Effects of high bone turnover on the biomechanical properties of the L3 vertebra in an ovine model of early stage osteoporosis.
METHODS
Investigations of the effects of high bone turnover on the L3 vertebra were carried out, using an ovariectomized (OVX) ovine model of early stage osteoporosis.


OBJECTIVE
To assess the contribution of bone turnover to the biomechanics of L3.


BACKGROUND
Clinically, dual energy x-ray absorptiometry (DEXA) is used to measure bone mineral density (BMD). However, this can only predict 60% to 70% of bone strength; the remainder is due to bone quality. There is currently little information available on how strength is affected by changes in bone quality parameters, particularly bone turnover. Turnover can be assessed clinically using biochemical markers; however, this provides systemic values, whereas localized values are required to predict site-specific fracture risk.


METHODS
Thirty-eight sheep were assigned to 2 groups (control, n = 19; OVX, n = 19). Both groups were intravenously administered a fluorochrome dye on the day of surgery and 3, 6, 9, and 12 months thereafter, to label sites of bone turnover. After 12 months, animals were killed and the spinal columns harvested. L3 vertebrae were scanned using DEXA. Bone turnover was quantified using epifluorescence microscopy, and microarchitecture was assessed by microCT scanning. Compressive testing was used to characterize the mechanical properties of the vertebrae.


RESULTS
BMD and microarchitecture were unchanged in OVX compared with controls. However, bone turnover, as measured by fluorochrome labeled sites, was significantly increased in the OVX group in cortical and trabecular compartments. As a consequence, the biomechanical properties were significantly reduced in that group.


CONCLUSIONS
These findings show that OVX resulted in changes in bone turnover, which reduced biomechanical properties in a model of early stage osteoporosis. These differences were present despite microarchitecture or BMD remaining unchanged. In the future, the ability to assess site-specific bone turnover would greatly enhance the accuracy with which fracture risk could be predicted.
Kennedy
Oran D
OD
Department of Anatomy, Royal College of Surgeons in Ireland, Dublin, Ireland. okennedy@rcsi.ie
Brennan
Orlaith
O
Mahony
Nicholas J
NJ
Rackard
Susan M
SM
O'Brien
Fergal J
FJ
Taylor
David
D
Lee
Clive T
CT
D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology; D016723:Bone Remodeling / Q000502:physiology*; D019245:Compressive Strength; D004195:Disease Models, Animal; D004548:Elasticity; D005260:Female; D005456:Fluorescent Dyes; D008159:Lumbar Vertebrae / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D010024:Osteoporosis / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D010052:Ovariectomy; D012756:Sheep
D005456:Fluorescent Dyes