Abstract
Introduction
Previous fluoroscopic studies of total knee arthroplasty (TKA) have revealed significant kinematic differences compared to the normal knee. Often, subjects having a TKA experienced kinematic patterns opposite of the normal knee. Therefore, the objective of this study was to determine the in vivo kinematics of subjects implanted with either a customized-individual-made (CIM) or the traditional (OTS) PS TKA to determine if customization offers a distinct advantage to the patient.
Methods
In-vivo kinematics were determined for 33 subjects, 15 having a CIM-TKA and 18 having OTS-TKA using a mobile fluoroscopic system and a 3D–2D registration technique. All of the subjects were implanted by a single surgeon and were scored to be clinically successful. Each subject underwent fluoroscopic observation while performing a weight-bearing (WB) deep knee bend (DKB) and chair rise (CR). The two groups were then compared for the range of motion, condyle translation, and axial rotation.
Results
During the DKB, subjects having CIM-TKA demonstrated on average 112° of WB flexion compared to 94° of WB flexion for subjects having the OTS-TKA design. The CIM-TKA subjects experienced an average −11.7mm (s = 7.1) of lateral condyle posterior femoral rollback (PFR) compared to −4.69mm (s = 3.1) for OST-TKA subjects (Figure 1). All the CIM-TKAs and in 89% of the OTS-TKAs demonstrated PFR. The CIM subjects demonstrated 10.9° (s = 5.1) of axial rotation compared to 7.6° (s = 4.1) for OTS subjects (Figure 2). During extension, The CIM-TKA subjects demonstrated 5.1mm (s = 4.8) of the lateral condyle translation compared to 4.3mm (s = 2.7) for OTS subjects and all CIM-TKA subjects demonstrated anterior roll forward (ARF) versus 83% of OTS subjects. CIM-TKA subjects experienced −7.9° (s = 6.1) axial rotation compared to 8.2° (s = 6.0) for the subjects having OTS-TKA during extension.
Discussion
During both activities, subjects with a CIM-TKA demonstrated a greater average range of motion and higher magnitudes of lateral condyle translation and axial rotation during both flexion and extension compared to OTS-TKA subjects. In addition to greater magnitudes of translation and rotation, the CIM subjects also demonstrated greater percentages of subjects with normal kinematic patterns, although less in magnitude compared to the normal knee. Further studies need be conducted and more subjects added to determine if the trends seen in this study are representative of a larger patient cohort.
Significance
Subjects in this study, having a CIM-TKA demonstrated kinematic patterns and greater magnitudes of motion compared to subjects with an OTS-TKA.
For any figures or tables, please contact the authors directly.
