A Surgical Technique for Percutaneous Intraoperative Monitoring of Proximal Femur Epiphyseal Perfusion

Abstract

Osteonecrosis of the femoral head is a potentially devastating complication that can occur after a slipped capital femoral epiphysis (SCFE) or a femoral head or neck fracture. It is hypothesized that osteonecrosis results from injury to the superior retinacular artery system that supplies the outer two thirds of the femoral head.1 This can occur at the time of the injury (during the slip or fracture) or at the time of surgical treatment when the slipped epiphysis or fracture is being reduced. Therefore, the ability to assess epiphyseal perfusion intraoperatively, before and/or after reduction of an unstable SCFE or femoral head or neck fracture can help the surgeon understand risk of avascular necrosis and provide an opportunity to intervene. Currently, a percutaneous method for measuring epiphyseal perfusion utilizes an intracranial pressure (ICP) monitor that is inserted down the shaft of a screw that crosses the epiphysis.2,3 This technique requires a patient’s anatomy to accommodate a screw large enough that the 2.7 mm ICP probe sheath can fit through the cannulated screwdriver. It also requires the reduction and internal fixation with a screw to have occurred prior to evaluation of perfusion. Without the ability to evaluate epiphyseal perfusion prior to reduction maneuvers, a surgeon cannot discern whether decreased perfusion is secondary to the initial injury or due to potentially reversible causes such as the reduction maneuver. We present a percutaneous technique that uses simple instrumentation that is readily available and does not require fixation or reduction of the SCFE or proximal femur before perfusion monitoring. Using a bone marrow biopsy needle and an arterial line monitoring set up, epiphyseal perfusion monitoring can safely occur before and/or after closed treatment of the femoral head or epiphysis. TECHNIQUE In a supine position on a radiolucent table, the operative limb is prepped and draped. Fluoroscopy is used to localize the hip joint. For unstable slips and upper femur fractures, monitoring can occur before and/or after the reduction. A bone marrow biopsy needle is placed in the metaphysis of the proximal femur with fluoroscopy guidance. The senior authors prefer to use a 15-G 4 inch Jamshidi Biopsy Needle (Medline, Northfield, IL) (Figs. 1A, 2A). An arterial line is set up by anesthesia and the tubing is primed with sterile saline and zeroed while the tubing is held at the level of the hip. Once the bone biopsy needle is in the metaphysis, sterile saline is injected into the needle and the arterial line tubing is connected to the needle. (Figs. 1B, C) A static interosseous pressure will be registered and the arterial line monitor scale is then adjusted to these levels so that the waveform can be seen. The monitor should show pulsatile waves in rhythm with the heartbeat (Fig. 3). This confirms the setup is working. Then, using fluoroscopic guidance, the bone biopsy needle is either replaced into the lateral epiphysis or is further advanced from the metaphysis across the physis into the epiphysis (Figs. 2B, C). Sterile saline is then reinjected into the needle and the arterial line tubing is reconnected to the needle. If there is perfusion to the epiphysis, the monitor should again show a pulsatile wave form similar to the reading within the metaphysis. The arterial line scale may need to be adjusted again to visualize the waveform. The femoral head fracture or SCFE can then be fixed according to the operative surgeon’s preferred technique guided by the fracture or slip pattern. If there is no perfusion waveform after a reduction maneuver, decompression of the hip capsule by needle aspiration or capsulotomy could be performed as a troubleshooting step before taking down the reduction as increased hip capsule pressure from hemarthrosis from the SCFE or femoral head fracture can be a source of loss of perfusion.4FIGURE 1: Bone biopsy needle: insertion (A), filled with saline (B), arterial line connected (C).FIGURE 2: Radiographs of bone marrow needle placement: metaphysis (A), epiphysis (option 1) (B), metaphysis into epiphysis (option 2) (C).FIGURE 3: Arterial line monitor (red line) showing pulsatile wave forms corresponding with the heartbeat.EXPECTED OUTCOMES This technique is a simple method that can be used to assess epiphyseal perfusion of the proximal femur through a percutaneous approach. It does not require initial screw fixation or the use of an ICP monitor which may not be readily available at all institutions. It uses equipment that is readily available and does not require a rigorous set up. This technique is also less expensive compared with the use of an ICP probe which can cost upwards of 15 times as much as a bone marrow biopsy needle depending on the institution. COMPLICATIONS There are a few potential complications that surgeons using our described technique must be aware of: Insertion of the bone biopsy needle can result in iatrogenic cartilage injury or injury to the retinacular flap if inserted at the wrong location. To avoid this, we recommend using fluoroscopy to guide appropriate placement of the device within the planned location in the epiphysis. In addition, the needle should be inserted perpendicular to the entry point within the epiphysis to avoid skiving across the chondral surface. Advancing the needle from the metaphysis, across the physis, and into the epiphysis can also avoid injury to the chondral surface of the femoral head. Another pitfall of this technique is that the pressure waveform of the proximal femur may not appear on the arterial line monitor if the monitor is not scaled appropriately. The pressure within the proximal femur is much lower than a patient’s mean arterial pressure and as such the scale on the monitor should be adjusted until a pressure reading is detected. It is important when placing the bone biopsy needle that it pierces past the cortex. If the sterile saline does not easily inject into the bone biopsy needle, it might need to be placed deeper into the bone. If the cortex is extremely difficult to pierce, it is recommended to change to a larger needle such as an 11-G to avoid damaging the cartilage or bending/breaking the bone biopsy needle inside the patient. Though our described technique enables surgeons to percutaneously evaluate epiphyseal perfusion of the proximal femur to potentially avoid osteonecrosis of the femoral head due to reduction maneuvers, the technique does not guarantee that loss of perfusion during a reduction maneuver is reversible. Surgeons should be diligent during the reduction of a SCFE or femoral head or neck fracture and use their best judgment to minimize injury to the epiphyseal blood supply. Finally, further study of this technique with long-term follow-up is necessary to correlate intraoperative perfusion findings with rate of subsequent avascular necrosis.