How common is end of stem pain post total hip replacement?

Depends: Cemented or non-cemented stem? Loosing of the prosthesis will cause pain at the bottom.

Stem pain: In a cemented stem the stem pain is usually due to loosening of the prosthesis. In a uncemented or press fit stem the pain is associated with micromotion of the implant which usually resolves with time. This can occur up to 10% o the time.

Not very common now: This is primarily a feature of femoral components implanted without cement. The early designs from the mid 1980s, especially the depuy aml, was stiff and produced activity-limiting thigh pain in 8%. Since then, less stiff metals have been employed (titanium is half the stiffness of cobalt-chrome) and implants with taper tips and flexible tips have been used with much improved results. Expect 2%.

Hip stem pain: Distal hip pain after tha is generally related to longer, stiffer, more cylindrical stems, especially those that do not "fit and fill" proximally.