title: Relationship between Patellar Tracking and the "Screw-home" Mechanism of Tibiofemoral Joint.
abstract: OBJECTIVE
  To demonstrate the effect of the screw-home motion on the stability of the patellofemoral joint, and investigate its mechanism of regulation of patellar tracking.
  
  
  METHODS
  Twenty volunteers who met the criteria were examined. All subjects had axial computed tomography (CT) scanning performed on bilateral knees at 0° and 30° of flexion. Scanning began above the femorotibial articulation and femoral trochlear groove, and moved sequentially down to the level of the anterior tibial tubercle. The following measurements were obtained: tibial rotation relative to the femur (TRRF), tibial tuberosity-trochlear groove (TT-TG) distance, lateral patellar displacement (LPD), patellar tilt angle (PTA), and congruence angle (CA). We assessed the change (Δ) in each variable at both flexion angles, and analyzed this to investigate the corresponding relationship between the patella, the femur, and the screw-home mechanism. The differences between the values measured at 0° and those measured at 30° flexion were analyzed using the paired sample t-test. The differences between men and women were analyzed using the t-test. Pearson's correlations were performed to determine the relationship between ΔTT-TG distance and ΔLPD, ΔPTA and ΔTRRF, and ΔCA and ΔTRRF.
  
  
  RESULTS
  There were 10 women and 10 men enrolled in the present study, with an average age of 25 years and an average body mass index of 21.8 kg/m2, and all volunteers had no history of knee injuries. Compared with measurements taken at 0° flexion, TRRF at 30° flexion was significantly increased, and the PTA, CA, LPD, and TT-TG distance were significantly decreased (all P < 0.01). There was no difference between men and women at 0° and 30° flexion, respectively (P < 0.01). In this respect, there was no sex difference, but the change was greater for men than for women. Both ΔPTA and ΔCA demonstrated significant correlation with the ΔTRRF (both P < 0.01); a significant correlation between ΔLPD and ΔTT-TG distance was also demonstrated (P < 0.01).
  
  
  CONCLUSIONS
  As the tibiofemoral joint rotated, the patellofemoral joint became more stable and aligned, which indicates that the screw-home mechanism plays an important role in regulating patellofemoral joint alignment.
authors.affiliation: Department of Orthopedics, Third Hospital of Hebei Medical University, Shijiazhuang, China.
authors.forename: Li-Kang
authors.initials: LK
authors.lastname: Zhang
authors.affiliation: Department of Orthopedics, Third Hospital of Hebei Medical University, Shijiazhuang, China.
authors.forename: Xiao-Meng
authors.initials: XM
authors.lastname: Wang
authors.affiliation: Department of Orthopedics, Third Hospital of Hebei Medical University, Shijiazhuang, China.
authors.forename: Ying-Zhen
authors.initials: YZ
authors.lastname: Niu
authors.affiliation: Department of Orthopedics, Third Hospital of Hebei Medical University, Shijiazhuang, China.
authors.forename: Hui-Xin
authors.initials: HX
authors.lastname: Liu
authors.affiliation: Department of Orthopedics, Third Hospital of Hebei Medical University, Shijiazhuang, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging / Q000502:physiology*; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging / Q000502:physiology*; D014057:Tomography, X-Ray Computed
keywords: Kinematics; Patellar tracking; Patellofemoral joint; Tibiofemoral joint; “Screw-home” mechanism