Introduction. Upright body posture is maintained with the alignment of the spine, pelvis, and lower extremities, and the muscle strength of the body trunk and lower extremities. Conversely, the posture is known to undergo changes with age, and muscle weakness of lower extremities and the restriction of knee extension in osteoarthritis of the knee (knee OA) have been considered to be associated with loss of natural lumbar lordosis and abnormal posture. As total knee arthroplasty (TKA) is aimed to correct malalignment of lower extremities and limited range of motion of knee, particularly in extension, we hypothesized that TKA positively affects the preoperative abnormal posture. To clarify this, the variation in the alignment of the spine, pelvis, and lower extremities before and after TKA was evaluated in this study. Patients and methods. Patients suffering from primary knee OA who were scheduled to receive primary TKA were enrolled in this study. However, patients with arthritis secondary to another etiology, i.e. rheumatoid arthritis, trauma, or previous surgical interventions to the knee, were excluded. Moreover, patients who suffered from hip and ankle OA, cranial nerve diseases, or severe spinal deformity were also excluded. The sagittal vertical axis (SVA), the horizontal distance between the posterosuperior aspect of the S1 endplate surface and a vertical plumb line drawn from the center of the C7 vertebral body, is an important index of sagittal balance of the trunk. Thus, patients were classified into two groups based on the preoperative SVA with preoperative standing lateral digital radiographs: normal (< 40mm) and abnormal (≥ 40mm) groups. The variations in the sagittal alignment of the spine, pelvis and lower extremities were evaluated preoperatively, and at 1 and 3 months postoperatively. This study was approved by an institutional review board, and informed consent for participation was obtained from the patients. Results. Forty-nine knees in 49 patients were enrolled. Three different patterns of postural changes as well as hip and knee angles following TKA were observed. After TKA, the preoperatively normal SVA patients (26.5%) showed extension of the hip and knee joints and decrease of lumbar lordosis, while the SVA remained almost within the normal range. In the preoperatively abnormal SVA group, 13 patients (26.5%) showed extension of the knee joint while the SVA remained abnormal, however, 23 of the preoperatively abnormal SVA group patients (47.0%) showed improvement of SVA into the normal range with the extension of the hip and knee joints. Discussion. As the spine, pelvis, and lower extremities together affect body alignment, once limitation of knee extension due to severe knee OA is corrected and lower extremity alignment is improved with TKA, the lumbar lordosis may increase, and SVA could decrease. Recently, the relationship between the imbalance of the sagittal plane of the body and the risk of falls was described. From this, it could be said that TKA not only helped in recovering knee function and lower extremity alignment in severe knee OA, but also helped to improve posture and to protect from falls

Introduction. Understanding hip-spine relationships and accurate evaluation of the pelvis position are key- points for the optimization of total hip arthroplasty (THA). Hip surgeons know the importance of pelvic parameters and the adaptation mechanisms of pelvic and sub-pelvic areas. Literature about posture after THA remains controversial and adaptations are difficult to predict. One explanation can be the segmental analysis focused on pelvic parameters and local planning. In a significant number of patients a global analysis may be important as a cascade of compensatory mechanisms is implemented, the hip being only one of the links of this chain reaction. 3 parameters can be measured on full body images:. SVA (sagittal vertical axis) : horizontal distance between the vertical line through the center of C7 and the postero-superior edge of S1. T1 pelvic angle (TPA) : line from femoral heads to T1center and line from the femoral heads to S1center. TPA combines informations from both the sagittal vertical axis and pelvic tilt. Global Sagittal Angle (GSA) : line from the midpoint of distal femoral condyles to C7 center and line from the midpoint between distal femoral condyles to the postero-superior S1corner. The objective of this preliminary study is to report the post-operative evolution of posture after THA. Material and Method. 49 patients (28 women, 21 men, mean age 61 years) were enrolled for full-body standing EOS images before and after THA. The sterEOS software was used to measure pelvic parameters (sacral slope SS, pelvic incidence PI) and global postural parameters (TPA, GSA, SVA). Sub-analysis was made, grouping the sample by TPA (<14°, 14°–22°, >22°), by PI (<55°, 55°–65°, >65°) and by SS (<35°, 35°–45°, >45°). Paired t-test was used to compare differences between preoperative and postoperative parameters within each subgroup. Statistical significance was set at p < 0.05. Results. TPA, SVA and GSA may change independently following THA surgery. In the 2 groups with TPA< 19° and 14° <TPA< 22°, GSA and SVA decreased significantly after THA (p < 0.05). The difference was not significant in the group with TPA>22°. In the group with SS between 35° and 45°, the GSA and SVA decreased after THA (p < 0.05). In the group with SS > 45° only GSA decreased. In the group with PI < 55°, GSA and SVA decreased after THA. There was no significant change in the remaining subgroups. Discussion. This preliminary study confirms a decrease of GSA and SVA after THA. Some preoperative characteristics are observed in patients with significant global sagittal postural modifications: low to standard TPA, low PI or standard to high SS. Conclusion. Planning and prediction of sagittal postural changes after THA implantation is challenging. It is an important topic in patients with stiff and degenerative spine or in case of spinal fusion. In case of complex hipspine cases, the timing of the procedures can be a real concern. The combined analysis of SVA, TPA and GSA may open new perspectives for a more rationale planning of THA