The authors report the results of preserving the infrapatellar branch of the saphenous nerve during unicompartmental knee arthroplasty to prevent lateral skin numbness.All 100 cases had medial compartmental osteoarthritis and a minimally invasive technique had been used. The mean follow-up duration was two years and eight months (range, 24 to 42 months).The classification according to the location of this nerve was observed as either Mochida Type I with 76 cases (76%), Type II with 16 cases (16%), and unclassified type with 8 cases (8%). In Type I, the nerve was saved in 62 cases (82%), but could not be preserved in Type II because of the surgical procedure. These results showed that the mean distance from the joint line to the nerve of Type I was 9.13 mm (range, 4 to 15 mm) and the nerve passed inferiorly.This study showed the location of this nerve can be predicted ahead of the procedure, which will help preserve it during the surgery.