Precision and Accuracy of Measurements on CT Scout View

Standing versus supine pelvic incidence in adult spinal deformity patients

PURPOSE

Pelvic incidence (PI) is commonly used to determine sagittal alignment. Historically, PI was believed to be a fixed anatomic parameter. However, recent studies have suggested that there is positionally-dependent motion that occurs through the sacroiliac joint (SIJ) resulting in changes in PI.

METHODS

We reviewed 100 consecutive adult spinal deformity (ASD) patients seen at our academic tertiary referral center. Two reviewers measured pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL) on standing radiographs and scout computed tomography scans (CT). Unilateral, bilateral, or absent SIJ vacuum sign (VS) was determined using CTs.

RESULTS

Eighty-six patients (42 M:44 F) were included with an average age of 64.1 years and BMI of 28.8 kg/m2. Standing PI was low (< 50°) in 35 patients (40.7%), average (50°-60°) in 22 (25.6%), and high (> 60°) in 29 (33.7%). Average and high PI patients had significant PI changes of 3.0° (p = 0.037) and 4.6° (p = 0.005), respectively. Bilateral SIJ VS was seen in 68 patients, unilateral VS in 9, and VS was absent in 9. The average change in PI between standing and supine was 2.1° in bilateral SIJ VS patients (p = 0.045), 2.2° in unilateral SIJ VS (p = 0.23), and - 0.1° in patients without SIJ VS (p = 0.93). The average absolute difference in PI between supine and standing was 5.5° ±5.5° (p < 0.001).

CONCLUSION

There is a change in PI from supine to standing. In patients with high PI and bilateral VS on CT, the change from supine to standing is significant, perhaps representing instability of the SIJ.

Correction of the acetabular index is more crucial than the type of acetabuloplasty in developmental dysplasia

BACKGROUND

Acetabular remodeling may not be predictable after open reduction in developmental dysplasia of the hip (DDH) in older children. Several acetabuloplasties have been developed, and all are aimed at correcting the dysplastic acetabulum. The goal of this study is to evaluate if the type of pelvic acetabuloplasty and the corrected (postoperative) acetabular index (AI) affect early follow-up femoral head coverage.

METHODS

A retrospective review of single-surgeon consecutive acetabuloplasties (Dega or Pemberton) from December 2012 to December 2015 was conducted. The inclusion criteria were a diagnosis of DDH, undergoing simultaneous primary open reduction, and follow-up of at least 18 months. Univariable analysis was based on the type of acetabuloplasty. The correlation between AI and final center edge angle (CEA) was tested. Multiple regression was performed.

RESULTS

Of the total 58 hips in 39 patients included, 41 underwent Dega acetabuloplasty, and 17 had Pemberton acetabuloplasty. The median follow-up was 40.50 months (interquartile range 27.25-57). Pemberton acetabuloplasty produced a lower corrected AI, but the difference was not significant in follow-up measurements. Corrected AI was significantly correlated with final CEA (R = - 0.31, P = 0.018). In the multiple regression, only corrected AI was independently associated with final CEA (B = - 0.29, SE = 0.15, P = 0.06), whereas the type of acetabuloplasty, age, and preoperative severity of the dislocation were not.

CONCLUSION

The correction obtained during acetabuloplasty affects early follow-up femoral head coverage. Ensuring proper sizing and placement of the grafted bone is probably more important than the type of acetabuloplasty chosen.

LEVEL OF EVIDENCE

Level III.

Scout-guided needle placement-a technical approach for dose reduction in CT-guided periradicular infiltration

PURPOSE

To develop and evaluate a technical approach for CT-guided periradicular infiltration using quantitative needle access and guidance parameters extracted from CT scout images.

METHODS

Five 3D-printed phantoms of the abdomen mimicking different patients were used to develop a technical approach for scout-guided periradicular infiltration. The needle access point, puncture depth, and needle angulation were calculated using measurements extracted from anterior-posterior and lateral CT scout images. Fifty needle placements were performed with the technique thus developed. Dose exposure and number of image acquisitions were compared with ten procedures performed using a conventional free-hand technique. Data were analyzed with the Mann-Whitney U test.

RESULTS

Parameters derived solely from scout images provided adequate guidance for successful and reliable needle placement. Needle guidance was performed with the same equipment as the standard periradicular infiltration. Two scout images and 3.5 ± 2.3 (mean ± SD) single-shot images for needle positioning were acquired. Mean DLP ± SD was 3.8 ± 2.5 mGy cm. The number of single-shot acquisitions was reduced by 68% and the overall dose was reduced by 84% in comparison with the conventional free-hand technique (p < 0.0001).

CONCLUSION

Scout-guided needle placement for periradicular infiltration is feasible and reduces radiation exposure significantly.