Achilles tendon rupture: experimental results on spontaneous repair in a sheep‐model

Abstract

We studied the course of spontaneous healing of Achilles tendons in a sheep model after transection and partial resection of the tendon by means of histological and biomechanical analyses. In 18 sheep used for another animal study the operated knee had to be excluded from weight-bearing; therefore the Achilles tendons were transected and for 1.5 cm partially resected in the middle substance of the tendon. For evaluation these spontaneously healed tendons (n = 18) were compared with the contralateral noninvolved tendons (n = 18). Specimens were analyzed 3, 6, and 12 months postoperatively by means of histology, polarized light, angiography, and mechanically analyzing the specific tensile strength and absolute tensile strength. We found that in all animals the resected tendon healed spontaneously. All animals exhibited a normal gait pattern at least 6 weeks postoperatively. Histologically, the tendinous area of healing demonstrated after 3 months a fibrous collagenous tissue with a loose fiber orientation. The cross-sectional area had at 3 months increased to maximum but decreased later. Concomitantly the fiber orientation improved with time and 12 months after transection the specimens showed a nearly normal histological structure of the healed tendon. Biomechanically the specimens exhibited a rather low specific rupture force after 3 months (28.8% of normal tendons) and 6 months (30.2%) but increased after 12 months (56.7%). In regard to the resulting total rupture force the decrease in the spontaneously healed tendons was less (75.6% after 3 months, 56.1% after 6 months, 81.18% after 12 months), because the cross-sectional area of the healing tendon had significantly (P < 0.05) increased to maximum after 3 and 6 months. Sheep Achilles tendons thus healed spontaneously without any immobilization. The initial healing mechanism is thickening of the scar tissue with improvement of the fiber orientation towards a tendonlike structure within 1 year. Parallel to this, the specific rupture force increased and the thickness of the newly tendonlike area decreased.

Pulsed ultrasound treatment accelerates the repair of Achilles tendon rupture in rats

“…32 Other studies using a sheep model to study the spontaneous repair of ruptured Achilles tendon found that, after 3 months and 12 months, the total rupture force of the injured tendon was about 75.6% and 81.18%, respectively. 1 Regardless of the surgical method or model used, these studies showed that a long period of time is required for the recovery of the biomechanical properties of an injured tendon. In clinical situations, especially for elite athletes, the strength of an Achilles tendon after rupture and repai, may not return to its original level, hindering the athletes' to return to their original level of activity, even after a long period of time.…”

“…The medial tendon, including the musculo-tendinous junction, was dissected and fixed in a 4% phosphatebuffered paraformaldehyde solution at room temperature. 1 After dehydration in graded ethanol, specimens were embedded in paraffin and then cut in 5-mm thick longitudinal sections. The sections were stained with Ehrlich's hemotoxylin/eosin (HE).…”

“…Open repair is thought capable of restoring the normal tension and length of the tendon with a lower rate of re-rupture. [1][2][3][4] However, the disadvantages of surgical intervention include wound infection and adhesion 4,5 and higher cost. 6 Cast immobilization is the most common method for conservative treatment of Achilles tendon rupture.…”

The Role of Mechanical Loading in Tendon Development, Maintenance, Injury, and Repair

“…On the basis of studies on horses, rabbits, and rats 39,40,[51][52][53][54][55][56] , given that obtaining human biopsy samples can be difficult, it has been shown that following tendon injury, the natural healing process forms scar tissue via a three-stage process: inflammation, matrix production, and remodeling and maturation 39,40 . The inflammatory stage initiates the response to injury, typically throughout the first week 39 .…”

“…Cell density and vascularity decrease as the tissue further repairs 40 . Studies have shown that natural healing leads to tendon biomechanical properties that fail to match normal levels at up to eight weeks, twenty-six weeks, and twelve months following injury in a murine and rabbit central patellar tendon model, and sheep Achilles tendon model, respectively [51][52][53] . Investigators have suggested the poor mechanical properties result from predominantly small fibrils in the resulting repair tissue, compared with the normal distribution of both large and small fibrils observed in normal adult human tendon 54,55 , but conflicting results exist.…”