Submitted on April 1, 2009
Revised on June 19, 2009
Accepted on June 20, 2009
MECHANICAL PROPERTIES AND COLLAGEN CROSS-LINKING OF THE PATELLAR TENDON IN OLD AND YOUNG MEN
Christian Couppe1, Philip Hansen2, Mads Kongsgaard2, Vuokko Kovanen3, Charlotte Suetta2, Per Aagaard4, Michael Kjaer5, and S. Peter Magnusson6*
1 Institute of Sportsmedicine-Copenhagen
2 Bispebjerg Hospital
3 University of Jyväskylä
4 University of Southern Denmark
5 Bispebjerg Hospital and Faculty of Health Sciences, University of Copenhagen
6 Bispebjerg Hospital and Faculty of Health Sciences,
* To whom correspondence should be addressed. E-mail: p.magnusson{at}mfi.ku.dk.
Age-related loss in muscle mass and strength impairs daily life function in the elderly. However, it remains unknown if tendon properties also deteriorate with age. Cross-linking of collagen molecules provides structural integrity to the tendon fibrils and has been shown to change with age in animals, but has never been examined in humans, in vivo. Purpose: To examine the mechanical properties and pyridinoline and pentosidine cross-link, and collagen concentrations of the patellar tendon, in vivo, in old (OM) and young men (YM). Methods: Seven OM (67±3 yrs, 86±10 kg) and 10 YM (27±2 yrs, 81±8 kg) with a similar physical activity level (OM 5±6 hrs/wk, YM 5±2 hrs/wk) were examined. MRI was used to assess whole tendon dimensions. Tendon mechanical properties were assessed using simultaneous force and ultrasonographic measurements during ramped isometric contractions. Percutaneous tendon biopsies were taken and analyzed for hydroxylysyl-pyridinoline (HP), lysyl-pyridinoline (LP) and pentosidine (PENT) as well as collagen concentrations. Results: There were no significant differences in the dimensions or mechanical properties of the tendon between OM and YM. Collagen concentration was lower in OM compared to YM (0.49±0.27 vs. 0.73±0.14 mg/mg dry weight, p<0.05). HP concentration was higher in OM compared to YM (898±172 vs. 645±183 mmol/mol, p<0.05). LP was higher in OM compared to YM (49±38 vs. 16±8 mmol/mol, p<0.01) and PENT was higher in OM compared to YM (73±13 vs. 11±2 mmol/mol, p<0.01). Conclusion: These cross-sectional data raise the possibility that age may not appreciably influence the dimensions or mechanical properties of the human patellar tendon, in vivo. Collagen concentration was reduced, while both enzymatic and non-enzymatic cross-linking of concentration was elevated in OM compared to YM, which may be a mechanism to maintain the mechanical properties of tendon with aging.
