The factors that contributed to the replantation rate were age <19 years, age >65 years, thumb amputation, concomitant diabetes, surgery on Sunday/during overtime, and educational institutions. The factors affecting the postoperative failure rate were age >65 years and urokinase use. However, the replantation success rate was influenced by thumb amputation in Kinki.
The rate of performing replantation for amputated digits in this study was 13.2%, which is close to the rates of 18% and 11.2% reported by Brown et al. [9] and Shale et al. [14], respectively. The failure rate of replantation in this study was 9.5%, which was similar to that of 8.4% reported in Taiwan [4]. The high frequency of replantation for thumb amputation and the similarly high frequency of replantation in younger patients were consistent with those in previous studies [15]. These data provide a comprehensive overview of digit replantation in Japan.
The higher rate of attempted replantation in elderly patients was unexpected with respect to the replantation rates. It is possible that patients aged 65 years or older were more willing to undergo replantation (even if the treatment time was long) than the working-age group, aged 20–64 years, who sought to return to work as soon as possible after injury. This study is the first to show that replantation is more often chosen for amputated digits than for amputations performed on Sundays or hours after replantation. This result may be attributed to the easier availability of surgeons and operating rooms on weekends and during overtime compared to during normal working hours.
However, this study showed that the replantation rate was high in educational institutions, which was comparable to previous reports [12,16]. Therefore, educational institutions play a role in replantation surgeries in Japan.
The success rate of replantation was 84.9% in 2013[14], while it was 83.4% in 2018. [12]. The success rate of replantation in this study was 90.54%, which is comparable with or better than previous results [17–19]. Age affects the failure rate after replantation [17,18]. The present study corroborated this finding by revealing a higher failure rate in patients over 65 years of age. Hospitals with a larger number of cases have lower failure rates after replantation [20]. However, the number of cases at each hospital had no effect on the success rate in this study. Furthermore, the success rate of replantation techniques was higher in the Kinki region than in other regions of the country. A possible reason for the better results in this area than in other areas is the presence of a facility with which Komatsu and Tamai were affiliated. In the United States and Germany, the decentralization of surgical procedures in recent years has been a concern because the rate of replantation and the success rate of replantation are declining [6,8]. However, this study indicated that the hospital case volume does not affect the success rate of replantation in Japan, and regional differences are small. This finding may be attributable to the standardization of reimplantation techniques in Japan and standardized results within the country.
Although the rate of replantation was higher among patients with diabetes, the postoperative failure rate was comparable to that among patients without diabetes, indicating that replantation is not necessarily refused owing to the presence of diabetes. Furthermore, antithrombotic therapy after replantation is widely used, and its effectiveness is based on data from studies in rat models [21,22]. Many negative reports exist on the efficacy of antithrombotic therapy after replantation. In this study, the use of heparinoids and PGE1 had no effect on the postoperative failure rate [23,24]. However, this study showed that urokinase use significantly correlated with failure, and it is possible that patients who received antithrombotic therapy were severely injured at the time of injury.
This study had several limitations. It was a retrospective observational study based on DPC data; therefore, the surgical details are unknown. Second, this study was limited to cases involving hospitals participating in the DPC. Therefore, it does not reflect the results of other institutions. Third, the detailed amputation levels and injury status at the time of amputation were unknown; therefore, this study did not standardize the cases. In particular, the amputation level and injury status are reported to affect the success rate after replantation of amputated digits. However, these data are not standardized and may not reflect the appropriate postoperative outcomes [25].
In the future, standardizing the treatment of amputated digits will be necessary by compiling a database of cases, including the amputation site and the degree of injury. This information will lead to stricter indications for the replantation of amputated digits that should increase the success rate of surgery.