JEEPGIRLTX- Just a couple of questions for you
1. Is the "malformed muscle" smaller than the other side, i.e. does it look like there has been a wasting of the muscle?
2. Is she putting weight on the leg that is showing a difference in the muscle?
I am asking these question because I went through a similar situation with my puppy at 10 months of age (she is now just over a year old). She was in doggie daycare and they called me in the middle of the day because Lola (my puppy) was favoring her right hind leg and would lift that leg when she stood still. I picked her up that afternoon and did notice that she was not putting the rear leg down much at all. After a week of her still favoring the leg, I took her in to see her vet (her daycare is affiliated with her vet's office). The vet thought it looked like she had a partially torn ACL probably secondary to a larger dog stepping on her the morning that she started to favor that leg(yikes!), and recommended that we give her pain meds and a week to see if she improved, the next week I took her back in (she was not showing any improvement) and the vet gave her more pain meds and said to give it another week, this happened one more time (i.e. 3 weeks had elapsed since the injury presented) and I noticed that the muscle on her rt rear quarter had completely atrophied and wasted away from lack of use.
Well, I decided that she needed to see a specialist asap, because I wanted to fix whatever was wrong with her, not just keep waiting to see if she would get better, because that route was obviously not working. And it was heartbreaking to see her hopping around on 3 legs.
I took her to an orthopedic surgeon at a very good local animal hospital that specializes in rare and trauma injuries. The surgeon immediately said he did not think it was her ACL (knee) at all, he thought it was more likely her hip, but they would need x-rays to be sure.
Well, the x-rays came back and she was diagnosed with Legg Calve Parthesis (avascular femoral necrosis) in layman's terms the top of her femur that goes into the hip socket had it's blood supply cut off (they think this is an inherited condition) and had died becoming weak and brittle. When the dog at daycare had stepped on her her femoral head (the top of the femur that goes into the hip socket) had collapsed which caused it to rub on her pelvis and cause pain when she put pressure on it while walking or standing. The only way to fix this was to perform a femoral head ostectomy (FHO), which basically meant they would cut off the top of the femur, and she would need to rest and then work on developing the muscles in her hind quarter to stabilize the joint.
All of the information I found on the internet said this condition is somewhat common in small dogs, and that it presents around 10 months of age.
I just thought I would throw this info out there as I had never even heard of it before Lola was diagnosed. I really hope that Daisy does not have this disorder or hip dysplasia. Good luck at the vets and make sure they take x-rays so they can give you an accurate diagnosis.