Volume VII, Number 1 | April 2023

Superior Pubic Ramus as a Landmark for Acetabular Cup Abduction Angle During Total Hip Arthroplasty

2Bujnak T, 1Miller Z,  2Blumenschein L, 2Toussaint K, 2Goldschmidt M, 3Dunn A
1Case Western Reserve University/University Hospitals Cleveland Medical Center/Regional Program, Cleveland Heights, OH, United States; 2 Case Western Reserve University/University Hospitals Cleveland Medical Center/ Regional Program, Cleveland, OH, United states; 3Precision Orthopaedic Specialties, Inc, Chardon,, OH, United States

Proper acetabular cup abduction has not been studied with the use of intraoperative radiographic landmarks. Our purpose was to determine if such a landmark exists as a reliable reference for placement of the acetabular cup within the abduction safe zone (SZ) for total hip arthroplasty (THA).

Patients from one surgeon, who underwent direct-anterior THA, between January 2016 to March 2020 were included. Excluded were THAs performed for fracture, posterior approach, revisions, hip dysplasia, and inadequate imaging. Intraoperatively, a line subtended from the inferior edge of the superior pubic ramus was drawn and the angle was measured against the horizon to create the superior pubic ramus angle (SRA). The intraoperative cup abduction angle (CAA) was also measured. If the CAA was within +/- 5 degrees of the SRA, it was considered matched. The CAA was then measured on postoperative weight-bearing Anterior-Posterior pelvis radiographs. Success was determined if the postoperative CAA was within 27-47 degrees of abduction as defined by Hevesi. (Hevesi M, J Bone Joint Surg Am. 2022;104(3):239-245)

There were 129 hips from 123 patients included in this study. Mean age (+/-SD) 64 years (+/-9.2), with 50 males (40.6%). Overall, 92.2% had successful postoperative CAA within the SZ. 79/129 hips had a CAA that was matched intraoperatively, while 50/129 were outside of 5 degrees. 77/79 matched hips were successfully within the SZ; success rate of 97.5%. 42/50 hips not matched were within the SZ; success rate of 84.0%. Fisher’s exact test was used to determine significance between having matched intraoperative CAA to SRA and having postoperative CAA within the SZ. There was a statistically significant association between the two variables (p=.008).

Acetabular cups placed within 5 degrees of the SRA intraoperatively had a 97.5% success rate of being within the SZ. Therefore, this technique may be used as a reliable adjunct for cup placement during THA.

Hevesi M, Wyles CC, Rouzrokh P, et al. Redefining the 3D Topography of the Acetabular Safe Zone: A Multivariable Study Evaluating Prosthetic Hip Stability. J Bone Joint Surg Am. 2022;104(3):239-245. doi:10.2106/JBJS.21.00406

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The Journal of the American Osteopathic Academy of Orthopedics

Steven J. Heithoff, DO, FAOAO

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