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TKR: Soft Tissue Balance and Collateral Ligaments

- See:
      - TKR Menu:
      - Medial Collateral Ligament
      - Lateral Collateral Ligament

- Discussion:
    - it is not possible to make a definitive assessment of soft tissue deformity or contracture preoperatively, since joint deformity pain &
             muscle spasm can mask the true condition;
            - osteophytes on the tibia (esp in posteromedial & posterolateral corners & on tibial spines) can prevent proper positioning of knee, 
                   leading to false impression of knee contracture or fixed soft tissue deformity;
    - once distal femur and proximal tibia have been resected, alignment can be more accurately assessed;
    - final alignment is determined by soft tissue balancing;
    - when inserted w/ trial femoral componenet it is possible to judge need for medial or lateral release by difficulty encountered in the 
           insertion of the trial tibia component;
    - after bone cuts have been made at right angles to mechanical axis, and after tension is appropriate on medial and lateral sides of joint, 
            the proper tibial polyethylene component size is apparent and a neutral mechanical alignment of the limb is achieved;
    - if this position is not obtained, then additional thin slivers of bone should be removed from the proximal tibia until correct extension is achieved;

- Collateral ligaments:
    - in severe varus or valgus deformity ligament on convexity is stretched as the tibio femoral angle increases, while opposite collateral ligament contracts;
    - valgus deformity:
            - in valgus knee, ligament balancing is more difficult to fix;
            - usually anatomic deformity is larger in Valgus than in varus, & it is on the femoral side;
            - one may have an atrophic lateral femoral condyle, and it is worn away on the distal surface and posterior surface;
            - posteriorly the knee may be really worn, and aligning the knee in a standard fashion will put femoral component in internal rotation;
            - answer is to line the cutting guides up w/ anterior/posterior axis or with the epicondyles, never with the posterior condyles;
            - rotational positioning of femoral component is important, for medial and lateral stability in both flexion and extension;
            - soft tissues are stripped from upper portion of lateral tibia, & iliotibial band is transected from within the joint;
            - if necessary, origin of LCL is stripped from lateral femoral condyle & popliteus is divided;
            - rarely, release of lataeral head of gastrocnemius & lengthening of biceps femoris tendon will be necessary;
    - varus deformity:
            - in varus deformities contracted soft tissues on medial side of thejoint are released by stripping from proximal tibia pes anserinus,
                   joint capsule, tibial collateral ligament, & esp tight posteromedial portion of joint capsule;
            - if necessary PCL can be released, in which case more posteriorly stabilized implant may be needed;
            - since these soft tissues are stripped from the bone rather than transected, they remain as an intact soft tissue tube and require no fixation to bone

The effect of postoperative collateral ligament laxity in total knee arthroplasty.