How to Interpret Radiographs of the Stifle Joint of the Young Performance Horse

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1 How to Interpret Radiographs of the Stifle Joint of the Young Horse Elizabeth M. Santschi, DVM, Diplomate ACVS Author s address: Department of Veterinary Clinical Sciences, The Ohio State University, 601 Vernon L. Tharp Street, Columbus, OH 43210; Elizabeth.Santschi@cvm.osu.edu AAEP. 1. Introduction Routine radiographic evaluation of young horses has become commonplace in Thoroughbreds (TB) but also occurs in other breeds. This practice has resulted in the frequent discovery of radiographic abnormalities (RA) that are often clinically silent but can cause concern for s and sellers of young stock. The prevalence of radiographic developmental orthopedic abnormalities with or without clinical significance in 6-month-old horses has been reported to be 25% in Warmbloods, 41% in Standardbreds, and 34% in TB. 1 In TB yearlings intended for racing, 86.3% exhibit RA 2 ; in young Standardbreds, 42% 3 ; in yearling Warmblood horses, 69.5% 4 ; and in 1- and 2-year-old Quarter Horses intended for cutting, 89%. 5 Predicting the significance of these RA to later can be challenging and frustrating for s and sellers, which is further complicated by the possibility of treatment, including surgery, on prognosis. 2. Identifying RA Because radiographic images are generally reviewed in sets of projections of a joint, this paper will discuss abnormalities by projection. Examiners are of course responsible for reading the entire image; however, there are areas that are more commonly affected, and they should receive the closest scrutiny. RA best detected on a projection are listed in bold but should be confirmed on other projections when possible. Finally, readers should always consider three general factors when reviewing radiographic images: (1) Make sure that the films are of the correct horse. (2) Make sure the date is appropriate and consistent. (3) Make sure all required views are present and of acceptable quality. Standard radiographic projections of the stifle joint (3 views) Lateral to medial, 20 caudoproximal-craniodistal (CC20 ), and caudolateral to craniomedial 20 oblique Lateral to medial projection (Fig. 1). Areas of greatest concern in the lateral projection of the juvenile stifle include the trochlear ridges, the NOTES AAEP PROCEEDINGS Vol

Fig. 2. Caudal to cranial elevated 20 projection of the stifle joint. This horse has an irregular lucency in the MFC (white circle). This radiograph will be discussed by the panel as Case 2. Fig. 1.

2 Fig. 2. Caudal to cranial elevated 20 projection of the stifle joint. This horse has an irregular lucency in the MFC (white circle). This radiograph will be discussed by the panel as Case 2. Fig. 1. Lateral to medial projection of the stifle joint. This horse has a lucency with fragments in the proximal LTR (white circle). This radiograph will be discussed by the panel as Case 1. articular surface of the patella, and the cranial proximal surface of the tibia. The caudal aspect of thestifle joint is often not included on the lateral to medial projection, which is acceptable if it is well projected on other views (Fig. 1). Abnormalities best assessed on the stifle lateral to medial projection are listed below. If the RA is in bold type, it is the best projection to detect that RA. (1) Osteochondral fragments or lucencies in the lateral trochlear ridge (LTR) (2) Osteochondral fragments or lucencies in the medial trochlear ridge (3) Osteochondral fragments or lucencies in the articular surface of the patella (4) Osteochondral fragments or lucencies in the proximal tibia Twenty-Degree Caudoproximal-Craniodistal Projection of the Stifle Joint (Fig. 2) The areas of greatest concern on the 20 caudoproximal-craniodistal projection of the juvenile stifle are the medial femoral condyle, the proximal medial tibial, the medial intercondylar eminence of the tibia including the attachment of the cranial menisco-tibial ligament, the proximal lateral tibial, and the lateral femoral condyle. Abnormalities best assessed on the stifle 20 caudoproximal-craniodistal projection are listed below. If the RA is in bold type, it is the best projection to detect that RA. Case Summary Case 1. Racing Lucency With Fragments in Proximal LTR Yes// Yes Yes Yes Case Summary Case 2. Irregular Lucency in Medial Femoral Condyle Yes// Racing Yes owner Yes owner Yes owner Vol. 59 AAEP PROCEEDINGS

Fig. 3. Caudolateral to craniomedial 20 oblique projection. This horse has a large irregular lucency in the proximallateral tibial (white circle and arrows).

(1) Lucencies and sclerosis in the medial femoral condyle (MFC) (2) Osteophytes on the medial intercondylar eminence, proximal medial tibial, or proximal abaxial articular margin of the MFC (3)

3 Fig. 3. Caudolateral to craniomedial 20 oblique projection. This horse has a large irregular lucency in the proximallateral tibial (white circle and arrows). This radiograph will be discussed by the panel as Case 3. (1) Lucencies and sclerosis in the medial femoral condyle (MFC) (2) Osteophytes on the medial intercondylar eminence, proximal medial tibial, or proximal abaxial articular margin of the MFC (3) Lucencies and sclerosis in the medial tibial (4) Lucencies and sclerosis in the lateral tibial (5) Lucencies and sclerosis in the lateral femoral condyle (6) Sclerosis at the attachment of cranial menisco-tibial ligament Case 4. Lucencies of the lateral trochlear ridge and patella. Caudolateral to Craniomedial 20 Oblique Projection of the Stifle Joint (Fig. 3) The areas of greatest concern on this view include the medial femoral condyle, the medial tibial, the proximal lateral tibial, and the LTR. Abnormalities best assessed on the caudolateral to craniomedial 20 oblique projection are listed below. If the RA is in bold type, it is the best projection to detect that RA. (1) Lucencies and sclerosis in the medial femoral condyle (2) Osteochondral fragments or lucencies in the LTR (3) Lucencies and sclerosis in the medial tibial (4) Lucencies and sclerosis in the lateral tibial Case Summary Case 3. Large Irregular Lucency in the Proximal Tibia Yes// Racing / owner / owner owner owner Case Summary Case 4. Lucencies of the Lateral Trochlear Ridge and Patella Yes// Racing Yes owner Yes owner Yes owner owner AAEP PROCEEDINGS Vol

5 Table 1 summarizes the reported prevalence by breed. 2,4 11 3.

4 Case 5. Calcinosis circumscripta. Case 6. Large LTR lucency with fragments. Stifle radiographic abnormalities are common in young stock and have been reported to have a prevalence as high as 45% in 1- to 2-year-old Quarter Horses at auction. 5 Table 1 summarizes the reported prevalence by breed. 2, Determining the Significance of an RA to There are several studies of young stock that have examined associations between stifle RA and. 2,12 16 These studies can be challenging to interpret by strict statistical methods (P 0.05) because they have many confounding factors, including varying definitions of RA and incomplete outcome information, usually racing data only. Because of the low numbers of affected horses, subclassifying lesions (size, severity, number of limbs affected, etc) to determine prognosis is usually not possible. However, these studies do have important information to help guide veterinarians examining young horses. Some stifle RA in these studies have been associated with poorer racing outcomes (P 0.05): debrided MFC subchondral bone cyst (SBC) (versus sibling controls) and large articular communication of MFC SBC after debridement 16 and osteochondrosis (OCD) of LTR and MFC SBC 6 mm in depth. 2 RA in the stifle associated with a tendency (P 0.2) for poorer racing include changes in the LTR of the femur and fragmentation of the distal patella. 12 Case Summary Case 5. Racing Large Calcinosis Circumscripta, Proximal Tibia, Dorso-Lateral Yes// Case Summary Case 6. Large LTR Lucency With Fragments Yes// Racing owner owner owner owner Vol. 59 AAEP PROCEEDINGS

Clinicians must apply clinical judgment on the basis of their experience with RA in young horses, carefully interpret available studies, and closely evaluate the appearance and clinical presentation

5 Case 8. Shallow and wide MFC lucency with deeper sclerosis. Case 7. Flattened proximal LTR. Many publications focus on the treatment of a specific stifle lesion, and some of these studies have been able to grade lesions and document an effect of severity or size on prognosis. Clinicians must apply clinical judgment on the basis of their experience with RA in young horses, carefully interpret available studies, and closely evaluate the appearance and clinical presentation of a specific RA. Table 1. Prevalence of Stifle Radiographic Abnormalities in Young Horses Stifle Radiographic Abnormality Breed Prevalence References Lateral trochlear ridge RA Thoroughbred 36% 6 Lateral trochlear ridge OCD Thoroughbred 0 4% 2, 7 9 Lateral trochlear ridge OCD Standardbred 10% 10 Femoropatellar joint RA Warmblood 39% 4 Lucencies in medial femoral condyle Thoroughbred 16% 9 RA in medial femoral condyle Quarter Horse 41% 5 Subchondral bone cyst medial femoral condyle Thoroughbred % 2, 8, 9 OCD any location Thoroughbred % 2, 7 9,11 RA any location Quarter Horse 43% 5 Case Summary Case 7. Racing Flattened Proximal LTR Yes// Case Summary Case 8. Shallow and Wide MFC Lucency With Deeper Sclerosis Yes// Racing Yes owner Yes owner Yes owner AAEP PROCEEDINGS Vol

lesions 20 mm, higher success rate achieved if operated as 3-year-old versus yearling.

6 Case 9. Large MFC subchondral bone cyst. Case 10. Fragment between intercondylar eminences. 4. for Stifle RA After Rest or Prognoses include the following: Femoropatellar OCD after arthroscopic debridement (multiple breeds): 64% returned to intended use, higher success rate was achieved with lesions 20 mm, higher success rate achieved if operated as 3-year-old versus yearling. 16 Warmbloods had 66% full return, 83% if a return to lesser activity was included; deeper lesions led to a worse prognosis. 17 Femoropatellar OCD after debridement of loose pieces and reattaching loose osteochondral flaps with absorbable pins, 95% were successful. 18 Subchondral bone cysts of the medial femoral condyle after 6 months rest, 50% full recovery, with an additional 20% improved. 19 Subchondral cystic lesions of medial femoral condyle after debridement: 64% to 74% returned to soundness. 20,21 Articular openings 15 mm had a worse prognosis. 21 Subchondral bone cyst injected with corticosteroids: 67% successful. Unilaterally affected horses had higher success (90%) and those without DJD also had a better rate of success (87%). 22 Subchondral bone cysts debrided and filled with bone substitute, growth factors, and chondrocytes: 74% were successful Cases The summary prognosis charts (cases 1 10) with each image are predicated on the lesion being detected in a yearling intended for one of the four disciplines. The focus is on and not resale blemishes. The prognosis given to a horse owner and the prognosis given to a potential, if different, is indicated. Case Summary Case Summary Case 9. Large MFC Subchondral Bone Cyst Case 10. Fragment Between Intercondylar Eminences Yes// Yes// Racing Yes owner Yes owner Yes owner Yes owner Racing owner owner owner owner Vol. 59 AAEP PROCEEDINGS

7 References 1. Lepeule J, Bareille N, Valette JP, et al. Developmental orthopaedic disease in the limbs of foals: between-breed variations in the prevalence, location and severity at weaning. Animal 2008;2: Jackson M, Vizard A, Anderson G, et al. A prospective study of presale radiographs of Thoroughbred yearlings. Australian Government Rural Industries Research and Development Corporation. RIRDC Publication. 09/ pdf. 3. Couroursé-Malblanc A, Leleu C, Bouchilloux M, et al. Abnormal radiographic findings in 865 French Standardbred trotters and their relationship to racing. Equine Vet J Suppl 2006;36: van Grevenhof EM, Ducro BJ, van Weeren PR, et al. Prevalence of various radiographic manifestations of osteochondrosis and their correlations between and within joints of Dutch Warmblood horses. Equine Vet J 2009;41: Contino EK, Park RD, McIlwraith CW. Prevalence of radiographic changes in yearling and 2-year-old Quarter Horses intended for cutting. Equine Vet J 2012;44: Kane AJ, McIlwraith CW, Park RD, et al. Radiographic changes in Thoroughbred yearlings, part 1: prevalence at the time of the yearling sales. Equine Vet J 2003;35: Howard BA, Embertson RM, Rantanan NW, et al. Survey radiographic findings in Thoroughbred sale yearlings, in Proceedings. Am Assoc Equine Pract 1992;38: Scott NJ, Hance S, Todhunter P, et al. Incidence of radiographic changes in Thoroughbred yearlings: 755 cases. In Pagan, ed. Adv Equine Nutrition III 2005: Oliver LJ, Baird DK, Baird AN, et al. Prevalence and distribution of radiographically evident lesions on repository films I the hock and stifle joints of yearling Thoroughbred horses in New Zealand. N Z Vet J 2008;56: Alvarado A, Marcoux M, Breton L. The incidence of osteochondrosis in a Standardbred farm in Quebec, in Proceedings. Am Assoc Equine Pract 1989;35: Preston SA, Zimmel DN, Chmielewski TL, et al. Prevalence of various presale radiographic findings and association of findings with sales price in Thoroughbred yearlings sold in Kentucky. J Am Vet Med Assoc 2010;236: Kane AJ, McIlwraith CW, Park RD, et al. Radiographic changes in Thoroughbred yearlings, part 2: associations with racing. Equine Vet J 2003;35: Cohen ND, Carter GK, Watkins JP, et al. Association of racing with specific abnormal radiographic findings in Thoroughbred yearlings sold in Texas. J Equine Vet Sci 2006;26: Whitman JA, Morehead JP, Prichard MA, et al. Radiographic lucencies in the medial femoral condyle of Thoroughbred yearlings; the effect on race records, in Proceedings. Am Assoc Equine Pract 2006;52: Barrett MF, McIlwraith CW, Contino EK, et al. Relationship between radiographic changes of the medial femoral condyle and in Quarter Horse cutting horses. relationship-radiographic-changes-cutting-horses.aspx. Accessed January 24, Foland JW, McIlwraith CW, Trotter GW. Arthroscopic surgery for osteochondrosis dissecans of the femoropatellar joint of the horse. Equine Vet J 1992;24: UpRichard K, Elce YA, Piat P, et al. Outcome after arthroscopic treatment of lateral femoral trochlear ridge osteochondrosis in sport horses. Vet Comp Ortho Trauma 2012; 26: Sparks HD, Nixon AJ, Fortier LA, et al. Arthroscopic reattachment of osteochondrosis dissecans cartilage flaps of the femoropatellar joint: long-term results. Equine Vet J 2011;43: Jeffcott LB, Kold SE. Clinical and radiological aspects of stifle bone cysts in the horse. Equine Vet J 1982;14: Howard RD, McIlwraith CW, Trotter GW. Arthroscopic surgery for subchondral cystic lesion of the medial femoral condyle in horses: 41 cases ( ). J Am Vet Med Assoc 1995;206: Sandler EA, Bramlage LR, Embertson RM, et al. Correlation of radiographic appearance, lesion size, and racing after arthroscopic surgical treatment of subchondral cystic lesions of the medial femoral condyle in Thoroughbreds: 150 cases. Vet Surg 2002;31: Wallis TW, rich LR, McIlwraith CW, et al. Arthroscopic injection of corticosteroids into the fibrous tissue of subchondral cystic lesions of the medial femoral condyle in horses: a retrospective study of 52 cases ( ). Equine Vet J 2008;40: Ortved KF, Nixon AJ, Mohammed HO, et al. Treatment of subchondral cystic lesions of the medial femoral condyle of mature horses with growth factor enhanced chondrocyte grafts: a retrospective study of 49 cases. Equine Vet J 2012;44: AAEP PROCEEDINGS Vol

Proceedings of the American Association of Equine Practitioners - Focus Meeting. First Year of Life Austin, Texas, USA 2008

www.ivis.org Proceedings of the American Association of Equine Practitioners - Focus Meeting First Year of Life Austin, Texas, USA 2008 Next AAEP Focus Meeting : Focus on the Foot Jul. 19-21, 2009 Columbus,