In Vivo Mechanics of Cam-Post Engagement in Fixed and Mobile Bearing TKA and Vibroarthrography of the Knee Joint

The objective of this dissertation was to determine the mechanics of the cam-post mechanism for subjects implanted with a Rotating Platform (RP) PS TKA, Fixed Bearing (FB) PS TKA or FB Bi-Cruciate Stabilized (BCS) TKA. Additionally, a secondary goal of this dissertation was to investigate the feasibility of vibroarthrography in correlating in-vivo vibrations with features exhibited in native, arthritic and implanted knees. In-vivo, 3D kinematics were determined for subjects implanted with nine knees with a RP-PS TKA, five knees with a FB-PS TKA, and 10 knees with a FB-BCS TKA, while performing a deep knee bend. Distance between the cam-post surfaces was monitored throughout flexion and the predicted contact map was calculated. A forward dynamic model was constructed for 3 test cases to determine the variation in the nature of contact forces at the cam-post interaction. Lastly, a different set of patients was monitored using vibroarthrography to determine differences in vibration between native, arthritic and implanted knees. Posterior cam-post engagement occurred at 34° for FB-BCS, 93o for FB-PS and at 97° for RP-PS TKA. In FB-BCS and FB-PS knees, the contact initially occurred on the medial aspect of the tibial post and then moved centrally and superiorly with increasing flexion. For RP-PS TKA, it was located centrally on the post at all times. Force analysis determined that the forces at the cam-post interaction were 1.6*body-weight, 2.0*body-weight, and 1.3*body-weight for the RP-PS, FB-BCS and FB-PS TKA. Sound analysis revealed that there were distinct differences between native and arthritic knees which could be differentiated using a pattern classifier with 97.5% accuracy. Additionally, vibrations from implanted knees were successfully correlated to occurrences such as lift-off and cam-post engagement. This study suggests that mobility of the polyethylene plays a significant role in ensuring proper cam-post interaction in RP-PS TKA. The polyethylene insert rotates axially in accord with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the FB-BCS and FB-PS TKAs

Quantitative Analysis of Three-Dimensional Cone-Beam Computed Tomography Using Image Quality Phantoms

In the clinical setting, weight-bearing static 2D radiographic imaging and supine 3D radiographic imaging modalities are used to evaluate radiographic changes such as, joint space narrowing, subchondral sclerosis, and osteophyte formation. These respective imaging modalities cannot distinguish between tissues with similar densities (2D imaging), and do not accurately represent functional joint loading (supine 3D imaging). Recent advances in cone-beam CT (CBCT) have allowed for scanner designs that can obtain weight-bearing 3D volumetric scans. The purpose of this thesis was to analyze, design, and implement advanced imaging techniques to quantify image quality parameters of reconstructed image volumes generated by a commercially-available CBCT scanner, and a novel ceiling-mounted CBCT scanner. In addition, imperfections during rotation of the novel ceiling-mounted CBCT scanner were characterized using a 3D printed calibration object with a modification to the single marker bead method, and prospective geometric calibration matrices

Development of a Computational Model to Predict the In Vivo Contact Mechanics of Modern Total Knee Arthroplasty

This dissertation focuses on the development of a computationally efficient and fast method that incorporates the kinematics obtained from fluoroscopy and extends it to the prediction of the in-vivo contact mechanics at the femoro-tibial articulation in modern knee implants for the deep knee bend activity. In this endeavor, this dissertation deals with the use of an inverse dynamic rigid body model characterizing the slip and roll behavior observed in the femoro-polyethylene articulation and a coupled deformation model where the polyethylene in knee implants are modeled as hexahedral discrete element networks. The performance of this method is tested by comparing force predictions from a telemetric knee and finite element analysis. Finally, the method is applied to study the in vivo contact mechanics and mechanics of the quadriceps mechanism in six popular knee designs. During the deep knee bend activity, the contact force generally increased with flexion. However, the medial lateral forces were not equally distributed and the medial lateral force distribution generally varied from 60%- 40% at full extension to as high as 75%-25% at full flexion in some patients. Also, the magnitude of axial force in the superior-inferior direction was the highest and was found to contribute around 98%-99% of the total load acting at the femorotibial joint. The forces in the medio-lateral and antero-posterior directions were low and the maximum magnitude observed was around 0.5BW. The contact areas and contact pressures were much more sensitive to the geometries involved and the in vivo kinematics. Though no definite pattern was observed for the variation of the contact areas throughout flexion, the contact pressures increased in both condyles with increasing flexion. Also, the contact pressures on the medial condyle were higher than the contact pressures observed in the lateral condyle. The patellofemoral and the quadriceps force ratio increased with the increase in flexion while the patellar ligament and the quadriceps force ratio decreased with increasing flexion. In some patients at high flexion, the quadriceps force and as a result the patellofemoral, patellar ligament and the knee contact forces were found to decrease due to the wrapping of the quadriceps coupled with posterior movement of the femoral condyles leading to the increase in the quadriceps moment arm

Assessment of Normal Knee Kinematics Using High-Speed Stereo-Radiography System

The measurement of dynamic joint kinematics in vivo is important in order to understand the effects of joint injuries and diseases as well as for evaluating the treatment effectiveness. Quantification of knee motion is essential for assessment of joint function for diagnosis of pathology, such as tracking and progression of osteoarthritis and evaluation of outcome following conservative or surgical treatment. Total knee arthroplasty (TKA) is an invasive treatment for arthritic pain and functional disability and it is used for deformed joint replacement with implants in order to restore joint alignment. It is important to describe knee kinematics in healthy individuals for comparison in diagnosis of pathology and understanding treatment to restore normal function. However measuring the in vivo dynamic biomechanics in 6 degrees of freedom with an accuracy that is acceptable has been shown to be technically challenging. Skin marker based methods, commonly used in human movement analysis, are still prone to large errors produced by soft tissue artifacts. Thus, great deal of research has been done to obtain more accurate data of the knee joint by using other measuring techniques like dual plane fluoroscopy. The goal of this thesis is to use high-speed stereo radiography (HSSR) system for measuring joint kinematics in healthy older adults performing common movements of daily living such as straight walking and during higher demand activities of pivoting and step descending in order to establish a useful baseline for the envelope of healthy knee motion for subsequent comparison with patients with TKA. Prior to data collection, validation and calibration techniques as well as dose estimations were mandatory for the successful accomplishment of this study

Assessment of Wear in Total Knee Arthroplasty Using Advanced Radiographic Techniques

Total knee arthroplasty (TKA) has become the gold standard approach for treating advanced osteoarthritis of the knee. Although the surgery continues to be very successful at relieving pain and restoring joint function, its longevity is challenged by wear and loosening of the implant components. This requires the patient to undergo a revision surgery to replace the implant, a much more challenging operation than primary arthroplasty. Wear of the polyethylene tibial inserts from TKA is assessed in vitro using mechanical wear simulator testing and by examining failed implants retrieved from patients during revision surgery, as well as with direct in vivo measurements. Current in vitro measurement tools provide only a global estimate of wear (failing to describe whether the wear has occurred on the articulating or backside surfaces, or stabilizing post), or are qualitative measurements, or lack resolution. Current in vivo measurement techniques are performed statically or quasi-statically, leading to the potential for an underestimation of wear volume as the contact area of the implant components change throughout flexion. The purpose of this thesis was to describe, validate, and utilize new advanced imaging techniques to measure TKA implant wear for both in vitro and in vivo applications. Micro-computed tomography (micro-CT), a non-destructive, high resolution imaging technique was utilized to provide detailed images of the geometry of tibial inserts used in wear simulator trials or retrieved from patients, and create surface deviation maps to accurately quantify wear. Ways to create an unworn reference geometry, for use in comparing to a worn retrieved tibial insert when the pre-wear geometry is unknown, were evaluated and a best practice approach was determined. These methods were then applied to study a group of tibial inserts retrieved from patients during revision surgery, which were found to be well functioning with a yearly wear rate equivalent to other contemporary implant designs. Finally, a pilot study to evaluate the use of dynamic single-plane flat panel digital radiography for use in measuring TKA implant wear in vivo was conducted. The system was determined to have a measurement accuracy and precision sufficient to begin a pilot clinical study with patients

Parameterization of a Next Generation In-Vivo Forward Solution Physiological Model of the Human Lower Limb to Simulate and Predict Demographic and Pathology Specific Knee Mechanics

The human knee from a mechanical perspective is arguably one of the more complex of the joints of the human body and for this very reason there are a number of pathological factors that can adversely affect knee function, leading to pain, stiffness and an overall reduced quality of life. To rectify these disease conditions, a variety of intervention techniques exist, all of which are predicated on a thorough understanding of the forces and motions that occur at the knee.Various techniques have been developed to further the understanding of how the knee functions; however, many of these strategies involve time and cost consuming processes in order to assess functionality of the knee. Mathematical modeling is a methodology that uses mathematical equations of motion to solve for forces, or in the case of forward modeling, motions given a known set of forces. Such a model is capable of replicating the functionality of the knee in vivo.One application of such a model is in the context of total knee arthroplasty design. Intended for the restoration of functionality after late stage osteoarthritis, total knee arthroplasty devices are highly dependent on their associated design features and the use of a theoretical model affords the opportunity to test the performance of a device without ever needing to manufacture or implant it.In addition, there are also surgical applications where a mathematical model can test joints that otherwise cannot be evaluated under conventional means. This includes modeling of the healthy knee, as well as various functionality-limiting pathological conditions. Perhaps more importantly is the ability to evaluate different intervention techniques to determine the effectiveness in doing so identify which technique most effectively resolves the pathological issues.Advances to the model have focused on parameterization while contributing to a validated normal knee model, an enhancement on the efficiency of the muscles that drive flexion, facilitated methods to evaluate articular geometries and enhancements providing more realistic physiological motions. The model has also been enhanced to account for demographics, as well as abnormal pathology with additional parameters added to better understand gait mechanics at the knee

Can a total knee arthroplasty be both rotationally unconstrained and anteroposteriorly stabilised? A pulsed fluoroscopic investigation

Objectives: Throughout the 20th Century, it has been postulated that the knee moves on the basis of a four-bar link mechanism composed of the cruciate ligaments, the femur and the tibia. As a consequence, the femur has been thought to roll back with flexion, and total knee arthroplasty (TKA) prostheses have been designed on this basis. Recent work, however, has proposed that at a position of between 0° and 120° the medial femoral condyle does not move anteroposteriorly whereas the lateral femoral condyle tends, but is not obliged, to roll back - a combination of movements which equates to tibial internal/femoral external rotation with flexion. The aim of this paper was to assess if the articular geometry of the GMK Sphere TKA could recreate the natural knee movements in situ/in vivo. Methods: The pattern of knee movement was studied in 15 patients (six male: nine female; one male with bilateral TKAs) with 16 GMK Sphere implants, at a mean age of 66 years (53 to 76) with a mean BMI of 30 kg/m2 (20 to 35). The motions of all 16 knees were observed using pulsed fluoroscopy during a number of weight-bearing and non-weight-bearing static and dynamic activities. Results: During maximally flexed kneeling and lunging activities, the mean tibial internal rotation was 8° (standard deviation (SD) 6). At a mean 112° flexion (SD 16) during lunging, the medial and lateral condyles were a mean of 2 mm (SD 3) and 8 mm (SD 4) posterior to a transverse line passing through the centre of the medial tibial concavity. With a mean flexion of 117° (SD 14) during kneeling, the medial and lateral condyles were a mean of 1 mm (SD 4) anterior and 6 mm (SD 4) posterior to the same line. During dynamic stair and pivoting activities, there was a mean anteroposterior translation of 0 mm to 2 mm of the medial femoral condyle. Backward lateral condylar translation occurred and was linearly related to tibial rotation. Conclusion: The GMK Sphere TKA in our study group shows movements similar in pattern, although reduced in magnitude, to those in recent reports relating to normal knees during several activities. Specifically, little or no translation of the medial femoral condyle was observed during flexion, but there was posterior roll-back of the lateral femoral condyle, equating to tibiofemoral rotation. We conclude that the GMK Sphere is anteroposteriorly stable medially and permits rotation about the medial compartment

Mobile-Bearing Total Ankle Replacement In Vivo Kinematic Assessment: A Prospective Study Protocol

Total ankle prosthesis as a surgical solution in the case of end-stage osteoarthritis has seen a considerable increase in the last two decades. This study protocol arises from the need to understand the in vivo kinematics of mobile-bearing, flat tibial component total ankle replacement, evaluating the real range of motion and the reciprocal relationships between the components during normal motor tasks through the use of model-based radio-stereometric analysis (MB-RSA). In addition, pre- and post-operative evaluation of walking kinematics with inertial motion sensors, proprioception through a dedicated workstation, and clinical outcomes are discussed. We expect that based on our study protocol researchers will be able to improve future prosthetic designs and validate the setup of MB-RSA, as well as to understand "how an ankle prosthesis moves" once implanted in the patient

The sense or nonsense of mobile-bearing total knee prostheses

The focus of this thesis was if the in vivo kinematics of total knee prostheses was consistent with the kinematics intended by design and to determine the additional value of insert mobility and thus __the sense or nonsense__ of mobile-bearing knee prostheses. The added value of this thesis to the current literature is the integration of different measurement techniques. Fluoroscopy is combined with RSA and motion analysis techniques to fully understand the in vivo knee kinematics beyond which can be obtained by either technique alone. Results demonstrate that the integration of different measurement techniques was indeed of great value to comprehend the in vivo knee kinematics.Anna Fonds Leiden, Dutch Arthritis Association, Stryker SA, J.E. Jurriaanse StichtingUBL - phd migration 201

In-vivo knee kinematics in rotationally unconstrained total knee arthroplasty.

Total knee replacement designs claim characteristic kinematic performance that is rarely assessed in patients. In the present study, in vivo kinematics of a new prosthesis design was measured during activities of daily living. This design is posterior stabilized for which spine-cam interaction coordinates free axial rotation throughout the flexion-extension arc by means of a single radius of curvature for the femoral condyles in the sagittal and frontal planes. Fifteen knees were implanted with this prosthesis, and 3D video-fluoroscopic analysis was performed at 6-month follow-up for three motor tasks. The average range of flexion was 70.1\ub0 (range: 60.1-80.2\ub0) during stair-climbing, 74.7\ub0 (64.6-84.8\ub0) during chair-rising, and 64.1\ub0 (52.9-74.3\ub0) during step-up. The corresponding average rotation on the tibial base-plate of the lines between the medial and lateral contact points was 9.4\ub0 (4.0-22.4\ub0), 11.4\ub0 (4.6-22.7\ub0), and 11.3\ub0 (5.1-18.0\ub0), respectively. The pivot point for these lines was found mostly in the central area of the base-plate. Nearly physiological range of axial rotation can be achieved at the replaced knee during activities of daily living