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Excessive Apoptosis in Patellar Tendinopathy in Athletes

Øystein Lian, MD^,,*, Alex Scott, Lars Engebretsen, MD, PhD^,||, Roald Bahr, MD, PhD, Vincent Duronio and Karim Khan, MD, PhD

From the Oslo Sport Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway, Kristiansund Hospital, Kristiansund, Norway, University of British Columbia, Vancouver, Canada, and ^|| Orthopaedic Center, Ullevål University Hospital, Oslo, Norway

^* Address correspondence to Øystein Lian MD, Oslo Sport Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, P.O. Box 4014, Ullevål Stadion, 0806 Oslo, Norway (e-mail: ostrc{at}nih.no).

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.

Hypothesis: Apoptosis contributes to the pathophysiology in patellar tendinopathy.

Study Design: 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 mm²) 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/mm² vs 98.9 nuclei/mm²), the apoptotic index was higher (0.42% vs 0.17%, P = .014).

Conclusion: 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.

Key Words: tendon • patellar tendinosis • apoptosis

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