There are a number of factors that affect tendon and ligament structural propertiesand may protect from or predispose to injury.
- The number and quality of collagen crosslinks increases, leading to an increase in the tensile strength and increased cross-sectional area of collagen fibrils. These changes occur up to the age of 20 years. As age increases, there is a concomitant drop in the collagen content and number of crosslinks in tendons and ligaments. Aging results in a continuous decline in the mechanical properties (strength, stiffness and ability to withstand/recover from deformation).
Mobilisation and training
- As in most musculoskeletal structures, tendons and ligaments remodel in response to mechanical stresses applied to them. They become stronger and stiffer when subjected to stress. Physical training has been shown to increase the tensile strength of tendons and the ligament–bone interface (in dogs). Conversely, tendons and ligaments become weaker and less stiff when immobilised or not subjected to regular stresses. Studies have shown that it takes up to 12 months to regain the strength and stiffness lost during immobilisation.
Non-steroidal anti-inflammatory drugs (NSAIDs)
- Research has demonstrated increased total collagen content and tensile strength in animals treated with indomethacin possibly due to increased crosslinkage of collagen. This suggests that short-term use of NSAIDs would not adversely affect tendon healing and may in fact be beneficial to the overall mechanical properties of the structure.
- Steroids: previously thought to inhibit healing in acute tendon/ligament injuries, animal studies with local steroid at the site of acute injury showed no difference when compared to those without steroid. Local steroids did, however, weaken the strength of the ligament–bone junction.
Pregnancy and hormonal changes
- There is a marked hormonally driven increase in laxity of tendons and ligaments, particularly in the pelvic region, at the end of pregnancy and during the postpartum period. This eventually returns to normal. Oestrogen fluctuations have also been shown to alter collagen production by up to 50% and may alter the composition of ligaments or tendons, making them susceptible to injury.