MAGNETIC RESONANCE IMAGING FINDINGS IN HORSES WITH RECENT ONSET NAVICULAR SYNDROME BUT WITHOUT RADIOGRAPHIC ABNORMALITIES

Seventy-two horses with recent onset of navicular syndrome and normal radiographs were assessed. Horses underwent magnetic resonance (MR) imaging of both front feet. All abnormalities were characterized and the most severe abnormality identified, if possible. Abnormal signal intensity in the navicular bone was the most severe abnormality in 24 (33%) horses. Pathologic change in the deep digital flexor tendon was the most severe abnormality in 13 (18%) horses. Pathologic change in the collateral sesamoidean ligament was the most severe abnormality in 11 (15%) horses. Pathologic change in the distal sesamoidean impar ligament was the most severe abnormality in seven (10%) horses. Multiple abnormalities were observed in 13 (18%) horses in which an abnormality that was more severe than the others could not be determined. Abnormalities were not observed in the navicular bone or its supporting soft tissues in four (5%) horses. Fifty-six horses had abnormalities that were most severe in one limb; in 52 (93%) horses, the most severe abnormalities were in the foot of the most lame limb. In 7% (4/56) of horses, the most severe findings were in the opposite limb, and in 16 horses, the findings on both limbs were similar. MR imaging is a useful technique for evaluating horses with navicular syndrome and can differentiate between multiple abnormalities. This provides a more specific diagnosis which affects further treatment of the horse. Pathologic changes in different locations in the foot can cause similar clinical signs that, before MR imaging, were categorized as one syndrome.     

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.     

MRI FINDINGS IN 232 HORSES WITH LAMENESS LOCALIZED TO THE METACARPO(TARSO)PHALANGEAL REGION AND WITHOUT A RADIOGRAPHIC DIAGNOSIS

Two hundred and thirty‐two horses with lameness localized to the metacarpo(tarso)phalangeal (MCP/MTP) region without a radiographic diagnosis were evaluated. All horses had high‐field magnetic resonance (MR) imaging of the MCP/MTP region performed for the lame limb and the contralateral limb for comparison. There were 46 horses that had bilateral abnormalities in the forelimbs; 27 of these horses were not lame in the contralateral limb at the time of examination. Bilateral hind limb abnormalities were observed in 37 horses; 22 horses were not lame in the contralateral limb. Soft tissue abnormalities alone were observed in 218 limbs (162 horses). Subchondral bone and articular cartilage abnormalities alone were observed in 43 limbs (34 horses). A combination of soft tissue, subchondral bone, and cartilage abnormalities were observed in 64 limbs (36 horses). The distribution of primary abnormalities was as follows; oblique distal sesamoidean ligament desmitis (73 limbs in 56 horses), straight distal sesamoidean ligament desmitis (44 limbs in 38 horses), chronic subchondral bone injuries (15 limbs in 12 horses), suspensory ligament branch desmitis (14 limbs in 12 horses), collateral ligament desmitis (12 limbs in 12 horses), tendonitis of the superficial and deep digital flexor tendons (10 limbs in 10 horses), osteochondral defects greater than 1 cm (nine limbs in six horses), osteochondral defects less than 1 cm (eight limbs in seven horses), bone marrow lesions (six limbs in five horses), intersesamoidean ligament desmitis (five limbs in four horses). MR imaging is useful in diagnosing bone and soft tissue injuries when radiographs and ultrasound fail to yield a diagnosis.     

RESOLUTION OF LESIONS ON STIR IMAGES IS ASSOCIATED WITH IMPROVED LAMENESS STATUS IN HORSES

Magnetic resonance (MR) imaging is important in diagnosing musculoskeletal injuries in horses. However, there is still much to learn regarding the significance of lesions identified in equine MR images. Of particular importance is the clinical significance of signal change as a function of pulse sequence. We hypothesized that a resolution of tendon, ligament, and bone marrow lesions on short‐tau inversion recovery (STIR) images would be associated with a return to soundness, and that a persistence of tendon and ligament lesions on only T1‐weighted (T1w) gradient recalled echo (GRE) images would not be associated with persistent lameness. The medical records and MR images of 27 horses that had a hyperintense lesion in initial STIR MR images followed by a subsequent follow‐up MR imaging examination were reviewed. Horses whose tendon or ligament lesions had resolved on STIR images at the time of the recheck examination were significantly more likely to be sound than horses whose lesions persisted on STIR images (P=0.039). This association did not exist in horses with bone marrow lesions (P=1.00). Horses whose tendon or ligament lesions persisted only on T1w GRE images were no more likely to be sound than horses whose lesion persisted on at least one other sequence type (P=0.26). However, the low number of horses included in this analysis may have precluded identification of a significant difference in lameness status. Tendon or ligament lesions visualized on STIR images may represent active lesions that may contribute to lameness in the horse.     

MAGNETIC RESONANCE IMAGING FEATURES OF PROXIMAL METACARPAL AND METATARSAL INJURIES IN THE HORSE

Magnetic resonance (MR) imaging abnormalities in horses with lameness localized to the proximal metacarpal or metatarsal region have not been described. To accomplish that, the medical records of 45 horses evaluated with MR imaging that had lameness localized to either the proximal metacarpal or metatarsal region were reviewed. Abnormalities observed in the proximal suspensory ligament or the accessory ligament of the deep digital flexor tendon included abnormal high signal, enlargement, or alteration in shape. Twenty-three horses had proximal suspensory ligament desmitis (13 hindlimb, 10 forelimb). Sixteen horses had desmitis of the accessory ligament of the deep digital flexor tendon. One horse had desmitis of the proximal suspensory ligament and the accessory ligament of the deep digital flexor tendon on the same limb and one horse had desmitis of the proximal suspensory ligament on one forelimb and desmitis of the accessory ligament of the deep digital flexor tendon on the other forelimb. Four horses did not have abnormalities in the proximal suspensory ligament or accessory ligament of the deep digital flexor tendon. Eighty percent of horses with forelimb proximal suspensory ligament desmitis and 69% of horses with hindlimb proximal suspensory ligament desmitis returned to their intended use. Sixty-three percent of horses with desmitis of the accessory ligament of the deep digital flexor tendon were able to return to their intended use. MR imaging is a valuable diagnostic modality that allows diagnosis of injury in horses with lameness localized to the proximal metacarpal and metatarsal regions. The ability to accurately diagnose the source of lameness is important in selecting treatment that will maximize the chance to return to performance.     

MAGNETIC RESONANCE IMAGING FEATURES OF OBLIQUE AND STRAIGHT DISTAL SESAMOIDEAN DESMITIS IN 27 HORSES

Injury to the oblique and straight distal sesamoidean ligaments is becoming recognized as a more common cause of lameness in horses than was previously thought. The purpose of this study was to review the magnetic resonance (MR) imaging findings of 27 horses affected with desmitis of the oblique and/or straight distal sesamoidean ligament and determine long-term prognosis for horses with this diagnosis. Imaging was performed with horses in right lateral recumbency in a high-field 1 T magnet. All horses had lameness localized to the digit or metacarpophalangeal/metatarsophalangeal joint region with diagnostic local anesthetic blocks. Ten horses had forelimb lameness and 17 horses had hind limb lameness. MR imaging revealed abnormalities in the oblique distal sesamoidean ligaments in 18 horses, in the straight distal sesamoidean ligament in three horses, and in both the oblique and straight distal sesamoidean ligament in six horses. Treatment consisted of a 6-month rest and rehabilitation program in all horses. The digital flexor tendon sheath was injected with methylprednisolone acetate and hyaluronic acid in 22 horses to decrease inflammation in the injured ligaments before starting the rest and rehabilitation program. Two horses had ligament splitting performed, one in the oblique distal sesamoidean ligament and one in the straight distal sesamoidean ligament. MR imaging is an effective method for diagnosing injury to the oblique and straight distal sesamoidean ligaments in horses. Treatment, primarily a 6-month rest and rehabilitation program, allowed 76% of the horses to successfully resume performance.     

ULTRASONOGRAPHIC FINDINGS IN HORSES WITH FOOT PAIN BUT WITHOUT RADIOGRAPHICALLY DETECTABLE OSSEOUS ABNORMALITIES

Foot pain is an important cause of lameness in horses. When horses with foot pain have no detectable radiographic abnormalities, soft‐tissue assessment remains a diagnostic challenge without magnetic resonance (MR) imaging. Ultrasonography can provide an alternative to MR imaging when that modality is not available but the extent of changes that might be seen has not been characterized. We reviewed the ultrasonographic findings in 39 horses with lameness responding positively to anesthesia of the palmar digital nerves and without radiographically detectable osseous abnormalities. Thirty of the 39 horses had lesions affecting the deep digital flexor tendon (DDFT), 27 had abnormalities in the distal interphalangeal joint of which six had a visible abnormality in the collateral ligament. Ultrasonographic abnormalities were seen in the podotrochlear bursa in 22 horses and in the ligaments of the navicular bone in two horses. Abnormalities of the navicular bone flexor surface were detected in eight horses. In three of the 39 horses, only the DDFT was affected. The other 36 horses had ultrasonographic abnormalities in more than one anatomical structure. Based on our results, ultrasonographic examination provides useful diagnostic information in horses without radiographic changes.     

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.     

ULTRASONOGRAPHY OF THE SOLAR ASPECT OF THE DISTAL PHALANX IN THE HORSE

Ultrasonographic examinations were performed on the solar aspect of the distal phalanx of 10 feet of five normal live horses (Group 1), 22 feet of seven normal cadavers (Group 2), and nine feet of five horses with pathology of the dorsal solar aspect of the distal phalanx (Group 3). Lateromedial radiographs of the distal phalanx were made in all groups, and in Group 2, digits were sagitally sectioned after imaging. The ultrasonographic and radiographic appearance of the sagittal solar aspect of the distal phalanx was described. Measurements of the distance between the sole and the distal tip of the distal phalanx (A), the solar aspect of the apex of the frog and the distal phalanx (B), and the body of the frog's surface and flexor surface of the distal sesamoid bone (C) were made ultrasonographically, radiographically, and on the sectioned cadaver specimens. There was no statistical difference between the radiographic, ultrasonographic, and direct cadaver measurements in A and C. In B, there was a statistical difference between the radiographic, ultrasonographic, and cadaver measurements-most likely as a result of the difference in trimming of the frog apex. Ultrasonographic and radiographic examination of the nine feet of the five horses in Group 3 were performed and the abnormalities described. Color flow and power Doppler ultrasonography were performed on the normal sagittal solar distal phalanx, on the impar distal sesamoidean ligament, and at the insertion of the deep digital flexor tendon on the facies flexoria of the distal phalanx. Power Doppler in these horses showed blood flow at 0.16-0.48 kHz at the tip of the distal phalanx and at 0.16 kHz at the deep digital flexor tendon insertion and in the impar distal sesamoidean ligament. Using color flow Doppler in normal horses mean blood flows ranged from 1.8 to 5.4 cm/s at the tip of the distal phalanx and 1.8-2.0 cm/s at the deep digital flexor tendon insertion and in the impar distal sesamoidean ligament.     

Magnetic resonance imaging findings in the carpus and proximal metacarpal region of 50 lame horses

Reasons for performing study: There is limited information on magnetic resonance imaging (MRI) findings in the carpus and proximal metacarpal region of lame horses. Objectives: To document MRI findings in horses with lameness localised to the carpus and/or proximal metacarpal region. Methods: Clinical records of horses that underwent MRI of the carpus and/or proximal metacarpal region at the Animal Health Trust between January 2003 and September 2010 were reviewed. Magnetic resonance images of all horses and available radiographs, ultrasonographic and scintigraphic images were assessed. When possible, MRI findings were related to the results of other diagnostic imaging techniques. Results: Seventy‐two MR studies of 58 lame limbs in 50 horses from a broad range of work disciplines and ages were reviewed. The most commonly detected primary abnormality was decreased signal intensity in T1‐ and T2‐weighted images in the medial aspect of the carpal bones and/or the proximomedial aspect of the metacarpal bones (n = 29). Nine horses had syndesmopathy between the second and third metacarpal bones. In 6 horses the primary abnormalities were identified in the palmar cortex of the third metacarpal bone (McIII). Significant abnormalities of the suspensory ligament (SL) with associated lesions in the adjacent palmar cortex of the McIII were seen in 4 limbs. Ligament and associated osseous abnormalities between the second and third carpal bones and second and third metacarpal bones were detected in 4 limbs. Conclusions and potential relevance: Magnetic resonance imaging enabled diagnosis of a variety of lesions not detected by conventional imaging in horses from a wide range of work disciplines. The distribution of injury types differed considerably from previous studies.     

Magnetic resonance imaging of the palmar aspect of the equine podotrochlear apparatus: normal appearance

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of MR imaging studies of 16 cadaver limbs. The articular aspect of the distal sesamoid bone was not evaluated in this study. Equine digits were imaged with a human knee radiofrequency coil in a 1.5 T magnetic field, using spin echo (SE) T1-weighted, turbo spin echo proton density (TSE PD)-weighted with and without fat saturation (FS), and FS TSE T2-weighted sequences. The limbs were dissected after imaging to validate the absence of gross abnormalities of the flexor aspect of the distal sesamoid bone, of the deep digital flexor tendon, and the distal impar sesamoidean ligament. Seven deep digital flexor tendons were subjected to histologic examination to exclude any microscopic tendon pathology. The anatomic structures of the podotrochlear apparatus were easily identified on MR images. Compact bone of the flexor cortex of the distal sesamoid bone had low intensity signal on all sequences. In 11 digits an increased signal was seen within the thickness of the sagittal eminence of the flexor cortex in SE T1-weighted images and in TSE PD-weighted images without FS. Trabecular bone had a granular appearance and high signal in SE T1-weighted sequences and TSE images without FS. The deep digital flexor tendon had low signal on FS T2-weighted images, while on short echo time sequences (T1- and PD-weighted sequences), the tendon signal varied depending on the relative orientation between its fibers and the static magnetic field. Seven tendons had stippled appearance due to small intratendonous foci of slightly increased signal on transverse T1-weighted images. MR imaging provides a thorough evaluation of the anatomical structure of the podotrochlear apparatus: A good knowledge of the MR imaging appearance and anatomy and an awareness of potential pitfalls will improve diagnostic specificity for the detection of pathologic changes.     

MAGNETIC RESONANCE IMAGING FINDINGS OF EQUINE SOLAR PENETRATION WOUNDS

The magnetic resonance (MR) imaging features, signalment, clinical history and outcome of 55 horses with a penetrating sole injury were evaluated. Our aim was to describe MR imaging findings within the hoof capsule, assess the utility of the technique and give recommendations for the optimal MR imaging protocol to evaluate such injuries. Data from five equine hospitals were analyzed retrospectively. The tract was more likely to be visualized in animals scanned within the first week postinjury. There was no significant predisposition based on breed, age, or gender. T2*W transverse sequences were the most useful for assessment of solar penetrations due to their orientation perpendicular to the deep digital flexor tendon, the reduced scanning time, and the T2* capability of enhancing magnetic susceptibility caused by hemorrhage.     

MAGNETIC RESONANCE IMAGING FINDINGS OF DESMOPATHY OF THE COLLATERAL LIGAMENTS OF THE EQUINE DISTAL INTERPHALANGEAL JOINT

We report the use of a low-field magnetic resonance (MR) imaging system for the detection of desmopathy of the collateral ligament of the distal interphalangeal joint and the long-term outcome. Twenty horses were studied and their medical records and MR images were reviewed retrospectively. Long-term follow-up information was obtained by telephonic questionnaires of owners, trainers, or referring veterinarians. Desmopathy of the medial collateral ligament (80%) and enthesopathy of the affected collateral ligament (80%) were common MR imaging features. Treatment consisted of stall rest followed by a rehabilitation period. Additional treatments included shoeing, extracorporeal shock wave therapy, application of a half limb or foot cast, and medication of the distal interphalangeal joint. Twelve (60%) horses returned to their previous level of exercise and maintained their previous level, whereas eight horses had a poor outcome. Low-field MR imaging in the standing patient can be used to detect collateral ligament desmopathy of the distal interphalangeal joint without a need for general anesthesia.     

MAGNETIC RESONANCE IMAGING OF THE EQUINE DIGIT WITH CHRONIC LAMINITIS

Chronic laminitis is a severe disease affecting the equine digit. It was hypothesized that magnetic resonance (MR) imaging would improve visualization of structures within the foot and pathology associated with chronic laminitis. This study aimed to describe the MR imaging findings in chronic laminitis, compare different pulse sequences for visualization of pathology, and to compare MR imaging with standard radiography. Twenty (10 forelimb, 10 hindlimb) cadaver limbs from 10 horses clinically diagnosed with chronic laminitis (group L) and 10 limbs without laminitis (group N) were used. Lateromedial radiographs and sagittal and transverse MR images of the foot were obtained. Radiographs and MR images were evaluated for anatomic definition and evidence of pathology. Dorsal hoof wall thickness and angle of rotation and displacement distance of the distal phalanx were measured. Comparisons were made between group L and N, forelimb and hindlimb within each horse, and MR imaging and radiography. Features consistently noted with MR images in group L, but not detected using radiography, included laminar disruption, circumscribed areas of laminar gas, laminar fluid, and bone medullary fluid. Other findings seen only on MR images included increased size and number of vascular channels, alterations in the corium coronae, and distal interphalangeal joint distension. Magnetic resonance imaging allowed better definition of laminar gas lines and P3 surface irregularity observed on radiographs. Based on measurements, group L had a greater angle of rotation, distal displacement, and dorsal hoof wall thickness than group N; forelimb hoof wall thickness was greater than hindlimb; and distal displacement and hoof wall thickness measurements were smaller using MR imaging than radiography, but had a similar pattern. It is concluded that there are features of chronic laminitis consistently observed using MR imaging and that these may be additional to features observed radiographically.     

INJURY OF THE COLLATERAL LIGAMENTS OF THE DISTAL INTERPHALANGEAL JOINT DIAGNOSED BY MAGNETIC RESONANCE

We describe the clinical, imaging, and necropsy findings of two horses with severe injury of the collateral ligaments of the distal interphalangeal (DIP) joint diagnosed using magnetic resonance (MR) imaging. In MR images it was possible to examine the collateral ligaments of the DIP joint from the origin at the middle phalanx to the insertion on the distal phalanx. Both horses in this report had abnormal high signal intensity within the collateral ligaments of the DIP joint, and one horse had abnormal high signal intensity within the bone of the distal phalanx on short tau inversion recovery (STIR) and T2-weighted imaging sequences. High signal intensity on STIR and T2-weighted images represents abnormal fluid accumulation indicative of inflammation, within ligament, tendon, or bone on these imaging sequences. Abnormalities were confirmed on necropsy in both horses. Injury of the collateral ligaments of the DIP joint should be considered as a source of pain in horses with lameness localized to the foot.     

ULTRASONIC ANATOMY OF THE TENDONS AND LIGAMENTS IN THE DISTAL METACARPAL-METATARSAL REGION OF THE EQUINE LIMB

In a two-phase study, ultrasound was used to delineate the normal sonographic anatomy of soft tissues of the equine distal limb. The study was limited to the soft tissues of the palmar surface of the limb just proximal to the fetlock joint. In the first phase, cadavers were evaluated with a B-mode ultrasound machine, † Then the limbs were radiographed and dissected to compare their gross, radiographic, and ultrasonographic appearances. In the second phase, nine normal adult horses were ultrasonographically scanned. The sonographic appearance of the normal animals was compared with that of the cadavers. Front and rear limbs of all horses had similar ultrasonographic appearances. Flexor tendons and the suspensory ligament were easily identified as having linear, uniformly intense ecogenicity. The borders of the digital sheath and of the proximal palmar pouch of the fetlock joint had a less organized and less intense ecogenic appearance than the flexor tendons and suspensory ligament, and they were poorly delineated unless distended with fluid. Ultrasonography was used in three lame horses and aided the diagnoses of synovial proliferation in the fetlock joint, tendosynovitis, and bowed tendon. Diagnostic ultrasonography was effective in identifying and characterizing soft-tissue structures of the distal equine limb. It is a valuable, noninvasive diagnostic aid.     

Evaluation of computed tomographic anatomy of the equine metacarpophalangeal joint

OBJECTIVE: To determine the detailed computed tomography (CT) anatomy of the metacarpophalangeal (MCP) joint in healthy horses. SAMPLE POPULATION: 10 cadaveric forelimbs from 10 adult horses without orthopedic disease. PROCEDURES: CT of the MCP joint was performed on 4 forelimbs. In 1 of the limbs, CT was also performed after intra-articular injection of 30 mL of contrast medium (40 mg of iodine/mL). Transverse slices 1-mm thick were obtained, and sagittal and dorsal planes were reformatted with a slice thickness of 2 mm. The CT images were matched with corresponding anatomic slices from 6 additional forelimbs. RESULTS: The third metacarpal bone, proximal sesamoid bones, and proximal phalanx could be clearly visualized. Common digital extensor tendon; accessory digital extensor tendon; lateral digital extensor tendon; superficial digital flexor tendon (including manica flexoria); deep digital flexor tendon; branches of the suspensory ligament (including its attachment); extensor branches of the suspensory ligament; collateral ligaments; straight, oblique, and cruciate distal sesamoidean ligaments; intersesamoidean ligament; annular ligament; and joint capsule could be seen. Collateral sesamoidean ligaments and short distal sesamoidean ligaments could be localized but not at all times clearly identified, whereas the metacarpointersesamoidean ligament could not be identified. The cartilage of the MCP joint could be assessed on the postcontrast sequence. CONCLUSIONS AND CLINICAL RELEVANCE: CT of the equine MCP joint can be of great value when results of radiography and ultrasonography are inconclusive. Images obtained in this study may serve as reference for CT of the equine MCP joint.     

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

Reasons for performing study: To date, few reports exist comparing magnetic resonance imaging (MRI) and computed tomography (CT) for imaging of the equine distal limb, yet clinicians are required to decide which modality to use regularly. Objectives: To report and compare anatomic visualisation scores obtained for CT, contrast enhanced CT (CECT) and standing low‐field MRI (LFMRI) in the equine foot. Hypothesis: Anatomic visualisation score discrepancies would exist between CT, CECT and LFMRI. Methods: Images of 22 lame horses (31 limbs) undergoing both CT and LFMRI of the foot were reviewed. When available, CECT images were reviewed. The deep digital flexor tendon (DDFT) was categorised into proximal to distal levels (A–D), structures were assigned visualisation scores (Grades 0–3) and technique comparisons were made using the paired marginal homogeneity test. Results: Computed tomography and LFMRI had similar visibility scores for the navicular bone, middle phalanx, DDFT‐B, collateral ligaments of the distal interphalangeal joint and collateral sesamoidean ligament of the navicular bone. The proximal and distal phalanx had lower visibility scores with LFMRI. The distal DDFT (C–D), distal sesamoidean impar ligament and synovial structures had higher scores with LFMRI. Contrast enhanced CT lowered DDFT and collateral sesamoidean ligament scores and raised distal interphalangeal synovium CT visualisation scores. Conclusions and potential relevance: Visualisation scores differ depending on imaging technique and anatomic structure of interest. This information increases our understanding of the limitations of CT, CECT and LFMRI to visualise anatomy in clinical cases.     

Desmotomy of the accessory ligament of the superficial digital flexor tendon in the horse with use of a tenoscopic approach to the carpal sheath

Objective— To describe a tenoscopic approach to the carpal sheath for desmotomy of the accessory ligament of the superficial digital flexor tendon. Study Design— The surgical procedure was developed with use of normal forelimbs from equine cadavers and experimental horses. Animals or Sample Population— Twelve equine cadaveric forelimbs, 4 forelimbs from 2 horses anesthetized for terminal surgical laboratories, and 10 forelimbs from five experimental horses were used. Methods— The limbs were positioned lateral side up with the carpus slightly flexed. After distention of the carpal sheath, a portal was made approximately 2 cm proximal to the distal radial physis for arthroscope insertion. An instrument portal was made approximately 0.2 cm proximal to the distal radial physis. After flexion of the limb to 90°, the accessory ligament of the superficial digital flexor tendon was palpated and desmotomy was performed. Cadaveric limbs were dissected to confirm complete desmotomy. Experimental horses were monitored for short- (perioperative) and long- (4 weeks) term postoperative complications. Results— A tenoscopic approach to the carpal sheath provided adequate surgical access to the accessory ligament of the superficial digital flexor tendon for desmotomy. Most of the accessory ligament of the superficial digital flexor tendon could be easily seen within the sheath, except for the proximal 2 cm that could be readily palpated and subsequently transected. Important technical considerations were location of the arthroscope portal, adequate sheath distention, limb flexion to 90°, and desmotomy location. It was beneficial, but apparently not essential, to avoid the proximal perforating vessel. Postoperatively, some horses had swelling but were not lame and had normal range of motion of the carpus. Conclusions— Desmotomy of the accessory ligament of the superficial digital flexor tendon could be performed by using a lateral tenoscopic approach to the carpal sheath. Clinical Relevance— Desmotomy of the accessory ligament of the superficial digital flexor tendon by using a tenoscopic approach to the carpal sheath is an alternative technique to the medial incisional approach.