How can one platelet injection after tendon injury lead to a stronger tendon after 4 weeks? Interplay between early regeneration and mechanical stimulation

Acta Orthop. 2006 Oct;77(5):806-12. doi: 10.1080/17453670610013033.


Background: Mechanical stimulation improves the repair of ruptured tendons. Injection of a platelet concentrate (platelet-rich plasma, PRP) can also improve repair in several animal models. In a rat Achilles tendon transection model, 1 postoperative injection resulted in increased strength after 4 weeks. Considering the short half-lives of factors released by platelets, this very late effect calls for an explanation.

Methods: We studied the effects of platelets on Achilles tendon regenerates in rats 3, 5 and 14 days after transection. The tendons were either unloaded by Botulinum toxin A (Botox) injections into the calf muscles, or mechanically stimulated in activity cages. No Botox injections and ordinary cages, respectively, served as controls. Repair was evaluated by tensile testing.

Results: At 14 days, unloading (with Botox) abolished any effect of the platelets and reduced the mechanical properties of the repair tissue to less than half of normal. Thus, some mechanical stimulation is a prerequisite for the effect of platelets at 14 days. Without Botox, both activity and platelets increased repair independently of each other. However, at 3 and 5 days, platelets improved the mechanical properties in Botox-treated rats.

Interpretation: Platelets influence only the early phases of regeneration, but this allows mechanical stimulation to start driving neo-tendon development at an earlier time point, which kept it constantly ahead of the controls.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Achilles Tendon / injuries
  • Achilles Tendon / physiology
  • Animals
  • Biomechanical Phenomena
  • Blood Platelets / physiology*
  • Botulinum Toxins, Type A / administration & dosage
  • Neuromuscular Agents / administration & dosage
  • Physical Stimulation
  • Rats
  • Rats, Sprague-Dawley
  • Regeneration / physiology*
  • Rupture
  • Tendon Injuries / physiopathology
  • Tendon Injuries / therapy*
  • Tensile Strength
  • Time Factors
  • Wound Healing / physiology*


  • Neuromuscular Agents
  • Botulinum Toxins, Type A