| This project was established to investigate the effects of loading on subchondral tissues in horses by clinical and histologic methods.;In the first part of this study the forelimbs of 12 horses were acquired from necropsy samples. One limb of each pair was loaded as either a whole limb or carpal joint preparation for 50,000 cycles, and the other limb served as a control. Loading force, third metacarpal bone strain and third carpal bone microdamage were compared between loading schemes. Third metacarpal bone strain in whole limbs increased throughout the 50,000 cycles, yet decreased in the carpal joint preparations. Microdamage in third carpal bones of whole limbs was greater than controls, but there was no difference between carpal joint preparations. Therefore, the resistance of the soft tissues in the whole limbs may have led to increases in third metacarpal bone strain, possibly increasing third carpal bone fatigue.;In the second part of the study, subchondral bone in the carpal and metacarpophalangeal joints of six exercised horses were compared to that of hand-walked horses by clinical imaging and histologic techniques. Treadmill exercised horses were more lame than hand-walked horses at the end of the study. Compared to hand-walked controls, treadmill exercised horses had greater uptake of radioisotope in the metacarpophalangeal joints, and higher density in the third metacarpal condyles, as demonstrated by CT Osteoabsorptiometry. Treadmill-exercised horses also had significantly more non-viable osteocytes in the subchondral bone of the radial carpal bone, the third carpal bone and the third metacarpal condyle than hand-walked horses. The radial carpal and third metacarpal bones from treadmill exercised horses had more bone in the subchondral area than those from hand-walked horses, and the third carpal bones of treadmill exercised horses had higher amounts of microdamage in the subchondral bone compared to those from hand-walked horses.;Many of the responses seen in this study may be initiating events in the response of subchondral bone to loading, but it is difficult to determine the point at which normal responses become pathologic. |
