Page 241 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 207

The normal subchondral bone surfaces should align significant, particularly when mild and/or when seen on
evenly. Positional changes of the horse or of the X‐ray low‐motion joints. Marginal bone lysis can be found on
VetBooks.ir joint appear slightly malaligned. and is also a hallmark finding for septic arthritis
joint margins in joints affected with more advanced OA
tube when the radiograph is made may make a normal
(Figure 3.29). In early stages, marginal changes may be
Radiographic Changes Associated with Joint Disease subtle, but with advanced or more severe disease, the
changes are easily identified.
Radiographs are a first‐line screening tool for assess­ Subchondral bone changes include sclerosis, lysis,
ing joint disease. The radiographic manifestations of and fragmentation (Figure 3.30). Subchondral bone
joint disease occur in the soft tissue and bone structures sclerosis is often found as an adaptive response to exer­
and may develop before or after clinical signs of the dis­ cise; however, with increasing sclerosis, the sclerosis
ease develop, depending on the type and severity of dis­ changes from adaptive to maladaptive and can be asso­
ease. Bone changes follow clinical signs in septic arthritis, ciated with degenerative disease and increased risk of
whereas bony changes may either precede or follow subchondral necrosis and fracture. 12,28,39,43 Subchondral
clinical evidence of disease with OA. bone lysis can have a local or general distribution within
Soft tissue changes associated with joint disease may the joint and may be seen in association with subchon­
be radiographically evident prior to bone change, dral bone fragments. Subchondral bone lysis may be
although this is somewhat joint dependent. Common present with septic arthritis, OA, and osteochondrosis,
soft tissue abnormalities include periarticular soft tissue as well as secondary to trauma. While lysis is a defining
thickening, joint distension due to effusion and/or syno­ characteristic of septic arthritis, subchondral bone lysis
vitis, and mineralization. The location of fat pads and is also seen with OA, particularly in low‐motion joints.
adipose tissue in fascial planes can be used to evaluate OA of low‐motion joints, particularly the distal tarsus
periarticular swelling and joint capsule distension. Joint and carpometacarpal joints, can present with extensive
distension is more readily identified in some joints than subchondral lysis, and it is important to differentiate
others; for example, effusion of the fetlock joint is typi­ this from a septic process. Localized, well‐defined lytic
cally obvious, whereas distension of the medial or lateral
femoral tibial joints is challenging to detect radiographi­
cally. Periarticular mineralization may be associated with
numerous causes but in the horse is predominantly dys­
trophic or secondary to blunt soft tissue trauma.
Periarticular osteophyte formation is the most com­
mon change found on the joint margin in the OA pro­
cess (Figure 3.28). Not all osteophytes are clinically

Figure 3.29. Lateromedial (LM) projection of the distal limb
showing radiographic changes consistent with advanced, severe
septic arthritis. Note the severe irregular subchondral bone lysis on
the adjacent articular surfaces of the distal interphalangeal (DIP)
joint with marked articular cartilage loss, circumferential irregular
Figure 3.28. Lateromedial projection of the carpus. Moderate periosteal proliferation, and the severe soft tissue thickening with
periarticular osteophytosis is present at the middle carpal and the irregular skin surface centered over the dorsal aspect of the DIP
carpometacarpal joints with mild sclerosis of the cuboidal bones joint. In addition, there is a coarse trabecular pattern on P1
involved. consistent with disuse osteopenia.