Lesions of the Achilles tendon. A sonographic, biomechanical and histological study.

Thirty-four Achilles tendons were explanted post-mortem. The explanation took place less than 24 h after death. The tendons were examined by means of ultrasonography and after explanation assessed histologically and biomechanically. In the sonograms 19 changes in echogenicity were noted. Changes in form with an increase in the diameter of the tendon of up to 10 mm (compared with the contralateral side) were found in 6 tendons. The changes in echogenicity and form were found most frequently 2-4 cm from the insertion of the tendon at the os calcis. At a speed of 5 mm/min, the average force needed until rupture occurred was calculated as 27.6 N/mm2. The tear was located on average 29.7 mm from the bony insertion of the tendon at the calcaneus. Histologically, necroses could be found most frequently in all regions of the tendon, followed by scars and fissures. When there were differences of more than 25% in tensile strength between the right and left sides, there was a histological change in the weaker tendon at the site of the tear. Sonographic changes in form pointed to histological lesions in this region. Changes in the echogenicity led to the detection of degenerative changes of the tendon, but they have to be analysed carefully, as they are prone to artefacts. There was not statistically relevant correlation either with regard to tensile strength or to the site of the rupture for sonographically proven changes in the area of the rupture. However, when there was a sonographically abnormal finding in the course of a tendon, the tendon tore at an earlier point than those exhibiting no abnormality. Sonography proved to be a useful method in the detection of degenerative lesions of tendons. A direct influence on the biomechanics of the tendon could not be found.