J Korean Neurosurg Soc.  2023 Jan;66(1):44-52. 10.3340/jkns.2022.0174.

Clinical Effect of Transverse Process Hook with K-Means Clustering-Based Stratification of Computed Tomography Hounsfield Unit at Upper Instrumented Vertebra Level in Adult Spinal Deformity Patients

• Cho J
• Ryu S
• Jang HJ
• Park JY
• Ha Y
• Kuh SU
• Chin DK
• Kim KS
• Cho YE
• Kim KH

• KMID: 2537847
• DOI: http://doi.org/10.3340/jkns.2022.0174

Abstract

Objective
: This study aimed to investigate the efficacy of transverse process (TP) hook system at the upper instrumented vertebra (UIV) for preventing screw pullout in adult spinal deformity surgery using the pedicle Hounsfield unit (HU) stratification based on K-means clustering.
Methods
: We retrospectively reviewed 74 patients who underwent deformity correction surgery between 2011 and 2020 and were followed up for >12 months. Pre- and post-operative data were used to determine the incidence of screw pullout, UIV TP hook implementation, vertebral body HU, pedicle HU, and patient outcomes. Data was then statistically analyzed for assessment of efficacy and risk prediction using stratified HU at UIV level alongside the effect of the TP hook system.
Results
: The screw pullout rate was 36.4% (27/74). Perioperative radiographic parameters were not significantly different between the pullout and non-pullout groups. The vertebral body HU and pedicle HU were significantly lower in the pullout group. K-means clustering stratified the vertebral body HU ≥205.3, <137.2, and pedicle HU ≥243.43, <156.03. The pullout rate significantly decreases in patients receiving the hook system when the pedicle HU was from ≥156.03 to < 243.43 (p<0.05), but the difference was not statistically significant in the vertebra HU stratified groups and when pedicle HU was ≥243.43 or <156.03. The postoperative clinical outcomes improved significantly with the implementation of the hook system.
Conclusion
: The UIV hook provides better clinical outcomes and can be considered a preventative strategy for screw-pullout in the certain pedicle HU range.

Keyword

Spinal deformity surgery; Screw pullout; Transverse process hook; K-means clustering; Hounsfield unit

Figure

• 

  Fig. 1. Estimation of bone density using Hounsfield unit (HU) values with preoperative computed tomography scan. A : The vertebral body HU value was measured on the axial plane of the mid-vertebral body. B : The elliptical region of interest (ROI) was drawn to include maximum possible amount of cancellous bone, while avoiding cortical edges and heterogeneous regions (white circle). C : The pedicle HU value was measured on the axial plane of the mid-pedicle where screw trajectory is commonly directed (white line). D : The elliptical ROI for the pedicle resembled that of vertebral body HU, except for the cortical bone (white circle). The diameter of the pedicle was measured at the narrowest segment of the pedicle (white line).

• 

  Fig. 2. The Kaplan-Meier curves for screw pullout-free survival : (A) 243.43 >UIV pedicle HU ≥156.03, (B) UIV pedicle HU <156.03, (C) 205.3> UIV vertebral body HU ≥137.2, and (D) UIV vertebral body HU <137.2 whether transverse process hook application or not. *p<0.05. UIV : upper instrumented vertebra, HU : Hounsfield unit.

Reference

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