IN-DEPTH: THE RELATIONSHIP BETWEEN IMAGING FINDINGS AND LAMENESS


racehorses given free-choice exercise had a favorable prognosis for return to racing with similar post- injury performance to pre-injury performance.16


8. Proximal Sesamoid Bone Pathology


Medial proximal sesamoid bone (PSB) and apical PSB fractures observed in 2-year-old training sale Thor- oughbred racehorses were less likely to race and earn money.17 Removal of apical fractures in horses is associated with good return to racing and career lon- gevity, however, there is a better prognosis for hindlimb (86%) than forelimb (55%) fractures, and a poorer prognosis for medial PSB fractures (44% to 47% raced postoperatively).18,19 Size of the apical fracture fragment was not observed to affect racing progno- sis.20 Uniaxial transverse PSB fracture repaired with lag screws resulted in 5 of 8 horses without con- current degenerative joint disease returning to racing.21


9. Sesamoiditis


Evidence for significance of sesamoiditis relative to racing performance is controversial. Whereas some studies observed that enlarged vascular chan- nels with non-parallel borders adversely affected racing performance, others using different criteria for sesamoiditis found no relationship.17,22,23 The observed relationships characterized sesamoiditis as the presence of vascular channels  2 mm width and abnormal or non-parallel sides. Thirty percent (30%) of severely affected horses raced at 2 years of age and 70% at 3 years of age compared to 51% and 79% of non-affected horses racing at 2 and 3 years of age respectively. Forelimb proximal sesamoid bone enthesophyte in yearlings and medial proximal sesamoid bone frac- ture in 2-year-old in training sales were associated with a lower proportion of horses starting a race (57% affected vs 82% non-affected; 71% vs 91%, re- spectively); however, if yearling horses started in a race there were no differences in places, money earned, or money earned per start.22


10. Proximal Phalanx (P1)


The presence of a forelimb and fore- or hind-limb articular margin osteochondral fragment was asso- ciated with a lower likelihood of starting in a race (38% and 76% vs 91% without the lesion) and a lower proportion who earned money.17 Ar- throscopic removal of dorsoproximal osteochondral fragments resulted in 89% to 92% of horses racing after surgery; 71% to 87% at the same or higher level, more commonly with lower earnings.24–27 Non-displaced fractures have been treated conser- vatively with 4 of 6 returning to racing perfor- mance.28 Displaced fractures have been treated successfully with screw fixation. Short, non- displaced dorsal fractures of the proximal articular margin (most commonly of the medial eminence) treated by arthroscopic debridement resulted in 91% return to racing.29 Length of career and earnings


were not different between cases and controls al- though injured horses had fewer post-operative starts. Eleven of 21 (52%) Thoroughbred horses with a non-comminuted P1 fracture (sagittal, dorsal fron- tal, oblique, physeal, and palmar process) returned to racing performance, 65% to a higher level.28 While moderately comminuted P1 fractures in Thor- oughbreds have been successfully repaired (92% positive outcome), none reported returned to rac- ing.30 Prognosis for survival was fair for severely comminuted fractures.


11. Carpus


Radiographic visualization of lucencies in the radial facet of the third carpal bone can be indicative of incomplete fracture or articular cartilage damage (Fig. 2).31,32 Similarly, lucencies in the distal as- pect of the radial carpal bone were associated with osteochondral or cartilage fragmentation in 71 horses. Eighty percent (80%) of the 55 surgically treated horses returned to racing, 63% of these at the same or better level. Only 42% of non-surgi- cally treated horses returned to racing, 14% at the same or better level.33 A recent comprehensive study of 828 Quarter


Horse and Thoroughbred racehorse with ar- throscopic removal of osteochondral fragments in the carpus found that 82% of horses raced after surgery, with 70% performing at the same or higher level than before surgery.34 Likelihood of racing after surgery was increased if horses had raced be- fore surgery, and decreased with increasing horse age, being female, and having a severe lesion with substantive subchondral bone removed. Similar findings have been reported in other studies.35,36 Whereas most studies compare pre- and post-sur- gery racing performance of affected horses, a com- parison of the performance of horses surgically treated for carpal osteochondral fragments with un- affected control horses found better racing perfor- mance in the affected treated horses.37 Of those control horses that raced, a lower percentage of con- trol racehorses (59%) won races than affected, sur- gically treated racehorses (75%). Palmar osteochondral fragments were removed in


31 horses, many that also had dorsal fragments. Fifty-two percent (52%) returned to racing, 48% earned money, and 32% had 5 or more starts.38 Performance decreased with increasing number of palmar fragments. Similar findings were observed in a study of horses of varied disciplines, 76% re- turned to intended use.39 Yearlings with evidence of dorsal medial intercar-


pal joint disease are less likely to start in a race (63% affected vs 82% non-affected); however, for horses that started in a race there were no differences in places, money earned, or money earned per start.22 No differences in race performance of sale yearlings was associated with accessory carpal bone osteo- chondral fragmentation.40


AAEP PROCEEDINGS  Vol. 66  2020 21


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