knee normal
the technique below demonstrates how to identify normal anatomy. remember to assess all 2022年世界杯预选赛规则图解 anatomy dynamically and thoroughly.
divide the knee into 4 compartments.
- anterior
- medial
- lateral
- posterior
anterior knee
the primary structures to examine anteriorly are:
the quadricep muscles and tendon.
comprised of:
- rectus femoris (central and most superficial)
- vastus medialis (medial)
- vastus lateralis (lateral)
- vastus intermedius (deep to rectus femoris)
the tendons of these 4 muscles insert to the patella forming the quadricep tendon. the main central band of which is comprised of rectus femoris and vastus intermedius.
there is also a fascial insertion to the medial and lateral patello-femoral retinaculae (advanced technique)
the suprapatella recess (also called the suprapatellar bursa)
- this is a pouch-like extension of the joint capsule extending superiorly from under the patella base to lie in the fat pad deep to the quadricep tendon.
the pre-patella bursa
- lies anterior to the apex (inferior) patella, overlying the patella tendon.
patella tendon (also called patella ligament and infrapatella tendon)
- runs in the midline from the apex of the patella to the tibial tuberosity.
- is a continuation of the quadricep tendon.
hoffa's fat pad (infrapatella fat pad)
a large trapezoid fat pad that lies deep to the patella tendon.
to scan the anterior knee:
patient should be positioned either:
- supine with their knee slightly flexed. (support may be required)
or
- seated on the side of the bed, their foot on your knee.
tip: the second position allows for controlled dynamic assessment better than when supine.
to examine the anterior knee:
longitudinal
- palpate the base (superior aspect) of the patella
- place the probe in a longitudinal plane over the patella base.
- slide medially and laterally to examine the width of the anatomy.
visualise the quadricep tendon, underlying fat pad, suprapatella joint recess and the femur.
transverse
- place the probe in a transverse plane at the patella
- slide superiorly to the distal 1 third of the thigh.
visualise the quadricep muscle bellies and musculo-tendinous junctions. also the underlying fat pad, suprapatella joint recess and the femur.
tip: if the patient can activate their quadriceps (pull knee flatter), a joint effusion may be more evident.
normal ultrasound appearance of the anterior knee:
quadricep tendon and suprapatellar recess
transverse:
- as seen in the image below, the quadricep muscles should be clearly visible as independent structures. rectus femoris the most superficial, midline and ovoid. each should be hypoechoic with interspersed echogenic lines.
- closer to the patella, the quadricep tendon should be an echogenic flat oval with a hypoechoic underlying fat pad.
- no fluid, or only a thin trace should be visible in the normal patient.
longitudinal:
- the quadricep tendon should be echogenic, fibrillar and tight (if there is any knee flexion). it should taper towards the patella.
infrapatella tendon
- longitudinal: echogenic, homogeneous and fibrillar.
- transverse: specular and echogenic. approximately 3cm wide
hoffa's fat pad
- hypoechoic.
- slightly heterogeneous.
- low/no vascularity on colour doppler.
- is it the quadricep tendon intact?
- is there any bony irregularity of the patella or femur?
- is there fluid in the suprapatella recess? if yes, simple or complex?
- is there synovial thickening +/- vascularity of the suprapatella recess?
- is the patella tendon intact, homogeneous, avascular (it should be)? is it tight with 45degrees flexion?
- is hoffa's fat pad normal?
transverse scan plane for the quadriceps
transverse suprapatella region:
•rf: rectus femoris •vi: vastus intermedius
•vl: vastus lateralis •vm: vastus medialis
suprapatella scan plane.
longitudinal suprapatella region showing the suprapatella bursa and quadriceps tendon.
prepatella scan plane
to avoid loss of contact, use plenty of thick gel or a standoff.
infrapatella scan plane.
the infrapatella tendon.
also called the patella ligament.
the insertion of the infrapatella tendon onto the tibial tuberosity. note: the normal physiological amount of fluid along the underside of the tendon.
transverse infrapatella tendon. note how wide it is, to then have an understanding of the area you need to examine in longitudinal.
medial knee
medial collateral ligament (mcl) – joint space/meniscus – pes anserinus.
the primary structures to examine medially are:
medial collateral ligament (mcl).
- runs from the medial femoral epicondyle to the metaphyseal aspect of the antero-medial tibia.
- 2 bands: deep layer inserts to the meniscus. superficial layer to the tibia.
- may be a small bursa between them at the joint.
medial joint space and meniscus
- only the superficial meniscal surface is visible.
pes anserine tendon and bursa
- common distal insertion of sartorius, gracilis and semitendinosis muscles. (tip: remember the tendons as sargent -sgt)
- the pes tendons cross over the medial collateral ligament just before it's insertion.
- there is the pes anserine bursa deep to the pes insertion.
to scan the anterior knee:
patient should be positioned either:
- supine with their knee slightly flexed and externally rotated (support may be required)
- seated on the side of the bed, their foot on your knee.
tip: the second position allows for controlled dynamic assessment better than when supine.
to examine the medial knee:
longitudinal
- palpate the medial femoral epicondyle.
- place the middle of the probe in a longitudinal plane on the epicondyle. (heel of the probe directed towards the medial malleolus)
- the mcl origin should be in the centre of your image.
- slide the probe distally, following the mcl to it's insertion. (enroute, assess the joint/meniscus).
- at the distal mcl insertion, rotate the probe in the direction of the medial hamstring tendons (semi-tendinosis) to visualise the pes anserinus tendon, bursa and insertion.
normal ultrasound appearance of the anterior knee:
quadricep tendon and suprapatellar recess
transverse:
- as seen in the image below, the quadricep muscles should be clearly visible as independent structures. rectus femoris the most superficial, midline and ovoid. each should be hypoechoic with interspersed echogenic lines.
- closer to the patella, the quadricep tendon should be an echogenic flat oval with a hypoechoic underlying fat pad.
- no fluid, or only a thin trace should be visible in the normal patient.
longitudinal:
- the quadricep tendon should be echogenic, fibrillar and tight (if there is any knee flexion). it should taper towards the patella.
infrapatella tendon
- longitudinal: echogenic, homogeneous and fibrillar.
- transverse: specular and echogenic. approximately 3cm wide
hoffa's fat pad
- hypoechoic.
- slightly heterogeneous.
- low/no vascularity on colour doppler.
- is it the mcl intact?
- is the mcl origin thickened, hypoechoic or hyperaemic?
- is there any bony irregularity of the medial joint.
- is the meniscus bulging, irregular or have any cysts?
- is the pes anserine tendon intact and fibrillar.
- is there fluid in the pes anserine bursa?
medial knee joint scan plane.
the medial collateral ligament (green) directly overlying the medial meniscus (purple).
pes anserinus scan plane.
the pes anserine bursa and tendon insertion are medial to the infrapatella tendon on the tibia, adjacent to the mcl insertion.
remember the pes anserine tendons as (sargent) sgt:
sartorius, gracilis and semi-tendinosis.
lateral knee
the primary structures to examine laterally are:
lateral collateral ligament (lcl).
- runs from the lateral femoral epicondyle to the head of the fibula.
lateral joint space and meniscus
- only the superficial meniscal surface is visible.
ilio-tibial band (itb)
- passes over the lateral femoral eipcondyle.
- inserts to the lateral aspect of the tibia.
- most superficial structure beneath the subcutaneous fat.
biceps femoris tendon
- the lateral hamstring.
- inserts to the fibula (with slips to the tibia and fascia.
popliteus
- lies deep to the lcl.
- runs transversely from the posterior tibia to the lateral femur with some fibres to the meniscus.
to scan the lateral knee:
patient should be positioned either:
- supine with their knee slightly flexed.
or
- seated on the side of the bed, their foot on your knee.
tip: the second position allows for controlled dynamic assessment better than when supine.
to examine the lateral knee:
- palpate the lateral femoral epicondyle.
- place the middle of the probe in a longitudinal plane on the epicondyle. (heel of the probe directed towards the medial malleolus)
- the lcl origin should be in the centre of your image.
- slide the probe distally, following the lcl to it's insertion on the fibula. (enroute, assess the joint/meniscus).
- at the distal lcl insertion, rotate the probe in the direction of the lateral hamstring tendon (bicep femoris) to visualise the insertion.
- return to the joint and assess the itb insertion.
- follow the itb proximally to the distal thigh.
tip: the lcl is best assessed with minimal knee flexion, sometimes with the knee fully extended.
normal ultrasound appearance of the lateral knee:
lateral collateral ligament (lcl)
- separated from the meniscus by a thin layer of fat/connective tissue. underlying fat pad.
- echogenic fibrillar architecture (the entire length is rarely seen in one plane)
ilio-tibial band
- very thin, broad fascia at the level of the femoral epicondyle.
- echogenic wide footprint at the tibial insertion.
popliteus
- oval tendon similar in appearance to the bicep in the shoulder.
- lies deep to the lcl on the femur.
biceps femoris
- echogenic fibrillar tendon.
- inserting just posterior to the lcl
- is it the lcl intact?
- is there any bony irregularity of the lateral joint.
- is the meniscus bulging, irregular or have any cysts?
- is the biceps femoris tendon intact and fibrillar.
- is there fluid around the popliteus tendon?
lateral knee joint scan plane.
assess the lateral collateral ligament, ilio-tibial band insertion and peripheral margins of the lateral meniscus. unlike the medial side, the lcl is separated from the meniscus by a thin tissue plane.
ilio-tibial band.
rotate the probe off the lcl, with the toe of the probe angled slightly posteriorly.
posterior knee
the primary structures to examine posteriorly are:
semimembranosus gastrocnemial bursa (baker's cyst).
- medial popliteal fossa
- between the head of the medial gastrocnemius muscle and the sembranosus tendon.
- usually descends the calf but may ascend.
popliteal artery and vein
- there are also several muscular vessels joining/arising from the deep vessels in the popliteal fossa
nerves
- sciatic nerve branches into the common fibular nerve and the tibial nerve approximately 5cm above the knee crease
hamstring tendons
- the lateral hamstring.
- semitendinosus and semimembranosus medially.
- biceps femoris laterally.
to scan the posterior knee:
patient should be positioned either:
- prone.
- place a support under the patient's ankle(s)
or
- seated on the side of the bed, their foot on your knee.
tip: the second position allows for controlled dynamic assessment better than when prone.
to examine the posterior knee:
- place the probe transversely across the knee crease.
- slide proximally and distally observing the neurovascular bundle.
- check the compressibility of the popliteal vein
- use colour doppler to confirm patency.
- slide medially looking for a baker's cyst.
normal ultrasound appearance of the posterior knee:
lateral collateral ligament (lcl)
- fibrillar architecture.
- less echogenic than the mcl.
- may have a slight dip distally as the biceps femoris tendon crosses.
popliteal vessels
- veins should be entirely compressible.
- uniform diameter popliteal artery, (no aneurysm).
- flow seen in both artery/vein on colour doppler
medial popliteal fossa
- if a baker's cyst is present, is it simple/complex?
posterior joint
- is there fluid in the intercondylar notch?
biceps femoris tendon
- echogenic fibrillar tendon.
- inserting just posterior to the lcl
- are the hamstring tendons intact and fibrillar.
- is there fluid around the popliteus tendon?
- any popa aneurysm?
- is there any thrombosis.
- any baker's cyst?
- any neuroma?
popliteal fossa scan plane
medial aspect of the popliteal fossa showing the semimembranosus/gastrocnemius plane.
ultrasound of the popliteal vein and artery in transverse.
without and with compression to exclude dvt.
confirm both arterial and venous flow and exclude a popliteal artery aneurysm. if a popliteal aneurysm is discovered, always extend the examination to the other leg and the abdomen. there is a risk of bilateral and high association with aortic aneurysm.
scan protocol
role of ultrasound
ultrasound is essentially used for the external structures of the knee. ultrasound is a valuable diagnostic tool in assessing the following indications; muscular, tendinous and ligamentous damage (chronic and acute) bursitis joint effusion popliteal vascular pathology haematomas masses such as baker’s cysts, lipomas classification of a mass eg solid, cystic, mixed post surgical complications eg abscess, oedema guidance of injection, aspiration or biopsy relationship of normal anatomy and pathology to each other. some bony pathology
limitations
it is recognised that ultrasound offers little or no diagnostic information for internal structures such as the cruciate ligaments. ultrasound is complementary with other modalities, including plain x-ray, ct, mri and arthroscopy.
patient preparation
- none required.
equipment setup
use of a high resolution probe (7-15mhz) is essential when assessing the superficial structures of the knee. careful scanning technique to avoid anisotropy (and possible misdiagnosis). beam steering or compounding can help to overcome anisotropy in linear structures such as tendons. good colour / power / doppler capabilities when assessing vessels or vascularity of a structure. be prepared to change frequency output of probe (or probes) to adequately assess both superficial and deeper structures.
common pathology
- joint effusion
- bakers cyst
- collateral ligament injury
- patella tendinopathy
- meniscal bulging/cysts
- quadriceps injury
- pes anserine bursitis/tendinopathy
- patella retinaculum pathology
scanning technique
posterior fossa
patient prone on bed, knee flexed slightly with a pad under the ankle for support. survey the entire fossa to identify the normal anatomy, including; popliteal artery and vein (patency. aneurysm, thrombosis) posterior joint (joint effusion) medial popliteal fossa bursa between semi-membranosus tendon and medial gastrocnemius muscle] (baker’s cyst) document the normal anatomy and any pathology found, including measurements and vascularity if indicated.
anterior knee
patient lies supine on bed with knee flexed 20 – 30 degrees. alternatively patient may sit on the side of a raised bed with foot resting on sonographer’s knee for support. identify the normal anatomy, including: quadriceps tendon (tears, m/t junction, tendonitis) suprapatella bursa (bursitis-simple/complex, synovial thickening, loose bodies) patella (gross changes eg erosion, bipartite, fracture) patella tendon (tears, tendonitis, insertion enthesopathy) infrapatella bursa (tendonosis, tears, bursitis, fat pad changes) infero-medial – pes anserine bursa
lateral and medial knee
may be scanned as above. assess the medial and lateral collateral ligaments and meniscal margins. joint lines (ligament tears or thickening, meniscal bulging/cysts, joint effusion, gross bony changes)
basic hardcopy imaging
a knee series should include the following minimum images;
- quadriceps tendon – long, trans +/- mt junction
- suprapatella bursa
- pre patella – long
- patella tendon – long, trans, insertion onto tibial tuberosity
- medial meniscus and mcl
- lateral meniscus and lcl
- popliteal artery and vein to demonstrate patency
- medial popliteal fossa
- document the normal anatomy and any pathology found, including measurements and vascularity if indicated.