Sequential Application of Autologous Platelet Rich Plasma and Muscle-Derived Mesenchymal Stem Cells for Acute Tendon Injuries in Horses: Early Clinical and Ultrasonographic Outcomes in a Randomized, Double-Blind Controlled Study.

Overview

• This study evaluated the early clinical and ultrasound-based effects of injecting horses with autologous muscle-derived mesenchymal stem cells (mdMSCs) following platelet-rich plasma (PRP) treatment for acute tendon injuries.
• The research was a randomized, double-blind, placebo-controlled trial demonstrating that mdMSCs improve tendon healing outcomes without significant adverse effects, with enhanced benefits after a second injection.

Background

• Tendon and ligament injuries are common in sport horses and often recur due to incomplete healing processes.
• Current regenerative treatments include platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs), but data on the efficacy of autologous (self-derived) MSCs in early healing stages is limited.
• Autologous treatment avoids immune rejection and logistical issues associated with donor-derived (allogeneic) cells.

Study Design

• A prospective randomized, double-blind, placebo-controlled clinical trial was conducted on horses with naturally occurring tendon injuries (tendinopathies).
• Initially, all horses received standardized PRP pretreatment as a baseline regenerative intervention.
• After PRP treatment, horses that did not show sufficient clinical improvement (“non-responders”) were randomized into two groups:
• mdMSC treatment group (n = 17): received intralesional injection of autologous muscle-derived mesenchymal stem cells.
• Placebo group (n = 6): received an injection of placebo (inactive substance).
• The study was double-blinded, meaning neither investigators nor horse owners knew which treatment was administered.
• Ultrasound (ultrasonographic) and clinical evaluations were conducted at multiple time points:
• T0: recruitment/baseline before PRP pretreatment
• T1: before local mdMSC or placebo administration
• T2: four weeks after injection
• T3: eight weeks after injection
• Additionally, at T2, some horses in both groups (n=18) received a second mdMSC injection if deemed necessary by the investigator; this phase was not randomized.

Key Findings

• Between T1 and T2 (first four weeks after injection), horses treated with mdMSCs showed significant improvement in:
• Clinical parameters such as lameness scores or tendon swelling.
• Ultrasonographic characteristics indicating better tendon healing (e.g., fiber alignment, lesion size).
• The placebo group showed no statistically significant changes between these time points.
• Comparison between groups at T2 confirmed the superiority of mdMSC treatment over placebo in early healing metrics.
• Among the 18 horses that received a second mdMSC injection at T2, further improvements were observed by T3 (eight weeks post-injection), suggesting cumulative benefits from a repeated dose.
• No systemic adverse events were reported throughout the study period.
• Local reactions to injections were mild and transient, indicating good safety and tolerability of mdMSC treatment.

Conclusions and Implications

• This randomized controlled trial provides evidence that autologous muscle-derived mesenchymal stem cells improve early tendon healing in horses when applied after PRP pretreatment.
• The use of autologous cells is advantageous because it reduces risks related to immune rejection and simplifies storage and logistical issues compared to donor cells.
• Additional benefit was observed with a second injection of mdMSCs, highlighting the potential for multi-dose treatment protocols.
• The study supports the safety and early efficacy of sequential regenerative therapies combining PRP and mdMSCs for equine tendinopathies.
• These results may contribute to improved therapeutic strategies to reduce recurrence and enhance full recovery in tendon injuries in sport horses.