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.
Animals—5 healthy horses.
Procedure—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 and Clinical Relevance—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. (Am J Vet Res 2002;63:276–281)
Objective—To determine effects of treadmill exercise
on subchondral bone of carpal and metacarpophalangeal
joints of 2-year-old horses.
Animals—12 healthy 2-year-old horses.
Procedure—Horses were randomly assigned to the
control (n = 6) or exercised (6) groups. Horses in the
exercised group ran on a high-speed treadmill 5 d/wk
for 6 months. Horses in the control group were hand
walked for the same amount of time. Results of clinical,
radiographic, nuclear scintigraphic, and computed
tomographic examinations, and serum and synovial
concentrations of biochemical markers of bone
metabolism were compared between groups.
Results—Exercised horses were significantly lamer
at the end of the study than control horses.
Radionuclide uptake in the metacarpal condyles, but
not in the carpal joints, was greater in exercised horses,
compared with control horses. Exercised horses
also had a higher subchondral bone density in the
metacarpal condyles than control horses, but such
differences were not detected in the carpal bones.
Conclusions and Clinical Relevance—None of the
diagnostic techniques evaluated was sufficiently sensitive
to detect all osteochondral damage. Computed
tomography and computed tomographic osteoabsorptiometry
were superior to conventional radiography
for detecting small osteochondral fragments.
Nuclear scintigraphy was a sensitive indicator of subchondral
bone change but lacked specificity for
describing lesions and discerning normal bone
remodeling from damage. Newer techniques such as
computed tomography may help clinicians better
diagnose early and subtle joint lesions in horses prior
to development of gross joint damage. (Am J Vet Res