Accuracy of Femoral Component Position in Primary Total Knee Arthroplasty Based on Valgus Cut Angle

Background The distal femur resection in total knee arthroplasty (TKA) is commonly made using a fixed angle by routine use of 5° or 6° for valgus cut angle(VCA). The present study aimed to determine the effect of specific VCA in each person on post-TKA limb alignment. Material and methods In this retrospective study all patients who underwent primary knee replacement surgery performed by a single surgeon by using the individualized VCA method from Imam Khomeini and Shafa hospitals in Sari from 2018 to 2020 were included. Preoperative and post-operative knee radiographs including a standing anteroposterior and lateral view and the long-leg standing anteroposterior radiograph alignment view were collected. Radiographic parameters including Mechanical Femoro-tibial angle (mFTA), Lateral distal femoral angle (LDFA), medial Proximal tibial angle (MPTA), and valgus cut angle (VCA) were compared before and after surgery. Results 139 knees associated with 119 patients were examined. The mean (standard deviation) age of patients was 64.35 Years (7.57). 89.3% were female. In 78% of the cases, the VCA was 5–7 degrees. All radiographic parameters improved significantly after surgery (P < 0.0001). The mean (SD) of Total varus correction (ΔmFTA) was 13.47 (5.64) and ranged from 2 to 26 degrees. mLDFA in 39.3% of knees was in a normal range (85–90). After surgery, this rate increased to 64%. Before surgery based on mFTA, 98.2% of patients' knees had varus alignment and after surgery mFTA in 73% of the patients were in the neutral range. There was a statistically significant association between the valgus cut angle (VCA) and LDFA, mFTA, and total varus correction (ΔmFTA) (p < 0.05). Conclusion This study demonstrates that in the absence of a computer-assisted navigation system, the use of an individual valgus cut angle improves achievement of a neutral, femoral component alignment(LDFA), and mFTA alignment after TKA especially in knees with severe varus deformity. Level of evidence: IV