My 16 year old horse who was training at 4th level dressage prior to his lameness has be off for 4 1/2 months.
It started in September, on a Monday he was completely sound and happy to work. My sister took him for light trail ride (literally just around a flat hayfield < 30mins nothing more than a walk) and he was fine the next day. By the Wednesday when my coach was back in the saddle IMMEDIATELY he noted that his left shoulder felt really stiff. He walked around the arena a few times and gently warmed him up, and he 'worked out' of the stiffness. The next day my horse was romping around in his field and tore his blanket. A few days later the massage therapist was at the barn to take a look at him. She noted that he seemed to be very uncomfortable in the shoulder and tight.
We gave my horse 1 week off and had our vet come out to assess him. Our vet couldn't find anything wrong and we gave him 1 more week off. He was turned out in his paddock and not stalled. At no point during these 2 weeks was he visibly lame. (not lame when handwalked or trotted)
After the 2 week break my coach was back in the saddle to see how he was doing. At this point we noticed my horse was not sound under saddle and it was only noticeable during the first few steps of trot. He was striding longer with the left front (more time in air), no bobbing of his head. It wasn't visible in the walk. It was worse going to the left (only visible in trot). He wasn't trotted in the corners or on circles (just down the long side). As the lameness was not every stride and only for a few steps when it did appear my horse 'worked out' of it after 15 minutes of a very very gentle warm-up.
We surmised that he still could use more time off and maybe he had strained a muscle is his shoulder. We had the massage therapist out again to work on his shoulder and gave him 2 more weeks off, and just handwalked him for 20mins/day.
After the other 2 week holiday (total 1 month 'rest'). We tried him under saddle again. Same problem occurred: sound when hand walked & trotted, sound when ridden in the walk and 'off' in the trot for a few strides on and off for the first 15-20mins of the warm-up. After this we had the vet out again for an evaluation. He couldn't find any ligament/tendon problems, on the hooftest he was slightly sore on the left. He did a nerve block to the left foot and my horse DID NOT improve.
We took xrays of both front feet thinking he may have osteoarthritis or that there could be something worse going on. The xrays showed moderate calcifications of the cartilage of BOTH FRONT FEET consistent with sidebone and his joints looked great. He was prescribed 20 days on a NSAID and 1 month on a vasodilator. We had bar shoes put on the same week.
Overall, he's been off for 4 months now with just handwalking for 20 mins/day. He never showed any signs of improvement on the NSAIDs (finished the prescription).
I have searched a lot electronically for information on sidebone both on the internet and equine veterinary journals and I know it's not a common cause of lameness in horses. I would LOVE to hear any ADVICE regarding management of sidebone and if you have any other thoughts based on the history you've just read.
I absolutely adore my horse and have owned him for the last 10 years. He has never had any major health problems. I really want to do what is best for him and am fully willing to acknowledge that might mean he never goes back to work and no more flying changes. But right now we just can't make him happy.