title: Excessive apoptosis in patellar tendinopathy in athletes.
abstract: BACKGROUND
  The pathogenesis of tendon overuse injuries is poorly understood. The histopathology underlying tendinopathy at various anatomical locations is similar and may reflect a common pathologic process.
  
  
  OBJECTIVE
  Apoptosis contributes to the pathophysiology in patellar tendinopathy.
  
  
  METHODS
  Case control study; Level of evidence, 3.
  
  
  METHODS
  We compared biopsy specimens from the patellar tendon in patients with patellar tendinopathy diagnosed clinically and with typical magnetic resonance image findings with biopsy specimens from a control group without any previous or current knee complaints to suggest patellar tendinopathy. The presence of apoptosis was examined with immunohistochemical methods using a polyclonal antibody recognizing active caspase-3, confirmed by labeling DNA strand breaks (F7-26 antibody) and nuclear morphology (fragmentation and condensation).
  
  
  RESULTS
  The number of apoptotic cells per unit area (4.5 mm(2)) was 0.91 +/- 0.81 (SD) in tendinopathic samples and 0.21 +/- 0.21 in controls (P = .026). Although the tendinopathic samples displayed increased cellularity (average 162.5 nuclei/mm(2) vs 98.9 nuclei/mm(2)), the apoptotic index was higher (0.42% vs 0.17%, P = .014).
  
  
  CONCLUSIONS
  Increased apoptotic cell death is a feature of patellar tendinosis. The role of apoptosis within the broader framework and time course of tendon overuse injury remains to be established.
authors.affiliation: Oslo Sport Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, Ullevål Stadion, Oslo, Norway. ostrc@nih.no
authors.forename: Øystein
authors.initials: Ø
authors.lastname: Lian
authors.forename: Alex
authors.initials: A
authors.lastname: Scott
authors.forename: Lars
authors.initials: L
authors.lastname: Engebretsen
authors.forename: Roald
authors.initials: R
authors.lastname: Bahr
authors.forename: Vincent
authors.initials: V
authors.lastname: Duronio
authors.forename: Karim
authors.initials: K
authors.lastname: Khan
mesh_terms: D000328:Adult; D017209:Apoptosis; D001265:Athletic Injuries; D016022:Case-Control Studies; D053148:Caspase 3; D003430:Cross-Sectional Studies; D053938:DNA Fragmentation; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D007150:Immunohistochemistry; D007718:Knee Injuries / Q000473:pathology* / Q000601:surgery; D008297:Male; D010329:Patella / Q000473:pathology* / Q000601:surgery; D013177:Sports; D011795:Surveys and Questionnaires; D052256:Tendinopathy / Q000473:pathology / Q000503:physiopathology* / Q000601:surgery; D013708:Tendon Injuries / Q000473:pathology* / Q000601:surgery
chemical_list: D053148:Caspase 3