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 injury.
Douglas E. Garland, MD; Rodney H. Adkins, PhD; Charles A. Stewart, MD; Roy Ashford, MD; Daniel Vigil, MD; Neurotrauma Division (D.E.G., R.A., and D.V.), Rehabilitation Research and Training Center on Aging with Spinal Cord Injury (D.E.G. and R.H.A.), Regional Spinal Cord Injury Care System of Southern California (D.E.G. and R.H.A.), and Department of Medical Imaging (C.A.S.), Rancho Los Amigos National Rehabilitation Center, 7601 East Imperial Highway, Downey, CA 90242