How to fix skin adhesions in neck after platysmaplasty?

Hello, It would be very helpful if you posted a photo of your problem.  If the scar tissue (dermal adhesion sites) are not very extensive, there may be another technique to correct the area without making the submental incision.  By first injecting dilute local anesthetic into the scar band, subcision can be performed to free the dermis up from the underlying muscle and fat can then be grafted into the region.  It may require more than one treatment.  The larger the scarred area is, the less effective this technique will be.  If the area of concern is a fair distance away from the submental incision site, sometimes a small incision on the neck, next to the scarred area is reasonable to gain access to the area in order to correct the problem.  A well placed incision on the neck with meticulous closure will typically heal nicely given enough time and care.  

Without photo, it's impossible to know what you're precisely asking.  Do give some thought though to the reality that if something needs to be fixed, the surgeon has to somehow "get to" where the fix needs to be done.  To get there, one needs an incision.  The closest place to make a hidden incision is under the chin.