The overall goal of total knee arthroplasty (TKA) is to facilitate the restoration of native function following late stage osteoarthritis and for this reason it is important to develop a thorough understanding of the mechanics of a normal healthy knee. While there are several methods for assessing TKA mechanics, these methods have limitations that make them prohibitive to both replicating physiological systems and evaluating non-implanted knees. These limitations can be circumvented through the development of mathematical models that use anatomical and physiological inputs to computationally simulate joint mechanics. This can be done in an inverse or forward manner to solve for either joint forces or motions respectively. The purpose of this study is to evaluate one such forward model and determine the accuracy of the predicted motions using fluoroscopy. In vivo kinematics were determined during flexion from full extension to 120 degrees for ten normal, healthy, subjects using fluoroscopy and a 3D-to-2D registration method. All ten subjects had previously undergone CT scans allowing for the digital reconstruction of native femur and tibia geometries. These geometries were then input into a ridged body forward model based on Kane's system of dynamics. The resulting kinematics determined through fluoroscopy and the mathematical model were compared for all of the ten subjects.Background
Methods
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:
