Page 331 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

306 CHAPTER 1

VetBooks.ir Fibre alignment score (FAS) Healing and chronic injuries
With time, the echogenicity of the lesion tends
Fibre alignment is a major factor when assessing the
severity of the injury (i.e. loss of the normal colla-
water content and diffuse cellular infiltrate and
gen fibre alignment). Ultrasonography provides a to increase because of decreased oedema, matrix
fair estimate of this criterion (Figs. 1.588–1.590), increased collagen deposition. Scar tissue is iso- to
echoes being generated by sufficiently long and thick hyperechogenic to normal tendon tissue but lacks
fibres. Non-aligned fibres (e.g. in immature or poor- a normal longitudinal fibrillar pattern on long-axis
quality scar tissue) may not be distinguishable from scans. Immature and early fibrous scar tissue is
total lack of fibres (i.e. in haematomas or early gran- fairly homogeneous and still fairly hypoechogenic
ulation tissue). Nevertheless, combining cross-sec- as small vessels and poorly arranged collagen fibres
tional and longitudinal views helps to differentiate accumulate in a diffuse pattern (Fig. 1.591). More
scar tissue from a recent tear. Quantifying align- mature scar tissue contains larger fibre bundles in a
ment is difficult but a semi-subjective grading from poorly organised pattern that creates a more brightly
0 to 3 has been proposed: FAS = 0 (normal) if fibres echogenic but heterogeneous pattern (Fig. 1.592).
normally aligned; FAS = 1 (mild injury) with slight Then, as scar tissue matures and remodels, the
loss of fibre pattern; FAS = 2 (moderate) with moder- fibre bundles rearrange into a more organised
ate loss of striation; FAS = 3 with marked loss of fibre linear pattern, yet never restoring the normal struc-
alignment (little to no striation). ture. Healed tendon injuries present as coarse,

1.588 1.589

1.590

Figs. 1.588–1.590 Fibre alignment score is
assessed on longitudinal sonograms and may be used
both at the acute/subacute stage or for follow-up.
(1.588) Grade 1 lesion with persistence of more than
half the fibres in the lesion; (1.589) grade 2 lesion with
marked loss of fibre; (1.590) grade 3 lesion with near
total loss of fibre (acute lesion filled by an echogenic
haematoma).