"Do you guys remember when I told you about my spine…

“Week” sounds like “weak.” A double pun is sometimes made, with “a week back” (time) for “a weak back” (a bad spine). The “weak back”/“week back” joke appeared in The Three Stooges film Uncivil Warriors (1935).

“I went to the doctors yesterday complaining of a sore spine. He asked me when i first felt any pain. I told him about a week back” was posted on Twitter by funny humour on March 30, 2010. “Do you guys remember when I told you about my spine issue? It was about a week back” was posted on Reddit—Jokes on November 13, 2019.

“What are the strongest days of the week?”/“Saturday and Sunday. The rest are weekdays” is another “week”/“weak” pun.

Wikipedia: Uncivil Warriors
Uncivil Warriors is a 1935 film directed by Del Lord and starring American slapstick comedy team The Three Stooges (Moe Howard, Larry Fine and Curly Howard). It is the eighth short film released by Columbia Pictures starring the comedians, who released 190 short films for the studio between 1934 and 1959.
(...)
Directed by Del Lord
Produced by Jules White
Written by Felix Adler

IMDb (The Internet Movie Database)
Uncivil Warriors (1935)
Quotes
Maj. ‘Bloodhound’ Filbert: Have long have you had a weak back?
Operator 12: Oh, about a week back!

Google Groups: alt.comedy.slapstick.3-stooges
Great One-Liners
J andrew Smith
4/19/96
(...)
9) Larry (as Major Dodge): “...I’ve got a weak back.”
Southern army officer: “How long have you had a weak back?”
Larry: “Oh, about a week back!”

14 January 2005, The Times (Shreveport, LA), “Back to the future” by Teddy Allen, pg. B1:
So far, the only thing we’ve had to cheer us is my favorite bad back joke.

“How long you had a weak back?”

“Oh, about a week back.”

Twitter
funny humour
@funnyhumour
I went to the doctors yesterday complaining of a sore spine
He asked me when i first felt any pain
I told him about a week back
2:41 AM · Mar 30, 2010·Twitter Web Client

YouTube
The Three Stooges - Weak Back / Week Back
Mar 19, 2011
Mrsilenciobackgammon
Absolute classic Stooges bit from ‘Uncivil Warriors (1935)’.

Twitter
Bob Kostic
@causticbob
I went to the doctors yesterday complaining of a sore spine. He asked me when i first felt any pain. I told him about a week back
4:56 PM · Jun 3, 2012·TweetDeck

Twitter
Dr. Leanne Warner
@Warner_Chiro
#FunnyFriday: I went to the doctor yesterday complaining of a sore spine. He asked when I first felt any pain, I told him about a week back!
8:01 PM · Aug 7, 2015·Posting Platform

26 March 2016, Sudbury (ON) Star, “New meaning for BLT; It stands for no bending, lifting or twisting after spine surgery” by Bonnie Kogos, pg. C3:
Nancy said, “As soon as I told John, our friend, about my upcoming surgery, he had to say, ‘Did you know that I have a weak back? Guess when I got it?’” Being polite, Nancy asked, “When?” “About a week back.” Jokes kept coming: ...

Twitter
Layton Health
@Healthwell_UT
I went to the doctors yesterday complaining of a sore spine. He asked me when I first felt any pain and I told him, “about a week back!”
9:56 AM · Aug 16, 2016·Posting Platform

Twitter
Jah
@JahDMan
I had a weak back, about a week back… still do actually ☹️ (at
@BackFitHealth
+ Spine in Chandler, AZ) https://swarmapp.com/c/0tibOO21shm
1:30 PM · Apr 1, 2017 from Chandler, AZ·Foursquare

Reddit—Jokes
Posted by u/OCDGrammarNazi June 8, 2019
I am surprised I didn’t get any upvotes on the joke about a spine that I posted recently.
It was about a week back.

Reddit—Jokes
Posted by u/B-man44 October 31, 2019
Do you remember the joke I told you about the piano movers spine?
It was about a week back

Reddit—Jokes
Posted by u/hamsteraaaaaah November 13, 2019
Do you guys remember when I told you about my spine issue?
It was about a week back.