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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5881_Библиотеки_им_академика_М_И_Перельмана.pdf
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
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The outstanding hardness of DLC coatings, akin to natural diamond, creates a
robust protective layer on the surfaces of knee and hip implants. This property
ensures resilience against abrasive wear, a critical consideration in the demanding
mechanical environment of joint articulation. The incorporation of DLC coatings on
articulating surfaces contributes to reduced friction between moving components,
facilitating smoother joint motion and improving patient comfort. This reduction in
friction not only enhances the overall performance of the implant but also mitigates
wear and tear, potentially extending the functional lifespan of the prosthetic joint
[160, 163].
Biocompatibility is a hallmark feature of DLC coatings, making them wellsuited for medical implants. The carbon-based composition of DLC is inherently
well-tolerated by the human body, minimizing the risk of adverse reactions or
inammatory responses. This biocompatible nature promotes a favorable biological
response to the implanted material, supporting tissue integration and overall implant
stability [164]. Additionally, DLC coatings exhibit remarkable corrosion resistance
due to the inert nature of carbon in the sp3 hybridization state. This corrosion resistance is pivotal for ensuring the longevity of the implant in physiological environments where exposure to bodily uids and joint lubrication is unavoidable. In
conclusion, Diamond-Like Carbon (DLC) coatings represent a multifaceted
advancement in knee and hip implant technology. Their combination of exceptional
hardness, low friction properties, biocompatibility, and corrosion resistance positions DLC-coated implants as promising solutions for improving patient outcomes
and extending the functional life of orthopedic prosthetics [160].
13.8.3 Metal Nitride Coatings
Metal nitride coatings, exemplied by titanium nitride (TiN) and zirconium nitride
(ZrN), have emerged as inuential players in advancing the efcacy of knee and hip
prosthetics. These coatings bring forth a dual contribution by signicantly enhancing wear resistance and fostering improved osseointegration, pivotal factors in the
success of orthopedic implants [160]. A key attribute of titanium nitride and zirconium nitride coatings lies in their remarkable capacity to elevate wear resistance
within joint implants. The application of these coatings forms a protective layer on
implant surfaces, effectively mitigating the impact of abrasive wear during articulation. This heightened wear resistance not only extends the durability of implant
components but also plays a pivotal role in ensuring the sustained success of knee
and hip prosthetics over the long term [165].
Moreover, metal nitride coatings, particularly titanium nitride, enhance osseointegration by providing a bioactive surface. This bioactivity facilitates interactions
with the surrounding bone tissue, promoting hydroxyapatite deposition and emulating the natural mineral composition of bone. The result is the formation of a robust
bond between the implant and the host bone, augmenting implant stability and overall xation. The biocompatibility of metal nitride coatings further underscores their
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suitability for orthopedic applications. Titanium nitride and zirconium nitride
exhibit excellent compatibility with the biological environment, minimizing the risk
of adverse reactions or inammatory responses. This biocompatible characteristic
supports a harmonious interaction between the implant and surrounding tissues,
creating an environment conducive to healing and integration [166].
Additionally, the corrosion-resistant nature of metal nitride coatings adds another
layer of resilience to knee and hip implants. This resistance ensures the longevity of
the implant in the presence of bodily uids and joint lubrication, further contributing to overall stability and structural integrity. So, the metal nitride coatings, particularly titanium nitride and zirconium nitride, represent a sophisticated
amalgamation of attributes crucial for advancing the eld of knee and hip rehabilitation. Their prowess in enhancing wear resistance, promoting osseointegration,
ensuring biocompatibility, and resisting corrosion positions these coatings as valuable components in improving the performance and longevity of orthopedic
implants, ultimately beneting patients undergoing joint replacement procedures [167].
13.8.4 Polymeric Coatings
Polymeric coatings, exemplied by materials like polyethylene and polytetrauoroethylene (PTFE), stand out as inuential contributors to the optimization of knee
and hip prosthetics. In joint interfaces, these coatings play a pivotal role by providing effective lubrication and reducing friction, thereby addressing critical aspects of
implant performance.
Polyethylene coatings, known for their versatility and biocompatibility, act as
efcient lubricants at the joint interface. Their capacity to create a low-friction surface contributes signicantly to the smooth articulation of knee and hip implants.
This reduction in friction not only enhances patient comfort but also serves as a
protective measure against wear-related issues, promoting the sustained functionality of the prosthetic joint [160, 168].
Similarly, polytetrauoroethylene (PTFE) coatings offer a compelling solution
to friction challenges in orthopedic implants. Renowned for its low friction coefcient and non-adhesive properties, PTFE creates a lubricious surface that facilitates
seamless movement between implant components. This characteristic is instrumental in reducing the mechanical stresses on the joint, ultimately extending the
implant’s lifespan and improving overall joint function. The use of polymeric coatings in knee and hip prosthetics aligns with the pursuit of enhancing patient outcomes through improved wear resistance and reduced friction. As these coatings
continue to evolve, their unique properties contribute to the development of implants
that not only mimic natural joint motion but also withstand the rigors of long-term
use. In conclusion, polymeric coatings, particularly polyethylene and PTFE, represent a signicant stride in the pursuit of optimal performance and durability in knee
and hip replacement prosthetics [164].
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
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13.8.5 Nanocomposite Coatings
Nanocomposite coatings, a product of cutting-edge nanotechnology, mark a signicant advancement in knee and hip prosthetics. These coatings, characterized by the
integration of nanoparticles with polymers or ceramics, represent a sophisticated
approach to achieving superior wear resistance and enhanced mechanical properties
in joint implants [169]. The marriage of nanomaterials with traditional coating components unleashes a host of benets. The introduction of nanoparticles brings about
a substantial increase in surface hardness and durability, critical factors in mitigating wear-related challenges in knee and hip implants. By harnessing the unique
properties of nanomaterials, these coatings effectively bolster the mechanical integrity of the implant components, contributing to prolonged implant lifespan.
Moreover, the synergistic combination of nanoparticles with polymers or ceramics
imparts additional strength and resilience to the coating [170, 171]. This not only
enhances the wear resistance of the implant surfaces but also forties their structural
stability, which is crucial for withstanding the demanding mechanical conditions of
joint articulation. The result is a nanocomposite coating that not only mimics the
natural biomechanics of joints but also exhibits a robust resistance to wear and tear,
promising sustained performance in orthopedic applications [172]. Therefore,
nanocomposite coatings represent a frontier in the evolution of knee and hip prosthetics, leveraging the unique properties of nanomaterials to achieve unparalleled
wear resistance and mechanical prowess [173]. As research in nanotechnology progresses, these coatings hold immense promise in shaping the future landscape of
joint replacement technologies, offering patients improved longevity and performance in their orthopedic implants [174].
13.9 Experimental Approaches toWear andFriction Studies
The current standards for wear simulation testing in hip and knee joint implants are
crucial for establishing a common ground across laboratories, enabling effective
comparisons. ASTM F732 is the prevailing standard for pin-on-disc (POD) wear
testing. For hip wear simulation, the ISO 14242 series is the predominant set of
standards aligned with ASTM standards. ISO 14242-1 outlines physiological loading and kinematics during a gait cycle, specifying sample orientation and lubricant
recommendations. The testing involves 5 million gait cycles, with 1 million cycles
considered equivalent to 1 year of clinical steps [175]. Part 2 of ISO 14242 focuses
on wear quantication using the gravimetric method, with weight measurements
and correction for uid uptake [176]. Part 3 is specic to orbital bearing machines,
aligned with ASTM F1714.
Similarly, the knee wear simulation adheres to the ISO 14243 series. ISO 14243-1
denes loading and displacement parameters, while Part 2 details wear quantication using the gravimetric method. Part 3 caters to displacement-controlled
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Table 13.8 Standards used for the hip and knee replacements [180]
Current standards for hip and knee wear simulation
Pin on Disk
[180]
Hip [177,
181, 182]
Knee [178,
179, 183]
ASTM F732-00(2006)
ISO 14242 implants for surgery—wear of total hip-joint prostheses.
ISO 14242-1 (2012E): Loading and displacement parameters for wear-testing
machines and corresponding environmental conditions for test.
ISO 14242-2 (2016E): Methods of measurement.
ISO 14242-3 (2009E): Loading and displacement parameters for orbital bearing
type wear testing machines and corresponding environmental conditions for test.
ISO 14243 implants for surgery—wear of total knee-joint prostheses.
ISO 14243-1(2009E): Loading and displacement parameters for wear-testing
machines with load control and corresponding environmental conditions for test.
ISO 14243-2 (2009E): Methods of measurement
ISO 14243-3 (2004E): Loading and displacement parameters for wear-testing
machines with displacement control and corresponding environmental conditions
for test
A. Choudhari et al.
simulators, aligning with ASTM F1715 [177]. The wear quantication methods
involve measuring weight changes, applying corrections for uid uptake, and determining wear rates. ISO 14242 Part 2 introduces the volumetric method, incorporating surface scans for volume loss determination. While these standards provide a
foundation for wear simulation, ongoing research endeavors aim to expand capabilities beyond standardized tests [178]. Efforts are directed towards advanced kinematics, loading conditions, and unique scenarios to generate higher wear levels.
This evolving research, subject to ASTM and ISO organizations, explores areas
such as edge loading, impingement, implant separation, mal-orientation, third-body
wear, and material aging [179] (Table13.8).
13.9.1 Pin-on-Disk Testing
Pin-on-disk (POD) testing is a pivotal methodology in the rigorous examination of
wear characteristics within hip and knee prosthetics. This experimental technique
involves the reciprocating motion of a pin against a rotating disk, emulating joint
articulation under controlled parameters as shown in the Fig.13.6 [184]. This controlled sliding contact allows for systematic investigations into the wear behavior of
materials, providing valuable insights into the frictional properties and durability of
components within orthopedic implants.
One of the primary strengths of pin-on-disk testing lies in its ability to simulate
specic wear conditions encountered in the complex biomechanics of hip and knee
joints. Researchers can recreate real-world scenarios by meticulously adjusting
parameters such as load, sliding distance, and lubrication, facilitating a comprehensive understanding of the interactions between materials and their degradation over
time [14]. This controlled simulation of wear conditions is essential for elucidating
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
Fig. 13.6 The simulation of pin-on-disk (POD) [184]
391
the nuanced factors inuencing the performance of prosthetic components. The
quantitative assessment of wear rates represents a critical outcome of pin-on-disk
testing. Researchers can derive wear rates under varying conditions by measuring
material loss on the pin and disk surfaces. This quantitative data is instrumental in
comparative analyses, providing valuable information for material selection, coating assessments, and surface modications in the design and manufacturing of hip
and knee implants. The controlled experimental conditions inherent in pin-on-disk
testing enhance the reproducibility of results, allowing for systematic investigations
into the impact of parameters such as load, speed, and lubrication on wear behavior.
Pin-on-disk testing is particularly germane to material studies, offering a robust
platform for evaluating the wear resistance of diverse materials, coatings, or surface
treatments [185]. This information is imperative for guiding material selection strategies, ensuring optimal performance, and extending the longevity of orthopedic
implants. As a cornerstone in wear studies, pin-on-disk testing not only advances
our understanding of wear dynamics but also contributes substantively to the ongoing renement and development of advanced materials, thereby optimizing joint
replacement outcomes [186].
13.9.2 Hip Joint Simulators
Hip joint simulators play a pivotal role in orthopedic research, particularly in the
study of wear, lubrication, and friction dynamics within the hip joint. The signicance of these simulators lies in their ability to faithfully replicate the multidirectional motion of the hip joint in a controlled and physiological environment.
Complex in nature, these simulators enable researchers to investigate intricate biomechanical aspects, providing valuable insights into the performance and durability
392
Fig. 13.7 The Hip Joint simulator, as illustrated (a), comprises distinct components: (I) the primary body, (II) an electrical motor, (III) eccentric sheaves, and (IV) the tank. (b) provides a sectional view of the tank, while (c–e) depict eccentric sheaves responsible for extension and exion,
abduction and adduction, and inwards and outwards rotation, respectively, and (f) hip join simulator of Shore Western [177]
A. Choudhari et al.
of hip implants. By mimicking real-world conditions, these simulators contribute to
a comprehensive understanding of the complex interplay between materials, lubrication, and friction, ultimately informing advancements in hip joint prosthetics and
enhancing the overall success of hip replacement procedures [177].
The 3-axis hip joint simulator, depicted in Fig.13.7, is designed considering ISO
14242 standards and accommodates limitations such as integration with an Instron®
press and a maximum height of 1 meter [177]. Utilizing CAD software, the simulator consists of a main body, an electrical motor, three eccentric sheaves for each
axis, and a tank lled with a uid mimicking the internal human body environment.
The eccentric sheaves play a crucial role in reproducing complex hip joint movements, with calculated radii at various points to precisely emulate human hip rotations during walking conditions. The simulator offers a sophisticated platform for
research on new hip joint materials [177].
Figure 13.8a provides a schematic diagram of the hip joint simulator designed
and built by Oliveira etal. for surface wear simulation of hip prosthetics [182]. The
simulator allows controlled articulation of the hip prostheses in three degrees of
freedom—exion/extension, abduction/adduction, and internal/external rotation.
The main structure consists of rigid welded steel tubing, providing a sturdy base.
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
Fig. 13.8 (a) Illustrative depiction of the apparatus constructed for simulating hip movements and
(b) In the test chamber, prostheses are placed within a lubricating uid [182]
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Two platforms oriented in the x- and y-axes move in tandem to generate the exion/
extension and abduction/adduction motions, respectively. The x-axis platform has a
range of ±50° while the y-axis platform has a range of ±35°. This allows the motion
proles specied in the ISO standards to be achieved. The z-axis contains the motor
providing internal/external rotational motion of the joint [187]. Figure13.8b shows
the test chamber (2.5 liters) designed to house the hip prostheses during the wear
testing experiments. This chamber is located at the intersection of the three motion
axes of the simulator. During testing, the hip prostheses are fully immersed in the
lubricant uid. This replicates the natural lubrication environment in the body.
Temperature is maintained at 37°C±2°C using a controller, heater, and temperature sensor [188]. The stainless steel base has a conical recess at its center to secure
the femoral head using a morse taper. This prevents motion of the femoral component during testing. The UHMWPE acetabular cup is xed to the end of the z-axis
drive link via the test machine’s cup holder xture [182].
Figure 13.9 provides evidence of abrasive, adhesive, and deformative wear
mechanisms, all contributing to the severe surface damage on the femoral heads
after just 1 million test cycles using SEM images. The variety of wear modes indicates a poor tribological environment was present during articulation [182].
Figure13.9a reveals the presence of micro-grooves of varying sizes and orientations
along the metallic surface. These abrasive wear tracks were likely formed by thirdbody wear from hard polymer or metallic debris particles trapped between the articulating surfaces. The depth and width of the grooves indicate signicant material
removal. Figure 13.9b shows plastic deformation regions, recognizable by the
smearing, pile-up, and displacement of material from its original orderly surface
structure. The intimate metal-on-polymer contact and friction generates stresses
exceeding the yield strength of the femoral head surface, resulting in permanent
deformation [182]. Figure13.9c highlights the apparent build-up of an adherent
layer, seen as brighter patches of material overlying the substrate. This suggests
material transfer from the polymeric acetabular cup occurred at regions of contact.
Partial delamination of this transferred layer can also be observed. Figure13.9d, e
394
A. Choudhari et al.
Fig. 13.9 The femoral heads exhibit surface characteristics such as (a) micro-grooves, (b) plastic
deformation, (c) adhered material, (d) Measurement of local roughness using four pathways on the
femoral heads, spaced at 45°, and (e) four pathways on the acetabular component, spaced at 90°
intervals, (f) Chemical composition analysis, acquired through Energy Dispersive Spectroscopy
(EDS), for the material adhered to the femoral heads’ surface and (g) surface wear of the acetabular
component containing embedded metal particles [182]
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
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outlines the consistent locations for roughness measurements on hip prosthetic
components, both in femoral heads and acetabular components. Trajectories for
measurements are shown, with four readings in femoral heads, 45° apart, and four
readings in the acetabular component, spaced 90° apart, ensuring a standardized and
comprehensive assessment. Figure13.9f provides EDS analysis conrming polymer material from the acetabular cup had transferred and adhered to the femoral
head surface. Figure13.9g shows the acetabular cup surface contained embedded
metallic debris transferred from the femoral head, as veried by EDS [182]. In
Fig.13.9f, an image of the femoral head reveals adhered material with characteristic
polymer elements (C, O, Ca, Al). X-ray analysis penetrates the layer, detecting
metallic substrate peaks in the EDS spectrum, indicating an adhesive wear mechanism. The polymer layer cracks and forms particles, indicative of material detachment. Similar phenomena were observed in studies with comparable prosthetic
components [54, 189]. Figure13.9g depicts worn acetabular surfaces, displaying
wear tracks characteristic of ISO 14242-3. Bright particles from the femoral head,
identied through EDS as (Fe, Cr, Ni, Mn, Mo, S), cause micro-grooves, indicative
of abrasive wear damaging the femoral heads [182].
13.9.3 Knee Joint Simulators
Simulators mimicking the intricate motion of the knee joint help evaluate wear and
friction performance in knee implants. Devices designed to replicate the complex
motion of the knee joint serve a crucial role in assessing the wear and friction performance of knee implants. These knee joint simulators provide a controlled environment for researchers to study the dynamic interactions between implant
components, enabling a comprehensive evaluation of the durability and functionality of knee prosthetics. By mimicking the intricate motions of the knee joint, these
simulators contribute valuable insights into the long-term performance of implants,
facilitating advancements in implant design and materials to enhance overall efcacy and patient outcomes.
Figure 13.10 shows the experimental setup used to validate the nite element
analysis (FEA) models [178]. An electromechanically controlled knee simulator
called Prosim (Fig. 13.10a) was used to perform the simulated gait movements
based on the modied ISO 14243-3 standard (positive AP displacement and positive
TR angle). Custom jigs made of ABS plastic (Fig.13.10a) were used to hold the
knee implant components in place during testing. Prior to the wear test, the articular
surfaces of the tibial insert were coated with marker dots to assess the wear patterns
(Fig.13.10c). The knee implant was then subjected to 5000 gait cycles in the simulator. Figure13.10f validates the FEA model by comparing the predicted wear con-
tours on the tibial insert surface to the experimental wear contours from the Prosim
knee simulator test. Figure13.10d shows the FEA model for simulating wear under
displacement control based on ISO 14243-3. In this model, the inputs are anteriorposterior (AP) displacement, tibial rotation (TR) angle, exion angle, and axial
396
A. Choudhari et al.
Fig. 13.10 The experimental arrangement consists of (a) a knee simulator controlled electromechanically using Prosim, (b) jigs made of ABS material, (c) test specimens designed for evaluating
wear contours, (d) Finite Element Analysis (FEA) models, comprising a model governed by displacement control in accordance with ISO14243-3, (e) a model regulated by load control as per
ISO14243-1, (f) estimated tibiofemoral wear contours from FEA model, and Wear contours from
the ve (g–k) FEA models [178]