Objectives In this study, serum levels of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) between patients with a history of Achilles tendon rupture and blood donor controls were compared, and their relation to mechanical properties of the tendons during healing were studied.
Methods More than 3 years after injury, serum levels of MMP-1, MMP-2, MMP-3, MMP-7, MMP-8, MMP-9 and MMP-13, TIMP-1 and TIMP-2 in eight patients who had Achilles tendon rupture were measured. Twelve blood donors served as controls. During the early phase of healing, the tendon modulus of elasticity was calculated from radiostereometric data and tendon cross-sectional area.
Results Patients with a history of Achilles tendon rupture had increased levels of MMP-2 (median difference 10%, p=0.01), MMP-7 (median difference 15%, p=0.02) and TIMP-2 (median difference 36%, p=0.02), compared with controls. Levels of MMP-7, measured 3 years after injury, correlated inversely to tendon modulus of elasticity (rs=20.83, p=0.02) and positively to tendon elongation (rs=0.74, p=0.05) during the early phase of healing. There was a trend towards positive correlation between MMP-7 and cross-sectional area during the early phase of healing (rs=0.67, p=0.08).
Conclusions Patients with a history of Achilles tendon rupture appear to have elevated levels of MMP-2, MMP-7 and TIMP-2 in serum. In these pilot data, the view that the MMP–TIMP system is involved in tendinopathy is supported and that disturbances in proteolytic control might be generalised are suggested.
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Funding The strategic research programme Materials in Medicine in Linköping, the Swedish Research Council and Landstinget i Östergötland research funds.
Competing interests PA and BP are co-inventors of a patented method for the coating of sutures with pharmacological agents, for example, MMP inhibitors. TS and PE have no conflict of interest.