title: Force measurements in the medial meniscus posterior horn attachment: effects of anterior cruciate ligament removal.
abstract: BACKGROUND
  Tears of the medial meniscus posterior horn attachment (PHA) occur clinically, and an anterior cruciate ligament (ACL)-deficient knee may be more vulnerable to this injury.
  
  
  OBJECTIVE
  The PHA forces from applied knee loadings will increase after removal of the ACL.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  A cap of bone containing the medial meniscus PHA was attached to a load cell that measured PHA tensile force. Posterior horn attachment forces were recorded before and after ACL removal during anteroposterior (AP) laxity testing at ±200 N and during passive knee extension tests with 5 N·m tibial torque and varus-valgus moment. Selected tests were also performed with 500 N joint load.
  
  
  RESULTS
  For AP tests with no joint load, ACL removal increased laxity between 0° and 90° and increased PHA force generated by applied anterior tibial force between 30° and 90°. For AP tests with an intact ACL, application of joint load approximately doubled PHA forces. Anteroposterior testing of ACL-deficient knees was not possible with joint load because of bone cap failures from high PHA forces. Removal of the ACL during knee extension tests under joint load significantly increased PHA forces between 20° and 90° of flexion. For unloaded tests with applied tibial torque and varus-valgus moment, ACL removal had no significant effect on PHA forces.
  
  
  CONCLUSIONS
  Applied anterior tibial force and external tibial torque were loading modes that produced relatively high PHA forces, presumably by impingement of the medial femoral condyle against the medial meniscus posterior horn rim. Under joint load, an ACL-deficient knee was particularly susceptible to PHA injury from applied anterior tibial force.
  
  
  CONCLUSIONS
  Because tensile forces developed in the PHA are also borne by meniscus tissue near the attachment site, loading mechanisms that produce high PHA forces could also produce complete or partial radial tears near the posterior horn, a relatively common clinical observation.
authors.affiliation: Biomechanics Research Section, Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA, Los Angeles, California, USA. kmarkolf@mednet.ucla.edu
authors.forename: Keith L
authors.initials: KL
authors.lastname: Markolf
authors.forename: Steven R
authors.initials: SR
authors.lastname: Jackson
authors.forename: David R
authors.initials: DR
authors.lastname: McAllister
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016118:Anterior Cruciate Ligament / Q000601:surgery; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008592:Menisci, Tibial / Q000502:physiology*; D008875:Middle Aged; D013718:Tensile Strength; D019415:Torque; D055815:Young Adult