New research suggests that underloading of the superolateral cortex leads to atrophic thinning with age, setting the stage for hip fracture during sideways falls.
However, targeted exercises that involve extension at the hip of the flexed femur under load, including cycling, sculling (rowing), gymnastics, and weights, may prevent such thinning, according to a just released study in The Lancet.1 Currently, walking is the main exercise for older individuals at risk of fracture, but it does not result in transmission of sufficient mechanical load to this region.
"As women age, hip fragility increases because underloading of the superolateral cortex leads to atrophic thinning,"conclude researchers led by Jonathan Reeve, DM, of the department of medicine at Addenbrooke's Hospital in Cambridge, UK. "Because walking does not sufficiently load the upper femoral neck, the fragile zones in healthy bones may need strengthening, for example, with more well targeted exercise."
To draw these conclusions, researchers used a special purpose computed tomography scanner to create 3-dimensional reconstructions of the mid-femoral neck of 77 proximal femurs from people who died suddenly at ages 20 to 95.
Specifically, female cortical thickness declined by 6.4% per decade and critical stress declined by 13.2% per decade in the superoposterior octant most compressed in a sideways fall. Similar, but smaller effects were seen among men, they report. This thinning compromises the capacity of the femur to absorb energy - independently of osteoporosis.
As the exponential increase in hip-fracture risk cannot be fully explained by loss of bone mineral density in the proximal femur, "these findings could profitably redirect the search for the real cause of the steep increase in hip fragility with age," Dr. Reeve and his colleagues point out. The new study's main strength is in detailing "how substantial the effect of superolateral cortical thinning and associated loss of elastic stability is, and in showing the need, apparently unmet, either for increased local curvature or for the preservation of the stout trabecular connections in this region of femoral cortex."
Importantly, "previously unrealized opportunities now exist for devising testable interventions to strengthen the aging hip," Dr. Reeve says.
Challenge is how to maintain bone in this region
The study authors "made a very good case that bone loss is not uniform throughout the hip," Charles H. Turner, PhD, professor of biomedical engineering at Purdue University in Indianapolis, observes in an editorial accompanying the new study.2 "People are losing bone in a place that they need bone to protect from fractures," Dr. Turner tells CIAOMed.
The study identifies a need for a more focused assessment of regional patterns of bone loss and the need for targeted interventions, but he notes that, as of now, "we don't know what type of exercise will be effective."
"We should learn which exercises are effective and certainly the evaluation of drugs for osteoporosis will become more sophisticated and we will look at different regions of the hip based on these new data," Dr. Turner says. "We need a better understanding of which drugs improve the regions of the hip that we think are most important for the prevention of hip fractures."
The new work "is pushing our understanding of hip fracture forward a great deal," he says.
References:
- Mayhew PM, Thomas CD, Clement JG, et al. Relation between age, femoral neck cortical stability, and hip fracture risk. Lancet. 2005; 366:129-135.
- Turner CH. The biomechanics of hip fracture. Lancet. 2005;366:98-100.