Particle migration and gap healing around trabecular metal implants

Biomechanics of Additively Manufactured Metallic Scaffolds-A Review

This review paper is related to the biomechanics of additively manufactured (AM) metallic scaffolds, in particular titanium alloy Ti6Al4V scaffolds. This is because Ti6Al4V has been identified as an ideal candidate for AM metallic scaffolds. The factors that affect the scaffold technology are the design, the material used to build the scaffold, and the fabrication process. This review paper includes thus a discussion on the design of Ti6A4V scaffolds in relation to how their behavior is affected by their cell shapes and porosities. This is followed by a discussion on the post treatment and mechanical characterization including in-vitro and in-vivo biomechanical studies. A review and discussion are also presented on the ongoing efforts to develop predictive tools to derive the relationships between structure, processing, properties and performance of powder-bed additive manufacturing of metals. This is a challenge when developing process computational models because the problem involves multi-physics and is of multi-scale in nature. Advantages, limitations, and future trends in AM scaffolds are finally discussed. AM is considered at the forefront of Industry 4.0, the fourth industrial revolution. The market of scaffold technology will continue to boom because of the high demand for human tissue repair.

Less polyethylene wear in monobloc compared to modular ultra-high-molecular-weight-polyethylene inlays in hybrid total knee arthroplasty: A 5-year randomized radiostereometry study

BACKGROUND

A modular polyethylene (PE) inlay in total knee arthroplasty (TKA) may wear on both sides. PE particles may induce osteolysis, which can lead to implant loosening. The aim of this study was to determine if PE wear in monobloc TKA differs from that ofmodular TKA at 60-month follow-up.

PATIENTS AND METHODS

In a prospective, patient-blinded trial, 50 patients were randomized to hybrid TKA surgery with either acementless high-porosity trabecular-metal tibial component with a monobloc UHMWPE inlay (MONO-TM) or a cementless low-porosity screw-augmented titanium fiber-mesh tibial component with a modular UHMWPE inlay (MODULAR-FM). Radiostereometry was used to measure PE wear and tibial component migration.

RESULTS

At 60-monthfollow-up, mean PE wear of the medial compartment was 0.24 mm and 0.61 mm and mean PE wear of the lateral compartment was 0.31 mm and 0.82 mm for the MONO-TM and the MODULAR-FM groups, respectively (p < 0.01). The PE wear-rate was 0.05 mm (95% CI 0.03-0.08) in the MONO-TM group and 0.14 mm (95% CI 0.12-0.17) in the MODULAR-FM group (p < 0.01). Total translation at 60 months was mean 0.30 mm (95% CI 0.10-0.51) less (p < 0.01) for MONO-TM compared with MODULAR-FM tibial components. The majority of tibial components were stable (<0.2 mm MTPM) from 12 to 24-month and 24 to 60-month follow-up.

CONCLUSION

At mid-term follow-up, monobloc PE inlay wear was approximately 40% of that of the modular PE inlay wear, which suggest that back-side wear of modular PE inlays is a significant contributor of PE wear in hybrid TKA.

Uncemented monoblock trabecular metal posterior stabilized high-flex total knee arthroplasty: similar pattern of migration to the cruciate-retaining design - a prospective radiostereometric analysis (RSA) and clinical evaluation of 40 patients (49 knees) 60 years or younger with 9 years' follow-up

Background and purpose - Uncemented monoblock cruciate retaining (CR) trabecular metal (TM) tibial components in total knee arthroplasty (TKA) work well in the long-term perspective in patients ≤ 60 years. Younger persons expect nearly normal knee flexion after TKA, but CR implants generally achieve less knee flexion compared with posterior stabilized (PS) implants. Cemented PS implants have higher revision rate than CR implants. Can an uncemented monoblock PS TM implant be used safely in younger patients? Patients and methods - 40 patients (49 knees) age ≤ 60 years with primary (20 knees) or posttraumatic osteoarthritis (OA) were operated with a high-flex TKA using an uncemented monoblock PS TM tibial component. Knees were evaluated with radiostereometric analysis (RSA) a mean 3 days (1-5) postoperatively, and thereafter at 6 weeks, 3 months, 1, 2, 5, and 9 years. Clinical outcome was measured with patient-related outcome measures (PROMs). Results - The implants showed a pattern of migration with initial large migration followed by early stabilization lasting up to 9 years, a pattern known to be compatible with good long-term results. Clinical and radiological outcome was excellent with 38 of the 40 patients being satisfied or very satisfied with the procedure and bone apposition to the entire implant surface in 46 of 49 knees. Mean knee flexion was 130°. 1 knee was revised at 3 months due to medial tibial condyle collapse. Interpretation - The uncemented monoblock PS TM implant works well in younger persons operated with TKA due to primary or secondary OA.

[Research progress of porous tantalum in bone tissue engineering]

Objective

To review the basical research progress of porous tantalum in bone tissue engineering.

Methods

The related basical research in fabrication, cytobiology, and surface modification of porous tantalum was reviewed and analyzed.

Results

The outstanding physiochemical properties of porous tantalum granted its excellent performance in biocompatibility and osteointegration, as well as promoting cartilage and tendon tissue restoration. However, the clinical utilization of porous tantalum is somehow greatly limited by the complex and rigid commercial fabrication methods and extraordinary high cost. Along with the publication of novel fabrication and surface modification technology, the application of porous tantalum will be more extensive, the promotion in bone tissue regeneration will be more prominent.

Conclusion

Porous tantalum has advantage in bone defect restoration, and significant breakthrough technology is needed in fabrication methods and surface modification.

Radiolucent lines are decreased at 3 years following total knee arthroplasty using trabecular metal tibial components

Objective To analyse location and frequency, and change over time, of radiolucent lines (RLLs) around trabecular metal tibial components in total knee arthroplasty (TKA). Methods Osteoarthritic knees in patients who had undergone TKA were retrospectively evaluated via analysis of RLLs on anteroposterior and lateral X-rays obtained at 2 and 6 months, and 1, 2 and 3 years following TKA. Results In 125 osteoarthritic knees from 90 patients (mean age, 75.0 ± 6.2; 21 male/69 female), frequency of RLLs around trabecular metal tibial components was generally highest at 2 and 6 months, and 1 year following TKA, then gradually decreased over the 3-year follow-up. Frequency of RLLs around trabecular metal tibial components was greater at the tip of the two pegs, particularly the medial peg, and around the pegs, versus other zones. No postoperative revisions were performed for loosening. Conclusions Over 3 years following TKA, RLLs were most frequently observed up to 1 year, then gradually decreased. RLLs were significantly more frequent in the medial peg zone and zones close to the medial peg than in other zones.

Arthrotomy-based preclinical models of particle-induced osteolysis: A systematic review

We completed a systematic literature review of in vivo animal models that use arthrotomy-based methods to study particle-induced peri-implant osteolysis. The purpose of the review was to characterize the models developed to date, to determine the questions addressed, to assess scientific rigor and transparency, and to identify gaps in knowledge. We probed three literature databases (Medline, Embase, and Scopus) and found 77 manuscripts that fit the search parameters. In the most recent 10 years, researchers mainly used rat and mouse models, whereas in the previous 20 years, large animal, canine, and rabbit models were more common. The studies have demonstrated several pathophysiology pathways, including macrophage migration, particle phagocytosis, increased local production of cytokines and lysosomal enzymes, elevated bone resorption, and suppressed bone formation. The effect of variation in particle characteristics and concentration received limited attention with somewhat mixed findings. Particle contamination by endotoxin was shown to exacerbate peri-implant osteolysis. The possibility of early diagnosis was demonstrated through imaging and biomarker approaches. Several studies showed that both local and systemic delivery of bisphosphonates inhibits the development of particle-induced osteolysis. Other methods of inhibiting osteolysis include the use of anabolic agents and altering the implant design. Few studies examined non-surgical rescue of loosened implants, with conflicting results with alendronate. We found that the manuscripts often lacked the methodological detail now advocated by the ARRIVE guidelines, suggesting that improvement in reporting would be useful to maximize rigor and transparency. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2595-2605, 2017.

Cementless Porous Tantalum Monoblock Tibia vs Cemented Modular Tibia in Primary Total Knee Arthroplasty: A Meta-Analysis

BACKGROUND

With the introduction of new fixation systems and designs, there has been a recent reemergence of interest in cementless fixation of the tibial component in total knee arthroplasty. However, little is known regarding the clinical features and survivorship of the cementless porous tantalum monoblock tibial component compared to the conventional cemented modular tibial component.

METHODS

We conducted a literature search of multiple databases for comparative studies published before June 2015 that investigated the outcomes of cementless porous tantalum monoblock tibia vs conventional cemented modular tibia. A pooled analysis was performed. The outcomes of interest were postoperative functional score, range of motion, Western Ontario and McMaster University Osteoarthritis Index, total complications, reoperation, radiolucent lines, loosening of the tibial component, and length of operation.

RESULTS

Six studies involving 977 patients were eligible for the meta-analysis. The use of a cementless porous tantalum monoblock tibial component may associate with a slightly higher functional score, fewer radiolucent lines, and shorter operation. No significant difference was seen in regard to the range of motion, Western Ontario and McMaster University Osteoarthritis Index, total complications, reoperation, and loosening of the component between the 2 groups.

CONCLUSION

However, due to variation among the included studies, the use of cementless porous tantalum monoblock tibia seems to achieve no substantial superiority over that of the conventional cemented modular tibia at 5-year follow-up. Data concerning the long-term prognosis of this novel implant should continue to be collected and analyzed.

Total Hip Arthroplasty Using Modular Trabecular Metal Acetabular Components for Failed Treatment of Acetabular Fractures: A Mid-term Follow-up Study

Background:

Porous-coated cups have been widely used in acetabular reconstruction after failed treatment of acetabular fractures, and good results have been reported with the use of these cups; however, the durability and functionality of modular trabecular metal (TM) acetabular components in acetabular reconstruction after failed treatment of acetabular fractures remain unclear. This study aimed to examine the radiographic and clinical outcomes associated with the use of modular TM acetabular components for failed treatment of acetabular fractures to assess the durability and functionality of these components in acetabular reconstruction after failed treatment of acetabular fractures.

Methods:

A total of 41 patients (41 hips) underwent total hip arthroplasty (THA) using modular TM acetabular components for failed treatment of acetabular fractures at our hospital between January 2007 and December 2012. Among these patients, two were lost to follow-up. Therefore, 39 patients (39 hips) were finally included in this study. The Harris hip score before and after the surgery, satisfaction level of the patients, and radiographic results were assessed.

Results:

The mean Harris hip score increased from 34 (range, 8–52) before surgery to 91 (range, 22–100) at the latest follow-up examination (P < 0.001). The results were excellent for 28 hips, good for six, fair for three, and poor for two. Among the 39 patients, 25 (64%) and 10 (26%) were very satisfied and somewhat satisfied, respectively. All cups were found to be fully incorporated, and no evidence of cup migration or periacetabular osteolysis was noted.

Conclusions:

Despite the technically demanding nature of the procedure, THA using modular TM acetabular components showed good durability and functionality and may be an effective reconstruction option for failed treatment of acetabular fractures.

Use of Oversized Highly Porous Cups in Acetabular Revision

This study assessed the efficacy of highly porous cups in revision total hip arthroplasty for Paprosky types II and III acetabular bone loss. The authors identified 33 acetabular revisions in 29 patients from a prospective database (66% type III, 7 with pelvic dissociation). Initial stability was achieved with interference fit between the anterior inferior iliac spine, pubis, and ischium with cups that were 2 to 4 mm larger than the reamed acetabulum and augmented with multiple screw fixations without allograft or wedges. At mean follow-up of 6 years (range, 2.7-7.7 years) after revision surgery, no dislocation, infection, or reoperation was noted. Mean satisfaction score was 6±3.2. Mean anteversion and abduction angles were 43°±4.6° and 21.5°±4.4°, respectively. Complications included limp in 13% of patients, wound issues in 10%, and heterotopic ossification in 17%. Osteointegration was seen in all cups, without any migration. Mean overall osteointegration, based on the average percentage of the 3 zones in both views, was 55%±21% (range, 25%-95%). The most osteointegration was seen in zone I (superior) and zone VI (posterior), and the least osseointegration was seen in zone II (medial) and zone IV (anterior). This method can provide reproducible results in acetabular revision arthroplasty.

Trabecular metal tibial knee component still stable at 10 years

Background and purpose - Total knee replacement (TKR) in younger patients using cemented components has shown inferior results, mainly due to aseptic loosening. Excellent clinical results have been reported with components made of trabecular metal (TM). In a previous report, we have shown stabilization of the TM tibial implants for up to 5 years. In this study, we compared the clinical and RSA results of these uncemented implants with those of cemented implants. Patients and methods - 41 patients (47 knees) aged ≤ 60 years underwent TKR. 22 patients (26 knees) received an uncemented monoblock cruciate-retaining (CR) tibial component (TM) and 19 patients (21 knees) received a cemented NexGen Option CR tibial component. Follow-up examination was done at 10 years, and 16 patients (19 knees) with TM tibial components and 17 patients (18 knees) with cemented tibial components remained for analysis. Results - 1 of 19 TM implants was revised for infection, 2 of 18 cemented components were revised for knee instability, and no revisions were done for loosening. Both types of tibial components migrated in the first 3 months, the TM group to a greater extent than the cemented group. After 3 months, both groups were stable during the next 10 years. Interpretation - The patterns of migration for uncemented TM implants and cemented tibial implants over the first 10 years indicate that they have a good long-term prognosis regarding fixation.

Current evidence and future directions for research into the use of tantalum in soft tissue re-attachment surgery

The use of tantalum is well established in orthopaedic surgery.

Trabecular metal tibia still stable at 5 years: an RSA study of 36 patients aged less than 60 years

BACKGROUND AND PURPOSE

Clinical results of total knee replacement (TKR) are inferior in younger patients, mainly due to aseptic loosening. Coating of components with trabecular metal (TM) is a new way of enhancing fixation to bone. We have previously reported stabilization of TM tibial components at 2 years. We now report the 5-year follow-up of these patients, including RSA of their TM tibial components.

PATIENTS AND METHODS

22 patients (26 knees) received an uncemented TM cruciate-retaining tibial component and 19 patients (21 knees) a cemented NexGen Option cruciate-retaining tibial component. Follow-up with RSA, and clinical and radiographic examinations were done at 5 years. In bilaterally operated patients, the statistical analyses included only the first-operated knee.

RESULTS

Both groups had most migration within the first 3 months, the TM implants to a greater extent than the cemented implants. After 3 months, both groups stabilized and remained stable up to the 5-year follow-up.

INTERPRETATION

After a high initial degree of migration, the TM tibia stabilized. This stabilization lasted for at least 5 years, which suggests a good long-term performance regarding fixation. The cemented NexGen CR tibial components showed some migration in the first 3 months and then stabilized up to the 5-year follow-up. This has not been reported previously.

Clinical and radiographic evaluation of total hip arthroplasties using porous tantalum modular acetabular components: 5-year follow-up of clinical trial

OBJECTIVES

Porous tantalum is a biomaterial newly applied for artificial joints. We present here 5-years follow-up report of a multicenter clinical trial of total hip arthroplasties (THA) with porous tantalum modular acetabular component (modular PTC).

METHODS

Study participants received 82 hips in 79 cases, with 61.2 months follow-up on average. Age at operation was 60.9 years. Clinical results were evaluated using Merle d'Aubigne Postel score. Presence of implant loosening, periacetabular radiolucency, osteolysis, and gap filling were examined for radiographic results.

RESULTS

Merle d'Aubigne Postel score improved from 10.0 to 16.4 points. All PTC were radiographically stable, with no evidence of progressive radiolucencies. Average polyethylene wear rate was 0.004 mm/year, with no periacetabular osteolysis. Fifteen hips (18.3%) showed a gap >1 mm; however, all showed bone filling within 12 months. PTC with oversized reaming was significantly less likely to have a gap. No implant failure was noted related to modularity. Resulting survival rate of modular PTC was 100% at 5 years.

CONCLUSIONS

Modular PTC showed excellent results at 5-years of follow-up. Some hips showed periacetabular gaps, which were filled with bone within 1 year. Further follow-up was needed to determine long-term efficacy.

Superior fixation of pegged trabecular metal over screw-fixed pegged porous titanium fiber mesh: a randomized clinical RSA study on cementless tibial components

BACKGROUND AND PURPOSE

Lasting stability of cementless implants depends on osseointegration into the implant surface, and long-term implant fixation can be predicted using radiostereometric analysis (RSA) with short-term follow-up. We hypothesized that there would be improved fixation of high-porosity trabecular metal (TM) tibial components compared to low-porosity titanium pegged porous fiber-metal (Ti) polyethylene metal backings.

METHODS

In a prospective, parallel-group, randomized unblinded clinical trial, we compared cementless tibial components in patients aged 70 years and younger with osteoarthritis. The pre-study sample size calculation was 22 patients per group. 25 TM tibial components were fixed press-fit by 2 hexagonal pegs (TM group) and 25 Ti tibial components were fixed press-fit and by 4 supplemental screws (Ti group). Stereo radiographs for evaluation of absolute component migration (primary effect size) and single-direction absolute component migration (secondary effect size) were obtained within the first postoperative week and at 6 weeks, 6 months, 1 year, and 2 years. American Knee Society score was used for clinical assessment preoperatively, and at 1 and 2 years.

RESULTS

There were no intraoperative complications, and no postoperative infections or revisions. All patients had improved function and regained full extension. All tibial components migrated initially. Most migration of the TM components (n = 24) occurred within the first 3 months after surgery whereas migration of the Ti components (n = 22) appeared to stabilize first after 1 year. The TM components migrated less than the Ti components at 1 year (p = 0.01) and 2 years (p = 0.004).

INTERPRETATION

We conclude that the mechanical fixation of TM tibial components is superior to that of screw-fixed Ti tibial components. We expect long-term implant survival to be better with the TM tibial component.

Porous tantalum stimulates the proliferation and osteogenesis of osteoblasts from elderly female patients

Porous tantalum (Ta) implants have been successful in various orthopedic procedures for patients with compromised bone-forming abilities. Previous studies demonstrated that human osteoblast (HOB) cultures from older female patients produced less bone on implant materials in vitro compared to HOBs from age-matched male and younger female patients. In this study, the responses of HOBs from younger (< 45) and older (> 60 years old) female patients were compared on Ta, titanium fiber mesh (TFM) and tissue culture plastic. Adhesion, proliferation, and mineralization were greater in cells from younger patients than from older patients. Cell adhesion was slightly higher on Ta than TFM or plastic. However, Ta highly stimulated cell proliferation with a 4- and 6-fold increase compared to TFM for cells from younger and older patients, respectively, and 12- and 16-fold increase in proliferation compared to cells on plastic (p ≤ 0.001). At 3 weeks, mineralization was significantly higher on Ta compared to TFM for HOBs from older patients (p ≤ 0.05). Expression levels of bone matrix markers demonstrated differences dependent on age and substrate. Scanning electron micrographs revealed HOBs covering the surfaces and entering the pores of both Ta and TFM. In conclusion, tantalum greatly stimulates cell proliferation, and improves the ability of HOBs from older patients to form bone.

Basic science considerations in primary total hip replacement arthroplasty

Total Hip Replacement is one of the most common operations performed in the developed world today. An increasingly ageing population means that the numbers of people undergoing this operation is set to rise. There are a numerous number of prosthesis on the market and it is often difficult to choose between them. It is therefore necessary to have a good understanding of the basic scientific principles in Total Hip Replacement and the evidence base underpinning them. This paper reviews the relevant anatomical and biomechanical principles in THA. It goes on to elaborate on the structural properties of materials used in modern implants and looks at the evidence base for different types of fixation including cemented and uncemented components. Modern bearing surfaces are discussed in addition to the scientific basis of various surface engineering modifications in THA prostheses. The basic science considerations in component alignment and abductor tension are also discussed. A brief discussion on modular and custom designs of THR is also included. This article reviews basic science concepts and the rationale underpinning the use of the femoral and acetabular component in total hip replacement.

Limb-sparing surgery using tantalum metal endoprosthesis in a dog with osteosarcoma of the distal radius

A 5-year-old, male neutered, mixed breed dog was presented for left forelimb lameness and swelling over the left distal radius. A primary bone tumor of the distal radius was diagnosed and limb-sparing surgery of the left forelimb was performed using a tantalum metal-DCP endoprosthesis. Post-operative histopathology confirmed osteosarcoma.

Relationship between solute transport properties and tissue morphology in human annulus fibrosus

Poor nutritional supply to the intervertebral disc is believed to be an important factor leading to disc degeneration. However, little is known regarding nutritional transport in human annulus fibrosus (AF) and its relation to tissue morphology. We hypothesized that solute diffusivity in human AF is anisotropic and inhomogeneous, and that transport behaviors are associated with tissue composition and structure. To test these hypotheses, we measured the direction-dependent diffusivity of a fluorescent molecule (fluorescein, 332 Da) in three regions of AF using a fluorescence recovery after photobleaching (FRAP) technique, and associated transport results to the regional variation in water content and collagen architecture in the tissue. Diffusivity in AF was anisotropic, with higher values in the axial direction than in the radial direction for all regions investigated. The values of the diffusion coefficient ranged from 0.38 +/- 0.25 x 10(-6) cm(2)/s (radial diffusivity in outer AF) to 2.68 +/- 0.84 x 10(-6) cm(2)/s (axial diffusivity in inner AF). In both directions, diffusivity decreased moving from inner to outer AF. Tissue structure was investigated using both scanning electron microscopy and environmental scanning electron microscopy. A unique arrangement of microtubes was found in human AF. Furthermore, we also found that the density of these microtubes varied moving from inner to outer AF. A similar trend of regional variation was found for water content, with the highest value also measured in inner AF. Therefore, we concluded that a relationship exists among the anisotropic and inhomogeneous diffusion in human AF and the structure and composition of the tissue.

Metallic Scaffolds for Bone Regeneration

Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

Activation of human leukocytes on tantalum trabecular metal in comparison to commonly used orthopedic metal implant materials

We analyzed leukocyte functions and cytokine response of human leukocytes toward porous tantalum foam biomaterial (Trabecular Metaltrade mark, TM) in comparison to equally sized solid orthopedic metal implant materials (pure titanium, titanium alloy, stainless steel, pure tantalum, and tantalum coated stainless steel). Isolated peripheral blood mononuclear cells (PBMC) and polymorphonuclear neutrophil leukocytes (PMN) were cocultured with equally sized metallic test discs for 24 h. Supernatants were analyzed for cytokine content by enzyme-linked immunosorbent assay. Compared to the other used test materials there was a significant increase in the release of IL (interleukin)-1ra and IL-8 from PMN, and of IL-1ra, IL-6, and TNF-alpha from PBMC in response to the TM material. The cytokine release correlated with surface roughness of the materials. In contrast, the release of IL-2 was not induced showing that mainly myeloid leukocytes were activated. In addition, supernatants of these leukocyte/material interaction (conditioned media, CM) were subjected to whole blood cell function assays (phagocytosis, chemotaxis, bacterial killing). There was a significant increase in the phagocytotic capacity of leukocytes in the presence of TM-conditioned media. The chemotactic response of leukocytes toward TM-conditioned media was significantly higher compared to CM obtained from other test materials. Furthermore, the bactericidal capacity of whole blood was enhanced in the presence of TM-conditioned media. These results indicate that leukocyte activation at the surface of TM material induces a microenvironment, which may enhance local host defense mechanisms.

Multicentre use of a porous tantalum monoblock acetabular component

The purpose of this study was to evaluate the minimum five-year prospective results from the multicentre use of a porous tantalum monoblock acetabular component for primary total hip arthroplasty (THA). A multicentre study was performed in 253 consecutive primary THAs in three separate surgical centres. All patients underwent identical postoperative protocols including radiological and clinical evaluation. The average preoperative total HHS score was 44.0 +/- 13.8 and increased at one-year follow-up to 95.2 +/- 4.8 (p <0.05), remaining constant through the five-year follow-up at 97.0 +/- 6.2 (p < 0.05). There was no radiographic evidence of gross polyethylene wear, progressive radiolucencies, osteolytic lesions, acetabular fracture, or component subsidence. From these results, we can recommend the continued use of this material for acetabular components in primary THA and that further review of the current multicentre population is warranted to determine the long-term durability of the acetabular composite.

Primary human osteoblasts grow into porous tantalum and maintain an osteoblastic phenotype

Porous tantalum (Ta) has found application in orthopedics, although the interaction of human osteoblasts (HOB) with this material has not been reported. The aim of this study was to investigate the interaction of primary HOB with porous tantalum, using 5-mm thick discs of porous tantalum. Comparison was made with discs of solid tantalum and tissue culture plastic. Confocal microscopy was used to investigate the attachment and growth of cells on porous Ta, and showed that HOB attached successfully to the metal "trabeculae," underwent extensive cell division, and penetrated into the Ta pores. The maturation of HOB on porous Ta was determined in terms of cell expression of the osteoblast phenotypic markers, STRO-1, and alkaline phosphatase. Despite some donor-dependent variation in STRO-1/AlkPhos expression, growth of cells grown on porous Ta either promoted, or did not impede, the maturation of HOB. In addition, the expression of key osteoblastic genes was investigated after 14 days of culture. The relative levels of mRNA encoding osteocalcin, osteopontin and receptor activator of NFkappaB ligand (RANKL) was not different between porous or solid Ta or plastic, although these genes were expressed differently by cells of different donors. However, bone sialoprotein and type I collagen mRNA species showed a decreased expression on porous Ta compared with expression on plastic. No substrate-dependent differences were seen in the extent of in vitro mineralization by HOB. These results indicate that porous Ta is a good substrate for the attachment, growth, and differentiated function of HOB.

What other biologic and mechanical factors might contribute to osteolysis?

An overwhelming consensus exists that wear particles are the primary driving force in aseptic loosening of orthopaedic implants. Nonetheless, considerable evidence has emerged demonstrating that various other factors can modulate the biologic activity of orthopaedic wear particles. Two of the most studied modulating factors are bacterial endotoxins and implant motion.

Platelet-rich plasma inhibits demineralized bone matrix-induced bone formation in nude mice

BACKGROUND

It is unclear whether platelet-rich plasma is a clinically effective adjunct to osteoinductive agents such as demineralized bone matrix. It contains platelet-derived growth factor (PDGF), which decreases osteoinduction by human demineralized bone matrix in nude-mouse muscle, suggesting that platelet-rich plasma may also have a negative impact. This study tested the hypothesis that platelet-rich plasma reduces demineralized bone matrix-induced bone formation and that this effect varies with donor-dependent differences in platelet-rich plasma and demineralized bone matrix.

METHODS

Human platelet-rich plasma was prepared from blood from six men (average age [and standard error of the mean], 29.2 +/- 2.4 years). Platelet numbers were determined, and growth factors were quantified before and after platelet activation. Human demineralized bone matrix from two donors (demineralized bone matrix-1 and demineralized bone matrix-2) was mixed with activated platelet-rich plasma and was implanted bilaterally in the gastrocnemius muscle in eighty male nude mice (eight implants per variable). Fifty-six days after implantation, the hindlimb calf muscles were harvested for histological analysis. Osteoinduction was evaluated with use of a qualitative score and morphometric measurements of ossicle size, new bone formation, and residual demineralized bone matrix.

RESULTS

Compared with platelet-poor plasma, platelet-rich plasma preparations exhibited a fourfold increase in the platelet count, a fifteenfold increase in the amount of transforming growth factor-beta, a sixfold increase in the amount of PDGF-BB, a fivefold increase in the amount of PDGF-AA, and a twofold increase in the amount of PDGF-AB. Demineralized bone matrix-1 was more osteoinductive than demineralized bone matrix-2, as determined on the basis of a greater ossicle area. The effect of platelet-rich plasma was either neutral or inhibitory depending on the demineralized bone matrix batch. When used with demineralized bone matrix-1, platelet-rich plasma did not alter the qualitative score or overall ossicle size, but it decreased the new bone area. When used with demineralized bone matrix-2, platelet-rich plasma reduced the qualitative score, ossicle area, and new bone area and increased the amount of residual demineralized bone matrix. The effects on osteoinduction also varied with the donor of the platelet-rich plasma.

CONCLUSIONS

Platelet-rich plasma decreased the osteoinductivity of demineralized bone matrix implanted in immunocom-promised mice, and the activities of both demineralized bone matrix and platelet-rich plasma were donor-dependent.

Applications of porous tantalum in total hip arthroplasty

Porous tantalum is an alternative metal for total joint arthroplasty components that offers several unique properties. Its high volumetric porosity (70% to 80%), low modulus of elasticity (3 MPa), and high frictional characteristics make it conducive to biologic fixation. Tantalum has excellent biocompatibility and is safe to use in vivo. The low modulus of elasticity allows for more physiologic load transfer and relative preservation of bone stock. Because of its bioactive nature and ingrowth properties, tantalum is used in primary as well as revision total hip arthroplasty components, with good to excellent early clinical results. In revision arthroplasty, standard and custom augments may serve as a structural bone graft substitute. Formation of a bone-like apatite coating in vivo affords strong fibrous ingrowth properties and allows for substantial soft-tissue attachment, indicating potential for use in cases requiring reattachment of muscles and tendons to a prosthesis. Development of modular components and femoral stems also is being evaluated. The initial clinical data and basic science studies support further investigation of porous tantalum as an alternative to traditional implant materials.

Bone remodelling around HA-coated acetabular cups : a DEXA study with a 3-year follow-up in a randomised trial

This study was designed to investigate bone remodelling around the cup in cementless THA. Previous studies indicate an advantage of better sealing of the bone-prosthesis interface by HA/TCP coating of implants, inhibiting polyethylene-induced osteolysis. One hundred patients gave informed consent to participate in a controlled randomized study between porous coated Trilogy versus Trilogy Calcicoat (HA/TCP coated). The cup was inserted in press-fit fixation. The femoral component was a cementless porous coated titanium alloy stem (Bi-Metric), with a modular 28-mm CrCo head. The Harris Hip Score (HHS) and bone mineral density (BMD) determined by DEXA scanning were used to study the effect. Measurements revealed no difference between the two groups after 3 years either in the clinical outcome or in terms of periprosthetic bone density. Patients with a body mass index above normal regained more bone mineral than patients with normal weight. This finding supports the assumption that load is beneficial to bone remodelling.