Differences in patellar tracking and knee kinematics among three different total knee designs

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device design

Background:

• Patellar complications are a leading cause of revision surgery for condylar-type knee replacement designs.
• Understanding patellar tracking is crucial for improving knee implant longevity and patient outcomes.

Purpose of the Study:

• To compare the patellar tracking of three different knee implant designs: Genesis II, NexGen, and P.F.C. Sigma.
• To evaluate how the trochlear groove curvature of these implants affects patellar kinematics.

Main Methods:

• Utilized nine unembalmed cadaveric lower extremities for testing.
• Applied simulated muscle loads to dissected quadriceps and hamstrings.
• Measured three-dimensional patellofemoral and tibiofemoral joint kinematics using a 3Space tracking system.
• Implanted each of the three knee prostheses sequentially onto the same cadaveric knees to control for soft tissue variations.

Main Results:

• No significant differences were observed in patellar rotation or lateral shift between the intact knees and the implanted prostheses.
• All three implant designs exhibited a significant increase in lateral patellar tilt compared to the intact native knee.
• At 60 degrees of flexion, lateral tilt increased from 0.44° in native knees to approximately 4.8° across the tested implants.
• Patellar displacement relative to the groove center remained comparable between native and resurfaced patellae.

Conclusions:

• The tested knee implant designs (Genesis II, NexGen, P.F.C. Sigma) demonstrate similar kinematic behavior to intact knees regarding rotation and lateral shift.
• A significant increase in lateral patellar tilt is a common characteristic across these prosthetic designs.
• Further modifications to implant geometry may be necessary to reduce excessive patellar tilt and potentially mitigate complications.