Myectomy and tenectomy are similar surgeries, and most veterinarians opt to perform them in a clean stall rather than a surgical facility.
Susan Holcombe, V.M.D., Ph.D., a researcher at Michigan State University who specializes in displacement of the soft palate, explained the differences in these three surgeries.
"A myectomy is a cutting of the two [strap] muscles to change the position of the larynx in the airway," Holcombe said. "Exactly what it does for horses with soft-palate displacement isn't known. The theory is that it prevents a backward traction on the larynx that might effectively be pulling the epiglottis off the soft palate. By transecting those muscles, that tension is released. It's a surgery that really doesn't have a proven efficacy; it doesn't have a known effect, although some people do feel it helps horses that have this problem.
"A myectomy doesn't seem to have any adverse side effects at rest, but there have been some experiments that show that transecting these muscles in normal horses actually was detrimental to their upper airway tract.
"The tenectomy is functionally quite similar to a myectomy. The myectomy transects the strap muscle; the tenectomy is done where the tendon inserts on the thyroid cartilage. That tendon is resected and a small bit of muscle is removed.
"There is a procedure that is a trimming of the [rear] margin of the soft palate that is referred to as a staphylectomy. Once again, there really is no known efficacy for that surgical procedure."
I obviously haven't done a formal study but I can say I will never do another myectomy again. Jump straight to the Llewellyn then if necessary go to the tie forward. None of the procedures seem to "work" for very long. Its a matter of months at best. The last horse I had that displaced won the MSW first time out after the Llewellyn and the 1x the second time out after the tie forward then ran last for NW3 for 5k a few months later and was retired.
I had (have) a neat horse I got who had (has) displacement at exercise. Got the tenectomy, with great success. Won his first (hurdle) start (he'd won 10 on the flat) but, it didn't take 4 weeks and it was back to where we'd started. (My vet told me it looked like he'd had a standard tie back earlier in his career at some point.)
He was a moderate racehorse so I stopped with the operations. He's a kick ass foxhunter/everythign else, but he still makes a noise - sometimes. I'm sure the tenectomy works - permanently, sometimes, but - one more vote for 'didn't work for me.'