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 evaluate clinical effects of immobilization
followed by remobilization and exercise on the
metacarpophalangeal joint (MPJ) in horses.
Animals—5 healthy horses.
Procedure—After lameness, radiographic, and force
plate examinations to determine musculoskeletal
health, 1 forelimb of each horse was immobilized in a
fiberglass cast for 7 weeks, followed by cast removal
and increasing amounts of exercise, beginning with
hand-walking and ending with treadmill exercise.
Lameness examination, arthrocentesis of both MPJ,
single-emulsion radiographic examination, nuclear
scintigraphic examination, ground-reaction force-plate
analysis, and computed tomographic examination
were done at various times during the study.
Results—All horses were lame in the immobilized
MPJ after cast removal; lameness improved slightly
with exercise. Force plate analysis revealed a significant
difference in peak forces between immobilized
and contralateral limbs 2 weeks after cast removal.
Range of motion of the immobilized MPJ was significantly
decreased, and joint circumference was significantly
increased, compared with baseline values,
during the exercise period. Osteopenia was subjectively
detected in the immobilized limbs. Significant
increase in the uptake of radionucleotide within
bones of the immobilized MPJ after cast removal and
at the end of the study were detected. Loss of mineral
opacity, increased vascular channels in the subchondral
bone, and thickening within the soft tissues
of the immobilized MPJ were detected.
Conclusions and Clinical Relevance—Results indicate
that 8 weeks of enforced exercise after 7 weeks
of joint immobilization did not restore joint function or
values for various joint measurements determined
prior to immobilization. (Am J Vet Res 2002;63:282–288)