It depends on what state you're in. I'm a work comp lawyer in IL, but this IS NOT legal advice - every case is different. Anyway, if you're in IL, there's a good chance it is work-related. Probably true in most other states, too. It'll be disputed regardless of what state you're in. Just get a comp lawyer with a good reputation (NOT a high-volume firm that just does a ton of advertising), and you'll be good.
In IL anyway, if your repetitive job duties are considered to be "a causative factor" (as opposed to THE cause or even a primary cause - a cause is enough) in accelerating or exacerbating your osteoarthritis, it's work-related. UPS will fight it, but you'll probably win. Obtain a "formal job description" from your union steward or business agent, bring the formal job description to your orthopedic surgeon, tell him how many years you've been working for UPS, and ask if he thinks that your repetitive duties at UPS over X number of years was a contributing factor in exacerbating or accelerating your condition. If he says yes, he'll need to include his opinion in his written medical report and also mention that he reviewed a copy of your job description.
Good luck!!!
