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Updated: Jul 22, 2025
Individualized Stem-positioning in Calcar-guided Short-stem Total Hip Arthroplasty
Published on: February 27, 2018
Determination of a Safe Zone for Ischial Screw Placement in Total Hip Arthroplasty
Nicholas J Bellas1, David Baltrusaitis1, Barrett B Torre1
1Department of Orthopedics, The University of Connecticut, Farmington, Connecticut.
Background:
Implantation of acetabular components with supplemental screw fixation is commonly performed to improve osteointegration and long-term stability in total hip arthroplasty (THA). Placement of ischial screws improves stability in biomechanical studies, but can be technically challenging. The study aimed to provide a safe zone for ischial screw placement with reference to easily identifiable intra-operative landmarks.
Methods:
A retrospective review of patients was performed and 27 preoperative pelvis computed tomography scans were collected. After converting these images to 3-dimensional reconstructions of the pelvis, a safe zone for ischial screw placement was established with reference to the anterior superior iliac spine (ASIS) and the acetabular center and rim.
Results:
The safe zone of an ischial screw in the en face sagittal plane was a median of 17 degrees (interquartile range [IQR]: 11,23) anterior to 13 degrees (IQR: 10,18) posterior to the reference line from the ASIS through the center of the acetabulum. The safe zone in the coronal plane was 34 degrees (IQR: 18,68) medial to 13 degrees (IQR: 8,19) lateral from a start point 1 centimeter medial to the inferior acetabular rim with a screw length of 25 millimeters. An ischial screw optimized for length directed down the center of the ischium was qualitatively demonstrated to have a start point unobtainable intraoperatively, originating within the cotyloid fossa.
Conclusion:
The ASIS, center of the acetabulum, and acetabular rim provide identifiable intraoperative landmarks for guiding ischial screw placement in hip arthroplasty.
