Over the past two decades, the number of Americans having total hip replacements has more than doubled, to more than 300,000 a year. Though most patients eventually walk again without pain or the aid of a cane, recovery and rehabilitation can be rigorous, painful and lengthy. The surgery is extensive: As its name suggests, it involves removing the joint — the damaged bone and cartilage — and replacing it with prosthetic parts made of metal, plastic or ceramics. Typically, surgeons enter the joint from the rear, which requires cutting through muscle and cartilage. But with a relatively new procedure, surgeons enter from the front and only stretch the muscles aside, avoiding the cutting and minimizing pain and recovery time. According to those who use this anterior technique, the benefits are substantial.