Fig 1.
Anteroposterior image of a patient illustrating how the degree of PO is measured.
A. A patient with type IC pelvic obliquity after total hip arthroplasty; the iliolumbar angle was 8.37°. B. A patient with type IIC pelvic obliquity before total hip arthroplasty; the iliolumbar angle was 7.79°. One line was drawn on the anteroposterior radiographs of the pelvis and lower lumbar spine, and this line connected the apices of both iliac crests (OA) and another along the bottom of the fourth lumbar vertebra (OB). The iliolumbar angle was measured at the convergence of these two lines or at the angle of the trans-teardrop (OC) and horizontal lines (OD) when the lower lumbar vertebra could not be completely viewed in the anteroposterior pelvic radiographs.
Fig 2.
Schematic indicating the method for measuring relevant parameters from anteroposterior pelvic and hip radiographs.
Point N is the center of the femoral head, line OP is the anatomic axis of the femur, NO is perpendicular to line OP, and the distance of line NO is the hip offset. Points C and D are the most prominent points of the lesser trochanter, line AB is the trans-teardrop line with lines CA and DB drawn perpendicular to line AB, and the distances of lines CA and DB are femoral vertical offsets. The discrepancy between the lengths of lines DB and CA was documented as the LLI.
Table 1.
Parameters based on preoperative pelvic obliquity.
Table 2.
Parameters for pelvic obliquity after total hip arthroplasty.
Fig 3.
Radiograph showing the forces acting on the hip joint during a single-leg stance under equilibrium conditions.
Gravitational force W, hip joint reaction force F, abductor force A, femoral shaft axial line S, abductor muscle moment arm l, force of gravity moment arm d, and femoral offset n.