title: Variation in the shape of the tibial insertion site of the anterior cruciate ligament: classification is required.
abstract: OBJECTIVE
  To propose a classification system for the shape of the tibial insertion site (TIS) of the anterior cruciate ligament (ACL) and to demonstrate the intra- and inter-rater agreement of this system. Due to variation in shape and size, different surgical approaches may be feasible to improve reconstruction of the TIS.
  
  
  METHODS
  One hundred patients with a mean age of 26 ± 11 years were included. The ACL was cut arthroscopically at the base of the tibial insertion site. Arthroscopic images were taken from the lateral and medial portal. Images were de-identified and duplicated. Two blinded observers classified the tibial insertion site according to a classification system.
  
  
  RESULTS
  The tibial insertion site was classified as type I (elliptical) in 51 knees (51 %), type II (triangular) in 33 knees (33 %) and type III (C-shaped) in 16 knees (16 %). There was good agreement between raters when viewing the insertion site from the lateral portal (κ = 0.65) as well as from the medial portal (κ = 0.66). Intra-rater reliability was good to excellent. Agreement in the description of the insertion site between the medial and lateral portals was good for rater 1 and good for rater 2 (κ = 0.74 and 0.77, respectively).
  
  
  CONCLUSIONS
  There is variation in the shape of the ACL TIS. The classification system is a repeatable and reliable tool to summarize the shape of the TIS using three common patterns. For clinical relevance, different shapes may require different types of reconstruction to ensure proper footprint restoration. Consideration of the individual TIS shape is required to prevent iatrogenic damage of adjacent structures like the menisci.
  
  
  METHODS
  III.
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.|Trauma Department, Hannover Medical School (MHH), Hannover, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Guenther
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Irarrázaval
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Nishizawa
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.
authors.forename: Cara
authors.initials: C
authors.lastname: Vernacchia
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Thorhauer
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.
authors.forename: Volker
authors.initials: V
authors.lastname: Musahl
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA.
authors.forename: James J
authors.initials: JJ
authors.lastname: Irrgang
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Kaufman Medical Building, Suite 1011, 3941 Fifth Avenue, Pittsburgh, PA, 15203, USA. ffu@upmc.edu.
authors.forename: Freddie H
authors.initials: FH
authors.lastname: Fu
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000033:anatomy & histology / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000145:classification* / Q000379:methods*; D001182:Arthroscopy; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D016037:Single-Blind Method; D013977:Tibia / Q000033:anatomy & histology / Q000601:surgery*; D055815:Young Adult
keywords: ACL; Anterior cruciate ligament; C-shape; Classification; Elliptical; Insertion site; Shape; Tibial insertion site; Triangular; Variation