Jan. 20, 2015
The use of minimally invasive surgical techniques and intraoperative CT navigation is a rapidly evolving practice at advanced spine centers. Surgical imaging technologies have improved in the past decade.
"Mayo Clinic orthopedic practice has found that intraoperative navigation and CT can be invaluable in the treatment of complex spinal deformity," says A. Noelle Larson, M.D., an orthopedic surgeon at Mayo Clinic, Rochester, Minnesota who researches the topic with colleagues at both Mayo Clinic and University of Minnesota. Adds Dr. Larson's Mayo Clinic orthopedic surgeon colleague and spine specialist Ahmad Nassr, M.D.: "The use of these technologies can allow for less morbid ways to treat our patients but accomplish the same goals as traditional techniques."
In 2012 Dr. Larson and collaborators published results in the Journal of Pediatric Orthopaedics on the accuracy of placement of pedicle screws using navigation and 3D image-guidance for correction of complex spine cases. They found CT-guided navigation contributed to the successful placement of 142 pedicle screws in patients with congenital deformity and altered anatomy, representing a 99.3 percent screw accuracy rate. In a related 2012 study in the journal Spine, the Mayo Clinic and University of Minnesota team reported 96.4 percent accuracy in pediatric pedicle screw placement using intraoperative CT and a 3D navigation system.
Prioritizing low-dose imaging
Minimizing radiation exposure is always of utmost concern, especially for young patients. Scoliosis patients historically faced an elevated risk of breast cancer due to childhood radiation exposure from frequent scoliosis radiographs. Recent addition of the EOS imaging technology has reduced radiation exposure for spine patients in the outpatient practice. Radiation exposure from traditional CT imaging, however, is far greater than standard radiography.
To address this, Mayo Clinic orthopedics' spine team has implemented an intraoperative CT pediatric dosing protocol for patients who weigh less than 80 kilograms (kg). This produces an 85 percent reduction in the effective dose compared with the manufacturer settings. Thus, 3-D imaging can be obtained with about the same radiation as six chest X-rays or one-third of annual background radiation.
Reducing malpositioned screws
"We find navigation is especially helpful in cases such as high-grade spondylolisthesis," explains Dr. Larson. These cases require a multidisciplinary approach, including expert collaborations with spine specialist Dr. Nassr and others. Explains Dr. Larson: "In female patients, we will perform an anterior lumbar interbody fusion (ALIF) through a small Pfannenstiel incision to achieve indirect decompression, and then position the patient in a prone position and place percutaneous instrumentation to achieve and maintain reduction. This seems to be a safe and effective way to gain correction."
Through percutaneous techniques surgeons avoid disturbing muscles in the back, which helps reduce trauma and facilitates recovery. "In general, navigation is a tool to place screws with a consistently high level of accuracy," she says.
Indications for use
According to Dr. Larson, intraoperative CT and image guidance systems are especially useful in the following cases:
- Complex spine fusions or revisions in which the anatomy is severely distorted
- Congenital spine deformity
Data on screw position
Data show that approximately 5 to 15 percent of pedicle screws in children are malpositioned, a rate confirmed across multiple U.S. centers in studies, with return to surgery for malpositioned instrumentation reported in up to 1 percent of patients.
According to a 2012 report in Spine on thoracic pedicle screw placement, CT-guided navigation resulted in more optimally placed screws, fewer potentially unsafe screws, and fewer screw removals. Data published in 2013 in the journal Spine by Dr. Larson and her Mayo Clinic research colleagues support that. Their results show that the use of intraoperative CT scanners and image guidance systems can reduce the rate of malpositioned screws to less than 3 percent, essentially eliminating return to the operating room due to screw malposition.
While not all malpositioned screws cause problems, there are rare reports of neurologic and vascular problems. Further, there is the potential to complicate future evaluation should malpositioned screws be detected on axial imaging studies obtained for other indications.
Optimizing screw use
Some surgeons believe that precise screw placement using intraoperative CT for improved purchase and fixation may enable physicians to safely use fewer screws. "Fewer screws with optimal dimensions and positioning within the pedicle should be the aim to improve surgical efficiency," Dr. Larson says.
She is currently participating in a randomized clinical trial evaluating the number of screws needed for adolescent idiopathic scoliosis surgery. "If equivalent clinical results can be obtained with fewer screws, this should become the standard of care for routine scoliosis surgery."
Randomized clinical trial of screw use
The Minimize Implants Maximize Outcomes (MIMO) Study Group, a consortium led by David Polly, M.D., at the University of Minnesota and Dr. Larson is currently conducting a randomized, controlled trial of screw use in pediatric scoliosis cases at12 sites throughout the U.S. and Canada. The goal of the research is to identify how many screws are necessary for optimal outcomes in adolescent idiopathic scoliosis.
Says Dr. Larson: "Some surgeons put two screws at every single level fused, because the traditional thinking is that more fixation is better. Some surgeons on average use one screw per level fused. Thus there is significant variation in clinical practice regarding screw use throughout the country."
In this trial, children are randomized to one of two treatment arms, one using more screws and the second using fewer screws in hopes of developing an evidence-based guide for practice. Says Dr. Larson: "If it turns out we can reliably use fewer screws, to achieve the same clinical result, this may result in shorter operative times and reduced blood loss without compromising outcomes."
For more information
Larson AN, et al. The accuracy of navigation and 3D image-guided placement for the placement of pedicle screws in congenital spine deformity. Journal of Pediatric Orthopaedics. 2012;32:E23.
Larson AN, et al. Pediatric pedicle screw placement using intraoperative computed tomography and 3-dimensional image-guided navigation. Spine. 2012;37:E188.
Ughwanogho E, et al. Computed tomography-guided navigation of thoracic pedicle screws for adolescent idiopathic scoliosis results in more accurate placement and less screw removal. Spine. 2012;37:E473
Baghdadi YM, et al. Complications of pedicle screws in children 10 years or younger: A case control study. Spine. 2013;38:E386.
University of Minnesota — Clinical and Translational Science Institute. MIMO Clinical Trial. ClinicalTrials.gov.