- Resection of the Distal Femur:
- cushing rongeur is used to remove osteophytes in medial & lateral aspects of the femoral condyles as well as the intercondylar space;
- this avoids, possible mis-sizing of the femoral component;
- femoral IM alignment rod: (discussion)
- mechanical axis
- anatomic axis
- distal femoral cutting guide:
- depth of cut:
- generally this is set for a length which makes up for the length of the femoral component (usually 8-9 mm);
- often surgeons will add, 1-2 mm to this length;
- if the patient has a knee flexion contracture, then consider cutting upto 2-3 mm beyond the templated length of the
- note, however, that it is important to avoid elevation of joint line, in which case the surgeon should select
a posterior stabilized knee rather than a PCL retaining component:
- author's preferred technique:
- note that the extension space will be affected by the ACL, deep MCL, and posteromedial capsule;
- 1/2 inch osteotome is used to elevate deep MCL and posteromedial capsule, and rongeur is used to remove ACL;
- once these releases have been completed, then reassess the delta change of knee extension (compared to preop);
- this technique will demonstrate that many patients that would have "required" elevation of the joint line (because
of preop contracture), will not require excessive resection of the distal femur;
- pitfalls of cutting jig:
- note that some patients may have a prominent medial trochlear ridge which will have the effect of "artificially"
elevating the distal femoral cutting guide off of the end of the femur;
- this will be manifest by an abnormally large gap over the lateral femoral condyle;
- the result will be an inadequate distal femoral cut and reduced extension gap;
- angulation of cut:
- ideally the tibio-femoral articulation should have an angulation of 3 to 7 deg;
- in early TKR designs, proximal tibia was cut in upto 3 deg of varus, which meant that the distal femoral cut was made in
7- 9 deg of valgus;
- if the proximal tibial cut is to be cut in neutral (this is now standard), then femoral cutting guide is set for the appropriate
right or left valgus angulation of +5 to 7 deg (in the tall thin patient try +5 deg, & in short obese patient try 7 deg);
- if the alignment rod is found to be too medial, then consider changing the valgus alginment from 5 deg to 6-7 deg;
- Natural distribution of the femoral mechanical-anatomical angle in an osteoarthritic population and its relevance to total knee arthroplasty.
- 5 degrees to 6 degrees of distal femoral cut for uncomplicated primary total knee arthroplasty: is it safe?
- Errors in Knee Alignment Using Fixed Femoral Resection Angles
The Variability of Intramedullary Alignment of the Femoral Component During Total Knee Arthroplasty.
Distal femoral cut perpendicular to mechanical axis may induce varus instability in flexion in medial osteoarthritic knees with varus deformity in total knee replacement: a pitfall of the navigation system.