Technique for creating the anterior cruciate ligament femoral socket: optimizing femoral footprint anatomic restoration using outside-in drilling.

PURPOSE: The purpose of this study was to investigate and optimize anterior cruciate ligament (ACL) femoral outside-in drilling technique with a goal of anatomic restoration of the footprint morphologic length, width, area, and angular orientation.
METHODS: Ex vivo, computer navigation was used to create virtual 3-dimensional maps of femoral bone tunnels for ACL drill guide pin insertion paths on small, medium, and large models of averaged femora considering various pin insertion angles to the femur. We then determined which pin insertion angle resulted in an ACL femoral footprint optimally matching normal human anatomic length, width, area, and angular orientation of the footprint long axis.
RESULTS: During outside-in drilling of the ACL femoral socket, a guide pin entrance angle of 60° to a line perpendicular to the femoral anatomic axis, combined with a guide pin entrance angle of 20° to the transepicondylar axis, results in the closest approximation of the gold standard of normal anatomic morphology of the human knee ACL femoral footprint length, width, area, and angular orientation.
CONCLUSIONS: During outside-in drilling of the ACL femoral socket, a guide pin entrance angle of 60° to a line perpendicular to the femoral anatomic axis, combined with a guide pin entrance angle of 20° to the transepicondylar axis, results in optimal reconstruction of the normal human anatomic ACL femoral footprint length, width, area, and angular orientation. CLINICAL RELEVANCE: We describe arthroscopic landmarks for anatomic ACL femoral socket creation that may be considered by practicing arthroscopic surgeons in the operating room, without open dissection or fluoroscopy and unaffected by type of drill guide or variations in the thickness of the femoral soft-tissue envelope.