ulnar nerve injury- finger extension

I understand that one would lose motor function of the hypothenar muscles and lumbricals III and IV. Therefore when asking the patient to straighten their fingers their would be the characteristic ulnar claw. However, i'm having difficulty understanding why this would be the case since the extensor muscles are still fully functionally. Would there a decreased ability to straighten the fingers as opposed to total loss? Therefore the patient could slightly straighten finger III and IV but not with full extension? Thanks in advance

Authored By Khalil Ali on Sunday 5th January 2014