FRANK J. MILNE STATE-OF-THE-ART LECTURE


their MRI appearance and were graded 1 to 5 on the basis of changes in the adjacent distal border of the navicular bone. Large fragments were usually grade 4 or 5, whereas small fragments were usually grade 3. There was a significant association be- tween the presence of a fragment and the total na- vicular bone grade (P  0.001), OCLLs (P  0.001), increased number and size of the synovial invagina- tions of the distal border (P  0.0067), increased signal intensity on fat-suppressed images in the dis- tal half of the navicular bone (P  0.001), and size of distal border entheseophytes (P  0.0067). There was an association between grade of the DSIL and grade 4 or 5 navicular bone fragments (P  0.0086). The majority of fragments were associated with proximal extension of abnormal signal intensity in the adjacent navicular bone. We also investigated the correlation between the presence of distal border fragments detected using high-field MRI and their radiological detection in 427 horses.96 Medium and large fragments were most likely to be detected radiologically especially if grade 4 or 5, but up to 43% of large fragments were missed. There were significant associations be- tween the presence of a fragment on radiography and the total MRI grade of the navicular bone (P  0.0001); the presence of a radiolucency at the junc- tion between the distal horizontal and sloping bor- ders of the navicular bone and both a fragment observed on MR images (P  0.0001) and OCLLs on MR images (P  0.0001). There was also an asso- ciation between an increased number and size of the synovial invaginations along the distal border on radiographs and the presence of both a distal border fragment on MR images (P  0.0001) and OCLLs on MR images (P  0.0001). On histology, partially detached bone islands were separated from the distal border by areas of fibro- plasia or fibrocartilaginous metaplasia and were associated with focal osteonecrosis.76,100 Thus, in- creased signal intensity on STIR images in the distal border of the navicular bone associated with some fragments may reflect bone necrosis. There may be transverse fissures at the origin of the DSIL (Fig. 18). It has been suggested that movement of a frag- ment relative to the navicular bone may be a poten- tial cause of pain.110 In addition, lesions of the DSIL observed in association with high-grade fragments could be painful because of the rich sen- sory innervation of the DSIL, particularly at its insertion.109


5. Conclusions


Accurate lameness diagnosis remains challeng- ing. As knowledge advances, more questions arise. Currently our diagnostic capabilities are superior to our ability to treat lameness successfully. Progress will be made by careful clinical observations, com- bined with accurate interpretation of diagnostic im- aging and evidence-based studies documenting the


responses to treatment in sufficiently large numbers of horses.


Acknowledgments


John Hickman is a pioneer of his time and my first teacher. Mentors in the United States include Charles Reid, Charles Raker, Bill Moyer, Dan Marks, Midge Leitch, and Ron Genovese. Col- leagues past and present at the Animal Health Trust include, particularly: Brian Singleton, An- drew Higgins, Leo Jeffcott, Joe Mayhew, Svend Kold, Jan Butler, Ian Wright, Chris Whitton, Mi- chael Schramme, Rachel Murray, Tony Blunden, Shelley Down, Annamaria Nagy, Marianna Biggi, Stephanie Dakin, and numerous interns. Thanks to Mike Ross for inspiration and friendship; my husband, John Wilkinson, for encouraging me to continue to look and see and ask questions; my superstar horses, McGinty, Kinvarra, and Otter- burn, and all the other ponies and horses who taught me so much.


References and Footnotes


1. Dyson S. Can lameness be reliably graded? Equine Vet J 2011;43:379–382.


2. Anonymous. Guide to Veterinary Services for Horse Shows. 7th edition. Lexington, Kentucky: American Association of Equine Practitioners; 1999.


3. Parkes B, Weller R, Groth A, et al. Evidence of the devel- opment of ‘domain-restricted’ expertise in the recognition of asymmetric motion characteristics of hindlimb lameness in the horse. Equine Vet J 2008;41:112–117.


4. Starke S, Willem E, Head M, et al. Proximal hindlimb flexion in the horse: effect on movement symmetry and implications for defining soundness. Equine Vet J 2012;44: 657–663.


5. May S, Wyn-Jones G. Identification of hindleg lameness. Equine Vet J 1987;19:185–188.


6. Ross M. Movement. In: Ross M, Dyson S, editors. Diag- nosis and Management of Lameness in the Horse. 2nd edi- tion. St Louis: Elsevier Science; 2010:64–80.


7. Greve L, Dyson S. An investigation of the relationship between hindlimb lameness and saddle slip. Equine Vet J 2013./doi.10.1111/evj/12029.


8. Schamhardt H, Merkens H, Vogel V, et al. External loads on the limbs of jumping horses at take off and land- ing. Am J Vet Res 1993;54:675–686.


9. Dyson S. Problems associated with the interpretation of the results of regional and intra articular anaesthesia in the horse. Vet Rec 1986;118:419–422.


10. Schumacher J, Livesey L, Schramme M, et al. Effect of anaesthesia of the palmar digital nerves on lameness caused by pain in the proximal interphalangeal joint, in Proceed- ings. Am Assoc Equine Pract 2003;49:287–290.


11. Werpy N. Metacarpophalangeal joint lesions identified on MRI with lameness that resolves with palmar digital anal- gesia and intra-articular analgesia, in Proceedings. Am Assoc Equine Pract 2012;58:534.


12. Nagy A, Bodo G, Dyson S, et al. Diffusion of contrast me- dium after perineural injection of the palmar nerves: an in vivo and in vitro study. Equine Vet J 2009;41:379–383.


13. Dyson S, Nagy A, Murray R. Clinical and diagnostic imag- ing findings in horses with subchondral bone trauma of the sagittal groove of the proximal phalanx. Vet Radiol Ultra- sound 2011;52:596–604.


14. Nagy A, Bodo G, Dyson S, et al. Distribution of radiodense contrast medium after perineural injection of the palmar and palmar metacarpal nerves (low four-point nerve block):


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