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TKR: Effects of Component Rotation

- Discussion:
    - if there is free movement at hip, subtalar & mid-tarsal joints rotation at the knee is not essential for restricted function of prosthetic joint;
           - in contrast, an arthrodesed ipsilateral hip is a relative contra indication to knee replacement, for it prevents rotation of thigh as well as changing
                   position of center of gravity of body;

- Prosthetic Design:
    - rotation of the femoral component:
    - rotation of tibial component:
    - need for component rotation:
           - in constrained components which eliminate rotation, aseptic loosening of components is the most common complication;
           - increased loosening forces created at limit of extension & lateral bending w/ constrained prosthesis result in higher rates of mechanical 
                     loosening of components;
    - rotation can be designed into the knee prosthesis by using a smaller radius of curvature for femoral component;
           - this will reduce the area of contact with the more open tibial surface, but will also increase joint pressure and wear;
    - in the report by Barrack et al, the authors sought to correlate anterior knee pain with TKR component malrotation;
           - significant anterior knee pain rating at least 3 of 10 on the visual analog scale was present in 16 knees (13 patients);
           - 11 patients with 14 symptomatic knees agreed to undergo CT scanning to accurately determine the rotation of the tibial and femoral components;
           - epicondylar axis and tibial tubercle were used as references using a previously validated technique;
           - there was a highly significant difference in tibial component rotation between the two groups w/ the patients w/ anterior knee pain averaging 6.2°
                   internal rotation compared with 0.4° external rotation in the control group;
           - there also was a significant difference in combined component rotation with the patients w/ anterior knee pain avg 4.7° internal rotation compared
                   with 2.6° external rotation in the control group;
           - there was no significant difference in the degree of radiographic patellar tilt or patellar subluxation between the two groups;
           - patients with combined component internal rotation were more than five times as likely to experience anterior knee pain after TKA compared
                   with those with combined component external rotation
           - ref: Component Rotation and Anterior Knee Pain After Total Knee Arthroplasty 

Effect of rotation on the axial alignment of the femur. Pitfalls in  the use of femoral intramedullary guides in total knee arthroplasty.

Varus-valgus and rotational stability in rotationally unconstrained  total knee arthroplasty.

Internal rotational error of the tibial component is a major cause of pain after total knee replacement

The effect of femoral component rotation on the kinematics of the tibiofemoral and patellofemoral joints after total knee arthroplasty.

Total Knee Arthroplasty Malalignment: Myth or Reality?