How to Interpret Radiographs of the Fetlock and Pastern Joints of the Young Performance Horse

Transcription

1 How to Interpret Radiographs of the Fetlock and Pastern Joints 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 performance horses has become commonplace in Thoroughbreds but also occurs in other performance breeds. This practice has resulted in the frequent discovery of radiographic abnormalities (RA) that are often clinically silent but can cause concern in buyers and sellers of young performance stock. The prevalence of radiographic developmental orthopedic disease in 6-month-old horses has been reported to be 25% in Warmbloods, 41% in Standardbreds, and 34% in Thoroughbreds (TB). 1 In Thoroughbred 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 The fetlock joints are often reported as the joints most commonly affected by RA. Predicting the significance of RA to later athletic performance can be challenging and frustrating for buyers and sellers, which is further complicated by the possibility of treatment, including surgery, on prognosis (Table 1 2,4,6 13 ). 2. Identifying RA Because radiographic images are reviewed in sets of projections of one joint, this paper will discuss abnormalities by each projection. Readers are, of course, responsible for reading the entire image. However, there are areas that should receive the closest scrutiny because of a greater frequency of abnormalities. These areas will be emphasized and the most common RA in young horses described. In the following section, the RA that is best detected on a specific projection will be listed in bold. This RA 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 projections are present and of acceptable quality. NOTES Vol. 59 AAEP PROCEEDINGS

2 Fetlock Radiographic Abnormality Breed Prevalence Reference RA (front fetlocks) Thoroughbred 41% 2 RA (front fetlocks) Warmblood % 4, 6 RA (hind fetlocks) Thoroughbred 21% 2 RA (hind fetlocks) Warmblood % 4, 6 RA (hind fetlocks) Quarter Horse 44% 5 RA (hind fetlocks) Standardbred 18% 3 RA in all four fetlocks Standardbred 13 18% 3, 7 Dorsal proximal P1 fragments; front Thoroughbred 0.7 4% 2, 8, 9 Dorsal proximal P1 fragments; front Quarter Horse 1% 5 Dorsal proximal P1 fragments; hind Thoroughbred Dorsal proximal P1 fragments; hind Quarter Horse 1% 5 Proximal palmar P1 fragments Thoroughbred 0.4 2% 2, 8, 10 Proximal plantar P1 fragments Thoroughbred % 8, 10 Proximal plantar P1 fragments Quarter Horse Proximal plantar P1 fragments Standardbred 17 23% 3, 11 Lucencies or fragments dorsal sagittal ridge Thoroughbred % 2, 8 Lucencies or fragments dorsal sagittal ridge German Coldblood 54% 12 Changes to shape, dorsal sagittal ridge Thoroughbred 20 27% 2, 8, 9 Supracondylar lysis (forelimb) Thoroughbred % 2, 8 Abnormal length or shape to PSB Thoroughbred % 2, 8 PSB fracture Thoroughbred 1 1.5% 2, 8 PSB fracture Quarter Horse 1% 5 PSB enthesophyte (front, hind) Thoroughbred 1.2%, 39% 8, 9 PSB lucency (all four limbs) Thoroughbred % 2, 8 2 PSB vascular channels Thoroughbred % 2, 8 Subchondral bone cyst distal MC/MT3 Thoroughbred % 8, 10, 13 Table 1. Prevalence of Fetlock Radiographic Abnormalities. P1 indicates first phalanx; PSB, proximal sesamoid bones; MC/MT3, third metacarpus or metatarsus. Standard radiographic projections of the fetlock joint (5 for forelimb, 4 for hind limb, flexed lateral is optional for hind limb) Dorsopalmar/plantar projection, elevated 15 Dorsolateral (30 ) to palmaromedial oblique (elevated 10 ) Dorsomedial (30 ) to palmarolateral oblique (elevated 10 ) Lateral to medial projection of the fetlock joint Lateral to medial (flexed) projection of the fetlock joint Dorsopalmar/plantar projection, elevated 15 of the fetlock joint (Fig. 1). At the public auction of Thoroughbreds, the pastern joint is included on the DP projection, therefore common RA in the pastern and the fetlock will be discussed. On this projection, the areas of greatest concern are the distal condyles of the third metacarpus/metatarsus (MC/MT3) and the distal P1 as well as the opposing articular surfaces on the proximal first phalanx (P1) and second phalanx (P2). The distal border of the proximal sesamoids should also be closely scrutinized. Abnormalities best identified on the fetlock DP view are listed below. If the RA is in bold type, it is the best projection to detect that RA. (1) Lucencies in distal MC/MT3, proximal P1, distal P1, or proximal P2 (2) Enthesophytes of distal aspect of proximal sesamoid bones (PSB) (3) Osteochondral fragments distal to the base of the proximal sesamoid bones (4) Osteochondral fragments at the articular margin of proximal P1 (5) Lucencies in the sagittal ridge of MC/MT3 (6) Peri-articular osteophytes affecting the medial and lateral joint margins Lateral to medial projection of the fetlock joint (Fig. 2). Areas of greatest concern on this projection include the proximal dorsal margin of P1, the dorsal sagittal ridge, the apex and base of the proximal sesamoid bones, the palmar/plantar fetlock joint recess, and the proximal palmar/plantar margin of P1. Abnormalities best identified on the fetlock lateral to medial projection are listed below. If the RA is in bold type, it is the best projection to detect that RA. (1) Axial dorsal-proximal P1 fragments: in young horses, these fragments are often axial in the sagittal groove and do not project well on oblique views (2) Irregularities or fragments of the sagittal ridge (3) Fragments of the base of the sesamoid bones AAEP PROCEEDINGS Vol

3 Fig. 2. Fetlock joint lateral to medial projection. This horse has moderate (3- to 4-mm) supracondylar lysis of the distal metacarpus (arrow). This radiograph will be discussed by the panel as Case 2. Fig. 1. Fetlock joint dorsopalmar/plantar projection, elevated 15. This horse has a lucency in the distal metacarpus (arrow). This radiograph will be discussed by the panel as Case 1. (4) Supracondylar lysis of MC/MT3 (5) Apical sesamoid fragments (6) Palmar/plantar proximal P1 fragments Lateral to medial (flexed) projection of the fetlock joint (Fig. 3). The area of greatest concern on this projection is the distal aspect of MC/MT3, particularly the sagittal ridge, and will detect fragments and lucencies in the mid-sagittal ridge. Case Summary Case Summary Case 1. Lucency in the Distal Metacarpal Condyle Case 2. Moderate Supracondylar Lysis of the Distal Metacarpus Guarded Poor Guarded Poor Racing No owner buyer performance No owner buyer performance No owner buyer purpose No owner buyer Racing No owner/buyer Vol. 59 AAEP PROCEEDINGS

4 Fig. 3. Fetlock joint flexed lateral to medial projection. This horse has large irregularity in the middle of the sagittal ridge. This radiograph will be discussed by the panel as Case 3. Fig. 4. Fetlock joint dorsolateral (30 ) to palmaromedial oblique (elevated 10 ). This horse has a large lateral proximal P1 palmar process fragment with two smaller intra-articular fragments. This radiograph will be discussed by the panel as Case 4. Dorsolateral (30 ) to palmaromedial oblique (elevated 10 ) and dorsomedial (30 ) to palmarolateral oblique (elevated 10 ) projections (Fig. 4). Areas of greatest concern on these projections are the proximal-dorsal aspect of P1, the abaxial aspect of the superimposed sesamoid, the apex and suspensory branch attachment of the palmar/plantar silhouetted sesamoid, and proximal P1. Abnormalities best identified on the fetlock oblique projections are listed below. If the RA is in bold type, it is the best projection to detect that RA. (1) Abaxial proximal-dorsal P1 osteochondral fragments (2) Sesamoid fractures: apex, abaxial, mid-body, base (3) Sesamoid enthesophytes (proximal or distal) (4) Osteochondral fragments at the palmar/ plantar margin of proximal P1 (5) Irregularorincompletelyossifiedpalmar/ plantar eminences (6) Irregularities or osteochondral fragments of the dorsal lateral/medial abaxial aspect of distal MC/MT3 (7) Lucencies or fragments in the palmar/ plantar condyle of MC/MT3 (8) Distal MC/MT2 and four fractures Case Summary Case Summary Case 3. Large Irregularity in the Middle Aspect of the Sagittal Ridge Case 4. Three Proximal P1 Palmar Process Fragments Racing No owner/buyer Racing Yes owner buyer performance Yes owner/buyer performance Yes owner/buyer purpose owner/buyer AAEP PROCEEDINGS Vol

5 Case 6. Lucency with fragment palmar metacarpus. Case 5. Multiple large fragments at the base of the sesamoid. 3. Determining the Significance of an RA Several studies of young stock have examined associations between fetlock and pastern RA and performance. 2,3,14 17 These studies can be challenging to interpret because they have many confounding factors, often have a selection bias, frequently struggle to achieve statistical significance, and have incomplete outcome information, usually racing data only. Also, retrospective performance studies of young stock vary in the classification of RA and have in general not been able to account for lesion size, the severity of associated changes (sclerosis, periosteal reaction), and the position in the joint, usually because of small numbers of affected horses. Further complicating the analysis is the impact of having multiple affected limbs or more than one kind of RA. However, there are several publications that focus on the treatment of a specific fetlock lesion, and these studies have been able to associate poorer prognosis with some lesion characteristics Clinicians must judge young stock with RA on the basis of careful reading of available studies, experience with RA in a given performance discipline, and evaluation of the appearance and clinical presentation of a specific RA. Case Summary Case Summary Case 5. Multiple Large Fragments, Base of Sesamoid Case 6. Lucency With Fragment Palmar Metacarpal Condyle Guarded Poor Racing No owner buyer performance No owner buyer Racing Yes owner buyer performance Yes owner buyer performance Yes owner buyer Vol. 59 AAEP PROCEEDINGS

6 Case 7. Irregular surface to proximal medial sesamoid and small chip fracture of axial base. Case 8. Large fragment at proximal MSR and irregular dorsal surface to distal metacarpus. 4. RA in the Fetlock or Pastern That Have Been Associated With Poorer Racing Outcomes Excluding Monetary Outcomes Values are statistically significant at P RA include the following. Greater than 4-mm supracondylar lysis of MC3 14 Enthesophyte formation on proximal sesamoids (fore or hind) 14 Midline pastern joint lucencies (large) 16 Abnormal shape of PSB 2 Sesamoid fracture (forelimb) 2 Large-defect sagittal ridge MT3 2 Enlarged ( 2 mm) vascular canals in PSB Trends Associated With Poorer Racing Values are significant at P 0.2. Trends include the following. Fragment dorsal-proximal palmar P1 14 Sesamoid of abnormal shape 14 Fragment proximal-palmar P1 14 Abnormal vascular channels in the proximal sesamoid bones 2,14 Defect of sagittal ridge MC3 2 PSB lucency 2 Fragment plantar P1 2 Case Summary Case Summary Case 7. Base Irregular Abaxial Surface of PSB and Small Chip Fracture, Axial Case 8. Large Fragment at Proximal Sagittal Ridge and Irregular Surface to Abaxial Metacarpus Guarded Poor Racing Yes owner/buyer Racing Yes owner buyer performance Yes owner/buyer performance Yes owner buyer purpose Yes owner/buyer AAEP PROCEEDINGS Vol

7 Case 10. Large circular lucency palmar margin of sesamoid. Case 9. Small osteochondral fragment dorso-proximal P1 and small apical fracture of proximal sesamoid. 6. for Fetlock RA After Treatment Prognoses for fetlock RA after treatment include the following. Sesamoid fracture; forelimbs have reduced racing (55%) versus hind limb (86%); medial forelimb fractures have the worst prognosis (44%) 18 Fragment removal dorso-proximal P1; 73% of TB return to racing, 25% at a lower class 19 Fragment removal palmar/plantar proximal P1; 76% to 91% return to racing 20,21 Debridement of subchondral bone cyst, distal MC3; 80% successful Cases The summary prognosis charts for Cases 1 through 10 summarize the opinion of the author and are predicated on the lesion being detected in a yearling intended for one of the four disciplines. The focus is on performance and not resale blemishes. The prognosis given to a horse owner and the prognosis given to a potential buyer, if different, is indicated. 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 No. 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 performance. Equine Vet J Suppl 2006;36: van Grevenhof EM, Ducro BJ, van Weeren PR, et al. Prevalence of various radiographic manifestations of osteochon- Case Summary Case 9. Small Fragment, Dorso-Proximal P1 and Small Apical Fracture PSB Case Summary Case 10. Large Lucency, Palmar Abaxial Margin of Medial Sesamoid Racing Yes owner/buyer performance owner/buyer performance owner/buyer Racing No owner buyer Vol. 59 AAEP PROCEEDINGS

8 drosis 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: Stock KF, Hamann H, Distl O. Prevalence of osseous fragments in distal and proximal interphalangeal, metacarpoand metatarsophalangeal and tarsocrural joints of Hanoverian Warmblood horses. J Vet Med 2005;52: Alvarado A, Marcoux M, Breton L. The incidence of osteochondrosis in a Standardbred farm in Quebec, in Proceedings. Am Assoc Equine Pract 1989;35: 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: 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: Furniss C, Carstens A, van den Berg SS. Radiographic changes in Thoroughbred yearlings. J South African Vet Assoc 2011;82: Lykkjen S, Roed KH, Dolvik NI. Osteochondrosis and osteochondral fragments in Standardbred trotters: prevalence and relationships. Equine Vet J 2012;44: Wittwer C, Hamann H, Rosenberger E, et al. Prevalence of osteochondrosis in the limb joints of south German Coldblood horses. J Vet Med 2006;53: Scott NJ, Hance S, Todhunter P, et al. Incidence of radiographic changes in Thoroughbred yearlings: 755 cases, in Adv Equine Nutrition III, Pagan JD, ed. 2005: Kane AJ, McIlwraith CW, Park RD, et al. Radiographic changes in Thoroughbred yearlings, part 2: associations with racing performance. Equine Vet J 2003;35: Cohen ND, Carter GK, Watkins JP, et al. Association of racing performance with specific abnormal radiographic findings in Thoroughbred yearlings sold in Texas. J Equine Vet Sci 2006;26: Vargas JV, Bramlage LR, Spike-Pierce DL. Racing prognosis of Thoroughbred yearlings with subchondral bone lucencies in the proximal interphalangeal joint, in Proceedings. Am Assoc Equine Pract 2011;57: Spike-Pierce DL, Bramlage LR. Correlation of racing performance with radiographic changes in the proximal sesamoid bones of 487 Thoroughbred yearlings. Equine Vet J 2003;35: Schnabel LV, Bramlage LR, Mohammed HO, et al. Racing performance after arthroscopic removal of apical sesamoid fractures in Thoroughbred horses age 2 years; 151 cases ( ). Equine Vet J 2007;39: Kawcak CE, McIlwraith CW. Proximodorsal first phalanx osteochondral chip fragmentation in 336 horses. Equine Vet J 1994;26: Houttu J. Arthroscopic removal of osteochondral fragments of the palmar/plantar aspect of the metacarpo/metatarsophalangeal joints. Equine Vet J 1991;23: Whitton RC, Kannegieter NJ. Osteochondral fragments of the palmar/planter proximal aspect of the proximal phalanx in racing horses. Aust Vet J 1994;71: Hogan PM, McIlwraith CW, Honnas CM, et al. Surgical treatment of subchondral cystic lesion of the third metacarpal bone: results in 15 horses ( ). Equine Vet J 1997;29: AAEP PROCEEDINGS Vol