FRIDAY, May 4 (HealthDay News) -- When swaddling an infant, make sure to leave the blankets loose enough to allow leg and hip movement, experts say.

They warn that wrapping infants too tightly may cause their hip joints to develop abnormally, causing the ball of the thighbone to dislocate from the socket. The condition, called developmental dysplasia of the hip, can lead to limping, differences in limb length, pain and arthritis, according to the Pediatric Orthopaedic Society of North America.

"Many cultures, and a growing number of Americans, practice traditional swaddling -- the tight wrapping of infants with their legs together and fully extended," said orthopedic surgeon Dr. Peter Waters, president of the society, in a news release.

"Unfortunately, this practice places infants at a high risk for dysplasia," he said. "Instead, the infant's arms and torso should be snugly wrapped, while the legs are wrapped loosely, ensuring the legs are bent up and out. The legs should be free to move, and, most importantly, the legs should never be wrapped in a straight-down position."

The society joined the American Academy of Pediatrics and the International Hip Dysplasia Institute in recommending an updated method of swaddling that allows more wiggle room for infants.

Animal studies have found that forcing the hip and knee to extend right after birth increases tension in the hamstring and hip muscles, increasing the risk of loose ligaments, instability and dislocation of the thigh bone from the hip socket.

More information

The International Hip Dysplasia Institute provides more information on infant hip dysplasia.