Do Derma Rollers help with treating old scars from razor bumps?

Not recommended, but if you want to 'try' use a 0.3 to 0.5 roller, 6-8 passes in a test spot.   Scars on legs do not respond well compared to facial scars. Scar revision is a sub-specialised field. For the best results, one should target the acne scar type with ideal treatments methods. Using one device is not optimal. As everyone has a unique pattern of acne scarring, the best solution is a tailored one.  The web reference below will take you to a resource to help you understand acne scar revision at a specialist level. I embedded all the videos in one page to help.
For example deep ice pick scars, and narrow box car scars can be treated with TCA CROSS peels, mixed scars, rolling, and atrophic scars treated with fractional devices such as Fraxel, fractional lasers, INFINI –Intensif –Intracel radiofrequency. Atrophic scars (depressions) can be treated with either fat grafts, PRP or with HA dermal fillers. Tethered and anchored scars are best treated with surgical techniques such as subcision. Other surgical techniques that we use include punch elevation, surgical elevation, punch excision and traditional excision of focal scars. Early and very mild acne scars respond well to eMatrix and non-energy microneedling, as well as vascular lasers.
 

The majority of patients will have a collection of different scar types, and hence a tailored treatment METHOD will be best. Careful examination, especially under angled lighting with scar mapping will give you an understanding of what are the best options for your scars. Additionally tactile examination or touch will give us an understanding of the amount of subdermal fibrosis, as special equipment is needed for this sub-set of acne scars.  In the majority of patients its finding the correct combination that give you best results, and everyone is unique! All the best,

Dr Davin Lim. Acne scar dermatologist specialist. Brisbane, Australia.