- See:
-
Total Knee Replacement Menu:
-
Axial Alignment:
-
Kinematics of the Knee Joint:
-
Metallurgy: TKR
-
Rotation of TKR:
-
Unconstrained Prosthesis:
- Discussion:
- inability to achieve precise alignment will ultimately lead to component loosening, the leading cause of TKA failure;
- designs with greater conformity between the femoral & tibial components tend to provide greater inherent stability;
-
requirements for TKR:
- axis of rotation: 15 - 20 deg
- medial-lateral motion of 5 -10 degrees;
-
flexion requirements:
- 65 degrees of flexion is required to walk at a normal pace
- 95 degrees of flexion to walk up and down stairs;
- 110 degrees is required to arise from chair;
-
femoral roll back:
- as knee flexes, femur rolls back on tibia, increasing potential for further flexion by preventing posterior structures from impinging;
- rollback increases the length of quadriceps moment-arm;
- if femoral roll back is not designed in prosthetic knee, effective strength of quadriceps is reduced by about 30%;
- w/ posterior cruciate sacrificing TKR, the posterior projection of
femoral condyle should, ideally, be as large as possible;
-
PCL retaining vs posterior stabilized prosthesis:
-
Posterior stabilized prosthesis
-
PCL retaining prosthesis:
-
effect of constraint on TKR:
-
unconstrained prosthesis:
-
semiconstrained prosthesis:
- may be used for knees w/
flexion contractures of up to 45 deg and angular deformities of 20 to 25 deg;
- these types of components have a more conforming articulation and the contact area remains the same throughout knee motion;
- theoretically there is minimal roll back with knee flexion;
- in many semiconstrained components, the saggital radius of the component is constant, and therefore knee flexion
would be expected to be limited to 120 deg;
-
IB2
- basic Insall Burstein Knee is modification of original modification of original total condylar design;
- problems w/ IB1 include poor stair climbing ability (only 22%);
-
total constrained prosthesis:
- these implants all restrict normal knee motion in one or more planes;
- stresses are high on implant & at implant-cement & bone-cement interfaces;
- higher incidence of loosening, breakage, and excessive wear;
- aseptic loosening of the components is most common complication;
- are more prone to wear from cement & polyethylene polyethylene particles;
Evaluation of the Noiles hinged knee prosthesis. A five-year study of seventeen knees.
Adventures in mobile bearing knee design: A mid life crisis.
JN Insall.
Orthopaedics Sep 1988. Vol 21. No 9.
p 1021.
Effects of total knee replacement design on femoral-tibial contact conditions.
Laxity and function in knee replacements. A comparative study of three prosthetic designs.
Optimizing Flexion After Total Knee Arthroplasty: Advances in Prosthetic Design.
Design may be Counterproductive for Optimizing Flexion After TKR.
