Accurate evaluation of lower limb coronal alignment is essential for effective pre-operative planning of knee arthroplasty. Weightbearing hip-knee-ankle (HKA) radiographs are considered the gold standard. Mako SmartRobotics uses CT-based navigation to provide intra-operative data on lower limb coronal alignment during robotic assisted knee arthroplasty. This study aimed to compare the correlation between the two methods in assessing coronal plane alignment. Patients undergoing Mako partial (PKA) or total knee arthroplasty (TKA) were identified from our hospital database. The hospital PACS system was used to measure pre-operative coronal plane alignment on HKA radiographs. This data was correlated to the intraoperative deformity assessment during Mako PKA and TKA surgery. 443 consecutive Mako knee arthroplasties were performed between November 2019 and December 2021. Weightbearing HKA radiographs were done in 56% of cases. Data for intraoperative coronal plane alignment was available for 414 patients. 378 knees were aligned in varus, and 36 in valgus. Mean varus deformity was 7.46° (SD 3.89) on HKA vs 7.13° (SD 3.56) on Mako intraoperative assessment, with a moderate correlation (R= 0.50, p<0.0001). Intraoperative varus deformity of 0-4° correlated to HKA measured varus (within 3°) in 60% of cases, compared to 28% for 5-9°, 17% for 10-14°, and in no cases with >15° deformity. Mean valgus deformity was 6.44° (SD 4.68) on HKA vs 4.75° (SD 3.79) for Mako, with poor correlation (R=0.18, p=0.38). In this series, the correlation between weightbearing HKA radiographs and intraoperative alignment assessment using Mako SmartRobotics appears to be poor, with greater deformities having poorer correlation

Several studies have reported the assessment of the femoral head coverage on plane radiograph and CT data in supine position, though young patients with the dysplastic hip often have symptoms during activities such as standing, walking, and running. On the other hand, some investigators have used a method of CT which allows standardization of the femoral head coverage against an anterior pelvic plane based on the anterior superior iliac spines and the pubic tubercle. We believe both the weight-bearing position and the standardized position to be more relevant for diagnosis and preoperative surgical assessment. So, we show the femoral head coverage in standardized position using 3D-CT method and in weight-bearing position using the plane radiograph and the three-dimensional lower extremity alignment assessment system before and after Curved periacetabular osteotomy (CPO). Especially the covered volume of the femoral head, a new concept, using the three-dimensional lower extremity alignment assessment system which differs from the affected area and is measured by the ratio of the covered area in the medial part of the line connecting the anterior point of the acetabulum with the posterior to the femoral head area in each axial slice, superior slices than the slice passing through the femoral head center, obtained from the reproduced 3D model of the pelvis and the femur in standing position allows us to integrate various measurements reported by past researchers. We studied the consecutive 16 patients treated with CPO. In standardized position the sagittal sectional angles on the slice passing through the femoral head center using 3D-CT method gave us how the anterior, lateral, and posterior coverage was lack compared with normal subjects and whether the adequate transfer of the rotated fragment was performed after operation. The covered volume of the femoral head decides generally the deficiency or the adequateness. In standing position, though the pelvic tilt changes, the femoral head coverage on plane radiograph, representation by the CE angle, the VCA angle, AHI and ARO, was significantly improved, and the covered volume of the femoral head was significantly improved from 25.7% preoperatively to 51.1% postoperatively. Our study showed the improvement of the femoral head coverage, including the covered volume of the femoral head as a new concept, after CPO in weight-bearing and standardized position. The morphological and functional assessment of the femoral head coverage on both pre- and post-CPO should be performed because we can obtain the objective information in standardized position and the femoral head coverage in standing position is closely connected with the pain