Use of Bone Graft Substitutes and Bioactive Materials in Treatment of Distal Radius Fractures

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CHAPTER 23 Use of Bone Graft Substitutes and Bioactive Materials in Treatment of Distal Radius Fractures

Brian J. Hartigan, MD, Richard L. Makowiec, MD

The goals of treating distal radius fractures include anatomical reduction, stable fixation to allow early movement, reliable and rapid osteosynthesis, and restoration of pain-free function. Bone healing can be delayed by the presence of large metaphyseal defects or voids that are often seen in distal radius fractures. These defects, as well as segmental defects or osteoporotic bone, are amenable to bone grafting. Autologous bone graft has been frequently used in the treatment of distal radius fractures to aid in healing in those cases. Over the past several years there has been significant interest in the development of biomaterials that can augment fracture healing to preclude the need for autologous graft.

Medically, there has been increasing interest in restoring alignment through minimal incisions and with less invasive fracture fixation. The increased number of fractures related to aging and osteoporosis has contributed to this trend. Goals of limited invasive surgery include earlier mobilization and earlier return to function. Currently available bone graft substitutes for the distal radius can help achieve these goals by restoring structural integrity with limited morbidity and possibly by achieving more rapid healing of bone.

Economically, the high market value of these products has created a stimulus for their development.¹ As such, physicians may now choose from several products that are now commercially available. Unfortunately, there is currently little consensus on the indications for use of bone graft substitutes and a paucity of comparative studies between products. Rigorous comparison of the commercially available bone graft substitutes has proved difficult because of their diversity and the lack of standardized assays. Furthermore, comparable clinical studies have not been performed.² The U.S. government has contributed to this confusion as regulatory control of the different types of products, even similar products, has fallen under different agencies within the Food and Drug Administration.³ This review will cover the indications and currently available materials for use as bone replacements in the treatment of distal radius fractures.

Bone Graft Properties

An ideal bone graft possesses four important properties: (1) osteogenic cells, which are naturally occurring cells with the potential to differentiate into bone forming cells; (2) osteoinductive factors, which are proteins, including growth factors, that stimulate and signal new bone growth; (3) osteoconductive matrix providing a scaffold for new bone growth; and (4) structural integrity.⁴ Both cancellous and cortical autogenous bone graft possess the first three properties. Although cortical grafts are able to provide structural integrity, they are less osteogenic and osteoinductive when compared with cancellous grafts. Iliac crest autologus graft has long been the gold standard of bone grafts.

Alternatives to autogenous graft, or bone graft substitutes, are judged by their ability to provide aspects of these four components. Substitutes now available include allograft bone, demineralized bone matrix (DBM), synthetic ceramic mineral substitutes, and recombinant bone morphogenetic proteins BMP-7 and BMP-2.¹ Unfortunately, comparison of one substitute with another or with autogenous graft is difficult. Each substitute is made of unique materials and participates in healing in different ways. Additionally, there are no standardized assays specific for osteoinduction and osteoconduction in humans, making it impossible to accurately quantify their role in bone healing.

Indications

The distal radius has been the center of attention for the development of many of the bone graft substitutes because it is a common area to fracture with a relative lack of associated confounding variables.⁵ The indications for the use of bone grafts or graft substitutes in the treatment of distal radius fractures, however, have not been clearly defined. Additionally, although autogenous graft has been proved to be beneficial,⁶^–⁹ there is no clear consensus with regard to bone graft substitutes.

The goal of treatment is to restore alignment of the radius and provide stability with minimal compromise of hand function.¹⁰ This can be accomplished with either a cast, external fixator, or a variety of internal fixation techniques, depending on the fracture pattern, degree of displacement, stability of the fracture, patient age, and physical demands. Fracture healing is typically not a problem, because the fracture involves metaphyseal bone with ample vascularity.¹¹ However, comminuted fractures or fractures in osteoporotic bone often result in cortical comminution and metaphyseal defects, which if left unsupported can lead to collapse of the distal fragments and loss of alignment. Additionally, osteopenic or osteoporotic bone can limit fixation and result in loss of reduction after internal fixation. In either case, healing will typically occur but may result in a shortened or malaligned radius, which can produce pain, stiffness, and loss of strength.^12,¹³ It is in these osteoporotic or comminuted fractures that bone graft substitutes provide structural support or act as a scaffold for new bone formation and are particularly desirable.

The use of autogenous bone graft has been shown to be advantageous to support metaphyseal defects after distal radius fractures.⁶^–⁹ In addition to providing structural support, autogenous graft can accelerate and augment bone healing due to the presence of growth factors and viable osteoblasts. However, use of autogenous bone graft has been associated with donor site morbidity, including infection, blood loss, and pain, as well as increased surgical time, hospital stay, and cost.¹⁴ These potential disadvantages have helped lead to the development of numerous bone graft substitutes.

The decision to use graft or graft substitute should be based on the particular injury, with emphasis on fracture pattern, stability, comminution, soft tissue injury, as well as patient factors. Another consideration should be the type of fixation employed and whether the bone graft substitute is expected to provide structural stability. None of the available graft substitutes is ideal for all situations. A structural and osteoconductive material may be considered to augment fixation in the treatment of fractures with metaphyseal or diaphyseal defects or significant cortical comminution. An osteoinductive material may be used in fractures with potential impaired healing. These include local factors such as those extending into the diaphysis or those with extensive soft tissue disruption and host factors such as diabetes, smoking, or poor nutritional status. Further study regarding growth factors may expand the indications to include even the simple fractures in an effort to accelerate healing. It is also worthwhile to note that many of the modern fixed-angle implants impart rigid support of the distal end of the radius and that the use of bone graft or bone graft substitutes with these implants may be superfluous.