Evaluation of collagen fiber maturation and ordering in regenerating tendons employing H-1 double quantum filtered NMR spectroscopy

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 ¹ H 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 ¹ H 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 ¹ H DQF NMR spectroscopy is a useful noninvasive 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 .