Distal border fragments and shape of the navicular bone: radiological evaluation in lame horses and horses free from lameness

Reasons for performing study: The significance of distal border fragments of the navicular bone is not well understood. There are also no objective data about changes in thickness and proximal/distal extension of the palmar cortex of the navicular bone. Objectives: To describe the distribution of distal border fragments and their association with other radiological abnormalities of the navicular bone and describe the shape of the navicular bone in sound horses and horses with foot‐related lameness, including navicular pathology. Methods: Sound horses had radiographs acquired as part of a prepurchase examination. Lame horses had forelimb lameness abolished by palmar nerve blocks performed at the base of the proximal sesamoid bones. Diagnosis was assigned prospectively based on results of local analgesia and all imaging findings. The thickness of the palmar cortex of the navicular bone and size of proximal/distal extensions were measured objectively. Other radiological abnormalities were evaluated subjectively and each navicular bone graded. Results: Fifty‐five sound and 377 lame horses were included. All measurements were larger in lame compared with sound horses except the size of the distal extension of the palmar cortex. Fragments were observed in 3.6 and 8.7% of sound and lame horses respectively and in 24.1% of horses with a diagnosis of primary navicular pathology. There was an association between fragments and overall navicular bone grade, radiolucent areas at the angles of the distal border of the navicular bone and number and size of the synovial invaginations. Conclusions and potential relevance: The palmar cortex of the navicular bone was thicker in lame compared with sound horses. Distal border fragments were most frequent in horses with navicular pathology. Evaluation of changes in shape of the navicular bone may also be important for recognition of pathological abnormalities of the bone.     

DISTAL BORDER FRAGMENTS OF THE EQUINE NAVICULAR BONE: ASSOCIATION BETWEEN MAGNETIC RESONANCE IMAGING CHARACTERISTICS AND CLINICAL LAMENESS

Distal border fragments of the navicular bone are increasingly being detected due to the improved capabilities of magnetic resonance imaging (MRI), but their clinical significance remains unclear. The purpose of this retrospective study was to describe the location, size, and frequency of fragments in a cohort of horses presented for MRI of the foot and to compare MRI findings with severity of lameness. Archived MRI studies and medical records were searched from March 2006 to June 2008. Horses were included if a distal border fragment of the navicular bone was visible in MRI scans. Confidence interval comparisons and linear regression analyses were used to test hypotheses that fragments were associated with lameness and lameness severity was positively correlated with fragment volume and biaxial location. A total of 453 horses (874 limbs) were included. Fragments were identified in 60 horses (13.25%) and 90 limbs (10.3%). Fifty percent of the horses had unilateral fragments and 50% had bilateral fragments. Fragments were located at the lateral (62.2%), medial (8.89%), or medial and lateral (28.9%) angles of the distal border of the navicular bone. There was no increased probability of being categorized as lame if a fragment was present. There was no significant difference in fragment volume across lameness severity categorizations. Confidence intervals indicated a slightly increased probability of being classified as lame if both medial and lateral fragments were present. Findings indicated that distal border fragments of the navicular bone in equine MRI studies are unlikely to be related to existing lameness.     

High-field magnetic resonance imaging investigation of distal border fragments of the navicular bone in horses with foot pain

Reasons for performing study: Distal border fragments of the navicular bone can be seen in lame and nonlame horses and their clinical significance remains open to debate. Objectives: To describe the magnetic resonance imaging (MRI) appearance of distal border fragments and the adjacent navicular bone. To investigate the relationship between fragments and other abnormalities of the navicular bone and the distal sesamoidean impar ligament (DSIL). Methods: Horses were included if pain causing forelimb lameness was localised to the foot and high‐field MR images were acquired. The size and location of distal border fragments were recorded. Abnormalities in the adjacent navicular bone were graded to obtain a fragment grade. A total navicular bone grade was assigned. The DSIL was also graded. A Chi‐squared test was used to test for associations between the presence of a fragment and specific lesions involving the distal border of the navicular bone, the total grade of the navicular bone, and the grade of the DSIL. Results: 427 horses were included and 111 fragments observed. There was a significant association between the presence of a fragment and the total navicular bone grade, osseous cyst‐like lesions, increased number and size of the synovial invaginations of the distal border, increased signal intensity on fat suppressed images and size of distal border entheseophytes. Conclusions: There is an association between distal border fragments and other pathological MRI abnormalities of the navicular bone. Potential relevance: Distal border fragments are part of navicular disease, but their contribution to pain and lameness remains to be clarified.     

Can distal border fragments of the navicular bone be a primary cause of lameness?

A horse with unilateral forelimb lameness and pain localised to the palmar aspect of the foot was evaluated using radiography and low field magnetic resonance (MR) imaging. A distal border fragment of the navicular bone, an osseous cyst‐like lesion (OCLL) in the distal third of the navicular bone and focal distal sesamoidean impar desmitis were identified as the most likely causes of pain and lameness. No other lesions likely to contribute to pain and lameness were identified on MR images or gross post mortem examination. The OCLL was characterised histologically by enlarged bone lacunae containing proliferative fibrovascular tissue. Focal lesions of the distal aspect of the navicular bone are rarely found in isolation but can be causes of pain and lameness in horses.     

NAVICULAR BONE FRACTURE IN THE PELVIC LIMB IN TWO HORSES

The case history, radiographic and scintigraphic findings of two horses with pelvic limb navicular bone fractures are presented. In both cases the fractures were of traumatic origin. One horse had a bilateral fracture of the navicular bone, distal border, the other horse had a fracture of the proximal articular border in one pelvic limb navicular bone.     

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.     

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.     

Hindlimb lameness associated with proximal suspensory desmopathy and injury of the accessory ligament of the suspensory ligament in five horses

The accessory ligament of the hindlimb suspensory ligament arises from the plantar aspect of the calcaneus and fourth tarsal bones and blends with the suspensory ligament in the proximal aspect of the metatarsus. The accessory ligament of the suspensory ligament of both hindlimbs of 12 mature horses, with no history of hindlimb lameness, was assessed ultrasonographically. The ligament comprised linear parallel echoes which were consistently shorter than those of the lateral digital flexor tendon; the dorsal and plantar borders were parallel. Lameness associated with injury of the accessory ligament of the suspensory ligament was identified in 6 of 8 lame hindlimbs of 5 horses, unilaterally in 4 horses and bilaterally in one horse. In all horses there was concurrent proximal suspensory desmopathy. There was localised oedematous swelling on the distal medial aspect of the chestnut extending distally in 2 horses. Lameness was best identified when the horses were ridden. Perineural analgesia of the deep branch of the lateral plantar nerve abolished lameness in 3 horses but perineural analgesia of the tibial nerve was required to abolish lameness in the hindlimb with injury of the accessory ligament of the suspensory ligament in 2 horses. Injury of the accessory ligament of the suspensory ligament was characterised by marked decrease in echogenicity of the ligament and loss of parallel alignment of the linear echoes, which were shorter than normal in longitudinal images.     

Pathological changes in the navicular bone and associated structures of the horse.

Navicular bones from 74 horses were examined at necropsy. Animals ranged in age from eight months to 30 years. Eight horses had a clinical history of navicular disease. Degenerative lesions in the fibrocartilaginous surface of the navicular bone and of the surface of the deep flexor tendons were age related changes not necessarily related to lameness. These lesions were more extensive in horses with a history of navicular disease, and were often accompanied by adhesions and subchondral cavitation of the fibrocartilaginous surface of the navicular bone. Osteophytes, present in 12 of the 74 horses, appeared to be age-related and were uncommon in horses with a history of navicular disease. Nutrient foramina on the distal border of the navicular bone were highly variable in size and shape; in horses with a history of navicular disease they often had a small external opening that became larger as it penetrated the bone. Occlusive vascular disease (arteriosclerosis) was found in sound horses and in horses with a history of navicular disease. Thrombosis of arteries or ischemic necrosis of bone was not identified in any case.     

Lameness in 46 horses associated with deep digital flexor tendonitis in the digit: diagnosis confirmed with magnetic resonance imaging

REASONS FOR PERFORMING STUDY: The differential diagnosis of foot pain has long proved difficult and the use of magnetic resonance imaging (MRI) offers the opportunity to further the clinical understanding of the subject. OBJECTIVES: To determine the incidence of deep digital flexor tendon (DDFT) injuries in a series of 75 horses with lameness associated with pain localised to the digit, with no significant detectable radiographic or ultrasonographic abnormalities, using MRI; and to describe a variety of lesion types and relate DDF tendonitis with anamnesis, clinical features, response to local analgesic techniques and nuclear scintigraphic and ultrasonographic findings. METHODS: All horses undergoing MRI of the front feet between January 2001 and October 2002 were reviewed and those with DDFT injuries categorised according to lesion type; horses with primary tendonitis (Group I) and those with concurrent abnormalities of the navicular bone considered to be an important component of the lameness (Group II). The response to perineural analgesia of the palmar digital nerves and palmar (abaxial sesamoid) nerves, intra-articular analgesia of the distal interphalangeal (DIP) joint and analgesia of the navicular bursa were reviewed. The result of ultrasonography of the pastern and foot was recorded. Lateral, dorsal and solar pool and bone phase nuclear scintigraphic images were assessed subjectively and objectively using region of interest (ROI) analysis. RESULTS: Forty-six (61%) of 75 horses examined using MRI had lesions of the DDFT considered to be a major contributor to lameness. Thirty-two horses (43%) had primary DDFT injuries and 14 (19%) a combination of DDF tendonitis and navicular bone pathology. Lesions involved the insertional region of the tendon alone (n = 3), were proximal to the navicular bone (n = 23) or were at a combination of sites (n = 20). Lesion types included core lesions, focal and diffuse dorsal border lesions, sagittal plane splits, insertional injuries and lesions combined with other soft tissue injuries. Many horses had a combination of lesion types. Lameness was abolished by palmar digital analgesia in only 11 of 46 horses (24%). Twenty-one of 31 horses (68%) in Group I showed > 50% improvement in lameness after intra-articular analgesia of the DIP joint, whereas 11 of 12 horses (92%) in Group II had a positive response. Twelve of 18 horses (67%) in Group I had a positive response to analgesia of the navicular bursa. Nineteen horses had lesions of the DDFT extending proximal to the proximal interphalangeal joint seen using MRI, but these were identified ultrasonographically in only 2 horses. Scintigraphic abnormalities suggestive of DDFT injury were seen in 16 of 41 horses (41%), 8 in pool phase images and 8 in bone phase images. CONCLUSIONS AND POTENTIAL RELEVANCE: DDFT injuries are an important cause of lameness associated with pain arising from the digit in horses without detectable radiographic abnormalities. Lameness is not reliably improved by palmar digital analgesia, but may be improved by intra-articular analgesia of the DIP joint in at least 68% of horses. Ultrasonography is not sensitive in detecting lesions of the DDFT in the distal pastern region, but a combination of pool and bone phase scintigraphic images of the digit is helpful in some horses. Further follow-up information is required to determine the prognosis for horses with lesions of the DDFT in the digit and to establish whether this is related to lesion severity and/or location.     

Endoscopic evaluation of the navicular bursa: observations, treatment and outcome in 92 cases with identified pathology

Reasons for performing study: Diagnostic navicular bursoscopy has been described in limited cases. Review of greater numbers is needed to define its contribution to case management and prognostic values. Objectives: To report: 1) clinical, diagnostic and endoscopic findings in a series of cases, 2) surgical techniques and case outcomes and 3) prognostic values. The authors hypothesise: 1) lameness localising to the navicular bursa is commonly associated with dorsal border deep digital flexor tendon (DDFT) lesions, 2) endoscopy allows extent of injuries to be assessed and treated, 3) case outcome relates to severity of DDFT injury and 4) the technique is safe and associated with little morbidity. Materials and methods: All horses that underwent endoscopy of a forelimb navicular bursa for investigation of lameness were identified. Case files were reviewed and those with injuries within the bursa selected for further analysis. Results: One‐hundred‐and‐fourteen horses were identified. Ninety‐two had injuries within the bursa and DDFT injuries were identified in 98% of bursae. Of those examined with magnetic resonance imaging (MRI), 56% had combination injuries involving the DDFT and navicular bone. Sixty‐one percent of horses returned to work sound, 42% returned to previous performance. Horses with extensive tearing and combination injuries of the DDFT and navicular bone identified with MRI, had worse outcomes. Conclusions: Lameness localising to the navicular bursa is commonly associated with injuries to the dorsal border of the DDFT. Endoscopy permits identification and characterisation of injuries within the navicular bursa and enables lesion management. Outcome following debridement is related to severity of injury but overall is reasonable. Potential relevance: Horses with lameness localising to the navicular bursa may have tears of the DDFT. Bursoscopy is able to contribute diagnostic and prognostic information and debridement of lesions improves outcome compared to cases managed conservatively.     

Injection of corticosteroids, hyaluronate, and amikacin into the navicular bursa in horses with signs of navicular area pain unresponsive to other treatments: 25 cases (1999-2002)

OBJECTIVE: To determine history, clinical and radiographic abnormalities, and outcome in horses with signs of navicular area pain unresponsive to corrective shoeing and systemic nonsteroidal anti-inflammatory drug administration that were treated with an injection of corticosteroids, sodium hyaluronate, and amikacin into the navicular bursa. DESIGN: Retrospective study. ANIMALS: 25 horses. PROCEDURE: Data collected from the medical records included signalment, history, horse use, severity and duration of lameness, shoeing regimen, results of diagnostic anesthesia, radiographic abnormalities, and outcome. RESULTS: 17 horses had bilateral forelimb lameness, 7 had unilateral forelimb lameness, and 1 had unilateral hind limb lameness. Mean duration of lameness was 9.2 months. All horses had been treated with corrective shoeing and nonsteroidal anti-inflammatory drugs for at least 6 months; 18 had previously been treated by injection of corticosteroids and sodium hyaluronate into the distal interphalangeal joint. Fourteen horses had mismatched front feet, and 21 horses had signs of pain in response to application of pressure over the central aspect of the frog. Palmar digital nerve anesthesia resulted in substantial improvement in or resolution of the lameness in all horses. Twenty horses (80%) were sound and returned to intended activities 2 weeks after navicular bursa treatment; mean duration of soundness was 4.6 months. Two horses that received numerous navicular bursa injections had a rupture of the deep digital flexor tendon at the level of the pastern region. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that navicular bursa treatment may provide temporary improvement in horses with signs of chronic navicular area pain that fail to respond to other treatments.     

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.     

Retrospective evaluation of equine prepurchase examinations performed 1991-2000

REASONS FOR PERFORMING STUDY: Prepurchase examinations of horses are used increasingly as a means of evaluating future soundness. Data is lacking in the literature of the radiographic findings and results of the lameness examination of comprehensive prepurchase examinations. OBJECTIVE: To summarise the clinical and radiographic findings of prepurchase examinations and determine if radiographic findings correlated with the lameness examination and sale outcome. METHODS: Records of 510 cases were reviewed, radiographs evaluated and grades assigned the navicular bone, distal phalanx, and tarsus. Follow-up information on the horse status was obtained by telephone interviews for 173 horses. RESULTS: Thoroughbred geldings represented the most common breed and sex, mean age 8 years, mean asking price 12,439.40 dollars, and 52.8% were lame. Radiography was the most common diagnostic procedure performed (61.6%), with views of the front feet requested most often (86.6%) followed by the tarsi (68.1%). Grade 1 was most common for the navicular bone while Grade 2 predominated for the distal phalanx. The number of sound horses decreased as grades became more severe. For the tarsi, Grades 0 and 1 were most common for the proximal intertarsal and distal intertarsal/metatarsal joints, respectively. Horses with significant tarsal changes were still able to compete at their expected level. With respect to the radiographic examination, the mean +/- s.d. grade of the horses which were not lame at follow-up was 1.2 +/- 0.9 for the navicular bone and 15 +/- 0.8 for the third phalanx. The mean +/- s.d. grade of sound horses for the distal intertarsal joint was 0.7 +/- 0.6 and 1.14 +/- 0.8 for the tarsometatarsal joint. Horses for which owner follow-up was available and which had a Grade 3 score were also evaluated. For the navicular bone, 17/31 with a Grade 3 remained in active use at follow-up and for the distal phalanx 21/27 were in active use. For the distal intertarsal and tarsometatarsal joints, 20/21 with a Grade 3 were still in active use. CONCLUSIONS: Prepurchase examinations can have a significant effect on the outcome of the sale. For the navicular bone and distal phalanx, higher grades were associated with lameness. In contrast, higher grades in the tarsus were less likely to be associated with lameness. Warmbloods tended to have more extensive changes in the navicular bone and distal phalanx relative to Thoroughbreds but were not as lame. POTENTIAL RELEVANCE: Radiographic changes detected in the navicular bone, distal phalanx and tarsus should be interpreted with consideration to the clinical examination.     

Comparison between radiological and magnetic resonance imaging lesions in the distal border of the navicular bone with particular reference to distal border fragments and osseous cyst-like lesions

Reasons for performing study: There are no data concerning the accuracy of conventional and computed or digital radiography for evaluation of the equine foot. Objectives: To compare conventional film‐screen and computed radiography with magnetic resonance imaging (MRI) for detection of distal border fragments of the navicular bone; and to establish which type of fragment was more likely to be detected radiologically. Methods: Horses were included if forelimb lameness was localised to the foot and both radiography and high‐field MR images had been acquired. Horses were divided into 2 groups based on acquisition of conventional (Group A) or computed (Group B) radiographs. The presence of distal border fragments was recorded. From MR images, distal border fragments were graded based on their size and changes in signal intensity in the adjacent navicular bone. Sensitivity and specificity of conventional and computed radiography for detection of fragments were calculated using MRI as the gold standard. A Chi‐squared test was used to test for associations between specific radiological and MRI findings in the distal border of the navicular bone. Results: In Group A 46 and 18 fragments were identified on MR and radiographic images, respectively; in Group B 45 and 17 fragments were seen. There was no significant difference between computed and conventional radiography. Grades 4 and 5 fragments or large‐sized fragments were identified most frequently; low‐grade fragments were unlikely to be observed. There was a significant correlation between radiological and MRI abnormalities of the distal border of the navicular bone. Conclusions: Conventional and computed radiography had similar, rather low sensitivity for identification of distal border fragments of the navicular bone, but specificity was high. Large‐sized and high‐grade fragments were most likely to be identified radiologically. Potential relevance: Fragments observed radiologically are likely to be associated with other pathological abnormalities of the distal border of the navicular bone.     

Navicular disease in the horse

Navicular disease results in a chronic, progressiveforelimb lameness that is usually bilateral. Although many different horse breeds can be affected, Quarter Horses and Warmbloods appear particularly susceptible. The peak age incidence appears to be in horses aged 6–10 years. The condition has been recognized for many years and has been the source of debate and conflict for at least the last 50 years. Much of the confusion has been caused by different criteria used to establish a diagnosis. In a large series of cases examined at the University of Sydney, only 30 percent of horses that were eventually diagnosed as having navicular disease showed a positive response to hoof testers applied across the middle third of the frog. In contrast, more than 80 percent of horses with navicular disease showed a marked increase in lameness following pastern and fetlock flexion. All horses diagnosed became sound following a palmar digital nerve block and all had positive findings on radiography. However, radiography could not be utilized as a sole diagnostic technique because some horses with radiographic abnormalities of the navicular bone did not show clinical signs of navicular disease.To establish a diagnosis of navicular disease, the following criteria should be met: 1) A chronic progressive unilateral or bilateral forelimb lameness, 2) Pain in areas proximal to the foot has been excluded as a possible cause of the lameness, 3) Other conditions that could cause pain in the palmar heel region are excluded, 4) The lameness is eliminated or substantially improved following a palmar digital nerve block, and 5) There are radiographic abnormalities on upright pedal and/or skyline views of the navicular bone.Treatment of navicular disease has usually fallen into categories of a) pain alleviation, b) drugs with vascular or hemodynamic effects, or c) changing biomechanics either by corrective trimming or corrective shoeing. None of these treatments have been universally accepted and debate about their efficacy is allied to theories about the etiology.     

Evaluation of foot pain in the standing horse by magnetic resonance imaging

The records of 41 horses with previously undiagnosed foot pain that had been examined by standing magnetic resonance imaging were reviewed and follow-up information was obtained from their owners two years after the examination. A range of soft tissue and osseous abnormalities were identified, with multiple lesions frequently occurring. Deep digital flexor tendonitis was recorded in 12 of the horses, and distension of the distal interphalangeal joint was identified in 15, but it was not always associated with lameness; in contrast, distension of the navicular bursa was always associated with lameness in the seven affected horses. Navicular bone lesions were identified in 13 of the horses, often in the absence of radiographic changes. Follow-up information was obtained for 35 of the horses, 27 of which were alive; of these, 16 had returned to their previous level of performance. Of the five horses with navicular bursal changes, four had been euthanased owing to lameness and the other had returned to work at a reduced level.     

Magnetic resonance imaging of the equine foot: 15 horses

REASONS FOR PERFORMING STUDY: Foot pain is a common cause of equine lameness and there have been significant limitations of the methods available for the diagnosis of the causes of foot pain (radiography, nuclear scintigraphy and ultrasonography). Until recently, magnetic resonance imaging (MRI) in the horse has been limited to examination of cadaver limbs. OBJECTIVES: Our purpose was to 1) describe MRI of the foot in live horses, 2) describe MRI findings in horses with foot pain in which a definitive diagnosis could not be established by alternative means and 3) correlate MRI findings with other methods of clinical investigation. METHODS: The feet of 15 horses with unilateral (12) or bilateral (3), forelimb (14) or hindlimb (1) lameness associated with foot pain of previously ill-defined origin were examined using MRI. The horses were examined in right lateral recumbency under general anaesthesia, with the feet positioned in the isocentre of a flared end 1.5 Tesla GE Signa Echospeed magnet. Images were obtained in sagittal, transverse and dorsal planes using 3-dimensional (3D) T2* gradient echo (GRE), spoiled gradient echo, fat-saturated 3D T2* GRE and short inversion recovery sequences. Image acquisition took approximately 1 h. RESULTS: Abnormalities of the distal interphalangeal joint (DIP) cartilage and/or subchondral bone, periarticular osteophyte formation, distension of the DIP joint capsule with or without synovial proliferation, distension of the navicular bursa with or without evidence of chronic inflammation, surface and core lesions in the deep digital flexor tendon, abnormal signal within the navicular bone, evidence of mineralised fragments in the distal sesamoidean impar ligament, irregular outline of and signal in the medial cortex of the distal phalanx, and an abnormal signal on the dorsal aspect of the distal phalanx consistent with laminitis were identified. CONCLUSIONS: MRI permits the diagnosis of a variety of lesions involving different structures within the foot that cannot be diagnosed using other means, thus enhancing our knowledge of the causes of foot pain. Potential relevance: With further experience it is likely that lesions involving other structures will also be identified. Long-term follow-up data is required to determine the prognosis for the injuries described.     

RADIOGRAPHIC APPEARANCE OF THE NAVICULAR BONE IN SOUND HORSES

Radiographs of the navicular bone in 523 sound horses were reviewed. Detailed evaluation criteria were used. The incidence of radiographic changes and variations in normal horses were recorded. Results were tested for right-left limb difference and for age relationship. Variation in shape and bone structure was commonly seen in the navicular bone. Radiographic changes with an incidence of less than 2% included flexor cortex defects and calcification on the flexor surface. Fragments at the distal navicular bone border, calcification in the impar ligament and enthesiophytes at the proximal border were radiographic findings with an incidence of 2% to 10%. Abnormal canals at the distal border were found in 11% horses. Elongation of the lateral proximal extremity was commonly found. The mean width of the flexor cortex was 3.6 mm.