Radiographic Landmarks for Locating the Femoral Origin of the Superficial Medial Collateral Ligament

Background: Little has been written about the use of radiographic landmarks for locating the origin of the superficial medial collateral ligament (sMCL). A standardized radiographic landmark for the sMCL origin using intraoperative fluoroscopic imaging may be of value in aiding the surgeon in accurate femoral tunnel placement in the setting of extensive soft tissue disruption and bony attrition. Purpose: To determine a reproducible radiographic landmark that will assist in correct femoral tunnel placement in sMCL repair and reconstruction. Study Design: Descriptive laboratory study. Methods: Ten fresh-frozen unmatched human cadaveric knees were dissected, and the origin of the sMCL was exposed. A 2-mm metallic marker was then placed at the center of the femoral origin of the sMCL. True lateral fluoroscopically assisted digital radiographs were obtained of the knee with the posterior and distal femoral condyles overlapping in a standardized fashion. With the use of computer software, reference lines were drawn on the images, creating 4 quadrants. Two independent examiners performed quantitative measurements of the sMCL origin in relation to this axis and to the Blumensaat line. Results: Mean measurements showed the sMCL origin to be closely related to the intersection point of the Blumensaat line and a line drawn distally from the posterior femoral cortex on a true lateral radiograph. The sMCL origin was found at a mean point 1.6 4.3 mm posterior and 4.9 2.1 mm proximal to the intersection of a line paralleling the posterior femoral cortex and a line drawn perpendicular to the posterior femoral cortical line, where it intersects the Blumensaat line. In 5 of 10 specimens, the center of the sMCL origin fell precisely on the Blumensaat line. The remaining specimens had sMCL origins anterior to the Blumensaat line. The femoral origin of the sMCL was found in the proximal and posterior quadrants in 8 of 10 specimens. Conclusion: With a relatively small amount of deviation, the sMCL origin can be consistently identified on a true lateral radiograph of the knee using reproducible reference lines on fluoroscopic imaging. Clinical Relevance: Accurate identification of the femoral origin of the sMCL can be accomplished by intraoperative fluoroscopic imaging. This information may be of significant benefit in repairing acute injuries and in reconstructive procedures complicated by bony attrition and soft tissue loss.