title: Passive Anterior Tibial Subluxation in the Setting of Anterior Cruciate Ligament Injuries: A Comparative Analysis of Ligament-Deficient States.
abstract: BACKGROUND
  Static anterior tibial subluxation after an anterior cruciate ligament (ACL) injury highlights the abnormal relationship between the tibia and femur in patients with ACL insufficiency, although causal factors including injuries to secondary stabilizers or the time from injury to reconstruction have not been examined.
  
  
  OBJECTIVE
  To determine static relationships between the tibia and femur in patients with various states of ACL deficiency and to identify factors associated with anterior tibial subluxation.
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  Patients treated for ACL injuries were identified from an institutional registry and assigned to 1 of 4 cohorts: intact ACL, acute ACL disruption, chronic ACL disruption, and failed ACL reconstruction (ACLR). Anterior tibial subluxation of the medial and lateral compartments relative to the femoral condyles were measured on magnetic resonance imaging (MRI), and an MRI evaluation for meniscal tears, chondral defects, and injuries to the anterolateral ligament (ALL) was performed.
  
  
  RESULTS
  One hundred eighty-six ACL-insufficient knees met inclusion criteria, with 26 patients without an ACL injury utilized as a control group. In the lateral compartment, the mean anterior tibial subluxation measured 0.78 mm for the control group (n = 26), 2.81 mm for the acute ACL injury group (n = 74), 3.64 mm for the chronic ACL injury group (n = 40), and 4.91 mm for the failed ACLR group (n = 72). In the failed ACLR group, 37.5% of patients demonstrated lateral compartment anterior subluxation ≥6 mm, and 11.1% of this group had anterior subluxation of the lateral compartment ≥10 mm. Multivariate regression revealed that the presence of both medial and lateral chondral defects was associated with a mean 1.09-mm increase in subluxation of the medial compartment ( P = .013). The combination of medial and lateral meniscal tears was an independent predictor of increased lateral tibia subluxation by 1.611 mm ( P = .0022). Additionally, across all knee states, an injury to the ALL was associated with increased anterior tibial subluxation in both the medial compartment ( P = .0438) and lateral compartment ( P = .0046). In 29.4% of knees with ALL injuries, lateral tibial subluxation was ≥6 mm, but with multivariate regression analysis, an ALL injury was not an independent predictor of anterior subluxation of the lateral compartment.
  
  
  CONCLUSIONS
  Knees with failed ACLR are associated with more anterior tibial subluxation than those with primary ACL deficiency. Using previously reported thresholds of 6 to 10 mm of lateral compartment subluxation for a positive pivot shift, between 11.1% and 37.5% of knees with failed ACLR may be in a "resting pivoted position." In primary ACL-deficient knees, anterior tibial subluxation is associated with chondral injuries and meniscal tears but not injury chronicity.
authors.affiliation: Department of Orthopaedic Surgery, Naval Medical Center San Diego, San Diego, California, USA.
authors.forename: Lucas S
authors.initials: LS
authors.lastname: McDonald
authors.affiliation: Department of Sports Medicine and Shoulder Surgery, Hospital for Special Surgery, New York, New York, USA.
authors.forename: Jelle P
authors.initials: JP
authors.lastname: van der List
authors.affiliation: Division of Sports Medicine and Shoulder Surgery, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
authors.forename: Kristofer J
authors.initials: KJ
authors.lastname: Jones
authors.affiliation: Department of Orthopaedic Surgery, Spaarne Hospital, Hoofddorp, the Netherlands.
authors.forename: Hendrik A
authors.initials: HA
authors.lastname: Zuiderbaan
authors.affiliation: Biostatistics Core, Healthcare Research Institute, Hospital for Special Surgery, New York, New York, USA.
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Nguyen
authors.affiliation: Department of Radiology and Imaging, Hospital for Special Surgery, New York, New York, USA.
authors.forename: Hollis G
authors.initials: HG
authors.lastname: Potter
authors.affiliation: Department of Sports Medicine and Shoulder Surgery, Hospital for Special Surgery, New York, New York, USA.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pearle
mesh_terms: D000293:Adolescent; D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries / Q000503:physiopathology; D059549:Anterior Cruciate Ligament Reconstruction / Q000009:adverse effects; D003430:Cross-Sectional Studies; D005260:Female; D005269:Femur / Q000503:physiopathology*; D006801:Humans; D004204:Joint Dislocations / Q000503:physiopathology*; D007593:Joint Instability / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D013977:Tibia / Q000503:physiopathology*; D017211:Treatment Failure; D055815:Young Adult
keywords: ACL; articular cartilage; knee ligaments; meniscus