Osteochondral Fragments within the Dorsal Pouch or Dorsal Joint Capsule of the Proximal Intertarsal Joint of the Horse

The anatomy of the dorsal pouch of the proximal intertarsal joint (PIJ) and its communication with the tarsocrural joint (TCJ) was studied in 15 pairs of hocks from young and mature horses. The mediolateral length of the TCJ-PIJ fenestration was 14 to 29 mm. The potential volume of the dorsal pouch of the PIJ was 3 to 5 ml, and a recess extended 10 to 28 mm medial to the medial commissure of the TCJ-PIJ fenestration. In a correlated clinical study, osteochondral fragments were identified radiographically within the dorsal pouch (category 1) or dorsal joint capsule (category 2) of the PIJ in 17 horses undergoing arthroscopic surgery of the TCJ. In six horses with category 1 lesions, osteochondral fragments were found free within the dorsal pouch and were removed. In five horses, category 1 fragments were not located. All 11 horses were reported by owners to be sound after surgery. In seven horses, a minimally displaced fragment was identified at the distal aspect of the medial trochlear ridge, within the insertion of the synovium separating TCJ and PIJ (one horse had both types of lesions in the same hock). Five of the seven category 2 fragments were removed at surgery. Of the seven horses with category 2 lesions, four were training or racing, two were unsound, and one was still convalescing at the time of follow-up.     

Quantitative Evaluation of Equine Deep Digital Flexor Tendon Morphology using Magnetic Resonance Imaging

Injury of the distal aspect of the deep digital flexor tendon (DDFT) is a recognized cause of lameness, but diagnosis is difficult. This study aimed to improve understanding of DDFT morphology and pathology using retrospective evaluation of magnetic resonance (MR) images. We hypothesized that: (1) The distal aspect of the DDFT in normal horses would have a repeatable proximal/distal pattern and symmetry between limbs and between lobes; (2) DDFT dimensions would be related to bodyweight, navicular bone dimensions and hoof size; (3) this symmetry and pattern would be lost in DDFT injury; and (4) DDFT size would increase with injury. MR images of 64 live horse limbs, 26 with no identified DDFT lesion and 38 with identified DDFT abnormalities, and 19 normal cadaver limbs were analyzed. Using standardized transverse images, measurements of DDFT cross-sectional area, medial-lateral (ML) width and dorsal-palmar depth were obtained at six preselected sites. A uniform distal to proximal shape pattern was identified in all horses. The flattened crescent shape at the insertion changed to a deeper bilobed shape more proximally, with the mid-navicular area having the greatest cross-sectional area. Strong ML (P < 0.0006) and left/right symmetry (P < 0.02) were observed. In addition, there was a strong association between DDFT cross-sectional area and horse weight (P = 0.005) and between DDFT and navicular bone ML width (P = 0.004). Symmetry between sides or between lobes was lost at sites with a unilateral lesion and correlation between horse weight and DDFT cross-sectional area was lost in the presence of lesions. DDFTs with core lesions had a consistent increase in cross-sectional area overall, but other lesion types had no significant increase in size. The shape and symmetry seen in normal tendons could be related to the mechanical demands placed upon individual lobes. The limited increase in cross-sectional area with injury may be explained by the restrictive structures of the hoof, possibly explaining the ongoing pain seen in such lesions.     

Magnetic Resonance Assessment of the Equine Distal Phalanx Facies Flexoria

Abnormalities of the facies flexoria of the distal phalanx (FF) of the horse associated with podotrochlear syndrome have been scarcely described in the literature. The objective of this retrospective study was to determine correlation between modification of the FF and lesions of the podotrochlear apparatus. This study includes 100 horses referred for forelimb lameness that underwent a standardized magnetic resonance (MR) imaging protocol of the affected foot. Of the 100 MR studies, 74 had podotrochlear lesions and 26 free of podotrochlear lesions served as controls. A comparison of the FF compact bone thickness between affected and control feet was performed. Presence and location of a deep digital flexor tendon (DDFT) lesion was noted. Grading systems were used to score: FF osseous resorption, FF bone marrow lesion, FF sclerosis and abnormalities of the navicular bursa and the distal interphalangeal joint. Compact bone thickness of the FF was not increased in case of tendinopathy of the DDFT or other podotrochlear lesions (P = .86). Significant correlation was observed between osseous resorption of the FF at the level of the distal recess of the navicular bursa and synovial proliferation of the navicular bursa (P = .05). Compact bone thickening at the DDFT enthesis is not predictive of podotrochlear syndrome and should rather be considered as an interindividual anatomical variation. Navicular bursitis may play a role in osseous resorption of the FF.     

Histologic Appearance and Distribution of Synovial Membrane Types in the Equine Stifle Joint

A study of the histologic organization of normal synovial membranes of the stifle joint of the horse is described. Three types of synovial membrane, which appear to be randomly distributed within the stifle joint, are described.     

Magnetic Resonance Imaging Findings in the Proximal Metacarpal Region of 359 Horses and Proximal Metatarsal Region of 64 Horses Acquired Under Standing Sedation

Standing magnetic resonance (MR) images of proximal metacarpal/metatarsal regions are increasingly being acquired. This study aimed at describing ranges of abnormalities detected in sport/racehorses, using retrospective evaluation of magnetic resonance imaging (MRI) reports from horses with lameness isolated to proximal metacarpal/metatarsal regions with images acquired standing. It was hypothesized that MRI features are different between metacarpal and metatarsal regions and between horses doing different sports. Reports from 359 forelimbs and 64 hindlimbs were included. Palmar/plantar metacarpal/metatarsal bone injury and suspensory desmopathy, which often occurred concurrently, were most frequently reported. Third metacarpal abnormalities were more likely at palmar/medial locations, including cortical (86.4%) and trabecular (38.2%) pathology with frequent thickening, irregularity, and periosteal/endosteal abnormalities. Fluid signal was reported in cortical (38.7%) and trabecular (22.6%) bone. Medial intermetacarpal articulation abnormalities were more frequently reported (52.5%) than lateral. Suspensory ligament pathology was reported in 83.8% forelimbs, frequently with cortical (74.1%) or trabecular (32.9%) pathology. Tarsal-joint abnormalities were significantly more likely than carpal-joint abnormalities. Third metatarsal cortical (57.8%) and trabecular (20.3%) pathology was most frequently plantar, but significantly more likely to be dorsal than forelimbs. Metatarsal fluid signal was significantly less likely than metacarpal. Lateral intermetatarsal articulation pathology (23.4%) was more frequent than medial; medial was significantly more likely in forelimbs. Suspensory ligament abnormalities were reported in 64.1% hindlimbs, 39.1% having concurrent cortical pathology. Metacarpal fluid signal was significantly more likely in endurance/racehorses than dressage/show jumping horses. Dressage was overrepresented in hindlimb suspensory origin pathology. These findings indicate different pathology patterns between forelimb/hindlimb and between different sports and may be useful for MRI interpretation.     

Magnetic Resonance Imaging of the Normal Canine Larynx

The purpose of this study was to define the normal anatomic structures in the canine larynx with magnetic resonance images. TI-weighted images were taken in the sagittal and transverse planes. The MR images were obtained comparing MR images to dissection planes. Magnetic resonance imaging provides excellent anatomic detail of laryngeal structures. Therefore, it is of value for diagnostic imaging of some respiratory diseases in the dog.     

Synovial Fluid and Clinical Changes After Arthroscopic Partial Synovectomy of the Equine Middle Carpal Joint

Changes in synovial fluid and clinical variables after arthroscopic partial synovectomy of the middle carpal joint were studied in 12 normal horses. A 7 mm motorized synovial resector was inserted into each middle carpal joint; one middle carpal joint of each horse was randomly selected to have arthroscopic synovectomy (treated) and the opposite joint was lavaged (control). Lameness examinations and synovial fluid analyses were performed before operation and at 8, 14, 21, and 28 days after operation. Lameness variables did not differ between treated and control legs. Middle carpal and carpometacarpal joint circumference measurements were increased for 4 weeks. Synovial fluid specific gravity, pH, total protein, albumin concentration, and alpha-1-, beta- and gamma-globulin concentrations, at 8 and 14 days were significantly higher than before operation in both treated and control middle carpal joints. No significant differences were found between treated and control middle carpal joints at any time for color, clarity, pH, mucin clot formation, total protein, albumin, and globulin fractions. Arthroscopic partial synovectomy and lavage did not cause significant lameness and resulted in a synovitis indistinguishable from synovitis related to arthroscopic lavage alone.