Biotherapeutics in Orthopaedic Medicine

Application of bone morphogenetic proteins to femoral non-unions: a 4-year multicentre experience

Fracture non-unions often complicate orthopaedic trauma. BMPs (bone morphogenetic proteins) are currently considered the most appealing osteoinductive agents. Applications of BMP-7 since January 2004 were prospectively recorded in a multicentre registry of aseptic femoral non-unions. The study included 30 patients who had undergone a median of 1 revision operation before BMP-7 application and who were followed up for a median 24 months. In 23/30 cases the application of BMP-7 was combined with revision of the fixation, and in 12 it was combined also with autograft. Non-union healing was verified in 26/30 cases in a median period of 6 months. No adverse events were associated with BMP-7 application. Our case series supports the safety and efficacy of BMP-7 in femoral non-unions. Multicentre networks and systematic, long-term follow-up of patients may improve understanding of this promising osteoinductive bone substitute.

[Regenerative medicine in orthopaedics. Cell therapy - tissue engineering - in situ regeneration]

Therapeutic approaches in regenerative medicine, irrespective of specific fields, comprise cell therapy, tissue engineering and in situ regeneration. Regenerative orthopaedics often leads the way on the path to clinical application. In cell therapy primary cells could be replaced by adult mesenchymal stem cells exhibiting almost unlimited regeneration capacity. More sophisticated biomaterial design allowing specific control of cell morphology and tissue organisation is the current focus of advancements in tissue engineering, while signalling to cells by intelligent biomaterials is a main focus of in situ regeneration. These new approaches to the reconstruction of structures and function in damaged or dysfunctional tissue will make it more often possible to achieve a sustainable improvement in terms of real regeneration rather than an acceptable repair.

Application of BMP-7 to tibial non-unions: a 3-year multicenter experience

The effective treatment of the often debilitating, longlasting and large-asset-consuming complication of fracture non-unions has been in the centre of scientific interest the last decades. The use of alternative bone substitutes to the gold standard of autologous graft includes the osteoinductive molecules named bone morphogenetic proteins (BMPs). A multicenter registry and database (bmpusergroup.co.uk) focused on the application of BMP-7/OP-1 was created in December 2005. We present the preliminary results, using the prospective case-series of aseptic tibial non-unions as an example. Sixty-eight patients fulfilled the inclusion criteria for this observational study, with a minimum follow-up of 12 months. The median duration of tibial non-union prior to BMP-7 application was 23 months (range 9-317 mo). Patients had undergone a median of 2 (range 0-11) revision procedures prior to the administration of BMP-7. In 41% the application of BMP-7 was combined with revision of the fixation at the non-union site. Non-union healing was verified in 61 (89.7%) in a median period of 6.5 months (range 3-15 mo). No adverse events or complications were associated with BMP-7 application. The safety and efficacy of BMP-7 was verified in our case series, and was comparable to the existing evidence. The establishment of multicenter networks and the systematic and long-term follow- up of these patients are expected to provide further information and significantly improve our understanding of this promising osteoinductive bone substitute.

The health economics of the treatment of long-bone non-unions

A review of the existing evidence on economic costs of treatment of long-bone fracture non-unions has retrieved 9 papers. Mostly the tibial shaft non-unions have been utilised as models for these economic analyses. Novel treatment strategies like BMP-7 grafting, Ilizarov ring external fixation or supplementary use of therapeutic ultrasound devices have been compared with standard methods of treatment focusing on direct and indirect costs and expenses. A cost-identification query was conducted and revealed costs of pound 15,566, pound 17,200 and pound 16,330 for humeral, femoral, and tibial non-unions respectively on a "best-case scenario". The existing scientific evidence can only imply the extent of the economic burden of long-bone non-unions. Further systematic studies are needed to assess the direct medical, direct non-medical, indirect, and monetised quality of life and psychosocial costs of non-unions.

Biological enhancement of tibial diaphyseal aseptic non-unions: the efficacy of autologous bone grafting, BMPs and reaming by-products

The mandatory stimulus that can optimise the healing pathway can be electrical, mechanical, biological, or a combination of all these parameters. A variety of means has been utilised for biological enhancement, including extracorporeal shock wave, electrical, ultrasound stimulation, the reaming technique of IM nailing, bone graft substitutes, osteogenic cells and bioactive molecules produced by tissue engineering techniques. The aim of this study is to present a review of the existing evidence for the efficacy of reaming, autologous bone grafting and the commercially available growth factors (BMP-2 and BMP-7) for the treatment of aseptic tibial non-unions. The gold standard method of enhancing bone healing in cases of tibial non-union remains the autologous bone graft. Autogenous bone grafts possess osteoconductive, osteoinductive properties and also osteoprogenitor cells. However, their harvesting is associated with high morbidity and many complications reaching percentages of 30%. Intramedullary reamed nailing, either used as an alternative fixation method or as an exchange to a wider implant, offers the unique biomechanical advantages of an intramedullary device, together with the osteoinductive stimulus of the by-products of reaming, and the aptitude for early weight-bearing and active rehabilitation. The safety of administration of the commercial distributed growth factors (BMP-2 and BMP-7), combined with the lack of the morbidity and the quantity restrictions that characterise autologous bone grafts, have given to this family of molecules a principal role between the other bone graft substitutes. On average the union rates reported in the 20 manuscripts that have been evaluated range from 58.3% to 100%, and the average time to union from 12.5 weeks to 48.4 weeks, indicating the significant discrepancies in the reported evidence and the multiplicity of different treatment strategies.

Growth factor delivery for bone tissue repair: an update

Growth factors (GFs) are endogenous proteins capable of acting on cell-surface receptors and directing cellular activities involved in the regeneration of new bone tissue. The specific actions and long-term effects of GFs on bone-forming cells have resulted in exploration of their potential for clinical bone repair. The concerted efforts have led to the recent approval of two GFs, bone morphogenetic protein-2 and osteogenic protein-1, for clinical bone repair, and human parathryroid hormone (1-34) for augmentation of systemic bone mass. This review provides a selective summary of recent (2001-2004) attempts for GF delivery in bone tissue regeneration. First, a summary of non-human primate studies involving local regeneration and repair is provided, with special emphasis on the range of biomaterials used for GF delivery. Next, efforts to administer GFs for systemic augmentation of bone tissue are summarised. Finally, an alternative means of GF delivery, namely the delivery of genes coding for osteogenic proteins, rather than the delivery of the proteins, is summarised from rodent models. To conclude, future avenues of research considered promising to enhance the clinical application of GFs are discussed.

Use of bone morphogenetic proteins in traumatology

An estimated 5-10% of all fractures show impaired healing, leading to delayed union, or non-union. Chemical, or physical methods to accelerate bone healing are of great interest to the orthopaedic and trauma community. Research over the last 20 years has established that successful fracture healing is steered by specific growth factors. Of these, the bone morphogenetic proteins (BMPs) are probably the most important. The signalling pathway of these proteins is tightly regulated, overseeing a finely orchestrated cascade of events that occur after a fracture. The promising results of BMPs in preclinical studies have recently cleared the way for their use in specific fractures, or non-unions in clinical practice. The purpose of this work is to give a brief overview of BMPs and to review the clinical data currently available on the use of BMPs in fracture healing.

A di(bisphosphonic acid) for protein coupling and targeting to bone

Proteins intended for treatment of bone diseases should ideally exhibit a high bone affinity, so that they are preferentially deposited to bones after systemic administration. This can be achieved by combining molecules having a high affinity to bone with the proteins. Bisphosphonates (BPs) are chemical analogs of pyrophosphate that possess exceptional bone mineral affinity. To this end, we synthesized a novel BP, 3,5-di(ethylamino-2,2-bisphosphono)benzoic acid (6), which contains two BP moieties on a single molecule, unlike conventional BPs that contain one BP moiety per molecule. 6 was then conjugated to two model proteins, bovine serum albumin and nonspecific bovine immunoglobulin G by the carbodiimide chemistry. By varying the reagent concentrations, the conjugation efficiency (i.e., number of 6 per protein) was readily controlled under the experimental conditions. The protein-6 conjugates exhibited an in vitro mineral affinity that was proportional to the number of conjugated 6. The 6-conjugates of both bovine serum albumin and immunoglobulin G were found to be bone seeking in rats, based on the increased concentration of 6-conjugated proteins in bone tissue after intravenous administration. We conclude that the novel BP synthesized (6) can serve as a carrier for bone delivery while reducing the extent of protein modification necessary for bone targeting.