- Discussion:
- see
flexion gap
- is space between transverse cut on distal femur & transverse proximal tibial cut while the knee is in complete extension;
- while minor loss of knee flexion or mild instability in flexion can be tolerated, priority is always be given to extension gap adjustments;
- although in terms of sequence of adjustments one must always correct
flexion gap first, extension gap status is functionally more important;
- certain soft tissues such as the
iliotibial band predominately affect the extension gap;
- Extension Gap Too Large:
- resultant instability in extension while the flexion gap may be too small, with resultant loss of flexion;
- may be from excessive ligament lengthening or excessive removal of bone from the femur, the tibia, or both;
- Extension Gap Too Small: loss of extension
- Residual Flexion Contracture (Extension Gap Too Tight)
- w/ trials in place, good flexion is obtained, however full extension is not;
- additional 2 or 4 mm of distal femur are resected;
- distal cut is accordingly revised;
- notch cut and chamfers are subsequently revised to maintain correct configuration, the anterior and posterior cuts are not;
- this maneuver affects ligamentous tension in extension but not in flexion;
- avoid
elevation of joint line:
- few degrees of hyperextension at knee are advantage because this over the center mechanism allows the patient to stand w/ quads relaxed and the knee joint stable;
- extensive hyper-extension makes the leg feel uncomfortable because
posterior capsule is under too much tension;
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