Effects of immobilization followed by remobilization on mineral density, histomorphometric features, and formation of the bones of the metacarpophalangeal joint in horses.
OBJECTIVE
To determine microradiographic appearance, bone histomorphometry, and mineral density of the long bones of the metacarpophalangeal joint in horses after immobilization followed by remobilization.


METHODS
5 healthy horses.


METHODS
One forelimb of each horse was immobilized in a fiberglass cast for 7 weeks, followed by 8 weeks of increasing exercise. Calcein and oxytetracycline were administered IV during the immobilization and exercise phases, respectively, for bone labeling and analysis after euthanasia. Sagittal sections of metacarpal bones and proximal phalanges were examined via radiography, dual energy x-ray absorptiometry, histomorphometry, and bone label analysis.


RESULTS
Radiography revealed loss of bone mineral opacity in the subarticular regions of the immobilized metacarpal bones and phalanges and subchondral lesions in metacarpal bones in 2 horses. In phalanges, a significant decrease in subarticular volumetric bone mineral density was detected. There was significantly less bone volume and calcein-labeled bone surface and more vascular volume and oxytetracycline-labeled bone surface in immobilized phalanges, compared with contralateral phalanges.


CONCLUSIONS
Eight weeks of exercise after single-limb immobilization is insufficient for recovery of volumetric bone mineral density. During immobilization and remobilization, the subchondral and trabecular bone appear to be actively remodeling.
van Harreveld
Philip D
PD
Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan 66506-5606, USA.
Lillich
James D
JD
Kawcak
Christopher E
CE
Turner
A Simon
AS
Norrdin
Robert W
RW
D015502:Absorptiometry, Photon / Q000662:veterinary; D000818:Animals; D015519:Bone Density; D001842:Bone and Bones / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006736:Horses / Q000033:anatomy & histology*; D008662:Metacarpophalangeal Joint / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008852:Microradiography / Q000662:veterinary; D010012:Osteogenesis / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012149:Restraint, Physical