Assessment of Acetabulum Deformity During Preoperative Planning for Hip Arthroplasty

Purpose of the study — to improve the two-dimensional planning of total hip joint arthroplasty to ensure precise positioning of the acetabular component in the deformed acetabulum. Materials and methods. Features of roentgenological anatomy of acetabulum and its coverage were studied on 1058 hip joint x-rays in the AP view in accordance with the procedure developed by the authors to define acetabular square — the site of standard positioning of a spherical femoral head in the acetabulum or of a hemispherical acetabular component. The method consisted of identifying the apex of “teardrop” figure; the most lateral points of the pelvic terminal line and roof of the acetabulum; superior part of the acetabular cavity; medial and inferior points of acetabular coverage, and building the sides of acetabular square — medial, inferior, lateral and superior boundary lines. Connection of “teardrop” apex and lateral point of the pelvic terminal line formed the medial side of acetabular square, and a perpendicular to that line drawn through the “teardrop” apex to its inferior side. The lateral side was drawn either through the intersection of the ascending diagonal line — bisector from the top of the “teardrop” figure with the contour of the acetabulum roof, or was a part of the projection of the most lateral point of the acetabular roof on the inferior side of the square. The superior side was a perpendicular connecting the intersection of the ascending diagonal and lateral bounding lines with the medial side of the acetabular square. The area of the deformed acetabular cavity located outside of the acetabular square was assessed as the acetabular defect. Results. Method of defining the acetabular square allowed to identify types of ratios between acetabular cavity and acetabular coverage in transverse (9 types) and longitudinal (7 types) direction. Combination of transverse ratio of acetabular cavity and coverage with longitudinal type allowed to define the options of acetabular deformities in two-dimensional view. The authors identified 25 types of acetabular deformities. Bone defects of acetabular walls were of the major importance among all anatomical features. Cranial defect of acetabulum was observed in 450 cases, medial wall defect — in 38 cases, defect including cranial and medial areas — in 7 cases. Conclusion. The method suggested by the authors to determine acetabular square and acetabular deformity variations allows to screen the anatomical features of the acetabulum during two-dimensional preoperative planning and to make an informed decision on the need to use other planning techniques. The type of acetabular deformity identified during preoperative planning allows to elaborate the indications for replacement of acetabular bone defects and/or resection of acetabular osteophytes.