Aidin Eslam Pour1, Ran Schwarzkopf2, Kunj Pareshkumar Patel1, Manan Anjaria1, Jean Yves Lazennec3, Lawrence D Dorr4. 1. Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, MI. 2. Department of Orthopaedic Surgery, New York University, New York, NY. 3. Department of Orthopaedic and Trauma Surgery, Pitié-Salpétrière Hospital Assistance Publique-Hopitaux de Paris, UPMC, Paris, France. 4. Dorr Institute for Arthritis Research and Education, Los Angeles, CA.
Abstract
BACKGROUND: To create a safe zone, an understanding of the combined femoral and acetabular mating during hip motion is required. We investigated the position of the femoral head inside the acetabular liner during simulated hip motion. We hypothesized that cup and stem anteversions do not equally affect hip motion and combined hip anteversion. METHODS: Hip implant motion was simulated in standing, sitting, sit-to-stand, bending forward, squatting, and pivoting positions using the MATLAB software. A line passing through the center of the stem neck and the center of the prosthetic head exits at the polar axis (PA) of the prosthetic head. When the prosthetic head and liner are parallel, the PA faces the center of the liner (PA position = 0, 0). By simulating hip motion in 1-degree increments, the maximum distance of the PA from the liner center and the direction of its movement were measured (polar coordination system). RESULTS: The effect of modifying cup and stem anteversion on the direction and distance of the PA's change inside the acetabular liner was different. Stem anteversion influenced the PA position inside the liner more than cup anteversion during sitting, sit-to-stand, squatting, and bending forward (P = .0001). This effect was evident even when comparing stems with different neck angles (P = .0001). CONCLUSION: Cup anteversion, stem anteversion, and stem neck-shaft angle affected the PA position inside the liner and combined anteversion in different ways. Thus, focusing on cup orientation alone when assessing hip motion during different daily activities is inadequate.
BACKGROUND: To create a safe zone, an understanding of the combined femoral and acetabular mating during hip motion is required. We investigated the position of the femoral head inside the acetabular liner during simulated hip motion. We hypothesized that cup and stem anteversions do not equally affect hip motion and combined hip anteversion. METHODS: Hip implant motion was simulated in standing, sitting, sit-to-stand, bending forward, squatting, and pivoting positions using the MATLAB software. A line passing through the center of the stem neck and the center of the prosthetic head exits at the polar axis (PA) of the prosthetic head. When the prosthetic head and liner are parallel, the PA faces the center of the liner (PA position = 0, 0). By simulating hip motion in 1-degree increments, the maximum distance of the PA from the liner center and the direction of its movement were measured (polar coordination system). RESULTS: The effect of modifying cup and stem anteversion on the direction and distance of the PA's change inside the acetabular liner was different. Stem anteversion influenced the PA position inside the liner more than cup anteversion during sitting, sit-to-stand, squatting, and bending forward (P = .0001). This effect was evident even when comparing stems with different neck angles (P = .0001). CONCLUSION: Cup anteversion, stem anteversion, and stem neck-shaft angle affected the PA position inside the liner and combined anteversion in different ways. Thus, focusing on cup orientation alone when assessing hip motion during different daily activities is inadequate.
Authors: Markus Weber; Michael Woerner; Benjamin Craiovan; Florian Voellner; Michael Worlicek; Hans-Robert Springorum; Joachim Grifka; Tobias Renkawitz Journal: Int Orthop Date: 2016-04-22 Impact factor: 3.075
Authors: Hiroyuki Ike; Lawrence D Dorr; Nicholas Trasolini; Michael Stefl; Braden McKnight; Nathanael Heckmann Journal: J Bone Joint Surg Am Date: 2018-09-19 Impact factor: 5.284