Spine CTs Research Articles

Computed tomography–based determination of a safe trajectory for placement of transarticular facet screws in the subaxial cervical spine

Placement of transarticular facet screws is one option for stabilization of the subaxial cervical spine. Small clinical series and biomechanical data support their role as a substitute for other posterior stabilization techniques; however, the application of transarticular facet screws in the subaxial cervical spine has not been widely adopted, possibly because of surgeon unfamiliarity with the trajectory. In this study, the authors' objective is to define insertion points and angles of safe trajectory for transarticular facet screw placement in the subaxial cervical spine. Thirty fine-cut CT scans of cervical spines were reconstructed in the multiplanar mode and evaluated for safe transarticular screw placement in the subaxial cervical spine (C2-3, C3-4, C4-5, C5-6, C6-7). As in placement of lateral mass screws, the vertebral artery and exiting nerve root were bypassed posterolaterally. The entry point was set 1 mm medial and 1 mm caudal to the center of the lateral mass. From this entry point, the sagittal angulation was set to traverse the facet joint plane approximately perpendicularly. For the axial angulation, the exit point was set posterolaterally to the transverse process. After ideal insertion angles and screw lengths were identified, the trajectory was simulated on CT scans of 20 different cervical spines to confirm safe screw placement. The mean optimal mediolateral insertion angles (± SD) were as follows: 23° ± 5° at C2-3; 24° ± 4° at C3-4; 25° ± 5° at C4-5; 25° ± 4° at C5-6; and 33° ± 6° at C6-7. The mean sagittal insertion angles measured to the sagittal projection of the facet joint space were as follows: 77° ± 10° at C2-3; 77° ± 10° at C3-4; 80° ± 11° at C4-5; 81°± 8° at C5-6; and 100° ± 11° at C6-7. The mean trajectory lengths were 15 ± 2 mm at C2-3; 14 ± 1 mm at C3-4; 15 ± 1 mm at C4-5; 16 ± 2 mm at C5-6; and 23 ± 4 mm at C6-7. Simulation of these insertion angles on 20 different cervical spine CTs yielded a safe trajectory in 85%-95% of spines for C2-3, C3-4, C4-5, C5-6, and C6-7. The calculated optimal insertion angles and lengths for each level may guide the safe placement of subaxial cervical transfacet screws.

Characterizing and Predicting Pathologic Spine Fractures in Myeloma Patients With FDG PET/CT and MR Imaging

Objectives: To determine if FDG PET/CT scans can be used to discriminate between old and new pathologic spine fractures in myeloma patients and also to determine if there is any combination of PET/CT and MR imaging findings that may indicate an impending spine fracture. Materials and methods: Retrospective review, after IRB approval, by two musculoskeletal radiologists and one nuclear medicine physician was done. PET/CT database was searched to identify studies performed in myeloma patients, using the search terms myeloma, plasmacytoma, or plasma cell. Records, for this group of 176 patients, were searched for concurrent spine MR imaging and report of fracture. The SUVmax was recorded for each vertebral level from C2 through L5. All other imaging studies carried out in each patient (spine radiographs, spine CTs, and spine MRIs) and clinical records also were reviewed. Spine fractures were identified using the Genant system. MR imaging findings noted included signal intensity, pattern of involvement, as well as the size and location, within the vertebral body, of individual focal lesions. Results: 31 of the 176 patients had concurrent spine MR imaging and report of fracture. Five of these 31 patients were excluded because they had no documentation of the age of fracture prior to PET/CT imaging. The 26 remaining patients (598 vertebral levels) included 17 men and 9 women. There were a total of 59 PET/CTs, 104 spine X-ray studies, 25 spine CT exams, and 71 spine MRI exams. There were a total of 134 vertebral body fractures: 27 were determined to be acute/subacute and pathologic due to active myeloma, 1 was determined to be new but owing to simple osteoporosis, and 106 were determined to be old. The mean SUVmax in the acute/subacute pathologic fractures was 2.9 with a range from 1.1 to 4.3 (standard deviation 0.98). The old fractures had a mean SUVmax of 1.6 with a range from 0.6 to 3.1 (standard deviation 0.55). This was a statistically significant difference with p value <.0001. The 464 vertebral bodies without fracture had a mean SUVmax of 1.8. SUVmax ≥2.5 was seen at 49 vertebral levels, including 27 with a fracture and 22 without a fracture. SUVmax ≥3.5 was found at 9 vertebral levels, including 6 with a fracture and 3 without a fracture. The combination of diffuse or multifocal MR patterns and SUV > 3.5 was seen at 7 levels, all but one with new pathologic fractures. Conclusion: PET/CT SUV > 3.2 alone can be used in myeloma patients to discriminate between old and new pathologic fractures, just as it has been reported in other types of cancer patients. The combination of PET/CT SUV > 3.5 and MR findings of diffuse or multifocal vertebral body involvement seems to indicate an impending fracture.

Nerve impulse propagation along central and peripheral fast conducting motor and sensory pathways in man

Forty-four limbs from 11 healthy volunteers were examined. Spinal and scalp somatosensory evoked potentials to median and peroneal nerve stimulation were recorded and the peripheral (wrist-Erb, Erb-cervical, knee-thoracic spine) and central (cervical-scalp, thoracic-cervical spine, spine-scalp) conduction times and velocities (CTs, CVs) were calculated. Sensory and mixed trunks of median and peroneal nerves were also stimulated and their motor and sensory CVs in mid-distal districts were measured. Motor responses to scalp (motor areas for hand and leg muscles) and spinal cord stimulation (cervical and lower thoracic levels) were carried out through skin rectangular plate electrodes delivering high voltage (880-1870 V) brief anodal pulses. The intracranial (scalp-cervical) and intraspinal (cervical-thoracic spine) CTs and CVs of motor pathways were measured. The elbow-cervical and knee-thoracic spines CTs of motor fibres were also calculated through the F wave method, which gave values almost superimposable on those obtained through direct spine stimulation. Nerve propagation was faster in sensory than in motor fibres in peripheral nerve mid-distal districts, while this difference was reduced or reversed in more proximal segments, including nerve roots. The scalp-cervical CT was slightly shorter in motor than in sensory fibres after subtraction of synaptic delays (6.12 vs. 6.18 msec). The scalp-lower thoracic spine, as well as the intraspinal, CVs were 7-12% faster in sensory than in motor pathways (45.3 vs. 38.7 m/sec for the former; 62.65 vs. 55.4 m/sec for the latter). The reported method allows the evaluation of fast conducting motor and sensory pathways along 'central' and 'peripheral' nerve structures of the entire body. Preliminary findings on scalp stimulation of brain motor areas with low voltage pulses are also included.