Radiographic and clinical features of carpal varus associated with chronic sprain of the lateral collateral ligament complex in 10 dogs.

Lameness associated with carpal varus deformity was recognised in 10 dogs, eight of which were Dobermann Pinschers. The dogs had a mean age of seven years and nine months. Carpal varus was usually bilateral with concurrent carpal hyperflexion and pronation. Carpal varus was present prior to the onset of lameness in four cases. With stress radiography the median angle of varus deviation in all carpi was 14.6 degrees , and an increase in the size of the ulnar /ulnar carpal bone joint space was seen in six of the seven dogs. Radiographic changes included: enthesophyte formation at the proximolateral aspect of metacarpal V, periarticular soft tissue swelling, especially lateral, bone proliferation at the carpometacarpal joint I and enthesophyte formation at metacarpophalangeal joint V. Four dogs were admitted for problems other than carpal varus and lameness was not treated. Five dogs were treated with nonsteroidal anti-inflammatory drugs, but lameness was not completely resolved and became exacerbated with exercise. One dog was successfully treated by pancarpal arthrodesis.     

MAGNETIC RESONANCE ANATOMY OF THE CARPUS OF THE HORSE DESCRIBED FROM IMAGES ACQUIRED FROM LOW‐FIELD AND HIGH‐FIELD MAGNETS

Cadaver carpi of 30 mature horses with no history of carpal or proximal metacarpal pain were examined using low‐field (0.27 T) and high‐field (1.5 T) magnetic resonance imaging (MRI). Normal MRI anatomy in transverse, sagittal, and dorsal plane images was determined by comparison with anatomical specimens and standard texts. Subchondral bone and cortical bone thickness measurements were obtained from standardised sites. There was variable subchondral bone thickness in the radius and carpal bones; subchondral bone thickness was consistently larger at dorsal compared with palmar sites in the proximal row of carpal bones. The endosteal surface of the subchondral bone was smooth. The shape of the ulnar carpal bone was variable and one or more small osseous fragments were identified palmar to the bone in 5/30 limbs. There was no evidence to suggest that these were pathological fractures or avulsions of the lateral palmar intercarpal ligament. The amount of muscle tissue in the superficial and deep digital flexor tendons in the proximal aspect of the carpus varied, but none was present at the level of the middle carpal joint and distally. Several structures could be evaluated that cannot be imaged using radiography, ultrasonography, or arthroscopy, including the transverse intercarpal ligaments, the radiocarpal ligament, the short palmar carpal ligaments, and the carpometacarpal ligaments. Anatomical variations not previously described were identified, including the layers of the medial aspect of the carpal fascia. Knowledge of the variation in MRI appearance of the carpus of nonlame horses is helpful for interpretation of MR images of lame horses.     

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

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

A Comparison of Methods for Proximal Palmar Metacarpal Analgesia in Horses

Three techniques for inducing analgesia of the proximal metacarpal region were evaluated for the frequency of inadvertent injection into the middle carpal and carpometacarpal joints. Using methylene blue solution as a marker dye and 30 fresh cadaver specimens each, three clinicians performed either 30 infiltrations at the origin of the suspensory ligament (method A), 30 palmar and palmar metacarpal nerve blocks at the proximal end of the metacarpus (method B), or 30 palmar and palmar metacarpal nerve blocks at the distal aspect of the accessory carpal bone (method C). The frequency of inadvertent injection into the distal carpal joints was 37, 17, and 0% for methods A, B, and C, respectively. The association between method and injection into the joints was significant (p less than 0.01). Infiltration of the distal carpal joints occurred with injection distances from the carpometacarpal joint of 1.5 to 4.5 cm. Although there was no joint injection with method C, the carpal synovial sheath was inadvertently infiltrated in 68% of the specimens. Injection into the distal carpal joints can occur when deep injections are made into the proximal palmar aspect of the metacarpus because of the distopalmar outpouchings of the carpometacarpal joint between the axial surfaces of the second and fourth metacarpal bones and the abaxial surface of the suspensory ligament.     

Low-field standing magnetic resonance imaging findings of the metacarpo/metatarsophalangeal joint of racing Thoroughbreds with lameness localised to the region: a retrospective study of 131 horses

Reasons for performing study: The metacarpo/metatarsophalangeal (MCP/MTP) joint is a common site of lameness in the Thoroughbred racehorse. Radiographs may fail to show pathology consistent with the degree of lameness. With a high incidence of stress fractures occurring in the distal third metacarpal/metatarsal (MC3/MT3) condyles and proximal phalanx, a definitive diagnosis as to the nature of the pathology is essential. Objective: To describe the low‐field magnetic resonance imaging (MRI) findings in Thoroughbred racehorses with MCP/MTP joint pain scanned under standing sedation. Methods: The MR images and clinical records of all Thoroughbred racehorses undergoing MRI of the MCP/MTP joint between October 2006 and August 2010 were reviewed. A total of 168 joints from 131 horses were selected for inclusion. The MRI finding considered most significant in the lame (or lamest) limb was noted. Results: Diagnostic quality images were obtainable in 97.8% of horses. The most common finding was palmar/plantar osteochondral disease in MC3/MT3 (54.9% of horses). Incomplete condylar fracture was diagnosed in 19.8% of horses, with the lateral condyle predominating. An incomplete sagittal fracure of P1 was diagnosed in 14.5% of horses and 11.4% were diagnosed with ‘dorsal joint disease’. Other findings included transverse MC3 stress fractures (1.5%), soft tissue injuries (12.2%) and proximal phalangeal ‘contusions’ (3.8%). No significant bone/soft tissue injury was detected in 5.4% of cases. Conclusions: Standing MRI can detect a spectrum of disease within the MCP/MTP joints of racehorses. The procedure is well tolerated and may lead to a definitive diagnosis where radiographic imaging is inconclusive. Potential relevance: A total of 35.8% of cases had MRI findings consistent with fracture pathology, which could not be confirmed radiographically at the time of the MRI examination. This has important therapeutic and prognostic implications and may help to prevent catastrophic injury.     

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

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

Concurrent proximal suspensory desmopathy and injury of the proximal aspect of the accessory ligament of the deep digital flexor tendon in forelimbs or hindlimbs in 19 horses

Clinical features of proximal suspensory desmopathy (PSD) and concurrent injury of the proximal aspect of the accessory ligament of the deep digital flexor tendon (ALDDFT) have not been documented. The objectives were to describe clinical signs and diagnosis. This was a retrospective study. Patient details, lame limb(s), response to diagnostic analgesia, and radiographic and ultrasonographic findings were recorded. PSD and injury of the proximal aspect of the ALDDFT were identified in 19 horses, 14 with forelimb lameness (unilateral 5, bilateral 9) and 5 with hindlimb lameness (unilateral 2, bilateral 3). Localising clinical signs were seen in 7/31 lame limbs (subtle thickening in the region of the ALDDFT [n = 3], pain on palpation of the body of the suspensory ligament (SL) [n = 6], heat in the proximal metacarpal or metatarsal region [n = 2]). Forelimb lameness was abolished by perineural analgesia of the palmar metacarpal (subcarpal) nerves in 17/23 limbs. In the remaining limbs intra‐articular analgesia of the middle carpal joint (n = 2) or an ulnar nerve block (n = 4) were required to eliminate the lameness. Hindlimb lameness was abolished by perineural analgesia of the deep branch of the lateral plantar nerve (n = 2) or local infiltration of the proximal plantar aspect of the metatarsus (n = 3); a tibial nerve block resolved lameness in the remaining 3 limbs. Lesions of the SL and of the ALDDFT were characterised ultrasonographically by enlargement, heterogeneous echogenicity and loss of long linear echoes in longitudinal images. In 3 horses adhesions between the ALDDFT and the SL were identified post mortem. Close apposition of these structures seen ultrasonographically may indicate adhesion formation. It was concluded that the clinical features of PSD and concurrent injury of the ALDDFT are similar to those for PSD alone, highlighting the need for comprehensive and systematic ultrasonographic assessment.     

Disorders of the origin of the suspensory ligament in the horse: a diagnostic challenge

Lameness in horses due to pain originating from the proximal metacarpal/metatarsal region remains a diagnostic challenge. In cases of obvious lameness the pain can be localised to this region by diagnostic anaesthesia. Because a variety of disorders can cause lameness in this region different imaging modalities including radiography, ultrasonography and scintigraphy should be used to arrive at an accurate diagnosis. Even though a precise anatomic-pathologic diagnosis can still be an enigma, because not only bone and joints, but also soft tissue structures including the proximal suspensory ligament, its origin at the proximal metacarpus/ metatarsus, its fascia, the superficial fascia, as well as the intermetacarpal/metatarsal ligaments, the accessory ligament of the deep digital flexor tendon and both digital flexor tendons may be involved. Magnet resonance tomography (MRT) shows a high diagnostic sensitivity in imaging soft tissue structures and bone. In horses MRT is still at the beginning. The MRT appearance of the proximal metacarpal/metatarsal region has not yet been evaluated in detail and there are only few anatomic studies of the origin of the suspensory ligament in horses. The first experiences showed, that more gross and histologic examinations are necessary to fully interpret MRT-images and to differentiate pathologic alterations from clinically not relevant variations.     

Spontaneous bilateral ankylosis of the carpometacarpal joint in a Paint Horse

An 8‐year‐old Paint Horse gelding was evaluated for a persistent left forelimb lameness (grade 4/5), with a hard swelling at the dorsomedial aspect of the carpometacarpal joint, due to osteoarthritis. Previous systemic and local anti‐inflammatory therapy had only a temporary effect. Partial carpal arthrodesis was suggested, but the owner elected for conservative treatment. The horse was confined to a small paddock and received phytotherapeutic supplementation with Harpagophytum procumbens. The lameness gradually resolved but a similar hard swelling developed on the right carpus. Radiographic follow‐up 1.5 years later revealed a spontaneous bilateral ankylosis of the carpometacarpal joint.     

Standing magnetic resonance imaging detection of bone marrow oedema‐type signal pattern associated with subcarpal pain in 8 racehorses: A prospective study

Reason for performing study: The proximal metacarpal region is a common site of origin of lameness in the performance horse. A number of disease entities are recognised as causes of proximal metacarpal lameness but a definitive diagnosis is often elusive. Magnetic resonance imaging (MRI) is hypothesised to offer advantages over traditional imaging modalities in the investigation of proximal metacarpal pain. Objective: To describe clinical and imaging features of cases of lameness in racehorses arising from the proximal metacarpal region in which standing MRI identified ‘bone marrow oedema‐type’ (BMO‐type) signal patterns. Methods: Records for all horses undergoing standing MRI of the proximal metacarpus/distal carpus from September 2006 to December 2008 were reviewed. Cases underwent a standardised protocol for diagnostic analgesia, radiography and ultrasonography of the proximal metacarpus and distal carpus. Cases with proximal metacarpal lameness displaying a characteristic BMO‐type signal pattern on MRI were identified and outcomes analysed. Results: Eight cases were identified with characteristic MRI findings of extensive hyperintensity on T2* gradient echo and short tau inversion fast spin echo sequences and corresponding hypointensity on T1 gradient echo images within the palmaroproximal aspect of the third metacarpal bone. Follow‐up information was available for all cases; at the time of writing 7/8 had returned to full work and were free from lameness. Conclusions: The BMO‐type signal patterns visible on MR images in these cases may signal the existence of a previously under‐diagnosed pathological process associated with proximal metacarpal lameness in racehorses. This finding is postulated to be associated with a stress reaction and possible prodromal stress fracture of the palmaroproximal metacarpus not appreciable radiographically or ultrasonographically. Potential relevance: MRI of the proximal metacarpal region permits detection of pathological processes, which may elude conventional imaging and, therefore, has important therapeutic and prognostic implications in these cases.     

Diffusion of contrast medium after four different techniques for analgesia of the proximal metacarpal region: an in vivo and in vitro study

Reasons for performing study: There is limited information on potential diffusion of local anaesthetic solution after various diagnostic analgesic techniques of the proximal metacarpal region. Objective: To document potential distribution of local anaesthetic solution following 4 techniques used for diagnostic analgesia of the proximal metacarpal region. Methods: Radiodense contrast medium was injected around the lateral palmar or medial and lateral palmar metacarpal nerves in 8 mature horses, using 4 different techniques. Radiographs were obtained 0, 10 and 20 min after injection and were analysed subjectively. A mixture of radiodense contrast medium and methylene blue was injected into 4 cadaver limbs; the location of the contrast medium and dye was determined by radiography and dissection. Results: Following perineural injection of the palmar metacarpal nerves, most of the contrast medium was distributed in an elongated pattern axial to the second and fourth metacarpal bones. The carpometacarpal joint was inadvertently penetrated in 4/8 limbs after injections of the palmar metacarpal nerves from medial and lateral approaches, and in 1/8 limbs when both injections were performed from the lateral approach. Following perineural injection of the lateral palmar nerve using a lateral approach, the contrast medium was diffusely distributed in all but one limb, in which the carpal sheath was inadvertently penetrated. In 5/8 limbs, following perineural injection of the lateral palmar nerve using a medial approach, the contrast medium diffused proximally to the distal third of the antebrachium. Conclusions and potential relevance: Inadvertent penetration of the carpometacarpal joint is common after perineural injection of the palmar metacarpal nerves, but less so if both palmar metacarpal nerves are injected using a lateral approach. Following injection of the lateral palmar nerve using a medial approach, the entire palmar aspect of the carpus may be desensitised.     

Carpal arthrodesis using a minimally invasive approach and locking compression plates: Three cases

Three horses with carpal instability due to comminuted second carpal bone fractures (Cases 1 and 3), fracture of the head of the second metacarpal bone (Case 1) or comminuted fractures of the fourth carpal bone, ulnar and intermediate carpal bones (Case 2) were treated by minimally invasive approach for partial (Cases 1 and 3) or pancarpal (Case 2) joint arthrodesis, using locking compression plates. The joint cartilage was removed by either an arthroscopic approach (middle carpal joint and antebrachiocarpal joint) or a percutaneous drilling technique (carpometacarpal joint). Two or 3 locking compression plates were contoured to the dorsolateral, dorsomedial and dorsoaxial aspects of the carpal joints using a custom‐made tunnelling tool and a minimally invasive tunnelling technique, and the screws were positioned through stab incisions. All cases recovered well, were lame free at the walk, were able to trot and gallop and could be used for leisure and pasture activities (partial carpal arthrodesis) and breeding (pancarpal arthrodesis). Post‐operative x‐rays showed progressive joint fusion after 12 months (Case 1), 5 months (Case 2) and 10 months (Case 3). Case 2 with a pancarpal arthrodesis showed a mechanical lameness at the walk due to the inability to flex the carpus. Carpal flexion after carpometacarpal and middle carpal arthrodesis in Case 1 was calculated to be 42.6° and 44° in Case 3.     

COMPUTED TOMOGRAPHIC ARTHROGRAPHY OF THE INTERCARPAL LIGAMENTS OF THE EQUINE CARPUS

Injuries of the intercarpal ligaments are an important cause of lameness in performance horses. The purpose of this prospective cadaver study was to determine whether computed tomography (CT) arthrography would be a feasible method for visualizing and characterizing intercarpal ligaments in the horse. One cadaver limb from each of eight nonlame horses was collected immediately after euthanasia. For each limb, overlapping 2.0 mm CT images were acquired before and after injection of iodinated contrast medium into the antebrachiocarpal joint, middle carpal joint, and carpal sheath. Spin echo magnetic resonance imaging (MRI) sequences were acquired in three planes using a 1.5 Tesla MRI scanner in three limbs. Following MRI, colored resin was injected into the synovial structures of these three limbs, limbs were frozen, and anatomic sections were obtained in three planes. Findings from CT arthrograms were compared to findings from precontrast CT, MRI, anatomic slices, and arthroscopy. Medial and lateral palmar intercarpal ligaments, radiocarpal and transverse intercarpal ligaments, and palmar carpal ligament were visible in CT arthrograms of all limbs. The proximal and distal entheses of all ligaments were readily identifiable. Findings indicated that CT arthrography is feasible for visualizing intercarpal ligaments and may be a useful adjunct imaging technique for diagnosing lameness due to suspected carpal ligament injury in horses.     

Incomplete Longitudinal Fracture of the Proximal Palmar Cortex of the Third Metacarpal Bone in Horses

Seven horses, 2 to 4 years of age, were examined because of moderate-to-severe forelimb lameness, mild effusion of the middle carpal joint (3 horses), and pain on palpation of the origin of the suspensory ligament (4 horses). The lameness was abolished by anesthetic infiltration of the middle carpal joint in six horses. In four of them, a high palmar nerve block also abolished the lameness. A linear radiolucency in the proximal end of the third metacarpal bone (McIII) was interpreted as an incomplete longitudinal fracture. In one horse, distinct intramedullary sclerosis limited to the palmar cortex was indicative of an incomplete fracture confined to the palmar cortex. No osteoproliferative lesions were identified on the dorsal cortex of any of the horses. Surgical treatment with cortical screws in lag fashion accompanied by a rest period was successful in one horse. In four horses, rest for at least 3 months resulted in clinical soundness. In two horses, a shorter rest period resulted in recurrence of the lameness even though the horses were sound when put back into training. Careful clinical and radiographic examinations helped differentiate incomplete longitudinal fractures from lesions involving the carpus and proximal aspect of the suspensory ligament.     

Magnetic resonance imaging and histological findings in the proximal aspect of the suspensory ligament of forelimbs in nonlame horses

Reasons for performing study: Detailed magnetic resonance imaging (MRI) and histological appearances of the proximal aspect of the suspensory ligament (PSL) in the forelimb of nonlame horses have not been previously documented. Objectives: 1) to describe detailed anatomy of the PSL, 2) describe high‐ and low‐field MRI and histological appearances of the PSL and surrounding structures in the forelimb of horses with no carpal or proximal metacarpal pain, 3) assess the relationship between age, breed, gender, height, bodyweight and MRI findings and 4) describe the histological appearance of the PSL and compare this with MRI findings. Methods: High‐ and low‐field MR images of the PSL and related structures from 30 cadaver limbs of nonlame horses were analysed subjectively and objectively. Univariable and multivariable linear regression analyses were used to assess the association of age, breed, gender, height and bodyweight with MRI findings. Histological and MRI findings of the PSL of 9 limbs were compared subjectively. Results: The collagenous tissue of the PSL had low to intermediate signal intensity depending on the pulse sequence. There was a large variation among horses in the amount, shape and signal intensity of the muscle and adipose tissue within the PSL. Comparison of MR images with histological slides revealed that the high signal intensity areas corresponded to adipose tissue and intermediate signal intensity areas to muscle tissue. The medial lobe of the PSL had a smaller cross sectional area (CSA) than the lateral lobe; there was a positive association between CSA of the PSL and both horse height and bodyweight (P<0.001). Conclusions and potential relevance: The large variability in the MRI appearance of the PSL in nonlame horses should be borne in mind when interpreting MR images of lame horses.     

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

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