These authors sectioned the right and left subscapularis tendon at the insertion in 32 rabbits and wrapped the torn tendon with a 10-mm-long silicone Penrose drain with an 8-mm outer diameter to inhibit adhesion to the surrounding soft tissue. There four study groups: (1) repair + stem cells, (2) repair + saline, (3) stem cells without repair, and (4) saline without repair. Repair was carried out using two suture anchors. The adipose derived stem cells had been previously cultured and were injected into the subscapularis muscle adjacent to the musculotendinous junction area. A fifth group of 8 rabbits served as normal controls. In each rabbit both shoulders were tested electromyographically, one side was additionally tested biomechanically and the other examined histologically.
At six weeks after surgery the animals were investigated.
The unprepared tendons (groups 3 and 4) did not heal.
On electromyographic evaluation, the stem cell +repair group exhibited a significantly larger compound muscle action potential area than the saline+repair group, achieving values almost at the level of the control group.
Comment: this is a nicely controlled animal study. Importantly, the authors investigated delayed repair in contrast to many prior studies that investigated only immediate repair after tendon sectioning. The authors were very forthcoming about he possible limitations of the study:
On electromyographic evaluation, the stem cell +repair group exhibited a significantly larger compound muscle action potential area than the saline+repair group, achieving values almost at the level of the control group.
The load-to-failure of the stem cell+repair group insignificantly higher than that of the saline+repair group.
The mean proportion of fatty infiltration in the subscapularis muscles was lower for the stem cell + repair group was lower than that of the other experimental groups.
Comment: this is a nicely controlled animal study. Importantly, the authors investigated delayed repair in contrast to many prior studies that investigated only immediate repair after tendon sectioning. The authors were very forthcoming about he possible limitations of the study:
(1) most human cuff repairs are performed more than 6 weeks after the tear; chronic rotator cuff tears typically develop slowly over a long period of time.
(2) the amount of fatty infiltration at the time of repair was not assessed.
(3) the histologic evaluation of tendon-to-bone healing was not evaluated.
(4) the level of fatty infiltration was only evaluated in a single section of muscle by histologic evaluation.
(5) muscle stimulation and contraction on EMG testing may not represent the functional aspects of the repaired muscle.
(6) the injected stem cells were not tracked and the molecular pathways involved in muscle regeneration were not explored.
Nevertheless, this study should stimulate investigation of the optimal dose, timing and longer term effects of stem cell injection prior to clinical application.
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