Study: In vivo kinematic comparison between an ultra-congrue
The aim of the present study was to compare the in vivo under weight-bearing kinematic behavior of a posterior-stabilized (PS) and an ultra-congruent (UC) total knee arthroplasty (TKA) model during a sit-to-stand motor task, a common activity of daily life.

A cohort of 16 randomly selected patients was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9 months after TKA, during the execution of a sit-to-stand. The anteroposterior (AP) translation of the femoral component and the AP translation of the low point of medial and lateral femoral compartments were compared through Student’s t test.

Results:
--A significantly greater anterior translation of the femoral component was found for the PS group compared to the UC group.

--The flexion interval where statistical significance was found was between 30° and 0°.

--Both groups showed a significantly greater anterior translation of the low point of the lateral compartment with respect to the medial one. This was consistent with a medial-pivot pattern.

--Furthermore, a significantly greater anterior translation of the medial compartment was found in the PS group compared to the UC group. The same pattern was observed for the lateral compartment.

Finally, in the present investigation, the TKA designs assessed revealed similar in vivo kinematics for the medial pivotal pattern, but with variances in the absolute translation of AP. In particular, more AP stability was shown by the UC design than the PS design. This could be favorable for the stability of implants, but negative for premature wear of polyethylene and therefore for implant failure.

Source: https://link.springer.com/article/10.1007/s00167-021-06629-1
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