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Flashcards in Musculoskeletal - Equine Deck (131)
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What are the radiographic signs of non-union?

  • > 3 months
  • Radiolucent line through the fracture site
  • Sealing off of the medullary cavity
  • Bone resorption or regional osteoporosis above and below the fracture site


Radiographic signs of physitis: 


  • Abnormal widening and widening and bony irregularlity at the epiphyseal and metaphyseal margins of the gowrth plate 
  • The metaphysis of the bone is boradened and assymetrical 
  • There is increased opacity of the metaphysis adjacent to the physis, which may be more irregular in appearance than normal, with paralle radiolucent lines reflecting retained cartlage cones 
  • The crotices of the metaphysis may be thick 
  • Soft tisseu swelling over the area of involvement is common 
  • Widened metahyseal and physeal bone may perisst throughout life, resulting in an irregular or flared appearance at the location of the physcal scare, although in many cases, considerable modelling towards normality occurs 
  • Most common site: 
    • Distal radius 


Equine primary bone tumors 

  • Primary tumors and metastatic malignancy of the long bones of horse are rare 
  • The majority of tumors involve bone occur in the skull or ocassionally the spine 


Osteitis and osteomyelitis 

  • Osteitis = inflammation of bone. '
    • Usually a result of trauma or inflammation in adjacent tissues.
    • It is characterized by new bone formagtion and sometimes bone resorption.
    • Differentiation should be made between aseptic osteitis and infectious osteitis. 
    • More common in adult horse 
  • Osteomyelitis = inflammation of cortical bone and its myeloid cavity 
    • More common in foals 
    • May occur simultaneously at several sites, often extending to adjacent joints 


Hallmarks of equine osteitis

  • Soft-tissue swelling with bone destruction and new bone formation 
  • An attempt to wall off infection resulting in radiopaque bone formaing adjacent to the area of bone infection and destruction 
  • Infection of bone may result in formation of a swquestrum surrounded by an involucrum (adjacent granulation tissue). A radiolucent tract may be visible extending from the infected area (a sinus). 
  • NOTE: the distal phalanx, distal sesamoid (navicular) bone and skull show a slightly different reaction to infection. In these bones, infection tends to cause destruction of bone with little evidence of new bone formation. 


Equine osteomyelitis 

  • Mroe common in foals than adults 
  • Can occur in many different sites and may extent to adjacent joints 
  • Osteomyelitis in foals tends to be very destructive and there is usually very little response by the bone to wall off the infection 


Hypertrophic Osteopathy in Horses

  • Formerly known as Marie's disease 
  • It has been shown that pulmonary involvement is NOT a pre-requisite as previoulsy beliced 
  • Mainly affects the metaphyses and diaphyses of the long bones, while sparing joints 
  • Typified by periosteal new bone that often appears to be forming perpendicular to the cortices of the bone and is irregular in outline in the acute stage 
  • In early stages, soft exposures must be used to avoid overexposure this relatively lucent new bone 
  • Later the margins of the new bone become more opaque and smoother, and the appearance of the original cortex of the bones becomes less clear 
  • The bony lesions develop secondary to a primary lesion usually in the thorax or ocassionally in the abdomen, such as tumors, an abscess or granulomatos disease 
  • Bone lesions may regress and remodel if the undelrying cause is treated


Enostosis-like lesions

Enostosis:  ~ panosteotis in dogs 

  • Bone developing within the medullary cavity or on the endosteum, resulting in a region of increased radiopacity 
  • Focal or multifocal, intramedullary sclerosis 
  • They usually happen in the dipahyseal region of long bones, near the nutrient foramen, often develooiung on the endosteal surface of bones 
  • The etiology and clinical significant is unknown. However, they may be associated with lameness and resolve with rest. 



  • Frequently associated with focal increased radiopharmaceutical uptake, wheter or not they are causing lameness.



  • Such focal radiopacitis should be differentialted from endosteal callys secondary to a fatigue or stress fracture


Fracture description: 

  • Location
    • Which bone
    • What part of the bone
  • Type of fracture 
    • Transverse
    • Oblique 
    • Spiral 
  • Unicortical or bicortical
  • Simple vs. open 
  • Multiple or comminuted 
  • Ahether articular involvement is present 
  • DEgree of displacement 
  • Concurrent pathology which adverse influcen the prognosis 


Salter Harris Type Fractures 

"Prison Makes Every Boy Cry" 


Infectious arthritis 

Radiographic features include: 

  • Periarticular soft tissue swelling 
  • Joint capsule distention, with or without apparent widening of the joint space
  • Irregularity of outline of the subchondral bone
  • Lucent zones in the subchondral bone, with or without areas of increased opacity 
  • Periarticular osteophyte formation, sude to secondary degenerative joint disease 
  • Partial collapse of subchondral bone 


What is Synovial Osteochondromatosis?


  • It is a very unusual synovial response in the horse and ca be primary vs. secondary.
  • The condition described metaplastic and focal formation of cartilage within the intimal layer of the synovial membrane. Cartilage may undergoe mineralization and become evident radiographically. 


  • Arthroscopic removal of osteochondral bodies and rescetion of abnormal synovium. 


  • Recurrence is quite common and malignant transformation rarely occurs, although, to this date has not been reported in horses. 


Pedal Osteitis Complex

Simply means inflammation of the distal phalanx. Septci vs. aspectic etiologies. 


Radiographic findings: 

Modelling of the solear margin of the bone: 

  • Changes are most evident on the dorsoproximal-palmarodistal oblique projections. 
  • The solar margins of the bone loses it smooth, opaque outline due to deminieralization.
  • In some cases the bone near the solaer margin may have some increased radiolucency, making its visualization difficult. 
  • In more severe cases, larger areas of bone may be resorbed from the solear margin of the bone, resulting in apperant widening of the vascular channels primaryly at the solear margin.
  • On the lateromedial projection, these changes may be evident as modelling ofthe tip of the bone, the solear margin no longer having a straight outline but curving proximally towards the dorsal aspect of the bone. This change appears magnified if the radiograph is not a true lateromedial projection.
  • In more advances cases, more bone may be laid down on the dorsal surface of the bone at the toes.

Changes to palmar process of the distal phalanx

  • Best assessed in the dorsoproximal-palmarodistal oblique projections
  • Discrete circular radiolcuent areas, 2mm-3mm in diamete, are present in the palmar processes of the bone, and these may be associated with new bone, particularly on the axial surfaces of the palamr process. 
  • There may be change in shape with elongation of the palmar processes, seen also in a dorsolateral-palmaromedial oblique view. 

Mineralized lesions on the dorsal aspect of the distal phalanx may be seen:

  • These are usually midway between the proximal border and loear margins of the bone 
  • The etiology is unknonw, although may be a reflection of abnormal stress on the suspensory apparatus of the distal phalanx 


  • Concussion of the bone 
  • May be related with poor foot conformation and shoeing imbalances 

Physical exam:

  • May be associated with lameness that is most significant on hard surfaces


  • Corrective trimming and shoeing 


  • Although condition may resolve clinically, the radiological changes usually remain throughout life 
  • Nuclear scintigraphy may help determine the significance of these radiographic changes within the distal phalanx. Increased radiopharmaceutical uptake would indicate active bone remodeling.




  • The most common space-occupying mass to involve the distal phalanx is a keratoma. 
  • May occur at any point of the hoof wall
  • May cause lameness as it enlarges and may be associated with secondary infection 
  • Treatment is by surgical removal of the keratoma and carries a reasonable prognosis although the mass may recurr up to several years later, especially if removal is incomplete. 

Radiographic findings: 

  • Mass occupying mass 
  • Pressure from the mass on the dorsal aspect of the distal phalanx causes resorption bone. This is most easily seen at the solear margin of the bone, where a distinct semicircular notch is evident on a dorsoproximal-palmarodistal oblique view. This has a smooth outline, the bone undelying the keratoma frequently having increased opacity, which helps to differentiate this lesion from infection
  • There is usually no new bone associated with the lesion. 


Ossification of Ungual Cartilages 



  • Some ossification of the ungular cartilages is a common finding, particularly in heavy breeds, cob-types and large British native ponies. Ossification usually occurs from the base of the cartilage at its attachemnt to the distal phalax and extends variablye distance proximally. 
  • Mild ossification is usually of no clinical significance. It is usually bilaterally symmetrical. 
  • If there is assyemteryc within a foot, the lateral cartilage is usually more extensively ossified. 
  • Marked assyemetry is usually unusual and may be associated with lameness
  • There may be one or more separate centers of ossification, which will be difficult to differentiate from fractures. Scintigraphy and MRI (increased signal intensity on fat-suppresion images). 
  • MRI is needed to diagnose soft tissue injury 


Enthesyophyte adjacent to the Extensor Process of the Distal Phalanx

The common digital extensor inserts immediately distal to the extensor process of the distal phalanx. Tearing of the insertion may result in lameness and entheseophyte formation of the proximodorsal aspect of the distal phalanx immediately dstal to the extensor process. 

This change must be differentiate from the normal variation in shape of the extensor process.

The outline caused by the entheseophyte is usually irregular, and there may be alterations in the opacity of the trabecular structure of the underlying bone. 



Osseous changes to the insertion of the deep digital flexor tendon and distal sesamoidean impar ligament 

The deep digital flexor tendon and distal sesamoidean impar ligament insert on the fascia flexoria of the distal phalanx, in a smoothly outlined concavity. The compact bone at this site should be smooth and regular. 

Insertional injury of the deep digital flexor tendon, or less commonly, the distal sesamoidean impar ligament may result in irregular new bone formation or an ill-defined lucent area of the normally uniform opque bone. This is usually associated with lameness. 


Additional diagnostics: may provide additional information 

  • Transcuneal ultrasound
  • MRI 
  • Contrast enhanced CT 


Subluxation of the distal interphalangeal joint

Dorsopalmar subluxation:

  • Usually result of partial or cpmplete disruption of the deep digital flexor tendon.
  • It is best identified on a lateromedial projection. 
  • There is mild widening of the joint space and the middle phalanx is displaced in a palmar direction

Mediolateral subluxation:

  • Occurs as a result of disruption of the collateral ligament of the distal interphalangeal joint. 
  • This can be difficult to identify in radiographs obtained with the foot bearing weight evenly. "Stressed" dorsopalmar radiographs may reveal abnormal widening of the joint sapce. 
  • The prognosis is very guarded. 


Fractures of the distal phalanx

(common sites)

A facture classification has been proposed although not all fractures fit this moder:

  • Type 1: non-articualr fractures of the palmar or plantar process
  • Type 2: articular fractures that are not mid-sagittal and extend from the distal interphalangeal joint to the medial or lateral aspect of the solear margin
  • Type 3: articular mid-sagitall fracures of the distal phalanx
  • Type 4: extensor process fracture
  • Type 5: multifragments fractures
  • Type 6: non-articular fractures involving the solear margin, and extending from one point of the solear margin to another
  • Type 7: non-articular fractures of the palmar or plantar process of the distal phalanx in foals 


Chronic laminitis

Radiographic findings: 

  • The primary radiographic findings associated with laminitis include chnages to dorsal hoof wall and lamellar structures. 
  • Inflammation, streching, or separation of the lamellae, and separation of distal phalanx from the hoof wall resulting in rotation and/or shrinking of the distal phalanx. 
  • The hoof-distal phalanx distance may be increased 
    <20 mm
  • Increase in the ratio of hoof-distal phalanx distance: palmar length >27%
  • In a normal foot there is a raduiolucent "halo" between the distal phalanx and both the hoof wall and sole. This is the lamellae and sublamellar dermis. Narrowing of this halo or increase in its opacity may reflect abnrmal lamellar epidermis, with the fromation of a lamellar wedge of amorphous horn. 
  • Rotation of the distal phalanx reflex loss of dunction of the suspensory apparatus of the distal phalanx due to lamellar stretching and separation, with the toe moving distally and away from the hoof wall. This results in the dorsal wll of the hoof ceasing to be parallel to the dorsal wall of the distal phalanx. 
  • As the condition progresses, on very high-quality radiographs, a faint radiolucent lines may appear between the distal phalanx and sole or hoof wall. This initially represent serum collected between the dermal and epidermal laminae and is visible becuase of the slight difference between fluid and horn densities. Subsequently this radiolucent line may become more apparent indicting necrotic laminar tissue
  • The degree of rotation may be important in assesing prognosis. Generally the more marked the rotation and faster it progresses, the worse the prognosis. 
  • Infection of the laminar tissue may be a complication of laminitis. This may result in gas shadows, ecident as areas of increased radiolucency between the distal phalanx and hoof wall, or distal phalanx and sole.
  • "Sinker syndrome" is a very severe form of laminitis where the entire distal phalanx sinks within the hoof capsule. Measure the distance between the coronary band and the extensor process of the distal phalanx and can be compared between radiographs. 


  • Systemic treatment 
  • Corrective ferriery 



Venography and Laminitis 

In a normal horse the laetral and medial digital veins, capillaries and arteries are filled in a retrograde manner, permitting visualization of the termina arch, coronary plexus, sublamellar vessles, circumflex veins, and veins in the solear and terminal papillae. The contrast material stays within the vessels and the distal phalanx is proximal to the circumflex vein. 

In laminitis there may be alteration of the vasculature, notably compression of vessels in the coronary plexus, sublamellar plexus, terminal and solear papillae and the circumflex vein. There may be distribution of contrast material into abnormal soft tissues. Venography allows evaluation of the severity of vascular changes and can predict osseous pathology before it happerns. 


Long-toe low-heel complex

On a lateromdial projection of a normal foot, the center of the radius of curvature of the distal interphalangeal joint should be vertically above the center of the bearing surface of the foot. If the joint is over the palmar third of the bearing surface, this indicated poor dorsopalmar hoof balance which contirbute to lamenes. 

On the lateromedial projection, it is also important to evaluate the solar margin of the distal phalanx relative to the ground. If the palmar process of the distal phalanx are closer to the ground than the toe, this indicated extreme poor hoof balance and is usually associated with lameness. 

Palmarproximal-palmarodistal oblique views of the distal phalanx should be obtained in these cases, to look for abnormal radiolucent areas within the palmar process, irregularities of the margins of the plamar processes and for increased lucency around the palmar processes indicative of separation of the lamellae at the heel. 

NOTE: These horses are painful on the palmar/plantar surface as apposed to the dorsal surface (as seen with navicular disease syndrome). 


Navicular Bone Syndrome

These horses are usually painful on the dorsal surface and tend not be responsive to shoeing or rest. 

Radiographic findings:

Lateromedial projection: 

  • Enthesiophyte formation, and proximal or distal elongation of the plamar compact bone may develop
  • The palmar compact bone may become thicker distally than proximally. In some cases the distal fossa may become more prominent. 

Dorsoproximal/palmardistal oblique projection:

  • There can be changes associated with teh lucent zines of the distal broder of the navicular bone, representing synovial invagination. The greater the number of lucent areas the greater the clinical significance. 
  • If there is a lucent area at the medial or lateral angle of the distal border of the navicular bone, it is liekly there is an associated distal border fragment. Fragments may occur laterally or medially. 
  • In advanced stages of the disease there may be an appreciable increase in opacity of the bone, with or without thickening of the plamar compact bone and loss fo definition between the palmar compact bone and the spongiosa. This warrants a very poor prognosis for treatmeht, 


Endosteal reaction and enthesyophyte formation in the area of attachement of the suspensory ligament 

The suspensory ligament originates from the proximal palmar aspect of the metacarpal bone. Tearing of attachment may result in enthesophytes formation (periostitis), due to subperiosteal hematoma formation, or endosteal new bone formation. 

Radiographic examination may reveal a localized increased opacity in the proximal aspect of the bone with or without small patchy lucent zones. 


Syndesmopathy between the 2nd & 3rd & 4th metacarpal bone


A syndesmosis is a slightly movable articulation where the contiguous bone surfaces are united by an interosseous ligament, e.g. the articulations between the 2nd, 3rd, and 4th metacarpal bone.

Synostosis means fusion of two bones. Focal or diffuse ossification of the interosseous ligament results in synostosis. 

Syndemopathy refers to injury of the syndesmosis between the 2nd, 3rd, and 4th metacarpal (metatarsal) bones and alteration in adjacent cortical or trabecular architecture, with or without osseous spurs developing on the dorsal or palmar articular margins. 

When palpable new bone develops between the 2nd, 3rd, and 4th metacarpal bones secondary to damage to the interosseous ligament, it is known as "splint". 


Degenerative joint disease of the carpometacarpal joint 

Radiographic signs: 

  • Narrowing of the carpometacarpal joint space
  • Ill-defined lucent area of the distal aspect of the second carpal bone
  • Generalized increased opacity of the trabecullary bone (modelling) 
  • Irregular periosteal new bone with overlying soft tissue swelling 
  • Periarticular osteophytosis 


Physitis of the 3rd metacarpal bones

Radiographic signs: 

  • May result in enlargement of the bone and angular limb deformity of the metacarpophalangeal joint
  • The metaphysis of the bone is broadened and asymmetrical 
  • There is increased opacity of the metaphysis adjacent to the physis, which may be more irregular in appearance than normal, with narrow vertical radiolucent lines or conical areas representing retained cartilage cores
  • The cortices of the bone may be abnormally thickened 
  • The epiphysis may appear wedge shaped 



  • Correction of the deviation using radical trimming and or shoeing of the foot may be successful 
  • Surgical correction of the deviation may be necessary, it should be performed before 8 weeks of age, despite the "open radiographic" appearance of the physis 


Common Fracture sites of the metacarpal/metatarsal bones 


What are the 5 standard views of the equine carpus?

  1. Lateromedial
  2. Dorsopalamar
  3. Dorsal 45° lateral-palmomedial oblique
  4. Dorsal 45° medial-palmarolateral oblique views 
  5. Lateromedial flexed - helpful in separating the dorsodistal margin of the radial and inetrmediate carpal bones, where bone fragmentation and laetration in subchondral bone opacity frequently occur in racehorses.