Long story short, DH went in for easy gall bladder surgery. One night turned into 12 and two hospitals. He is now using a walker. He is home and we have home visit from nurses and PT. PT recommended putting tennis balls on the walker. We had a few old ones lying around, so I used them. A week later with only a trip to Walmart and church (all other walking inside house), they are worn thru. Is this common. Is it just that the ones we had, were already old? If things process as we hope, I see using walker for a month or two. If plan B comes into play, 3 or 4 months of use. Should I buy a gross of tennis balls?