Back pain is a bitch. I have had severe back pain since turning 30. I had to give up tennis because of it. Though I can still snow ski. I have declined back fusions and other surgeries. They all result in more complicatins in time. So I have an indoor hot tub in my house here in the back sun room. I also make lots of topicals here with all my leftover buds and with any strain that I do not like or that I am not interested in smoking, as well as a variety of cold sifted hash powder. I got the original recipes from my niece but I have changed them a lot. Her recipes call for decarbing the weed, but I want more acid forms and more raw forms of active cannabinoids and terpenes and flavinoids. So I do not decarb, other than drying and curing my weed before making it into cold sifted hash using a converted ice cream machine in a chest freezer. That works great for making hashish.
I do not know about the best strains, though I have been told that Alaska Thunderfuck was the best for pain relief by several older stoners that I have come across in my time. I have tried to find a valid source of Alaska Thunderfuck beans for many years, but it seems to be a myth like Greek Kalamata, Pune Buddah or Zacatecas Purple, and is lost to time. There was apparently a fire involved and exactly where it was grown and who had the real deal remains a mystery. Some say that the real ATF is Matanuska Tundra, or Matanuska Thunderfuck. I hvae given up trying to find any of those beans. Personally I go for plants with a particular tested cannabinoid and terpene profile rather than strain name. Some terpenes are analgesic and/or psychotropic. Also you can get pure isolate forms of some terpenes and cannabinoids. Some cannabinoids and most terpenes are available in essential oil form. Some cannabinoids are hard to grow or get, as they are rare in the strains available out there.
THC, CBG and CBD and their acid forms have the most research regarding being effective in pain relief. THC is an analog to human anandamide (ananda is the Sanskrit word for bliss). THC is the main psychoactive cannabinoid, but is also an analgesic and anti-inflammatory. Growing CBD can be a challenge. I tried growing hemp strains 2 years ago, and they are early and funky compared to Marijuana strains. So I use pure CBD isolate crystals from Colorado (mail order) which is pretty scheap and 99.9% pure. CBD works best when THC is present. CBD has little binding affinity for either CB1 or CB2 receptors, but it is capable of antagonizing them in the presence of THC. So CBD alone is not so great, but with it is a better analgesi. CBD is also an anti-inflammatory without THC. CBG is the latest studied cannabinoid on the block, and has been found to be extremely effective at relieving pain and inflammation. CBG is not that common in mature cannabis though. CBGa is the master cannabinoid from which most other cannabinoids are derived from in the plant. You can buy pure CBG crystals now, but they are expensive. Similarly cannabinoids like CBC are rare and very expensive in pure form, so I grow several strains that have tested higher in CBC, like Maui Waui Cherry Bomb. CBC will not crystalize but it is available as a more or less pure oil now. CBC is known to intensify CBN and THC, and likely intensifies the effects of other cannabinoids. Some report that it is psychotropic like THC, even alone. this is likely as CBC activates the release of anandamide, which THC is an analog of. CBC has limited testing and little research, but some studies show it to be effective for pain relief in arthritis. CBC binds with the 'pain perception' receptors TRPV1 and TRPA1, which when activated, release anandamide. CBC also appears to inhibit the uptake of anandamide, allowing it to remain longer in the bloodstream. CBC combined with THC also has effective anti-inflammatory indications. See why I grow CBC strains? Now there is also CBN, the cannabinoid that THC breaks down to over time. Tests showed that about 10% of THC in weed will convert to CBN after a year on the shelf. For that reason I keep old weed and hash around. Anyway, CBN has been shown to greatly reduce migraine pain. CBN is also said to act like Valium as a muscle relaxant. 5 mg of CBN is said to be the equivalent of taking 10 mg of Valium but with few psychoactive effects. For me CBN puts me to sleep. Old weed is good for bedtime when I am jacked up. So I think that is the Big 6 when it comes to cannabinoids. The more, the better!
Terpenes are also known to be effective for pain relief. Particularly beta-caryophyllene, linalool, myrcene, limonene, and bisabolol. These can all be bought as essential oils on their own, and also occur in many Mj strains. They are also found in other plants. There are many other terpenes in Mj and other plants as well. For example, I also have a large potted Turkish Bay tree here. The culinary kind. The local Oregon Myrtle/California Bay trees are related and about twice as strong. Both can also be used for culinary purposes and for topicals. I add Bay diced leaves to some of my topical batches in rather strong form. Like 20 leaves in a batch. Use fresh leaves, old stale bay eaves in the stores are pretty sad. That can be said for a lot of this stuff, except when you want CBN. Then you need old weed.
So that may not answer your question though. I grow multiple strains every year, and so I tend to dump in a lot of different bud and hash and some other stuff into my topical salves, along with CBD isolate. The basis of my salves are a combination of oils and fats, mainly based on palm oil. Palm oil is cheap and it works well as a base. It is in a lot of skin care products. It also sets hard at room temperature, so I do not have to deal with oils which tend to drip. I also use shea butter, as it is softer and works as a good carrier of compounds to be absorbed into your skin. I also use coco butter for the smell and skin feel, and bees wax to get the right consistency of the final salve. I test the oil when it is still melted and dip and ice cube in it to test consistency. If it is too fluid, I add more bees wax to firm it up. So say 10 parts palm oil, 2 part Shea butter, 1 part coco butter, 0.2-1 part bees wax. I melt this in a pan on the stove and add crushed bay leaves, fresh or crumbled cured Mj colas, hash powder, and maybe some old weed from the back room. I may also add turmeric, ginger, cinnamon stick or several other herbs and spices. Every batch is different. Then I turn the stove off and let the plants steep, and every few hours I will re-melt the oil if it solidifies. After a few days I strain it into small baby food size jars that I get at Dollar Tree, or a mason jar. Then I smear it on my back, neck, right or left knee, and right shoulder. I have osteoarthritis. I also use it for neuropathy pain in my forearms (from having shingles).