Nonsurgical treatment and early return to activity leads to improved Achilles tendon fatigue mechanics and functional outcomes during early healing in an animal model

Abstract

Achilles tendon ruptures are common and devastating injuries; however, an optimized treatment and rehabilitation protocol has yet to be defined. Therefore, the objective of this study was to investigate the effects of surgical repair and return to activity on joint function and Achilles tendon properties after 3-weeks of healing. Sprague Dawley rats (N=100) received unilateral blunt transection of their Achilles tendon. Animals were then randomized into repaired or non-repaired treatments, and further randomized into groups that returned to activity after 1-week (RTA1) or after 3-weeks (RTA3) of limb casting in plantarflexion. Limb function, passive joint mechanics, and tendon properties (mechanical, organizational using high frequency ultrasound, histological, and compositional) were evaluated. Results showed that both treatment and return to activity collectively affected limb function, passive joint mechanics, and tendon properties. Functionally, RTA1 animals had increased dorsiflexion ROM and weight bearing of the injured limb compared to RTA3 animals 3-weeks post injury. Such functional improvements in RTA1 tendons were evidenced in their mechanical fatigue properties and increased cross sectional area compared to RTA3 tendons. When RTA1 was coupled with nonsurgical treatment, superior fatigue properties were achieved compared to repaired tendons. No differences in cell shape, cellularity, GAG, collagen type I, or TGF-β staining were identified between groups, but collagen type III was elevated in RTA3 repaired tendons. The larger tissue area and increased fatigue resistance created in RTA1 tendons may prove critical for optimized outcomes in early Achilles tendon healing following complete rupture.

Complete Achilles Tenotomy: A New Improved Experimental Surgical Technique in Rats

“…Achilles tendon ruptures are common and devastating injuries in humans [34]. Despite improved knowledge of Achilles tendon pathology, the optimal treatment and the best rehabilitation protocol after an acute rupture remain a matter of controversy in orthopaedic and sports medicine [35].…”

Tendon Healing: Mechanical Loading, Microdamage and Gene Expression

“…We have shown that full loading improves Achilles tendon healing and this has also been shown in other studies (3,9,16,18,19,22,38,42,43). The improvement by mechanical loading is usually evaluated in the early phases of Achilles tendon healing, 1-3 weeks after injury (3,9,16,18,22,27), but later evaluation has also been made (21,43).…”

“…The timing of return to mobilization has been tested by other groups and some suggests that immobilization during the early phase of tendon healing is beneficial for the healing process (22,27). Godbout et al showed that full loading immediately after injury impaired mechanical properties after 3 weeks (27).…”

“…The improvement by mechanical loading is usually evaluated in the early phases of Achilles tendon healing, 1-3 weeks after injury (3,9,16,18,22,27), but later evaluation has also been made (21,43). Most animal studies evaluating the effect of full loading during the early phase of Achilles tendon healing have shown beneficial effects (3,9,16,18,19,22).…”

“…Mechanical loading can improve tendon healing both when applied during the inflammatory, proliferative and remodeling phase of the healing process (16,22). Although beneficial in all three phases, the mechanism and the response to mechanical loading might be different as the tissue composition is different in the different phases (25,41).…”