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Am J Sports Med. 2007 Apr;35(4):605-11. Epub 2007 Jan 23.

Excessive apoptosis in patellar tendinopathy in athletes.

Author information

  • 1Oslo Sport Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, Ullevål Stadion, Oslo, Norway. ostrc@nih.no



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.


Apoptosis contributes to the pathophysiology in patellar tendinopathy.


Case control study; Level of evidence, 3.


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).


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).


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.

[PubMed - indexed for MEDLINE]
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