My guinea pig has been spayed a few months ago the recently had bladder stone surgery. The vet removed the stones but

You're speaking to Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply. Please be patient. This may take a few minutes.

I'm sorry that your question wasn't answered in a timely manner. To answer you directly, mineralization of tissue only tells us that a chronic disease process in those tissues has been present. The etiopathogenesis of urolithiasis (stones) in guinea pigs is unknown but it's reasonable to assume that the etiology for stone formation is the same as for mineralization. Current thinking is that the alkaline pH and high mineral content of normal guinea pig urine may favor crystal formation and precipitation and urinary tract infections were also suggested to be associated with the presence of urinary calculi. Affected guinea pigs were more likely to be fed a diet high in overall percent pellets, low in percent hay, and a lesser variety of vegetables and fruits. Alfalfa-based pellets and hay contain higher concentrations of calcium; it has been suggested this may also contribute to urinary calculi in guinea pigs.

In general, mineralization of tissues is irreversible and likely to cause chronic clinical signs as you're currently seeing. Treatment for a urinary tract infection and X-rays looking for new stone formation should be considered at this time. Please respond with further questions or concerns if you wish.