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Large segmental bone loss and bone resection due to trauma and/or the presence of tumors and cysts often results in a delay in healing or non-union. Currently, the bone autograft is the most frequently used strategy to manage large bone loss. Nevertheless, autograft harvesting has limitations, namely sourcing of autograft material, the requirement of an invasive procedure, and susceptibility to infection. These disadvantages can result in complications and the development of a bone substitute materials offers a potential alternative to overcome these shortcomings. Among the biomaterials under consideration to date, beta-tricalcium phosphate (β-TCP) has emerged as a promising material for bone regeneration applications due to its osteoconductivity and osteoinductivity properties as well as its superior degradation in vivo. However, current evidence suggests the use β-TCP can in fact delay bone healing and mechanisms for this observation are yet to be comprehensively investigated. In this review, we introduce the broad application of β-TCP in tissue engineering and discuss the different approaches that β-TCP scaffolds are customized, including physical modification (e.g., pore size, porosity and roughness) and the incorporation of metal ions, other materials (e.g., bioactive glass) and stem cells (e.g., mesenchymal stem cells). 3D and 4D printed β-TCP-based scaffolds have also been reviewed. We subsequently discuss how β-TCP can regulate osteogenic processes to aid bone repair/healing, namely osteogenic differentiation of mesenchymal stem cells, formation of blood vessels, release of angiogenic growth factors, and blood clot formation. By way of this review, a deeper understanding of the basic mechanisms of β-TCP for bone repair will be achieved which will aid in the optimization of strategies to promote bone repair and regeneration.

Background: The treatment of proximal femoral fractures in geriatric osteoporotic patients continues to be a challenge in orthopaedic trauma. Various kinds of cephalomedullary nails, such as gamma nail, InterTan and PFNA were used clinically. The latest generation PFNA II, specially designed for Asian population, is commonly used for geriatric per-/intertrochanteric fractures. The aim of this study was to determine whether the current PFNA-II proximal segment length is suitable for the greater trochanter height, as assessed by postoperative radiograph measurements. Materials and Methods: 51 consecutive patients with per-/intertrochanteric fractures treated with the PFNA-II between July 2012 and December 2012 were enrolled in this study. There were 19 males and 32 females, with an average age of 78.6 years (range 66-92 years). According to AO/OTA classification system, there were 4 cases of 31A1 fractures, 35 cases of 31A2 fractures, and 12 cases of 31A3 fractures. The nail protrusion height over the lateral greater trochanter and the Parker ratio of the helical blade tip in the femoral head were measured and compared using pelvic digital anteroposterior radiographs taken within 2 weeks postoperatively. Patients were followed up for a minimum period of 1 year to check whether they had lateral trochanter pain. Results: Postoperative digital anteroposterior (AP) films were used for assessment and any prominence was recorded as positive. Overall, nail protrusion over the greater trochanter occurred in 87.8% of cases. In 60.8% of the cases, protrusion height was >5 mm. The average protrusion height was 6.25 ± 4.27 mm (male average 4.84 ± 4.38 mm, and female average 7.09 ± 4.70 mm). The average Parker ratio of all cases was 51.0 ± 6.9% (male average 49.8 ± 7.5% and female average 51.7 ± 6.5%). Protrusion height was positively correlated (r = 0.394, P = 0.004) with the helical blade position in the femoral head (Parker ratio). Clinically, a total of 42 patients were followed up at an average of 15.0 ± 2.6 months (range 12--24 months) they were able to walk independently or with a stick. There were 13 patients with lateral trochanter pain on the injured side. Protrusion height of these patients was 11.13 ± 3.75 mm, whereas the protrusion height of the remaining 29 patients was 3.87 ± 3.39 mm. Conclusions: There was a morphologic mismatch between the proximal segment length of the PFNA-II and the greater trochanter in the Asian population, which may be the cause of postoperative lateral trochanter pain. A modification to shorten the proximal part of the nail is proposed to avoid protrusion over the greater trochanter. [ABSTRACT FROM AUTHOR]