Hi Becky,
so sorry not to have replied sooner. I am in the middle of a lot of domestic hassle right now.
To be honest, pinpointing a specific procedure as the cause for your arachnoiditis may well be fruitless: the main thing is for you to find a way forward in managing the symptoms.
I would caution strongly against any further invasive interventions (injections) as they could possibly exacerbate the problems and in any case are highly unlikely to be effective.
Hope this helps,
Take care,
DocSarah