Abstract
Previosuly, Komistek et al. have shown that the kinematics of the patellofemoral joint is altered after a TKA surgery. Specifically the implanted patella experiences significantly less rotation than the natural patella. Also, in early flexion, the patellofemoral contact positions differed significantly between implanted and non-implanted patellae. It was also found that some of TKA subjects experience patellofemoral separation. These kinematical differences may lead to adverse mechanical conditions and increase fatigue or cause loosening of the implant components. This study’s objective was to determine the three-dimensional patellofemoral kinematics and correlate it with the in vivo sound (vibrations) detected using accelerometers for subjects having a TKA and a non-implanted knee under in vivo, weight bearing conditions. The correlation of the knee mechanical conditions with the vibration data may indicate new parameters that may be used to diagnose the condition of the articular cartilage or implant components.
Fifteen subjects (average age 71.8 ±7.4years) having one implanted knee (mobile bearing Hi-Flex PS) and the healthy contralateral knee, performed
-
deep knee bend to maximum flexion,
-
chair rise and
-
stair climb activities under fluoroscopic surveillance.
Three miniature, piezoelectric, three-axial accelerometers were attached to the patella and femoral epicondyle. The study was approved by the Institutional Review Board and informed consent was obtained from all subjects. The sensors detected the vibration magnitudes and frequencies of the articulating patellofemoral joint surfaces. The signals were amplified and low-pass filtered at 5 kHz by a signal conditioner. The 3D tibiofemoral and patellofemoral kinematics were derived for both knees using a previously published 3D-to-2D registration technique. The 3D bone models were recovered from CT scans, while implant models were obtained from the manufacturer. The patellofemoral rotations were described using the Grood and Suntay convention. The kinematics and sound data were synchronized and recorded under fluoroscopic surveillance, for 10 patients. Then a subset of seven subjects having a TKA was re-analyzed for their contralateral (non-implanted) knee. The vibration signal was then converted to audible sound and correlated with the 3D kinematics.
On average, the subjects achieved more flexion with their TKA (103.4°±15.9°) than with their contralateral knee (96.3°±18.3°). The patellofemoral kinematics varied between the TKA and nonimplanted patella groups; the resurfaced patella experienced less flexion, less medial rotation and less tilt than the contralateral patella. The patellar flexion results were consistent with previously reported literature for both TKA and non-implanted patellae. Also, the resurfaced patellae contacted the femur more proximally than healthy patellae. Audible signals were found for both groups of subjects. The frequency analysis demonstrated that specific frequencies were in similar range for both groups, but the magnitudes and variations were different for the TKA and contralateral knees.
This study correlated 3D patellofemoral kinematics with sound under in vivo conditions for three different activities. Variable audible signals were detected for TKA and non-implanted knees. Vibration magnitude and frequency identification, under in vivo conditions, for TKA may lead to a better understanding of wear and failure modes with respect to the patellofemoral mechanics, more specifically, the patellar insert. Currently this initial study is being expanded to degenerated knee joints and failed TKAs for possible applications of the vibration analysis to the early diagnosis of knee arthritis, detection of implant loosening or wear and monitoring of implant osteointegration progress.
Correspondence should be addressed to Diane Przepiorski at ISTA, PO Box 6564, Auburn, CA 95604, USA. Phone: +1 916-454-9884; Fax: +1 916-454-9882; E-mail: ista@pacbell.net
