Segmental Surface Referencing during Intraoperative Three-dimensional Image-Guided Spine Navigation: An Early Validation with Comparison to Automated Referencing

Ultrasound propagation characteristics within the bone tissue of miniature ultrasound probes: implications for the spinal navigation of pedicle screw placement

Background

The accuracy of pedicle screw fixation is crucial for patient safety. Traditional navigation methods based on computed tomography (CT) imaging have several limitations. Therefore, this study aimed to investigate the ultrasonic propagation characteristics of bone tissue and their relationship with CT imaging results, as well as the potential application of ultrasound navigation in pedicle screw fixation.

Methods

The study used three bovine spine specimens (BSSs) and five human vertebral allograft bones (HABs) to progressively decrease the thickness of the cancellous bone layer, simulating the process of pedicle screw perforation. Five unfocused miniature ultrasound probes with frequencies of 2.2, 2.5, 3, 12, and 30 MHz were employed for investigating the ultrasonic propagation characteristics of cancellous and cortical bone through ultrasound transmission and backscatter experiments. The CT features of the bone tissue was obtained with the Skyscan 1174 micro-CT scanner (Bruker, Billerica, MA, USA).

Results

The experimental results demonstrated that low-frequency (2-3 MHz) ultrasound effectively penetrated the cancellous bone layer up to a depth of approximately 5 mm, with an attenuation coefficient below 10 dB/cm. Conversely, high-frequency (12 MHz) ultrasound exhibited significant signal attenuation in cancellous bone, reaching up to 55.8 dB/cm. The amplitude of the backscattered signal at the cancellous bone interface exhibited a negative correlation with the bone sample thickness (average r=-0.84), meaning that as the thickness of the cancellous bone layer on the cortical bone decreases, the backscattered signal amplitude gradually increases (P<0.05). Upon reaching the cortical bone interface, there was a rapid surge in echo signal amplitude, up to 8 times higher. Meanwhile, the statistical results indicated a significant correlation between the amplitude of the echo signal and the micro-CT scanning results of bone trabecular structure.

Conclusions

Theoretically, using multiple ultrasonic probes (≥3) and regions of interest (ROIs) (≥5) has the potential to provide surgeons with early warning signals for pedicle perforation based on three or more successive increases in echo signal amplitude or a sudden substantial increase. The statistical results indicate a significant correlation between the amplitude of the echo signal and the micro-CT scanning results of bone trabeculae, suggesting the potential use of ultrasound as opposed to CT for real-time intraoperative bone navigation.

Minimally Invasive Cochlear Implantation Assisted by Intraoperative CT Scan Combined to Neuronavigation

OBJECTIVE

The objective of this work was to study the feasibility of minimally invasive cochlear implantation under intraoperative computerized tomography-scan coupled to navigation.

MATERIALS AND METHODS

Five human resin temporal bones (two adults and three children) were used. Initially, a temporal bone imaging was obtained by the intraoperative CT-scan coupled to the navigation (O-ARM). The navigation-assisted drilling began at the mastoid surface creating a conical tunnel (4-2 mm in diameter) through the facial recess and down to the round window. A cochleostomy was performed based on the navigation. A sham electrode array was inserted in the drilled tunnel and into the cochlea.Postoperative CT-scan and dissection were performed to evaluate the trajectory, and possible injury to the external auditory canal, ossicles, or facial nerve.

RESULTS

The mean duration of the procedure was 24.4 ± 3.79 minutes (range, 15-35). Cochleostomy was possible in all cases without injury to other structures. The sham array was inside the cochlea in all cases. The mean distance between the drilled canal and the mastoid portion of the facial nerve was 1.2 ± 0.07 mm (range, 1.08-1.38). The mean tracking error was 0.6 ± 0.26 mm (range, 0.20-0.72) at the entry point, 0.6 ± 0.33 mm (range, 0.2-1.02) at the facial nerve and 0.4 ± 0.07 mm (range, 0.36-0.51) at the cochleostomy.

CONCLUSION

Cochlear implantation through a minimally invasive approach assisted by intraoperative imaging combined with navigation was feasible in operating room environment and experimental conditions.

Nutrient foramen location on the laminae provides a landmark for pedicle screw entry: a cadaveric study

Background

Nutrient foramina are often encountered around the entry point of pedicle screws. Further, while probing the pedicle for pedicle screw insertion around the nutrient foramen, bleeding from the probe insertion hole is often observed. The purpose of this study was to investigate the frequency of occurrence of nutrient foramina, the association between the nutrient foramen and pedicle, and the safety and accuracy of cervical and thoracic pedicle screw placement using the nutrient foramen as the entry point.

Methods

We identified the location of the nutrient foramina for the dorsal branches of the segmental artery and their anatomical association to the pedicles and bony landmarks in the vertebrae for C3–T12 in seven cadavers. We also determined the frequency with which the nutrient foramina were present in 119 cadaveric vertebrae. We identified the pedicle location, base of the superior articular facet, and lateral border of laminae with respect to the nutrient foramen.

Results

The overall presence of the nutrient foramina was 63% (150/238) in the specimens, with 60% (42/70) and 64% (108/168) identifiable in the cervical and thoracic vertebrae, respectively. In the cervical vertebrae, the nutrient foramen was located on the outer wall of the pedicle and was positioned between the cephalad and caudal walls. In the thoracic spine, 98% (106/108) nutrient foramina were located inside the pedicle walls.

Conclusions

Our study findings confirm that the location of the nutrient foramen can be used for identifying the entry point for pedicle screws. In the cervical vertebrae, the nutrient foramina are located lateral to pedicle but within the cranial and caudal margins. In the thoracic vertebrae, the nutrient foramina are located in the medial and caudal regions of the pedicle. Thus, to decrease the risk of overshoot, the entry point for thoracic pedicle screws should be positioned a few millimeters cephalad and lateral to the nutrient foramen.

Quantitative assessment of vertebral artery anatomy in relation to cervical pedicles: surgical considerations based on regional differences

OBJECTIVE

To quantify the anatomic relationship between the Cervical pedicle screw (CPS), vertebral artery (VA), and related anatomic structures in the Saudi population.

METHODS

This retrospective single center study included 50 consecutive patients (35 males) with normal neck findings on computed tomography angiography performed for trauma or vascular evaluation between 2012 and 2014. Radiologic parameters were assessed and correlated with age, weight, height, and body mass index (BMI).

RESULTS

Mean age, weight, height, and BMI were 45.74+/-18.93 years, 79.72+/-21.80 kg, 164.74+/-11.53 cm, and 29.38+/-6.13 kg/m2, respectively. Mean cervical pedicle diameter (PD) increased from the cranial to caudal vertebrae (p=0.0001). Mean free zone (FZ) value, defined as the distance between the lateral CP border and medial VA border, was 1 mm (range 0.95-1.16 mm). The VA entry into the transverse foramina was at C6 level on both the right 92% and left side in most patients 94%. However, the right and left side level of VA entry differed in 14% of individuals.

CONCLUSION

The PD and FZ are smaller in Saudi Arabians than in western populations. Assessment of VA entry at each level should be performed on an individual basis as the level of VA entry can differ in the same patient. Anatomic variations between different geographic areas should be studied to provide better surgical guidance.

CORRECTION OF SEVERE STIFF SCOLIOSIS THROUGH EXTRAPLEURAL INTERBODY RELEASE AND OSTEOTOMY (LIEPO)

ABSTRACT Objective: To report a new technique for extrapleural interbody release with transcorporal osteotomy of the inferior vertebral plateau (LIEPO) and to evaluate the correction potential of this technique and its complications. Method: We included patients with scoliosis with Cobb angle greater than 90° and flexibility less than 25% submitted to surgical treatment between 2012 and 2016 by the technique LIEPO at the National Institute of Traumatology and Orthopedics (INTO). Sagittal and coronal alignment, and the translation of the apical vertebra were measured and the degree of correction of the deformity was calculated through the pre and postoperative radiographs, and the complications were described. Results: Patients had an average bleed of 1,525 ml, 8.8 hours of surgical time, 123° of scoliosis in the preoperative period, and a mean correction of 66%. There was no case of permanent neurological damage and no surgical revision. Conclusion: The LIEPO technique proved to be effective and safe in the treatment of severe stiff scoliosis, reaching a correction potential close to the PEISR (Posterior extrapleural intervertebral space release) technique and superior to that of the pVCR (posterior Vertebral Column Resection) with no presence of infection and permanent neurological deficit. New studies are needed to validate this promising technique.