Rachel C. Murray

Lameness associated with foot pain: results of magnetic resonance imaging in 199 horses (January 2001‐December 2003) and response to treatment

REASONS FOR PERFORMING STUDY The diagnosis of foot-related lameness often remains elusive and it can be difficult to offer rational treatment, or to predict outcome. OBJECTIVES To describe the spectrum of injuries of the foot identified using magnetic resonance imaging (MRI), to determine their relative prevalence among MRI diagnoses and to establish the long-term results of treatment. METHODS The MR images of horses examined from January 2001--December 2003 were reviewed. Horses were selected for MRI if the pain causing lameness was localised to the foot using perineural analgesia but any clinical, radiological or ultrasonographic abnormalities were insufficient to explain the degree of lameness. The clinical significance of lesions identified using MRI was determined with reference to the results of local analgesia, radiography, ultrasonography and nuclear scintigraphy. Follow-up information was obtained in January 2004 for horses which had been examined 6-36 months previously and the outcome classified as excellent (horse returned to full athletic function without recurrent lameness), moderate (sound, but only in light work), or poor (persistent or recurrent lameness). RESULTS One hundred and ninety-nine horses underwent MRI examinations. Deep digital flexor (DDF) tendonitis was the most common injury (59%) with primary injury in 65 horses (33%) and a further 27 horses (14%) having lesions of the DDF tendon and navicular bone. Seventeen percent of horses had injuries to multiple structures, including 24 with DDF tendonitis. Desmitis of a collateral ligament (CL) of the distal interphalangeal (DIP) joint was the second most common injury (62 horses, 31%), with primary injuries in 30 horses (15%) and a further 32 horses (16%) that had CL desmitis in conjunction with other injuries. Prognosis was best for horses with traumatic injuries of the middle or distal phalanges, with 5 of 7 horses (71%) having an excellent outcome. Horses with primary lesions of the DDF tendon or CL of the DIP joint had excellent results in only 13 of 47 (28%) and 5 of 17 horses (29%), respectively. Horses with combined injuries of the DDF tendon and navicular bone, or primary navicular bone abnormalities, had a poor outcome, with the majority of horses suffering persistent lameness. CONCLUSIONS A wide variety of lesions associated with foot pain were identified using MRI, a high proportion of which were primary soft tissue injuries with a guarded prognosis for return to full athletic function. POTENTIAL RELEVANCE It is now possible to propose more rational treatment strategies for the variety of foot injuries identified using MRI than had previously been possible; however, further information concerning aetiopathogenesis of these injuries is needed to improve their management.

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.

Identification of risk factors for lameness in dressage horses.

The aim of this study was to describe the prevalence of illness and lameness at different anatomical sites in registered United Kingdom dressage horses and to identify risk factors for lameness. A questionnaire was sent to all 11,363 registered members of British Dressage in 2005, with one questionnaire assigned per horse. Four multivariable logistic regression models were developed for each section of the questionnaire. A final mixed effects logistic regression model was developed which combined the results from all prior models. Owners reported that 33% of horses had been lame at some time during their career, with 24% of these within the previous 2 years. A number of factors were associated with the occurrence of lameness in the last 2 years, including age, height, indoor arenas, horse-walkers, lunging (as protective), back problems, arenas that become deeper in wet conditions and sand-based arenas. These factors were included as variables in a final model to provide information for selection of horses, development of safer arenas and more effective training regimens to minimise the onset of lameness.

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.

Magnetic resonance imaging evaluation of 264 horses with foot pain: the podotrochlear apparatus, deep digital flexor tendon and collateral ligaments of the distal interphalangeal joint.

REASONS FOR PERFORMING STUDY To improve understanding of the interrelationships between injuries of the podotrochlear apparatus and deep digital flexor tendon (DDFT). HYPOTHESES There is a difference in frequency of different types of lesions at different anatomical sites of the DDFT. Lesions of the collateral sesamoidean ligament (CSL), distal sesamoidean impar ligament (DSIL), distal interphalangeal (DIP) joint and navicular bursa are seen in association with lesions of the navicular bone. METHODS The magnetic resonance (MR) images of 264 horses with unilateral or bilateral foot pain were analysed and graded. Descriptive statistics were performed to establish the frequency of occurrence of DDFT lesion types at different anatomical levels, and lesions of the CSL, DSIL, navicular bursa, DIP joint and collateral ligaments (CLs) of the DIP joint. A Chi-square test was used to test for a difference in the proportion of navicular bone grades between limbs with and without DDFT lesions at each level, and to compare navicular bone grades for limbs with and without each of DSIL, CSL, navicular bursa or DIP joint lesions. RESULTS Lesions of the DDFT occurred in 82.6% of limbs, occurring most commonly at the level of the CSL (59.4%) and the navicular bone (59.0%). Core lesions predominated at the level of the proximal phalanx (90.3%), whereas at the level of the CSL and navicular bone core lesions, sagittal splits and dorsal abrasions were most common. There was a positive association between DDFT lesions and navicular bone pathology involving all aspects of the bone. Lesions of the DSIL (38.2% limbs) were more common than those of the CSL (10.5%), but the presence of either was associated with abnormalities of the navicular bone, especially involving the proximal or distal borders and the medulla. CONCLUSIONS AND CLINICAL RELEVANCE There are close interactions between injuries of the components of the podotrochlear apparatus, the DDFT, the navicular bursa and the DIP joint. Further knowledge about the biomechanical risk factors for injury may have importance for both disease prevention and management.

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.

Subchondral bone thickness, hardness and remodelling are influenced by short‐term exercise in a site‐specific manner

It was hypothesised that subchondral bone thickness, hardness and remodelling are influenced by exercise intensity, and by location within a joint. Dorsal carpal osteochondral injury is a major cause of lameness in horses undergoing high intensity training. This project aimed to determine the subchondral bone thickness, formation, resorption and hardness at sites with high and low incidence of pathology in 2 year‐old horses undergoing 19 weeks high intensity treadmill training or low intensity exercise, and to compare these factors between exercise groups. Dorsal and palmar test sites were identified on radial, intermediate and third carpal articular surfaces after euthanasia. Adjacent osteochondral samples from each test site underwent histomorphometric analysis (for subchondral bone thickness, osteoid perimeter, osteoid seam width, eroded cavity area and eroded cement line surface length) and microhardness testing. Bone from horses undergoing high intensity training was thicker with a greater osteoid perimeter, and at individual sites had a smaller osteoid seam width and eroded cavity. Exercise‐related differences were most marked at dorsal locations. Maximal differences in bone formation indices were observed at dorsal radial and medial third carpal locations. Overall subchondral bone from dorsal sites was thicker with a greater osteoid perimeter. Subchondral bone from dorsal sites was approximately 35% harder than bone from palmar sites. These results show topographical variations in subchondral bone structure, formation, resorption and material properties and a site‐specific response to exercise. The maximal response to exercise was at high load sites with a clinical predisposition to injury. These findings indicate that the combined effect of exercise and local load variations within a joint may lead to maximal adaptive responses or overload of these responses at sites predisposed to injury.

Pain associated with the sacroiliac joint region: a clinical study of 74 horses.

REASONS FOR PERFORMING STUDY There has been no large study of horses with suspected sacroiliac (SI) joint region pain in which the clinical diagnosis has been supported by either abnormal radiopharmaceutical activity in the SI joint region or by periarticular infiltration of local anaesthetic solution. OBJECTIVES To describe the clinical features of horses with SI joint region pain, to document the age, breed, sex, discipline, size and conformation of affected horses and to compare these with the authors (SD) normal case population and to document the results of infiltration of local anaesthetic solution around the SI joint region. METHODS Horses were selected for inclusion in the study based upon the exclusion of other causes of lameness or poor performance, together with clinical signs suggestive of SI joint pain and abnormal radiopharmaceutical activity in the SI joint region and/or a positive response to periarticular infiltration of local anaesthetic solution. RESULTS Sacroiliac joint region disease was identified in 74 horses between November 1997 and March 2002. Dressage and showjumping horses appeared to be at particular risk (P < 0.001). Affected horses were generally slightly older than the normal clinic population (P < 0.0001), taller at the withers (P < 0.0001) and of greater bodyweight (P < 0.01). There was a significant effect of breed (P < 0.001), with a substantially higher proportion of Warmblood horses (51%) in the SI pain group compared to the normal clinic population (29%). There was no correlation between conformation and the presence of SI joint region pain. The tubera sacrale appeared grossly symmetrical in most (95%) horses. Poor development of the epaxial muscles in the thoracolumbar region and asymmetry of the hindquarter musculature were common. Twenty-six horses (35%) showed restricted flexibility of the thoracolumbar region and 10 (16%) had an exaggerated response to pressure applied over the tubera sacrale. Fourteen horses (19%) were reluctant to stand on one hindlimb for prolonged periods. The majority of horses (75%) had a straight hindlimb flight and only 18% moved closely behind or plaited. In all horses restricted hindlimb impulsion was the predominant feature; invariably this was most obvious when the horse was ridden. Stiffness, unwillingness to work on the bit and poor quality canter were common. Sacroiliac joint region pain was seen alone (47%), or in conjunction with thoracolumbar pain (16%), hindlimb lameness (20%), forelimb lameness (7%) or a combination of problems (10%). Seventy-three horses (99%) had abnormalities of the SI joint region identified using nuclear scintigraphy. Infiltration of local anaesthetic solution around the SI joint region produced profound improvement in gait in all 34 horses in which it was performed. CONCLUSIONS AND POTENTIAL RELEVANCE Careful clinical examination combined with scintigraphic evaluation of the SI joint region and local analgesia can enable a more definitive diagnosis of SI joint region pain than has previously been possible.

The Mineral Phase of Calcified Cartilage: Its Molecular Structure and Interface with the Organic Matrix

We have studied the atomic level structure of mineralized articular cartilage with heteronuclear solid-state NMR, our aims being to identify the inorganic species present at the surfaces of the mineral crystals which may interact with the surrounding organic matrix and to determine which components of the organic matrix are most closely involved with the mineral crystals. One-dimensional (1)H and (31)P and two-dimensional (1)H-(31)P heteronuclear correlation NMR experiments show that the mineral component is very similar to that in bone with regard to its surface structure. (13)C{(31)P} rotational echo double resonance experiments identify the organic molecules at the mineral surface as glycosaminoglycans, which concurs with our recent finding in bone. There is also evidence of gamma-carboxyglutamic acid residues interacting with the mineral. However, other matrix components appear more distant from the mineral compared with bone. This may be due to a larger hydration layer on the mineral crystal surfaces in calcified cartilage.

Lesions of the deep digital flexor tendon in the digit: a correlative MRI and post mortem study in control and lame horses.

REASONS FOR PERFORMING STUDY Lameness associated with lesions of the deep digital flexor tendon (DDFT) in the digit is now recognised as an important cause of lameness, but there is currently limited information about the pathological nature of the lesions. OBJECTIVES To compare: signal intensity changes on magnetic resonance images with histopathology; and histopathological changes in the DDFT from horses with no history of foot-related lameness (Group C) and horses with lesions of the DDFT confirmed using magnetic resonance imaging (MRI) (Group D). METHODS Transverse sections of the DDFT were harvested from 3 sites in all horses: (1) immediately proximal to the navicular bursa (E1); (2) at the level of the navicular bone (E2); and (3) close to the tendons insertion (E3). If lesions were identified at E1 or had been identified further proximally using MRI, additional sections were obtained until, in most cases, the proximal limit of the lesion was identified. All DDFTs were graded histopathologically using predefined criteria. The MR images were reviewed to determine the location and sequences in which increased signal intensity was seen. RESULTS No haemorrhage or inflammatory cell infiltration was seen in any horse. At level E1, septal thickening, ghosting of blood vessels and blood vessel occlusion were common in Group D, but were not seen in Group C. Less commonly, there was core necrosis, only seen in Group D. At level E2, septal and vascular changes were most obvious in Group D. Core necrosis, dorsal splitting, crevicing and fibrillation were seen only in Group D. Septal and vascular changes were present in both Groups C and D at level E3, but fibrocartilaginous metaplasia, splitting, crevicing and fibrillation, or core necrosis or fibroplasia were seen only in Group D. Core lesions in Group D often extended proximal to E1, and ranged in length from 0.5-13 cm. Core necrosis was generally associated with increased signal intensity in fat suppressed images. CONCLUSIONS Lesions of the DDFT in the digit appear to be primarily degenerative, and may be a sequel to vascular compromise. Increased signal intensity on fat suppressed MR images is not necessarily associated with frank fluid or evidence of inflammation, but may reflect major matrix changes in the tendon. POTENTIAL RELEVANCE Further information about the causes of these lesions is required to develop preventative strategies.