title: Open-MRI measures of cam intrusion for hips in an anterior impingement position relate to acetabular contact force.
abstract: Open MRI in functional positions has potential to directly and non-invasively assess cam femoroacetabular impingement (FAI). Our objective was to investigate whether open MRI can depict intrusion of the cam deformity into the intra-articular joint space, and whether intrusion is associated with elevated acetabular contact force. Cadaver hips (9 cam; 3 controls) were positioned in an anterior impingement posture and imaged using open MRI with multi-planar reformatting. The β-angle (describing clearance between the femoral neck and acetabulum) was measured around the entire circumference of the femoral neck. We defined a binary "MRI cam-intrusion sign" (positive if β < 0°). We then instrumented each hip with a piezoresistive sensor and conducted six repeated positioning trials, measuring acetabular contact force (F). We defined a binary "contact-force sign" (positive if F > 20N). Cam hips were more likely than controls to have both a positive MRI cam-intrusion sign (p = 0.0182, Fisher's exact test) and positive contact-force sign (p = 0.0083), which represents direct experimental evidence for cam intrusion. There was also a relationship between the MRI cam-intrusion sign and contact-force sign (p = 0.033), representing a link between imaging and mechanics. Our findings indicate that open MRI has significant potential for in vivo investigation of the cam FAI mechanism.
authors.affiliation: Department of Mechanical Engineering, Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada.
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Buchan
authors.affiliation: Department of Orthopaedics, Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada.
authors.forename: Honglin
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Orthopaedics, Vancouver General Hospital, Vancouver, Canada.
authors.forename: Sujith
authors.initials: S
authors.lastname: Konan
authors.affiliation: Department of Radiology, University of British Columbia, Vancouver, Canada.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Heaslip
authors.affiliation: Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.
authors.forename: Charles R
authors.initials: CR
authors.lastname: Ratzlaff
authors.affiliation: Department of Orthopaedics, Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada.
authors.forename: David R
authors.initials: DR
authors.lastname: Wilson
mesh_terms: D000368:Aged; D005260:Female; D057925:Femoracetabular Impingement / Q000175:diagnosis* / Q000503:physiopathology; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged
keywords: Femoroacetabular impingement; biomechanics; hip; open MRI; osteoarthritis