Analysis of the causes of proximal junctional kyphosis following spinal instrumented fixation in patients with bone mineral density deficiency

Objective To explore causes of proximal junctional kyphosis (PJK) following instrumented fixation of lumbar spine in patients with degenerative scoliosis due to mineral bone density deficiency. Material and methods A retrospective analysis was conducted on 308 patients with degenerative lumbar scoliosis surgically treated with decompression of neural elements, deformity correction and stabilization of FSU using rigid transpedicular fixation systems. The patients were followed up for 2 years of surgery and were subdivided into 2 groups, those who developed PJK (n=132) and those who did not (n=176). Variable risk factors for PJK described in the literature were analyzed. They could be categorized into patient related factors (age, gender, osteoporosis, body mass index (BMI), smoking habits), surgical factors (type of osteotomy performed, a magnitude of lordosis correction, long fixation to the sacrum) and radiographic parameters (PI, TK, LL, SVA, PI-LL, PJA). Results Osteoporosis (53–33 %, p = 0.032), BMI >25 (51–37 %, p = 0.042) and greater than 30° lordosis correction (51–34 %, p = 0.038) were found to be statistically significant for PJK. Lumbar lordosis restored in more than 30% increases the risk of PJK by 2.3 times. The proximal junctional angle (PJA) ≥ 11° is a statistically significant risk factor for PJK and associated with increased occurrence of PJK by 2.9 times (p = 0.022). An increase in PJA by 1° increases the risk of PJK by 11.8 % (making the risk 1.118 times higher). Osteoporosis coupled with PJA entails a statistically significant impact on PJK (p = 0.002) with PJA increased by 1° in osteoporosis scenario increasing the risk of PKJ by 66.4 % (making the risk 1.664 times higher). Conclusion Osteoporosis, body mass index > 25 and a surgical correction of lumbar lordosis by more than 30° have been shown to be significantly associated with PJK in patients with lumbar curves. PJA of 11° is the significant risk factor for PJK making the occurrence of PJK 2.9 times higher (p = 0.022). Osteoporosis coupled with PJA entails a statistically significant impact on PJK (p = 0.002) with PJA increased by 1° in osteoporosis cases increasing the risk of PKJ by 66.4 %.