitis (AS). Inflammatory and traumatic causes have been proposed to define this lesion. Different surgical approaches including anterior, posterior, and combined anterior and posterior procedure have been used to address the complications, consisting of mechanical pain, kyphotic deformity, and neurologic deficits. However, the preferred surgical procedure remains controversial. The aim of this study was to illustrate the safety, efficacy, and feasibility of a modified posterior wedge osteotomy for the ALs with kyphotic deformity in AS.Methods: From June 2008 to January 2013, 23 patients (18 males, 5 females) at an average age of 44.8 years (range 25–69 years) were surgically treated for thoracolumbar kyphosis with ALs in AS via a modified posterior wedge osteotomy in our department. All sagittal balance parameters were assessed by standing lateral radiography of the whole spine before surgery and during the follow-up period. Assessment of radiologic fusion at follow-up was based on the Bridwell interbody fusion grading system. Ankylosing spondylitis quality of life (ASQoL) and visual analog scale (VAS) scores were performed to evaluate improvements in daily life function and back pain pre-operatively and post-operatively. Pairedt tests were used to compare clinical data change in parametric values before and after surgery and the Mann-WhitneyU test was employed for non-parametric comparisons. The radiographic data change was evaluated by repeated measure analysis of variance.Results: The mean operative duration was 205.4 min (range 115–375 min), with an average blood loss of 488.5 mL (range 215–880 mL). Radiographical and clinical outcomes were assessed after a mean of 61.4 months of follow-up. The VAS back pain and ASQoL scores improved significantly in all patients (7.52 ± 1.31vs. 1.70 ± 0.70,t= 18.30,P < 0.001; 13.87 ± 1.89vs. 7.22 ± 1.24,t= 18.53,P < 0.001, respectively). The thoracolumbar kyphosis (TLK) changed from 40.03 ± 17.61° pre-operatively to 13.86 ± 6.65° post-operatively, and 28.45 ± 6.63° at final follow-up (F = 57.54,P < 0.001), the thoracic kyphosis (TK) changed from 52.30 ± 17.62° pre-operatively to 27.76 ± 6.50° post-operatively, and 28.45 ± 6.63° at final follow-up (F = 57.29,P < 0.001), and lumbar lordosis (LL) changed from -29.56 ± 9.73° pre-operatively to -20.58 ± 9.71° post-operatively, and -20.73 ± 10.27° at final follow-up (F = 42.50,P < 0.001). Mean sagittal vertical axis (SVA) was improved from 11.82 ± 4.55 cm pre-operatively to 5.12 ± 2.42 cm post-operatively, and 5.03 ± 2.29 cm at final follow-up (F = 79.36,P < 0.001). No obvious loss of correction occurred, according to the lack of significant differences in the sagittal balance parameters between post-operatively and the final follow-up in all patients (TK: 27.76 ± 6.50°vs. 28.45 ± 6.63°, TLK: 13.86 ± 6.65°vs. 14.42 ± 6.7°, LL: -20.58 ± 9.71°vs. -20.73 ± 10.27°, and SVA: 5.12 ± 2.42 cmvs. 5.03 ± 2.29 cm, allP > 0.05, respectively).Conclusions: The modified posterior wedge osteotomy is an accepted surgical procedure for treating thoracolumbar kyphosis with ALs in AS and results in satisfactory local kyphosis correction, solid fusion, and good clinical outcomes.