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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5361_Библиотеки_им_академика_М_И_Перельмана.pdf
13 Wear and Friction Mechanism Study in Knee and Hip Rehabilitation…
Table 13.3 Commonly used materials in hip and knee implants [17]
Sr.
no. Materials Applications
1 Stainless
steel
2 Cobalt-based Cobalt-based alloys Porous coatings, femoral stems, heads, tibial and
3 Titanium-
based
4 Ceramics Bioinert
5 Polymers PMMA Acetabular cups, tibial and patellar components,
6 Composites Polymer-based Femoral stems
SS 316L Femoral stems, heads
Cast Co-Cr-Mo
Wrought Co-Ni-Cr
Mo
Wrought Co-Cr-W
Ni
CP Ti Porous coatings second phase in ceramic and
Ti-6Al-4V Femoral stems, heads, tibial and femoral
Ti-5Al-2.5Fe Femoral stems, heads
Ti-Al-Nb Femoral stems, heads
Carbon Coatings on metallic femoral stems, the second
Alumina Femoral stems, heads, acetabular cups
Zirconia Femoral stems, acetabular cups
Bioactive
Calcium Phosphates Coatings on metallic and ceramic femoral stems,
Bioglasses Coatings on metallic and ceramic femoral stems
UHMWPE/HDPE metallic and ceramic femoral stems
Polysuffolene Femoral stems, porous coatings on metallic femoral
PTFE Femoral stems, porous coatings on metallic femoral
Polysulone- carbon Femoral stems
Polycarbonate- carbon Femoral stems
Polysulfone- Kevlar Femoral stems
Polycarbonate- Kevlar Femoral stems
femoral components
PMMA composites
components, porous coatings
phase in composites and bone cement
scaffold materials, the second phase in PMMA and
UHMWPE composites
porous coatings on
stems
stems
367
femoral stems. This comprehensive array of materials and their respective applications in orthopedic implants underscores the multidisciplinary nature of implant
design, with the choice of materials playing a pivotal role in achieving optimal clinical outcomes [17].
In Table13.4, a comprehensive overview of commonly employed material combinations in hip and knee prosthetics is provided, delineating the specic femoral
368
Table 13.4 Commonly used combination of materials in hip and knee prosthetics [17]
Hip replacement
Femoral
components
Co-Cr-Mo Co-Cr-Mo Premature high rates of loosening and restricted utilization
Co-Cr-Mo UHMWPE Widely employed; minimal wear
Alumina/
zirconia
Alumina Alumina Minimum wear rate observed when components are matched;
Ti-6Al-4V UHMWPE Occurrences of elevated Ultra-High Molecular Weight
Surface-coated
Ti-6Al-44
Knee replacement
Femoral
component
Cobalt-
chromium
Cobalt-
chromium
Cobalt-
chromium
Titanium alloy UHMWPE It is a lightweight alternative, good for younger patients.
Titanium alloy Ceramic Lightweight and improved wear resistance, but more
Titanium alloy Metal-on-metal It is not recommended due to high wear rates and potential
Socket
components Results
were observed initially; however, recent advancements
indicate the lowest wear rates.
UHMWPE Exceptionally low wear rate: Zirconia exhibits enhanced
impact resistance.
not currently utilized in clinical practice in the United States.
Polyethylene (UHMWPE) wear attributed to the deterioration
of the titanium surface.
UHMWPE Enhanced resistance to abrasion demonstrated; achievement
limited to a thin-treated
Tibial
component Results
UHMWPE Standard combination, good wear resistance, and
biocompatibility.
Ceramic Improved wear resistance, but more susceptible to fracture.
Metal-on-metal High wear rates are not recommended for most patients.
expensive.
metal ion release.
A. Choudhari et al.
and socket components used in hip replacements and the femoral and tibial components utilized in knee replacements [17]. For hip replacement femoral components,
alloys such as Co-Cr-Mo and titanium alloy (Ti-6Al-4V) are extensively utilized.
Initial challenges of premature high rates of loosening and restricted usage were
encountered; nevertheless, recent advancements, particularly in Co-Cr-Mo components, have demonstrated signicant progress, showcasing the achievement of the
lowest wear rates. Noteworthy alternatives involve using zirconia in combination
with UHMWPE, showcasing exceptionally low wear rates and heightened impact
resistance. However, certain material combinations, such as alumina, are not currently employed in clinical practice in the United States due to limitations in
observed wear rates. In knee replacement, the presented femoral and tibial components include combinations of cobalt-chromium, titanium alloy, ceramic, and metalon- metal [74]. These combinations are tailored to address specic considerations
such as wear resistance, biocompatibility, fracture susceptibility, and suitability for
13 Wear and Friction Mechanism Study in Knee and Hip Rehabilitation…
369
different patient demographics. For instance, cobalt-chromium with UHMWPE is
recognized as a standard combination with good wear resistance and biocompatibility. At the same time, alternatives like metal-on-metal congurations are cautioned
against due to elevated wear rates and potential metal ion release. The inclusion of
surface-coated Ti-6Al-4V with UHMWPE demonstrates enhanced resistance to
abrasion, albeit achieved through a thin-treated layer. The detailed insights provided
in Table13.4 offer valuable information for researchers and practitioners in the eld
of orthopedics, aiding in the selection of optimal material combinations for hip and
knee prosthetics based on specic performance criteria [17].
13.6.1 Metallic Implants
Metallic implants, including stainless steel, cobalt-chromium alloys, and titanium
alloys, are frequently employed in orthopedic applications owing to their commendable mechanical properties and biocompatibility. Stainless steel, characterized by
its corrosion resistance and strength, is suitable for various implant components.
Cobalt-chromium alloys, known for their high strength and wear resistance, are
often preferred for load-bearing applications. Titanium alloys exhibit excellent biocompatibility, low density, and high strength, making them suitable for implants to
reduce overall implant weight. Surface treatments play a crucial role in enhancing
the performance of metallic implants. Polishing procedures improve the surface nish, reducing friction and wear. Surface coatings, such as diamond-like carbon
(DLC) or hydroxyapatite, can be applied to augment wear resistance and encourage
Osseo integration. These treatments aim to optimize the tribological behavior of
metallic implants, ensuring longevity and functionality in orthopedic applications.
The historical evolution of metallic components in Total Joint Replacements (TJR)
witnessed a transition from stainless steel [75] to Cobalt-Chromium (CoCr) alloy
[76] to address friction-related concerns. The introduction of the second-generation
metal-on-metal (MoM) total hip replacements (THRs) in the early 1990s aimed to
mitigate polyethylene wear and resist the initiation of osteolysis [77]. Recent ndings by Wimmer etal. emphasize the presence of a nano-crystalline mechanically
mixed zone in MoM components, incorporating organic material from synovial
uid [78]. This “mechanical mixing” alters the bearing surface, transitioning from
pure metallic to an organic composite material within the uppermost 50–200nm.
This mechanism impedes direct metal contact, preventing adhesion and limiting
wear. The identication of this mechanically mixed zone contributes foundational
insights into particle release dynamics in MoM arthroplasty.
A comprehensive study scrutinizing the tribological mechanisms of metal components in TJR reveals that MoM hip joints articulate under ultra-mild sliding wear
conditions, forming nano-crystalline tribolayers [79]. These tribolayers, with a
thickness below 300nm, exhibit distinct chemical and mechanical properties compared to bulk materials [80, 81]. Various factors inuence wear rates and metal ion
release in TJRs, including changes in surface wettability, oxidative wear of metal
370
A. Choudhari et al.
surfaces, micro-abrasion from oxide lm damage, and surface abrasion from thirdbody debris [80].
The selection of materials for hip and knee prosthetics is a critical aspect that
considers the biological response to implanted materials. In recent biomedical engineering research, β-Ti alloys have garnered attention for their excellent biocompatibility, corrosion resistance, non-magnetism, and radiopacity. These alloys often
contain alloying elements from the 3d, 4d, and 5d transition metal groups [82]. The
interaction of these elements with the human body environment is crucial, and
Table13.5 summarizes the biological responses of various metallic elements in the
context of tissue engineering. For hip and knee prosthetics, the biological compatibility of materials is of utmost importance. Highly biocompatible elements such as
Ti, Zr, Nb, Ru, Ta, Au, Mo, and Sn are preferred choices. These elements exhibit
favorable characteristics, making them suitable for implant applications. Conversely,
elements like Co, Cu, Ni, V, Cr, and Pt are deemed non-compatible. They should be
avoided in implant fabrication due to concerns related to carcinogenicity, mutagenicity, genotoxicity, cytotoxicity, allergic response, and bio-corrosion resistance.
In the synthesis of implants for hip and knee prosthetics, the choice of alloying
elements plays a crucial role. Incorporating elements such as Nb or Ta is common,
as they contribute to the desirable properties of implants. Recent developments
focus on designing implants with a lower cost without compromising biocompatibility. The substitution of traditional Ti alloying elements with more economical
options like Fe, Mn, Mo, and Sn has paved the way for the development of costeffective implants. Xu etal. [83] synthesis designed Ti-5Mo-Fe-3Sn alloy demonstrated attractive bio-favorable properties, highlighting the potential for economical
yet biocompatible implants. Considering the nancial burden on patients, the of
low-cost implants becomes signicant. The incorporation of low- cost alloying elements like Mo, Fe, or Sn not only reduces costs but also maintains high biocompatibility [84]. This approach aligns to develop implants that are not only clinically
successful but also nancially accessible for a broader patient population. Notably,
these considerations are vital for both short-term and long-term implants, emphasizing the importance of material selection in the success of hip and knee prosthetics
[82, 85].
13.6.1.1 Stainless Steel
Medical-grade stainless steel’s high corrosion resistance is advantageous for implant
applications, especially in environments rich in bodily uids. The austenitic microstructure of these alloys, characterized by a face-centered cubic (FCC) phase, contributes to their favorable mechanical properties [90–92]. Because of its excellent
strength and low cost, medical grade 316L stainless steel has been utilized for many
years in orthopedics, mostly for total joint replacements. Because of its superior
biocompatibility, it is the preferred material for joint replacements. Because of the
12% Cr content, which aids in the production of an adherent coating of corrosionresistant oxide, Cr2O3, it is resistant to a variety of corrosive chemicals. This
Pt No Yes Yes Yes Yes Yes No 181,350
13 Wear and Friction Mechanism Study in Knee and Hip Rehabilitation…
Powder
price
( USD/kg)
371
Elements BiocompatibleCarcinogenicGenotoxic MutagenicCytotoxicityAllergenicCorrosivity
Ti Yes No No No Medium No No 2790
Zr Yes No No No No No No 6045
Nb Yes No No No No No No 2232
Ru Yes No No No Medium No No 34,782
Ta Yes No No No No No No 7812
Au Yes No No No Yes No No 193,440
Mo Yes Disputed No No No Yes No 930
Sn Yes No No No No No No 27,900
Al No No Yes No No No No 465
Ag No No No No Yes Yes No 23,250
Mn No No Yes No Yes No Yes1023
Fe No No Yes Disputed Medium No Yes372
W No Yes Yes No Medium No Yes1860
Zn No No No No Yes No No 22,971
Ir | No No No Yes Yes No No 161,448
3 Cu No No Yes Yes Yes Yes Yes 26,970
|| Pd No Yes No Disputed Medium Yes No 176,820
> V No Yes Yes Yes Yes Disputed No 18,600
Cr No Disputed Yes Yes Yes Yes No 1395
Co No Yes Yes Yes Yes Yes Yes7254
Recommended
Acceptable
Ni No Yes Yes Yes Yes Yes Yes465
Avoid
Table 13.5 Summary of biological responses of elements [86–88] and their cost [89]
372
A. Choudhari et al.
facilitates the process of self-healing. Despite its notable fatigue strength, medicalgrade stainless steel has an elastic modulus approximately ten times higher than
cortical bone, resulting in a stiffness mismatch. This disparity can lead to stress
shielding effects, altering stress distribution in the adjacent bone, which may, in
turn, inuence bone remodeling and implant-bone interface integrity [93, 94].
Medical-grade stainless steel is a vital biomaterial extensively employed in the fabrication of orthopedic implants, particularly in joint replacement surgeries. These
implants, composed primarily of low-carbon austenitic stainless steel, exhibit superior fatigue strength, rendering them well-suited for load-bearing applications in the
musculoskeletal system [93, 95]. Typically containing 17–19% chromium (Cr),
14–16% nickel (Ni), and 2.3–4.2% molybdenum (Mo), medical-grade stainless
steel leverages the protective properties of chromium oxide to form a thin, durable
passivating oxide layer on its surface. This layer enhances corrosion resistance,
while molybdenum further forties corrosion resistance by improving the stability
of grain boundaries [95].
13.6.1.2 Co-Cr Alloys
In orthopedic prostheses, the evolution from stainless steel to cobalt-based alloys
has been pivotal, driven by the pursuit of superior mechanical properties [96].
Presently, cobalt-based alloys stand out as one of the safest biomaterials for hip and
knee replacements due to their exceptional corrosion resistance and mechanical
strength [97]. The key attribute dening the efcacy of cobalt-based alloys lies in
their remarkable corrosion resistance in chloride environments, attributed to alloying additions and the formation of a chromium oxide passive layer [98, 99]. This
versatility is evident in the fabrication processes, allowing orthopedic implants
made from cobalt alloys to be cast, wrought, or forged, each method offering distinct advantages [100, 101]. CoNiCrMo alloy, recognized for its approximately
35% cobalt and nickel composition, exhibits high corrosion resistance to seawater
under stress [102, 103]. Its superior fatigue and ultimate tensile strength make it
particularly well-suited for applications requiring prolonged service life without
fracture or stress fatigue, such as hip joint prosthesis stems [17]. Furthermore,
advancements in fabrication techniques, including low-carbon wrought versions
and hot forging or HIP [97, 104, 105] processes, have enhanced the mechanical and
fatigue properties of cobalt-based alloys, offering promising avenues for continual
improvements in orthopedic implant materials. CoCr alloys used in MoM congurations demonstrated signicantly lower linear wear rates compared to metal-onpolyethylene (MoP) congurations [50, 106]. Moreover, CoCr alloys exhibited
lesser damage on ultra-high molecular weight polyethylene (UHMWPE) than
Ti-6Al-4V alloys [36, 107] in MoP couplings. In addition to material properties,
geometric considerations play a pivotal role in MoM hip joints. Studies, such as
Leslie etal. [108], highlight that larger diameter MoM hip joints exhibit lower wear
rates compared to smaller counterparts over specic rubbing periods. Cobalt levels
were found to be higher in smaller-diameter hip joints after a designated number of
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
Table 13.6 The property comparison of Co-based alloys with different conditions (annealed, cold
worked, and hot worked) [17]
Cast
Material
Condition: AN AN CW HW AN C WA CW C WA AN CW
Density (g/
cm3)
E (tensile)
(GPa)
Hardness
(HV)
00.2%
(MPa)
OUTS
(MPa)
Elong
(min%)
Notes: AN annealed, CW cold worked, CWA cold worked aged, HW hot worked, Hv Vicker hardness, Hc Rockwell C hardness
CoCrMo
7.8 9.15 9.15 – – – – . . –
200 230 230 – – – . . – .
300 240 450 28 – – . . – .
455 310 1000 700 241
665 860 1500 1000 793
8 30 9 12 50 8 – 1.0–17 50 12
Wrought
CoCrMo
Wrought
CoNiCrMo
449
1000
Wrought
CONiCrMoFe
1585 – 1240
1450
1795 1515
1795
1860
2275
Wrought
CoNiCrMoWFe
275 1310
600 1172
373
cycles. Similarly, clearance, as seen in diametrical clearances, inuences friction
and wear rates in MoM hip joints, with a mean diametrical clearance of 94μm demonstrating signicantly lower friction and wear rates [109].
The mechanical properties and corrosion resistances of these alloys are intricately tied to the specic weight percentages of base elements and alloy additions in
their compositions, as indicated in Table 13.6 [17]. Notably, casting and forging
bars made with cobalt-based alloys with varying nickel content are designated as
F75, F799, F90, and F562 [17, 110].
Compared to wrought alloys, cobalt-based casting alloys exhibit higher contents
of high melting metals, such as chromium, tungsten, tantalum, titanium, and zirconium, as well as elevated carbon contents [102]. Molybdenum, a constituent in these
alloys, contributes to ner grains, resulting in heightened strength, while silicon and
manganese enhance oxidation resistance [17, 102]. The CoNiCrMo alloy, initially
known as MP35N, exhibits approximately 35% cobalt and nickel each and demonstrates high corrosion resistance to seawater under stress. While cold working
enhances the alloy’s strength, its application, especially in the fabrication of large
devices like hip joint stems, presents challenges, necessitating the use of hot forging
for large implant production. In terms of abrasive wear properties, wrought
CoNiCrMo alloy performs similarly to cast CoCrMo alloy in joint simulation tests
with ultra-high molecular weight polyethylene acetabular cups. However, the former is not recommended for bearing surfaces due to poor frictional properties. The
superior fatigue and ultimate tensile strength of wrought CoNiCrMo alloy render it
suitable for applications requiring prolonged service life without fracture or stress
fatigue, particularly in hip joint stem applications. The microstructure of cobaltbased alloys typically consists of a cobalt-rich solid-solution matrix containing carbides within the grains and at grain boundaries. Early versions of cobalt- based
374
Table 13.7 Wear of hip implants made from Co-Cr-Mo material [65]
Run-in wear at 1 ×
Test no.
a
1
a
2
3 0.58 0.96 0.112
4 0.77 1.02 0.08
5 0.81 1.13 0.11
6ª 0.81 1.45 0.214
7 1.9 2.56 0.18
a
8
Mean±SD 0.76±0.51 1.11±0.67 0.11+0.055
9 0.16 0.34 0.07
10 0.22 0.46 0.089
11 0.38 0.62 0.086
12 0.61 0.74 0.054
13 0.02 0.15 0.047
14 0.06 0.23 0.055
Mean±SD 0.24±0.22 0.42±0.23 0.067+0.018
15 0.04 0.37 0.153
16 0.1 0.47 0.126
17 0.28 0.4 0.038
18 0.24 0.38 0.038
19 0.28 0.45 0.045
20 0.03 0.16 0.034
21 0.25 0.4 0.039
22 0.42 0.54 0.033
Mean±SD 0.21±0.14 0.40±0.11 0.063±0.048
Notes: SD standard deviation
a
Implants tested without ethylenediaminetetraacetic acid additive
106cycles (mm3)
0.27 0.46 0.075
0.68 0.81 0.057
0.24 0.52 0.079
Total volumetric wear at
3 × 106cycles (mm3)
Steady-state wear rate for 1–3 ×
106cycles (mm3/million cycles)
A. Choudhari et al.
alloys used for hip implants had higher carbon contents and were produced by
investment casting. Recent advancements include low-carbon wrought versions
with superior mechanical properties and corrosion resistance, outperforming their
cast counterparts [97].
Table 13.7 presents the results of wear testing conducted on cobalt-chromiummolybdenum (CoCrMo) hip implants fabricated from alloys with varying carbon
contents [65]. The tests measured the volumetric wear of the implants after run-in
and steady-state periods in a simulator modeling million-cycle intervals. Specimens
fabricated from a low-carbon CoCrMo alloy (F1537-94) exhibited higher run-in and
overall wear volumes compared to high-carbon formulations. After 1 million cycles,
average run-in wear was 0.76 ± 0.51mm3, increasing to 1.11 ± 0.67mm3 after 3
million cycles. The steady-state wear rate between 1 and 3 million cycles averaged
0.11 ± 0.055mm3/million cycles for the low-carbon alloy implants [65]. In contrast,
CoCrMo hip implants made from two different high-carbon alloys demonstrated
13 Wear andFriction Mechanism Study inKnee andHip Rehabilitation
375
signicantly lower wear. For the F1537-94 high carbon alloy, run-in wear averaged
0.24 ± 0.22 mm3 after 1 million cycles, with a total volumetric wear of 0.42 ±
0.23mm3 after 3 million cycles. The steady-state wear rate was 0.067 ± 0.018mm3/
million cycles from 1 to 3 million cycles. Similarly, implants fabricated from the
F75-92 high carbon alloy had average run-in wear of 0.21 ± 0.14mm3, total wear of
0.40 ± 0.11mm3 after 3 million cycles, and a steady state rate of 0.063 ± 0.048mm3/
million cycles [65]. Overall, the high carbon CoCrMo alloy implants exhibited substantially reduced wear volumes and wear rates compared to the low carbon alloy in
these simulator tests. The results indicate that increasing the carbon content signicantly improves the wear resistance and tribological performance of CoCrMo alloys
intended for hip implant applications [65, 70].
13.6.1.3 Ti-Alloy
Titanium alloys have become a cornerstone in hip and knee implants, presenting a
wealth of properties that render them exceptionally well-suited for orthopedic applications. Comprising a blend of titanium, aluminum, and vanadium, these alloys
exhibit a unique combination of mechanical strength, biocompatibility, and corrosion resistance, making them an ideal choice for implant materials [111].
One of the primary advantages of titanium alloys lies in their remarkable biocompatibility. The human body readily accepts titanium implants, fostering a strong
osseointegration process. This biocompatibility is essential for hip and knee
implants, promoting effective integration with surrounding bone tissue and minimizing the risk of adverse reactions [112]. Additionally, the low modulus of elasticity of titanium alloys closely approximates that of natural bone, reducing stress
shielding effects and enhancing the overall biomechanical compatibility of the
implant within the joint. Furthermore, the corrosion resistance of titanium alloys is
crucial for the longevity of hip and knee implants [111]. These alloys form a protective oxide layer on their surface, preventing degradation and corrosion in the
demanding physiological environment. This corrosion resistance ensures the structural integrity of the implant over time, contributing to its durability and sustained
performance within the biomechanically demanding hip and knee joints. In terms of
mechanical properties, titanium alloys offer an optimal balance of strength and exibility. This characteristic is particularly advantageous for hip and knee implants, as
they must withstand substantial loads and provide stability during various movements. The high tensile strength of titanium alloys ensures the implant’s structural
integrity, while their exibility allows for more natural joint movement, contributing to improved patient outcomes [113]. Titanium-based alloys have garnered signicant popularity in total hip replacement (THR) applications, owing to their
distinctive characteristics that make them exceptionally well-suited for hip and knee
implants. With a low density of approximately 4700kg/m3, these alloys boast high
specic strength, providing the necessary structural integrity for load-bearing joints.
The formation of an adherent TiO2 oxide layer contributes to excellent corrosion
resistance, ensuring the implants’ durability over time. Notably, titanium alloys
376
A. Choudhari et al.
exhibit complete inertness alongside biocompatibility, facilitating seamless integration with the human body and minimizing the risk of adverse reactions [114].
The moderate elastic modulus of approximately 110GPa, which is only half that
of surgical stainless steel or cobalt-based alloys and ve times that of cortical bone,
plays a pivotal role in achieving physiologically sound stress distribution within the
implant-bone interface. This characteristic reduces stress shielding effects and promotes a more natural distribution of forces, enhancing the biomechanical compatibility of the implant within the hip and knee joints. Unlike stainless steel and
cobalt-chromium alloys, the use of titanium implants eliminates the need for an
intermediate cement layer, further simplifying the implantation process. Two primary titanium alloys commercially employed for implants are commercially pure
titanium and Ti-6Al-4V.The latter stands out due to its exceptional mechanical
strength and is increasingly replacing commercially pure titanium. However, it is
essential to note that long-term usage of titanium alloys may pose health concerns,
such as the potential development of Alzheimer’s disease and neuropathy, attributed
to the release of aluminum and vanadium. Researchers are actively exploring alternatives, such as Nb-based materials, to address these concerns [115].
13.6.2 Ceramic Implants
Ceramics like alumina and zirconia are known for their high hardness and biocompatibility. Ceramic-on-ceramic implants have shown low wear rates and excellent
long-term performance. Ceramics have emerged as highly promising materials for
hip and knee implants, presenting distinctive properties that make them particularly
well-suited for orthopedic applications. Compared to metals, ceramics are associated with reduced osteolysis, establishing them as favorable choices for joints or
joint surface materials [116]. Alumina, a conventional ceramic, stands out due to its
exceptional properties, including high strength, good biocompatibility, and stability
in physiological environments. While the lack of chemical bonding between sintered alumina and tissue limits its potential as a bone substitute, it nds extensive
use in wear surfaces for joint replacement prostheses. Alumina femoral heads in hip
replacements, coupled with metallic femoral stems and acetabular cups made from
ultra-high molecular weight polyethylene (UHMWPE), have demonstrated superior
wear resistance, with rates up to 20 times less than metal on UHMWPE [117].
In addition to alumina, zirconia ceramics, specically tetragonal zirconia polycrystals (TZP), have gained prominence, particularly in ball heads for hip replacements. The over 300,000 TZP ball heads implanted showcase the material’s
effectiveness [118]. The advantageous match between the bulk material properties
of ceramic implants and natural bone reduces issues associated with stress shielding, often encountered with coated metallic implants. Calcium phosphates, such as
tricalcium phosphate (TCP) and hydroxyapatite (HAP), exhibit biocompatibility
and osteoconductive properties, making them widely used for hard tissue replacement. Porous forms of these ceramics, with 100–300 μm pores, promote bone