Twenty years ago the concept of "tissue engineering" emerged from the field of regenerative medicine. This area of study and
investigation applied the principles of engineering to the field of medicine with the goal of repairing and restoring damaged
or missing tissue and organs.
The ACell product that was developed from this tissue approach is a "resorbable bioscaffold" made into a sheet or powder and
derived from porcine urinary bladder tissue. ACell provides a matrix for cell growth, promotes new blood-vessel formation
and constructive remodeling of damaged tissue, because cells around the Acell implant grow into it and begin a cycle of growth,
degradation and replacement by tissues that are needed in that location.
Essentially, placing Acell into a tendon or ligament defect allows cells to grow into that area and to differentiate into
tendon cells rather than traditional healing where tendon defects fill with some version of fibrosis or scar tissue.
The loss of strength and elasticity with fibroblastic healing of tendons and ligaments is believed to account for the decrease
in performance post-injury for many equine athletes. Any product that can promote more normal cell healing in these structures
will greatly potentiate their athletic lives.
Acell is fairly expensive, however, and cannot be used with the following: alcohol, detergents and/or soaps, iodine products,
silver nitrate, hydrogen peroxide and cortisone. It must be injected into soft-tissue injuries and carries a somewhat higher
risk of infection because of the invasive nature of the procedure.
With less than 10 years of clinical availability, Acell already has become a popular choice of therapy for many clinicians.
There are no studies testing it against similar products, however, and bone-marrow cells can provide scaffolding for tendon
and ligament repair as well.
Regenerative medicine has given practitioners the option of using stem cells for tendon and ligament repair. "The definition/identification
of stem cells is constantly evolving," according to Dr. Lisa Fortier of the Department of Veterinary Clinical Sciences at
the New York State College of Veterinary Medicine at Cornell University.
This evolution adds to the confusion as to which type of stem cell practitioners might choose for various tendon and ligament
Stem cells can be embryonic (derived from the umbilical cord and able to differentiate into any cell types), or adult-derived
(obtained from fat, muscle, bone marrow and other tissues and having a restricted number of cell lineages into which they
There is fairly strong clinical evidence for the use of stem cells in tendon and ligament repair.
A study of 168 national hunt horses in the U.K. showed that re-injury following stem-cell therapy for superficial digital
flexor tendon injuries in the three years following repair was 24 percent, compared to 56 percent in horses getting tendon
There are two techniques currently available that produce two different populations of stem cells for tendon and ligament
Bone-marrow-derived stem cells have been the most studied and currently are favored because of their superior performance.
To produce them, marrow is collected from the sternum of the standing, anesthetized horse. The cells are cultured over a period
of weeks and then suspended in a bone-marrow supernatant.
These cultured bone-marrow cells derive benefits from the rich growth factors in the supernatant. This mix of cells and nutrient
broth is then injected into the structural lesion via ultrasound.
Research shows these cells perform well and have an ability to differentiate more readily into known cell types (more
tendon-like, less fibrosis-like).
Disadvantages include the need for bone-marrow sampling surgery, a relatively lengthy culturing period, ultrasound-guided
implantation and the expense of the procedures.
Fat-derived stem cells are surgically harvested from the tail head of the horse. They are not cultured, and are then implanted
This technique provides a large number of stem cells but without the differentiation potential of cultured bone-marrow cells.
This procedure is quicker, contains no culturing period so it is shorter, and it is less expensive.
Though the results with fat-derived stem cells are not as good as with cultured cells, there is still significant improvement
with this treatment over more standard tendon and ligament treatments.
In a review article on the future of stem-cell treatment, Dr. (Rodger) Smith writes, "This technology (stem cell) has shown
encouraging, but not yet proven, efficacy for treating acute tendon lesions in horses."
He cites the relatively small number of horses in the study and the difficulty in doing controlled studies in a working equine
environment (training track or racing barn) as a weakness in conclusions reached.
Further studies are under way, and more information and recommendations on the use of stem cells should be available soon.