MSK US Flashcards
Skin & subcutaneous tissue
- high freq* linear probe
- only need a shallow depth of penetration & high detail
- use B-mode & Colour Doppler
- watch yr probe pressure
- use a good layer of gel or a water bath (glove filled w water)
Abscess formation
- often starts w separation of fatty areas, like cellulitis
- maybe be hypoechoic but may not be
- will have increased vascularisation with time
- May swirl or appear to move in increased fluid, but not always if more solid contents
Benign masses US
- anechoic - true cyst is benign
- thin walled
- well defined
- wider than tall
- a vascular/minimally vascular
- hyperechoic non-shadowing
- does not cross tissue layers
Benign soft tissue masses
- well defined
- avascular
- variable echogenicity from hypo/hyper or mixed
- rare to be in muscle
Epithelial inclusion/sebaceous cyst
- sebaceous cells push into deeper layers
- typically not anechoic
- may have edge shadowing
- may be at varied depths
- Check: sinus, leaking and adjacent structures
Pilonidal cyst
- abscess
- sinus
- hair
- often hypoechoic compared to surrounding
- white evidence of hair within cyst
- can be quite large so ensure U define its entire extension under the skin
Malignant masses US
- cannot diagnose precisely from ultrasound alone
Suggestive if:
- large
- not from synovial space (bursa or tendon sheath)
- hyperechoic & hypervascular
- Ill-define & solid
- posterior shadowing
- invading tissue planes/destructive (very suspicious!!)
- thick walled
Vascular subcut* masses
Haemangiomas
Arteriovenous malformations
Bone shaft & Joints
- highest freq* probe possible
- excellent for joints, not so great for bone shafts (except for stress #s)
- scan in two planes: if u can’t see it in both planes, it’s not real
- use colour to ensure it’s not a nutrient channel
- lots of gel/stand off pad/bath
- move & stress joints: to get movement to move fluid/items to show things better
- be aware of heating: esp in smaller places (esp hands)
- talk to the Pt, esp when looking for stress #s, they’ll be quite tender & a Pt’s response shows if neurological Vs MSK
Normal adult bone Appearance
- echogenic
- linear
- reverberation artifacts: mirror images
- nutrient channels present: vessels going thru periosteum
Normal child bone Appearance
- echogenic
- linear
- reverb* artifacts
- periosteum
- Sharpeys fibres - thicker cortical bone layer (creates hypo echoic line on cortical surface.
Normal Adult joint appear*
- echogenic
- reverb* artifact
- articulate/hyaline cartilage: hypoechoic layer between joint capsule & bone
- joint capsule
Normal child joint Appear*
- echogenic
- growth plate/physis
- reverb* artifact
- articular/hyaline cartilage: thicker than Adults, still quite dark (not joint effusions, compare to collateral side!!)
Abnormal bone appearance
Fractures:
- stress #s in kids - bone bruising (bony bruising, wider sharpeys fibres, along the cortex)
- trauma
- pathological
Adult #s:
- step deformity & adjacent soft tissue inflammation/haematoma
Aged #s:
- loss of normal tissue planes & raised cortical surface with healing
Shoulders:
- # humeral head may be found, not just a torn tendon!
Pubic symphysis:
- erosive changes possible
- bowing out of the joint capsule indicates underlying changes
Pathological #s:
- normal cortical margin that gets lost
- adjacent soft tissue mass, normal tissue planes have been disrupted
- cloud like appearances around bone
- loss of smooth cortical surfaces
Exostosis:
- benign, bony outgrowth if cartilaginous tissue
- bursitis around bony outgrowth
Abnormal joint appearance
Traumatic:
- simple effusion: twisted knee
- complex effusion: rheumatoid/septic arthritis
- can be hypoechoic or echogenic region
Infective: septic Arthritis
Degenerative:
- erosions: deterioration in cortical surface, fluid & swelling around joint region
- osteophytes: loss of smoothness of bone surface, loss of volume of joint space,
Vascularity:
- bowing out of joint capsules
- colour: vasc*
- no colour: synovial hypertrophy
Cartilage:
- articular: hard cartilage, graded changes, 0-3 (often involves osteophyte formation: grades 0-3)
- fibrocartilage: spongy cart*, meniscus can protrude w trauma/degenerative changes (MRI better at detecting)
Normal tendon & sheath Appearance
- type 1 tendon: straight from muscle to bone
- type 2 tendon: crosses over a synovial joint
Type 1:
- peritenon
- paratenon
- epitenon- fills spaces between fascicles & contains collagen & elastic fibres
- endotenon
- fascicles
Type 2:
- synovial lining/bursa (internal & external linings)
- epitenon (fills space between fascicles & contains collagen & elastic fibres)
- endotenon
- fascicles
Elastography
- assess the elasticity of structures
- tendon should have a high elastic modulus or be ‘stiff’
- abnormal tendons become less stiff & less able to store & release energy.
Subluxation
Causes:
- acute
- chronic
- congenital laxity if fibrous hood
- congenitally shallow grove
Intermittent/reducible?
Permanent subluxation
Permanent dislocation
Assoc* abnormalities:
- associated inflammation & disruption of tissues
- cystic changes
- changes to cortical surface
Abnormal Tendon Sheath appearance
Type 1:
- hypoechoic, inflammation shown by increased vascularity
Type 2:
- thickening of the sheath around the tendon
- increased fluid & vascularity
Synovial Proliferation (Panus)
- rheumatological Dx; rheumatoid & psoriatic arthritis
- colour very useful esp if thickened synovium quite hypoechoic
- probe pressure & dynamic assessment also essential to increase sensitivity
Infective synovial fluid
- US not 100% sensitivity to detecting this
- tends to be more echogenic with synovial thickening & increased vascularity BUT cannot be sure based solely on US
Abnormal tendon appearance: grades
Grade 1:
- no fibre disruption
- often hypoechoic
- excessive activity may appear as diffuse hyper echogenicity
- let the Pt’s symptoms guide U
- use colour/power Doppler
Grade 2:
- partial tear, moderate disruption
- often at myotendinous junction but direct trauma may result in muscle body tear
- can be difficult to define edges, so use movement
- can be massive
Grade 3:
- complete disruption
- define size
- distance from attachment
- use movement
Enthesis - normal appearance
- change in orientation in fibres & results in thin black line where tendons joint the bone
- manual labour/exercise => double the thickness
Can be mistaken for a tear, but it’s the enthesis:
- change position or change Pt’s position to test
Enthesis - abnormal appearances
- irregularity
- subchondral cysts
- calcific stripes
- osteophytes
- failure
- bursa/fat pad
- seronegative arthropathy (rheumatoid issues)
Muscle injuries: extrinsic Vs intrinsic
Extrinsic:
- external trauma; contusion or laceration (thigh & the vastus intermedius is against the femur)
Intrinsic:
- often exercise induced; disruption of the muscle fibres
- usually near a myotendonus junction
Pathobiology if muscle injury
1- distructive phase: 0-3 days
2- early remodelling: 3-12 days
3- late remodelling: >12 days
Grades muscle strain injuries
Grade 0 - normal
Grade 1 - tear affecting small No of muscle fibres w an intact fascia (elongation injury; flame shaped hypoechoic defects one cm or longer in muscle belly)
Grade 2 - mod tear w fascia remaining intact (partial rupture; more than 5% muscle but less than full diameter of muscle)
Grade 3 - tear of many fibres w partial tearing of the fascia
Grade 4 - complete tear of the muscle & fascia (complete rupture; muscle totally torn, the muscle stump floats in fluid ‘clapper in the bell sign’)
Complications of muscle tears
- cysts
- myositis ossificans
- calcific myonecrosis (rare)
Myositis ossificans (MO)
- ongoing symptoms/failure to improve 2wks post injury
- intense inflammatory reaction around tear site; hypervascularity and oedema
- usually anterior muscles of thigh or arm
- comorbid conditions can increase risks
- CAN look like aggressive tumour like growths!
Scanning techniques of muscle imaging
Look for;
- haematoma
- inflammatory reaction
- regeneration & scar
- denervation change & MO!!
Inflamm* & ischaemia cond*
- idiopathic inflammatory myopathies
- pyomyositis & hydatid Dx
- diabetic muscle infarction & rhabdomyolysis
Acute compartment syndrome US
- increased pressure within the muscle compartment
- single insult; trauma or exercise overload
- increasing pain w movement
- pain can be delayed up to 12 hrs post exercise
- most often anterior, posterior & lateral lower leg compartments
- increased compartment size
- sometimes bowing or fascia
Rhabdomyolysis
- skeletal muscle necrosis
- accompanied by an acute rise in enzymes
- often involves gluteal muscles
- IVDU & statins users
- hard to diagnose
Diabetic myonecrosis
- usually lower limbs or pelvis
- usually poorly controlled diabetic pts
