Healing of human Achilles tendon ruptures: radiodensity reflects mechanical properties

This study tests the idea of using radiodensity from computed tomography to quantitatively evaluate the healing of ruptured Achilles tendons.

The radiodensity of the healing tendons in sixty-five patients who were treated for Achilles tendon rupture was measured. The hypothesis was that density would correlate with an estimate for e-modulus, derived from strain, measured by radiostereometry with different mechanical loadings.

Radiodensity 7 weeks after injury was decreased to 67 % (SD 11) of the contralateral, uninjured tendon. There was no improvement in radiodensity from 7 to 19 weeks, whereas at 1 year, it had increased to 106 % (SD 7). Only 2 of 52 measured values at 1 year were lower than the highest value at 19 weeks, i.e. there was minimal overlap. The variation in radiodensity could explain 80 % of the variation in e-modulus, but radiodensity correlated only weakly with e-modulus at each time point separately. At 1 year, both radiodensity and e-modulus correlated with functional results, although weakly.

From 19 weeks onwards, radiodensity appears to reflect mechanical properties of the tendon and might to some extent predict the final outcome. Radiodensity at 7 weeks is difficult to interpret, probably because it reflects both callus and damaged tissues.