Wheeless' Textbook of Orthopaedics
C.R. Wheeless MD
Wheeless' Textbook of Orthopaedics
- See:
- Flexion Contracture of TKR:
- Flexion Gap:
- Extension Gap:
- Joint Line Position
- Valgus Deformity
- Varus Deformity
- Discussion:
- first: Malalignment should always be corrected first;
- second: soft tissue adjustments which must be made before bone is recut;
- for example, if extension gap is too small (ie knee does not
extend normally), it is vital to release the soft tissue structures
posteriorly (and to remove any osteophytes when present), before
removing more bone;
- also it is important to note that if the extension gap is too small
whether more bone will be removed from the femur or the tibia will
depend on the status of Flexion Gap;
- third: always "normalized" Flexion Gap before extension gap;
- since we must always normalize Flexion Gap first, inserting thicker
tibial implant will stabilize the knee in flexion but will decrease knee in
extension, which is then corrected by recutting distal femur more proximally;
- following the insertion of the trial prosthesis, it may be noted that
gap in flexion and/or extension may be either too small (w/
resultant loss of motion), or too large (w/ resultant instability);
- knee is brought into full extension and lamina spreaders are applied
medially and laterally;
- extension gap must be rectangular in configuration;
- where it is trapezoidal, medial & lateral soft tissues must be balanced;
- bone cuts are not altered in order to create rectangular extension gap;
- distal femoral cut and proximal tibial cut mark the upper and
lower limits of the extension space;
- posterior femoral cut and the proximal tibial cut mark the upper
and lower limits of the flexion space;
- to determine the size of the flexion and extension spaces, knee must
be distracted until Collateral ligaments are tight;
- if reconstructed knee is to be stable, both the flexion & extension
spaces must be filled by prosthesis;
- it is obvious that whenever distal femoral cut is moved proximally,
size of only the extension space is increased;
- whenever the tibia cut is moved distally, however, both the flexion
and the extension spaces are increased;
- flexion space is bounded by the resected surfaces of the posterior
distal femur and proximal tibia;
- extension space is defined by the resected surfaces of distal femur
and proximal tibia;
- flexion and extension spaces should be equal in size;
- excessive laxity that cannot be corrected by insertion of larger tibial
component or ligament advancement must be managed by a more
constrained prosthesis;
- this is often the case in knees with severe valgus & incompetent medial
Collateral ligaments;
---------------------------------------------------------------------------
Extension Flexion Problem
loose varus or valgus same tibial malposition
tight loose varus or valgus femoral malroation
tight loose varus and valgus joint line malposition
----------------------------------------------------------------------------
- Residual Tightness in Flexion and Extension:
- where tightness persists in both positions with the 8 mm tibial trial,
it is recommended that the tibial cut be revised;
- additional 2 mm are removed by returning the Steinmann pins to their
original holes in the anterior cortex and repositioning the tibial
cutting block using the holes designated +2;
- Residual Tightness:
- where tension is correct in extension but tight in flexion, and
appropriate soft tissue releases have been performed, 5 deg
Posterior Slope is created on the tibial plateau;
- steinmann pins are returned to their original holes in anterior cortex
and the 5 deg cutting block positioned on the pins, using the
hole designated 0 deg;
- tibia is most likely to sublux or dislocate in flexion as a result of
Flexion Gap that is larger & more lax than extension gap;
- 3 common causes of AP instability in PCL sacrificing arthroplasty;
- collateral ligament laxity in flexion (mismatched gaps)
- Collateral ligaments are lax in flexion due to removing excess bone
from femoral condyles, rendering ligaments functionally lax by
increasing the size of the Flexion Gap relative to extension gap;
- patellar dislocation;
- prior patellectomy;
- See:
- Flexion Contracture of TKR:
- Flexion Gap:
- Extension Gap:
- Joint Line Position
- Valgus Deformity
- Varus Deformity
- Discussion:
- first: Malalignment should always be corrected first;
- second: soft tissue adjustments which must be made before bone is recut;
- for example, if extension gap is too small (ie knee does not
extend normally), it is vital to release the soft tissue structures
posteriorly (and to remove any osteophytes when present), before
removing more bone;
- also it is important to note that if the extension gap is too small
whether more bone will be removed from the femur or the tibia will
depend on the status of Flexion Gap;
- third: always "normalized" Flexion Gap before extension gap;
- since we must always normalize Flexion Gap first, inserting thicker
tibial implant will stabilize the knee in flexion but will decrease knee in
extension, which is then corrected by recutting distal femur more proximally;
- following the insertion of the trial prosthesis, it may be noted that
gap in flexion and/or extension may be either too small (w/
resultant loss of motion), or too large (w/ resultant instability);
- knee is brought into full extension and lamina spreaders are applied
medially and laterally;
- extension gap must be rectangular in configuration;
- where it is trapezoidal, medial & lateral soft tissues must be balanced;
- bone cuts are not altered in order to create rectangular extension gap;
- distal femoral cut and proximal tibial cut mark the upper and
lower limits of the extension space;
- posterior femoral cut and the proximal tibial cut mark the upper
and lower limits of the flexion space;
- to determine the size of the flexion and extension spaces, knee must
be distracted until Collateral ligaments are tight;
- if reconstructed knee is to be stable, both the flexion & extension
spaces must be filled by prosthesis;
- it is obvious that whenever distal femoral cut is moved proximally,
size of only the extension space is increased;
- whenever the tibia cut is moved distally, however, both the flexion
and the extension spaces are increased;
- flexion space is bounded by the resected surfaces of the posterior
distal femur and proximal tibia;
- extension space is defined by the resected surfaces of distal femur
and proximal tibia;
- flexion and extension spaces should be equal in size;
- excessive laxity that cannot be corrected by insertion of larger tibial
component or ligament advancement must be managed by a more
constrained prosthesis;
- this is often the case in knees with severe valgus & incompetent medial
Collateral ligaments;
---------------------------------------------------------------------------
Extension Flexion Problem
loose varus or valgus same tibial malposition
tight loose varus or valgus femoral malroation
tight loose varus and valgus joint line malposition
----------------------------------------------------------------------------
- Residual Tightness in Flexion and Extension:
- where tightness persists in both positions with the 8 mm tibial trial,
it is recommended that the tibial cut be revised;
- additional 2 mm are removed by returning the Steinmann pins to their
original holes in the anterior cortex and repositioning the tibial
cutting block using the holes designated +2;
- Residual Tightness:
- where tension is correct in extension but tight in flexion, and
appropriate soft tissue releases have been performed, 5 deg
Posterior Slope is created on the tibial plateau;
- steinmann pins are returned to their original holes in anterior cortex
and the 5 deg cutting block positioned on the pins, using the
hole designated 0 deg;
- tibia is most likely to sublux or dislocate in flexion as a result of
Flexion Gap that is larger & more lax than extension gap;
- 3 common causes of AP instability in PCL sacrificing arthroplasty;
- collateral ligament laxity in flexion (mismatched gaps)
- Collateral ligaments are lax in flexion due to removing excess bone
from femoral condyles, rendering ligaments functionally lax by
increasing the size of the Flexion Gap relative to extension gap;
- patellar dislocation;
- prior patellectomy;