Page 320 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.8 Soft-tissue injuries 295

VetBooks.ir ways to determine the level of the image planes to bones [zones IIIA and IIIB]; an additional zone
IIIC corresponds to the area palmar to the sesa-
standardise the procedure and allow for later com-
parisons. Some operators prefer to measure the dis-
tance in centimetres from the distal border of the moid bones).
In the hindlimb, the same system may be used
accessory carpal bone/point of the calcaneus. The from the tarsometatarsal joint to the ergot, but
limitation of this system, however, is that the meta- many operators include the plantar hock area and
carpal length will vary depending on the animal’s thus divide the area from the tuber calcanei to the
size and conformation. It is therefore only possible ergot into nine zones, with zones IA and IB span-
to compare images from the same animal. A more ning the plantar aspect of the hock, the metatarsus
generally accepted standard is to divide the meta- being divided into zones IIA to IVB and the fetlock
carpal region from the carpometacarpal joint to the area being referred to as IVC. The palmar or plantar
ergot into seven equal areas (Fig. 1.556) (i.e. six pastern area is divided into three equal zones (PI to
equal zones between the carpometacarpal joint and PIII) from the ergot to the deepest part of the pas-
the proximal border of the fetlock palmar annular tern notch (above the heels).
ligament: zone I corresponds to the proximal third The limb is first assessed from the palmar aspect
of the metacarpus and is further divided into zones in transverse planes, then in longitudinal sections
IA at the level of the carpometacarpal joint and IB; (using both sagittal and parasagittal planes). The
zone II is the middle third of the metacarpus [zones whole area should be assessed, including the SL.
IIA and IIB]; and zone III is the distal third of the This is evaluated from the palmar aspect to the
metacarpus, to the proximal edge of the sesamoid middle of the metacarpus or metatarsus, and then
each branch of the SL is assessed abaxially from its
corresponding side (lateral for the lateral branch,
1.556 etc.) in both transverse and longitudinal planes.
The origin of the SL in the hindlimb can be chal-
A lenging to assess, the head of the fourth metatarsal
I bone curving slightly plantarly and partly obscur-
B
ing the lateral head of the interosseous muscle.
Adequate imaging may be achieved by placing the
A
II probe slightly plantaromedial to the limb in zone
B II. This may be more easily achieved using a curved
array transducer from a plantaromedial approach.
A Lowering the frequency will help to assess the SL
III and care should be taken to optimise the image gain
B and focal point positions depending on the depth of
the tissues evaluated.
IIIC Normal tendon tissue is homogeneously granu-
lar on cross-sectional images (Fig. 1.557), echoes
being induced by interfaces in the regularly
arranged fibre bundles. Endotenon (connective
tissue surrounding the fibres and containing very
small diameter vessels) is not normally distin-
guished but participates in the hypoechogenic areas
surrounding fibre bundles. There is some variation
between tendons, the SDFT being less echogenic
Fig. 1.556 Definition of zones I to III and than the deep digital flexor tendon (DDFT) and
subdivision into zones A and B for each area of the the SL being more heterogeneous. On longitudinal
palmar metacarpus. (long-axis) images (Figs. 1.558, 1.559), obtained