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Saturday, March 13, 2004

Rotator cuff repair halts fatty infiltration in rabbits

The process of fatty infiltration into a torn rotator cuff muscle can be halted from further progression by surgical repair, according to the presenters of Scientific Paper 218.

To determine if the process of fatty infiltration that occurs following a rotator cuff tear could be reversed by surgical repair and unrestrained activity of the injured shoulder, researchers detached one supraspinatus muscle from the greater tuberosity in 15 New Zealand white rabbits. At 6 weeks after detachment, 5 rabbits were sacrificed to halt the process of fatty infiltration. The remaining 10 rabbits underwent repair of the rotator cuff tear. Following repair the rabbits were housed in open pens to allow unrestricted activity.

At 6 months post repair, the remaining 10 rabbits were sacrificed and underwent whole body perfusion. Researchers examined the muscle specimens microscopically to determine if the process of fatty infiltration reversed. Fatty infiltration was evident at 6 weeks post detachment of the supraspinatus tendon (p = 0.0012), progressing from the musculotendinous junction to the origin. The presence of fat was measured as a percent of total muscle volume. At 6 months post repair, the muscle showed no increase in the percentage of fat compared to that of the unattached muscle at 6 weeks (p = 0.3). The fatty infiltration process had stabilized after surgical repair of the rotator cuff.

"In our study, the rabbits that had repair were allowed unrestricted mobility in large pens," noted the presenters. "They were able to run about and move freely. This limited ability of the rabbits to exercise is greater than they would have been able to achieve in their individual cages. Allowing unrestricted mobility of the animal subjects could have contributed to the halting of the process of fatty infiltration that we observed."

In the rabbit model, researchers found that the process of fatty infiltration into a torn rotator cuff muscle could be halted from further progression by surgical repair. However, the process was not reversed within the 6-month period of this study. No formal rehabilitation program for muscle strengthening after the surgical repair was instigated. Whether this would have any effect on reversal of fatty infiltration is not yet known and is the focus of a follow-up study presently underway.

Researchers included Dominic Sprott, MBBS; Lynn A. Crosby, MD; Harold F. Stills, Jr, DVM, and L. Joseph Rubino, MD, all of Dayton, Ohio.

Figure 1  
Pre-reattachment housing
 
Post reattachment housing
  Prior to surgery the rabbits were housed in individual cages. Following surgery the rabbits were placed in pens, which allowed limited unrestricted activity.

Figure 2     Group 1 (detached supraspinatus muscle at 6 weeks) v/s Group 2 (reattached supraspinatus muscle at 6 months).

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