In an unusual twist, many survivors of the San Francisco airline crash on Saturday are experiencing a surprising pattern of spine injuries.

Thus far, two survivors cannot move their legs and may remain in a permanent state of paraplegia, while several others have recovered from surgery to stabilize their spines to allow movement, Dr. Geoffrey Manley, neurosurgery chief at San Francisco General Hospital, told reporters.

Some of the patients experienced crushed vertebrae compressing the spinal cord, and damaged ligaments incapable of holding the neck and back in place, stretched and torn in the crash, Manley said on Monday.

Although 305 of the 307 passengers survived and 180 were taken to the hospital with injuries, only a handful were critically injured — reflecting improvements in airline safety from previous years. However, the pattern of spinal injuries emerging from this crash troubles medical experts. The pattern among those who suffered only minor spinal trauma mirrors injuries suffered by car accident victims before the government required shoulder straps as part of the safety belt.

In the plane crash, the upper bodies of survivors were flung forward — their midsections strapped to their seats by lap belts — and then violently flung backward. However, the kinetics of a plane crash may not be totally analogous to those of an automobile crash.

"If you put in the shoulder belt, it might just move the injuries up further," said Manley. "Your head weighs a tremendous amount."

The airline industry has thus far resisted calls for three-point shoulder safety belts on seats, arguing the redesign would compromise comfort and raise ticket prices. However, experts such as Dr. David Okonkwo of the University of Pittsburgh Medical Center say the recommended head-down "crash position" may provide protection for crash survivors, limiting the back-and-forth motion resulting in spinal trauma.

It is unclear whether survivors of Saturday's crash had enough time to assume the crash position, given the suddenness of the crash as the pilot attempted to abort the landing less than two seconds before impact.