title: Functional adaptation of human joints to mechanical stimuli.
abstract: OBJECTIVE
  This study tests the hypothesis that functional adaptation occurs in human joints, and that substantial differences in joint 'loading history' explain the phenotypic variability observed in human cartilage morphology.
  
  
  METHODS
  We examined 18 triathletes (nine men and nine women) who had been physically active throughout life (training for >10 h per week for the last 3 years), and 18 volunteers that had never been physically active on a regular basis. The right knee joints were imaged with a previously validated fat-suppressed gradient-echo MR sequence. Cartilage volume, thickness, joint surface areas, and normalized cartilage signal intensity were determined with post-processing software, specifically designed for these applications.
  
  
  RESULTS
  The knee joint cartilage thickness, and signal intensity were not significantly different between athletes and inactive volunteers, but male athletes displayed significantly larger knee joint surfaces (P< 0.01; +8.8%). Female athletes displayed a significantly larger medial tibia (P< 0.05; +18.9%), the difference in the total knee surface area reaching borderline significance (P=0.08; +7.0%).
  
  
  CONCLUSIONS
  The results suggest that joint size can be modulated during growth, but that (opposite to muscle and bone) the thickness of the cartilage does not adapt to mechanical stimulation. This finding may reveal a general principle in the development and functional adaptation of diarthrodial joints, elucidating an important mechanism for reducing mechanical stress in biphasic cartilage layers.
authors.affiliation: Musculoskeletal Research Group, Institute of Anatomy, Ludwig-Maximilians-Universität München, Pettenkoferstrasse 11, 80336 München, Germany. eckstein@anat.med.uni-muenchen.de
authors.forename: F
authors.initials: F
authors.lastname: Eckstein
authors.forename: S
authors.initials: S
authors.lastname: Faber
authors.forename: R
authors.initials: R
authors.lastname: Mühlbauer
authors.forename: J
authors.initials: J
authors.lastname: Hohe
authors.forename: K-H
authors.initials: KH
authors.lastname: Englmeier
authors.forename: M
authors.initials: M
authors.lastname: Reiser
authors.forename: R
authors.initials: R
authors.lastname: Putz
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000033:anatomy & histology / Q000502:physiology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007719:Knee Joint / Q000033:anatomy & histology / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D012727:Sex Characteristics; D013177:Sports / Q000502:physiology*; D018709:Statistics, Nonparametric; D016474:Weight-Bearing