Intraoperative axial patellar imaging: a new technique

Abstract

Background: The medial patellofemoral ligament (MPFL) functions by providing patellar stability and preventing lateral displacement of the patella. Surgical fixation is commonly recommended for MPFL tears in the form of MPFL reconstruction via anatomic techniques. Intraoperative fluoroscopy is critical for identifying anatomical landmarks during surgery. Using the C-arm, both anteroposterior and lateral views are routinely obtained, leaving the surgeon blinded to the angle of approaching the patella. Thus, our team saw a need to develop a method to capture an axial-type view of the patella using available intraoperative imaging technology. Technique: After guide-pin insertion, fluoroscopy is positioned for an anteroposterior view. The knee is hyperflexed while externally rotating the tibia and ankle. The patient’s ankle is slightly below the edge of the operating table, causing the tibia to rotate out of view of the radiograph. The C-arm is angled cephalad, approximately 20 to 30 degrees with the C-arm lowered, the operating table is raised until the knee almost touches the C-arm. The angle of tibial rotation and knee flexion is adjusted to obtain a view that closely resembles is the Merchant view. Our axial patellofemoral fluoroscopic technique augments traditional anteroposterior and lateral views by providing increased accuracy of patellar fixation in relation to the patellofemoral joint. Discussion: As MPFL reconstruction and repair procedures become more common, there will be a desire to improve upon the technique and approach to the procedure. Anatomic positioning of the graft is the most important prognostic factor in determining success of the operation. To decrease complications, such as patellar fracture, accuracy of patellar fixation placement is paramount, and any measure to ensure proper graft placement should be utilized. Conclusions: Our technique established more precise guide-pin placement for the patellar tunnel. It also reduced time spent evaluating patellar fixation via additional orthogonal imaging. This could be associated with better outcomes and avoidance of common complications such as patellar fracture attributed to violation of the anterior cortex. Level of Evidence: Level V.