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TKR: Femoral Component Box Cut:

- Box Cut:
          - ensure that box cutting jig is placed flush on anterior and distal femoral surfaces;
          - box cutting jig is centered over the intercondylar notch (or IM drill hole);
                 - if the knee has a valgus deformity, consider slighly lateralizing the jig;
          - once box cut is peformed, the transected box fragment is placed under tension and the ACL and PCL are removed;
          - leave a margin of PCL behind inorder to protect the popliteal vein which lies directly posterior;
          - pitfalls:
                 - patellar subluxation:
                        - if there is a tendency for patellar subluxation, then the box cut should be slightly lateralized;
                        - it is essential that the box cuts not be medialized in relation to the intercondylar notch;
                        - this will force a corresponding medialization of the tibial component (resulting in increased Q angle and possible patellar subluxation);
                 - size of box cuts:
                        - be aware that in many TKR components that the box cut is the same size for small, medium, and larger sizes, and therefore in small and medium sizes the smaller lateral condyle is at risk for fracture if careless or rough technique is used to perform the box cut and broaching;
                 - femoral-tibial mismatch:
                        - note that depending on the design, there may be a narrow range of compatability between femoral and tibial component sizes

- references: 

The effect of femoral component position on patellar tracking after total knee arthroplasty.  

The trochlea is medialized by total knee arthroplasty: an intraoperative assessment in 61 patients