Effects of selective paralysis of the supraspinatus muscle using botulinum neurotoxin a in rotator cuff healing in rats

Abstract

We hypothesized that a temporary rotator cuff paralysis using botulinum-neurotoxin A (BoNtA) would lead to an improved tendon-to-bone healing after repair of supraspinatus lesions. One hundred sixty Sprague-Dawley rats were randomly assigned to either the BoNtA or the control (saline) group. BoNtA/saline-solution was injected into the supraspinatus muscle 1 week prior to surgery. A supraspinatus defect was made; we distinguished between a lesion with normal and increased repair load. Furthermore, one subgroup had the operated shoulder immobilized in a cast. Histologic analysis and biomechanical testing followed. Specimens from the BoNtA-group, which were treated with an increased repair load, showed less cellularity and more organization in the interface tissue compared to the saline control group. In addition, we found that the collagen 1-3 quotient in the BoNtA specimen was significantly (p ¼ 0.0051) higher than in the control group. Ultimate load at failure between the groups was not significantly different (p > 0.05). We did not observe any significant differences between the mobilized and immobilized specimen (p ¼ 0.2079). The study shows that tendon-to-bone healing after rotator cuff repair can be altered positively using BoNtA pre-operatively. Tears with increased repair load seem to benefit the most-at least histologically. Keywords: rotator cuff tear; tendon-healing; biologic tendon repair; bioprotection; botulinum neurotoxin A Rotator cuff tears are one of the most common degenerative diseases of the upper extremity and are seen in up to 30% of the population aged older than 65 years.

Tissue characteristics in tendon-to-bone healing change after rotator cuff repair using botulinumneurotoxin A for temporary paralysis of the supraspinatus muscle in rats

“…The available studies, addressing BoNtA in tendon healing, all injected the drug intra-operatively although it unfolds its full effect after one week (19). We were already able to demonstrate that preoperative BoNtA injection can positively alter tendon-to-bone healing (18). Our hypothesis in this study was that BoNtA application to the muscle influences tissue characteristics positively and might be used as a neoadjuvant prior to rotator cuff repair.…”

“…Tissue characteristics, especially load to failure, were inferior when compared with the saline injected control group. Contrary to that observation Hettrich et al (16) and Ficklscherer et al (18) found no difference in mechanical properties but rather in collagen fiber organization.…”

“…No atrophy was seen in the saline injected group. In the group in which a lesion with increased repair load was simulated, 2 mm of the distal part of the supraspinatus tendon were resected (using a forceps with whose tip was exactly 2-mm wide) prior to tendon refixation (18,22). For tendon refixation a 5-0 double armed Prolene suture (Ethicon, Somerville, NJ) was passed through the supraspinatus tendon via a Mason-Allen stitch.…”

“…This effect of temporarily lowering the tension at the tendon-to-bone interface was tested several times in an animal model (15)(16)(17)(18).…”

The role of animal models in tendon research

“…Current research has not clearly elucidated the role of mechanical loading in the pathological shoulder joint, but also the benefits/drawbacks of post-operative immobilisation continue to be confounding. 5 Methods such as casting immobilisation, 49,55 botulinum toxin injections, 56,57 and overuse activity 51,52 have been used to alter the mechanical loads imparted upon the shoulder joint before and after surgical intervention. Results suggest that pre-operative immobilisation may have beneficial effects on long-term healing because this approach has resulted in improved cellularity and collagen organisation, while simultaneously increasing the Collagen I:Collagen III ratio, which is indicative of the end stages of tendon healing.…”