Right Thoracic Adolescent Idiopathic Scoliosis
The patient is a 14-year-old male who presents with a 52-degree thoracic scoliosis at T4-T12. His Risser Sign is Grade 3.
- right thoracic prominence
- asymptomatic heart murmur
- neurologically normal
Figure 1A is an anteroposterior (AP) x-ray demonstrating a right thoracic curve. Figure 1B is the patient's lateral x-ray and Figures 2C and 2D, respectively, are right bending and left bending x-rays.
Primary, right thoracic idiopathic scoliosis
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O-arm™ and StealthStation® Navigation (Medtronic, Inc.) are utilized to perform posterior thoracic fusion from T4 to L2 using convex sagittally fixed apical screws for direct vertebral rotation.
Prior to surgery, a traction film is obtained and all films are available on PACS in the operating room (Figures 1A-1D). The leads for pre-op Holter monitoring, which was normal, are apparent on the patient's films.
Using sagittally fixed apical convex pedicle screws:
- allows equivalent three-dimensional (3D) correction of the spinal deformity
- allows two direct vertebral de-rotations (DVR)
- apical convex pedicles are larger and more reliable than concave pedicles in that the spinal cord hugs the concave pedicles and the aorta moves into the concavity, making a missed screw in the concavity more problematic
View O-arm setup in the operating room
Intra-operative video features:
- attaching the probe and reference arc
- 3D reconstruction; real time views, a "bird's eye view"
- rotational correction
- four hours skin-to-skin
All screws verified intra-osseously by O-arm and accuracy of O-arm verified by CT on post-op day three (Figures 2A, 2B).
Figure 2A. AP x-ray, 3 days post-op
Figure 2B. Lateral x-ray, 3 days post-op
View Dr. Bennett's complete video presentation.
At the patient's one-year post-operative evaluation, we found spinal correction is well-maintained and global spinal balance is achieved.
Author's Case Discussion
With more than 10 years of experiencing using StealthStation Navigation and 2 years experience with O-arm, we have revised 2 screws: one, adjacent to the aorta but no impingement; at one week post-op; and one, breaching the medial pedicle wall. And while this was not a significant breach and SSEP and MEP monitoring and pedicle stimulation were all normal, we were able to revise immediately following the verification scan with the O-arm in the OR, avoiding a return trip to the operating room.
Peer Case Discussion
This case demonstrates two important deformity concepts. First the use of convex screws is safer in terms of canal and vascular compromise. As mentioned, larger screws were used for the convex side where near segmental fixation was achieved.
Second, intra-operative verification of pedicle screws in the thoracic spine is a luxury. Some papers have cited thoracic pedicle screw malposition rates of up to 55%.1 His paper presents a nice up-to-date overview of the technical and procedural aspects of image-guided surgery. As expected, image-guided and image-verified constructs have been shown to reduce re-operation rates. Furthermore, image guidance greatly reduces if not eliminates radiation exposure to the OR team as a number of recent studies have demonstrated.2, 3
CT source image guidance is somewhat more accurate than using a fluoroscopic source. However, that accuracy comes at a price. Schaeren4 showed that CT guidance markedly increases exposure rates to the patient compared to fluoroscopy. These differences persisted even when exposure reduction techniques were used with fluoroscopy. One case series5 reported up to 15x higher radiation exposure to patients using CT guided screw placement than spot fluoroscopy shots.
If you use standard fluoroscopy you can take the following measures to reduce your exposure:
- use appropriate shielding with leaded gowns and thyroid shields
- wear radiation attenuating sterile gloves (approximately $40 USD/pair)
- use leaded eye-ware
- cannulate several pedicles at once using multiple probes
- collimate the beam
- use low-dose settings in thin patients
- use remote foot pedal control away from the field
- have the surgeon control the C-arm
1. Tjardes T, Shafizadeh S, Rixen D, Paffrath T, Bouillon B, Steinhausen ES, Baethis H. Image-guided spine surgery: state of the art and future directions. Eur Spine J. 2010 Jan;19(1):25-45.
2. Wood MJ, Mannion RJ. Improving accuracy and reducing radiation exposure in minimally invasive lumbar interbody fusion. J Neurosurg Spine. 2010 May;12(5):533-9.
3. Zausinger S, Scheder B, Uhl E, Heigl T, Morhard D, Tonn JC. Intraoperative computed tomography with integrated navigation system in spinal stabilizations. Spine. 2009 Dec 15;34(26):2919-26.
4. Schaeren S, Roth J, Dick W. Effective in vivo radiation dose with image reconstruction controlled pedicle instrumentation vs. CT-based navigation. Orthopade. 2002 Apr;31(4):392-6.
5. Slomczykowski M, Roberto M, Schneeberger P, Ozdoba C, Vock P. Radiation dose for pedicle screw insertion. Fluoroscopic method versus computer-assisted surgery. Spine. 1999 May 15;24(10):975-82; discussion 983.