Selection of primary studies and data extraction
After retrieving the references, the titles and abstracts were screened in duplicate by two reviewers. Once it is determined that relevant studies may be included, the full text will be screened. If there was any doubt about eligibility, a third reviewer will be the arbitrator. Upon completion of the above work, two reviewers used a tested data extraction form to abstract data independently. This included the characteristics of the references, the year of publication, first author, study period, definition of PUL and the outcomes, experimental design, study methodology, management protocol, and final clinical results.