| Summary: | Abstract Background Proximal junctional kyphosis (PJK) following adult spinal deformity (ASD) surgery in elderly patients is markedly influenced by osteoporosis causing additional vertebral fracture and loosening of pedicle screws (PS). This study aimed to investigate the association between mean bone density represented in Hounsfield units (HU) on spinal computed tomography (CT) and revision surgery for PJK or postoperative additional vertebral fracture following ASD surgery in elderly patients. Methods The subjects were 54 ASD patients aged 65 years or older who were treated with correction and fusion surgery of four or more levels and could be followed for 2 years or longer. Bone density was measured before surgery using lumbar dual-energy X-ray absorptiometry (DXA) and spinal CT in all patients. The patients were divided into group A (n = 14) in which revision surgery was required for PJK or additional vertebral fracture and group B (n = 40) in which revision surgery was not required. We retrospectively investigated incidences of PJK, additional vertebral fracture, and PS loosening, perioperative parameters, radiographic parameters before and after surgery, and osteoporosis treatment administration rate. Results No significant difference was noted in young adult mean (YAM) on DXA between groups A and B, respectively (P = 0.62), but the mean bone densities represented in HU of the T8 (P = 0.002) and T9 (P = 0.01) vertebral bodies on spinal CT were significantly lower in group A, whereas those of the L4 (P = 0.002) and L5 (P = 0.01) vertebral bodies were significantly higher in group A. The incidence of PJK was not significantly different (P = 0.07), but the incidence of additional vertebral fracture was significantly higher in group A (P < 0.001). The incidences of uppermost PS loosening within 3 months after surgery were 71% and 40% in groups A and B, respectively (P = 0.04). Conclusions In elderly patients who required revision surgery, the mean bone densities of vertebral bodies at T8 and T9 were significantly lower. The mean bone density represented in HU on spinal CT may be useful for risk assessment of and countermeasures against revision surgery after ASD surgery in elderly patients.
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