It is difficult to monitor the chronic stage of the healing process of ruptured tendons employing the present diagnostic modes. However, the results of this study have shown that ¹H double quantum filtered (DQF) NMR spectroscopy is sensitive to the later stages of the healing process. Regenerated tendons of rabbits were dissected and measured at the end of the acute phase (three weeks), the subacute phase (nine weeks), and the chronic phase (13 and 18 weeks after tenotomy). Four parameters were determined by ¹H DQF NMR spectroscopy: (a) the maximum signal intensity (h_max) relative to the single quantum spectrum, (b) the creation time of the maximum signal intensity (τ_max), (c) the decay time from the maximum signal intensity to a value half of that intensity (τ_1/2) and (d) the residual dipolar splitting of water (δ), representing the order of the collagen fibers. The values of h_max, τ_max, τ_1/2, and δ of the intact Achilles tendons were 11.3 ± 1.0%, 0.48 ± 0.03 ms, 0.67 ± 0.04 ms and 732 ± 62 Hz (mean ± SEM, n = 6), respectively. In the regenerating tendon, h_max increased from 0.41 ± 0.12% at three weeks to 7.07 ± 0.77% at 18 weeks, τ_max decreased from 1.88 ± 0.31 ms at three weeks to 0.72 ± 0.04 ms at 18 weeks, τ_1/2 decreased from 11.6 ± 1.8 ms at 3 weeks to 1.48 ± 0.16 ms at 18 weeks, and δ increased from 129 ± 8 Hz at three weeks to 414 ± 29 Hz at 18 weeks. We have concluded that reordering of collagen fibers proceeds continuously even in the chronic stage of healing. Thus, the ¹H DQF NMR spectroscopy is a useful non‐invasive technique to evaluate the reconstruction and the order of collagen fibers in regenerating tendon. It is also suggested that τ^1/2 and h_max are most useful for in vivo DQF NMR spectroscopy and imaging, respectively, in combination with τ_max.

© 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved.