The use of radiograph repositories has long been included as standard practice as part of the sale process for Thoroughbred yearlings intended for racing.1,2 As such, multiple studies3–6 have been performed with the objective of examining the clinical importance of presale radiographic findings in Thoroughbreds. Repository radiographic findings must be interpreted with consideration of the various breeds and athletic disciplines involved.7 The Western performance horse industry has notably grown in recent years, and articles8,9 have been published describing the results of prepurchase examinations of Western performance horses. Radiographic abnormalities and characteristics of conditions causing lameness have been reported for horses competing in barrel racing10 and roping competitions.11 Western performance horses are typically Quarter Horses, and the individual competitive disciplines have different athletic demands, which may play a role in the clinical importance of various repository radiographic findings.9,12
With this focus on specific competitive disciplines in mind, our research group recently published a study13 evaluating the prevalence of radiographic lesions on repository radiographs of 458 yearling and 2-year-old Quarter Horses competing in cutting events. The findings of that study were the foundation for the present study, with the objective of the study reported here being to investigate potential associations between repository radiographic findings and subsequent performance of Quarter Horses competing in cutting events. Our aim was to obtain objective data to guide veterinarians and buyers in determining the potential clinical importance of various radiographic lesions identified at the time of sale. We hypothesized that many mild radiographic lesions would not be associated with reduced performance, whereas more severe lesions would be more likely to be clinically important. In particular, we hypothesized that severe lesions of the medial femoral condyle and severe lesions of the distal tarsal joints would be associated with a decreased likelihood of competing and, for horses that did compete, with lower mean earnings.
Materials and Methods
Case selection criteria
Repository radiographs were obtained from the Western Bloodstock radiograph repository for horses offered at NCHA sales held between December 2005 and December 2006 and from a privately owned cutting horse ranch, as previously described.13 For study inclusion, horses were required to have a complete radiographic study available for review. For this purpose, a complete radiographic study was defined as a minimum of 22 images of the following 10 joints: lateromedial and dorsopalmar or dorsoplantar views of the left and right metacarpophalangeal and left and right metatarsophalangeal joints (including the phalanges); flexed lateral views of the left and right carpal joints; lateromedial, dorsoplantar, dorsolateral-plantaromedial oblique, and dorsomedial-plantarolateral oblique views of the left and right tarsal joints; and caudocranial and caudal 30° lateral-craniomedial oblique views of the left and right stifle joints.
Performance data
Performance data were obtained through review of performance records from the NCHA database and through the use of mailed questionnaires and telephone calls to owners. Outcome parameters were as follows: Did the horse compete in a cutting competition (yes or no)? Did the horse earn money in a cutting competition (yes or no)? If so, how much? If the horse did not compete, why not? All earnings data were calculated from records provided by the NCHA, and the amount of money earned in the horse's third and fourth years was recorded. In no case did the researchers communicate the radiographic findings with the owners; however, because these were sale radiographs, some owners were aware of the findings as described by their veterinarian or agent.
Analysis of repository radiographs
Radiographs stored in DICOM format were reviewed on a dedicated workstation with a medical-grade monitor by an experienced board-certified radiologist (RDP) and a veterinary student (EKC). Images were graded by consensus, and if there was a discrepancy, the radiologist's score was used. If a radiographic change could not be confidently identified or was determined to be a potential artifact, it was not recorded as a lesion. After an initial screening for identification of all radiographic abnormalities,13 7 radiographic findings were identified for inclusion in statistical analyses.
Lesions of the stifle joint—Abnormalities affecting the medial femoral condyle were analyzed on the caudocranial and caudolateral-craniomedial oblique views. The grading system used to describe the medial femoral condyle was as follows: grade 0 = normal appearance of the medial femoral condyle; grade 1 = flattened contour of the medial femoral condyle but no radiographic evidence of changes in the subchondral bone; grade 2 = subchondral bone sclerosis, defects in the subchondral bone that did not extend all the way through the deep portion of the subchondral bone plate, or both; grade 3 = defects that extended through the subchondral bone, such as wide, shallow subchondral lucencies; and grade 4 = a well-defined, round or oval radiolucent area in the middle of the medial femoral condyle that extended to and communicated with the femorotibial joint (Figure 1).13
Representative caudocranial repository radiographic images of the stifle joint included in a study evaluating possible associations between repository radiographic findings and performance outcome for Quarter Horses (n = 343) competing in cutting events. These images illustrate the grading scheme for evaluation of the medial femoral condyle. A—A flattened contour of the medial femoral condyle is present but without any evidence of changes to the subchondral bone (grade 1). B—Notice the mild subchondral bone sclerosis and a subtle shallow defect in the subchondral bone that does not extend all the way through the deep portion of the subchondral bone plate (grade 2). C—A shallow concave defect that extends through the subchondral bone is evident (grade 3). D—A well-defined, round radiolucent cyst-like lesion is present in the trabecular subchondral bone of the medial femoral condyle (grade 4).
Citation: Journal of the American Veterinary Medical Association 252, 1; 10.2460/javma.252.1.108
Lesions of the tarsal joint—The lateromedial, dorsoplantar, dorsolateral-plantaromedial oblique, and dorsomedial-plantarolateral oblique views of the tarsal joints were examined for radiographic evidence of osteophytes, subchondral lysis, and sclerosis of the distal portions of the tarsal joint and for malformation of the central and third tarsal bones. The presence of osteophytes was graded from 0 to 4, corresponding to none, very small, small, medium, and large (Figure 2). Subchondral lysis was also graded on a scale of 0 to 4, ranging from none to severe. The severity of lysis was evaluated on the basis of both the extensiveness of the lysis and the depth of the subchondral bone affected. Sclerosis was graded from 0 to 3, ranging from none to severe, with severe designated as increased bone density affecting > 50% of the bone. Malformation was defined as an abnormal wedge shape or crushing and graded on a scale from 0 to 2, with 0 representing no evidence of malformation, 1 representing mild dorsal wedging, and 2 representing unequivocal severe asymmetry in the proximal-distal diameter of the bone or central crushing (Figure 3).
Representative repository radiographic images of the tarsal joint for the study in Figure 1. These images illustrate the grading scheme for osteophytosis of the distal aspect of the tarsal joint. A—On a dorsoplantar image, a very small osteophyte (arrow) can be seen extending from the lateral aspect of the central tarsal bone across the centrodistal tarsal joint (grade 1). B—On a lateromedial image, a small osteophyte (arrow) is evident at the proximodorsal aspect of the third metatarsal bone associated with the tarsometatarsal joint (grade 2). C—On a dorsoplantar image, a medium-sized osteophyte (arrow) is present at the distomedial aspect of the central tarsal bone extending into the centrodistal tarsal joint (grade 3). D—On a dorsolateral-plantaromedial oblique image, a large osteophyte (arrow) can be seen on the proximodorsal aspect of the third metatarsal bone associated with the tarsometatarsal joint (grade 4). (Adapted from Contino EK, Park RD, McIlwraith CW. Prevalence of radiographical changes in yearling and two-year-old Quarter Horses. Equine Vet J 2012;44:185–195. Reprinted with permission.).
Citation: Journal of the American Veterinary Medical Association 252, 1; 10.2460/javma.252.1.108
Dorsolateral-plantaromedial oblique radiographic image of the tarsal joint for the study in Figure 1. Notice the grade 2 malformation of the third tarsal bone characterized by dorsal wedging, grade 3 sclerosis of the central and third tarsal bones, grade 3 subchondral lysis of the centrodistal joint, and grade 4 osteophyte formation.
Citation: Journal of the American Veterinary Medical Association 252, 1; 10.2460/javma.252.1.108
Lesions of the proximal interphalangeal (pastern) joint—Evaluation of the pastern region was included in evaluation of the metacarpophalangeal and metatarsophalangeal joints. Thickening of the dorsoproximal cortex of the middle phalanx of the hind limb was graded as absent (grade 0), mild (grade 1), moderate (grade 2), or severe (grade 3). If the dorsal border was irregular, a minimum of grade 2 was applied. Osteophytosis of the dorsoproximal aspect of the hind limb middle phalanx was graded as 1 (present) or 0 (absent; Figure 4).
Lateromedial image of the proximal interphalangeal joint for the study in Figure 1. An osteophyte is present on the dorsoproximal aspect of the middle phalanx, without any other radiographic evidence of joint disease.
Citation: Journal of the American Veterinary Medical Association 252, 1; 10.2460/javma.252.1.108
Statistical analysis
Data were analyzed with statistical software.a Data for the right and left limbs were combined for analysis. For bilateral lesions, if grades differed between limbs, the higher grade was used. Initial screening evaluated a set of 30 previously reported radiographic findings.13 A forward selectionb procedure for both categorical and continuous variables was performed with a cutoff value of P < 0.05. This analysis resulted in identification of a subset of 7 radiographic lesions of interest that were considered for final analyses.
For binary outcome variables, logistic regression was performed.c The binary outcome variables (yes vs no) consisted of whether the horse was known to have competed and whether the horse earned money as a 3-year-old, as a 4-year-old, or as a 3-and 4-year-old combined. For analysis of continuous outcome variables (the amount of money earned as a 3-year-old, the amount of money earned as a 4-year-old, and the amount of money earned as a 3- and 4-year-old combined), only data for horses that had actually earned money were used. Dollar values were log transformed to normalize the data distribution, and a general linear modeld was fit to compare least squares mean earnings among horses grouped on the basis of radiographic findings. Values of P < 0.05 were considered significant.
A power analysis was performed to determine the power for detecting a 15% difference in outcome parameters with a 2-tailed test and α value of 0.05.14 The Hosmer-Lemeshow goodness-of-fit test was performed, and there was no evidence of lack of fit. The likelihood ratio test of full versus intercept-only models was performed for logistic regression analyses and was significant for all models, with P < 0.05 in all cases. Values for coefficients of variation (r2) for the linear regression analyses and Nagelkerke r2 values for the logistic regression analyses were calculated. Only r2 values for significant findings are reported.
Results
Of 458 eligible horses, 343 had complete radiographic studies available for review and were included in the study. For 27 of these horses, radiographs were obtained from the privately owned cutting horse ranch.
Earnings data were available from the NCHA database for 178 of the 343 (52%) horses included in the study. Horses for which earnings data were not available either did not compete or competed but did not earn any money. Therefore, for all horses for which earnings data were not available, an attempt was made to determine whether the horse had or had not competed through the use of a mailed questionnaire or telephone calls to the owner.
Reasons for not competing
Information on whether the horse did or did not compete was available for 103 of the 165 (62%) horses for which earnings data were not available. Of these 103 horses, 29 (28%) competed but did not earn money and 74 (72%) did not compete. For horses that did not compete, lameness diagnosed by a veterinarian was the most commonly reported reason (n = 16 [22%]). Lameness referable to the stifle region was reported in 2 of the 16 horses, 1 of which had radiographically normal stifle joints and 1 of which had bilateral grade 3 medial femoral condyle lesions. Lameness affecting both the tarsal and stifle joints was reported in 1 horse that radiographically had mild osteophytosis of the distal tarsal joints and radiographically normal stifle joints. Lameness affecting the tarsal joints only was reported in 2 horses, 1 of which had radiographically normal tarsal joints and 1 of which had mild osteophytosis of the distal tarsal joints. Four horses had lameness attributable to suspensory ligament injuries. Other reported reasons that horses did not compete included that they were used for other disciplines, had insufficient talent, had medical restrictions unrelated to lameness, and were still in training.
Radiographic findings associated with performance outcome
Analysis of the likelihood (yes vs no) that horses would compete included data only for the 281 horses that were definitively known to have (n = 207) or to have not (74) competed (Table 1). Analyses of the likelihood (yes vs no) that horses earned money as a 3-year-old, as a 4-year-old, or as a 3- and 4-year-old combined were performed with data for all 343 horses included in the study (Table 2). Analyses of the amount of money earned as a 3-year-old, as a 4-year-old, and as a 3- and 4-year-old combined were performed with data for the 178 horses for which earnings data were available.
Repository radiographic findings for 281 Quarter Horses that subsequently did (n = 207 [74%]) or did not (74 [26%]) compete in cutting events.
| Radiographic finding and score | Competed | Did not compete |
|---|---|---|
| Medial femoral condyle | ||
| Grade 0 | 119 (75) | 39 (25) |
| Grade 1 | 44 (75) | 15 (25) |
| Grade 2 | 22 (79) | 6 (21) |
| Grade 3 | 13 (68) | 6 (32) |
| Grade 4 | 9 (53) | 8 (47) |
| Tarsal joint Osteophytes | ||
| Grade 0 | 121 (79) | 32 (21) |
| Grade 1 | 35 (74) | 12 (26) |
| Grade 2 | 33 (59) | 23 (41) |
| Grade 3 | 12 (67) | 6 (33) |
| Grade 4 | 6 (86) | 1 (14) |
| Subchondral lysis | ||
| Grade 0 | 171 (75) | 58 (25) |
| Grade 1 | 13 (72) | 5 (28) |
| Grade 2 | 18 (64) | 9 (36) |
| Grade 3 | 5 (71) | 2 (29) |
| Grade 4 | 0 (0) | 0 (0) |
| Sclerosis | ||
| Grade 0 | 197 (74) | 68 (26) |
| Grade 1 | 9 (64) | 5 (36) |
| Grade 2 | 0 (0) | 1 (100) |
| Grade 3 | 1 (100) | 0 (0) |
| Malformation | ||
| Grade 0 | 195 (74) | 67 (26) |
| Grade 1 | 10 (59) | 7 (41) |
| Grade 2 | 2 (100) | 0 (0) |
| Middle phalanx of hind limb Thickening of dorsoproximal cortex | ||
| Grade 0 | 174 (72) | 67 (28) |
| Grade 1 | 26 (84) | 5 (16) |
| Grade 2 | 6 (100) | 0 (0) |
| Grade 3 | 1 (33) | 2 (67) |
| Osteophytes | ||
| Grade 0 | 178 (74) | 63 (26) |
| Grade 1 | 29 (73) | 11 (27) |
See text for description of grading schemes.
Association between repository radiographic findings and performance outcome for 343 Quarter Horses competing in cutting events.
| No. (%) of horses that earned money | Mean earnings ($) for horses that earned money (n = 178) | ||||||
|---|---|---|---|---|---|---|---|
| Radiographic finding and score | No. of horses | As a 3-year-old | As a 4-year-old | As both a 3-and 4-year-old | As a 3-year-old | As a 4-year-old | As both a 3-and 4-year-old |
| Medial femoral condyle | |||||||
| Grade 0 | 196 | 44 (22) | 96 (49) | 36 (18) | 10,355 | 17,378 | 20,423 |
| Grade 1 | 71 | 20 (28) | 36 (50) | 17 (24) | 12,473 | 14,234 | 19,536 |
| Grade 2 | 35 | 5 (14) | 13 (37) | 2 (6) | 3,711 | 4,216 | 4,586 |
| Grade 3 | 23 | 3 (13) | 9 (39) | 3 (13) | 12,867 | 9,513 | 13,802 |
| Grade 4 | 18 | 4 (22) | 9 (50) | 4 (22) | 11,048 | 6,112 | 11,022 |
| Tarsal joint Osteophytes | |||||||
| Grade 0 | 186 | 45 (24) | 102 (55) | 38 (20) | 11,249 | 17,861 | 21,358 |
| Grade 1 | 60 | 17 (28) | 24 (40)* | 12 (20) | 11,622 | 7,535 | 13,049 |
| Grade 2 | 66 | 6 (9)* | 22 (33)* | 6 (9) | 5,238 | 9,829* | 11,258 |
| Grade 3 | 22 | 7 (32) | 10 (45) | 5 (22) | 8,848 | 13,677 | 16,559 |
| Grade 4 | 9 | 1 (11) | 5 (55) | 1 (11) | 9,300 | 4,111 | 5,971 |
| Subchondral lysis | |||||||
| Grade 0 | 278 | 65 (23) | 134 (48) | 53 (19) | 10,971 | 16,474 | 20,004 |
| Grade 1 | 24 | 4 (16) | 9 (38) | 3 (12) | 9,386 | 1,841 | 5,412 |
| Grade 2 | 31 | 6 (19) | 16 (52) | 5 (16) | 7,327 | 5,745 | 7,993 |
| Grade 3 | 10 | 1 (10) | 4 (40) | 1 (10) | 11,843 | 15,051 | 18,012 |
| Grade 4 | 0 | — | — | — | — | — | — |
| Sclerosis | |||||||
| Grade 0 | 321 | 75 (23) | 153 (47) | 61 (19) | 10,595 | 14,960 | 18,464 |
| Grade 1 | 19 | 1 (5) | 9 (47) | 1 (5) | 11,843 | 8,875 | 10,191 |
| Grade 2 | 2 | 0 (0) | 0 (0) | 0 (0) | 0 | 0 | 0 |
| Grade 3 | 1 | 0 (0) | 1 (100) | 0 (0) | 0 | 7,395 | 7,395 |
| Malformation | |||||||
| Grade 0 | 320 | 72 (23) | 152 (48) | 58 (18) | 10,860 | 15,037 | 18,479 |
| Grade 1 | 21 | 3 (14) | 9 (43) | 3 (14) | 4,843 | 7,482 | 9,097 |
| Grade 2 | 2 | 1 (50) | 2 (100) | 1 (50) | 10,000 | 9,097 | 16,610 |
| Middle phalanx of hind limb Thickening of dorsoproximal cortex | |||||||
| Grade 0 | 295 | 63 (21) | 132 (45) | 50 (17) | 11,570 | 15,386 | 19,034 |
| Grade 1 | 38 | 9 (23) | 26 (68) | 9 (24) | 7,559 | 9,936 | 12,553 |
| Grade 2 | 6 | 4 (67) | 5 (83) | 3 (50) | 2,375 | 17,378 | 16,066 |
| Grade 3 | 4 | 0 (0) | 0 (0) | 0 (0) | 0 | 0 | 0 |
| Osteophytes | |||||||
| Grade 0 | 299 | 65 (21) | 134 (45) | 51 (17) | 10,849 | 14,613 | 17,996 |
| Grade 1 | 44 | 11 (25) | 29 (66)* | 11 (25) | 9,206 | 14,415 | 17,907 |
Value is significantly (P ≤ 0.05) different from value for horses without this abnormality (ie, grade 0).
— = Not applicable.
See text for description of grading schemes.
Only 2 of the 7 radiographic lesions included in the analyses were significantly associated with performance outcomes: presence of osteophytes involving the distal aspect of the tarsal joint, and presence of osteophytes on the dorsoproximal aspect of the hind limb middle phalanx. The presence of grade 2 osteophytosis involving the distal aspect of the tarsal joint was associated with significantly increased odds of not earning money as a 3-year-old (P = 0.01; OR, 3.19; 95% CI, 1.29 to 7.91; r2 = 0.05) and as a 4-year-old (P = 0.003; OR, 2.5; 95% CI, 1.38 to 4.56; r2 = 0.08). The presence of grade 1 osteophytosis of the distal aspect of the tarsal joint was also associated with a significantly increased odds of not earning money as a 4-year-old (P = 0.014; OR, 2.18; 95% CI, 1.17 to 4.06; r2 = 0.08). Conversely, the presence of an osteophyte on the dorsoproximal aspect of the hind limb middle phalanx was associated with significantly decreased odds of not earning money as a 4-year-old (P = 0.004; OR, 0.36; 95% CI, 0.18 to 0.71; r2 = 0.08).
Analysis of earnings for the 178 horses known to have earned at least $1 indicated that the presence of grade 2 osteophytosis of the distal aspect of the tarsal joint was significantly (P = 0.01; r2 = 0.06) associated with decreased earnings as a 4-year-old, compared with earnings for horses without osteophytosis.
The remaining 5 radiographic lesions included in the analyses (abnormalities of the medial femoral condyle, subchondral lysis of the distal aspect of the tarsal joint, sclerosis of the distal aspect of the tarsal joint, malformation of the central and third tarsal bones, and thickening of the dorsoproximal cortex of the middle phalanx of the hind limb) were not significantly associated with performance outcomes.
Discussion
Results of the present study suggested that most abnormalities identified on repository radiographs of Quarter Horses competing in cutting events were not significantly associated with subsequent performance. However, the number of horses included in the study likely affected our results. In particular, some radiographic findings of interest affected a small number of horses, resulting in a low power to detect significant associations between the radiographic findings and subsequent performance. Nonetheless, to our knowledge, the present study represented the largest study evaluating performance outcomes for horses competing in cutting events to date. The 2 radiographic findings that were significantly associated with performance outcome in the present study were osteophytosis of the dorsoproximal aspect of the middle phalanx of the hind limb and osteophytosis of the distal aspect of the tarsal joint. Interestingly, mild (grade 1 or 2) osteophytosis of the distal aspect of the tarsal joint was the only finding that was significantly associated with decreased performance (ie, decreased likelihood of earning money as a 3-year-old and as a 4-year-old and decreased earnings as a 4-year-old). These findings were surprising, as we had hypothesized that mild changes would be unlikely to be clinically important, in contrast with severe lesions, which we expected to be more likely to be significantly associated with performance.
Potential earnings for young horses competing in cutting events vary from low payments at local weekend events to moderate payments at regional events, with the highest entry fees and possible earnings in select events for horses of a particular age. It is possible for a horse to have performed well in futurity events (ie, elite-level cutting events restricted to 3-year-olds) but subsequently to have performed poorly. However, in the present study, we followed earnings of horses through their fourth year to account for this possibility.
Whereas we, as other clinicians, have anecdotally considered small osteophytes of the distal aspect of the tarsal joint to be of questionable clinical importance, the results of the present study may lead us to question this assumption. Further research with a larger number of horses may be warranted to further evaluate the potential association between osteophytosis of the distal aspect of the tarsal joint and subsequent performance. However, in the present study, the power to detect a 15% difference in outcomes was 49% for this comparison, which must be taken into account when considering our results. In addition, further investigation might allow for separate analysis of horses with osteophyte formation on the distal aspect of the central tarsal bone, osteophyte formation on the proximal and distal aspects of the third tarsal bone, and new bone formation on the dorsoproximal aspect of the third metatarsal bone (which could be osteophytosis or enthesopathy).15,16 Although the prevalence of those lesions was previously described,13 the low numbers in each group in the present study led to insufficient statistical power to evaluate the groups individually with respect to performance.
The finding of the present study that the presence of medium and large osteophytes (grades 3 and 4) was not significantly associated with performance outcome could have been a result, in part, of the low number of horses with these lesions (31/343 [9%] horses) and the unequal numbers of horses in the osteophytosis categories, resulting in a low power to detect differences among groups. It is not uncommon in cutting horses for intra-articular medication of the tarsal joint to be administered without prior diagnostic analgesia to confirm the joint as the source of lameness. Therefore, we suggest that it would also not be surprising to find that horses with moderate to marked radiographic changes were more likely to be treated empirically with intra-articular joint medications, which may have helped improve their performance. Conversely, milder osteophytosis may have been more likely to be dismissed as unimportant, such that these horses would then be less likely to receive intra-articular treatments. An additional consideration is that horses that already had mild tarsal osteophytosis at a young age (eg, as evident on repository radiographs) may have had progressive disease that affected them as they began or progressed in training. Unfortunately, for the horses in the present study, radiographs obtained at a later age were not available for comparison; therefore, this is only speculation.
In other studies, tarsal osteophytosis has generally been regarded as clinically unimportant. In a study3 of yearling Thoroughbreds, the authors reported that osteophytes or enthesophytes of the centrodistal and tarsometatarsal joints were significantly associated with a decreased likelihood of starting a race. A radiographic survey17 of French Trotters found that osteophytosis of the distal tarsal joints was not significantly associated with performance outcome. Additionally, when osseous spur formation of the proximal aspect of the metatarsal bones was examined, there was no significant association with lameness.15 Furthermore, in a study18 of a mixed group of horses with lameness attributable to the tarsal joint, no significant association was found between radiographic changes of the distal tarsal joints and the severity or duration of lameness. A 2013 study19 of radiographic abnormalities and Thoroughbred racehorse performance found no significant association between osteoarthrosis of the distal tarsal joints and performance. However, none of the aforementioned studies included mainly or solely Western performance horses, and direct comparison of findings among studies must take differences in disciplines into consideration. Importantly, the types of movement required of horses competing in cutting competitions are unique to this discipline; therefore, findings that may not be relevant for horses competing in other disciplines could be a contributor to decreased athletic outcomes for Western performance horses.
In the present study, horses with osteophytosis of the dorsoproximal aspect of the hind limb middle phalanx were almost 3 times as likely to earn money as a 4-year-old as were horses without this finding. The presence of middle phalangeal osteophytes in young horses may be a result of the stresses placed on the hind limbs when horses are pivoting on their hind feet, performing cutting-type movements. The 2-year-old horses evaluated in the present study had already been in training for several months, which may have contributed to the radiographic changes identified. Although obliquity can falsely create the appearance of osteophyte formation of the middle phalanx, the radiographs were evaluated conservatively in an effort to minimize false-positive grading of the presence of osteophytes. However, although attempts were made to reduce multiple testing errors, we cannot completely rule out a false-positive result.
Interestingly, although lameness referable to the stifle joint, particularly the medial femoral condyle, is a major concern for veterinarians treating horses competing in cutting events, radiographic abnormalities of the medial femoral condyle were not significantly associated with performance outcome in the present study. This result was in contrast to our hypothesis that moderate to severe lesions of the medial femoral condyle would be associated with a poorer performance outcome. Our results suggested that lesions of the medial femoral condyle may not restrict a cutting horse's ability to perform successfully, at least for the limited period of time early in its career that, in the cutting horse industry, is the time of greatest earning potential. As for other lesions, it is possible that the lack of significant findings could have been a result of a low power in some analyses, particularly analyses of earnings. However, the power for detecting a 15% difference in odds of earning money was 80%. Thus, we suggest that it should have been possible to detect a clinically relevant difference if one were present. However, it must be keep in mind when interpreting the results of the present study that lameness was not an outcome variable. Whereas an attempt was made to contact the owners of horses that did not earn money to find out why, further follow-up information was not obtained for horses that earned money. Thus, it is possible that there were horses with stifle joint lesions that were able to compete and earn money, yet still developed manageable lameness. Obtaining records of individual horses’ medical histories may have been of limited value, as it is not uncommon for cutting horses to receive intra-articular tarsal and stifle joint injections without undergoing a full diagnostic examination for lameness. Ultimately, we suggest that the finding that horses with radiographic stifle joint lesions did not have significantly different earning ability in the present study may be useful information for potential buyers.
As in any study evaluating radiographs submitted to a repository, there was a risk that horses with more severe lesions may not have been included in the sale, decreasing the number of radiographs evaluated in the present study from horses with moderate to severe radiographic lesions. As such, we may have underestimated both the prevalence and potential effect that more severe lesions could have on performance outcome in the overall population of horses competing in cutting events. Nonetheless, we suggest that despite these limitations, the radiographic findings of the present study are a useful representation of the lesions found in horses sold for cutting events at major sales, and it is the performance outcome of these horses that is of particular concern in the cutting horse industry.
As with any discipline, there are numerous other factors that can affect performance outcome, including training methods, horse temperament, talent, and genetic makeup. Cutting competition results are further complicated by the unpredictability of the cattle involved. However, despite these confounding factors, the goal when purchasing a horse is to attempt to maximize the chance of a positive outcome by proactively identifying potential risk factors for poor performance. The radiograph repository is 1 component of this risk assessment. Further investigation including regular lameness evaluations and monitoring of efficacy of joint medications is suggested, but will require available horses and dedicated owners and veterinarians. Studies that follow horses beyond their fourth year may help to indicate specific repository radiographic changes that affect the longevity of the athletic career of Western performance horses.
Acknowledgments
Supported by Colorado State University and the NCHA Stallion Auction.
The authors thank Dr. Taryn Yates for help with data collection, and Drs. Ann Hess and Sangeeta Rao for assistance with statistical analyses.
ABBREVIATIONS
| CI | Confidence interval |
| NCHA | National Cutting Horse Association |
Footnotes
SAS, version 9.4, SAS Institute Inc, Cary, NC.
PROC GLMSELECT, SAS, version 9.4, SAS Institute Inc, Cary, NC.
PROC GLIMMIX, SAS, version 9.4, SAS Institute Inc, Cary NC.
PROC GLM, SAS, version 9.4, SAS Institute Inc, Cary NC.
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