Extracorporeal shockwave therapy improves the strength of degenerated achilles tendon : a rat model

Abstract

Purpose: This study examined the effect of extracorporeal shockwave therapy (ESWT) on the mechanical strength of overused Achilles tendon in a rat model.

Relevance: Tendon degeneration due to overuse is very common among athletes and the treatment of which is usually with physical modalities and exercise. ESWT is a relatively new physical modality used in treating musculoskeletal conditions and its effectiveness on promoting tissue healing is well reported. However, due to the lack of a suitable animal model that simulates the pathologies of tendon degeneration in human, the effect of ESWT on treating tendon degeneration has not been well reported, in particular its effect on the biomechanical strength of the tissue is not known. Recently, we developed an Achilles tendinopathy model in rat with an enforced exercise of eccentric bipedal running programme on the hind limbs. The establishment of tendinopathy in the Achilles tendon was evident after 8 weeks of running and this model formed the basis of studying the effect of ESWT for treating Achilles tendinopathy.

Participants: Twenty sexually matured female Sparague Dawley rats were used in this study.

Methods: All the rats were subject to a daily running programme of 1 hour for 8 weeks in an animal treadmill at a speed of 17 meter/minute and a 20◦ decline slope. In order to load the Achilles tendon effectively, the rats were trained to adopt a bipedal running style by suspending their upper body with a harness so that the entire body weight was bore by the hind limbs. The rats were divided into 2 groups of 10. The rats in Group 1 received ESWT on day 7, 21, 35 and 49 at 0.12 mJ/mm2 EFD; 5mm penetration depth, 1000 shocks at the frequency of 4 Hz focusing directly onto the Achilles tendon with ultrasound gel as the medium, whereas the rats in Group 2 received no treatment after running.

Analysis: The animals were killed at week 9 and the right Achilles tendons were harvested for biomechanical testing of viscoelastic load-relaxation behavior, structural stiffness and ultimate tensile strength (UTS). Results of the two groups were analyzed by t-tests with significance at 0.05.

Results: Both groups have similar load-relaxation (Group 1: 52.7%; Group 2: 56.2%; p = 0.96) and structural stiffness (Group 1: 36.2; Group 2: 41.1; p = 0.77) but the ESWT group has significantly higher UTS than the control group (Group 1: 147.7N; Group 2: 134.9 N; p = 0.013).

Conclusions:We conclude that ESWT could produce a more favorable outcome on the mechanical strength of Achilles tendon after a prolonged eccentric loading exercise regime.

Implications: The present study demonstrates that ESWT can strengthen the tendon and improve the energy absorption capacity so that the structure can withstand higher loading during exercise and mechanically stressful conditions.