Table 3.

The research question defined as PICOS of the preclinical animal study [37].

PICOS	Definition
Population	Studies that include animal models of bone defects, with no limitations on the animal species nor modeling methods
Intervention	Degradable metals and their alloys, modified degradable metals and their alloys (composites, coating and surface modification)
Control	① Non-degradable metals, such as titanium, titanium alloy, stainless steel and cobalt chromium alloy; ② Degradable polymers, such as polylactic acid; and ③ Other materials, such as calcium phosphate ceramic, autogenous bone, allogeneic bone, or degradable composites used in traditional clinical applications (e.g. ceramic-polymer composites)
Outcome	Outcome measures for bone defect repair: ① New bone formation; ② Defect repair; ③ The percentage of bone volume/tissue volume around the implant; and ④ Bone implant contact. Implant-related outcome measures: ① Degradation; ② Hydrogen generation
Study designs	Controlled studies were included, with no restriction on whether they were randomly grouped. In order to ensure the quality of included studies, self-control studies were excluded because metallic ions from both experiment and control groups may influence each other in terms of their effects on bone defects repair