Abstract
Introduction
Many fluoroscopic studies on total knee arthroplasty (TKA) have identified kinematic variabilities compared to the normal knee, with many subjects experiencing paradoxical motion patterns. The intent of this research study was to investigate the results of customized-individual-made (CIM) and off-the-shelf (OTS) PS and PCR TKA to determine kinematic variabilities and to assess these kinematic patterns with those previously documented for the normal knee.
Methods
In vivo kinematics were assessed for 151 subjects – 44 with CIM-PCR, 75 with OTS-PCR, 14 with CIM-PS, and 18 with OTS-PS TKA – using a mobile fluoroscopic system and then evaluated using a 3D-2D registration technique. This was a multicenter evaluation so the group of implants were implanted by two surgeons and selected based on recruitment criteria. Each subject performed a deep knee bend activity (DKB) while under fluoroscopy. The kinematics assessed for each subject were condyle translation (LAP/MAP) and rotation (axial rotation).
Results
During the DKB, the average LAP of the CIM-PCR was −2.0 mm (s = 4.0), the OTS-PCR was −2.1 mm (s = 3.0), the CIM-PS was −9.0 mm (s = 6.0), and the OTS-PS was −4.3 mm (s = 3.3) (Figure 1). The average MAP of the CIM-PCR was 2.0 mm (s = 2.9), the OTS-PCR was 2.4 mm (s = 3.3), the CIM-PS was −1.2 mm (s = 5.2), and the OTS-PS was 1.1 mm (s = 1.7) (Figure 2). The average axial rotation of the CIM-PCR was 4.6° (s = 5.8), the OTS-PCR was 5.7° (s = 4.8), the CIM-PS was 9.3° (s = 4.8), and the OTS-PS was 7.5° (s = 3.5) (Figure 3). Eleven of 44 (25%) subjects having a CIM-PCR TKA, 16/75 (21.3%) subjects having an OTS-PCR TKA experienced an anterior slide of their lateral condyle, while no subjects having a CIM-PS TKA and 3/18 (16.6%) of OTS-PS subjects experienced this slide. Nine of 44 (20.5%) CIM- PCR, 8/75 (10.6%) OTS-PCR experienced a reverse axial rotation pattern, while only one subject having a CIM-PS and not OTS-PS subjects experienced this non-normal rotation pattern.
Discussion
Subjects having a CIM-PS TKA experienced the greatest amount of lateral condyle posterior femoral rollback and axial rotation, although less in magnitude to the normal knee seen in previous fluoroscopic studies. This was the only group to experience posterior motion of their medial condyle during flexion. More subjects having a PCR TKA experienced a paradoxical anterior lateral condyle sliding pattern and reverse axial rotation pattern, which was not commonly seen in the subjects having a PS TKA.
Significance
Subjects that had a CIM-PS TKA demonstrated greater magnitudes of lateral condyle rollback and subjects having a PS TKA experienced more normal axial rotation patterns.
