The use of minimally invasive techniques to perform spinal surgeries has gained acceptance as standard of care for many procedures. Previous reports and advocates cite minimally invasive spine surgery's lower infection rate, better tolerated post-operative pain and shorter hospital stays relative to open surgery counterparts. Procedures ranging from microdiscectomies to interbody fusions to tumor resections have been performed using these minimally invasive techniques that utilize a series of tubes, less than 2 cm in diameter, to gain access to the surgical site. A drawback of this approach is that multiple fluoroscopic images must be taken to ensure the correction positioning of the tubes, which exposes the surgeon and surgical team to increased doses of ionizing radiation relative to the traditional open procedures.
Multiple studies have examined radiation exposure to surgeons for procedures such as kyphoplasty and transforaminal lumbar interbody fusion (TLIF). However, there is little data comparing open to minimally invasive lumbar microdiscectomies, one of the most common spine operations. Mariscalco and colleagues at the Cleveland Clinic prospectively compared radiation exposure during open vs minimally invasive lumbar microdiscectomies (Spine. 2011:36(3):255-260).
Patients with isolated herniated lumbar discs, refractory to conservative management were prospectively enrolled in the study. Five spine surgeons, experienced in both procedures, performed either an open or minimally invasive lumbar microdiscectomy on the enrolled patients, until 10 patients in each group received operations. The type of surgery was at the surgeons' discretion. Surgeons wore digital dosimeters over the thyroid to approximate eye (specifically lens) exposure, over their chests to measure whole-body exposure and on their forearms to approximate hand radiation exposure. Surgeons performing minimally invasive surgeries, all of which required the use of fluoroscopy, wore the dosimeters outside of the lead aprons and thyroid shields. The open procedures were performed with the use of standard lateral radiographs for localization purposes. A minimum of 2 x-rays (mean = 2.3) were taken by radiology technicians, while the surgeons waited in an adjacent, sub-sterile room 12 feet away from the x-ray machine. Surgeons in the open cases did not wear lead protection, but donned dosimeters in identical locations to measure their exposure while in the sub-sterile room.
The mean measured radiation to the surgeon's thyroid (eye), chest and hand in the open cohort was 0.16, 0.21 and 0.20 mR (millirads) while in the minimally invasive cohort; exposure was 1.72, 3.08, and 4.45 mR, respectively. The difference between the values at the same location among the 2 cohorts were statistically significant (P values were .10, .013, and .006, respectively). While the exposure was greater during the minimally invasive surgery as expected, the exposure during the open procedure was not zero, despite the surgeon being in a different room. An additional comparison of measurements was performed from readings from surgeons standing on the same side of the OR table to the fluoroscope (n = 5) and those standing on the opposite side (n = 5). The only statistically significant site reading was that of the chest (5.02 vs 1.14 mR; P = .049).
While surgeons performing the minimally invasive operations received 10 to 22 times more radiation than those performing open operations; the authors argued that this statistic was likely not clinically significant. Using the National Council on Radiation Protection and Management's “occupational exposure limits,” a surgeon would need to perform 1623 minimally invasive lumbar microdiscectomies in 1 year to exceed the limits for whole body radiation. This calculation assumes that the surgeon receives no other forms of radiation exposure, which is unlikely. However, the scenario also measured exposure without any protective equipment (dosimeters were outside the lead). Therefore, it is unlikely that a single surgeon would receive radiation beyond the proposed limit from performing only minimally invasive microdiscectomies. In combination with other procedures requiring more frequent fluoroscopic imaging, such as minimally invasive instrumentation, exposure doses do accumulate.
This study was the first to compare radiation exposure to surgeons from open and minimally invasive lumbar microdiscectomies. The authors proposed recommendations to limit surgeons' exposure during minimally invasive surgery: monitoring of OR staff's annual exposure to radiation, wearing protective leaded equipment and glasses, standing on the opposite side from the fluoroscope's radiation source and using mobile leaded shields even when in an adjacent room for localization of levels during open microdiscectomies. As the number of minimally invasive spine surgeries continues to grow, it will be important to be mindful of this invisible, but potential risk to the surgeon.
Alexander E. Ropper
John H. Chi