title: The in vivo relationship between anterior neutral tibial position and loss of knee extension after transtibial ACL reconstruction.
abstract: BACKGROUND
  Restoration of anterior tibial stability while avoiding knee extension deficit are a common goal of anterior cruciate ligament (ACL) reconstruction. However, achieving this goal can be challenging. The purpose of this study was to determine whether side-to-side differences in anterior tibial neutral position and laxity are correlated with knee extension deficit in subjects 2 years after ACL reconstruction.
  
  
  METHODS
  In the reconstructed and contralateral knees of 29 subjects with transtibial reconstruction, anterior tibiofemoral neutral position was measured with MRI and three-dimensional modeling techniques; terminal knee extension at heel strike of walking and during a seated knee extension were measured via gait analysis; and anterior laxity was measured using the KT-1000.
  
  
  RESULTS
  Knees that approached normal anterior stability and anterior tibial position had increased extension deficit relative to the contralateral knee. On average the reconstructed knee had significantly less (2.1±4.4°) extension during active extension and during heel strike of walking (3.0±4.3º), with increased anterior neutral tibial position (2.5±1.7 mm) and anterior laxity (1.8±1.0 mm). There was a significant correlation between side-to-side difference in anterior neutral tibial position with both measures of knee extension (walking, r=-0.711, p<0.001); active knee extension, r=-0.544, p=0.002).
  
  
  CONCLUSIONS
  The results indicate a relationship between the loss of active knee extension and a change in anterior neutral tibial position following non-anatomic transtibial ACL reconstruction. Given the increasing evidence of a link between altered kinematics and premature osteoarthritis, these findings provide important information to improve our understanding of in vivo knee function after ACL reconstruction.
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA, USA. Electronic address: scanlansean@gmail.com.
authors.forename: Sean F
authors.initials: SF
authors.lastname: Scanlan
authors.affiliation: Sports Orthopedic and Rehabilitation Medicine Associates (SOAR), Redwood City, CA, USA.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Donahue
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, CA, USA; Palo Alto VA, Bone and Joint Center, Palo Alto, CA, USA; Department of Orthopedic Surgery, Stanford University, Stanford, CA, USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Andriacchi
mesh_terms: D000125:Achilles Tendon / Q000637:transplantation; D000328:Adult; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D053587:Arthrometry, Articular; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D005269:Femur / Q000473:pathology / Q000503:physiopathology; D005500:Follow-Up Studies; D005684:Gait / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional; D007593:Joint Instability / Q000473:pathology / Q000503:physiopathology*; D007719:Knee Joint / Q000473:pathology* / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D013977:Tibia / Q000473:pathology / Q000503:physiopathology; D016138:Walking / Q000502:physiology; D055815:Young Adult
keywords: ACL reconstruction; Anterior laxity; Extension loss; Kinematics; Knee