Diagnostic imaging modalities for DDFT lesions include MRI,1 ultrasonography,2 a nd CT.3 Although ultrasonography is widely available and used to evaluate lesions in the foot,2,4,5 image quality is limited by equipment capability and affected by operator proficiency.2 Magnetic resonance imaging is considered the gold standard for soft tissue imaging, especially for conditions affecting the feet of horses1,5; limitations of this modality include relatively low-resolution images generated with low-field MRI and the need for inhalation anesthesia when high-field MRI is used. Additionally, the cost of MRI equipment purchase and maintenance and the expertise required for its use greatly limit its availability.
Computed tomography has been used in horses since at least 19846,7 and is commonly used for imaging of the head and limbs; this modality is superior to radiography because of its multiplanar imaging capability and capacity to image bone and soft tissue structures with greater detail.8,9 Reports of CT identification of DDFT lesions exist, and injectable contrast medium has been used to improve soft tissue detail in these evaluations.10–13 The purpose of the study reported here was to describe the use of non–contrast-enhanced CT to identify DDF tendinopathy in the affected digit of lame horses.
Materials and Methods
Case selection
The radiologic information system of the Washington State University College of Veterinary Medicine was searched to identify horses that underwent CT with or without contemporaneous high-field MRI as part of an evaluation for lameness localized to areas distal to the metacarpophalangeal or metatarsophalangeal joint in ≥ 1 limb between July 1, 2014, and June 30, 2016. Contrast-enhanced CT was not performed at the facility during the study period. Horses were included in the study if they had CT performed and ≥ 1 DDFT lesion (DDF tendinopathy) was identified and considered to be contributing to signs of pain and lameness.
Medical records review
Medical records were reviewed by 1 investigator (AREJ). The following information was extracted for descriptive analysis: breed, sex, age at the time of the evaluation, discipline or purpose for which the horse was used, the limb or limbs and regions where signs of pain causing lameness were localized, site of the primary lameness, lameness grade and duration, response to perineural anesthesia, diagnostic imaging modality or modalities used, anesthetic medications administered, duration of anesthesia (measured from the time of induction until discontinuation of anesthetic agents and placement of the horse in the recovery area), and imaging findings. One author (AREJ) retrospectively evaluated all of the diagnostic images (and performed described measurements), and the findings were corroborated with the radiology report.
Lameness examinations and diagnostic imaging
All procedures were performed with informed client consent. Lameness examinations were performed by board-certified veterinary surgeons. Lameness was graded on a scale of 0 to 5 according to American Association of Equine Practitioners guidelines.14 Diagnostic perineural anesthesia was performed with previously described techniques.15 In addition to physical lameness examination results, the percentage improvement in lameness following local anesthetic administration was evaluated and corroborated with a wireless inertial sensor systema as described elsewhere.16 Once the presumptive cause of lameness was localized, diagnostic imaging options were discussed with the owner. When CT was pursued, radiographs were not obtained.
Horses were premedicated with xylazine hydrochlorideb (0.7 mg/kg [0.32 mg/lb], IV) and butorphanol tartratec (0.02 mg/kg [0.01 mg/lb], IV). General anesthesia was induced with ketamined (2.2 mg/kg [1 mg/lb], IV) and diazepame (0.05 mg/kg [0.02 mg/lb], IV). For CT, general anesthesia was maintained with a combined solution of guaifenesin (50 mg/mL), ketamine (1 mg/mL), and xylazine (0.5 mg/mL) administered IV to effect; for MRI, horses were orotracheally intubated and anesthesia was maintained with isofluranef in 100% oxygen.
Non–contrast-enhanced CT examinations were performed with a 16-slice helical CT scanner.g Horses were positioned in lateral recumbency on a table designed for equine patients. Both forelimbs or both hind limbs (if lameness was present in ≥ 1 forelimb or hind limb, respectively) were positioned adjacent to each other in the gantry. Simultaneous scanning of the area of interest (from the metacarpophalangeal or metatarsophalangeal joint to the most distal aspect of the hoof wall) for both limbs was performed according to a standardized protocol (exposure, 135 kVp; current, 250 mA; rotation speed, 750 milliseconds; and helical pitch, 11). The helical volume data in 2- or 3-mm contiguous slices with 512 × 512 matrix dimensions were reformatted into axial, sagittal, and coronal planes for interpretation, with both bone and soft tissue algorithms applied. The DICOM images were evaluated with a window width of 220 HU and window level of 120 HU for soft tissues; a window width of 2,700 HU and window level of 350 HU were used for bone. For radiodensity and lesion length measurements, DICOM images were imported into an open-source medical image viewing programh; for affected limbs, apparently normal regions of the DDFT in close proximity to the lesion and the lesion area were each circumscribed, and the difference in radiodensity (HU) was recorded. In addition to CT, MRI of both limbs was performed for a subset of horses during the same anesthetic episode, as requested by the attending clinician in accordance with the owner's decision.
Non–contrast-enhanced MRI sequences were acquired with a 1.0-T high-field magneti and a human knee quadrature receiver coil on the digit to be imaged. Each limb was imaged sequentially. Dual-echo (proton density and T2-weighted), short tau inversion recovery, and 3D gradient echo sequences were used for image acquisition in axial, sagittal, and coronal planes, with 4- or 5-mm slice thickness and 5-mm gap.
The CT was performed prior to MRI in all cases, and the CT images were read and reported by radiology department staff without knowledge of the MRI results and vice versa. Images were interpreted by board-certified veterinary radiologists. The length of DDFT lesions from the most proximal to the most distal extent was measured on CT images or both CT and MRI images. Lesion lengths were measured on sagittal DICOM images from the first axial slice in which the lesion was visible to the last, following along the curvature of the tendon. These measurements were performed by 1 evaluator (AREJ).
Results
One hundred eight horses with lameness attributed to pain in regions distal to ≥ 1 metacarpophalangeal or metatarsophalangeal joint underwent non–contrast-enhanced CT with or without high-field MRI during the study period. Of these, 28 horses had a diagnosis of DDF tendinopathy and were included in the study. Nineteen horses underwent CT only, and the remaining 9 horses had CT followed immediately by MRI. None of the 9 horses that underwent CT and MRI had a DDFT lesion identified by only one of the modalities.
The study population included 24 American Quarter Horses, 1 Irish Sport Horse, 1 Hanoverian, 1 American Paint, and 1 Thoroughbred-Holsteiner crossbred horse. Sixteen were geldings and 12 were mares, and the median age at the time of the examination was 9 years (range, 4 to 16 years). The horses were used for barrel racing (n = 8), trail riding (7), western pleasure riding (4), dressage (3), eventing (1), pleasure riding (1), roping (1) polo (1), ranch work (1), and horse shows (1).
Bilateral forelimb lameness was detected in 20 horses, unilateral forelimb lameness was identified in 6 horses, and unilateral hindlimb lameness was found in 2 horses. The primary lameness was isolated to the left forelimb in 15 horses, right forelimb in 11 horses, left hind limb in 1 horse, and right hind limb in 1 horse. The wireless inertial sensor system was used in all cases and corroborated the clinicians’ subjective assessment of lameness in each horse. The median lameness grade was 3 of 5 (range, 2 to 4), and median duration of lameness was 8 months (range, 0.5 to 84 months). There was > 90% improvement in lameness after perineural analgesia in 26 horses and 60% to 90% improvement in 2 horses. Lameness was improved by injection of a local anesthetic solution in proximity to the palmar digital nerves (n = 22), palmar or plantar nerves (at the base of the proximal sesamoid bones; 5), or plantar (at the level of the proximal extent of the digital flexor tendon sheath) and plantar metatarsal (at the distal end of the second and fourth metatarsal bones) nerves (1).
No difficulties were encountered during image acquisition, anesthesia, or anesthetic recovery. The median CT image acquisition time was 20 seconds (range, 15 and 30 seconds), with both forelimbs or hind limbs scanned simultaneously. Median anesthesia time when CT was performed alone was 15 minutes (range, 7 to 30 minutes). The median number of MRI sequences produced for the 9 horses that also had this procedure performed was 18 (range, 12 to 22), and median MRI acquisition time was 80 minutes (range, 63 to 118 minutes). The median anesthesia time was 110 minutes (range, 80 to 135 minutes) when both imaging procedures were performed.
For the 56 limbs imaged by CT in 28 horses, DDF tendinopathy was found in 48. Core lesions were present in 46 of 48 (96%) affected limbs, and dorsal border irregularities were present in 35 of 48 (73%). Only 1 horse had DDF tendinopathy without a core lesion. Core lesions within the DDFT were characterized by a hypoattenuating focus, with alteration of the architecture in some cases, observed within ≥ 1 of the lobes of the tendon (Figure 1). Median density of the lesion-free regions of DDFTs (deemed normal tissue) was 97 HU (range, 80 to 117), and the median decrease in attenuation within lesions was 34 HU (range, 21 to 63). Lesions in DDFTs were bilateral in 20 of 28 (71%) horses and unilateral in 8 (29%). Four horses with unilateral lameness had bilateral DDFT lesions.
Representative images (axial CT slices) depicting core lesions in DDFTs (arrows) in a study to describe the use of non–contrast-enhanced CT to diagnose DDF tendinopathy in 28 horses with lameness attributed to pain in regions distal to the metacarpophalangeal or metatarsophalangeal joints. Lateral is to the left and dorsal is to the top of the images. A—The enlarged medial lobe of the DDFT contains a large lesion at the level of the midregion of the proximal phalanx. B—Lesions are evident in both lobes of the DDFT at the level of the midregion of the middle phalanx. There is hyperattenuation on the dorsal aspect of the DDFT, and a substantial amount of navicular bursa effusion (asterisks) as well as distal interphalangeal joint effusion (dagger) is present. C—Small lesions are present in both lobes of the DDFT at the level of the navicular bone. D—Lesions are present in both lobes of the DDFT just proximal to its insertion on the distal phalanx. The medial lobe lesion is more hypoattenuating (density, 38 HU) than that in the lateral lobe (density, 54 HU) relative to the rest of the tendon in the image (mean density, 80 HU).
Citation: Journal of the American Veterinary Medical Association 254, 7; 10.2460/javma.254.7.852
Twenty-eight imaged limbs had DDFT lesions in both the medial and lateral lobes, and 28 had lesions in just 1 lobe of the tendon. The median length of DDFT lesions (n = 48) measured on CT was 45 mm (range, 10 to 143). Lesion lengths of < 30 mm (n = 18), 30 to 60 mm (16), > 60 to 90 mm (8), > 90 to 120 mm (3), and > 120 mm (3) were recorded.
Fifteen limbs from the 9 horses that were evaluated by MRI after CT was completed had DDFT lesions (Figure 2; Table 1). The proton density and short tau inversion recovery sequences most frequently detected DDFT lesions. Four limbs had the same lesion length determined by both methods. For the remaining limbs, the CT measurement exceeded the MRI measurement in each case; in 2 instances, the determination of lesion limits was hindered by MRI slice thickness and gap.
Representative CT (A) and MRI (B) images depicting the same DDFT lesion in a horse. Images were obtained at the level of the proximal aspect of the middle phalanx; lateral is to the left and dorsal is to the top of the images. A—The CT image shows a large hypoattenuating lesion (arrow) in the medial lobe of the DDFT. The dorsal abaxial margin is indistinct, and the palmar abaxial area of the medial lobe of the DDFT is hypoattenuating (mean density, 66 HU), compared with the axial portion of the medial lobe and the lateral lobe (mean density, 104 HU). Navicular bursa effusion (asterisks) is also present. B—A proton density MRI image of the same region as in panel A shows a large area of hyperintensity (arrow) in the medial lobe of the DDFT.
Citation: Journal of the American Veterinary Medical Association 254, 7; 10.2460/javma.254.7.852
Measurements of DDFT lesion length in a study to describe the use of non–contrast-enhanced CT to diagnose DDF tendinopathy in 28 horses with lameness attributed to pain in regions distal to the metacarpophalangeal or metatarsophalangeal joints.
| Limb | Lesion length measured by MRI (mm) | Additional lesion length measured by CT (mm) |
|---|---|---|
| 1 | 53* | 44 |
| 2 | 21* | 6 |
| 3 | 72* | 7 |
| 4 | 17† | 5 |
| 5 | 48* | 6 |
| 6 | 18 | 0 |
| 7 | 45† | 10 |
| 8 | 28* | 39 |
| 9 | 45* | 30 |
| 10 | 22* | 13 |
| 11 | 92* | 29 |
| 12 | 21* | 26 |
| 13 | 65 | 0 |
| 14 | 41 | 0 |
| 15 | 23 | 0 |
Nine horses underwent bilateral forelimb or hind limb imaging by both CT and MRI; 15 limbs had DDFT lesions detected.
The lesion extended further proximally than the region imaged by MRI.
The definition of the lesion limits was hindered by the MRI slice thickness and gap.
Concurrent lesions frequently identified via CT in horses with DDF tendinopathy included navicular bone degeneration (n = 44 limbs), navicular bursa effusion (21), collateral sesamoidean desmopathy (16), distal interphalangeal joint effusion (14), erosion of the palmar compact bone of the navicular bone (14), fragmentation of a corner of the navicular bone (10), and digital flexor tendon sheath effusion (9). Lesions present in ≤ 5 limbs included enthesopathy at the insertion of the distal sesamoidean impar ligament; enthesopathy of the collateral ligaments of the distal interphalangeal joint; arthrosis of the proximal or distal interphalangeal or metacarpophalangeal joints; subchondral bone defects at the distal articulation (condyles) of the third metacarpal bone or the proximal aspect of the proximal phalanx; desmopathy of the distal digital annular ligament, oblique sesamoidean ligament, or straight sesamoidean ligament; metacarpophalangeal joint effusion; and a navicular osseous cyst-like lesion.
Discussion
To the authors’ knowledge, the present study was the first to investigate DDFT lesions in horses with lameness attributed to pain in regions distal to the metacarpophalangeal or metatarsophalangeal joints for which results of CT and contemporaneous high-field MRI were available for some cases. Lately, CT has been more frequently selected as the imaging modality of choice for distal aspects of the limbs of horses at our institution. This is because the data can be rapidly acquired and processed to enhance osseous and soft tissue detail, including the DDFT, with a short anesthesia time.
In the present study, lesions of the DDFT were easily recognized by use of CT without the use of contrast medium. Lesions were characterized by a hypoattenuating focus within a lobe of the tendon or alteration of the tendon architecture such as enlargement or loss of a discrete fiber pattern. The use of contrast-enhanced CT has been shown to have good sensitivity for detection of DDFT lesions, compared with macroscopic and histopathologic examination results.11,13 However, the addition of contrast medium can hinder visualization of soft tissues or complicate image interpretation in some situations.17
Non–contrast-enhanced CT has been used to identify DDFT lesions proximal to the navicular bone; however, there were difficulties distinguishing DDFT lesions from the level of the proximal aspect of the navicular bone distally.10,17 We were able to detect such lesions in the present study, possibly because of their severity or because the CT machine used in our study was a multislice helical scanner, which can improve 3D contrast and spatial resolution, compared with a single-slice CT scanner.18 This improvement in image quality with newer machines should change the paradigm that CT is useful only for bone imaging. Previous investigations10–12,19 that involved DDFT imaging also used helical CT scanners, similar to the present study. The additional information that contrast enhancement has been reported to provide includes increased lesion conspicuity and increased presence of small blood vessels on the palmar surface of the DDFT.12 The soft tissue detail achieved by CT without contrast medium in the present study allowed for lesion detection, saving the additional time and expense needed for contrast medium administration, which also requires technical expertise. Owing to common familiarity with radiographic technology, images obtained by CT are easier to interpret than those acquired by MRI,8,20 which requires additional training and expertise. Similar to MRI,21,22 CT not only allows for detection of DDF tendinopathy but also provides better imaging detail for navicular bone degeneration, compared with radiography.9,23
Lesions such as adhesions between the dorsal aspect of the DDFT and other structures have been reported in an MRI study of horses.24 Histopathologic data, if available, were not reviewed in our study, preventing confirmation of the presence of adhesions. However, the dorsal border irregularities identified in this study had an appearance on CT that was similar to those in contemporaneously acquired high-field MRI images.
Complications were not identified in horses that underwent MRI in the present study (requiring substantially longer anesthesia time than CT as well as the use of inhalation anesthetic), although decreased anesthesia time has been shown to increase recovery quality25 and total IV anesthesia has been shown to decrease the risk of death in horses, compared with that for inhalation anesthesia in other studies.26,27 Rapid acquisition with a large scan area facilitated CT detection of the full proximal extent of DDFT lesions and lesions in the distal aspect of the third metacarpal bone. To prevent excessive time under general anesthesia, repositioning of the radiofrequency coil during MRI and acquisition of extra sequences to follow DDFT lesions proximally were not always performed after a lesion had been identified.
Four horses in the present study that had unilateral lameness had bilateral DDFT lesions. Similar findings have been previously reported for horses evaluated by contrast-enhanced CT19 and MRI.28 Computed tomography, as an advanced, sensitive imaging modality, may reveal lesions that are not clinically characterized by lameness. Other possible explanations for these findings included low sensitivity of the lameness examination or false-positive lesion classification. Another 4 horses had bilateral lameness but had DDF tendinopathy identified in only 1 limb. This was not unexpected, as other causes of lameness can develop in the region distal to the metacarpophalangeal or metatarsophalangeal joints, and the imaging modalities detect anatomic and physiologic features rather than pain. All horses that required perineural anesthesia at the base of the proximal sesamoid bones to abolish lameness had lesions extending more proximally than a palmar digital nerve block, up to the level of the proximal portion of the proximal phalanx.
Interestingly, 44 of 48 (92%) limbs with DDF tendinopathy had navicular bone degeneration detected, a higher prevalence than that reported in previous MRI studies.1,21,29 Unlike MRI, CT technology cannot demonstrate signal changes within the navicular bone. However, reasons for this higher prevalence could have included the population of horses in our study, which primarily comprised Quarter Horses, or that CT can more frequently detect osseous remodeling in the navicular bone.9,10 Additionally, horses with prior radiographic abnormalities may have been excluded from advanced imaging in other studies. The frequent concurrence of these lesions could have been attributable to their anatomic proximity and the fact that when there is remodeling of the navicular bone, especially on the palmar or plantar surface, disruption of the DDFT fibers can occur.30–32 Many of the other lesions detected in the limbs of horses affected by DDF tendinopathy can cause or contribute to pain, which can manifest as lameness. Although DDFT lesions are among the most common causes of foot pain in horses,1 additional abnormalities were detected in the same limb and region for several horses in the present study, and it was unknown whether the DDFT lesions were the primary cause of lameness.
To the authors’ knowledge, there is 1 report33 of CT being adapted for use in standing horses, and if this technology continues to be developed and becomes more widely accessible, it may be the most practical and cost-effective imaging modality for investigation of the sources of pain causing lameness in the distal aspects of equine limbs. Compared with low-field MRI, standing CT would provide better spatial resolution,34,35 decreased acquisition time, and potentially less motion artifact because of the shorter time needed for image acquisition.
The present study was restricted to a small number of horses; because it was performed in clinical cases, histologic examination to evaluate the microscopic structure of the DDFTs was lacking. Without this type of evidence, it was not possible to calculate the number of false-positive and false-negative results for diagnostic imaging. Although this represented a substantial limitation of the study, histologic examination has shown that the hypoattenuating core lesions seen on CT reflect collagen lysis and cell necrosis.11 The consistency of non–contrast-enhanced CT findings for 9 horses in the present study, compared with results of contemporaneously performed high-field MRI, supported that CT is a useful tool for detection of DDF tendinopathy; however, further research is needed to confirm this, and the authors are not suggesting that MRI can be replaced by CT. However, helical CT did provide detailed and useful multiplanar images of bone and soft tissue structures in these horses.
Acknowledgments
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
ABBREVIATIONS
| DDF | Deep digital flexor |
| DDFT | Deep digital flexor tendon |
Footnotes
Lameness Locator, Equinosis LLC, Columbia, Mo.
Anased, Lloyd Inc, Shenandoah, Iowa.
Torbugesic, Fort Dodge Animal Health, Madison, NJ.
Ketaset, Fort Dodge Animal Health, Madison, NJ.
Hospira, Lake Forest, Ill.
VetOne, Boise, Idaho.
Aquilion 16, Toshiba Medical Systems Corp, Tochigi-ken, Japan.
Horos, version 1.17. Sponsored by Nimble Co LLC, dba Purview, Annapolis, Md. Available at: www.horosproject.org. Accessed Feb 15, 2016.
Philips Gyroscan, Medical Systems, Best, Netherlands.
References
1. Dyson SJ, Murray R, Schramme MC. Lameness associated with foot pain: results of magnetic resonance imaging in 199 horses (January 2001–December 2003) and response to treatment. Equine Vet J 2005;37:113–121.
2. Seignour M, Pasquet H, Coudry V, et al. Ultrasonographic diagnosis of injuries to the deep digital flexor tendon and associated structures in the equine foot (suprasesamoidean area). Equine Vet Educ 2011;23:369–376.
3. Tietje S. Computed tomographic evaluation of the distal aspect of the deep digital flexor tendon (DDFT) in horses. Pferdeheilkunde 2001;17:21–29.
4. Olivier-Carstens A. Ultrasonography of the solar aspect of the distal phalanx in the horse. Vet Radiol Ultrasound 2004;45:449–457.
5. Sherlock CE, Kinns J, Mair TS. Evaluation of foot pain in the standing horse by magnetic resonance imaging. Vet Rec 2007;161:739–744.
6. Barbee DD, Allen JR, Gavin PR. Computed tomography in horses. Vet Radiol 1987;28:144–151.
7. Barbee DD, Allen JR. Computed tomography in the horse: general principles and clinical applications, in Proceedings. 32nd Annu Conv Am Assoc Equine Pract 1986;483–493.
8. Kraft SL, Gavin PR. Physical principles and technical considerations for equine computed tomography and magnetic resonance imaging. Vet Clin North Am Equine Pract 2001;17:115–130.
9. Widmer WR, Buckwalter KA, Fessler JF, et al. Use of radiography, computed tomography and magnetic resonance imaging for evaluation of navicular syndrome in the horse. Vet Radiol Ultrasound 2000;41:108–116.
10. Vallance SA, Bell RJ, Spriet M, et al. Comparisons of computed tomography, contrast-enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 2: lesion identification. Equine Vet J 2012;44:149–156.
11. van Hamel SE, Bergman HJ, Puchalski SM, et al. Contrast-enhanced computed tomographic evaluation of the deep digital flexor tendon in the equine foot compared to macroscopic and histological findings in 23 limbs. Equine Vet J 2014;46:300–305.
12. Puchalski SM, Galuppo LD, Hornof WJ, et al. Intraarterial contrast-enhanced computed tomography of the equine distal extremity. Vet Radiol Ultrasound 2007;48:21–29.
13. Puchalski SM, Galuppo LD, Drew CP, et al. Use of contrast-enhanced computed tomography to assess angiogenesis in deep digital flexor tendonopathy in a horse. Vet Radiol Ultrasound 2009;50:292–297.
14. AAEP Horse Show Committee. Guide to veterinary services for horse shows. 7th ed. Lexington, Ky: American Association of Equine Practitioners 1999.
15. Moyer W, Schumacher J, Schumacher J. A guide to equine joint injection and regional anesthesia. Chadds Ford, Pa: Academic Veterinary Solutions, 2007.
16. McCracken MJ, Kramer J, Keegan KG, et al. Comparison of an inertial sensor system of lameness quantification with subjective lameness evaluation. Equine Vet J 2012;44:652–656.
17. Vallance SA, Bell RJW, Spriet M, et al. Comparisons of computed tomography, contrast-enhanced computed tomography and standing low-field magnetic resonance imaging in horses with lameness localised to the foot. Part 1: anatomic visualisation scores. Equine Vet J 2012;44:51–56.
18. Kalender WA, Polacin A, Süss C. A comparison of conventional and spiral CT: an experimental study on the detection of spherical lesions. J Comput Assist Tomogr 1994;18:167–176.
19. Hunter BG, Huber MJ, Nemanic S. The use of computed tomography to diagnose bilateral forelimb tendon pathology in a horse with unilateral lameness. Equine Vet Educ 2016;28:439–443.
20. Schramme MC. Treatment of deep digital flexor tendonitis in the foot. Equine Vet Educ 2008;20:389–391.
21. Dyson S, Murray R. Use of concurrent scintigraphic and magnetic resonance imaging evaluation to improve understanding of the pathogenesis of injury of the podotrochlear apparatus. Equine Vet J 2007;39:365–369.
22. Schneider RK, Gavin PR, Tucker RL. What MRI is teaching us about navicular disease, in Proceedings. 49th Ann Convention Am Assoc Equine Pract 2003;210–219.
23. Whitton RC, Buckley C, Donovan T, et al. The diagnosis of lameness associated with distal limb pathology in a horse: a comparison of radiography, computed tomography and magnetic resonance imaging. Vet J 1998;155:223–229.
24. Schramme MC. Deep digital flexor tendinopathy in the foot. Equine Vet Educ 2011;23:403–415.
25. Young SS, Taylor P. Factors influencing the outcome of equine anaesthesia: a review of 1,314 cases. Equine Vet J 1993;25:147–151.
26. Johnston GM, Eastment JK. The confidential enquiry into perioperative equine fatalities (CEPEF): mortality results of phases 1 and 2. Vet Anaesth Analg 2002;29:159–170.
27. Bidwell LA, Bramlage LR, Rood WA. Equine perioperative fatalities associated with general anaesthesia at a private practice—a retrospective case series. Vet Anaesth Analg 2007;34:23–30.
28. Dyson SJ, Murray RC, Schramme M, et al. Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging. Equine Vet J 2003;35:681–690.
29. Martinelli MJ, Rantanen NW. Relationship between nuclear scintigraphy and standing MRI in 30 horses with lameness of the foot, in: Proceedings. 51st Ann Convention Am Assoc Equine Pract 2005;359–365.
30. Hickman J. Navicular disease—what are we talking about? Equine Vet J 1989;21:395–398.
31. Murray RC, Schramme MC, Dyson SJ, et al. Magnetic resonance imaging characteristics of the foot in horses with palmar foot pain and control horses. Vet Radiol Ultrasound 2006;47:1–16.
32. Blunden A, Dyson S, Murray R, et al. Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 2: the deep digital flexor tendon. Equine Vet J 2006;38:23–27.
33. Desbrosse FG, Vandeweerd J-MEF, Perrin RAR, et al. A technique for computed tomography (CT) of the foot in the standing horse. Equine Vet Educ 2008;20:93–98.
34. d'Anjou M-A. Principles of computed tomography and magnetic resonance imaging. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 6th ed. St Louis: Elsevier, 2013;50–73.
35. Bushberg JT, Seibert JA, Leidholdt EM Jr, et al eds. Introduction to medical imaging. In: The essential physics of medical imaging. 2nd ed. Philadelphia: Lippincott, Williams and Wilkins, 2002;3–15.
