Refer to Wells et al. (6) for a description of Newcastle–Ottawa Quality Assessment Scale for cohort studies. In general, more stars denote higher quality. Representativeness is awarded a star if the cohort is truly or somewhat representative of the population of interest. For selection of the nonexposed cohort, a star is awarded if it is drawn from the same population as the exposed cohort. The relevant exposure in this review is the surgical procedure performed in the live tissue; we considered a nonexposed cohort to be one that performed the procedure in another simulation method. Exposure is satisfactorily ascertained if data are collected from a secure record. A star is awarded if the outcome is not present at the start of the study. A maximum of 2 stars can be given for comparability of controls for controlling of confounders in either the design (matching) or analysis (statistical adjustment) phase. We also gave 1 star when selection criteria appeared to create comparable groups via restriction. Assessment of outcome is awarded a star if the outcomes were assessed by independent blind assessment or record linkage. The duration of follow-up was considered adequate if it was long enough for the outcomes to occur. Completeness of follow-up was considered adequate if all participants were accounted for or if the number lost to follow-up was sufficiently low to be unlikely to introduce bias.