- 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
- References:
The significance of an asymmetric extension gap on routine radiographs after total knee replacement: A new sign and its clinical significance.
Influence of a secondary downsizing of the femoral component on the extension gap: a cadaveric study.
Recutting the distal femur to increase maximal knee extension during TKA causes coronal plane laxity in mid-flexion.
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