Equine Distal Limb Ultrasound PDF

Basics of Equine distal limb ultrasound M. Larson VM 8824- Moving February 20, 2023 Objectives Describe basic techniques of tendon ultrasound Be able to apply the anatomy of the metacarpal/metatarsal flexor tendons to ultrasound images and appropriately identify structures Identify tendons in both l...

Basics of Equine distal limb ultrasound M. Larson VM 8824- Moving February 20, 2023 Objectives Describe basic techniques of tendon ultrasound Be able to apply the anatomy of the metacarpal/metatarsal flexor tendons to ultrasound images and appropriately identify structures Identify tendons in both longitudinal and transverse images Why do we use ultrasound? Injury to flexor tendons are common Radiographs unable to visualize tendons well US is relatively inexpensive and readily available to equine practitioners Standards for normal size, shape and appearance of tendons have been established Quick review of ultrasound Transmitted sound pulse from the transduser Reflected sound back to the transducer Image made of multiple scan lines of gray scale dots placed side by side to form a 2 dimensional image gall bladder B-mode image Brightness/darkness depends on how reflective the object is tendon Quick review of ultrasound basics Frequency of the sound wave > poorer - penetration deeper penetration HIGHER frequency  BETTER resolution Lendons ; 10-18 meganurts) LOWER frequency  DECREASED resolution (2 -3 mH) The higher the frequency, the poorer the penetration A 12 MHz (high frequency) transducer has higher resolution, but cannot penetrate deep into the body Superficial structures are seen with greater clarity (better resolution) A 5 MHz (lower frequency) transducer has lower resolution, but can penetrate deeper into the body More of the body can be seen, but at the cost of decreased clarity (resolution) 5-18 MH7 in dogs/cats ↑ resolution , a penetration spleen ↓ resolution , a penetration Ultrasound Terminology hyper (bright) hypo (darker) Echogenicity , (so (same) Appearance using shades of gray Anechoic/hypoechoic Dark Isoechoic Similar shade of gray as an adjacent structure Hyperechoic Bright Ultrasound exam preparation Air completely reflects the sound wave! Hair clipping No. 40 blade Clean skin with warm water or isopropyl alcohol after clipping Apply ultrasound gel ↓ gives nice interface Ultrasound equipment Ultrasound machine High frequency linear transducer creates an anechoic Standoff pad face Can help with d visualizing superficial structures > - Without Standoff Pad With Standoff Pad Imaging technique Systematic approach MUST KNOW NORMAL ANATOMY Evaluate structures individually Scan from proximal to distal Scan in both planes (transverse and longitudinal) Limb should be weight-bearing Anatomy Palmar to dorsal direction From carpus to mid MCIII Skin Superficial digital flexor (SD) Deep digital flexor (DD) Check ligament (IC); joins DD at midpoint of metacarpus Suspensory ligament (SL); branches in distal third of metacarpus Third metacarpal bone (MC3) Anatomy Palmar to dorsal direction Mid MCIII to sesamoid bones Skin Superficial digital flexor (SD) Deep digital flexor (DD) Suspensory ligament (SL) Third metacarpal bone (MC3) Imaging technique Label images properly Patient info RF, LF, RH, LH Location Two methods for location of image Zones Reference points cm distal to a standard point Accessory carpal bone Point of hock ie. 5 cm DACB (distal to the accessory carpal bone) Forelimb Zones Begin at proximal metacarpus 3 zones (7 levels) 1 A/1B 2A/2B 3A/3B/3C Each zone is ~ 4 cm wide Hindlimb Zones More zones in hindlimb due to increased length 4 zones (9 levels) 1A/1B 2A/2B 3A/3B 4A/4B/4C distal prox cranial Lateral medial toward right patient's side scan Sonographic evaluationLongitudinal plane (long axis) As viewed on screen prox distal What your hand is actually doing… distal Parallel fiber pattern of ligaments/tendons prox to Palmar Prox Dist Prox Dorsal Palmar Dorsal Dist On Screen Reality Transverse plane (short axis) Palmar (skin surface) Lateral Medial Dorsal Sonographic evaluation of structures Cross sectional area (normals are published for each tendon and location) Echogenity acute lesions (hypo) Fiber pattern · Imaging techniques acute hemorrhage edema Look for pathology in both planes Otherwise, suspected lesion could be due to an artifact Transverse Longitudinal , Sonographic anatomy SD DD SDE DDF la MIL interior check St MC3 From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998 MA IC St M63 Sonographic anatomy SD DD I Su SD DD From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998 I St SDFT DDFT Medial ICL SL Palmar surface of MCIII SDFT DDFT Proximal ICL SL Palmar surface of MCIII Dorsal SDFT DDFT ICL SL Palmar margin of MCIII is indistinct SDFT DDFT * DISTAL ICL – note how it thins and angles to join with the DDFT distally*. SL Palmar surface of MCIII Dorsal SDFT DDFT ICL SL splitting into branches SDFT DDFT ICL joining into DDFT SL splitting into branches – so… no longer on midline Sonographic anatomy SP DD MC3 From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998 SDFT DDFT Branch of Suspensory Ligament MCIII SDFT DDFT Sonographic anatomy SFT DDFT MPSB ISL From: Rantanen NW, McKinnon AO. Equine Diagnostic Ultrasonography Williams and Wilkins Philadelphia, 1998 LPSB SDFT DDFT Intersesamoidean ligament Margin of sesamoid bone Palmar annular ligament Tendon abnormalities on ultrasound Increased cross sectional area Regions of decreased echogenicity (disruption of fibers, hemorrhage, edema) Corresponding region of fiber pattern abnormality Which tendon is affected? SDE DDF Check suspensory Superficial digital flexor tendon! --- - - check - check --- - - - Inferior Check ligament D Anatomy Review -... - - - - --- SDFT DDFT IC SL Longitudinal or transverse? - - - - Transverse Longitudinal Goals Describe basic techniques of tendon ultrasound Be able to apply the anatomy of the metacarpal/metatarsal flexor tendons to ultrasound images and appropriately identify structures Identify tendons in both longitudinal and transverse images