Abstract
Introduction
Recently, a mobile-fluoroscopy unit was developed which can capture subjects performing unconstrained motions, more accurately replicating everyday demands that patients place on their TKA. The objective of this study was to analyze normal knee and various TKA while subjects perform both traditional and more challenging activities while under surveillance of a mobile fluoroscopy unit.
Methods
Two hundred and seventy-five knees were evaluated using mobile fluoroscopy, which tracks the patient and the joint of interest as they perform a set of activities. Mobile fluoroscopic surveillance was used to investigate patients with customized TKA and off the shelf TKA as well as subjects with posterior stabilized (PS) or posterior cruciate retaining (PCR) TKAs while performing the following activities: (1) deep knee bend, (2) chair-rise, (3) walking up and down steps, (4) normal walking, and/or (5) walking up and down a ramp (Figure 1). The mobile fluoroscopic unit captures images at 60 Hz using a flat panel X-ray detector and the unit follows the patient, using a marker-less system, while the patients perform each activity. Each video was digitized and analyzed to determine the 3D kinematics.
Results
During more traditional activities, such as a deep knee bend (DKB) and chair-rise (CR), subjects having a customized PCR TKA experienced between 1.2 to 4.5 mm of more lateral condyle posterior femoral rollback (PFR) during a DKB compared to two traditional PCR TKAs, and 1.8 to 4.6 mm of more condylar roll forward during a CR, compared to two traditional TKAs. Interestingly, subjects having a single radius PCR TKA did experience more axial rotation than subjects having a multi-radius PCR TKA or a customized PCR TKA, but subjects having an asymmetric PCR TKA did experience a high incidence of reverse axial rotation. During more challenging activities such as walking up and down stairs and up and down a ramp, subjects having an asymmetric PCR TKA did experience greater sliding of their femoral component, more variability in AP positioning, and the femoral component experienced a higher angular orientation throughout the activity, compared to the other TKA designs. Subjects having a PS TKA did achieve greater rollback of their lateral condyle during a deep knee bend than the PCR TKA, but similar magnitudes of weight-bearing knee flexion.
Discussion
In this present study, using a mobile fluoroscopy unit, it was determined that subjects having a TKA experienced different kinematic patterns than previously seen with stationary fluoroscopy, especially with respect to axial rotation as some TKA designs revealed a higher incidence of reverse axial rotation. While using a mobile fluoroscopy unit, we were able to assess in vivo kinematics while walking up and down stairs and a ramp, which did reveal higher magnitudes of femoral sliding, possibly due to the patient's ability to perform these activities in a less constrained environment. Mobile fluoroscopy has proven to be a very valuable tool for assessing a patients “true” motion patterns.
