Fig 1.
Sagittal alignment parameters in the standing position.
Spinal parameters, TK (thoracic kyphosis), LL (lumbar lordosis), and the SVA (sagittal vertical axis), were measured on a lateral whole-spine radiograph (a). Pelvic parameters, the PT (pelvic tilt), SS (sacral slope), and PI (pelvic incidence), were measured (b). Lower limb parameters, the FOA (femur obliquity angle) and KFA (knee flexion angle), were measured (c).
Fig 2.
The constructed musculoskeletal model using the Anybody Modeling System.
The constructed model altered the thorax, muscle attachment points, and pathways.
Fig 3.
The method for simulating pelvic lower limb alignment in the musculoskeletal models.
“θ” is the difference between the model default angle “α” and the patient’s actual measured value “β,” indicating the actual angle to be input into the model. Input “θPT” to be the patient measured value “βPT” (a). Input the values of “θhip” “θknee” for hip and knee joint angles (b). Input “θss” to be the patient measured value “βSS” (c).
Fig 4.
A patient’s full body lateral radiograph and images of the modified musculoskeletal model.
This image shows the full-body lateral radiograph of a patient. A modified musculoskeletal model was used to input the patient’s sagittal alignment.
Fig 5.
Hip joint diagram for the calculation of muscle contribution to the HCF.
The hip penetration force was the force exerted by an adjacent body segment. Muscle tension alone contributed to the HCF. Using the inverse dynamics analysis, the HCF was calculated using three components: anterior/posterior (AP), proximal/distal (PD), and medial/lateral (ML). The HCF was calculated by combining these three force vectors.
Table 1.
Clinical characteristics of all patients.
Table 2.
Spearman’s rank correlation coefficients of the HCF with patients’ sagittal alignment parameters.
Fig 6.
Correlation between the sagittal vertical axis (SVA) and hip contact force (HCF).
Table 3.
Comparison of the low SVA and high SVA groups.
Fig 7.
An example case of the high SVA group.
Lateral radiographs of the whole spine and lower limb in the standing position.TK, thoracic kyphosis; LL, lumbar lordosis; PT, pelvic tilt; SS, sacral slope; PI, pelvic incidence; SVA, sagittal vertical axis; FOA, femur obliquity angle; KFA, knee flexion angle.