title: In vivo tibiofemoral kinematics during 4 functional tasks of increasing demand using biplane fluoroscopy.
abstract: BACKGROUND
  The anterior cruciate ligament (ACL) has been well defined as the main passive restraint to anterior tibial translation (ATT) in the knee and plays an important role in rotational stability. However, it is unknown how closely the ACL and other passive and active structures of the knee constrain translations and rotations across a set of functional activities of increasing demand on the quadriceps.
  
  
  OBJECTIVE
  Anterior tibial translation and internal rotation of the tibia relative to the femur would increase as the demand on the quadriceps increased.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  The in vivo 3-dimensional knee kinematics of 10 adult female patients (height, 167.8 ± 7.1 cm; body mass, 57 ± 4 kg; body mass index [BMI], 24.8 ± 1.7 kg/m(2); age, 29.7 ± 7.9 years) was measured using biplane fluoroscopy while patients completed 4 functional tasks. The tasks included an unloaded knee extension in which the patient slowly extended the knee from 90° to 0° of flexion in 2 seconds; walking at a constant pace of 90 steps per minute; a maximum effort isometric knee extension with the knee at 70° of flexion; and landing from a height of 40 cm in which the patient stepped off a box, landed, and immediately performed a maximum effort vertical jump.
  
  
  RESULTS
  Landing (5.6 ± 1.9 mm) produced significantly greater peak ATT than walking (3.1 ± 2.2 mm) and unweighted full extension (2.6 ± 2.1 mm) (P < .01), but there was no difference between landing and a maximum isometric contraction (5.0 ± 1.9 mm). While there was no significant difference in peak internal rotation between landing (19.4° ± 5.7°), maximum isometric contraction (15.9° ± 6.7°), and unweighted full knee extension (14.5° ± 7.7°), each produced significantly greater internal rotation than walking (3.9° ± 4.2°) (P < .001). Knee extension torque significantly increased for each task (P < .01): unweighted knee extension (4.7 ± 1.2 N·m), walking (36.5 ± 7.9 N·m), maximum isometric knee extension (105.1 ± 8.2 N·m), and landing (140.2 ± 26.2 N·m).
  
  
  CONCLUSIONS
  Anterior tibial translations significantly increased as demand on the quadriceps and external loading increased. Internal rotation was not significantly different between landing, isometric contraction, and unweighted knee extension. Additionally, ATT and internal rotation from each motion were within the normal range, and no excessive amounts of translation or rotation were observed.
  
  
  CONCLUSIONS
  This study demonstrated that while ATT will increase as demand on the quadriceps and external loading increases, the knee is able to effectively constrain ATT and internal rotation. This suggests that the healthy knee has a safe envelope of function that is tightly controlled even though task demand is elevated.
authors: Biomechanics Research Laboratory, Steadman Philippon Research Institute, Vail, Colorado, USA.
authors: Casey A
authors: CA
authors: Myers
authors: Michael R
authors: MR
authors: Torry
authors: Kevin B
authors: KB
authors: Shelburne
authors: J Erik
authors: JE
authors: Giphart
authors: Robert F
authors: RF
authors: LaPrade
authors: Savio L-Y
authors: SL
authors: Woo
authors: J Richard
authors: JR
authors: Steadman
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging*; D001696:Biomechanical Phenomena; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D005471:Fluoroscopy; D006801:Humans; D021621:Imaging, Three-Dimensional; D012399:Rotation; D013647:Task Performance and Analysis; D013977:Tibia / Q000000981:diagnostic imaging*; D019415:Torque