Just to add to what gumtree said…nuc scans also only look for active bony remodeling. Some soft tissue related issues will show up this way, such as ligament problems, because there’s often strain put on the bone it connects to. However, there is an art to interpreting the results, as has been said.
For example, my horse didn’t have a very large latissimus dorsi muscle when he went in for his scan. So, some normal “noise” on some of his ribs made the resident conclude we had fractured ribs, possibly more than one. Until the head radiologist took a look and said no way and downgraded that finding by a lot. A note was put in regarding the lack of overlying muscle. This is also why some SI diagnoses are missed on bone scan (some are not)… I think it depends on the horse here. It was missed on mine, yet a friend’s horse lit up like a Christmas tree in the SI area.
There’s also an art to running the scan. The horses are in and out of the gamma camera pretty much all day long. They give them breaks, let them go pee in an area prepped for the radioactive material. It takes some time for uptake to happen throughout the body, and I think it’s possible sometimes the imaging of one area is timed wrong. But, I do agree that if you are going to go through the expense of a bone scan, just do the whole horse.
Don’t let anyone sell you on the so-called “soft tissue scan”–it’s far less reliable.
And then even if you have some places of concern on bone scan, you’ve then got to go look for actual pathology. Bone scan won’t really tell you any of that. So, if there’s something in the neck or hocks or feet or whatever, you then have to go Xray and do your typical workup.
A couple of my vets like bone scans for vague performance problems. Or behavioral changes where there is no clear lameness. But blocks can also show performance improvements…if you have an inkling of where to start blocking. I think with this horse you probably could start there, and I’d want to do blocks in hand and ridden to see if there’s a change. With the lead swapping type stuff of the causes of it can be exacerbated by a rider (SI issue is a good example of this), so say you’re blocking the hocks first or stifle, be sure to ride to make sure the problem doesn’t appear improved just because you’ve alleviated a secondary compensatory problem which is good enough to draw false conclusions on the longe.