[Comparative analysis of pathological structure between acute closed and open Achilles tendon rupture]

To investigate the morphological, histological and ultrastructural changes of acute closed rupture of Achilles tendon, in order to clarify the pathological basis of the injury and to explore the significance.

From January 2015 to January 2019, 35 patients with acute Achilles tendon rupture who underwent the minimally invasive Achilles tendon suture technique were retrospectively analyzed. Among these patients, 12 cases in acute open Achilles tendon rupture group included 10 males and 2 females, with an average age of (35.1±9.7) years old ranging from 19 to 50, and the time from injury to operation was 2 to 8 hours with an average of(5.6±1.8);23 cases in acute closed Achilles tendon rupture group included 21 males and 2 females, with an average age of (35.5±6.6) years old ranging from 18 to 50, and the time from injury to operation was 3 to 15 hours with an average of (7.5±3.1). The gross appearance and imaging findings of the broken end of Achilles tendon tissue in the two groups were compared by naked eye observation and foot and ankle MRI at 4 to 6 hours before operation. HE staining, scanning and fluoroscopic electron microscopy, immunohistochemistry(Sirius red staining) were performed on the intraoperative Achilles tendon tissue specimens at 1 to 2 days after operation, the collagen fiber degeneration and local fat infiltration, collagen fiber shape, cell morphology and function, and the distribution of typeⅠand type Ⅲ collagen fibers in Achilles tendon were compared between the two groups.

Compared with the acute open Achilles tendon rupture group, the acute closed Achilles tendon rupture group had poor elasticity, hard texture, moderate edema, irregular shape of Achilles tendon broken end, horsetail shape, and more calcification around the broken end. HE staining results:the collagen fibers in the Achilles tendon of the acute open Achilles tendon rupture group were arranged irregularly, with hyaline degeneration and fat infiltration;The results of electron microscopy showed that collagen arranged disorderly and fibroblasts atrophied in the acute closed Achilles tendon rupture group. Immunohistochemical(Sirius staining) results:the proportion of collagenⅠin the acute open Achilles tendon rupture group and the acute closed Achilles tendon rupture group was(91.12±4.34)% and(54.71±17.78)% respectively, and the proportion of collagen Ⅲ was (8.88±4.34)% and (45.29±17.78)% respectively. The content of collagenⅠin the acute closed Achilles tendon rupture group was lower than that in the acute open Achilles tendon rupture group, and the content of collagen Ⅲ in the acute closed Achilles tendon rupture group was higher than that in the acute open Achilles tendon rupture group(P<0.05).

The morphology, histology and ultrastructure of the acute closed ruptured Achilles tendon are significantly altered compared with the normal Achilles tendon. The original fine and orderly spatial structure cannot be maintained, part of collagen Ⅰ is replaced by collagen Ⅲ, and the toughness and strength of the tendon tissue decreased, which may be the feature of degeneration of the Achilles tendon and an important pathological basis for closed Achilles tendon rupture.