Sentient arm film

I may have some of the details wrong… but roughly…

– Language: English
– I would guess it is from the 1990s.
– The main character is a (geeky/nerdy) younger man, with a (possibly mute) younger woman love interest, and the antagonist is his mother. All of European descent.
– The only other characters I can recall are the mother had a boyfriend (also of European descent), and the main character most commonly was seen speaking to an older man of African descent (his friend?).
– The main character had lost his arm at some point, and it was replaced with a new one. This arm was cloned (?) from a serial killer, was capable of moving on it own, could attach or de-attach from the man, and was aggressive.
– It may have taken place partly underground… possibly in a mine.
– It ended quite unhappily, with the mother “winning,” and seeming to take over the son’s girlfriend’s body with the use of some sort of giant blender… or at least a see-through object large enough to hold a human.

It seemed to be a made-for-TV film. The most notable characteristic of the film was it contained a sentient arm which could move by itself, and attach/de-attach from its host.

Any possible leads would be appreciated.