Incidence and risk factors for proximal junctional kyphosis: a meta-analysis

To analyse the incidence and risk factors associated with proximal junctional kyphosis (PJK) following spinal fusion, we collect relative statistics from the articles on PJK and perform a meta-analysis. An extensive search of literature was performed in PubMed, Embase, and The Cochrane Library (up to April 2015). The following risk factors were extracted: age at surgery, gender, combined anterior-posterior surgery, use of pedicle screw at top of construct, hybrid instrumentation, thoracoplasty, fusion to sacrum (S1), preoperative thoracic kyphosis angle (T5-T12) > 40A degrees, bone mineral density (BMD) and preoperative to postoperative sagittal vertical axis (SVA difference) > 5 cm. Data analysis was conducted with RevMan 5.3 and STATA 12.0. A total of 14 unique studies including 2215 patients were included in the final analyses. The pooled analysis showed that there were significant difference in age at surgery > 55 years old (OR 2.19, 95 % CI 1.36-3.53, p = 0.001), fusion to S1 (OR 2.12, 95 % CI 1.57-2.87, p < 0.001), T5-T12 > 40A degrees (OR 2.68, 95 % CI 1.73-4.13, p < 0.001), low BMD (OR 2.37, 95 % CI 1.45-3.87, p < 0.001) and SVA difference > 5 cm (OR 2.53, 95 % CI 1.24-5.18, p = 0.01). However, there was no significant difference in gender (OR 0.98, 95 % CI 0.74-1.30, p = 0.87), combined anterior-posterior surgery (OR 1.55, 95 % CI 0.98-2.46, p = 0.06), use of pedicle screw at top of construct (OR 1.55, 95 % CI 0.67-3.59, p = 0.30), hybrid instrumentation (OR 1.31, 95 % CI 0.92-1.87, p = 0.13) and thoracoplasty (OR 1.55, 95 % CI 0.89-2.72, p = 0.13). The incidence of PJK following spinal fusion was 30 % (ranged from 17 to 62 %) based on the 14 studies. The results of our meta-analysis suggest that age at surgery > 55 years, fusion to S1, T5-T12 > 40A degrees, low BMD and SVA difference > 5 cm are risk factors for PJK. However, gender, combined anterior-posterior surgery, use of pedicle screw at top of construct, hybrid instrumentation and thoracoplasty are not associated with PJK.