title: Protrusio acetabuli: joint loading with severe pincer impingement and its theoretical implications for surgical therapy.
abstract: Severe pincer impingement (acetabular protrusio) is an established cause of hip pain and osteoarthritis. The proposed underlying pathomechanism is a dynamic pathological contact of the prominent acetabular rim with the femoral head-neck junction. However, this cannot explain the classically described medial osteoarthritis in these hips. We therefore asked: (1) Does an overload exist in the medial aspect of the protrusio joint? and (2) What is the influence of three contemporary joint-preserving procedures on load distribution in protrusio hips? In vivo force and motion data for walking and standing to sitting were applied to six 3D finite element models (normal, dysplasia, protrusio, acetabular rim trimming, acetabular reorientation, and combined reorientation/rim trimming). Compared with dysplasia, the protrusio joint resulted in opposite patterns of von Mises stress and contact pressure during walking. In protrusio hips, we found an overload at the medial margin of the lunate surface (54% higher than normal). Isolated rim trimming further increased the medial overload (up to 28% higher than protrusio), whereas acetabular reorientation with/without rim trimming reduced stresses by up to 25%. Our results can be used as an adjunct for surgical decision making in the treatment of acetabular protrusio.
authors.affiliation: Department of Orthopaedic Surgery, Inselspital, University of Bern, Switzerland; Institute for Surgical Technology and Biomechanics, University of Bern, Switzerland.
authors.forename: Emanuel F
authors.initials: EF
authors.lastname: Liechti
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Ferguson
authors.forename: Moritz
authors.initials: M
authors.lastname: Tannast
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000473:pathology; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology; D020342:Finite Element Analysis; D006617:Hip Dislocation / Q000473:pathology; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D006801:Humans; D008953:Models, Anatomic; D019637:Orthopedic Procedures; D011859:Radiography; D016059:Range of Motion, Articular; D016474:Weight-Bearing
keywords: biomechanics; finite element; hip joint; pincer impingement; protrusio acetabuli