Stem Cell Injection for Healing Chronic Rotator Cuff Tears in a Rat Model  
Wendy S. Burke PT, DPT, MS, OCS, C.T.Vangsness, Jr., M.D., Bo Han, PhD.

Rotator cuff tears are common in individuals over the age of 50 resulting in siginificant loss of function, loss of wages for times of f and high costs for treatment.  Surgical treatment requires 6 weeks of relative immobilization and early restrictions on the tissures to assist in tendon healing.  Despite biologic healing, failure rates are reported to range between 5-70%. 

Faster healing of the repaired tendon may prevent early re-rupture and post operative stiffness by allowing active use of the shoulder in a shorter period of time.  There are multiple biologic treatment interventions being examined such as bipolar radiofrequency energy (bRFE), and BMP2. Several allo/xenograft tissue patches to augment cuff repairs have already been examined in animal models and are under clinical investigation. 

One potential source of rotator cuff repair augmentation is the use of adult mesenchymal stem cells (MSCs).  Mesenchymal stem cells are derived from bone marrows donations and have demonstrated an ability to induce bone, tendon, cartilage and ligament tissue healing and formation.  Adult mesenchymal stem cells are already in use within clinical trials for regeneration of knee meniscus after a meniscectomy, in graft vs. host disease, for prevention of cardiomyopathy after an acute myocardial infarction, and in Chron’s disease.  There are no studies that have attempted to evaluate the use of stem cells to enhance rotator cuff tear healing.

In this study 72 athymic rats will undergo a surgical bilateral rotator cuff incision at the tendon insertion with 2 mm resected.  After 6 weeks each rat with under go a rotator cuff repair bilaterally.  The rats will be randomly assigned to two groups.  The left shoulder repairs will serve as the control within each rat.  The right shoulders will be the study shoulders between the groups.  36 rats will receive a stem cell injection with a carrier post operatively and 36 will not.  Comparisons between the right and left shoulder of the rats will provide bias of treatment information.

12 rats in each group will be sacrificed at 4 weeks, 12 at  8 weeks, and 12 rats at 12 weeks.  The surgical site will be inspected after sacrifice for tendon healing, inflammation, and character of the healed tendon.  After inspection, the specimens will be wrapped in saline soaked guaze, placed in two plastic bags, and frozen at -20 degrees Celsius for later analysis.8 of the 12 in each group will undergo biomechanical testing.  4 in each group will undergo histology blindly read by two different pathologists. 

Data analysis will be evaluated using SPSS v 11.5 software.  Descriptive statistics including frequencies, mean, standard deviation, minimum and maximum values will be calculated.  Analysis with student t-tests will be used for comparison of means between groups.  Chi squared analysis will be used for nominal data.  Results will considered statistically significant when p< 0.05.