title: Effect of lateral meniscal root tear on the stability of the anterior cruciate ligament-deficient knee.
abstract: BACKGROUND
  Meniscal root tears are an increasingly recognized subset of meniscal injury. The menisci are critical secondary stabilizers of the anterior cruciate ligament (ACL). The kinematic effect of lateral meniscus posterior root tear in the setting of ACL injury is not known.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effect of tear of the lateral meniscal root on stability of the ACL-deficient knee. The hypothesis was that disruption of the lateral meniscal root will further destabilize the ACL-deficient knee during a simulated pivot shift.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Pivot-shift testing of 8 fresh-frozen cadaveric knees was performed after attachment of photoreflective flags and preparation of CT scans. Each knee was mounted in a custom activity simulator and dynamically loaded from 15° to 90° of flexion with all the permutations of the following: iliotibial band force (50, 75, 100, 125, 150, and 175 N), internal rotation moments (1, 2, and 3 N·m), and valgus moments (5 and 7 N·m). In addition, anterior stability tests were performed by applying a 90-N anterior force to the tibia at flexion angles of 15°, 30°, 45°, 60°, and 90°. During each test, the anterior tibial translation and rotation of the tibia were measured with a high-resolution multiple infrared camera motion analysis system for the following 3 conditions: ACL-intact (ACL-I), ACL-deficient (ACL-D), and ACL-deficient/lateral meniscal posterior root avulsion (ACL-D/LMR-A).
  
  
  RESULTS
  A pivot-shift phenomenon was observed in the ACL-D and ACL-D/LMR-A conditions. The mean tibial translation of the lateral tibial condyle during the pivot-shift maneuver was 2.62 ± 0.53 mm for the ACL-I knees, 6.01 ± 0.51 mm for the ACL-D knees (P value vs. intact: .0005), and 8.13 ± 0.75 mm for the ACL-D/LMR-A knees (P value vs intact: <.0001). During the pivot-shift maneuver, translation was significantly increased in the ACL-D/LMR-A condition compared with the ACL-D condition (P = .0146). Compared with the intact group, anterior tibial translation during the Lachman maneuver also increased at 30° and 90° of flexion in the ACL-D group (P < .0001) and the ACL-D/LM group (P < .0001). No statistically significant difference was found between the ACL-D and ACL-D/LMR-A groups during the Lachman maneuver at 30° and 90° (P = .16 and .72, respectively).
  
  
  CONCLUSIONS
  A tear of the lateral meniscal posterior root further reduces the stability of the ACL-deficient knee during rotational loading.
  
  
  CONCLUSIONS
  This study shows that lateral meniscal root injury further destabilizes the ACL-deficient knee and thus advances the concept that the lateral meniscus is a secondary stabilizer of the knee under pivot-shift loading. In the absence of stronger evidence, the study data suggest a rationale for surgical repair of lateral meniscal root tears encountered in the setting of ACL tears.
authors.affiliation: Baylor College of Medicine, Houston, Texas, USA shybut@bcm.edu.
authors.forename: Theodore B
authors.initials: TB
authors.lastname: Shybut
authors.affiliation: Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Vega
authors.affiliation: Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Jebran
authors.initials: J
authors.lastname: Haddad
authors.affiliation: The Institute of Orthopedic Research and Education, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Jerry W
authors.initials: JW
authors.lastname: Alexander
authors.affiliation: The Institute of Orthopedic Research and Education, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Jonathon E
authors.initials: JE
authors.lastname: Gold
authors.affiliation: The Institute of Orthopedic Research and Education, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Philip C
authors.initials: PC
authors.lastname: Noble
authors.affiliation: University of Texas Health Science Center at Houston, Houston, Texas, USA.
authors.forename: Walter R
authors.initials: WR
authors.lastname: Lowe
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D012399:Rotation; D013977:Tibia / Q000473:pathology; D000070600:Tibial Meniscus Injuries; D014057:Tomography, X-Ray Computed
keywords: anterior cruciate ligament; knee kinematics; lateral meniscus; meniscal root tear; pivot shift