Clinical findings, surgical techniques, prognostic factors for short-term survival and long-term outcome in horses with acquired inguinal hernias: Ninety-eight cases (2005-2020).

OBJECTIVE: To report findings, outcome and determine variables associated with survival in horses with acquired inguinal hernia (AIH). STUDY DESIGN: Retrospective study. ANIMALS: A total of 98 cases in 97 horses. METHODS: The medical records (2005-2020) of horses diagnosed with AIH were reviewed. Retrieved data included signalment, history, clinical variables, surgical aspects, postoperative complications, and short- and long-term outcomes. Logistic regression analyses were used to determine factors associated with short-term survival (p < .05). RESULTS: Manual reduction was attempted in a third of the cases (32/98, 33%) and emergency surgery to reduce the hernia was performed in 64 of 98 (65%) cases. Concurrent small intestinal (SI) volvulus was identified in 26 (26/98, 27%) cases. Castration was the most common technique used to prevent recurrence (64/94, 68%). Overall AIH recurrence rate was 11% (11/98). A total of 59 (59/98, 60%) cases survived to hospital discharge and 49 of 52 (94%) cases were still alive after 12 months. Cases admitted within 10 h of colic signs had increased odds of survival (72%) compared to those admitted after 10 h (26%; p < .001). Draft breeds (p = .021), high heart rate on admission (p = .001) and concurrent SI volvulus (p = .048) were associated with reduced survival to hospital discharge. CONCLUSIONS: Horses with AIH had a higher risk of concurrent SI volvulus and lower survival than reported. Draft breeds, high heart rate on admission and concurrent SI volvulus were associated with reduced short-term survival. CLINICAL SIGNIFICANCE: The results of this study should help in prognostication for horses with AIH.

CT is a feasible imaging technique for detecting lesions in horses with elbow lameness: A study of 139 elbows in 99 horses.

Computed tomography (CT)is increasingly available in veterinary referral practices; however, published studies describing CT lesions of the equine elbow are currently lacking. In this single-center, retrospective, observational study, horses undergoing elbow CT at Equitom between July 2015 and October 2018 were reviewed. Subchondral bone sclerosis; resorption of the radius, ulna, and humerus; osteophyte; and enthesophyte lesions were graded. One hundred thirty-nine elbows of 99 horses (16 with elbow pain and 123 control elbows) were included (median age, 9 years). Osseous cyst-like lesions (n = 13), only seen in the proximomedial radius and medial humerus, were the most common cause of lameness in horses with elbow pain (n = 16), with significantly higher grades of bone resorption (including osseous cyst-like lesions) in this group. One elbow had an avulsion fracture of the lateral epicondyle, two others showed signs of osteoarthritis. Significantly higher grades of sclerosis in the proximomedial radius were seen in horses with elbow pain; however, mild to moderate subchondral bone sclerosis was seen in all horses at the medial aspect of the joint. Osteochondral fragmentation lesions of the weight-bearing surface of the medial radius (2/16 vs 1/123; P = .0025) and intra-articular gas (4/16 vs 2/123; P < .0001) were significantly more common in horses with elbow pain compared to control horses. Mild linear resorptive subchondral bone lesions were often not clinically relevant (32/123 vs 5/16 in medial humerus; 19/123 vs 2/16 in medial radius). In conclusion, elbow CT is a feasible method for detecting clinically relevant lesions in adult Warmblood horses with elbow pain.

Standing low-field MRI of the equine proximal metacarpal/metatarsal region is considered useful for diagnosing primary bone pathology and makes a positive contribution to case management: A prospective survey study.

High-field MRI of the proximal metacarpal/metatarsal region has been associated with great diagnostic potential and clinical reports of standing low-field MRI of the forelimb suggest the same. To better understand diagnostic outcomes with standing low-field MRI of the proximal suspensory region, a prospective survey study was conducted and users of a widely available system questioned on their experience, operating procedures, and interpretation of standing low-field MRI findings. Response data included scores on a modified Likert scale from which weighted ratings were calculated for statistical analyses. Depending on the question, responses were obtained from 17 to 29 of the 38 invited facilities. Users indicated that standing low-field MRI was most frequently performed in the face of equivocal diagnostic findings; compared to Sports horses, general purpose riding horses were thought less likely to have detectable abnormalities and standing low-field MRI was rated most useful for the detection of primary bone pathology in the proximal metacarpal region. Standing low-field MRI signal change involving both the suspensory ligament and adjacent bone concurrently was rated most relevant and abnormalities solely affecting the muscle/adipose tissue bundles least relevant for diagnosing suspensory ligament injury. Transverse scans and in decreasing order T1-weighted gradient echo, short-tau inversion recovery FSE, T2*-weighted gradient echo, and T2-weighted FSE sequences were most frequently acquired and judged most useful by the majority of users experienced in imaging of the target area. This survey supports the relevant impact of standing low-field MRI on clinical case management, particularly in the context of imaging the proximal metacarpal region.

Comparison of efficacy and safety of single versus repeated intra-articular injection of allogeneic neonatal mesenchymal stem cells for treatment of osteoarthritis of the metacarpophalangeal/metatarsophalangeal joint in horses: A clinical pilot study.

The purpose of this prospective study was to evaluate the effects of single and repeated intra-articular administration of allogeneic, umbilical cord-derived, neonatal mesenchymal stem cells (MSC) in horses with lameness due to osteoarthritis (OA) of a metacarpophalangeal joint (MPJ). Twenty-eight horses were included. Horses were divided into two groups. Horses in group MSC1 received an MSC injection at M0 and a placebo injection at M1 (1 month after M0). Horses in group MSC2 received MSC injections at M0 and at M1. Joint injections were performed with a blinded syringe. Clinical assessment was performed by the treating veterinarian at M1, M2 and M6 (2 and 6 months after M0), including lameness evaluation, palpation and flexion of the joint. Radiographic examination of the treated joints was performed at inclusion and repeated at M6. Radiographs were anonymized and assessed by 2 ECVDI LA associate members. Short term safety assessment was performed by owner survey. A 2-month rehabilitation program was recommended to veterinarians. There was a significant improvement of the total clinical score for horses in both groups. There was no significant difference in the total clinical score between groups MSC1 and MSC2 at any time point in the study. There was no significant difference in the total radiographic OA score, osteophyte score, joint space width score and subchondral bone score between inclusion and M6. Owner-detected adverse effects to MSC injection were recorded in 18% of the horses. Lameness caused by OA improved significantly over the 6-month duration of the study after treatment with allogeneic neonatal umbilical cord-derived MSCs combined with 8 weeks rest and rehabilitation. There is no apparent clinical benefit of repeated intra-articular administration of MSCs at a 1-month interval in horses with MPJ OA when compared to the effect of a single injection.

Bone marrow lesions of the distal condyles of the third metacarpal bone are common and not always related to lameness in sports and pleasure horses.

The metacarpophalangeal joint is a common site of pain in horses. Little information is available about bone marrow lesions in the distal condyles of the third metacarpal bone in sports and pleasure horses. Aims of this prospective, retrospective, observational study were to evaluate the prevalence of bone marrow lesions in the distal condyles of the third metacarpal bone, to describe their anatomic distribution and to correlate lesions with the presence of lameness and the level and type of activity. All sports and pleasure horses undergoing standing low-field MRI of the front fetlock region between 2009 and 2016 were included and divided into three lameness groups according to the results of diagnostic analgesia. Bone marrow lesions were analyzed and graded by one reader. Grades were compared between anatomical locations and between lameness groups. A total of 166 horses were sampled. The prevalence of bone marrow lesions was 76.5% (127/166). The dorsal aspects of the medial condyle (31%, 39/127) and of the sagittal ridge (28%, 36/127) were the most commonly affected locations. There was no significant difference between both forelimbs (lame limb and non-lame limb) of the same horse. Lesion severity was neither significantly associated with the lameness group nor with the type or level of activity. The prevalence of bone marrow lesions in the distal condyles of the third metacarpal bone is high in this population and the clinical significance is not always clear. Further studies are required to elucidate the clinical significance of this finding in sports and pleasure horses.

Successful Treatment of a Persistent Oroantral Fistula via Transbuccal and Transnasal Endoscopic Debridement in a Horse.

We report an unusual case of a young Quarter Horse with a large dental fracture fragment displaced into the maxillary sinus, leaving an oroantral communication that caused food impaction and metaplastic calcification in the sinus and facial deformation with cutaneous fistulation. Oral extraction of a remaining tooth fragment from its alveolus was succeeded by a maxillary sinusotomy for removal of the abnormal sinus contents. Since the oroantral fistula did not heal spontaneously following the placement of a silicone dental prosthesis, minimally invasive transbuccal and transnasal endoscopic approaches were used to encourage closure of the oroantral fistula by alveolar granulation. The clinical, diagnostic, and therapeutic features of this case may be helpful to clinicians when dealing with similar cases.

LOW-FIELD MAGNETIC RESONANCE IMAGING APPEARANCE OF POSTARTHROSCOPIC MAGNETIC SUSCEPTIBILITY ARTIFACTS IN HORSES.

An awareness of magnetic susceptibility artifacts is important for interpreting prepurchase and postoperative magnetic resonance imaging (MRI) studies in horses. These artifacts occur when a metallic or a paramagnetic substance creates a local magnetic field deformity. Aims of the current experimental study were to determine prevalence of these artifacts after arthroscopy in a sample of nonlame horses, and to describe effects of time and type of pulse sequence on low-field MRI signal intensity and detection of the artifacts. Ten, nonlame Standardbred horses were prospectively recruited. All horses underwent arthroscopy of both metacarpophalangeal joints for purposes unrelated to the study. Serial low-Field MRI examinations were performed on each horse and each joint (before, and 6 and 12 weeks postsurgery). In two horses, more detailed longitudinal evaluations were performed with additional MRI examinations. Magnetic susceptibility artifacts were detected postoperatively at the surgical access sites in eight metacarpophalangeal joints at both 6 and 12 weeks after surgery (40% prevalence). Neither of the two longitudinally followed horses had artifacts at any time. Artifacts were only detected on gradient echo (GRE) sequences. Findings indicated that magnetic susceptibility artifacts can be present in postarthroscopy MRI studies in horses and can persist up to 12 weeks after arthroscopy. For this sample of horses, the artifacts did not interfere with evaluation of the joint. Further longitudinal studies are needed to determine the full duration of magnetic susceptibility artifact persistence in affected tissues.

Ultrastructural analysis of healthy synovial fluids in three mammalian species.

A better knowledge of synovial fluid (SF) ultrastructure is required to further understand normal joint lubrication and metabolism. The aim of the present study was to elucidate SF structural features in healthy joints from three mammalian species of different size compared with features in biomimetic SF. High-resolution structural analysis was performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and environmental SEM/wet scanning transmission electron microscopy mode complemented by TEM and SEM cryogenic methods. Laser-scanning confocal microscopy (LCM) was used to locate the main components of SF with respect to its ultrastructural organization. The present study showed that the ultrastructure of healthy SF is built from a network of vesicles with a size range from 100 to a few hundred nanometers. A multilayered organization of the vesicle membranes was observed with a thickness of about 5 nm. LCM study of biological SF compared with synthetic SF showed that the microvesicles consist of a lipid-based membrane enveloping a glycoprotein gel. Thus, healthy SF has a discontinuous ultrastructure based on a complex network of microvesicles. This finding offers novel perspectives for the diagnosis and treatment of synovial joint diseases.

Effect of anesthetizing individual compartments of the stifle joint in horses with experimentally induced stifle joint lameness.

OBJECTIVE: To evaluate the effects of sequential anesthesia of the individual compartments of the equine stifle joint on lameness induced by intra-articular deposition of interleukin (IL)-1ß. ANIMALS: 6 horses. PROCEDURES: For each horse, baseline hind limb lameness was first evaluated. A randomly selected compartment of 1 stifle joint was then injected with IL-1ß to induce synovitis and lameness; subsequently, the same compartment was anesthetized with 2% mepivacaine hydrochloride, and lameness was reevaluated. Two weeks later, baseline lameness was evaluated, and lameness was similarly induced; thereafter, the 2 synovial compartments of the stifle joint not injected with IL-1ß were anesthetized sequentially in random order (ie, first and second blocks); lameness was evaluated after each block. Finally, the IL-1ß-treated compartment was anesthetized (third block); lameness was again evaluated. This second experiment was repeated for the contralateral stifle joint 2 weeks later. Throughout the study, lameness was quantified objectively by assessing vertical pelvic movement asymmetry with a wireless, inertial sensor-based system. RESULTS: Intra-articular deposition of IL-1ß induced lameness in all injected limbs. In the first experiment, anesthesia of the compartment injected with IL-1ß resulted in a significant decrease in lameness, with vertical pelvic movement asymmetry approaching baseline. In the second experiment, lameness improved significantly after the second and third blocks and was almost completely abolished after all 3 synovial compartments were anesthetized. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, lameness caused by a lesion in 1 compartment of a stifle joint can be improved more by instillation of local anesthetic solution into that compartment than by anesthesia of the other compartments.

Characterization of the origin and body of the normal equine rear suspensory ligament using ultrasonography, magnetic resonance imaging, and histology.

The suspensory ligament is difficult to image accurately, partly because it contains ligamentous fibers, as well as noncollagenous adipose and muscle tissue in the normal horse. Our hypothesis was that magnetic resonance (MR) imaging would be more accurate than ultrasonography in identifying the size of the suspensory ligament and the presence and size of noncollagenous tissues within the ligament. Eleven horses were used for ultrasonographic and MR imaging and histologic evaluation of the rear suspensory ligament. The origin and body of the normal suspensory ligament had a heterogenous appearance on MR images with two separate islands of mixed signal intensity evident throughout its otherwise hypointense cross-sectional area. Histologically, there were isolated islands of muscle, adipose, loose connective tissue and dense collagenous partitions, organized in two separate bundles that extended through the full length of the suspensory ligament origin and body to the level of its bifurcation. Comparison of MR images with corresponding histologic sections confirmed that islands of heterogenous signal intensity in normal suspensory ligaments correlated well with these bundles. Using ultrasonography, it was impossible to distinguish these islands from surrounding dense collagenous tissue consistently. MR imaging determined the cross-sectional area of the suspensory ligament more accurately than ultrasonography. Based upon these results, MR imaging is superior to ultrasonography for assessment of the suspensory ligament. The appearance associated with normal ligament anatomy needs to be understood before MR signal variation can be considered as indicative of disease in the suspensory ligament.

Evaluation of four techniques for injecting the trochanteric bursa of horses.

OBJECTIVE: To describe the anatomic features of the equine trochanteric bursa and to evaluate 4 techniques for bursa centesis. STUDY DESIGN: Prospective, randomized design. ANIMALS: Equine cadavers (n=2) and 20 live horses. METHODS: The trochanteric bursae of 2 equine cadavers were injected with latex to identify the boundaries of the bursae. Four techniques for centesis of the trochanteric bursa were evaluated by attempting to inject dye into both trochanteric bursae of 20 live horses. Techniques included injection of the bursa with the limb-bearing weight and injection with the limb nonweight bearing and supported on a block, with or without ultrasonographic guidance of the needle. Ultrasonographic guidance of the needle was performed with or without the use of a guide channel attached to the ultrasound probe. Each of the 4 techniques was used to inject 10 bursae. The region of the bursa was dissected after horses were euthanatized to determine the location of the dye. RESULTS: The trochanteric bursa was most successfully injected with the limb positioned caudally with the foot on a block, even though topographic landmarks for centesis were more difficult to identify when the limb was in this position. The highest incidence of success was achieved when the needle was inserted using ultrasonographic guidance with the foot in a Hickman block. CONCLUSION: Positioning the limb caudally with the foot nonweight bearing and on a block facilitated centesis of the trochanteric bursa.

MRI features of metacarpo(tarso)phalangeal region lameness in 40 horses.

Lameness originating from the metacarpo(tarso)phalangeal (MP) joint has a significant effect on the use and athletic competitiveness of a horse. The identification of the cause of lameness originating from the MP joint can be challenging, given the limitations of radiography, ultrasonography, and nuclear scintigraphy. Our purpose was to describe the injury types and incidence in magnetic resonance imaging (MRI) studies from 40 horses with lameness attributable to the MP joint region where it was not possible to reach a clinically plausible diagnosis using other imaging modalities. Horses were examined in a 1.5 T magnet (Siemens Medical Solutions) under general anesthesia. The frequency of occurrence of MR lesions was subchondral bone injury (19), straight or oblique distal sesamoidean desmitis (13), articular cartilage injury and osteoarthritis (eight), suspensory branch desmitis (seven), osteochondral fragmentation (seven), proximal sesamoid bone injury (seven), inter-sesamoidean desmitis (four), deep digital flexor tendonitis (four), collateral desmitis (three), superficial digital flexor tendonitis (two), enostosis-like lesions of the proximal phalanx or MCIII (two), desmitis of the palmar annular ligament (one), desmitis of the proximal digital annular ligament (one), and dystrophic calcification of the lateral digital extensor tendon (one). Twenty-five horses had multiple MR abnormalities. MRI provided information that was complementary to radiography, ultrasonography, and nuclear scintigraphy and that allowed for a comprehensive evaluation of all structures in the MP joint region and a diagnosis in all 40 horses.

Mr imaging features of surgically induced core lesions in the equine superficial digital flexor tendon.

Tendon injuries are common in athletic humans and horses. Ultrasonography is the diagnostic method of choice in horses with tendon injuries but there is increasing application of magnetic resonance (MR) imaging to monitor and follow-up tendon healing. A core lesion was created in the superficial digital flexor tendon (SDFT) of each forelimb of four horses. One of the four horses was euthanized at 2, 4, 8, and 12 weeks after creation of the lesion. MR examinations of the SDFT were performed immediately post mortem in a 1.5 T Siemens Symphony magnet and compared with histologic findings. Measurements from the MR images were also compared to ultrasonographic measurements available from the same lesions. Tendon lesions appeared as well-circumscribed hyperintensities in the core of the SDFT on all pulse sequences. Lesions were most conspicuous on fat-suppressed fast low angle shot (FLASH) sequences and least conspicuous on T2 transverse dual turbo spin echo (T2 TSE) sequences. The signal-difference-to-noise ratio decreased with the age of the lesion in all sequences in this study. Twelve-week-old lesions were not visible on T2 TSE images but in all other sequences the lesion remained hyperintense. The lesion volume and maximum cross-sectional area of core lesions were significantly smaller in T2 TSE images than in other MR sequences. The lesion volume and maximum cross-sectional area of core lesions were significantly larger in proton density, T1, and FLASH sequences and significantly smaller in T2 sequences than when measured from ultrasonographic images. Through comparison between sequences, MR imaging may be able to provide information on various stages of tendon healing.

Clinical, magnetic resonance, and sonographic imaging findings in horses with proximal plantar metatarsal pain.

Sonography is commonly used for diagnosis of desmopathy of the proximal part of the suspensory ligament in horses. However, magnetic resonance (MR) imaging has been stated to be superior for detecting disease and localizing lesions. In this retrospective study of 39 horses or 46 hind limbs with lameness due to proximal plantar metatarsal pain, the clinical and diagnostic findings are discussed and sonography and MR imaging compared for examination of the proximal part of the suspensory ligament. With MR imaging interpreted as the clinical gold standard, desmopathy of the proximal part of the suspensory ligament was diagnosed in 21 hind limbs, proximal plantar metatarsal pain of unknown cause in 12, an osseous injury at the origin of the suspensory ligament in four and a condition unrelated to the suspensory ligament in nine. Based on these findings, sonography had a sensitivity of 0.77 and 0.66 and specificity of 0.33 and 0.31 for diagnosing proximal suspensory desmopathy and for accurately localizing lesions, respectively. MR imaging changes consistent with proximal suspensory desmopathy were signal hyperintensities and an increase in cross-sectional area compared with the contralateral limb. Anesthesia of the deep branch of the lateral plantar nerve is not specific neither for proximal suspensory desmopathy, as conditions unrelated to the suspensory ligament were diagnosed, nor for diagnosis of proximal plantar metatarsal pain, as conditions outside the proximal plantar metatarsal region were also diagnosed.

Improved identification of the palmar fibrocartilage of the navicular bone with saline magnetic resonance bursography.

Fibrocartilage degeneration is the earliest pathologic finding in navicular disease but remains difficult to detect, even with magnetic resonance (MR) imaging. We hypothesized that injection of the navicular bursa with saline would improve accuracy of MR imaging evaluation of palmar fibrocartilage. Thoracic limbs were collected from 11 horses within 6 h of death. Imaging was performed with a 1.5 T magnet using sagittal 2D proton density and transverse 3D FLASH sequences with fat saturation. For the purpose of determining sensitivity and specificity of the MR images, fibrocartilage was classified as normal or abnormal, based on combination of the findings of gross and microscopic pathology. Thickness of fibrocartilage was measured on histologic sections and corresponding transverse FLASH MR images before and after injection of saline. A paired Student's t-test was used for comparison of measurements. Partial thickness fibrocartilage loss was present in 6 of 22 limbs. Sensitivity of precontrast MR images for detection of lesions was 100% while specificity was 6%. Saline MR arthrography resulted in both sensitivity and specificity of 100% based on consensus review. Mean histologic fibrocartilage thickness was 0.75 +/- 0.12 mm. Mean fibrocartilage thickness on precontrast transverse FLASH images was 0.93 +/- 0.065 and 0.73 +/- 0.09 mm on postsaline images. The histologic cartilage thickness was signficantly different from that in precontrast images (P<0.001) but not in images acquired after saline injection (P = 0.716). Based on our results, and using pulse sequences as described herein, navicular fibrocartilage can only be evaluated reliably for the presence of partial thickness lesions after intrabursal injection of saline.

Compressive damage to the deep branch of the lateral plantar nerve associated with lameness caused by proximal suspensory desmitis.

OBJECTIVE: To describe pathologic changes in the deep branch of the lateral plantar nerve (DBLPN) of horses determined to be lame because of proximal suspensory desmitis (PSD), and to report the outcome after treatment by excision of a segment of the horses' DBLPN. STUDY DESIGN: Retrospective case series. ANIMALS: Adult horses (n=16). METHODS: Horses determined to be lame on one or both pelvic limbs because of PSD were treated by excision of a segment of the DBLPN, and 30 nerves were examined histologically. Owners were contacted to obtain information about the horses >or=6 months after surgery. RESULTS: Histologic changes suggestive of chronic nerve compression were identified in both nerves of 11 bilaterally lame horses and in the lame limb of 5 unilaterally lame horses. The nerve of the sound limb of 2 of 3 unilaterally lame horses that had bilateral nerve resection also had histologic changes compatible with nerve compression. Ten of 16 horses (62.5%) with follow-up information returned to soundness after excision of the DBLPN. CONCLUSIONS: Pathologic changes of the DBLPN associated with compression may complicate PSD of the pelvic limbs. Excision of the nerve may resolve lameness caused by PSD. CLINICAL RELEVANCE: Horses lame because of PSD of the pelvic limb may remain lame after desmitis has resolved because of compression of the DBLPN. Excising a portion of this nerve may resolve lameness.

Magnetic resonance imaging characteristics of the foot in horses with palmar foot pain and control horses.

Palmar foot pain is a common cause of lameness. Magnetic resonance imaging (MRI) has the potential to detect damage in all tissues of the equine foot, but an understanding of the differences in magnetic resonance (MR) images between feet from horses with and without palmar foot pain is required. This study aimed to describe MR findings in feet from horses with no history of foot-related lameness, and to compare these with MR findings in horses with lameness improved by palmar digital local analgesia. Thirty-four limbs from horses euthanized with a clinical diagnosis of navicular syndrome (ameness >2 months duration, positive response to palmar digital nerve blocks and absence of other forelimb problems) (Group L), and 25 feet from age-matched horses with no history of foot pain (Group N) were examined. For each anatomic structure, MR signal intensity and homogeneity, size, definition of margins, and relationships with other structures were described. Alterations in MR signal intensity and homogeneity were graded as mild, moderate, or severe and compared between Groups L and N. Results revealed that there were significant differences in MR images between Groups N and L. Multiple moderate-severe MR signal changes were present in 91% of limbs from Group L and moderate (none were graded severe) in 27% of limbs from Group N. In most Group L limbs, more than three structures and frequently six to eight structures were abnormal. Concomitant abnormalities involved most frequently the deep digital flexor tendon, distal sesamoidean impar ligament, navicular bone, collateral sesamoidean ligament, and navicular bursa (with significant associations in severity grade between these structures), sometimes with involvement of the distal interphalangeal joint and/or its collateral ligaments. It was concluded that findings on MR images were different between horses with and without foot pain, and that pain localized to the foot was associated with MR changes in a variety of structures, indicating that damage to several structures may occur concurrently and that MR imaging was useful for evaluation of foot pain.

How does magnetic resonance imaging represent histologic findings in the equine digit?

Magnetic resonance (MR) imaging is increasingly used in the diagnosis of equine foot pain, but improved understanding of how MR images represent tissue-level changes in the equine foot is required. We hypothesized that alterations in signal intensity and tissue contour would represent changes in tissue structure detected using histologic evaluation. The study objectives were to determine the significance of MR signal alterations in feet from horses with and without lameness, by comparison with histopathologic changes. Fifty-one cadaver feet from horses with a history of lameness improved by palmar digital analgesia (n = 32) or age-matched control horses with no history of lameness (n = 19) were stored frozen before undergoing MR imaging and subsequent histopathological examination at standard sites (deep digital flexor tendon, navicular bone, distal sesamoidean impar ligament, collateral sesamoidean ligament, and navicular bursa). Using MR images, signal intensity and homogeneity, size, definition of anatomic margins, and relationships with other structures were described. Alterations were graded as mild, moderate, or severe for each structure. For each anatomic site examined histologically the structures were described and scored as no changes, mild, moderate, or severe abnormalities, also taking into account adhesion formation within the navicular bursa detected on macroscopic examination. Alterations in MR signal intensity were related to changes at the tissue level detected by histologic examination. A sensitivity and specificity comparison of MR imaging with histologic examination was used to evaluate the significance of MR signal alterations for detection of moderate-to-severe lesions of the deep digital flexor tendon (DDFT), navicular bone, distal sesamoidean impar ligament (DSIL), collateral sesamoidean ligament (CSL) and navicular bursa. Agreement between the MR and histologic grading was assessed for each structure using a weighted kappa agreement. Direct comparison between histology and MR imaging for individual limbs revealed that signal alterations on MR imaging did represent tissue-level changes. These included structural damage, fibroplasia, fibrocartilaginous metaplasia, and hemosiderosis in ligaments and tendons; trabecular damage, osteonecrosis, fibroplasia, cortical defects, and increased vascularity in bone; and fibrocartilage defects. MR imaging had a high sensitivity and specificity for most structures. MR imaging had high specificity for lesions of the DDFT, CSL and navicular bursa, quite high specificity for lesions of the medulla of the navicular bone and its proximal aspect, with moderate specificity for the DSIL, and distal, dorsal and palmar aspects of the navicular bone, and was sensitive for detection of abnormalities in all structures except the dorsal aspect of the navicular bone. When MR and histologic grades alone were compared, there was good agreement between MR and histologic grades for the navicular bursa, DDFT, navicular bone medulla and CSL; moderate-to-good agreement in grades of the distal and palmar aspects of the navicular bone; fair to moderate in grades of the DSIL, and poor agreement for the dorsal and proximal aspects of the navicular bone. The results of this study support our hypothesis and indicate the potential use and limitations of MR imaging for visualization of structural changes within osseous and soft tissue structures of the equine foot.

Quantitative evaluation of equine deep digital flexor tendon morphology using magnetic resonance imaging.

Injury of the distal aspect of the deep digital flexor tendon (DDFT) is a recognized cause of lameness, but diagnosis is difficult. This study aimed to improve understanding of DDFT morphology and pathology using retrospective evaluation of magnetic resonance (MR) images. We hypothesized that: (1) The distal aspect of the DDFT in normal horses would have a repeatable proximal/distal pattern and symmetry between limbs and between lobes; (2) DDFT dimensions would be related to bodyweight, navicular bone dimensions and hoof size; (3) this symmetry and pattern would be lost in DDFT injury; and (4) DDFT size would increase with injury. MR images of 64 live horse limbs, 26 with no identified DDFT lesion and 38 with identified DDFT abnormalities, and 19 normal cadaver limbs were analyzed. Using standardized transverse images, measurements of DDFT cross-sectional area, medial-lateral (ML) width and dorsal-palmar depth were obtained at six preselected sites. A uniform distal to proximal shape pattern was identified in all horses. The flattened crescent shape at the insertion changed to a deeper bilobed shape more proximally, with the mid-navicular area having the greatest cross-sectional area. Strong ML (P < 0.0006) and left/right symmetry (P < 0.02) were observed. In addition, there was a strong association between DDFT cross-sectional area and horse weight (P = 0.005) and between DDFT and navicular bone ML width (P = 0.004). Symmetry between sides or between lobes was lost at sites with a unilateral lesion and correlation between horse weight and DDFT cross-sectional area was lost in the presence of lesions. DDFTs with core lesions had a consistent increase in cross-sectional area overall, but other lesion types had no significant increase in size. The shape and symmetry seen in normal tendons could be related to the mechanical demands placed upon individual lobes. The limited increase in cross-sectional area with injury may be explained by the restrictive structures of the hoof, possibly explaining the ongoing pain seen in such lesions.