Bony landmarks, distances and their correlations to each other, which can be used during periacetabular osteotomy: a CT study performed on dysplastic hips

As a surgical technique for hip dysplasia, Bernese periacetabular osteotomy (PAO) still poses technical difficulties and unclear surgical steps like the depth of the first ‘ischial’ cut, the start of the iliac cut and the width of the retroacetabular cut to prevent either iatrogenic joint entrance or posterior column fracture. Twenty-seven dysplastic hips (CE < 25°) were randomly matched with nondysplastic hips (n: 27, CE > 25°). 3D CT sections of the hips were evaluated and the width of the ischium, the distance from the infra-acetabular groove to the ischial spine, from the anterior superior iliac spine (ASIS) to the joint or sciatic notch or the sciatic spine, from the most medial point at the acetabulum to the posterior column, ischial spine or sciatic notch were measured for each group and correlated. The distances (mm) from the infra-acetabular groove to the ischial spine (42 ± 4, 44 ± 4, P: 0.03), the anterior superior iliac spine to the joint (52 ± 6, 60 ± 3, P: 0.03), the most medial point at the acetabulum to the posterior column (34 ± 2, 36 ± 2, P: 0.005) were shorter in the dysplastic group. The distance from the ASIS to the sciatic notch was correlated with the distance from the infra-acetabular groove to the ischial spine, from the ASIS to the joint and the most medial point at the acetabulum to the posterior column. The distance from the ASIS to the sciatic notch can be used intraoperatively to guess the X-ray guided or blindly osteotomized stages to predict the width or depth of the osteotomy to prevent intraarticular extension or posterior column fracture.

Periacetabular osteotomy using three-dimensional cutting and reposition guides: a cadaveric study

The goal of periacetabular osteotomy (PAO) is to reorient the acetabulum in a more physiological position. Its realization remains challenging regarding the final position of the acetabulum. Assistance with custom cutting- and reorientation-guides would thus be very helpful. Our purpose is to present a pilot study on such guides. Eight cadaveric hemipelvis were scanned using CT. After segmentation, 3D models of each specimen were created, a PAO was virtually performed and reorientation of the acetabula were defined. A specific guide was designed aiming to assist in iliac, posterior column and superior pubic ramus cuts as well as in acetabulum reorientation. Furthermore, the acetabular position was planned. Three-dimensional printed guides were used to perform PAO using the modified Smith-Peterson approach. The post-operative CT images and virtually planned acetabulum reorientation were compared in terms of acetabular index (AC), lateral centre edge angle (LCE), acetabular anteversion angle (AcetAV). There was no intra-articular or posterior column fracture seen. Two cadavers showed very low bone quality with insufficient stability of fixation and were excluded from further analysis. Correlation between the post-operative result and planning of the six included cadavers revealed the following mean deviations: 5° (SD ±3°) for AC angle, 6° (SD ±4°) for LCE angle and 15° (SD ±11°) for AcetAV angle. The use of 3D cutting and reorientation blocks for PAO was possible through a modified Smith-Peterson approach and revealed accurate fit to bone, accurate positioning of the osteotomies and acceptable planned corrections in cadavers with good bone quality.