Knots are part of the massage lexicon, they are little swollen, hard tender bits of muscle and are thought to occur when there is injury, possibly in response to increased calcium in the area causing localised bunching of muscle fibres with an inflammatory response. Except sometimes...
It's a rib! - ribs 2-10 start at the spine and wrap around to form your ribcage before joining your sternum at the front. These ribs start out pointing backwards and to the side and then after approximately an inch there is a sharpish corner, after which they point to the side and even a little forward. This corner is called a rib angle and at this point the rib has a joint with the transverse process of the vertebra. If the vertebra is twisted to one side then that costotransverse joint will be prominent on that side, or if the joint isn't functioning properly the rib may sit a little out of line, or indeed there may be inflammation that can be palpated, all of these will feel like a 'knot' between the spine and the shoulder blade and they will be covered with muscle that may be sore, because it is being permanently stretched over a lump.
When it's an inflamed facet joint! In the neck, the little joints on the back of the spine can be felt...and when they are inflammed the soft tissues of the joint swell...and make a lump...that feels like a knot
All in all, whilst knots may appear over joints, the chances are that if there is a lump localised over a joint it is related to that rather than the overlying muscle. working on the muscle over the joint may release the joint and resolve the issue but...the issue was not a knot!