Risk Factors of Proximal Junctional Kyphosis after Multilevel Fusion Surgery: More Than 2 Years Follow-Up Data

Abstract

Objective: Proximal junctional kyphosis (PJK) is radiologic finding, and is defined as kyphosis of >10° at the proximal end of a construct. The aim of this study is to identify factors associated with PJK after segmental spinal instrumented fusion in adults with spinal deformity with a minimum follow-up of 2 years.

Methods: A total of 49 cases of adult spinal deformity treated by segmental spinal instrumented fusion at two university hospitals from 2004 to 2011 were enrolled in this study. All enrolled cases included at least 4 or more levels from L5 or the sacral level. The patients were divided into two groups based on the presence of PJK during follow-up, and these two groups were compared to identify factors related to PJK.

Results: PJK was observed in 16 of the 49 cases. Age, sex and mean follow-up duration were not statistically different between two groups. However, mean bone marrow density (BMD) and mean back muscle volume at the T10 to L2 level was significantly lower in the PJK group. Preoperatively, the distance between the C7 plumb line and uppermost instrumented vertebra (UIV) were no different in the two groups, but at final follow-up a significant intergroup difference was observed. Interestingly, spinal instrumentation factors, such as, receipt of a revision operation, the use of a cross-link, and screw fracture were no different in the two groups at final follow-up.

Conclusion: Preoperative BMD, sagittal imbalance at UIV, and thoracolumbar muscle volume were found to be strongly associated with the presence of PJK.

Keywords: Adult spinal deformity; Back muscle; Complication; Osteoporosis; Proximal junctional kyphosis; Sarcopenia.

Fig. 1

C7PL was defined distance between C7 plumb line which is the vertical line originating the center of the C7 vertebral body and the posterior superior corner of S1, and its length was measured preoperatively and at ÿnal follow-up. The distance between the center of the UIV and C7PL was also measured early postoperatively and at final follow-up. C7PL: C7 plumb line, UIV: uppermost instrumented vertebra.

Fig. 2

Thoracolumbar back muscle volumes were measured from T10 to L2 in T2 weighted magnetic resonance images.

Fig. 3

Di°erences in muscle volume (mm²) of two study groups. PJK: proximal junctional kyphosis.

Fig. 4

Scatter plot showed correlation between preoperative C7PL (mm) and mean muscle volume (mm²).