Traditional inert materials used in internal fixation have caused many complications and generally require removal with secondary surgeries. Biodegradable materials, such as magnesium (Mg)-, iron (Fe)- and zinc (Zn)-based alloys, open up a new pathway to address those issues. During the last decades, Mg-based alloys have attracted much attention by researchers. However, the issues with an over-fast degradation rate and release of hydrogen still need to be overcome. Zn alloys have comparable mechanical properties with traditional metal materials, e.g., titanium (Ti), and have a moderate degradation rate, potentially serving as a good candidate for internal fixation materials, especially at load-bearing sites of the skeleton. Emerging Zn-based alloys and composites have been developed in recent years and in vitro and in vivo studies have been performed to explore their biodegradability, mechanical property, and biocompatibility in order to move towards the ultimate goal of clinical application in fracture fixation. This article seeks to offer a review of related research progress on Zn-based biodegradable materials, which may provide a useful reference for future studies on Zn-based biodegradable materials targeting applications in orthopedic internal fixation.

Osteonecrosis of the femoral head (ONFH) has an exceedingly high prevalence and disability rate, causing a tremendous socioeconomic burden. The prevalence of ONFH is increasing, while the population of the patients with ONFH is becoming younger. Once the femoral head collapses, treatment becomes difficult and often requires a hip joint replacement, which is not favorable for young patients. Therefore, hip joint-preserving treatments at an early stage of ONFH are particularly important. This study provides a comprehensive review on hip-preserving strategies for treating ONFH, including nonoperative treatments (e.g., protective weight bearing, hyperbaric oxygen, pulsed electromagnetic, extracorporeal shockwave, bisphosphonate, anticoagulants, hypolipidemics, vasodilators, and traditional Chinese medicine) and operative treatments (e.g., core decompression, osteotomy, bone grafting, mesenchymal stem cell transplantation, tantalum rods, and tissue engineering). Nonoperative treatments aim to slow down the progression of the disease and delay the need for joint replacement; however, they usually cannot effectively prevent the progression of the disease, except in cases of small necrosis areas (<10 %). Additionally, nonoperative treatments have unclear mechanisms that require further investigation. In contrast, operative treatments may stop the negative outcomes of necrosis and therefore appear to be more promising. Currently, an emerging area in operative treatments is regenerative medicine, which could promote the generation of bone tissues and blood vessels and restore hip joint function to pre-necrotic levels as much as possible. This review seeks to not only provide an important reference for clinicians when choosing appropriate strategies for treating ONFH but also offer certain guidance for future basic research in developing ONFH treatments. The incidence of ONFH is increasing, and patients are becoming younger on average. Therefore, the development of hip joint-preserving strategies to treat ONFH at earlier stages is urgently needed, particularly for young patients. However, a comprehensive review is lacking regarding the currently-available hip joint-preserving strategies and their effectiveness. This study is motivated to fill this gap and serve as an important reference for clinicians in choosing appropriate strategies to treat ONFH.