Anatomy of a Fracture as a Result of Systemic Bone Loss

Our skeletons have evolved to
be able to resist most fractures but the extreme
loading associated with trauma can create sufficient stresses
and strains within bone tissue
to cause fractures. Following
the fracturing of bone, a blood clot forms
between the two broken bones. Various inflammatory mediators are released
at the site of damage, which recruits cells involved
in the repair process. Following inflammation, connective tissue
such as cartilage starts to form around
the site of the fracture, forming a bridge between
the ends of the broken bone. New blood vessels form
by the process of angiogenesis to replace the vessels
that were lost as a result of the fracture. Cells associated with these
new blood vessels are involved
in osteogenesis, or the formation
of new bone tissue. Osteoblasts rapidly
form woven bone, bridging the gap between
the two pieces of broken bone. Once the fracture has been
bridged and stabilized, remodeling occurs
in which osteoclasts, together with osteoblasts
remodel woven bone callous
to normal lamellar bone, and to gradually restore
the typical bone structure. While extreme loading
can fracture any bone, fragility fractures can occur
with less than extreme loading, because of skeletal
aging and structural decay. Vertebral collapse is often
secondary to osteoporosis and is more prevalent
in women. Loss of bone mass
can be accelerated following the onset
of the menopause, which can give rise
to osteoporosis. This loss includes early
and progressive declines in trabecular bone, which is more
metabolically active along with progressive
declines in cortical bone. Cortical bone comprises
80 percent of skeletal mass. Cortical bone loss caused
primarily by increases in cortical porosity may contribute to the increased
risk of fracture. Another common fracture site
is the hip, which is comprised of both
cortical and trabecular bone. It is thought that cortical bone may play a greater role
in trabecular bone in maintaining bone strength
at the hip. Fractures of the hip
have been associated with substantial morbidity,
mortality and healthcare costs. These events underscore
the important role of cortical and trabecular
bone in resisting fractures, and highlight the importance
of maintaining a lifestyle that helps to build
and preserve bone strength. It is also important for older
patients in particular to be aware of their
personal risk of fracture, and seek medical advice
on how best to reduce that risk.