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Wheeless' Textbook of Orthopaedics

Wheeless' Textbook of Orthopaedics

C.R. Wheeless MD

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Wheeless' Textbook of Orthopaedics

Flexion and Extension Spaces:


- 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;

Flexion and Extension Spaces:


- 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;

 
 
 
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