No kinematical difference between ultra-congruent and medial-congruent total knee arthroplasty when implanted with mechanical alignment: an in vivo dynamic RSA study - Report - MDSpire
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No kinematical difference between ultra-congruent and medial-congruent total knee arthroplasty when implanted with mechanical alignment: an in vivo dynamic RSA study
Kinematic Comparison of Ultra-Congruent vs Medial-Congruent TKA Using Dynamic RSA
Overview
This study compared in vivo knee kinematics of ultra-congruent (UC) and medial-congruent (MC) total knee arthroplasty (TKA) designs using dynamic radiostereometric analysis (RSA). The MC group demonstrated significantly greater range of motion (ROM) than the UC group, while both groups exhibited a medial pivot pattern without differences in antero-posterior translation ranges.
Background
Modern TKA designs aim to replicate native knee kinematics, with ultra-congruent (UC) bearings providing high tibiofemoral conformity for stability but raising concerns about non-physiological rollback and reduced motion. The medial-congruent (MC) design was developed to improve on these issues by allowing medial stability with lateral compartment freedom, theoretically enhancing flexion and reducing impingement. However, in vivo kinematic data under weightbearing conditions comparing these designs have been lacking. This study used dynamic RSA to evaluate and compare the kinematics of UC and MC bearings in patients undergoing mechanically aligned cruciate-retaining TKA.
Data Highlights
Parameter
MC Group (n=8)
UC Group (n=8)
p-value
Mean Age (years)
77.6 ± 2.7
70.9 ± 9.0
>0.05
Range of Motion (degrees)
126°
101°
0.003
VAS Score <= 3
All patients
All patients
Not significant
Medial Compartment AP Translation Range (mm)
Data not significantly different
Data not significantly different
>0.05
Lateral Compartment AP Translation Range (mm)
Data not significantly different
Data not significantly different
>0.05
Medial to Lateral AP Translation Ratio
3.2 ± 2.7
2.3 ± 3.1
Not significant
Key Findings
MC group exhibited significantly greater knee flexion ROM (126°) compared to UC group (101°), p=0.003.
Both UC and MC groups demonstrated a medial pivot kinematic pattern during sit-to-stand movement.
No significant differences were found between UC and MC groups in antero-posterior translation ranges of medial or lateral femoral compartments.
The ratio of medial to lateral compartment AP translation was similar between groups, indicating comparable medial pivot behavior.
No patients reported significant pain (VAS <= 3) at follow-up in either group.
Clinical Implications
The medial-congruent TKA design may offer improved postoperative knee flexion without compromising the medial pivot kinematic pattern compared to the ultra-congruent design. Both designs provide stable antero-posterior femoral translation under weightbearing conditions, supporting their use in mechanically aligned cruciate-retaining TKA. Surgeons may consider the MC design to potentially enhance functional range of motion in appropriate patients.
Conclusion
In vivo dynamic RSA demonstrated that medial-congruent and ultra-congruent TKA designs yield comparable medial pivot kinematics, with the medial-congruent design providing superior knee flexion. These findings support the clinical viability of the medial-congruent bearing as an evolution of the ultra-congruent design.
References
Study Authors/IRCCS Rizzoli Orthopaedic Institute/2024 -- Comparative Kinematic Analysis of Ultra-Congruent and Medial-Congruent Total Knee Arthroplasty Using Mechanical Alignment
