Injectable bone-graft substitutes: current products, their characteristics and indications, and new developments

Orthopaedic surgeons have long sought alternatives to autologous bone grafts for fracture repair. Injectable bone substitutes have been available for over ten years, yet their use remains underutilized. Traditional bone grafting carries risks such as donor site morbidity, prompting interest in synthetic options. Calcium phosphate and calcium sulphate are the two primary materials in current injectable substitutes. These materials offer advantages like ease of application and in situ hardening. However, their mechanical properties differ significantly from natural bone. Calcium sulphate dissolves more quickly and lacks the same structural resilience as calcium phosphate. Despite these differences, both materials aim to support bone healing in weakened or fractured areas. Clinical adoption has been slow due to limited awareness and understanding of their indications and limitations.

This review aims to clarify the current state of injectable bone substitutes in orthopaedic trauma. It focuses on the materials, their properties, and clinical applications. The goal is to help surgeons determine when these substitutes might be useful. The authors highlight the two main types: calcium phosphate and calcium sulphate. They compare the mechanical strengths and biological behaviors of these materials. The review also addresses the limited clinical data for calcium sulphate products. By summarizing recent developments, the authors hope to guide future use and research. They emphasize the need for more studies to confirm long-term outcomes and optimal applications.

The authors conducted a literature review of injectable bone substitutes in orthopaedic trauma. They categorized products based on their primary components: calcium phosphate or calcium sulphate. They analyzed the mechanical properties of these materials in compression, bending, and shear. The review included clinical studies on calcium phosphate for metaphyseal fractures. They examined the remodelling processes of both materials—cell-mediated for calcium phosphate and dissolution-based for calcium sulphate. The authors also explored new formulations, such as fibre-reinforced composites. They considered combinations of calcium phosphate and calcium sulphate to improve performance. Finally, they assessed the potential of these materials as carriers for antibiotics and growth factors.

Calcium phosphate products have been shown to be effective in metaphyseal fractures, particularly in tibial plateau cases. Randomized trials support their use as an alternative to conventional bone grafting. The mechanical strength of calcium phosphate in compression is comparable to cancellous bone. However, it performs less well in bending and shear forces. Calcium sulphate dissolves more rapidly and lacks the same structural resilience. Clinical studies on calcium sulphate are limited, making it harder to assess its efficacy. New developments include premixed or directly mixed products to improve usability. Fibre-reinforced composites are being tested to enhance mechanical properties. Combining calcium phosphate and calcium sulphate may offer a balance of fast dissolution and structural support. These materials also show promise as carriers for antibiotics and growth factors.

Injectable bone substitutes are a viable option in specific orthopaedic trauma scenarios. Calcium phosphate has demonstrated effectiveness in certain metaphyseal fractures. Calcium sulphate remains under-researched but may have unique advantages in short-term applications. The authors suggest that new formulations could improve mechanical performance and usability. Combining calcium phosphate and calcium sulphate may provide a more versatile solution. These materials may also serve as delivery systems for therapeutic agents. Surgeons should consider the available evidence when selecting a substitute. More clinical studies are needed to confirm long-term outcomes and optimal use.