Use of mesenchymal stem cells for tendon healing in veterinary and human medicine: getting to the "core" of the problem through a one health approach

Abstract

The purpose of this manuscript, which is part of the Currents in One Health series, is to take a comparative approach to stem cell treatment for tendon injury and consider how the horse might inform treatment in other veterinary species and humans. There is increasing experimental and clinical evidence for the use of bone marrow-derived mesenchymal stem cells to treat tendon injuries in the horse. The same evidence does not currently exist for other species. This manuscript will review why the equine superficial digital flexor tendon core lesion might be considered optimal for stem cell delivery and stem cell interaction with the injury environment and will also introduce the concept of stem cell licensing for future evaluation. The companion Currents in One Health by Koch and Schnabel, AJVR, October 2023, addresses in detail what is known about stem cell licensing for the treatment of other diseases using rodent models and how this information can potentially be applied to tendon healing.

Keywords: Achilles tendon; core lesion; mesenchymal stem cell; one health; superficial digital flexor tendon.

Figure 1—

Transverse plane ultrasound images of a normal superficial digital flexor tendon (SDFT) from an eventing horse outlined in white (A) and compared to an enlarged SDFT from a different eventing horse outlined in white with a typical hypoechoic core lesion outlined in red (B). DDFT = Deep digital flexor tendon.

Figure 2—

The same superficial digital flexor tendon (SDFT) core lesion as shown in Figure 1, panel B, now slightly off angle to allow for ultrasound-guided intralesional injection of mesenchymal stem cells (MSCs). Image with hyperechoic needle in place within the outlined SDFT core lesion preinjection (A) and postinjection with MSCs and hyperechoic air bubbles filling the outlined SDFT core lesion (B). DDFT = Deep digital flexor tendon.

Figure 3—

Schematic overview of the treatment decision-making process and general rehabilitation protocol for a typical equine superficial digital flexor tendon (SDFT) core lesion. Created with BioRender.com. PRP = platelet-rich plasma. RLP = regional limb perfusion.

Figure 4—

Example lateral (A) and skyline (B) radiographs and sagittal plane ultrasound images (C and D) of the tarsus in a German Shorthair Pointer hunting dog with a common calcaneal tendon (CCT) injury. On the radiographs, dystrophic mineralization and/or avulsion fragments are present near the insertion of the CCT on the calcaneus, as outlined in the red circles (A and B). On the ultrasound images, there is evidence of superficial digital flexor tendon (SDFT) tearing (arrows) and diffuse tendonitis, gastrocnemius tendon fiber pattern disruption at the insertion onto the calcaneus consistent with partial rupture (asterisk), and calcaneal bursitis (D).