Purpose

To compare the in-vivo under weight-bearing kinematic behavior of a posterior-stabilized (PS) and of an ultra-congruent (UC) total knee arthroplasty (TKA) during a sit-to-stand motor task.
The hypothesis was that UC and PS designs would present a comparable kinematics.

Methods

A cohort of 16 randomly selected patients (8 PS Persona Zimmer, 8 UC Persona Zimmer; mean age 70.0 ± 7.3 years old) was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9 months after TKA, during the execution of a sit-to-stand motor task. The anteroposterior (AP) translation of the femoral component and the AP translation of the Low Point (tibio-femoral contact point) of medial and lateral femoral compartments were compared through Student’s t test (p < 0.05).

Results

A significantly greater anterior translation of the femoral component was found for the PS group compared to the UC group, mainly to almost complete extension (p=0.017). Both groups showed a significantly greater anterior translation of the Low Point of the lateral compartment with respect to the medial one (PS: p=0.0117, UC: p= 0.0181). This was consistent with a medial-pivot pattern. Furthermore, a comparison of the anterior translation of the medial compartment between the PS group and the UC group was statistically significant and showed a greater excursion in the PS group (p= 0.001). The same pattern was observed for the lateral compartment (p=0.0065).

Conclusions

The TKA designs evaluated in the present study by dynamic RSA showed comparable in-vivo kinematics in terms of medial pivot pattern, but differences in terms of absolute AP translation.