Background: Regional bone loss in patients who
have a spinal cord injury has been evaluated in males. In addition,
there have been reports on groups of patients of both genders who
had an acute or chronic complete or incomplete spinal cord injury. Regional
bone loss in females who have a complete spinal cord injury has
not been reported, to our knowledge.
Methods: In a study of thirty-one women who had
a chronic, complete spinal cord injury, we assessed bone mineral
density in relation to age, weight, and time since the injury. The
results were compared with the bone mineral density in seventeen
healthy, able-bodied women who had been age-matched by group (thirty
years old and less, thirty-one to fifty years old, and more than
fifty years old). Dual-energy x-ray absorptiometry was used to measure
the bone mineral density of the lumbar spine, hip, and knee; Z-scores
for the hip and spine were calculated.
Results: The mean bone mineral density in the spine
in the youngest, middle, and oldest spinal-cord-injury groups was
98%, 108%, and 115% of the densities
in the respective age-matched control groups (p < 0.0001),
and the mean bone mineral density in the oldest spinal-cord-injury
group was equal to that in the youngest control group. This gain
in bone mineral density in the spine was reflected by the spine
Z-scores, as the mean score in the oldest injured group averaged
more than one standard deviation above both the norm and the mean
score in the control group. The mean loss of bone mineral density
in the knee in the youngest, middle, and oldest spinal-cord-injury groups
was 38%, 41%, and 47% compared with the
densities in the corresponding control age-groups (p < 0.0001).
Furthermore, the oldest injured group had a mean reduction of knee
bone mineral density of 54% compared with the youngest
control group. The mean loss of bone mineral density in the hips
of the injured patients was 18%, 25%, and 25% compared
with the densities in the control subjects in the respective age-groups
(p < 0.0001).
Conclusions: The bone mineral density in the spine
either was maintained or was increased in relation to the time since
the injury. This finding is unlike that seen in healthy women, in
whom bone mineral density decreases with age. The bone mineral density in
the hips of the injured patients initially decreased approximately
25%; thereafter, the rate of loss was similar to that in the
control group. The bone mineral density in the knees of the injured
patients rapidly decreased 40% to 45% and then further
decreased only minimally.
Clinical Relevance: The results provide a partial
explanation of the fracture patterns seen after spinal cord injuries.
Vertebral fractures rarely occur, whereas the knee is at risk for
fracture soon after the spinal cord injury. The potential for fracture
of the hip also occurs soon after the spinal cord injury. This risk
increases with age and the amount of time since the spinal cord