Biomaterials

Metals, ceramics, and polymers in hip arthroplasty: material properties, wear rates, and the impact of bearing surfaces on osseointegration and implant survival.

Overview

Selecting a graft or implant material for orthopaedic reconstruction requires balancing efficacy, safety, cost, and convenience [1]. Biomaterials in total hip arthroplasty encompass polymers, metals, and ceramics, with bearing surface characteristics undergoing ongoing development [2]. Similarly, biologic and material-related advantages and inadequacies of current and potential spinal implant materials guide further research and development [3]. For polymeric scaffolds, current coating materials for PLGA-based cell scaffolds present distinct advantages and disadvantages that inform clinical selection [6].

Biologic augmentation strategies show promise in soft-tissue repair. Preclinical and clinical studies on biologic augmentation for rotator cuff repair demonstrate improved structural healing and functional scores [18]. Specifically, the use of extracellular matrix (ECM) for augmentation of arthroscopic repairs of large to massive rotator cuff tears reduces the incidence of retears [20]. ECM augmentation also improves patient outcome scores in these repairs [20], making it a viable option during complicated rotator cuff repair cases where a significant failure rate is anticipated [20]. However, a lack of standardized protocols in biologic augmentation research leads to heterogeneity in outcomes [18].

In joint arthroplasty, hypoallergenic coated implant systems are not associated with inferior outcomes compared to standard implants in total knee arthroplasty [35]. Contemporary metal-metal and ceramic-ceramic bearing systems require careful patient selection and monitoring for long-term safety and effectiveness [44]. For complex reconstructions, resurfaced allograft-prosthesis composites can preserve bone stock and achieve good functional outcomes in very young children with proximal humerus bone tumors [37], though success may be limited by a high risk of complications [37]. Regarding highly porous titanium acetabular cups, there is only moderate quality evidence due to their recent introduction and limited use [42]. Prospective, comparative trials and active surveillance of arthroplasty registries are desirable for these devices [42].

Anatomy & Pathophysiology

Osseous Geometry and Biomechanics

Hip resurfacing accurately restores femoral offset without statistical difference compared to the non-operative hip [47]. Among compared procedures, hip resurfacing best achieves restoration of normal hip biomechanics [47]. Reconstruction of hip geometry using a single-version novel short-stem-system is achievable with comparable results to stem-systems offering multiple options [82]. However, a mismatch exists between the proximal femoral anatomy of a relevant proportion of adult hips and the implant geometry of the most common femoral component in total hip arthroplasty [106].

In dysplastic hip arthroplasty, an acetabular reinforcement ring with an additional hook effectively disperses stress and improves initial fixation strength in three-dimensional finite element analyses [92]. The hip center of rotation can be moved superiorly and/or medially to permit cup inclination below 45° with correct cup coverage [111]. Abduction angles of ≥45° are associated with a 40% increase in mean linear polyethylene wear compared to angles <45° [85]. The position of the acetabular component influences femoral head penetration of modern highly cross-linked polyethylene (HXLPE) [95].

Femoral Neck Fractures and Necrosis

For young patients with nonanatomically reduced femoral neck fractures, biomechanical studies of the femoral neck system show that positive buttress is more stable than negative buttress when the Pauwels angle is 30° [101]. The ratio between screw distance and femoral neck width on lateral radiography is a reliable predictor of femoral head necrosis [80]. Optimization of screw trajectories through broader screw spacing facilitated by a navigation system improves the local biomechanical environment and reduces the likelihood of femoral head necrosis [80].

Vascularized iliac bone flaps for treating femoral head necrosis resulted in improved biomechanical gain and clinical outcomes when a fenestration was placed at the center of the femoral neck [116].

Soft Tissue, Cartilage, and Microinstability

Hip microinstability is characterized by abnormal femoral head micromotion within the acetabulum, leading to cartilage damage and osteoarthritis, and is often associated with acetabular dysplasia or femoroacetabular impingement syndrome [91]. Proper diagnosis and treatment of complex hip pathologies has the potential to alter early degenerative changes in the adult hip [102]. Arthroscopic three-dimensional autologous chondrocyte transplantation using spheroids for full-thickness cartilage defects of the hip joint has shown encouraging early results [97].

Hip capsular injury in a professional soccer player was treated with platelet-rich plasma and bone marrow aspirate concentrate therapy, resulting in marked improvement in kinematic and kinetic performance measures and MRI appearance of the torn hip capsule and gluteus minimus tendon [59].

Bearing Surface Wear and Phenomena

Observed rates of volumetric polyethylene wear in total hip arthroplasty suggest that hips may require revision in the future [103]. Dimensional changes in acetabular components are largely due to creep or plastic flow rather than true wear, which accounts for only 3 to 30 percent of the total change [110]. Contemporary hip and knee simulator studies provide good information for screening new UHMWPE formulations for clinical wear performance, but comparable methodologies are lacking for screening for fracture resistance [113]. Squeaking hip is a peculiar phenomenon unique to hard-on-hard bearing surfaces [75].

Classification

Bearing Surfaces: Total hip arthroplasty implants utilize polymers, metals, and ceramics as commonly used biomaterials for bearing surfaces [2]. Ceramic bearings do not exhibit lower bacterial adhesion compared to other biomaterials [72].

Spinal Implants: Surface modification techniques are employed to enhance the osseointegration of spinal implants [3].

Scaffolds and Coatings: Current coating materials for poly(lactic-co-glycolic acid) (PLGA) scaffolds have distinct advantages and disadvantages that guide selection [6]. Biocompatible poly(L-lactic acid) (PLLA) scaffolds can be efficiently loaded with mesenchymal stem cells (MSCs), supporting chondrogenic differentiation and extracellular matrix (ECM) deposition to improve scaffold mechanics [66]. Differences in the extracellular matrix composition of scaffolds significantly impact their potential to promote the differentiation of bone marrow-derived MSCs [68]. Human MSC responses to biologic scaffolds vary significantly, with differences in adhesion, proliferation, and scaffold morphology across evaluated types [79].

Platelet-Based Products: A standardized classification system for platelet-based blood-derived products is essential to precisely document characteristics such as platelet count, activation state, and bioactive molecule interactions [61].

Osteochondral Implants: Implants with mechanical modification and hyaluronic acid (HA) impregnation in the cartilage phase outperform other implant types in osteochondral regeneration [63].

Antibiotic-Loaded Cement: The type of antibiotic selected for antibiotic-loaded cement has an important impact on cement properties [64].

Joint Replacement Stabilization: Artificial joint replacement types are mechanically stabilized in quantity [69].

Tissue Engineering Modalities: Tissue engineering for ligament and tendon healing and regeneration utilizes cells, bioactive molecules, and scaffolds [70].

Regeneration Requirements: Successful regeneration requires advanced biomaterials that regulate cell function and phenotype development in a spatiotemporally controlled manner [77].

Other Considerations: Particulate prosthetic debris in tissues around failed uncemented femoral components consists predominantly of particles less than one micrometer in size, present in amounts exceeding one billion particles per gram of tissue [74].

Clinical Presentation

Biomaterials utilized in total hip arthroplasty encompass polymers, metals, and ceramics [2]. In the context of knee articular surface lesions, implantation of a biomimetic osteochondral scaffold demonstrates a high long-term survival rate of 93.1% [4]. For meniscus defects, implantation of resorbable collagen scaffolds provides satisfactory clinical and structural outcomes in most cases [15]. Early results for tissue engineering approaches to cartilage restoration are encouraging, although long-term outcomes and data from larger study populations remain to be reported [5].

Porous tantalum implants yield good to excellent early clinical results in primary and revision total hip arthroplasty, with potential utility in cases requiring reattachment of muscles and tendons [11]. Specifically for early-stage osteonecrosis, porous tantalum implants show favorable intermediate-term performance, characterized by increased Harris hip scores and a lack of device-related clinical complications [27].

Metal-on-metal implants present specific clinical considerations regarding wear and biocompatibility. Excessive wear combined with a hypersensitivity response may underlie early adverse tissue reactions in some patients [13]. While intermediate-term clinical performance of metal-on-metal bearings is favorable, lingering concerns persist regarding the biologic consequences of metal release, including local tissue effects and potential systemic effects [32]. However, at 20 years, soft-tissue imaging and serum metal ion studies suggest that metal-on-metal resurfacing implants can be well tolerated in young patient groups [14].

Systemic distribution of metallic and polyethylene wear particles is a common finding in patients with both failed and primary total joint prostheses [28]. In total knee arthroplasty, approximately 12% by weight of wear products are metallic; these particles and ions may become clinically relevant for patients sensitive to these materials [29].

Taper corrosion provides essential background for orthopedic surgeons regarding diagnosis and treatment, though diagnostic and therapeutic methods are expected to advance as more information becomes available [26]. Significant strides are being made in understanding implant-associated infections and developing technologic approaches such as implant coatings and new bioactive molecules. Nevertheless, challenges in diagnostics, antibiotic resistance, and cost-effectiveness remain before mainstream clinical acceptance [31].

In arthroscopic double-row rotator cuff repair, both bio-absorbable and non-resorbable anchors lead to osseous reaction. The consequences of pronounced fluid in poly-L-lactic acid (PLLA) patients remain unclear [8].

Investigations

Plain radiography: Standard X-rays demonstrate osseous integration of spongy hydroxyapatite after 6 weeks in hand surgery patients, with active bone remodeling continuing after several years [67]. Radiographic signs of loosening suggest that surrounding bone does not form a stable interface with pyrolytic carbon implants [88]. The appearance of radiolucencies in the osteointegration of uncemented femoral stems is multi-factorial [89]. High pore count and porosity in neat and composite bone cement mantles were not visible on standard clinical radiographs [71]. Radiographic wear data on conventional polyethylene are consistent with laboratory studies showing that radiation-induced cross-linking has a beneficial effect on wear resistance [94]. Novel porous metal pillars provided reliable radiological evidence of fixation for tibial bone defects in primary total knee arthroplasty with a minimum 2-year follow-up [90].

MRI: Magnetic resonance imaging indicates that donor sites after autologous osteochondral mosaicplasty for elbow cartilaginous lesions are resurfaced with fibrous tissue [60]. The overall short-term clinical and MRI outcome of osteochondral scaffold plugs for cartilage repair in the knee is modest [62]. MRI supports the use of preoperative planning and postoperative assessment of fragment healing for cartilage lesions repaired with bioabsorbable devices [65]. The regenerative potential of cell-free biomimetic osteochondral scaffolds is limited, as signal alterations persist over time on MRI scans [57]. At 20 years, soft-tissue imaging and serum metal ion studies suggest that a metal-on-metal resurfacing implant can be well tolerated in young patients [14]. All-polymer PEEK knee prostheses demonstrate favourable imaging characteristics in a cadaveric setting, without clinically relevant metal-related artefacts [50]. All-polymer PEEK knee prostheses allow good visibility of simulated implant complications across radiography, CT, and MRI in a cadaveric setting [50]. No neoplastic complications were detected at autologous adipose tissue-derived stem cell (ADSC) implantation sites using MRI tracking and telephone follow-ups in 100 joints in 91 patients [78].

CT: Pre-surgical MRI imaging should be considered as effective as CT for bone assessment of neurogenic heterotopic ossification (NHO) and their features [93].

Other Considerations: Surgeons must consider efficacy, safety, cost, and convenience when choosing a graft material for revision acetabular reconstruction [1]. Technologic advances in implant materials, design, amputee care, and imaging continue to drive improvements in patient care and outcomes [9]. Both bio-absorbable and non-resorbable anchors lead to osseous reaction in rotator cuff repair [8]. The consequences of pronounced fluid in poly-L-lactic acid (PLLA) patients remain unclear following rotator cuff repair with bio-absorbable anchors [8]. Magnetic targeting of autologous mesenchymal stem cells was safely performed for cartilage repair [76]. Magnetic targeting of autologous mesenchymal stem cells showed complete coverage of defects with cartilage-like tissues 48 weeks after treatment [76]. Magnetic targeting of autologous mesenchymal stem cells showed significant improvement in clinical outcomes 48 weeks after treatment [76]. Biologic chondrofacilitation using bone marrow aspirate concentrate or mesenchymal stem cells augments microfracture for cartilage lesions with osseous involvement [81]. Biologic chondrofacilitation using bone marrow aspirate concentrate or mesenchymal stem cells improves clinical outcomes for cartilage lesions with osseous involvement [81]. Biologic chondrofacilitation using bone marrow aspirate concentrate or mesenchymal stem cells improves radiographic outcomes for cartilage lesions with osseous involvement [81]. Autologous collagen-induced chondrogenesis (ACIC) demonstrates sustained good clinical results as an enhancement of standard microfracture [83]. MRI evidence suggests successful chondral regeneration with autologous collagen-induced chondrogenesis (ACIC) [83].

Treatment

Non-Operative

Promising and established treatment modalities for osteonecrosis include nonweightbearing, pharmacological treatments, extracorporeal shock wave therapy, pulsed electromagnetic fields, core decompression surgery, and cellular therapies [96]. Minimally invasive necrotic bone washing leads to significantly greater bone volume compared to non-weight-bearing alone after femoral head ischemic osteonecrosis [87]. Fibrin glue is a viable non-invasive treatment option for persistent post-arthroscopic knee seromas, although larger studies are needed [86].

Operative

Indications: Surgical options for osteonecrosis of the femoral head aim to preserve the joint if diagnosed before collapse [16]. A cautious approach is recommended for shoulder arthroplasty in patients with a history of metal hypersensitivity, including careful evaluation of suspected sensitivities [38]. Metal-on-metal bearing couples are contraindicated in cases of metal allergies or end-stage renal dysfunction [40].

Surgical Approach / Technique: Nonvascularized bone grafting for hip osteonecrosis yields short-term results that compare similarly to nonoperative treatment and other reports of nonvascularized bone grafting [55]. Three differing methods of treating intraoperative nondisplaced calcar fractures demonstrated little radiographic stem subsidence, but the risk of reoperation was much higher than expected [100].

Implant Selection: Surgeons must consider efficacy, safety, cost, and convenience when choosing a graft material for revision acetabulum procedures [1]. The choice of prosthesis for total hip arthroplasty in osteoarthritis should be determined by the rate of revision, local costs, and the preferences of the surgeon and patient [36]. The degree of arthritis should not affect the choice of prosthetic material for hemiarthroplasty, though this suggestion needs further investigation [39].

Adjuncts: Biologics and scaffolds are considered key components of future anterior cruciate ligament (ACL) treatment, with ACL reconstruction with improved outcome, ACL repair, and ACL tissue engineering being promising goals [33]. The use of extracellular matrix (ECM) for augmentation of arthroscopic repairs of large to massive rotator cuff tears reduces the incidence of retears, improves patient outcome scores, and is a viable option during complicated cases with anticipated significant failure rates [20]. In a chronic rotator cuff tear model, the control group demonstrated a similar outcome to augmented repairs with demineralized cortical bone matrix [98]. Current research on biologic augmentation for rotator cuff repair presents mixed results, with preclinical and clinical studies showing improved structural healing and functional scores, but a lack of standardized protocols leading to heterogeneity in outcomes [18]. The effectiveness of orthobiologic agents is currently being studied; while they have the potential to improve local biology and expedite healing, it is difficult to interpret current literature to determine their efficacy and clinical usefulness due to heterogeneity in preparations and lack of consensus [34]. Bone Marrow Aspirate (BMA) Matrix represents a suitable alternative for the enhancement of tissue repair mechanisms by modulating inflammation and acting as a natural biological scaffold, though more clinical studies are warranted to further clarify its efficacy [51].

Other Considerations: Biomimetic osteochondral scaffolds present a high survival rate of 93.1% at long-term follow-up for the treatment of knee articular surface lesions [4]. Early results of tissue engineering approaches for cartilage restoration are encouraging, though long-term outcomes and data from larger study subjects remain to be reported [5]. Hydrogel implants are as effective as osteochondral autologous transplantation for treating focal cartilage knee injury at 24 months, showing satisfactory results compared to preoperative status and being safe and effective [46]. A 3D printed network hydrogel composite scaffold for total meniscus replacement holds promise for enhancing surgical strategies and delivering superior long-term results for individuals with severe meniscus tears in a rabbit model [49]. Implantation of resorbable collagen scaffolds for the treatment of meniscus defects provides satisfactory clinical and structural outcomes in most cases [15]. Intermediate-term follow-up data suggest that alternative bearing materials (metal-on-metal, highly cross-linked polyethylene, ceramic-on-ceramic) may reduce the prevalence and severity of osteolysis compared with conventional metal-on-polyethylene couples, but long-term data are unavailable and future performance awaits clinical validation [7]. The survival of non-hydroxyapatite-coated femoral stems was similar to hydroxyapatite-coated stems, and hydroxyapatite coating did not seem to have an advantageous effect in terms of fixation and survival of the stem at 8- to 12-year follow-up [43]. Surface modification of PLGA-based cell scaffolds involves various coating materials with distinct advantages and disadvantages, guiding selection for specific applications [6]. Investigation into newer bone graft substitute materials for managing glenoid bone defects is warranted [12]. Advances in minimally invasive and biologic therapies are reshaping treatment paradigms for aneurysmal and simple bone cysts, yet standardized outcome measures and head-to-head comparative trials remain needed [99].

Complications

Polyethylene wear: Cross-linked polyethylene demonstrates superior survivorship (100%) compared to non-cross-linked liners (94.7%) at 10-year follow-up when revision for wear-related complications is the endpoint [19]. In patients aged 50 years and younger, long-term analysis of highly cross-linked polyethylene reveals negligible wear, no aseptic loosening, and excellent clinical outcomes at and beyond 15 years of follow-up [41]. Conversely, at minimum 5-year follow-up, conventional and crosslinked polyethylene show no difference in total knee arthroplasty regarding survivorship, clinical, radiographic, and safety outcomes [22]. Early wear or mechanical failure of polyethylene was absent in the CRP group at short-term follow-up [52]. Alternative bearing materials may reduce the prevalence and severity of osteolysis compared with conventional metal-on-polyethylene surfaces in intermediate-term data, though long-term data are unavailable [7]. Pigmented villonodular synovitis occurring 14 years after total hip arthroplasty is believed to represent a reaction to polyethylene, metal, and cement wear or trauma initiated by the prosthesis [115].

Metal-on-metal complications: Excessive wear and hypersensitivity responses may cause early adverse tissue reactions in patients with metal-on-metal implants [13]. Patients with new or evolving hip symptoms and a prior history of total hip arthroplasty warrant orthopaedic surgical evaluation for potential systemic cobalt toxicity [105].

Ceramic complications: Longer follow-up is necessary to identify possible deleterious effects, such as ceramic fracture, in cementless alumina-on-alumina total hip arthroplasty [17].

Other Considerations: Surgeons must consider efficacy, safety, cost, and convenience when choosing graft materials for revision acetabular reconstruction [1]. No complications related to bioabsorbable materials were experienced in a study using quadrupled hamstring tendon grafts with bioabsorbable interference screw fixation [10]. Porous tantalum offers good to excellent early clinical results in primary and revision total hip arthroplasty [11]. At minimum 5-year follow-up, there was no difference between conventional and crosslinked polyethylene in total knee arthroplasty regarding survivorship, clinical, radiographic, and safety outcomes [22]. Longer-term follow-up is required to assess wear and loosening for cementless modular centroid reconstruction cups in young adults with congenital dysplasia of the hip [23]. The 20-year survivorship of hip resurfacing arthroplasties was 83.5%, surpassing that of total hip arthroplasties in use 20 years ago in young patients [24]. Autologous platelet-rich plasma showed a positive tendency in tissue evolution over time, whereas the placebo group showed negative evolution in a rabbit model of full-thickness articular defects [25]. Biologic resurfacing of the glenoid with meniscal allograft exhibits inconsistent results and high complication rates with long-term follow-up [45]. Both uncemented tantalum metal components and cemented tibial components have excellent survivorship up to 15 years after implantation in total knee arthroplasty [48]. The occurrence of arthritis of the implanted surfaces is a cause of concern in bipolar fresh osteochondral allografts for glenohumeral post-traumatic arthritis, although it was unrelated to the clinical result [104]. Despite major primary complications and a high incidence of radiographic signs of degenerative changes after 8.8 years, bipolar radial head arthroplasty achieved mainly good clinical results [107]. Continued follow-up is needed to determine the long-term results of cementless total hip arthroplasty in patients with osteopoikilosis, hip dysplasia, and advanced osteoarthritis [21].

Recovery

Light activity (weeks): The provided evidence does not specify a week-range for light activity, desk work, or driving.

Full activity (months): The provided evidence does not specify a month-range for manual work, sport, or full range of motion/strength return.

Complete recovery / outcome plateau (months): The provided evidence does not specify a month-range for the stabilization of pain, strength, or final functional outcomes.

Rehabilitation protocol: The provided evidence does not detail physical therapy phasing, immobilization duration, weight-bearing progression, or sling/brace removal timing.

Functional milestones: The provided evidence does not report validated patient-reported outcome measure (PROM) trajectories or specific benchmark scores (e.g., Constant, ASES, WOMAC).

Other Considerations: Choosing a graft material requires consideration of efficacy, safety, cost, and convenience [1]. Biomimetic osteochondral scaffold implantation for knee articular surface lesions has a long-term survival rate of 93.1% [4]. Early results for tissue engineering approaches to cartilage restoration are encouraging, but long-term outcomes and data from larger study subjects remain to be reported [5]. Intermediate-term follow-up suggests alternative bearing materials may reduce the prevalence and severity of osteolysis compared with conventional metal-on-polyethylene couples, but long-term data are unavailable and future performance awaits clinical validation [7]. Longer follow-up is necessary to identify possible deleterious effects, such as ceramic fracture, in cementless alumina-on-alumina total hip arthroplasty in patients younger than 50 years [17]. At 10-year follow-up, cross-linked polyethylene demonstrated superior survivorship (100%) compared to non-cross-linked liners (94.7%) for total hip arthroplasty when using revision for wear-related complications as an endpoint [19]. Continued follow-up is needed to determine the long-term results of cementless total hip arthroplasty in a patient with osteopoikilosis, hip dysplasia, and advanced osteoarthritis [21]. At minimum 5-year follow-up, there was no difference between conventional and crosslinked polyethylene in total knee arthroplasty regarding survivorship, clinical, radiographic, and safety outcomes [22]. Longer-term follow-up is required to assess wear and loosening for cementless modular centroid reconstruction cups in young adults with congenital dysplasia of the hip [23]. The 20-year survivorship of the Conserve Plus hip resurfacing arthroplasty was 83.5%, surpassing that of total hip arthroplasties in use 20 years ago in young patients, suggesting satisfactory lifelong durability for almost all remaining patients [24]. Autologous platelet-rich plasma (PRP) treatment of full-thickness articular defects in rabbits showed a positive tendency in tissue evolution over time, whereas the placebo group showed negative evolution [25]. Further study is necessary to determine the long-term durability of the prosthesis-bone interface for the porous-coated anatomic total hip prosthesis inserted without cement [53]. A long-term outcome study is required to assess late mechanisms of failure and the effects of bone mineral density (BMD) related changes for primary stability of a proximally coated and tapered stem [54]. Further study is necessary to assess the long-term durability of tantalum acetabular augments in one-stage exchange of infected total hip arthroplasty [56]. At an average of 127 months follow-up, no significant differences were found in clinical results, radiographic results, and survival distributions regarding the presence or absence of hydroxyapatite/tricalcium-phosphate (HA/TCP) coating on cementless femoral stems [58]. Graft ultrastructural maturation, characterized by large-diameter collagen fibrils and a bimodal collagen fibril distribution, is a common phenomenon in autogenous hamstring grafts after anterior cruciate ligament reconstruction and is not time dependent in the midterm to long term [109]. Within the relatively short time-frame of the study, there appeared to be no clinical or radiographic advantage to the use of hydroxyapatite in primary total hip arthroplasties [112]. Use of biphasic interpositional allograft for rotator cuff repair augmentation resulted in a histological profile essentially equivalent to that of a standard rotator cuff repair at 3-, 6-, and 12-week postoperative timepoints in an ovine model [117]. Metal-carbon fiber composite femoral stems showed promising results at early follow-up, with clinical outcomes similar to those of an all-metal stem at ten-year follow-up [118]. Temporal histologic changes during the 6- to 24-month postoperative period of graft maturation were observed in tendon grafts treated with an endogenous preparation rich in growth factors (PRGF), with newly formed connective tissue enveloping most grafts [119]. Clinical and radiological data support the use of the cemented Contemporary acetabular component in patients under 50 years of age, resulting in a ten-year survival rate greater than 90% [120].

Key Evidence

• [L5] The surgeon must consider efficacy, safety, cost, and convenience when choosing a graft material. (10.1302/0301-620x.96b11.34452)
• [L5] This review discusses various aspects of commonly used biomaterials in total hip arthroplasty implants, including polymers, metals, and ceramics, to provide updated information on their development and bearing surface characteristics. (10.1186/s42836-021-00092-6)
• [L5] Highlighting the biologic- and material-related advantages and inadequacies of current and potential implant materials may guide further research and development. (10.5435/jaaos-d-17-00645)
• [L4] The implantation of this scaffold for the treatment of knee articular surface lesions presents a high survival rate of 93.1% at long-term follow-up. (10.1177/23259671261418010)
• [L5] Early results of the described tissue engineering approach for cartilage restoration are encouraging, though long-term outcomes and data from larger study subjects remain to be reported. (10.1016/j.arthro.2021.03.014)
• [L4] This review summarizes and discusses the advantages and disadvantages of current coating materials used in PLGA scaffolds to provide guidance for selecting surface coating materials. (10.3390/polym16010165)
• [L4] Intermediate-term follow-up data suggest that the prevalence and severity of osteolysis may be reduced with alternative bearing materials compared with conventional metal-on-polyethylene bearing surface couples, but long-term data are presently unavailable and future performance awaits clinical validation. (10.5435/00124635-200800001-00008)
• [L3] Both materials lead to osseous reaction, whereas consequences of pronounced fluid in PLLA patients remain unclear. (10.1007/s00167-013-2510-3)
• [L4] Complications related to the use of bioabsorbable materials were not experienced in this study. (10.1177/03635465030310040701)
• [L5] The material offers good to excellent early clinical results in primary and revision total hip arthroplasty with potential for use in cases requiring reattachment of muscles and tendons. (10.5435/00124635-200611000-00008)
• [L5] However, investigation into these newer materials and their use and applicability to managing glenoid defects seems warranted. (10.1016/j.jse.2006.12.001)
• [L5] Excessive wear along with a hypersensitivity response may be at the origin of the early adverse tissue reactions reported in some patients with metal-on-metal implants. (10.2106/jbjs.j.01877)
• [L4] At 20 years, soft-tissue imaging and serum metal ion studies suggest that a metal-on-metal resurfacing implant can be well tolerated in a group of young patients. (10.1302/0301-620x.105b9.bjj-2022-0713.r2)
• [L1] Implantation of resorbable collagen scaffolds for the treatment of meniscus defects provides satisfactory clinical and structural outcomes in most cases. (10.1016/j.arthro.2014.11.019)
• [L5] There is no consensus yet on a particular treatment, with surgical options aiming to preserve the joint if diagnosed before collapse, while future therapies include biologically active molecules and implants. (10.1302/2058-5241.4.180036)
• [L3] However, longer follow-up is necessary to identify possible deleterious effects, especially ceramic fracture. (10.1016/j.arth.2006.02.169)
• [L5] Current research on biologic augmentation presents mixed results; while preclinical and clinical studies show improved structural healing and functional scores, a lack of standardized protocols leads to heterogeneity in outcomes. (10.1016/j.xrrt.2026.100705)
• [L1] At 10-year follow-up, cross-linked polyethylene demonstrated superior survivorship with 100% survivorship compared to 94.7% for non-cross-linked liners (P = .003) when using revision for wear-related complications as an endpoint. (10.1016/j.arth.2012.03.048)
• [L3] The use of ECM for augmentation of arthroscopic repairs of large to massive RCTs reduces the incidence of retears, improves patient outcome scores, and is a viable option during complicated cases in which a significant failure rate is anticipated. (10.1016/j.arthro.2015.02.032)
• [Case_report] Continued follow-up is needed to determine the long-term results. (10.1186/s12891-021-04258-w)
• [L3] Longer-term follow-up is registered concerning wear and loosening. (10.1016/j.arth.2007.01.003)
• [L3] The 83.5% 20-year survivorship of this initial series surpasses that of total hip arthroplasties in use 20 years ago in these young patients, suggesting satisfactory lifelong durability of the device for almost all of the remaining patients. (10.1302/0301-620x.103b7.bjj-2020-2256.r1)
• [L5] The evolution of tissue treated with autologous PRP showed a positive tendency over time, while the placebo group was negative. (10.1007/s00167-012-2141-0)
• [L5] The material presented provides a strong background about taper corrosion for the practicing orthopedic surgeon and practical information about diagnosis and treatment, though methods will advance as more information becomes available. (10.1016/j.arth.2018.07.008)
• [L4] The early clinical results associated with the porous tantalum implant have been favorable, with increased Harris hip scores and a lack of device-related clinical complications. (10.2106/jbjs.e.00490)
• [L4] Systemic distribution of metallic and polyethylene wear particles was a common finding in patients with both failed and primary total joint prostheses. (10.2106/00004623-200004000-00002)
• [Paper] Approximately 12% by weight of the wear products were metallic, and these particles and ions may become clinically relevant for patients sensitive to these materials in particular. (10.1007/s00264-013-2162-4)
• [L5] Significant strides are being made in understanding implant-associated infections and developing technologic approaches such as implant coatings and new bioactive molecules, but challenges remain in diagnostics, antibiotic resistance, and cost-effectiveness before mainstream clinical acceptance. (10.5435/jaaos-20-07-478)
• [L5] Intermediate-term clinical performance of metal-on-metal bearings has been favorable, but lingering concerns exist regarding biologic consequences of metal release, including local tissue effects and potential systemic effects. (10.5435/00124635-200902000-00003)
• [L5] Biologics and scaffolds are considered key components of future ACL treatment, with ACL reconstruction with improved outcome, ACL repair, and ACL tissue engineering being promising goals. (10.1016/j.arthro.2022.11.006)
• [L1] In comparable patient cohorts, the use of this coated implant system does not appear to be associated with inferior outcomes. (10.1016/j.arth.2025.11.018)
• [L2] We would recommend that the choice of prosthesis should be determined by the rate of revision, local costs and the preferences of the surgeon and patient. (10.1302/0301-620x.97b4.34242)
• [L4] Although its success may be limited owing to a high risk of complications, a resurfaced allograft-prosthesis composite could be an alternative surgical option in order to preserve the bone stock and achieve good functional outcomes in very young children. (10.1097/corr.0000000000002969)
• [L5] The review recommends a cautious approach to patients with a history of metal hypersensitivity, including careful evaluation of suspected sensitivities and the use of metallic implants with low to no nickel content if available, while noting that evidence-based recommendations for shoulder arthroplasty are currently lacking. (10.1016/j.jse.2015.01.015)
• [L5] Although the degree of arthritis should not affect the choice of prosthetic material, this suggestion needs to be further investigated. (10.1016/j.jse.2019.09.041)
• [Paper] Metal-on-metal bearing couples are contraindicated in cases of metal allergies or end-stage renal dysfunction, and small size resurfacing should be used cautiously. (10.1016/j.otsr.2010.05.008)
• [L3] This long-term analysis found negligible polyethylene wear, no incidence of aseptic loosening, and excellent clinical outcomes at and beyond 15 years of follow-up. (10.1302/0301-620x.103b7.bjj-2020-2443.r1)
• [L5] The authors agree with the systematic review that there is only moderate quality evidence for highly porous titanium cups due to their recent introduction and limited use, and they suggest that prospective, comparative trials and active surveillance of arthroplasty registries are desirable. (10.1016/j.arth.2020.04.065)
• [L1] The survival of non-hydroxyapatite-coated stems was similar to hydroxyapatite-coated stems, and hydroxyapatite coating did not seem to have an advantageous effect in terms of fixation and survival of the stem. (10.1016/j.arth.2007.11.007)
• [L5] Contemporary metal-metal and ceramic-ceramic systems show promise but require careful patient selection and monitoring for long-term safety and effectiveness. (10.2106/00004623-200100022-00002)
• [L4] With long-term follow-up, biologic resurfacing of the glenoid with meniscal allograft exhibits inconsistent results and high complication rates. (10.1016/j.jse.2012.04.019)
• [L1] Both techniques showed satisfactory results compared to preoperative status, with the Hydrogel implant being safe and effective. (10.1007/s00167-018-4834-5)
• [L4] Restoration of normal hip biomechanics is best achieved with hip resurfacing, as it accurately restored femoral offset without statistical difference compared to the non-operative hip. (10.1186/1749-799x-6-65)
• [L1] However, both have excellent survivorship up to 15 years after implantation. (10.1302/0301-620x.102b8.bjj-2019-1448.r1)
• [Paper] This novel meniscus scaffold holds promise for enhancing surgical strategies and delivering superior long-term results for individuals with severe meniscus tears. (10.1002/ksa.12139)
• [L5] All-polymer PEEK knee prostheses demonstrate favourable imaging characteristics in a cadaveric setting, without any clinically relevant metal-related artefacts and with good visibility of simulated implant complications across radiography, CT, and MRI. (10.1186/s13018-026-06736-0)
• [L5] The BMA Matrix represents a suitable alternative for the enhancement of tissue repair mechanisms by modulating inflammation and acting as a natural biological scaffold, though more clinical studies are warranted to further clarify its efficacy. (10.3390/ijms22052762)
• [L2] Further study is necessary to determine the long-term durability of the prosthesis-bone interface. (10.2106/00004623-199301000-00011)
• [L2] A long-term outcome study is required to assess late mechanisms of failure and the effects of bone mineral density (BMD) related changes. (10.1302/0301-620x.103b4.bjj-2020-1648.r1)
• [L4] The short-term results compare similarly to nonoperative treatment and other reports of nonvascularized bone grafting. (10.1007/s11999-008-0211-x)
• [L4] The regenerative potential of this scaffold is limited, as demonstrated by the signal alterations persisting over time on MRI scans. (10.1177/03635465211029292)
• [L1] At an average of 127 months follow-up, no significant differences were found in clinical results, radiographic results, and survival distributions with regard to the presence or absence of HA/TCP coating. (10.1016/j.arth.2006.06.005)
• [L4] He also demonstrated marked improvement in kinematic and kinetic performance measures and MRI appearance of the torn hip capsule and gluteus minimus tendon. (10.1007/s00167-012-2232-y)
• [L4] However, magnetic resonance imaging indicates that the donor site is resurfaced with fibrous tissue. (10.1177/0363546507306465)
• [L5] A standardized classification system is essential for research and clinical application, emphasizing precise documentation of products' characteristics, including platelet count, activation state and bioactive molecule interactions. (10.1002/ksa.12655)
• [L4] The overall short-term clinical and MRI outcome of the osteochondral scaffold plug for cartilage repair in the knee is modest. (10.1016/j.arthro.2011.07.017)
• [L5] The implants with mechanical modification and HA impregnation in the cartilage phase outperformed all other types of implant. (10.1007/s00167-013-2467-2)
• [L4] It supports the use of MRI for both preoperative planning and postoperative assessment of fragment healing. (10.1016/j.arthro.2007.07.025)
• [L5] Biocompatible PLLA scaffolds have been developed that can be efficiently loaded with MSCs, supporting chondrogenic differentiation and ECM deposition that improves the mechanics of the scaffold. (10.1007/s00167-012-2148-6)
• [L4] Standard X-rays showed osseous integration after 6 weeks in all patients, with active bone remodeling still occurring after several years. (10.1054/jhsb.2001.0686)
• [L5] Differences in the extracellular matrix composition of scaffolds significantly impact their potential to promote differentiation of bone marrow-derived mesenchymal stem cells. (10.1016/j.arthro.2016.04.033)
• [L5] Mechanically, all four artificial joint replacement types are stabilized in quantity. (10.1186/s12891-017-1651-9)
• [L5] The field of tissue engineering has evolved to include cells, bioactive molecules, and scaffolds, with bioscaffolds showing potential for ligament and tendon healing and regeneration in animal models, warranting continued multidisciplinary efforts to improve outcomes. (10.1007/s00167-009-0776-2)
• [L5] The high pore count and porosity were not visible on standard clinical radiographs. (10.1016/j.arth.2007.03.040)
• [L5] Ceramic bearings appeared not to be related to a lower bacterial adhesion than other biomaterials. (10.1016/j.otsr.2018.03.003)
• [L4] Particulate prosthetic debris in tissues around failed femoral components inserted without cement constitutes a class of particles predominantly less than one micrometer in size and present in amounts exceeding one billion particles per gram of tissue. (10.2106/00004623-199509000-00002)
• [L2] The squeaking hip is a peculiar phenomenon unique to hard-on-hard bearing surfaces. (10.1016/j.arth.2006.12.010)
• [L4] Magnetic targeting of MSCs was safely performed and showed complete coverage of the defects with cartilage-like tissues and significant improvement in clinical outcomes 48 weeks after treatment. (10.1007/s00167-018-4898-2)
• [L4] Using both MRI tracking and telephone follow ups in 100 joints in 91 patients treated, no neoplastic complications were detected at any ADSC implantation sites. (10.1186/1471-2474-14-337)
• [L5] Significant differences in the response of human MSCs to biologic scaffolds existed, with MSC adhesion, proliferation, and scaffold morphology varying throughout the evaluated types. (10.1016/j.arthro.2013.11.020)
• [L3] The optimization of screw trajectories, particularly through broader screw spacing facilitated by a navigation system, emerges as a promising strategy for improving the local biomechanical environment and reducing the likelihood of femoral head necrosis. (10.1186/s13018-024-05243-4)
• [Commentary] Both treatment options improve clinical and radiographic outcomes. (10.1016/j.arthro.2021.05.056)
• [L3] Reconstruction of hip geometry using a single-version novel short-stem-system is achievable with comparable results to stem-systems offering multiple options. (10.1186/s12891-022-05923-4)
• [L4] The study demonstrates sustained good clinical results from an enhancement of a standard microfracture technique that is reinforced with MRI evidence suggestive of successful chondral regeneration. (10.1007/s00167-020-05884-y)
• [L4] The orientation of the acetabular component affects polyethylene wear, with abduction angles of ≥45° associated with a 40% increase in mean linear polyethylene wear compared to angles <45°. (10.2106/00004623-200300004-00007)
• [L5] Although larger studies are certainly needed, this case suggests fibrin glue is a viable non-invasive treatment option for persistent post-arthroscopic knee seromas. (10.1007/s00167-013-2505-0)
• [L5] The study demonstrates that minimally invasive necrotic bone washing leads to significantly greater bone volume compared to non-weight-bearing alone. (10.2106/jbjs.20.00578)
• [L5] The clinical outcomes and radiographic signs of loosening suggest that the surrounding bone does not form a stable interface with pyrolytic carbon implants. (10.2106/jbjs.k.00527)
• [L4] The appearance of radiolucencies is multi-factorial. (10.1186/s42836-024-00274-y)
• [L4] The use of novel porous metal pillars yielded satisfactory clinical outcomes and reliable radiological evidence of fixation in this study with a minimum 2-year follow-up. (10.1186/s12891-023-06962-1)
• [Paper] In biomechanical analyses, the hook effectively dispersed stress and improved the initial fixation strength of the acetabular reinforcement ring. (10.1186/s13018-018-1023-7)
• [L4] This preliminary study suggests that pre-surgical MRI imaging should be considered as effective as CT for bone assessment of NHO and their features. (10.1186/s13018-021-02869-6)
• [L3] Radiographic wear data on conventional polyethylene are consistent with laboratory studies showing that radiation-induced cross-linking has a beneficial effect on wear resistance. (10.2106/00004623-200405000-00020)
• [L3] The position of the acetabular component can influence the femoral head penetration of modern HXLPEs. (10.1302/0301-620x.107b5.bjj-2024-1083.r1)
• [L5] Promising and established treatment modalities for osteonecrosis include nonweightbearing, pharmacological treatments, extracorporeal shock wave therapy, pulsed electromagnetic fields, core decompression surgery, and cellular therapies. (10.1016/j.arthro.2021.08.032)
• [L3] As the first results have been encouraging, the ACT 3D with spheroids at the hip should be continued. (10.1007/s00167-014-3293-x)
• [L5] The control group demonstrated a similar outcome to augmented repairs. (10.1016/j.jse.2017.01.003)
• [L4] Advances in minimally invasive and biologic therapies are reshaping treatment paradigms for aneurysmal and simple bone cysts, yet standardized outcome measures and head-to-head comparative trials remain needed. (10.1186/s13018-026-06792-6)
• [L3] The three described methods of managing intraoperative nondisplaced calcar fractures demonstrated little radiographic stem subsidence; however, the risk of reoperation was much higher than expected. (10.1016/j.arth.2024.03.049)
• [L5] From the perspective of biomechanics, when the Pauwels angle was 30°, positive buttress was more stable to negative buttress. (10.1186/s12891-022-06124-9)
• [L4] The observed rates of volumetric wear suggest that the hips may require revision in the future. (10.2106/00004623-199505000-00014)
• [L5] Although unrelated to the clinical result, the occurrence of arthritis of the implanted surfaces is cause of concern. (10.1007/s00167-011-1793-5)
• [L5] Patients with new or evolving hip symptoms and a prior history of total hip arthroplasty warrant orthopaedic surgical evaluation. (10.1302/0301-620x.98b1.36374)
• [L4] The present study revealed a mismatch between proximal femoral anatomy of a relevant proportion of adult hips and implant geometry of the most common femoral component in total hip arthroplasty. (10.1016/j.arth.2016.02.015)
• [L4] Despite major primary complications and high incidence of radiographic signs of degenerative changes after 8.8 years, mainly good clinical results were achieved with Judet's bipolar prosthesis. (10.1016/j.jse.2010.05.022)
• [L4] Graft ultrastructural maturation, characterized by large-diameter collagen fibrils and a bimodal collagen fibril distribution, is a common phenomenon and is not time dependent in the midterm to long term. (10.1177/0363546515584039)
• [L5] Dimensional changes in acetabular components are largely due to creep or plastic flow rather than true wear, which accounts for only 3 to 30 percent of the total change. (10.2106/00004623-198062040-00007)
• [L3] The hip center of rotation can be moved superiorly and/or medially to permit cup inclination below 45° with correct cup coverage. (10.1016/j.arth.2007.06.008)
• [L3] Within the relatively short time-frame of this study, there appeared to be no clinical or radiographic advantage to the use of hydroxyapatite in primary total hip arthroplasties. (10.2106/00004623-199603000-00001)
• [L5] Contemporary hip and knee simulator studies provide good information for screening new UHMWPE formulations for clinical wear performance, but comparable methodologies are lacking for screening for fracture resistance. (10.5435/00124635-200800001-00019)
• [L4] The authors believe the disease represents a reaction to polyethylene, metal, and cement wear or trauma initiated by the prosthesis. (10.1016/j.arth.2009.11.016)
• [L4] A fenestration at the center of the femoral neck resulted in improved biomechanical gain and clinical outcomes. (10.1186/s13018-024-05390-8)
• [L5] Use of the biphasic interpositional allograft resulted in a histological profile that was essentially equivalent to that of a standard RCR at 3-, 6-, and 12-week postoperative timepoints. (10.1016/j.arthro.2023.03.018)
• [L2] The implant showed promising results at the time of early follow-up, and the clinical outcomes were similar to those of an all-metal stem at the time of a ten-year follow-up. (10.2106/jbjs.m.01542)
• [L3] We have shown temporal histologic changes during the 6- to 24-month postoperative period of graft maturation, with newly formed connective tissue enveloping most grafts treated with PRGF. (10.1016/j.arthro.2009.08.019)
• [L3] The clinical and radiological data resulting in a ten-year survival rate > 90% in young patients support the use of the Contemporary acetabular component in this specific patient group. (10.1302/0301-620x.95b12.31292)

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[82] Restoration of hip geometry after total hip arthroplasty: retrospective comparison of two short stems and one straight stem. BMC Musculoskeletal Disorders. 2022. DOI: 10.1186/s12891-022-05923-4

[83] Articular cartilage repair using autologous collagen-induced chondrogenesis (ACIC): a pragmatic and cost-effective enhancement of a traditional technique. Knee Surgery, Sports Traumatology, Arthroscopy. 2020. DOI: 10.1007/s00167-020-05884-y

[85] POLYETHYLENE WEAR AND ACETABULAR COMPONENT ORIENTATION. The Journal of Bone and Joint Surgery-American Volume. 2003. DOI: 10.2106/00004623-200300004-00007

[86] Fibrin glue as a non‐invasive outpatient treatment for post‐arthroscopic knee seromas. Knee Surgery, Sports Traumatology, Arthroscopy. 2013. DOI: 10.1007/s00167-013-2505-0

[87] Minimally Invasive Necrotic Bone Washing Improves Bone Healing After Femoral Head Ischemic Osteonecrosis. Journal of Bone and Joint Surgery. 2021. DOI: 10.2106/jbjs.20.00578

[88] Questions about Implant-Bone Interface with Pyrolytic Carbon. Journal of Bone and Joint Surgery. 2011. DOI: 10.2106/jbjs.k.00527

[89] Influence of proximal femoral morphology on osteointegration of the AMIS uncemented femoral stem in modern hip arthroplasty. Arthroplasty. 2024. DOI: 10.1186/s42836-024-00274-y

[90] Using novel porous metal pillars for tibial bone defects in primary total knee arthroplasty. BMC Musculoskeletal Disorders. 2023. DOI: 10.1186/s12891-023-06962-1

[91] Chapter 12 Hip Microinstability. 2019.

[92] Acetabular reinforcement ring with additional hook improves stability in three-dimensional finite element analyses of dysplastic hip arthroplasty. Journal of Orthopaedic Surgery and Research. 2018. DOI: 10.1186/s13018-018-1023-7

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