Ultrasonographic Anatomy of the Equine Distal Limb

Lisa J. Zekas, DVM, DABVP –Eq, DACVRand Chess Adams, DVM, DACVR

Objectives

Brief introduction to ultrasound and the imaging procedure.

Be able to identify a transverse and a longitudinalimage.

Be able to apply the anatomy of the distal equine extremity to ultrasound images and identify structures.

Brief Introduction to Ultrasound

• Transducer produces sound waves and also receives reflected sound waves.

• Sound waves travel in a plane through tissue.• Sound waves are transmitted, absorbed or reflected by

tissues.• Computer forms image – in shades of gray.

From: Zagzebski, JA; Essentials of Ultrasound Physics, Mosby, © 1996

MusculoskeletalPalmar distal extremity

ReproductionUterine cysts

AbdomenLiver - cholelithiasis

Infected umbilicusEchocardiographyPericardial effusion

ThoraxPleuropneumonia

Patient Preparation

Clip the areaClean areaCoupling medium

alcoholcommercial gel

Imaging technique

Systematic organized approach – must be familiar with normal

Scan from proximal to distalEvaluate structures individuallyTransducer perpendicular to structureLimb should be weight bearing

Imaging TechniquesLabel images - patient info, directions and

locationTwo methods for location1. Zones2. Reference points

- cm distal to standard pointaccessory carpal bonepoint of hockpoint of ergot

i.e. 5 cm DACB

Ultrasonographic evaluation of structuresSize

• cross sectional area (cm2)• dorsal-palmar thickness

• medial-lateral width• proximal-distal length

From: Reef VB. Equine Diagnostic Ultrasound. WB Saunders, Philadelphia, PA. 1998

Ultrasonographic evaluation of structures

Echogenicity - Appearance using shades of gray-within structure itself-compared to other structures-compared to normal

anechoichypoechoichyperechoicisoechoic

Ultrasonographic evaluation of structures

Parallel fiber pattern (tendons and ligaments)

Transverse imagesPalmar (skin surface)

Dorsal

LateralMedial

Longitudinal imagePalmar (skin surface)

Dorsal

Proximal Distal

Imaging Techniques As in radiography – it is best when pathology can

be seen in both planes -(artifactual “lesions” can be created)

Longitudinal Transverse

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

Transverse

Longitudinal

Proximal metacarpal region

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

SDFTDDFT

ALDDFT (or ICL)

TIOM (or SL)Palmar surface of MCIII

SDFT

DDFT

ALDDFT (or ICL)

TIOM (or SL)Palmar surface of MCIII

Proximal

Dorsal

Medial

ForelimbHindlimb

Relation of SDFT to DDFT in proximal region

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

Transverse

Longitudinal

Mid 1/3 of metacarpal area

SDFTDDFT

ALDDFT (or ICL)

TIOM (or SL)Palmar margin of MCIII is indistinct

SDFTDDFT

ALDDFT (or ICL) – note how it thins and angles to join with the DDFT distally*.

*DISTAL

Dorsal

TIOM (or SL)

Palmar surface of MCIII

SDFTDDFTALDDFT joining into DDFT

SL splitting into branches - so no longer on midline

SDFTDDFT

ALDDFT

SL splitting into branches

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

Transverse Longitudinal

Transverse Longitudinal

SDFT

DDFT

Branch of Suspensory Ligament

SDFT

DDFT

MCIII

Suspensory Branches: imaged obliquely from medial and lateral sides

Transverse

LongitudinalLongitudinal at insertion on prox. sesamoid bone

Abaxial border oflat prox sesamoid bone

Longitudinal view of lateral suspensory branch

Lateral suspensory branch

Lateral suspensory branch

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

Transverse Longitudinal

SDFTDDFT

Margin of sesamoid bone

SDFTDDFT

Margin of sesamoid bone

Intersesamoidean ligament

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

Palmar Annular LigamentUsually difficult to identify unless thickened

Superfical Digital Flexor Tendinitis

Deep Digital Flexor Tendonitis

Suspensory ligament body desmitis

Normal (for comparison) Affected limb

Suspensory branch desmitis

Distal extremity Imaging

• Always image in two planestransverse and longitudinal

• Image from palmar / plantar aspect• Try to keep orientation consistent – label

images

Summary: ObjectivesBe able to identify a transverse and a longitudinalimage.

Be able to apply the anatomy of the distal equine extremity to ultrasound images and identify structures.

Questions?

Ultrasonographic Anatomy

From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998

Transverse: slightly off to lateral margin

Midpastern

PROXIMAL

DORSAL

LATERAL

Longitudinal

Effusion in tendon sheath

DDFT

Straight or superficial sesamoidean ligament

DDFTLateral branch of SDFTStraight or superficial sesamoidean ligament

Oblique or middle sesamoideanligament – (lateral aspect)

Palmar aspect P1

Palmar aspect of P1

PROXIMAL