He just needs more practice and he needs to rebuild the muscle that he has lost while he has been down. Atrophy doesn't take long to settle in, and the most critical muscle groups for swinging around an entire prosthetic leg are the ones in the lower back. Tell him to get his physical therapist to concentrate on that and get them to stretch out his groin and hip flexors and those will make walking exponentially more fluid and easier.

Microprocessor are getting better and better as a new model comes out,the biggest improvement is stability from falling,it's very hard to fall on a Microprocessor knee,cos it learns with walkkng pattern.But like all Knee joints,from Hydraulic mechanical polycentric, single axis that are cheaper and still very good to use,marjority of amputees still use Mechanical knees,the Microprocessors,all require sheer determination,body strengthening,hours of physio and alot of gait training.