Hi, Vil! It's good to hear from you, again!
Cheers,Let's see if we can clarify this for you, Vil!
“Sometimes, immobilisation of the back in a plaster jacket for six weeks, cures the pain, or it may take a special injection to do the trick.”
I know that “do the trick” = “bring about a desired result, succeed, yield good results, bring good results,take effect, have as a result”
Re-write your sentence and see what develops:
“Sometimes, immobilisation of the back in a plaster jacket for six weeks, cures the pain, or it may take a special injection to do the trick. ( to bring about the desired result.) To 'do the trick' in this context does not have a sexual meaning.
On the other hand, I think this expression might be interpreted in a misrepresented manner. My perverse subconsciousness put a sexual implied meaning in my brain where the term “trick” has a sexual sense.
* From a sexual perspective, the word 'trick' is slang for a prostitute's customer.
* To 'do the trick' is slang for having sex with the customer.
* Example: "The prostitute will do her tricks in a local motel.
* Example: "On average, a prostitute can turn 8 to 10 tricks per night."
Vil, you should have very little difficulty recognizing the differences between the contextual meanings of the expression 'do the trick'. If it walks like a duck, looks like a duck, and swims like a duck...it's a duck! If a doctor is providing an injection it is not a sexual act. If a prostitute is servicing customers, it is definitely a sexual act. The contextual clues should be able to help you differentiate between the meaning of the expression.