Arnica Montana also known as wolf's bane, leopard's bane, mountain tobacco and mountain arnica is a homeopathic remedy that is used for medicinal purposes since the 1500's.
According to the National Library of Medicine, Arnica Montana has "been reported to possess antibacterial, antitumor, antioxidant, anti-inflammatory, antifungal and immunomodulatory activity. A wide range of chemical compounds including sesquiterpene lactones and their short-chain carbonic acid esters, flavonoids, carotenoids, essential oils, diterpenes, arnidiol, pyrrolizidine alkaloids, coumarins, phenolic acids, lignans and oligosaccharides, etc., are found in different parts of the plant" (Read more here)
Basically, it helps the body speed up its' recovery process post any kind of physical trauma. It can be used topically in a salve or cream form to help soothe rashes or skin irritations as well as taken orally in pellet form to help the body recover from any physical trauma including injury, surgery, aches, pains, arthritis, really anything.
According to another study published in the National Library of Medicine, "Arnica presents comparable activity to standard medications, such as ibuprofen and diclofenac, for pain management under different medical conditions. It also shows fewer adverse effects along with lower costs. Arnica could be an adjunct approach for acute and chronic pain management" (Read more here).
Unfortunately, if you take your dog to the vet because he or she is in pain, you will likely be prescribed with steroids or antibiotics that most likely eliminate the symptoms, but will not actually cure the root cause and carries the potential for side effects, especially if taken long term.
Trying Arnica Montana before jumping to a prescription could help your dog heal faster, at a lower price and without the risk of side effects.
Generally, Arnica Montana 200c is highly effective when used to treat acute ailments, like an injury or post surgery. Arnica Montana in lower potencies, like 6c or 30c better support chronic conditions in the body like arthritis. You can find Arnica on amazon including 200c, 30c and 6c as well as a cream few bucks each.