“It is true that proper position in the sling/carrier is important for the infant’s hip, pelvis and spine growth. A carrier should not put all of a baby’s weight on a narrow band of fabric at the crotch.”
http://www.ergobabycarrier.com/ask-the-doctor/2007/10/best-way-to-transport-our-baby#more
“If the carrier positions the infant upright, with the legs hanging down and the bodyweight supported at the base of the baby’s spine (i.e. at the crotch), it puts undue stress on the spine which can adversely affect the development of the spinal curves and, in some cases, cause spondylolisthesis.”
http://www.continuum-concept.org/reading/spinalStress.html
There are more than just the bjorn typa carriers out there
-moby wrap http://www.toysrus.com/product/index.jsp?productId=3546629&fromWidget=BRU%3ACategory%3ATop+Sellers
-pouch sling http://www.toysrus.com/product/index.jsp?productId=3776829&isTopSellingItem=true
-ring sling http://www.etsy.com/search_results.php?search_type=handmade&search_query=ring+sling
-mei tai http://www.etsy.com/search_results.php?search_type=handmade&search_query=mei+tai
-ergo http://www.ergobabycarriers.com/babycarriers/category/carrier/