title: Evidence of patellar tendon buckling during passive knee extension.
abstract: OBJECTIVE
  The purpose of this study was to investigate and describe buckling of the patellar tendon.
  
  
  METHODS
  Healthy young adults (28±4years, 10F/10M) underwent passive knee flexion/extension during the simultaneous measurement of knee angle and collection of cine ultrasound from the patellar tendon. Patellar tendon buckling was observed visually in ultrasound images, and the corresponding knee angle at which evidence of buckling disappeared was identified.
  
  
  RESULTS
  All subjects showed evidence of distal buckling which occurred on average at 23±8° flexion. Proximal buckling was only observed in fourteen subjects (10F/4M) at an average of 15±8°. Buckling patterns varied between subjects, but with high within-subject consistency. Buckling magnitude increased with age (p=0.03) and decreased with more weekly exercise (p=0.02).
  
  
  CONCLUSIONS
  The patellar tendon exhibited significant buckling in knee extension suggesting that buckling is a component of healthy knee function. Like tendon crimp, buckling may serve as a protective mechanism, allowing the tissue to unwrinkle prior to undergoing pure strain. The links between increased buckling magnitude and both age and reduced activity suggest that excessive buckling may be maladaptive, though future work is necessary to elucidate this relationship. Buckling is relevant to consider when estimating tendon length, as buckling can lead to significant underestimation of resting length and thus overestimation of strain.
  
  
  CONCLUSIONS
  This study demonstrates the complexity of tendon behavior even in healthy adults undergoing passive motion, suggesting that buckling may be relevant to an improved understanding of tendon health and pathology.
authors.affiliation: KU Leuven, Institute for Orthopaedic Research and Training, Oude Markt 13, 3000 Leuven, Belgium. Electronic address: laura.c.slane@gmail.com.
authors.forename: Laura Chernak
authors.initials: LC
authors.lastname: Slane
authors.affiliation: KU Leuven, Institute for Orthopaedic Research and Training, Oude Markt 13, 3000 Leuven, Belgium; University Hospitals Leuven, Campus Pellenberg, Weligerveld 1 Blok 1, 3212 Pellenberg, Belgium.
authors.forename: Stijn
authors.initials: S
authors.lastname: Bogaerts
authors.affiliation: KU Leuven, Institute for Orthopaedic Research and Training, Oude Markt 13, 3000 Leuven, Belgium.
authors.forename: Irina
authors.initials: I
authors.lastname: Mihejeva
authors.affiliation: KU Leuven, Institute for Orthopaedic Research and Training, Oude Markt 13, 3000 Leuven, Belgium; University Hospitals Leuven, Campus Pellenberg, Weligerveld 1 Blok 1, 3212 Pellenberg, Belgium.
authors.forename: Lennart
authors.initials: L
authors.lastname: Scheys
mesh_terms: D000328:Adult; D053587:Arthrometry, Articular; D001696:Biomechanical Phenomena; D064368:Healthy Volunteers; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000503:physiopathology; D017847:Patellar Ligament / Q000000981:diagnostic imaging* / Q000503:physiopathology; D016059:Range of Motion, Articular; D013708:Tendon Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology; D014463:Ultrasonography; D055815:Young Adult
keywords: Buckling; Crimp; Extension; Flexion; Patellar tendon; Slack length