Tips and Pearls
The percentage of Americans over the age of 50 years is steadily increasing. Along with this there has been a steady increase in the annual number of extracapsular proximal femur fractures. Although controversy still exists on implant choice for fixation of pertrochanteric femur fractures, cephalomedullary devices are gaining acceptance within the community, and use of these devices is rapidly increasing.1 The use of these devices is not without significant risk of complication.
Two of the more significant complications that are seen with cephalomedullary nailing are iatrogenic femur fractures and proximal lag screw cutout.2 The rate of iatrogenic fracture is decreasing due to better understanding of proximal femoral anatomy with regard to nail insertion location.3 In addition, the newer generation implants have been designed to decrease proximal femoral hoop stresses as well as improve the mismatch between femoral bow and the radius of curvature of the nails.4 In contradistinction, lag screw cutout is associated with technical error rather than lag screw design.
The incidence of screw cutout increases as the position of the screw tip varies from the center position.5 Currently, the most frequently reported rate of lag screw cutout in pertrochanteric fractures is 4% to 6%.6–9 One of the challenges to consistently achieving proper screw orientation is the limitation of fluoroscopic imaging. Standard lateral views of the operative hip project the femoral neck at an oblique angle to the image intensifier. Insertion of the proximal lag screw in this semilateral orientation creates a situation in which the surgeon must estimate the precise anatomic location of the screw within the head during insertion. Simple modifications to the fluoroscopic technique during lag screw insertion can ensure proper positioning of the screw in the center of the femoral head on the lateral view.
All patients undergoing insertion of a cephalomedullary device by 1 surgeon at our institution had proximal femoral lag screws inserted using a standardized fluoroscopic technique. All patients underwent nailing on an OSI (Mizuho Orthopedics Systems Inc.) fracture table with the operative leg in traction by the use of a boot attachment or through a proximal tibial traction pin. The contralateral foot is placed in a boot and the leg is positioned inferior to the operative leg to improve fluoroscopic imaging (scissor position). The image intensifier is positioned on the side contralateral to the patient’s fracture, distal to the patient’s hip. The image intensifier is introduced over the operative field from a position distal to the operative hip. The base is rotated such that the arm is angled cranially, crossing the contralateral thigh and the image intensifier is centered over the operative hip. This angle is approximately 30 to 40 degrees cranial to a line connecting the patient’s femoral heads. This positioning allows the operative hip to be viewed in the lateral position without obstruction from the contralateral hip and hemipelvis. Orienting the fluoroscope in this manner also reduces overlap of the femoral head and proximal femoral shaft, improving visualization. The base of the machine is locked in this position to ensure consistent imaging.
After insertion of the nail, an anteroposterior (AP) image of the hip is used to seat the nail to a depth that allows insertion of the guide pin into an ideal central or slightly inferior location in the femoral head. The image intensifier is then rotated to a direct lateral position, parallel to the operative table. The extramedullary jig attached to the nail is then rotated out of the fluoroscopic field, and the operative hip is centered on the image display (Fig. 1).
The image intensifier is then rotated toward the AP direction until the nail is in the center of the femoral head. This defines the axis of screw insertion from the nail to the center of the head. The image intensifier is then locked at this angle (Fig. 2).
The extramedullary guide is then rotated until it is parallel with the orientation of the image intensifier. This is the case when the nail is seen in the center of the radiolucent shadow of the locking guide. At this point, the nail will be centered in the shadow of the jig, which is centered in the femoral head. A screw that is placed now will be directed into the center of the femoral head (Fig. 3).
The proximal lag screw cannula is then inserted. The orientation is again checked to ensure that all components are precisely transposed and remain collinear. The threaded guide pin is then inserted on a trajectory that will travel through the rotational center of the femoral head to the desired subchondral depth (Figs. 4 and 5).
The image intensifier is then rotated back to the AP position (orthogonal to the prior image) and the depth of the guide pin is assessed in that plane. The lag screw path is now ready for drilling and the remainder of the procedure can be performed using the standard technique for the device that is used.
Eighty-two consecutive patients, from 1998 to 2008, with intertrochanteric and subtrochanteric fractures (AO 31-A.2, A.3, and 32-A.1, A.2, A.3) deemed unstable based on comminution and fracture obliquity underwent cephalomedullary nailing of their fracture by a single surgeon. The lag screw or screws were inserted using the standardized technique described above using 1 of 2 devices (Gamma Nail, Stryker or Intertan Nail, Smith & Nephew). Postoperative rehabilitation protocols included weight bearing in all cases. No patient had loosening or cut out of their central screw.
The use of a standardized fluoroscopic technique to obtain a lateral image of the hip in the plane of the implant-head axis reduces the possibility of surgeon error when inserting the proximal lag screw in a cephalomedullary device. The indications for using this technique include all patients requiring insertion of a cephalomedullary device for a femur fracture. The technique is compatible with any nailing system that utilizes a radiolucent guide oriented in parallel to the nail. Limitations of this technique are related to the quality of obtainable fluoroscopic images. Technical difficulties achieving appropriate visualization of the femoral head can be attributed to poor patient positioning or improper angling of the image intensifier. We have had good results obtaining appropriate images by ensuring that the contralateral leg is positioned below operative leg at a height that still allows for passage of the image intensifier. Angling of the image intensifier approximately 30 degrees cranially significantly reduces superimposition of the contralateral hip on the image, improving visualization. Strengths of using this technique include ease of use and excellent reproducibility. Malpositioning of the nail entry portal does not affect the use of this technique, as the lag screw can still be inserted in the optimal position of the femoral head. Currently, we have not found any limitations for using this technique based on patient body habitus, fracture pattern, or type of cephalomedullary device used.
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Keywords:© 2013 Lippincott Williams & Wilkins, Inc.
cephalomedullary nailing; nailing intertrochanteric fractures; lag screw cutout