The sound of the drill begins to pierce the air.
Gao Yuan picks up the guide pin and presses it against the medial side wall of the lateral femoral condyle. The tip of the guide pin nestles precisely into the center of the native footprint—a depression he had located with a probe. He adjusts the angle twice: the first for preliminary positioning, the second for fine-tuning. Both adjustments are subtle, likely only one or two degrees, but it's these slight differences that determine if the tunnel direction will be parallel to the intercondylar notch roof or slightly angled. Parallel is ideal because the path of the graft closely mimics that of the native ligaments, optimizing biomechanics.
