title: Differential forces within the proximal patellar tendon as an explanation for the characteristic lesion of patellar tendinopathy: an in vivo descriptive experimental study.
abstract: BACKGROUND
  Patellar tendinopathy is a common condition affecting the posterior region of the proximal patellar tendon, but the reason for this typical location remains unclear.
  
  
  OBJECTIVE
  The posterior region of the proximal patellar tendon is subjected to greater tendinous forces than is the corresponding anterior region.
  
  
  METHODS
  Descriptive laboratory study.
  
  
  METHODS
  An optic fiber technique was used to detect forces in both the anterior and the posterior regions of the proximal patellar tendon in 7 healthy persons. The optic fiber force sensor works on the principle of the amplitude modulation of transmitted light when the optic fiber is geometrically altered owing to the forces acting on it. Longitudinal strain in the tendon or ligament produces a negative transverse strain, thus causing a force that effectively squeezes the optic fiber. Measurements were recorded during the following exercises: closed kinetic chain quadriceps contraction (eccentric and concentric), open kinetic chain quadriceps contraction (eccentric and concentric), a step exercise, and a jump exercise.
  
  
  RESULTS
  During all the exercises, the peak differential signal output in the posterior location of the proximal patellar tendon was greater than in the corresponding anterior location. The greatest differential signal output was found in the jump and squat exercises.
  
  
  CONCLUSIONS
  The posterior region of the proximal patellar tendon is subjected to greater tendinous forces than is the corresponding anterior region. This finding supports the tensile-overload theory of patellar tendinopathy.
  
  
  CONCLUSIONS
  Jump activities and deep squat exercises expose the patellar tendon to very large tendinous forces.
authors.affiliation: Knee Clinic Stellenbosch, Department of Orthopaedic Surgery, Stellenbosch University, Stellenbosch, South Africa. dillon@orthoclinic.co.za
authors.forename: Edwin Mark
authors.initials: EM
authors.lastname: Dillon
authors.forename: Pieter J
authors.initials: PJ
authors.lastname: Erasmus
authors.forename: Jacobus H
authors.initials: JH
authors.lastname: Müller
authors.forename: Cornie
authors.initials: C
authors.lastname: Scheffer
authors.forename: Richard V P
authors.initials: RV
authors.lastname: de Villiers
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000502:physiology; D017847:Patellar Ligament / Q000503:physiopathology*; D013314:Stress, Mechanical; D052256:Tendinopathy / Q000209:etiology*; D055815:Young Adult