Abstract
Each of the seven cuts required for a total knee arthroplasty has its own science, and can affect the outcome of surgery.
Distal Femur
Sets the axial alignment (along with the tibial cut), and too little or too much depth affects ligament tension in extension.
Anterior Femur
Sets the rotation of the femoral component, which affects patellar tracking. Internal rotation results in patellar maltracking. External rotation will either notch the femur, or cause too large a femoral component to be selected. Anterior and posterior femoral cuts also determine femoral component size selection. Too small a femoral component causes notching, flexion instability, and mismatch to the tibial component. Too big a femoral component causes overstuffing, periarticular pain, and patellar maltracking.
Posterior Femur
Posterior referencing usually works, and the typical knee requires 3 degrees of external rotation to align with the transepicondylar axis. In valgus knees, there may be significant hypoplasia of the lateral femoral condyle, and posterior referencing has to be adjusted to avoid internal rotation.
Posterior chamfer
A 4-in-one block saves time.
Anterior chamfer
Deeper anterior chamfer allows a deeper trochlear groove, for patellar tracking.
Tibia
Sets axial alignment with distal femoral cut. Posterior slope loosens flexion gap. Oversizing results in painful medial overhang. Lateral overhang usually not a problem. Undersizing results in inadequate bone support and subsidence.
Patella
Inset or onset. Central peg associated with fracture. Err to medial and superior to assist tracking and avoid impingement on the tibial insert.
