Fixation of slipped femoral capital epiphysis is a technically demanding procedure. Numerous studies have examined the most effective surgical technique and have investigated methods of fixation (either pins or screws), number of screws/pins, positioning of the patient (fracture vs. radiolucent table), determination of entry point, and the exact positioning of the screws [2
]. In a recent paper reviewing a large series (241 patients), the method producing the least complications (avascular necrosis, chondrolysis) was in situ pinning with a single cannulated screw [12
]. In this procedure, the precise aiming of the cannulated screw in all planes in a deformed proximal femur remains technically challenging. The narrow safe zone available for the screw requires utmost precision to avoid deleterious complications [11
]. By using computerized navigation, the lateral view as well as they AP and additional oblique views are constantly available while the screw is being inserted. Therefore, by aiming to the center of the femoral head on all views simultaneously, readily done by navigation, this complication can be avoided. We used computerized fluoroscopic navigation in a similar fashion with percutaneous fixation of pelvic fractures [17
], and found the technique to be helpful in planning the exact route of the screw in a three-dimensional, anatomically complex structure with a very limited “safe-zone.” Also, correct estimation of the screw's length can prevent penetration, and direct measurement of distances on the computer screen can be carried out. However, a virtual exact image of the screw is still not available commercially, although such systems are under development and investigation. This modification will also enable the surgeon to visualize the threads of the screw and their relation to the physeal line.
The navigation system can also help the surgeon preplan the incision site because the tracked drill guide is approximated to the femoral shaft on the patient's thigh prior to skin incision. The displayed virtual image can guide the surgeon to the correct starting point and therefore to the incision. Soft tissue dissection and skin incision are minimized. This is especially beneficial for obese children who constitute the majority of patients with slipped femoral capital epiphysis.
The amount of radiation is significantly reduced with the new technique. Essentially, only four images are needed for the surgery regardless of the number of screws placed. These include the two images for registration and two final verification images. Reduction of radiation to the pelvis is extremely important, considering the characteristic adolescent age group of patients. Several studies had measured intraoperative radiation while performing similar tasks, and demonstrated the benefit of these systems on several applications [18
]. Altough gonadal shielding may prevent some of the radiation delivered, the amount of radiation delivered to the human pelvis in 1 min of fluoroscopy amounts to 40 mSV, which is equivalent to 250 chest x-rays [20
]. Therefore, we believe that this is an important advantage of the system. Use of navigation does not significantly lengthen operative time because the system can be set up while the patient is being prepped and draped.
Computer-aided orthopedic surgery (CAOS) is gaining popularity and allows for precise minimally invasive techniques and increases the accuracy of implants placement. We think the percutaneous screw fixation of slipped femoral capital epiphysis is an excellent implementation of the technique because it requires utmost precision, narrow safe zone, and minimal amount of radiation. This is one of the first steps in implementing this technique in pediatric orthopedic surgery.