Parathyroid hormone treatment increases fixation of orthopedic implants with gap healing: a biomechanical and histomorphometric canine study of porous coated titanium alloy implants in cancellous bone

Periprosthetic fractures after medial unicompartmental knee arthroplasty: a narrative review

INTRODUCTION

On rare occasions, fractures of the tibial plateau may occur after uni-compartmental knee arthroplasty (UKA) and account for 2% of total UKA failures. The purpose of this narrative review is to identify and discuss potential risk factors that might lead to prevention of this invalidating complication.

MATERIALS AND METHODS

Electronic database of Pubmed, Scopus, Cochrane and Google Scholar were searched. A total of 457 articles related to the topic were found. Of those, 86 references were included in this narrative review.

RESULTS

UKA implantation acts as a stress riser in the medial compartment. To avoid fractures, surgeons need to balance load and bone stock. Post-operative lower limb alignment, implant positioning, level of resection and sizing of the tibial tray have a strong influence on load distribution of the tibial bone. Pain on weight-bearing signals bone-load imbalance and acts as an indicator of bone remodeling and should be a trigger for unloading. The first three months after surgery are critical because of transient post-operative osteoporosis and local biomechanical changes. Acquired osteoporosis is a growing concern in the arthroplasty population. Split fractures require internal fixation, while subsidence fractures differ in their management depending of the amount of bone impaction. Loose implants require revision knee arthroplasty.

CONCLUSION

Peri-prosthetic fracture is a rare, but troublesome event, which can lead to implant failure and revision surgery. Better knowledge of the multifactorial risk factors in association with a thorough surgical technique is key for prevention.

Intermittent parathyroid hormone increases stability and improves osseointegration of initially unstable implants

Aims

To develop an early implant instability murine model and explore the use of intermittent parathyroid hormone (iPTH) treatment for initially unstable implants.

Methods

3D-printed titanium implants were inserted into an oversized drill-hole in the tibiae of C57Bl/6 mice (n = 54). After implantation, the mice were randomly divided into three treatment groups (phosphate buffered saline (PBS)-control, iPTH, and delayed iPTH). Radiological analysis, micro-CT (µCT), and biomechanical pull-out testing were performed to assess implant loosening, bone formation, and osseointegration. Peri-implant tissue formation and cellular composition were evaluated by histology.

Results

iPTH reduced radiological signs of loosening and led to an increase in peri-implant bone formation over the course of four weeks (timepoints: one week, two weeks, and four weeks). Observational histological analysis shows that iPTH prohibits the progression of fibrosis. Delaying iPTH treatment until after onset of peri-implant fibrosis still resulted in enhanced osseointegration and implant stability. Despite initial instability, iPTH increased the mean pull-out strength of the implant from 8.41 N (SD 8.15) in the PBS-control group to 21.49 N (SD 10.45) and 23.68 N (SD 8.99) in the immediate and delayed iPTH groups, respectively. Immediate and delayed iPTH increased mean peri-implant bone volume fraction (BV/TV) to 0.46 (SD 0.07) and 0.34 (SD 0.10), respectively, compared to PBS-control mean BV/TV of 0.23 (SD 0.03) (PBS-control vs immediate iPTH, p < 0.001; PBS-control vs delayed iPTH, p = 0.048; immediate iPTH vs delayed iPTH, p = 0.111).

Conclusion

iPTH treatment mediated successful osseointegration and increased bone mechanical strength, despite initial implant instability. Clinically, this suggests that initially unstable implants may be osseointegrated with iPTH treatment.

Cite this article: Bone Joint Res 2022;11(5):260–269.

Parathyroid hormone enhances gap healing and osseointegration in orthopedic porous coated titanium implants: a correlative micro-computed tomographic, histomorphometric and biomechanical analysis

Background

Parathyroid hormone, with its anabolic effect on bone formation, has shown excellent outcomes of curing postmenopausal osteoporosis as well as enhancing osseointegration around orthopaedic and stomatologic implants.The purpose of the present study is to test if low-dose intermittent PTH (1–34) treatment could achieve a satisfactory osseointegration in 2-mm peri-implant gaps, as to provide a new idea for improving the stability of such prosthesis, which will be of great clinical value.

Methods

A custom-made titanium implant was implanted on the calvarium of New Zealand White rabbits. 48 male rabbits were randomly divided into control and PTH group. PTH group received subcutaneous injection of PTH (20 μg/day, 5 days/week). Animals were sacrificed at 4 and 8 weeks after surgery. Quantitative micro-computed tomography, histology and biomechanical pull-out testing were performed to evaluate the gap healing at implantation site.

Results

Analysis of micro-computed tomography demonstrated that PTH group achieved more new bone formation in 2-mm gaps and on bone-implant interface. Quantitatively, significant differences were observed between two groups in regard to BIC and BV/TV at each time-point. Histological staining revealed that PTH group had a superiority in trabecular number, thickness, separation and better osseointegration compared to control group. As for biomechanical pull-out testing, PTH group also showed significant improvement of ultimate force than control group.

Conclusions

Low-dose intermittent administration of PTH for 4 and 8 weeks enhances early osseointegration and fixation of orthopedic implants surrounded by a 2-mm gap in terms of increased bone regeneration and mechanical stability. These findings suggest PTH a potential for reducing the postoperative complications of implants by improving bone healing at peri-implant gaps.

Inhibition of osteoclastogenesis by histone deacetylase inhibitor Quisinostat protects mice against titanium particle-induced bone loss

Periprosthetic osteolysis (PPO) and subsequent aseptic loosening are major long-term complications after total joint arthroplasty and have become the first causes for further revision surgery. Since PPO is primarily caused by excessive bone resorption stimulated by released wear particles, osteoclast-targeted therapy is considered to be of great potential for PPO prevention and treatment. Accumulating evidences indicated that inhibition of histone deacetylases (HDACs) may represent a novel approach to suppress osteoclast differentiation. However, different inhibitors of HDACs were shown to exhibit distinct safety profiles and efficacy in inhibiting osteoclastogenesis. Quisinostat (Qst) is a hydroxamate-based histone deacetylase inhibitor, and exerts potent anti-cancer activity. However, its effect on osteoclastogenesis and its therapeutic potential in preventing PPO are still unclear. In this study, we found that Qst suppressed RANKL-induced production of TRAP-positive mature osteoclasts, expression of osteoclast-specific genes, formation of F-actin rings, and bone resorption activity at a nanomolar concentration as low as 2 nM in vitro. Furthermore, we found that as low as 30 μg/kg of Qst was sufficient to exert preventive effect on titanium particle-induced osteolysis in the murine calvarial osteolysis model. Mechanistically, we found that Qst suppressed osteoclastogenesis by interfering with NF-κB and c-Fos/NFATc1 pathways. Thus, our study revealed that Qst may serve as a potential therapeutic agent for prevention and treatment of PPO and other osteoclast-mediated diseases.

Present and future scope of recombinant parathyroid hormone therapy in orthopaedics

Parathyroid Hormone (PTH) has a significant role in calcium metabolism. Its intermittent administration has an anabolic effect on bone mineralization. Teriparatide (PTH 1-34), a recombinant form of parathyroid hormone, is useful in the treatment of osteoporosis, fracture healing, non-union, stress fracture, augmentation of implant fixation with bone, and chondroprotection in osteoarthritis. The present review article will elaborate on the potential approved uses of recombinant PTH in orthopedics and its evolving role in the management of fracture osteosynthesis and other common challenging bone pathologies.

Osseointegration Pharmacology: A Systematic Mapping Using Artificial Intelligence

Clinical performance of osseointegrated implants could be compromised by the medications taken by patients. The effect of a specific medication on osseointegration can be easily investigated using traditional systematic reviews. However, assessment of all known medications requires the use of evidence mapping methods. These methods allow assessment of complex questions, but they are very resource intensive when done manually. The objective of this study was to develop a machine learning algorithm to automatically map the literature assessing the effect of medications on osseointegration. Datasets of articles classified manually were used to train a machine-learning algorithm based on Support Vector Machines. The algorithm was then validated and used to screen 599,604 articles identified with an extremely sensitive search strategy. The algorithm included 281 relevant articles that described the effect of 31 different drugs on osseointegration. This approach achieved an accuracy of 95%, and compared to manual screening, it reduced the workload by 93%. The systematic mapping revealed that the treatment outcomes of osseointegrated medical devices could be influenced by drugs affecting homeostasis, inflammation, cell proliferation and bone remodeling. The effect of all known medications on the performance of osseointegrated medical devices can be assessed using evidence mappings executed with highly accurate machine learning algorithms.

Parathyroid hormone for bone regeneration

Delayed healing and/or non-union occur in approximately 5-10% of the fractures that occur annually in the United States. Segmental bone loss increases the probability of non-union. Though grafting can be an effective treatment for segmental bone loss, autografting is limited for large defects since a limited amount of bone is available for harvest. Parathyroid hormone (PTH) is a key regulator of calcium homeostasis in the body and plays an important role in bone metabolism. Presently PTH is FDA approved for use as an anabolic treatment for osteoporosis. The anabolic effect PTH has on bone has led to research on its use for bone regeneration applications. Numerous studies in animal models have indicated enhanced fracture healing as a result of once daily injections of PTH. Similarly, in a human case study, non-union persisted despite treatment attempts with internal fixation, external fixation, and autograft in combination with BMP-7, until off label use of PTH1-84 was utilized. Use of a biomaterial scaffold to locally deliver PTH to a defect site has also been shown to improve bone formation and healing around dental implants in dogs and drill defects in sheep. Thus, PTH may be used to promote bone regeneration and provide an alternative to autograft and BMP for the treatment of large segmental defects and non-unions. This review briefly summarizes the unmet clinical need for improved bone regeneration techniques and how PTH may help fill that void by both systemically and locally delivered PTH for bone regeneration applications. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2586-2594, 2018.

The challenges of promoting osteogenesis in segmental bone defects and osteoporosis

Conventional clinical management of complex bone healing scenarios continues to result in 5-10% of fractures forming non-unions. Additionally, the aging population and prevalence of osteoporosis-related fractures necessitate the further exploration of novel ways to augment osteogenesis in this special population. This review focuses on the current clinical modalities available, and the ongoing clinical and pre-clinical research to promote osteogenesis in segmental bone defects, delayed unions, and osteoporosis. In summary, animal models of fracture repair are often small animals as historically significant large animal models, like the dog, continue to gain favor as companion animals. Small rodents have well-documented limitations in comparing to fracture repair in humans, and few similarities exist. Study design, number of studies, and availability of funding continue to limit large animal studies. Osteoinduction with rhBMP-2 results in robust bone formation, although long-term quality is scrutinized due to poor bone mineral quality. PTH 1-34 is the only FDA approved osteo-anabolic treatment to prevent osteoporotic fractures. Limited to 2 years of clinical use, PTH 1-34 has further been plagued by dose-related ambiguities and inconsistent results when applied to pathologic fractures in systematic human clinical studies. There is limited animal data of PTH 1-34 applied locally to bone defects. Gene therapy continues to gain popularity among researchers to augment bone healing. Non-integrating viral vectors and targeted apoptosis of genetically modified therapeutic cells is an ongoing area of research. Finally, progenitor cell therapies and the content variation of patient-side treatments (e.g., PRP and BMAC) are being studied. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1559-1572, 2018.

Anabolic agents: what is beyond osteoporosis?

Osteoporosis is a common skeletal disorder characterized by low bone mass, which leads to reduced bone strength and an increased risk of fractures. Anabolic agents have been shown to improve bone mass and decrease fracture risk in osteoporosis patients by directly stimulating osteoblasts to produce new bone. Currently, two anabolic agents are available in the USA: recombinantly produced teriparatide (TPTD), which is the fully active (1-34) amino active sequence of human parathyroid hormone (PTH), and abaloparatide (APTD), a synthetic analog of parathyroid hormone-related peptide (PTHrP). At present, both agents are approved only for treatment of patients with osteoporosis at high risk of fracture. Nonetheless, their anabolic properties have led to off-label application in additional settings which include spine fusion, osteonecrosis of the jaw, arthroplasty, and fracture healing. In this article, we summarize available scientific literature regarding the efficacy, effectiveness, and safety of TPTD in these off-label settings.

High dose teriparatide (rPTH1-34) therapy increases callus volume and enhances radiographic healing at 8-weeks in a massive canine femoral allograft model

Small animal studies have demonstrated significant high-dose recombinant parathyroid hormone1-34 (rPTH1-34) effects on intercalary allograft healing. Towards a human adjuvant therapy to decrease non-unions, we evaluated rPTH1-34 safety and efficacy in a clinically relevant canine femoral allograft model. Adult female mongrel hounds (n = 20) received a 5cm mid-diaphyseal osteotomy reconstructed with a plated allograft, and were randomized to: 1) Placebo (n = 5; daily saline), 2) Continuous rPTH1-34 (n = 7; 5 μg/kg/day s.c. from day 1-55 post-op), or 3) Delayed rPTH1-34 (n = 8; 5 μg/kg/day s.c. from day 14-28 post-op). Safety was assessed by physical behavior and blood calcium monitoring. Cone beam CT (CB-CT) was performed on days 14, 28 and 56 post-op to assess 2D cortical healing, 3D bone volume, and Union Ratio. Biomechanical testing and dynamic histomorphometry were also performed. The high drug dose was poorly tolerated, as most dogs receiving rPTH1-34 had to be given intravenous saline, and one dog died from hypercalcemia. Continuous rPTH1-34 significantly increased 2D healing and callus volumes at 4-weeks versus Placebo, and sustained the significant increase in cortical union at 8-week (p<0.05). These rPTH1-34 effects were confirmed by histomorphometry, revealing significant increases in mineral apposition rates (MAR) on host bone and graft-host junctions (p<0.05). Delayed rPTH1-34 significantly increased callus volume and MAR at 8 weeks (p<0.05). Although no biomechanical differences were observed, as expected for early healing, the results demonstrated that 2D RUST scoring significantly correlated with torsional biomechanics (p<0.01). In conclusion, 8-weeks of intermittent high-dose rPTH1-34 treatment significantly increases callus formation and accelerates bony union of intercalary massive allografts in a clinically relevant canine model, but with serious side-effects from hypercalcemia.

Experimental and Numerical Models of Complex Clinical Scenarios; Strategies to Improve Relevance and Reproducibility of Joint Replacement Research

This research review aims to focus attention on the effect of specific surgical and host factors on implant fixation, and the importance of accounting for them in experimental and numerical models. These factors affect (a) eventual clinical applicability and (b) reproducibility of findings across research groups. Proper function and longevity for orthopedic joint replacement implants relies on secure fixation to the surrounding bone. Technology and surgical technique has improved over the last 50 years, and robust ingrowth and decades of implant survival is now routinely achieved for healthy patients and first-time (primary) implantation. Second-time (revision) implantation presents with bone loss with interfacial bone gaps in areas vital for secure mechanical fixation. Patients with medical comorbidities such as infection, smoking, congestive heart failure, kidney disease, and diabetes have a diminished healing response, poorer implant fixation, and greater revision risk. It is these more difficult clinical scenarios that require research to evaluate more advanced treatment approaches. Such treatments can include osteogenic or antimicrobial implant coatings, allo- or autogenous cellular or tissue-based approaches, local and systemic drug delivery, surgical approaches. Regarding implant-related approaches, most experimental and numerical models do not generally impose conditions that represent mechanical instability at the implant interface, or recalcitrant healing. Many treatments will work well in forgiving settings, but fail in complex human settings with disease, bone loss, or previous surgery. Ethical considerations mandate that we justify and limit the number of animals tested, which restricts experimental permutations of treatments. Numerical models provide flexibility to evaluate multiple parameters and combinations, but generally need to employ simplifying assumptions. The objectives of this paper are to (a) to highlight the importance of mechanical, material, and surgical features to influence implant-bone healing, using a selection of results from two decades of coordinated experimental and numerical work and (b) discuss limitations of such models and the implications for research reproducibility. Focusing model conditions toward the clinical scenario to be studied, and limiting conclusions to the conditions of a particular model can increase clinical relevance and research reproducibility.

Teriparatide Versus Alendronate for the Preservation of Bone Mineral Density After Total Hip Arthroplasty - A randomized Controlled Trial

In this study, the effect of teriparatide for the prevention of bone mineral density (BMD) loss after THA was compared with alendronate in a randomized controlled trial. Forty-eight patients were assigned to three groups, namely, the teriparatide, alendronate, and no medication groups. Dual-energy x-ray absorptiometry (DEXA) was performed at 1 week post-surgery as a baseline reference, followed by subsequent measurements at 12, 24, and 48 weeks postoperatively. For periprosthetic BMD loss, a significant effect of teriparatide was demonstrated, though its effect was similar to alendronate. On the other hand, higher lumbar BMD was observed in the teriparatide group than in the alendronate group at 48 weeks post-surgery. Teriparatide administration may be one reasonable option for osteoporotic patient to preserve the periprosthetic BMD after THA.

In vitro osteogenic capacity of bone marrow MSCs from postmenopausal women reflect the osseointegration of their cementless hip stems

Age-related dysfunction of mesenchymal stromal cells (MSCs) is suggested as a main cause of altered bone repair with aging. We recently showed that in postmenopausal women undergoing cementless total hip arthroplasty (THA) aging, low bone mineral density (BMD) and age-related geometric changes of the proximal femur are risk factors for increased early migration and delayed osseointegration of the femoral stems. Extending these analyses, we have here explored how the in vitro osteogenic capacity of bone marrow MSCs from these patients reflects implant osseointegration, representing the patient's in vivo bone healing capacity. A total of 19 postmenopausal women with primary hip osteoarthritis (mean age 65 years, range 50–78) and well-defined bone quality underwent successful preoperative in vitro analysis of osteogenic capacity of iliac crest bone marrow MSCs as well as two-year radiostereometric (RSA) follow-up of femoral stem migration after cementless THA. In patients with MSCs of low osteogenic capacity, the magnitude of cumulative stem subsidence after the settling period of three months was greater (p = 0.028) and the time point for translational osseointegration was significantly delayed (p = 0.030) compared to patients with MSCs of high osteogenic capacity. This study suggests that patients with MSCs of low in vitro osteogenic capacity may display increased stem subsidence after the settling period of 3 months and thereby delayed osseointegration. Our study presents a novel approach for studying the biological progress of hip implant osseointegration and to verify the impact of decreased MSCs function, especially in patients with age-related dysfunction of MSCs and bone healing capacity.

•

Age-related dysfunction of MSCs is a main cause of altered bone repair with aging.

•

MSCs play a critical role in osseointegration of cementless hip replacement.

•

We explored if hip implant osseointegration in postmenopausal women is mirrored by in vitro osteogenic ability of their MSCs.

•

Low osteogenic differentiation of MSCs correlated with increased implant migration.

Parathyroid hormone and its receptor gene polymorphisms: implications in osteoporosis and in fracture healing

Parathyroid glands secrete parathyroid hormone (PTH) which plays multiple roles in calcium homeostasis and in bone remodeling. Secretion of PTH is regulated by extracellular calcium levels and other humoral factors including 1α,25(OH)2D3. PTH regulates gene expression and induces biological effects directly and indirectly. The human gene encoding PTH is located on chromosome 11. In this review, we study the diverse PTH along with its receptor gene polymorphisms and their association with osteoporosis and fracture healing. Genetic factors are associated with osteoporosis by influencing bone mineral density (BMD), bone turnover, calcium homeostasis, and susceptibility to osteoporotic fractures. Polymorphisms in genes encoding PTH may contribute to genetic regulation of BMD and thus susceptibility to fracture risk. PTH stimulates the proliferation of osteoprogenitor cells, production of alkaline phosphatise, and bone matrix proteins that contribute to hard callus formation and increases strength at the site of fractured bone. During remodeling, PTH promotes osteoclastogenesis restoring the original shape, structure, and mechanical strength of the bone. Some PTH polymorphisms have shown an association with fracture risk. Further research is needed to elucidate the relative importance of PTH genetics and the mechanisms of genetic contributions to gene-gene interactions in the pathogenesis of osteoporosis and in fracture healing.

Intermittent Parathyroid Hormone Enhances Cancellous Osseointegration of a Novel Murine Tibial Implant

BACKGROUND

Long-term fixation of uncemented joint implants requires early mechanical stability and implant osseointegration. To date, osseointegration has been unreliable and remains a major challenge in cementless total knee arthroplasty. We developed a murine model in which an intra-articular proximal tibial titanium implant with a roughened stem can be loaded through the knee joint. Using this model, we tested the hypothesis that intermittent injection of parathyroid hormone (iPTH) would increase proximal tibial cancellous osseointegration.

METHODS

Ten-week-old female C57BL/6 mice received a subcutaneous injection of PTH (40 μg/kg/day) or a vehicle (n = 45 per treatment group) five days per week for six weeks, at which time the baseline group was killed (n = 6 per treatment group) and an implant was inserted into the proximal part of the tibiae of the remaining mice. Injections were continued until the animals were killed at one week (n = 7 per treatment group), two weeks (n = 14 per treatment group), or four weeks (n = 17 per treatment group) after implantation. Outcomes included peri-implant bone morphology as analyzed with micro-computed tomography (microCT), osseointegration percentage and bone area fraction as shown with backscattered electron microscopy, cellular composition as demonstrated by immunohistochemical analysis, and pullout strength as measured with mechanical testing.

RESULTS

Preimplantation iPTH increased the epiphyseal bone volume fraction by 31.6%. When the data at post-implantation weeks 1, 2, and 4 were averaged for the iPTH-treated mice, the bone volume fraction was 74.5% higher in the peri-implant region and 168% higher distal to the implant compared with the bone volume fractions in the same regions in the vehicle-treated mice. Additionally, the trabecular number was 84.8% greater in the peri-implant region and 74.3% greater distal to the implant. Metaphyseal osseointegration and bone area fraction were 28.1% and 70.1% higher, respectively, in the iPTH-treated mice than in the vehicle-treated mice, and the maximum implant pullout strength was 30.9% greater. iPTH also increased osteoblast and osteoclast density by 65.2% and 47.0%, respectively, relative to the values in the vehicle group, when the data at post-implantation weeks 1 and 2 were averaged.

CONCLUSIONS

iPTH increased osseointegration, cancellous mass, and the strength of the bone-implant interface.

CLINICAL RELEVANCE

Our murine model is an excellent platform on which to study biological enhancement of cancellous osseointegration.

Intermittent PTH administration and mechanical loading are anabolic for periprosthetic cancellous bone

The purpose of this study was to determine the individual and combined effects on periprosthetic cancellous bone of intermittent parathyroid hormone administration (iPTH) and mechanical loading at the cellular, molecular, and tissue levels. Porous titanium implants were inserted bilaterally on the cancellous bone of adult rabbits beneath a loading device attached to the distal lateral femur. The left femur received a sham loading device. The right femur was loaded daily, and half of the rabbits received daily PTH. Periprosthetic bone was evaluated up to 28 days for gene expression, histology, and µCT analysis. Loading and iPTH increased bone mass by a combination of two mechanisms: (1) Altering cell populations in a pro-osteoblastic/anti-adipocytic direction, and (2) controlling bone turnover by modulating the RANKL-OPG ratio. At the tissue level, BV/TV increased with both loading (+53%, p < 0.05) and iPTH (+54%, p < 0.05). Combined treatment showed only small additional effects at the cellular and molecular levels that corresponded to a small additive effect on bone volume (+13% compared to iPTH alone, p > 0.05). This study suggests that iPTH and loading are potential therapies for enhancing periprosthetic bone formation. The elucidation of the cellular and molecular response may help further enhance the combined therapy and related targeted treatment strategies.

Long-term implant fixation and stress-shielding in total hip replacement

Implant fixation implies a strong and durable mechanical bond between the prosthetic component and host skeleton. Assuming the short-term impediments to implant fixation are successfully addressed and that longer-term issues such as late infection and mechanical failure of the components are avoided, the biological response of the host tissue to the presence of the implant is critical to long-term success. In particular, maintenance of adequate peri-prosthetic bone stock is a key factor. Two major causes of bone loss in the supporting bone are adverse bone remodeling in response to debris shed from the implant and stress-shielding. Here, I review some of the major lessons learned from studying stress-shielding-induced bone loss. It is well known that stress-shielding can be manipulated by altering implant design, but less well appreciated that the development of bone anabolic agents may make it possible to reduce the severity of stress-shielding and the associated bone loss by augmenting the host skeleton through the use of locally or systemically delivered agents. In most cases, mechanical, material and biological factors do not act in isolation, emphasizing that it is often not possible to optimize all boundary conditions.

Are biologic treatments a potential approach to wear- and corrosion-related problems?

WHERE ARE WE NOW?: Biological treatments, defined as any nonsurgical intervention whose primary mechanism of action is reducing the host response to wear and/or corrosion products, have long been postulated as solutions for osteolysis and aseptic loosening of total joint arthroplasties. Despite extensive research on drugs that target the inflammatory, osteoclastic, and osteogenic responses to wear debris, no biological treatment has emerged as an approved therapy. We review the extensive preclinical research and modest clinical research to date, which has led to the central conclusion that the osteoclast is the primary target. We also allude to the significant changes in health care, unabated safety concerns about chronic immunosuppressive/antiinflammatory therapies, industry's complete lack of interest in developing an intervention for this condition, and the practical issues that have narrowly focused the possibilities for a biologic treatment for wear debris-induced osteolysis. WHERE DO WE NEED TO GO?: Based on the conclusions from research, and the economic, regulatory, and practical issues that limit the future directions toward the development of a biologic treatment, there are a few rational approaches that warrant investigation. These largely focus on FDA-approved osteoporosis therapies that target the osteoclast (bisphosphonates and anti-RANK ligand) and recombinant parathyroid hormone (teriparatide) prophylactic treatment to increase osseous integration of the prosthesis to overcome high-risk susceptibility to aseptic loosening. The other roadblock that must be overcome if there is to be an approved biologic therapy to prevent the progression of periprosthetic osteolysis and aseptic loosening is the development of radiological measures that can quantify a significant drug effect in a randomized, placebo-controlled clinical trial. We review the progress of volumetric quantification of osteolysis in animal studies and clinical pilots. HOW DO WE GET THERE?: Accepting the aforementioned rigid boundaries, we describe the emergence of repurposing FDA-approved drugs for new indications and public (National Institutes of Health, FDA, Centers for Disease Control and Prevention) and private (universities and drug and device manufactures) partnerships as the future roadmap for clinical translation. In the case of biologic treatments for wear debris-induced osteolysis, this will involve combined federal and industry funding of multicenter clinical trials that will be run by thought leaders at large medical centers.

The effects of PTH, loading and surgical insult on cancellous bone at the bone-implant interface in the rabbit

Enhancing the quantity and quality of cancellous bone with anabolic pharmacologic agents may lead to more successful outcomes of non-cemented joint replacements. Using a novel rabbit model of cancellous bone loading, we examined two specific questions regarding bone formation at the bone-implant interface: (1) does the administration of intermittent PTH, a potent anabolic agent, and mechanical loading individually and combined enhance the peri-implant cancellous bone volume fraction; and, (2) does surgical trauma enhance the anabolic effect of PTH on peri-implant bone volume fraction. In this model, PTH enhanced peri-implant bone volume fraction by 30% in loaded bone, while mechanical loading alone increased bone volume fraction modestly (+10%). Combined mechanical loading and PTH treatment had no synergistic effect on any cancellous parameters. However, a strong combined effect was found in bone volume fraction with combined surgery and PTH treatment (+34%) compared to intact control limbs. Adaptive changes in the cancellous bone tissue included increased ultimate stress and enhanced remodeling activity. The number of proliferative osteoblasts increased as did their expression of pro-collagen 1 and PTH receptor 1, and the number of TRAP positive osteoclasts also increased. In summary, both loading and intermittent PTH treatment enhanced peri-implant bone volume, and surgery and PTH treatment had a strong combined effect. This finding is of clinical importance since enhancing early osseointegration in the post-surgical period has numerous potential benefits.

Teriparatide in the treatment of non-unions: scientific and clinical evidences

INTRODUCTION

Each fracture has a failing risk which can lead to a non-union. Among the non-invasive strategies proposed to improve bone healing, also in non-union, the use of teriparatide, a drug for the treatment of the osteoporosis, has increasing supporting data.

EXPERIMENTAL DATA

Many studies mainly on rats, but also on primates, demonstrate the positive effect on fracture healing of teriparatide, both in physiological and pathological conditions, with a more rapid evolution of the reparative callus.

CLINICAL DATA

A double blinded randomized controlled study on wrist fractures demonstrated a positive effect, in term of healing speed, of teriparatide at the dose of 20 μg/day, but not at the higher dose of 40 μg/day. A prospectic randomized study on pelvic fractures showed a faster healing in teriparatide treated patients. The use of teriparatide in non-unions is reported as effective in numerous case report. The effect of teriparatide seems very useful in the non-unions consequent to an atypical femoral fracture after long-term administration of bisphosphonates.

CONCLUSIONS

A conceivable positive effect of teriparatide on fracture healing is well-documented on animals, and very likely on humans, however further studies are needed to confirm these hopeful hypotheses.