Wheeless' Textbook of Orthopaedics
C.R. Wheeless MD
Wheeless' Textbook of Orthopaedics
- Definition:
- is space between the posterior coronal cut on the distal femur &
transverse cut on the proximal tibia, while knee is in flexion;
- Small Flexion Gap:
- causes of incomplete knee flexion are:
- tibial cut that is too proximal (w/ or w/o a Posterior Slope);
- an anterior femoral coronal cut which is inadequate, ie too anterior
- patellar cut which is inadequate (too superficial) with a
resultant increase in total patellar thickness (bone and implant);
- if the knee cannot flex normally and is unstable in extension there is
situation in which the gap problems are diametrically opposed;
- this is due to surgeon error;
- if the knee cannot fully flex but extends normally;
- verify ROM with the patella reduced;
- either the Posterior Slope is inadequate, the patella is too thick,
or the anterior cut is too anteior;
- if knee cannot fully flex nor extend, then recutting the tibia more
proximally will correct the problem;
- Large Flexion Gap (unstable in flexion)
- may be due to a tibial cut which is too distal
- posterior femoral coronal cut which was too anterior;
(ie removing too much posteior femoral condyle);
- if extension gap is also too small, then solution is to recut the femur more
proximally;
- if extension gap is normal (extends normally and is stable in extension)
- if instability is mild, then accept the deformity;
- if instability in flexion is gross, it should be corrected by
inserting a thicker tibial component, & resultant loss of extension
is then corrected by recutting the distal femor more proximally;
- flexion space may be larger than the extension space;
- this most commonly occurs after release of large fixed varus or valgus
contracture;
- in such a situation the thickness of implant that is required for flexion stability is
too thick in extension and the knee does not fully extend;
- too correct this it is necessary to resect an additional amount of
distal femur to equalize the spaces;
- one should not increase the size of the extension space by a resection
of the distal femur since this would concomitantly increases the
flexion space, perpetuating the problem;
- flexion space may be smaller than the extension space;
- this may happen if too much distal femur is resected (which is almost
always due to a surgical error in the use of distal femoral cutting jig;)
- correction of this problem consists of either resecting more posterior
femur (and here you are limited by the actual size of posterior
femur and the presence of posterior femoral cortex) or of adding
bone grafts to distal femur to decrease extension space;
- neither of these options works well;
- increased flexion gap (loose in flexion & tight in extension) is more
common and can be corrected by resecting more of the distal femur;
- increased extension gap (loose in extension & tight in flexion) is
usually the result of a technical error and can be corrected by
resecting posterior femoral condyles or converting the flat tibial
surface to posteriorly sloping surface;
- when the knee is tight in both flexion and extension, more proximal
tibia should be resected;
- when knee is tight in both flexion extension, and more proximal tibia
should be resection;
- patellar height can also result in tight flexion and may require
additional patellar resection;
- w/ extension gap is adequate, but flexion gap is too narrow:
- resecting additional distal femur will increase extension gap while
preserving the flexion gap, resulting in excessive laxity in full extension;
- resecting more proximal tibia will increase the extension and flexion gaps
simultaneously & will also result in excessive laxity in full extension.
- relying on fixation to correct problems as a result of malposition
of components will eventually result in loosening of the implant
and should be avoided.
- by increasing the posterior inclination of the proximal tibial
resection, femoral rollback is facilitated, effectively
increasing the flexion gap - extension gap is unaffected;
- Definition:
- is space between the posterior coronal cut on the distal femur &
transverse cut on the proximal tibia, while knee is in flexion;
- Small Flexion Gap:
- causes of incomplete knee flexion are:
- tibial cut that is too proximal (w/ or w/o a Posterior Slope);
- an anterior femoral coronal cut which is inadequate, ie too anterior
- patellar cut which is inadequate (too superficial) with a
resultant increase in total patellar thickness (bone and implant);
- if the knee cannot flex normally and is unstable in extension there is
situation in which the gap problems are diametrically opposed;
- this is due to surgeon error;
- if the knee cannot fully flex but extends normally;
- verify ROM with the patella reduced;
- either the Posterior Slope is inadequate, the patella is too thick,
or the anterior cut is too anteior;
- if knee cannot fully flex nor extend, then recutting the tibia more
proximally will correct the problem;
- Large Flexion Gap (unstable in flexion)
- may be due to a tibial cut which is too distal
- posterior femoral coronal cut which was too anterior;
(ie removing too much posteior femoral condyle);
- if extension gap is also too small, then solution is to recut the femur more
proximally;
- if extension gap is normal (extends normally and is stable in extension)
- if instability is mild, then accept the deformity;
- if instability in flexion is gross, it should be corrected by
inserting a thicker tibial component, & resultant loss of extension
is then corrected by recutting the distal femor more proximally;
- flexion space may be larger than the extension space;
- this most commonly occurs after release of large fixed varus or valgus
contracture;
- in such a situation the thickness of implant that is required for flexion stability is
too thick in extension and the knee does not fully extend;
- too correct this it is necessary to resect an additional amount of
distal femur to equalize the spaces;
- one should not increase the size of the extension space by a resection
of the distal femur since this would concomitantly increases the
flexion space, perpetuating the problem;
- flexion space may be smaller than the extension space;
- this may happen if too much distal femur is resected (which is almost
always due to a surgical error in the use of distal femoral cutting jig;)
- correction of this problem consists of either resecting more posterior
femur (and here you are limited by the actual size of posterior
femur and the presence of posterior femoral cortex) or of adding
bone grafts to distal femur to decrease extension space;
- neither of these options works well;
- increased flexion gap (loose in flexion & tight in extension) is more
common and can be corrected by resecting more of the distal femur;
- increased extension gap (loose in extension & tight in flexion) is
usually the result of a technical error and can be corrected by
resecting posterior femoral condyles or converting the flat tibial
surface to posteriorly sloping surface;
- when the knee is tight in both flexion and extension, more proximal
tibia should be resected;
- when knee is tight in both flexion extension, and more proximal tibia
should be resection;
- patellar height can also result in tight flexion and may require
additional patellar resection;
- w/ extension gap is adequate, but flexion gap is too narrow:
- resecting additional distal femur will increase extension gap while
preserving the flexion gap, resulting in excessive laxity in full extension;
- resecting more proximal tibia will increase the extension and flexion gaps
simultaneously & will also result in excessive laxity in full extension.
- relying on fixation to correct problems as a result of malposition
of components will eventually result in loosening of the implant
and should be avoided.
- by increasing the posterior inclination of the proximal tibial
resection, femoral rollback is facilitated, effectively
increasing the flexion gap - extension gap is unaffected;