Kangaroo tendons may offer an ideal replacement for damaged human ligaments

The new study helps athletes tackle one of the most serious injuries that can happen to them – a ruptured anterior cruciate ligament (ACL). An ACL rupture, which necessitates reconstructive surgery and months of rehabilitation, might signal the end of a season or possibly a career.

Years of research on the matter have led Dr. Hartnell and his colleagues to now initiate a human xenograft study to treat injuries such as a ruptured anterior cruciate ligament (ACL) using kangaroo tendons. 

Kangaroo tendons are six times stronger

Studies into the matter were driven by Dr. Hartwell's curiosity about how the kangaroo body can support their intense athletic abilities. 

"Watching them in action, I started to wonder how much of this athletic ability was related to the way their tendons were formed, and whether they might be used to replace ruptured human ligaments," said Dr. Hartwell's, who also works as an orthopedic surgeon practicing at the MQ Health Orthopaedic Clinic and at hospitals in the Southern Highlands.

Detailed analysis of their knee structure using a dead kangaroo from a local farmer led to the discovery that they are up to six times stronger than human tendons, making it one of the best materials to reconstruct connective tissue.

An ideal option for ligament replacement

The team meticulously researched the properties of kangaroo tendons, including which limbs give the greatest alternative for different human ligaments, and compared them to existing ligament replacement solutions, according to the study.

The team also claimed to have devised a method to prevent kangaroo xenografts from being rejected after transplant. Dr. Hartwell said a "special sauce" is crucial to this, and it has been trademarked for further use. Their study findings found that not only will kangaroo tendons not be rejected, but they will also be stronger and more durable than any other graft option currently available around the world.

Regarding the availability to meet the increasing demand globally, the team is hopeful that it can fulfill such a scenario. “Australia could easily meet the entire world’s need for ligament reconstruction using tendons from the kangaroos that are already being harvested for meat."

The team is currently in the last phases of pre-clinical studies and hopes to commence human clinical trials in 2024.

The study detailing their work has been published in the American Journal of Sports Medicine.

Abstract:

Background: The use of allograft tendons has increased for primary and revision anterior cruciate ligament reconstruction, but allograft supply is currently limited to a narrow range of tendons and donors up to the age of 65 years. Expanding the range of donors and tendons could help offset an increasing clinical demand.

Purpose: To investigate the effects of donor age, sex, height, and specific tendon on the mechanical properties of a range of human lower leg tendons.Descriptive laboratory study.

Methods: Nine tendons were retrieved from 39 fresh-frozen human cadaveric lower legs (35 donors [13 female, 22 male]; age, 49-99 years; height, 57-85 inches [145-216 cm]) including: Achilles tendon, tibialis posterior and anterior, fibularis longus and brevis, flexor and extensor hallucis longus, plantaris, and flexor digitorum longus. Tendons underwent tensile loading to failure measuring cross-sectional area (CSA), maximum load, strain at failure, ultimate tensile strength, and elastic modulus. Results from 332 tendons were analyzed using mixed-effects linear regression, accounting for donor age, sex, height, and weight.

Results: Mechanical properties were significantly different among tendons and were substantially greater than the effects of donor characteristics. Significant effects of donor sex, age, and height were limited to specific tendons: Achilles tendon, tibialis posterior, and tibialis anterior. All other tendons were unaffected. The Achilles tendon was most influenced by donor variables: greater CSA in men (β = 15.45 mm2; Šidák adjusted P < .0001), decreased maximum load with each year of increased age (β = −17.20 N per year; adjusted P = .0253), and increased CSA (β = 1.92 mm2 per inch; adjusted P < .0001) and maximum load (β = 86.40 N per inch; adjusted P < .0001) with each inch of increased height.

Conclusion: Mechanical properties vary significantly across different human tendons. The effects of donor age, sex, and height are relatively small, are limited to specific tendons, and affect different tendons uniq uely. The findings indicate that age negatively affected only the Achilles tendon (maximum load) and challenge the exclusion of donors aged >65 years across all tendon grafts.