To compare the incidence of anterior femoral notching in total knee arthroplasty (TKA) using the anterior versus posterior reference system, and to investigate the reason of anterior femoral notching by calculating the cutting error caused during osteotomy by the oscillation of saw blade through the guide-slot.

Patients who underwent TKA for primary osteoarthritis between September 2015 and December 2020 were enrolled in this study. The patients were divided into either an anterior reference group or a posterior reference group according to the femoral component sizing method used. The incidence of anterior femoral notching was compared between the two groups according to the Tayside classification on postoperative lateral X-ray images of the knee joint. The height and depth of the slot as well as the thickness and the cutting length of saw blade were measured. The maximum oscillatory amplitude of blade and the maximum cutting depth of the anterior cortex were calculated using the measured value of the slot height, slot depth and saw blade thickness.

A total of 195 patients (239 knees) were enrolled in the study with 107 and 132 knees in the anterior and posterior reference groups, respectively. There was no significant difference between the two groups in the incidence of general anterior femoral notching (26.2% vs 18.9%, χ²=1.789, P=0.181) or the incidence of severe anterior femoral notching (Tayside grades Ⅲ and Ⅳ; 4.7% vs 6.1%, χ²=0.221, P=0.638). The maximum oscillatory amplitude of blade and the maximum cutting depth of the anterior cortex at a cutting length of 5 cm were 2.98 mm and 0.75 mm in the anterior reference group and 3.15 mm and 0.80 mm in the posterior reference group, respectively.

The anterior reference system does not seem to be definite advantages over the posterior reference system in avoiding anterior femoral notching during TKA. The reason may be the special design of the femoral prosthesis of the posterior reference system. The cutting error caused by the oscillation of saw blade in the guide-slot during osteotomy and other factors may play an important role in leading to anterior femoral notching.