- Location of Entry Hole:
- use a rongeur to remove any residual osteophytes from the intercondylar notch;
- use intercondylar drill guide to drill hole into center of medullary canal of the femur;
- use a cannulated guide rod to help prevent fat embolism
- normally the entry hole is placed slightly anterior to the insertion of the PCL (6 mm from center) on to the femur;
- excessive posterior placement most often results from mis-judging top of intercondylar notch (due to inadequate debridement of notch osteophytes);
- placement of the drill hole too posterior can lead to flexion of the femoral component, which will complicate the subsequent femoral cuts,
and will lead to incomplete knee extension;
- generally the drill hole should be made 1 cm above the roof of the intercondylar notch, which will keep the guide rod in center of medullary canal;
- vent the intramedullary canal by widening the drill hole in an AP direction (using a ronguer);
- this will allow the fatty contents of the medullary can to exit thru the drill rather than be embolized as the alignment rod is driven retrograde;
- to assure that the medullary canal is unobstructed, pass the medullary rod into the drill hole and up the medullary canal of the femur;
- avoid pushing IM guide too far in, as the femoral bow will add some extension to the distal cutting block and may lead to notching and fracture;
- Meduallary Guides:
- if properly applied, IM femoral alignment systems are accurate to w/in 1-2 degs of varus or valgus, & are more accurate than extramedullary jigs;
- use of extrameduallary alignment systems may be indicated in the case of ipsilateral hip arthroplasty with a long femoral
component, mal-alignment following a femoral fracture, or in the case of excessive excessive anterior bowing;
- radiograph of the entire femur is needed, so that when the IM guide is used, allowances can be made for bowing or deformity;
Effect of rotation on the axial alignment of the femur. Pitfalls in the use a of femoral intramedullary guides in total knee arthroplasty.
Blood-gas and circulatory changes during total knee replacement. Role of the intramedullary alignment rod.
Extramedullary versus intramedullary alignment guides in total knee arthroplasty.
The effect of prosthetic patellar thickness and anterior femoral surface on limiting flexion in total knee arthroplasty.
J Holtgrew et al. Trans. Orthop. Res. Socl. Vol 14. 1989. p 369.
The accuracy of femoral intramedullary guides in total knee arthroplasty.
