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

Reasons for performing study: No previous study compares computed tomography (CT), contrast‐enhanced computed tomography (CECT) and standing low‐field magnetic resonance imaging (LFMRI) to detect lesions in horses with lameness localised to the foot. This study will help clinicians understand the limitations of these techniques. Objectives: To determine if CT, CECT and LFMRI would identify lesions within the distal limb and document discrepancies with lesion distribution and lesion classification. Methods: Lesions in specific structures identified on CT and MR images of feet (31 limbs) from the same horse were reviewed and compared. Distributions of lesions were compared using a Chi‐squared test and techniques analysed using the paired marginal homogeneity test for concordance. Results: Lesions of the deep digital flexor tendon (DDFT) were most common and CT/CECT identified more lesions than LFMRI. Deep digital flexor tendon lesions seen on LFMRI only were frequently distal to the proximal extent of the distal sesamoid and DDFT lesions seen on CT/CECT only were frequently proximal to the distal sesamoid. Lesions identified on LFMRI only were core (23.3%) or splits (43.3%), whereas lesions identified only on CT were abrasions (29.8%), core (15.8%), enlargement (15.8%) or mineralisation (12.3%). Contrast‐enhanced CT improved lesion identification at the DDFT insertion compared to CT and resulted in distal sesamoidean impar ligament and collateral sesamoidean ligament vascular enhancement in 75% of cases. Low‐field MRI and CT/CECT failed to identify soft tissue mineralisation and bone oedema, respectively. Conclusions and potential relevance: Multiple lesions are detected with CT, CECT and LFMRI but there is variability in lesion detection and classification. LFMRI centred only on the podotrochlear apparatus may fail to identify lesions of the pastern or soft tissue mineralisation. Computed tomography may fail to identify DDFT lesions distal to the proximal border of the distal sesamoid.     

Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 2: The deep digital flexor tendon

REASONS FOR PERFORMING STUDY: Causes of palmar foot pain and the aetiopathogenesis of navicular disease remain poorly understood, despite the high incidence of foot-related lameness. HYPOTHESES: Abnormalities of the deep digital flexor tendon (DDFT) may contribute to palmar foot pain; ageing degenerative changes may be seen in horses free from lameness; and horses with lameness are likely to have a greater severity of abnormalities than age-matched horses with no history of foot pain. METHODS: Feet were selected from horses with a history of uni- or bilateral forelimb lameness of at least 2 months' duration. Histology of the DDFT from the level of the proximal interphalangeal joint to its insertion were examined and the severity of lesions for each site graded. Associations between lesions of the navicular bone, collateral sesamoidean ligaments (CSL), distal sesamoidean impar ligament, navicular bursa, distal interphalangeal (DIP) joint synovium and collateral ligaments of the DIP joint and DDFT were assessed. RESULTS: There was no relationship between age and grade of histological abnormality of the DDFT. There were significant histological differences between groups for lesions of the dorsal layers of the DDFT, but not for lesions of the palmar aspect. There were significant associations between histological grades for the superficial dorsal layer of the DDFT and flexor aspect of the navicular bone; and between the deep dorsal layer of the DDFT and the proximal border and medulla of the navicular bone. The navicular bursa grade was correlated with grades for the superficial dorsal, deep dorsal and deep palmar layers of the DDFT. The histological grades for the CSL and the superficial dorsal layer of the DDFT were also associated. CONCLUSIONS: Pathological abnormalities in lame horses often involved the DDFT in addition to the navicular bone. Vascular and matrix changes may precede changes in the fibrocartilage of the navicular bone. POTENTIAL RELEVANCE: Identification of factors leading to vascular changes within the interstitium of the DDFT and changes in matrix composition, may help in future management of palmar foot pain.     

Ultrasonographic Evaluation of the Distal Extremity

Despite the increasing use of magnetic resonance imaging (MRI), ultrasound remains a valuable tool to diagnose injuries that cause distal extremity lameness in the horse. The key to a successful examination is a strong knowledge of anatomy in combination with proper ultrasonographic technique and the patience and dedication to learn these skills. Similar to all imaging modalities, it is equally important to recognize and consider the limitations of ultrasound in this region so that findings can be interpreted appropriately. Ultrasound can be used to diagnose injuries to the deep digital flexor tendon (DDFT), straight distal sesamoidean ligament and branches of the superficial digital flexor tendon using standard pastern ultrasonographic technique. The addition of newer techniques to image the DDFT at the level of P2, the navicular bursa and the collateral sesamoidean ligament can enhance the diagnostic utility of ultrasound in horses with distal extremity lameness. Although visibility is limited, ultrasound can be used to diagnose collateral ligament injuries of the coffin joint in many affected horses. Transcuneal imaging may be useful in some horses to detect abnormalities of the distal sesamoidean impar ligament and navicular bone, but evaluation of the DDFT is limited. Ultrasound should be considered in all horses with distal extremity lameness, regardless of the ability to perform advanced imaging procedures. Information gained is often complementary to other imaging modalities and may provide the basis for recheck examination purposes.     

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.     

Collateral desmitis of the distal interphalangeal joint in conjunction with concurrent ossification of the cartilages of the foot in nine horses

The purpose of this study was to describe the frequency of occurrence of severe ossification of the collateral cartilages (sidebone) coexistent with collateral desmitis of the distal interphalangeal joint (DIPJ) in lame horses. Sidebone was diagnosed and graded on standard radiographs and soft tissue injuries of the foot were diagnosed using standing low‐field magnetic resonance imaging (MRI). Of 15 horses with forelimb lameness and severe sidebone, 9 had evidence of concurrent collateral desmitis of the DIPJ. All 15 horses had damage to other structures (including the deep digital flexor tendon, distal sesamoidean impar ligament, collateral sesamoidean ligament, navicular bone and distal phalanx) within the affected feet as identified on MRI. The clinical and pathophysiological significance of concurrent collateral desmitis of the DIPJ and sidebone is currently uncertain. However, this study shows that injuries to multiple structures within the foot are common and that collateral desmitis of the distal interphalangeal joint is frequently seen in lame horses in conjunction with severe ossification of the collateral cartilages.     

Histopathology in horses with chronic palmar foot pain and age-matched controls. Part 1: Navicular bone and related structures

REASONS FOR PERFORMING STUDY: Causes of palmar foot pain and the aetiopathogenesis of navicular disease remain poorly understood, despite the high incidence of foot-related lameness. HYPOTHESES: Abnormalities of the collateral sesamoidean ligaments (CSLs), distal sesamoidean impar ligament (DSIL), deep digital flexor tendon (DDFT), navicular bone, navicular bursa, distal interphalangeal (DIP) joint or collateral ligaments (CLs) of the DIP joint may contribute to palmar foot pain. METHODS: Feet were selected from horses with a history of unilateral or bilateral forelimb lameness of at least 2 months' duration that was improved by perineural analgesia of the palmar digital nerves, immediately proximal to the cartilages of the foot (Group 1, n = 32); or from age-matched control horses (Group 2, n = 19) that were humanely destroyed for other reasons and had no history of forelimb foot pain. Eight units of tissue were collected for histology: the palmar half of the articular surface of the distal phalanx, including the insertions of the DDFT and DSIL; navicular bone and insertion of the CSLs; DDFT from the level of the proximal interphalangeal (PIP) joint to 5 mm proximal to its insertion; synovial membrane from the palmar pouch of the DIP joint and the navicular bursa; CLs of the DIP joint and DSIL. The severity of histological lesions for each site were graded. Results were compared between Groups 1 and 2. RESULTS: There was no relationship between age and grade of histological abnormality. There were significant histological differences between groups for lesions of the flexor aspect, proximal and distal borders, and medulla of the navicular bone; the DSIL and its insertion and the navicular bursa; but not for lesions of the CSLs, the dorsal aspect of the navicular bone, distal phalanx and articular cartilage, synovium or CLs of the DIP joint. CONCLUSIONS: Pathological abnormalities in lame horses often involved not only the navicular bone, but also the DSIL and navicular bursa. Abnormalities of the navicular bone medulla were generally only seen dorsal to lesions of the FFC. POTENTIAL RELEVANCE: Adaptive and reactive change may be occurring in the navicular apparatus in all horses to variable degrees and determination of the pathogenesis of lesions that lead to pain and biomechanical dysfunction should assist specific preventative or treatment protocols.     

Effect of contact stress in bones of the distal interphalangeal joint on microscopic changes in articular cartilage and ligaments

OBJECTIVE: To examine articular cartilage of the distal interphalangeal (DIP) joint and distal sesamoidean impar ligament (DSIL) as well as the deep digital flexor tendon (DDFT) for adaptive responses to contact stress. SAMPLE POPULATION: Specimens from 21 horses. PROCEDURE: Pressure-sensitive film was inserted between articular surfaces of the DIP joint. The digit was subjected to a load. Finite element models (FEM) were developed from the data. The navicular bone, distal phalanx, and distal attachments of the DSIL and DDFT were examined histologically. RESULTS: Analysis of pressure-sensitive film revealed significant increases in contact area and contact load at dorsiflexion in the joints between the distal phalanx and navicular bone and between the middle phalanx and navicular bone. The FEM results revealed compressive and shear stresses. Histologic evaluation revealed loss of proteoglycans in articular cartilage from older horses (7 to 27 years old). Tidemark advancement (up to 14 tidemarks) was observed in articular cartilage between the distal phalanx and navicular bone in older clinically normal horses. In 2 horses with navicular syndrome, more tidemarks were evident. Clinically normal horses had a progressive increase in proteoglycans in the DSIL and DDFT. CONCLUSIONS AND CLINICAL RELEVANCE: Load on the navicular bone and associated joints was highest during dorsiflexion. This increased load may be responsible for microscopic changes of tidemark advancement and proteoglycan depletion in the articular cartilage and of proteoglycan production in the DSIL and DDFT Such microscopic changes may represent adaptive responses to stresses that may progress and contribute to lameness.     

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.     

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.     

Anatomic variations and degenerative changes in the collateral cartilages and middle and distal phalanges of the forelimb in Ardenner colts

The anatomic variations and the degenerative changes in the collateral cartilages and middle and distal phalanges in 6 Ardenner colts were characterized by radiography, scintigraphy, and magnetic resonance imaging (MRI). The radiographic changes were assessed between the ages of 16.5 and 25 months. An anatomic variation of the middle and distal phalanges was demonstrated in some of the colts. MRI examination of the 6 colts revealed an association between the deep digital flexor tendon cross-sectional area and body weight as well as foot circumference. Also, a thin collateral sesamoidean (suspensory navicular) ligament was observed subjectively. The presence of an extensive ossification of the collateral cartilages of the foot was found in these young horses. The ossification was characterized by the existence of 2 separate ossification centers, which had a tendency to unite. The radiographic interphalangeal degenerative lesions seen appear as bone remodeling of the dorsal edges of the middle and distal phalanx, on the insertion sites of collateral ligaments of the distal interphalangeal joint, the digital extensor tendon, and the distal interphalangeal joint capsule.     

Diagnostic analgesia of the equine digit

Analgesia usually occurs within 5 min after administration of local anaesthetic solution into joints or around nerves in the distal portion of the limb. Gait should be assessed within 10 min after diagnostic regional analgesia of the distal portion of the limb because rapid diffusion of anaesthetic solution can result in anaesthesia of other nerve branches, thus confusing results of the examination. A palmar digital nerve block (PDNB) anaesthetises most of the foot, including the distal interphalangeal (DIP) joint (coffin joint), rather than just the palmar half of the foot, as was once commonly believed. To avoid partially anaesthetising the proximal interphalangeal joint (pastern joint), the palmar digital nerves should be anaesthetised near or distal to the proximal margin of the collateral cartilages. Clinicians should be aware that an abaxial sesamoid nerve block (ASNB) may ameliorate or abolish pain within the metacarpo/metatarso‐phalangeal joint (fetlock joint). Mepivacaine administered into the DIP joint desensitises the DIP joint and probably the palmar digital nerves to also cause anaesthesia of the navicular bursa, the navicular bone, the toe region of the sole, the digital portion of the deep digital flexor tendon (DDFT) and the distal portions of the collateral ligaments of the DIP joint. When a large volume of mepivacaine HCl (e.g. 10 ml) is administered, the heel region of the sole may also be desensitised. Only a small percentage of horses with disease of the collateral ligament(s) of the DIP joint show a significant improvement in lameness after intra‐articular analgesia of the DIP joint, and no horse is likely to improve after intrabursal analgesia of the navicular bursa. A PDNB, however, improves lameness substantially in most horses that are lame because of disease of the collateral ligament(s) of the DIP joint, and all affected horses are likely to become sound after an abaxial sesamoid nerve block. The degree of improvement in lameness associated with injury to one or both collateral ligaments of the DIP joint after PDNB is determined by the extent of the injury and the level at which the palmar digital nerves are anaesthetised. The further proximal the level of the injury within the collateral ligament, the less likely that lameness is ameliorated by analgesia of the DIP joint or a PDNB. Verschooten's technique appears to be the most accurate technique for centesis of the navicular bursa. Even though analgesia of the DIP joint results in analgesia of the navicular bursa, analgesia of the navicular bursa does not result in analgesia of the DIP joint. Pain arising from the DIP joint can probably be excluded as a cause of lameness when lameness is attenuated by analgesia of the navicular bursa. Analgesia of the digital flexor tendon sheath (DFTS) is likely to desensitise only structures that are contained within or border on the sheath itself (i.e. the superficial and deep digital flexor tendons, the straight and oblique distal sesamoidean ligaments, the annular ligaments of the fetlock and pastern, and the portion of the DDFT that lies within the foot). Because lameness caused by disease of the DDFT within the foot may fail to improve appreciably after analgesia of the palmar digital nerves, the DIP joint, or the navicular bursa, a portion of the DDFT within the foot and distal to the DFTS probably receives its sensory supply from more proximal deep branches of the medial and lateral palmar digital nerves that enter the DFTS. Performing intrathecal analgesia of the DFTS on horses with lameness that is unchanged after anaesthesia of the palmar digital nerves but resolves after an ASNB, may be useful in localising lameness to that portion of the DDFT that lies within the foot. Resolution of lameness after intrathecal analgesia of the DFTS justifies suspicion of a lesion within the digital portion of the DDFT or within structures contained within the DFTS. The belief that concurrent or sequential intra‐articular administration of medication substantially increases the risk of joint infection or that inflammation caused by the local anaesthetic solution may dampen the therapeutic response to intra‐articular medication appears to be unfounded.     

POSITIVE CONTRAST MAGNETIC RESONANCE BURSOGRAPHY FOR ASSESSMENT OF THE NAVICULAR BURSA AND SURROUNDING SOFT TISSUES

Magnetic resonance (MR) imaging is often performed to determine the cause of palmar heel pain. We evaluated how distension of the navicular bursa affected the MR appearance of the navicular bursa and associated structures. An MR evaluation was performed on normal cadaver limbs and cadaver limbs from horses with lameness localized to the foot. The normal navicular bursae were injected with 2, 4, or 6 ml of solution. The bursae of the feet from lame horses were injected with 4 or 6 ml, and the MR study was repeated. All bursae were examined grossly to verify the presence or absence of adhesions. Clinical patients that had initial MRI abnormalities suggesting adhesions were also evaluated. Distension of the proximal recess of the normal navicular bursa, proximal to the collateral sesamoidean ligament was achieved with 2 ml. Separation of the collateral sesamoidian ligament from the deep digital flexor tendon (DDFT) was achieved with 4 ml. The separation of the navicular bone from the DDFT and distal sesamoidian impar ligament required 6 ml. Adhesions were more clearly defined in the bursa of the two pathologic cadaver limbs following distension. MR bursography used on clinical patients allowed the determination of the presence or absence of adhesions. In these horses, this determination could not have been definitively made without this technique. MR bursography is useful in horses where the presence of adhesions cannot be clearly defined by MRI.     

Osseous cyst‐like lesions in the feet of lame horses: Diagnosis by standing low‐field magnetic resonance imaging

Osseous cyst‐like lesions (OCLLs) were diagnosed by standing low‐field magnetic resonance (MR) imaging in 9 mature horses (age range 6–17 years). All horses had been subjected to a routine lameness evaluation (including standard foot radiographs) with no diagnosis being reached prior to MR imaging. The duration of lameness ranged from one month to one year. OCLLs were diagnosed in 12 feet. The site of the lesions included the distal phalanx in 11 feet (subchondral bone in 4, insertion of collateral ligaments of the distal interphalangeal joint in 4, insertion of the distal sesamoidean impar ligament in 3) and the subchondral bone of the distal aspect of the middle phalanx in one foot. OCLLs were characterised by discrete spherical or elliptical areas of high or intermediate signal in all MR sequences. In most cases the lesion was surrounded by a rim of bone with abnormally low signal.     

Magnetic resonance imaging changes of the navicular bursa following navicular bursoscopy in seven horses

Navicular syndrome is a multifactorial disease process in horses with multiple structures in the foot contributing to lameness. Surgical debridement is a treatment option for lesions of the navicular bursa and deep digital flexor tendon. This retrospective case series describes the magnetic resonance imaging (MRI) appearance of the navicular bursa following bursoscopy. Seven horses (three being bilaterally affected) with forelimb lameness isolated to the foot, and pre- and post-operative MRI were included. All limbs had concurrent lesions associated with the deep digital flexor tendon, navicular bone, impar ligament, collateral sesamoidean ligament and/or distal interphalangeal joint. All bursae developed or had progression of proliferative bursal tissue following surgery. At recheck MRI, following rehabilitation protocols, almost all horses had improved to resolved lameness with relatively unchanged concurrent lesions despite the navicular bursa appearance worsening. Outcomes for return to work were poor with only two horses going back to the previous level of work.     

Standing MRI lesions of the distal interphalangeal joint and podotrochlear apparatus occur with a high frequency in warmblood horses

Foot pain is a common presenting complaint in Warmblood horses. The aim of this retrospective, cross‐sectional study was to determine the spectrum of foot lesions detected by magnetic resonance imaging (MRI) in Warmblood horses used for dressage, jumping, and eventing. The medical records of 550 Warmblood horses with foot pain that were scanned using standing MRI were reviewed and the following data were recorded: signalment, occupation, lameness, diagnostic analgesia, imaging results, treatments, and follow‐up assessments. Associations between standing MRI lesions and chronic lameness following treatment were tested. Abnormalities of the navicular bone (409 horses, 74%), distal interphalangeal joint (362 horses, 65%), and deep digital flexor (DDF) tendon (260 horses, 47%) occurred with the highest frequency. The following abnormalities were significantly associated (P < .05) with chronic lameness following conservative therapy: moderate to severe MRI lesions in the trabecular bone of the navicular bone, mild or severe erosions of the flexor surface of the navicular bone, moderate sagittal/parasagittal DDF tendinopathies, and moderate collateral sesamoidean desmopathies. Also, identification of concurrent lesions of the DDF tendon, navicular bone, navicular bursa, and distal sesamoidean impar ligament was associated with chronic lameness after conservative therapy. Development of effective treatment options for foot lesions that respond poorly to conservative therapy is necessary.     

High‐field (3 Tesla) MRI of the navicular apparatus of sound horses shows good agreement to histopathology

Magnetic resonance imaging and the correlation to histopathological findings of the equine palmar foot of lame horses have been described previously, using 0.27 and 1.5 T systems. Compared to these, 3 T systems provide superior spatial resolution and imaging contrast. The aim of our prospective anatomic study was to characterize the imaging anatomy of the navicular region on 3 T MRI in comparison to histopathological findings. We hypothesized that 3 T MRI allows a good visualization of the entire navicular apparatus and reliable measurements of navicular cartilage and cortical bone thickness. Twenty front feet of sound horses were examined using a 3 T MRI system. For histopathological examination, sagittal tissue sections of the navicular bones and adjacent ligaments were prepared. Alterations in magnetic resonance signal were graded for each region and compared to corresponding histological slices. Overall, there was good visualization of the anatomical detail and a very good agreement between MRI and histology for compact bone and spongiosa, good agreement for the fibrocartilage and the distal sesamoidean impar ligament, but only moderate agreement for the hyaline cartilage and the collateral sesamoidean ligament. A comparative measurement of cartilage and cortical bone thickness on magnetic resonance images and histological sections was performed. In MRI, the hyaline cartilage of the articular surface appeared significantly thinner and the fibrocartilage of the flexor surface appeared significantly thicker compared to histology. Findings indicated that MRI at a field strength of 3 T allows reliable depiction of anatomic details of the navicular apparatus.     

Current concepts of navicular disease

Navicular disease is unlikely to be a single disease. The close anatomical and functional relationships between the navicular bone, collateral sesamoidean ligament, distal sesamoidean impar ligament, deep digital flexor tendon, navicular bursa and distal interphalangeal joint result in the frequent occurrence of combinations of injuries. There are a number of different pathological processes that affect the navicular bone, which probably have different aetiopathogeneses. While there is strong evidence that biomechanical forces may result in failure of functional adaptation and excessive modelling, it is likely that each disease or injury type has a multifactorial cause.     

Collateral desmitis of the distal interphalangeal joint in 18 horses (2001-2002)

REASONS FOR PERFORMING STUDY: There have been no previously published case series of horses examined using either scintigraphy or MRI to diagnose collateral ligament injuries not detectable using ultrasonography or radiography, nor have other concurrent soft tissue lesions been described. OBJECTIVES: To describe the clinical features of horses with desmitis of the collateral ligaments of the distal interphalangeal (DIP) joint and to evaluate the results of radiographic, ultrasonographic, scintigraphic and magnetic resonance imaging (MRI) examinations. METHODS: Horses were examined between January 2001 and January 2003 and were selected for inclusion in the study if there was unequivocal evidence of collateral desmitis of the DIP joint based on ultrasonography or MRI. Subject details, case history, results of clinical examination and responses to local analgesic techniques were reviewed. The results of radiographic, ultrasonographic, scintigraphic and MRI examinations were assessed. RESULTS: Eighteen horses were identified with desmitis of a collateral ligament of the DIP joint, 3 horses (Group 1) based on ultrasonography alone, 7 (Group II) with positive ultrasonographic and magnetic resonance images and 8 (Group III) with no lesion detectable using ultrasonography, but lesions identified using MRI. Seventeen horses had forelimb injuries and one a hindlimb injury. The medial collateral ligament was injured most frequently (13 horses). In the majority of horses, no localising clinical signs were seen. Lameness was invariably worse in circles compared with straight lines. Lameness was improved by palmar digital analgesia in 16 horses (87%), but only 6 were nonlame. Intra-articular analgesia of the DIP joint produced improvement in lameness in 6/15 horses (40%). In 16 horses, no radiographic abnormality related to the DIP joint or collateral ligament attachments was identified. Eight of 14 horses (57%) had focal, moderately or intensely increased radiopharmaceutical uptake (IRU) at the site of insertion of the injured collateral ligament on the distal phalanx. Alteration in size and signal in the injured collateral ligament was identified using MRI. In addition, 5 horses had abnormal mineralisation and fluid in the distal phalanx at the insertion of the ligament. Eleven horses had concurrent soft tissue injuries involving the deep digital flexor tendon, distal sesamoidean impar ligament, navicular bursa or collateral ligament of the navicular bone. CONCLUSIONS AND POTENTIAL RELEVANCE: Collateral desmitis of the DIP joint should be considered as a cause of foot lameness. Although some injuries are detectable ultrasonographically, false negative results occur. Focal IRU at the ligament insertion on the distal phalanx may be indicative of injury in some horses. MRI is useful for both characterisation of the injury and identification of any concurrent injuries. Further follow-up information is required to determine factors influencing prognosis.     

Magnetic resonance imaging of navicular bursa adhesions

Adhesions occur in the navicular bursa between the deep digital flexor tendon (DDFT) and other structures. Our objectives were to describe the appearance of navicular bursa adhesions on high-field magnetic resonance (MR) images, to compare these findings to findings at navicular bursoscopy, and to determine the prevalence of lesions in the remainder of the podotrochlear apparatus. Sixteen forelimbs from 14 horses that underwent MR imaging and navicular bursoscopy were evaluated. Adhesions were considered type 1 when characterized by a discontinuity in the navicular bursa fluid signal between two structures, type 2 when the navicular bursa fluid signal was disrupted and ill-defined tissue was present between two structures, and type 3 when the fluid signal was disrupted and well-defined tissue was present between two structures. Twenty-six adhesions were suspected on MR images and nineteen were visualized at surgery. The positive predictive value was 50% for type 1 adhesions, 67% for type 2 adhesions, and 100% for type 3 adhesions. Additional lesions were detected in the navicular bursa in 15 limbs, the DDFT in 13, the navicular bone in 15, the collateral sesamoidean ligaments in 9, and the distal sesamoidean impar ligament in 8. A discontinuity in the navicular bursa fluid signal with well-defined tissue between two structures detected on high-field MR images is diagnostic for a navicular bursa adhesion. Additional lesions in the podotrochlear apparatus are common in horses with navicular bursa adhesions.