Several studies have followed large groups of patients after joint replacement surgery. These studies have consistently found that the average patient will be a similar weight after having their joint arthritis addressed. In fact, some studies have shown that patients are more likely to gain weight after joint replacement surgery.
This does not mean that you cannot lose weight after joint replacement, but rather that, on average, most patients will not lose weight simply by having their joint pain addressed with joint replacement surgery.
Woodruff MJ, Stone MH "Comparison of weight changes after total hip or knee arthroplasty" J Arthroplasty. 2001;16:22–4.
Middleton1 FR, Boardman DR "Total Hip Arthroplasty Does not Aid Weight Loss" Ann R Coll Surg Engl. 2007 April; 89(3): 288–291.