gms | German Medical Science

Objectives: Recently, patient specific posterior cruciate retaining (PCR) total knee arthroplasty (TKA) have been individually made replicating the patient's femur and tibia geometry. The objective of this study was to determine the in vivo kinematics for subjects having a either a traditional, off-the-shelf (OTS) TKA or a customized, individually made (CIM) TKA.

Methods: In vivo kinematics for 108 subjects, 44 having the CIM-PCR-TKA and 64 having one of three standard OTS-PCR-TKA designs, were assessed. A mobile fluoroscopic system was used to observe subjects during a weight-bearing deep knee bend (DKB), Chair Rise and Normal Gait. All the subjects were implanted by one of two surgeons and were considered clinically successful (HSS Score>90).

Results and Conclusion: During the DKB, CIM-TKA subjects experienced -3.3 (-5.0 to -14.3 SD=2.8) mm of lateral condyle posterior femoral rollback (PFR) compared to -2.6 (2.4 to -9.7 SD=3.1) mm, -0.7 (6.0 to -6.5 SD=3.6) mm and -1.2 (5.7 to -8.1 SD=3.9) for subjects having the three OTS-TKA designs. Subjects having a CIM-TKA achieved 105° of weight-bearing knee flexion, while subjects having an OTS-TKA achieved 100°, 97° and 102°, respectively. These trends were similar during Chair Rise.

All CIM-TKA subjects experienced directionally normal posterior femoral rollback patterns of the lateral condyle while 19-28% of OTS-TKA subjects experienced lateral motion paradoxical to the normal knee pattern. In general the CIM-TKA demonstrated a larger range of motion (p=0.05) with translation and rotation patterns more closely resembling the normal knee. CIM-TKAs demonstrated less variability between patients, particularly with respect to condyle translation.