title: Knee joint laxity and its cyclic variation influence tibiofemoral motion during weight acceptance.
abstract: OBJECTIVE
  to better understand how sex differences in anterior knee laxity (AKL) affect knee joint biomechanics, we examined the consequence of greater absolute baseline (males and females) and cyclic increases in AKL during the menstrual cycle (females) on anterior tibial translation (ATT) as the knee transitioned from non-weight-bearing to weight-bearing conditions, while also controlling for genu recurvatum (GR).
  
  
  METHODS
  males and females (71 females and 48 males, aged 18-30 yr) were measured for AKL and GR and underwent measurement of ATT. Women were tested on the days of their cycle when AKL was at its minimum (T1) and maximum (T2); males were matched in time to a female with similar AKL. Linear regressions examined relationships between absolute baseline (AKLT1, GRT1) and cyclic changes (Δ = T2 - T1; AKLΔ, GRΔ) (females only) in knee laxity with ATT as measured at T1 and T2 and Δ (T2 - T1) (females only).
  
  
  RESULTS
  AKL and GR increased in females, but not in males, from T1 to T2. Greater AKLT1 and GRT1 predicted greater ATTT1 and ATTT2 in males (R = 21.0, P < 0.007). The combination of greater AKLT1, AKLΔ, and less GRΔ predicted greater ATTT1 and ATTT2 in females (R = 12.5-13.1, P < 0.05), with AKLΔ being a stronger predictor (coefficient, P value) of ATTT2 (0.864, P = 0.027) compared with ATTT1 (0.333, P = 0.370). AKLΔ was the sole predictor of ATTΔ (R = 0.104 and 0.740, P = 0.042).
  
  
  CONCLUSIONS
  greater absolute baseline and cyclic increases in AKL were consistently associated with greater ATT produced by transition of the knee from non-weight-bearing to weight-bearing. Because the anterior cruciate ligament is the primary restraint to ATT, these findings provide insight into the possible mechanisms by which greater AKL may be associated with at-risk knee biomechanics during the weight acceptance phase of dynamic tasks.
authors.affiliation: 1School of Health and Human Performance, University of North Carolina at Greensboro, Greensboro, NC 27402, USA. sjshultz@uncg.edu
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Shultz
authors.forename: Randy J
authors.initials: RJ
authors.lastname: Schmitz
authors.forename: Anh-Dung
authors.initials: AD
authors.lastname: Nguyen
authors.forename: Beverly
authors.initials: B
authors.lastname: Levine
authors.forename: Hyunsoo
authors.initials: H
authors.lastname: Kim
authors.forename: Melissa M
authors.initials: MM
authors.lastname: Montgomery
authors.forename: Yohei
authors.initials: Y
authors.lastname: Shimokochi
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Beynnon
authors.forename: David H
authors.initials: DH
authors.lastname: Perrin
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D005269:Femur / Q000502:physiology*; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008597:Menstrual Cycle / Q000502:physiology; D011446:Prospective Studies; D012737:Sex Factors; D013977:Tibia / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult