I have zero clue how bad your back is (however I know back injuries as I've had a lot plus 4 surgeries) so take this comment with a 'grain of salt' .

lets say your original cycle was 8 week of test prop. your now injured at week 5. but your not bed ridden or debilitated, you can probably still get an arm pump. whats it going to hurt you to go ahead and run test for a few more weeks? heck there are 80 year old men that run test and do nothing lol .. my point is, whats the harm in running some test and see how it goes. its not going to hurt you. if anything it may help you heal.
(after most my injuries and surgeries I ran gear just for the healing properties . . . think people forget thats one of the main reason AAS was invented and prescribed to people) .