Determine the opening of the femoral canal
Nov. 20, 2019
Determine the opening of the femoral canal
As the femoral side, it is important to confirm the anatomy and exposure of the intercondylar notch, and confirm the insertion of the posterior cruciate ligament (PCL). Osteophytes of intercondylar notch should be removed with osteotome, and then dissected the PCL (Fig. 1).
The location of the opening of the femoral canal is about 1cm above the insertion of the PCL and slightly medial in the real center of the intercondylar notch (Fig. 2).
The anterior-posterior femur radiographs help to identify the entry point of the femoral intramedullary (IM) positioning rod.Confirm the location of the enter point on the coronal plane in the femoral intercondylar notch by draw a line from the midpoint of the femoral shaft to the distal on the anterior-posterior radiographs before operation (Fig. 3).
As mentioned above, the entry point is usually slightly medial in the real center of the intercondylar notch.If the enter point is actually in the center of the intercondylar notch, the valgus angle may increase by several degrees actually.This may be the most common cause of excessive valgus of the femoral prosthesis.Usually, the IM rod is placed at the true center of the intercondylar notch, and a 7 °valgus guide osteotomy is used, while the valgus angle of the actual distal femur osteotomy becomes 9 °or 10 °valgus.
Once the enter point is selected, a sharp smaller drill should be used to open a hole so that the subsequent drill can go into the cavity right at the enter point; then, a drill with the same diameter as the IM rod should be used to drill the medullary cavity. Finally, a drill with a diameter slightly larger than the IM rod should be used to enlarge the opening of the medullary cavity (JUST SKI Knee Instrument Set provides a IM drill with 2 diameters (Fig. 4), suck out the fat in the femoral canal if necessary, and flush the medullary cavity.The IM rod usually has grooves, it should move gently and slowly when inserted. If it is difficult to insert the IM rod, the enter point must be enlarged (Fig. 5).
