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Page 6 of 7 Sugihara et al. Mini-invasive Surg 2018;2:11 I http://dx.doi.org/10.20517/2574-1225.2018.14

and improve outcomes in laparoscopic nephrectomy. Furthermore, several documents and videos useful
for brushing up surgical skills are now easily available via the Internet, and these favorable multimedia
[18]
educational tools can be useful to prevent a surgeon’s skill from decaying .
Several limitations to the present study should be mentioned. First, we should the stress the lack of
individual surgeon data or actual operation-room time because of the nature of the database. The interval
for a particular surgeon’s laparoscopic experience must be longer than that for a hospital. Therefore, our
results were statistically robust in terms of operation intervals, and indicated that the skills of individual
surgeons would be more well maintained even after a long absence. Second, the laparoscopic time we
used in the present study could be affected by several clinical factors that were lacking in the database.
For example, performance of lymph node dissection, transperitoneal or retroperitoneal approach, and
method for bladder cuff resection (laparoscopic or open) have an impact on overall laparoscopic time. In
addition, information regarding conversion to open surgery was not available. An amount of blood loss or
Clavien-Dindo classification were not registered in the database, however, we believe that several types of
technical difficulties would be directly reflected in elongating laparoscopic time. Third, another laparoscopic
experience other than the five surgical modalities we extracted could be performed by surgeons. Based on
the authors’ clinical experience in Japan, we believe urologists would rarely perform other laparoscopic
surgeries, however the concern could not be completely removed.

In conclusion, regarding laparoscopic nephrectomy and nephroureterectomy, an absence interval of more
than 15 days lengthened the surgery time, although the difference was slight. The present results suggest the
existence of a mild degree of a laparoscopic skill- degradation retention effect in laparoscopic surgery.

DECLARATIONS
Authors’ contributions
Conception and design: Sugihara T
Acquisition of data: Yasunaga H, Matsui H, Fushimi K, Homma Y
Analysis and interpretation of data: Sugihara T
Drafting of the manuscript: Sugihara T
Critical revision of the manuscript for important intellectual content: Ishikawa A, Fujimura T, Fukuhara H,
Homma Y, Kume H
Statistical analysis: Sugihara T
Obtaining funding: Yasunaga H, Matsui H, Fushimi K, Homma Y
Administrative, technical or material support: Yasunaga H, Matsui H, Homma Y, Kume H
Supervision: Yasunaga H, Ishikawa A, Fujimura T, Fukuhara H, Kume H

Data source and availability
The patient data used in the present study were selected from a Japanese nationwide clinical administrative
database named the Diagnosis Procedure Combination database. Please have a contact to Prof. Yasunaga
<yasunagah-tky@umin.ac.jp> for data request.

Financial support and sponsorship
The study has been financially supported by grants from the Japanese Ministry of Health, Labour and
Welfare (H29-Policy-Designated-009 and H29-ICT-Genral-004).

Conflicts of interest
The authors declare that they have no conflicts of interest.

Patient consent
Not applicable.