Preoperative Hounsfield Units at the Planned Upper Instrumented Vertebrae May Predict Proximal Junctional Kyphosis in Adult Spinal Deformity

Abstract

Study Design. Retrospective cohort study. Objective. To investigate the association between Hounsfield units (HU) measured at the planned upper instrumented vertebra (UIV) and UIV+1 and proximal junctional kyphosis (PJK) in patients with adult spinal deformity (ASD). Summary of Background Data. PJK is a common complication following surgery for ASD and poor bone quality is noted to be one of the risk factors. HUs from standard computed tomography (CT) scans can be used for evaluating regional bone quality. Methods. Sixty-three patients were included from a single institution. The demographic characteristics and radiographic parameters were recorded. Local vertebral HUs at the planned UIV and UIV+ 1 were measured using preoperative CT scans. The patients were divided into three groups: no PJK, non-bony PJK, and bony PJK. The risk factors between the three groups and the correlation between the mean HU and increase in the PJK angle were analyzed. Results. The incidence of PJK was 36.5%. The mean HU was significantly lower in the bony PJK group (HU: 109.0) than in the no PJK group (HU: 168.7, P = 0.038), and the mean HU in the non-bony PJK group (HU: 141.7) was not different compared to the other two groups. There was a significant negative correlation between the mean HU values and the increase in the PJK angles (r = −0.475, P < 0.01). The cutoff value for the mean HU used to predict bony PJK was 120 and a HU value less than 120 was a significant risk factor for bony PJK (OR: 5.74, 95% CI [1.01–32.54], P = 0.04). Conclusions. We noted a significant inverse relationship between the mean HUs at the UIV and UIV+ 1 and increase in the PJK angles postoperatively. In ASD patients, the HUs may be used preoperatively to identify patients with a higher risk of bony PJK. Level of Evidence: 3

Effects of Perioperative Teriparatide Treatment on the Hounsfield Unit Values at the Upper Instrumented Vertebra in Adult Spinal Deformity Surgery

“…The L1 vertebral body is commonly chosen for DXA, and it has an indicated threshold value of 110 for detecting osteoporosis and 135 for detecting osteopenia 7 . In the case of ASD patients, several studies have indicated that PJK is associated with lower HU values at the UIV or UIV + 1, 8–10 and HU <120 was a significant risk factor for PJF 8,10 . On the contrary, it is not clear how much increase in HU values is anticipated after TPTD treatment in cases of ASD surgery.…”

“…7 In the case of ASD patients, several studies have indicated that PJK is associated with lower HU values at the UIV or UIV + 1, 8-10 and HU <120 was a significant risk factor for PJF. 8,10 On the contrary, it is not clear how much increase in HU values is anticipated after TPTD treatment in cases of ASD surgery. Mikula et al 14 showed that TPTD treatment increased the average HU and BMD of the lumbar spine (L1 to L4) by 22% and 9%, respectively.…”

“…6,7 Several studies have demonstrated that patients with PJK have low HU values at UIV. [8][9][10] However, the effect of TPTD treatment on HU values at the UIV after ASD surgery remains unclear. Therefore, we aimed to investigate the effect of pre and post-operative TPTD treatment on HU values at the UIV 1 year after ASD surgery.…”

What’s New in Spine Surgery

“…Post hoc analysis demonstrated significantly lower mean HU in the osseous PJK group than in the non-osseous PJK group. Patients with ≤120 HU had a risk of osseous PJK that was 5.74 times higher compared with those with >120 HU 10 .…”

Single-position Minimally Invasive Surgery for Correction of Adult Spinal Deformity

“…Based on a study from our institution, a UIV with a HU of 120 or less is at high risk for junctional failure. 18 Therefore, we try to select a UIV with an HU of >120, extending into the upper thoracic spine if necessary. During surgery, meticulous end plate preparation is a must, and safe decancellation of any visual posterior elements should also be done.…”