gms | German Medical Science

Objectives: The objective of this study is to compare in vivo kinematics of posterior cruciate retaining (PCR) total knee arthroplasty (TKA) subjects implanted with one of two consecutive designs of a traditional, off-the-shelf (OTS) TKA or a customized-individually-made (CIM) TKA replicating individual femur and tibia geometries.

Methods: In vivo kinematics for 65 clinically successful patients, 25 CIM-PCR-TKA, 15 OTS-PCR-TKA of a legacy design and 25 OTS-PCR-TKA of a modern design, both currently on the market, were assessed using mobile fluoroscopy and 2D-3D registration during weight-bearing deep-knee-bend (DKB), chair-rise, and gait activities.

Results and Conclusion: During DKB, CIM patients experienced 3.99mm of femoral rollback vs. 1.17mm (p=0.05 vs CIM) and 2.06mm (p=0.129) for the legacy and modern design OTS subjects respectively. The CIM-TKA's demonstrated 6.25° of axial rotation compared to 4.41 (p=0.35) and 1.54° (p=0.005) for the legacy and modern design OTS-PCR-TKAs. On average, CIM subjects experienced similar weight-bearing flexion to the modern design OTS-TKA (103°vs105°), compared to 95° for legacy design OTS-TKA subjects.

During DKB, CIM subjects experienced greater lateral condyle femoral rollback and axial rotation. OTS subjects experienced entirely external femoral rotation, different from normal knee motion, whereas CIM subjects experienced a change from internal to external rotation throughout the DKB, consistent with normal knee motion. Additionally, patients with a CIM-TKA experienced significantly higher rollback than the legacy design and higher rotation than the modern design.

While kinematic variability was observed between subjects in all the groups, the CIM-PCR-TKA subjects demonstrate kinematics patterns more closely resembling the normal knee.