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Comparative Study
. 2025 Jul;33(7):2527-2536.
doi: 10.1002/ksa.12624. Epub 2025 Feb 13.

Improved quadriceps efficiency with a medial pivot in comparison to a cruciate-retaining design in total knee arthroplasty

Leandra Bauer  1   2 , Thomas R Niethammer  1 , Christoph Thorwächter  1 , Matthias Woiczinski  1   2 , Peter E Müller  1 , Florian Simon  3 , Boris M Holzapfel  1 , Johanna-Maria Simon  1
Affiliations
Comparative Study

Improved quadriceps efficiency with a medial pivot in comparison to a cruciate-retaining design in total knee arthroplasty

Leandra Bauer et al. Knee Surg Sports Traumatol Arthrosc. 2025 Jul.

Abstract

Purpose: The posterior cruciate-retaining (CR) design offers rotational freedom but risks abnormal kinematics and instability. The medial pivot (MP) design mimics native joint motion with a high-conformity medial and flat lateral interface. Within clinical studies, the MP design outclassed the CR design, but biomechanical studies are lacking. This study investigates the tibiofemoral and patellofemoral kinematics of both implant designs compared to native kinematics.

Methods: Eight fresh-frozen cadaveric knee specimens underwent total knee arthroplasty using MP and CR designs. Testing was performed in a dynamic knee rig simulating active knee flexion (30-130°) under muscle load. Biomechanical assessments included tibial rotation, tibiofemoral translation, patellar tilt/shift, patellofemoral contact/pressure patterns and quadriceps force. Functional regressions were used to analyse the effects of the component designs on the native situation.

Results: The MP design exhibited increased tibial rotation (130° flexion: MP 9.4° vs. CR 6.6°) and lateral anterior tibial translation during flexion (130° flexion: MP 25.8 mm vs. CR 22.6 mm). Both designs showed no significant differences in patellar tilt or shift and similar patellofemoral pressure (CR 3.2 MPa, MP 3.4 MPa) and contact patterns (CR 213.8 mm2 vs. MP 230.4 mm2). The MP design required lower quadriceps force, particularly in deep flexion (NS 452.6 N, CR 407.8 N and MP 367.3 N).

Conclusion: The MP design provides a more native-like knee kinematic profile than the CR design, with a more pronounced MP motion pattern and reduced quadriceps loading.

Level of evidence: Not applicable.

Keywords: cruciate retaining; knee rig; medial pivot; medial stabilized; total knee arthroplasty.

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Conflict of interest statement

Peter E. Müller is a consultant for the Medacta shoulder system and B. Braun Aesculap; this in no way influenced the results of this study. The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
(a) MP TKA (Medacta GMK Sphere) (with permission of Medacta International, Castel San Pietro, Switzerland). (b) CR TKA (Medacta GMK Primary) (with permission of Medacta International, Castel San Pietro, Switzerland). CR, cruciate retaining; MP, medial pivot; TKA, total knee arthroplasty.
Figure 2
Figure 2
Femorotibial kinematics with (a) AP translation medial; (b) difference to NS for AP translation medial; (c) AP translation lateral; (d) difference to NS for AP translation medial; (e) tibial rotation and (f) difference to NS for tibial rotation; mean and 95% confidence interval for CR design (orange), MP design (blue) and native situation (black). AP, anterior‐posterior; CR, cruciate retaining; NS, native situation/state; TKA, total knee arthroplasty.
Figure 3
Figure 3
Mean rotation point of femur on tibia plateau for (a) CR design (35–75°; 75–115° flexion) and (b) MP design (35–75°; 75–115° flexion). CR, cruciate retaining; MP, medial pivot.
Figure 4
Figure 4
Patellofemoral kinematics for (a) patella shift, (b) difference to NS for patella shift, (c) patella tilt and (d) difference to NS for patella tilt; mean and 95% confidence interval for CR design (orange), MP design (blue) and NS (black). CR, cruciate retaining; MP, medial pivot; NS, native situation/state.
Figure 5
Figure 5
Knee joint loading represented by peak pressure (a), contact area (b) and quadriceps force (c) for CR design (orange), MP design (blue) and native situation (black) with mean and 95% confidence interval. CR, cruciate retaining; MP, medial pivot.
See this image and copyright information in PMC

References

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