title: Size and shape of the lunate surface in different types of pincer impingement: theoretical implications for surgical therapy.
abstract: OBJECTIVE
  Acetabular rim trimming is indicated in pincer hips with an oversized lunate surface but could result in a critically decreased size of the lunate surface in pincer hips with acetabular malorientation. There is a lack of detailed three-dimensional anatomy of lunate surface in pincer hips. Therefore, we questioned how does (1) size and (2) shape of the lunate surface differ among hips with different types of pincer impingement?
  
  
  METHODS
  We retrospectively compared size and shape of the lunate surface between acetabular retroversion (48 hips), deep acetabulum (34 hips), protrusio acetabuli (seven hips), normal acetabuli (30 hips), and hip dysplasia (45 hips). Using magnetic resonance imaging (MRI) arthrography with radial slices we measured size in percentage of the femoral head coverage and shape using the outer (inner) center-edge angles and width of lunate surface.
  
  
  RESULTS
  Hips with retroversion had a decreased size and deep hips had normal size of the lunate surface. Both had a normal shape of the outer acetabular rim. Protrusio hips had an increased size and a prominent outer acetabular rim. In all three types of pincer hips the acetabular fossa was increased.
  
  
  CONCLUSIONS
  Size and shape of the lunate surface differs substantially among different types of pincer impingement. In contrast to hips with protrusio acetabuli, retroverted and deep hips do not have an increased size of the lunate surface. Acetabular rim trimming in retroverted and deep hips should be performed with caution. Based on our results, acetabular reorientation would theoretically be the treatment of choice in retroverted hips.
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: simon.steppacher@insel.ch.
authors.forename: S D
authors.initials: SD
authors.lastname: Steppacher
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: till.lerch@bluewin.ch.
authors.forename: T D
authors.initials: TD
authors.lastname: Lerch
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: kaveh.gharani@gmail.com.
authors.forename: K
authors.initials: K
authors.lastname: Gharanizadeh
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: emanuel.liechti@gmail.com.
authors.forename: E F
authors.initials: EF
authors.lastname: Liechti
authors.affiliation: Department of Radiology, Sonnenhof Clinic, Bern, Switzerland. Electronic address: stefan.werlen@sonnenhof.ch.
authors.forename: S F
authors.initials: SF
authors.lastname: Werlen
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: marcpuls@bluewin.ch.
authors.forename: M
authors.initials: M
authors.lastname: Puls
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: moritz.tannast@insel.ch.
authors.forename: M
authors.initials: M
authors.lastname: Tannast
authors.affiliation: Department of Orthopaedic Surgery and Traumatology, Inselspital, University of Bern, Bern, Switzerland. Electronic address: klaus.siebenrock@insel.ch.
authors.forename: K A
authors.initials: KA
authors.lastname: Siebenrock
mesh_terms: D000077:Acetabulum / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D005260:Female; D057925:Femoracetabular Impingement / Q000473:pathology* / Q000601:surgery*; D006617:Hip Dislocation / Q000473:pathology; D006621:Hip Joint / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D019637:Orthopedic Procedures; D012189:Retrospective Studies; D055815:Young Adult
keywords: Coxa profunda; Hip; Joint preserving surgery; Lunate surface; Pincer impingement; Protrusio; Retroversion