Regeneration of Grade 3 Ankle Sprain, Using the Recombinant Human Amelogenin Protein (rHAM+), in a Rat Model

: Lateral ligament tears, also known as high-grade ankle sprains, are common, debilitating, and usually heal slowly. 10-30% of patients continue to suffer from chronic pain and ankle instability even after 3-9 months. Previously, we showed that the recombinant human amelogenin (rHAM+ ) induced regeneration of fully transected rat medial collateral ligament (MCL), a common proof-of-concept model. Our aim was to evaluate whether rHAM+ can regenerate torn ankle calcaneo-fibular ligament (CFL), an important component of the lateral ankle stabilizers. Right CFLs of Sabra rats were transected and treated with 0, 0.5 or 1µg/µl rHAM+ dissolved in propylene glycol alginate (PGA). Results were compared to the normal group, without surgery. Healing was evaluated 12 weeks after treatment by mechanical testing (ratio between the right and left, un-transected ligaments of the same rat), and histology including immunohistochemical staining of collagen I and S100. The mechanical properties, structure, and composition of transected ligaments treated with 0.5μg/μl rHAM+ (experimental) were similar to un-transected ligaments. PGA (control) treated ligaments were much weaker, lax and unorganized compared to un-transected ligaments. Treatment with 1μg/μl rHAM+ was not as efficient as 0.5μg/μl rHAM+ . Normal arrangement of collagen I fibers and of proprioceptive nerve endings, parallel to the direction of the force, was detected in ligaments treated with 0.5μg/μl rHAM+ , and scattered arrangement, resembling scar tissue, in control ligaments. In conclusion, we showed that rHAM+ induced significant mechanical and structural regeneration of torn rat CFLs, which might be translated into treatment for grade 2-3 ankle sprain injuries. This article is protected by copyright. All rights reserved.