The Bi-Cruciate Stabilized (BCS) total knee arthroplasty (TKA) incorporates two cam-post mechanisms in order to replicate the functionality and stability provided by the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) in the native knee. Recently (2012), a second generation BCS design has introduced femur and tibial bearing modifications that are intended to delay lateral femoral condyle rollback and encourage more stable positioning of the medial femoral condyle to more closely replicate normal knee kinematics. The purpose of this study was to compare the kinematics of this TKA to the normal knee during a weight bearing flexion activity. In vivo kinematics were derived for 10 normal non-implanted knees and 40 second generation BCS TKAs all implanted by a single surgeon. Computed tomography (CT) scans were obtained for each normal patient, and 3D reconstruction of the femur, tibia/fibula, and patella was performed. Fluoroscopic images were captured at 60 Hz using a mobile fluoroscopic unit that tracked the knee while patients performed a deep knee bend (DKB) from full extension to maximum flexion. A 3D-to-2D image registration technique was used at 30° increments to determine the transformations of the segmented bones or TKA components. The anterior-posterior motion of the lateral femoral condyle contact point (LAP) and the medial femoral condyle contact point (MAP), as well as tibio-femoral axial rotation, were measured at 30° increments from full extension to maximum flexion. Statistical analysis was conducted at the 95% confidence level.Background
Methods
The Bi-Cruciate Stabilized (BCS) total knee arthroplasty (TKA) incorporates two cam-post mechanisms to reproduce the functionality and stability provided by the anterior cruciate ligament and posterior cruciate ligament in the native knee. The anterior cam-post mechanism provides stability in full extension and early flexion (≤20°) while the posterior cam-post mechanism prevents anterior sliding of the femur during deeper flexion (≥60°). Recently (2012), a second generation BCS design introduced more normal shapes to the femur and tibial bearing geometries that provides delayed lateral femoral condyle rollback and encourages more stable positioning of the medial femoral condyle. The purpose of this study was to compare the in vivo kinematics exhibited by the two generations during weight bearing flexion. In vivo kinematics were derived for 126 patients. Eighty-six subjects were implanted with a first generation BCS (BCS 1) TKA and 40 with the second generation BCS (BCS 2) TKA. Fluoroscopic videos were captured for patients while they performed a deep knee bend (DKB) from full extension to maximum flexion. Anterior-posterior motion of the lateral femoral condyle (LAP) and the medial femoral condyle (MAP), as well as tibio-femoral axial rotation, were analyzed at 30° increments from full extension to maximum flexion using a 3D-to-2D image registration technique. Statistical analysis was conducted at the 95% confidence level.Introduction
Methods
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. 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.Introduction
Methods
Stationary fluoroscopy has been a viable resource for determining in vivo knee kinematics, but limitations have restricted the use of this technology. Patients can only perform certain normal daily living activities while using stationary fluoroscopy and must conduct the activities at speeds that are slower than normal to avoid ghosting of the images. More recently, a Mobile Tracking Fluoroscopic (MTF) unit has been developed that can track patients in real-time as he/she performs various activities at normal speeds (Figure 1). Therefore, the objective of this study was to compare in vivo kinematics for patient's evaluated using stationary and mobile fluoroscopy to determine potential advantages and disadvantages for use of these technologies. The MTF is a unique mobile robot that can acquire real-time x-ray records of hip, knee, or ankle joint motion while a subject walks/manoeuvres naturally within a laboratory floor area. By virtue of its mechanizations, test protocols can involve many types of manoeuvres such as chair rises, stair climbing/descending, ramp crossing, walking, etc. Because the subjects are performing such actions naturally, the resulting fluoroscope images reflect the full functionality of their musculoskeletal anatomy. Patients in the study were initially fluoroscoped using a stationary unit and then using the MTF unit.INTRODUCTION:
METHODS:
A Tracking Fluoroscope System (TFS), the first of its kind, has been developed and the design of this new technology has been previously presented. The TFS is a unique mobile robot that can acquire real-time x-ray records of hip, knee, or ankle joint motion while a subject walks/maneuvers naturally within a laboratory floor area. By virtue of its mechanizations, test protocols can involve many types maneuvers such as chair rises, stair climbing/descending, ramp crossing, walking, etc. Because the subjects are performing such actions naturally, the resulting fluoroscope images reflect the full functionality of their musculoskeletal anatomy. The goal of this follow-up study is to conduct a comparative analysis with traditional stationary fluoroscopy units to determine if this new technology does offer clinical and research advantages. Technical trials with human subjects and active fluoroscope operation were designed to evaluate and refine the TFS engineering and operational features. These trials have been completed and the key results were compared with the traditional stationary fluoroscopic units. The technical trials verified that the TFS is ready for actual clinical diagnostic use and provides the researcher an opportunity to evaluate in vivo kinematics of subjects while performing normal daily activities at various speeds. Using the mobile fluoroscopic unit, patients performed activities that were not possible to capture with a stationary unit. Also, with the upgrade to an image recording rate of 60 frames per second, the quality of the fluoroscopic images using the TFS were superior to stationary units. Further analyses are now being conducted to compare the kinematic results for a deep knee bend and gait, traditionally analyzed in the past using stationary fluoroscopic units to determine if there are unique advantages. It is hypothesized that the more normal-like gait patterns may produce kinematic patterns that differ from stationary fluoroscopic units. At present, the TFS has proven to be superior over other fluoroscopic units and will allow clinicians to evaluate patients under and unrestricted kinematic environment. Also, future research studies will be able to compare patients with or without a TKA under more challenging kinematic conditions, producing kinematic patterns that may lead to incites pertaining to TKA failure and/or concerns.
Commercial C-arm fluoroscopes are routinely used to analyze human skeletal joints during motions such as deep knee bends, or chair rises. Such diagnostics are used to characterize pre and post operative arthoplasty results, particularly in association with total joint replacement procedures. Stationary fluoroscopes restrict the patient motion and load conditions, thus diminishing the diagnostic utility of the results. A new class of fluoroscopy has been developed in which a robotic mechanization is used to allow selected joints to be x-rayed while the human subjects perform natural motions such as walking. The tracking fluoroscope system (TFS) is a mobile robot that acquires real-time x-ray records of hip, knee, or ankle joint motion while the patient walks normally. Because the fluoroscope line of sight dynamically tracks the joint of interest, the TFS provides clearer and contained joint images. The technical features of the TFS will be reviewed, recent development testing summarized, and the results of preliminary patient trials presented.
