title: Constrained acetabular cups: a cadaveric biomechanical evaluation.
abstract: Reports indicate that constrained acetabular cups may reduce range of motion and catastrophically fail, although the biomechanics of dislocation have not been reported. We measured the available motion in 6 constrained cups (from 2 manufacturers) when anatomically placed in cadaver pelves. We measured the torque and rotation necessary to dislocate the hip. Range of motion was measured using a custom jig and revealed a functional range of motion with all cup positions. Extension was limited to 0 degrees with anteversion of 11 degrees to 29 degrees. Thus, anteversion of <10 degrees is recommended. Torque and rotation to produce dislocation was 7 ft-pounds and 11 ft-pounds and 82 degrees and 72 degrees, for each manufacturer. Torques were reduced with subsequent dislocations. We recommend consideration of polyethylene replacement if dislocation occurs. Dislocation occurred at the ball-polyethylene interface without catastrophic failure.
authors.affiliation: Department of Orthopaedics, University of Texas-Houston Medical School, Houston, Texas 77030, USA.
authors.forename: Terry A
authors.initials: TA
authors.lastname: Clyburn
authors.forename: Amanda
authors.initials: A
authors.lastname: Weitz-Marshall
authors.forename: Catherine G
authors.initials: CG
authors.lastname: Ambrose
mesh_terms: D000077:Acetabulum / Q000503:physiopathology / Q000601:surgery; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D002102:Cadaver; D006617:Hip Dislocation / Q000503:physiopathology*; D006622:Hip Prosthesis; D006801:Humans; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012307:Risk Factors; D012399:Rotation; D019415:Torque