MRI Anatomy Flashcards · MSK

Knee Anatomy

Learn to identify every labeled structure on a Knee MRI, plane by plane.

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Knee anatomy, structure by structure

Knee MRI is one of the highest-volume musculoskeletal exams a technologist will run, and clean images start with knowing the normal anatomy cold. This reference walks through every structure in our knee flashcard deck across the three standard planes (sagittal, coronal, and axial), with a plain-language definition, how each structure looks on MRI, and the pathology you will actually encounter at the scanner.

Bones

The bony framework of the knee. Cortical bone is dark on every sequence; the fatty marrow inside is bright on T1 and suppressed (dark) on fat-saturated PD/T2, where a bright bruise stands out.

Femur

The thigh bone, whose distal end forms the rounded condyles that make up the upper half of the knee joint.

On MRI: The large bone entering from above on every plane. The cortex is a dark rim and the marrow is bright on T1, darkening on fat-saturated PD/T2. On sagittal it is the bone behind the patella; on coronal it splits into the medial and lateral condyles.

Common pathology: Distal femoral marrow edema (bone bruise) from trauma, osteochondral lesions of the condyles, and stress reaction.

Tip: On any plane the femur is the bone coming in from the top of the field; the tibia comes in from the bottom.

Tibia

The shin bone, whose flat upper surface (the plateau) forms the lower half of the knee joint and supports the menisci.

On MRI: The large weight-bearing bone entering from below. Dark cortex with bright T1 marrow; on sagittal it sits beneath the femur with the menisci wedged between them.

Common pathology: Tibial plateau fractures, pivot-shift bone bruise pattern (posterolateral tibia and lateral femoral condyle), and stress fractures.

Fibula

The thin lateral bone of the lower leg; its head sits just below and behind the lateral tibial plateau.

On MRI: A smaller bone on the lateral side, best seen on coronal images as a separate structure lateral to the tibia. Dark cortex with bright T1 marrow.

Common pathology: Fibular head fractures, the anchor point of the LCL and biceps femoris, and a clue to posterolateral corner injury.

Patella

The kneecap, a sesamoid bone embedded in the extensor mechanism that glides in the trochlear groove of the femur.

On MRI: Triangular in cross-section on axial, where its articular cartilage and tracking in the trochlear groove are assessed; on sagittal it sits in front of the femur between the quadriceps and patellar tendons.

Common pathology: Chondromalacia and cartilage loss on the undersurface, maltracking/subluxation, bipartite patella, and lateral patellar dislocation with a medial retinacular tear.

Tip: Axial is the plane for patellar cartilage and tracking; sagittal shows its tendon attachments above and below.

Apex of Patella

The pointed lower tip of the patella, where the patellar tendon takes its origin.

On MRI: The inferior point of the kneecap on sagittal, immediately above the proximal patellar tendon.

Common pathology: Patellar tendinopathy (jumper's knee) and Sinding-Larsen-Johansson syndrome center on the apex.

Tibial Plateau

The flat upper articular surface of the tibia, divided into medial and lateral compartments that carry the menisci.

On MRI: The horizontal top of the tibia on sagittal and coronal; the menisci sit on its surface and the cartilage caps it.

Common pathology: Plateau fractures (often with marrow edema), subchondral insufficiency fractures, and articular cartilage loss in osteoarthritis.

Tibial Tuberosity

The bony bump on the front of the upper tibia where the patellar tendon inserts.

On MRI: A forward-projecting prominence on the anterior tibia on sagittal, marking the lower end of the patellar tendon.

Common pathology: Osgood-Schlatter disease (fragmentation and edema in adolescents) and distal patellar tendinopathy at the insertion.

Lateral Condyle

The lateral rounded prominence of the distal femur that articulates with the lateral tibial plateau.

On MRI: The outer of the two femoral condyles on coronal, separated from the medial condyle by the intercondylar notch. Bright T1 marrow under a dark cortical rim.

Common pathology: A classic site for the pivot-shift bone bruise (anterolateral femoral condyle) seen with ACL tears, and osteochondral lesions.

Medial Condyle

The medial rounded prominence of the distal femur that articulates with the medial tibial plateau.

On MRI: The inner femoral condyle on coronal, on the same side as the medial collateral ligament and medial meniscus.

Common pathology: Spontaneous osteonecrosis of the knee (SONK) and osteochondral lesions favor the weight-bearing medial condyle.

Tibiofibular Joint

The articulation between the lateral tibia and the head of the fibula below the knee joint line.

On MRI: A small joint on the lateral side on coronal, between the tibia and the fibular head, with a thin cartilage interface.

Common pathology: Proximal tibiofibular joint cysts, instability, and dislocation; ganglia here can cause peroneal nerve symptoms.

Cruciate ligaments

The crossing central stabilizers inside the joint. Normal ligaments are dark, low-signal bands; bright fluid signal through the fibers means a tear.

Anterior Cruciate Ligament

The ligament running from the anterior tibia up and back to the lateral femoral condyle, the primary restraint to anterior tibial translation.

On MRI: A taut, dark band coursing obliquely up and back in the intercondylar notch, best evaluated on sagittal (often a slightly angled oblique sagittal) with coronal confirmation; its fibers are normally straight and parallel.

Common pathology: ACL tear is the headline knee MRI finding: discontinuity or bright fluid signal through the fibers, a wavy/absent ligament, and a pivot-shift bone bruise of the lateral femoral condyle and posterolateral tibia.

Tip: Angle the sagittal slightly along the lateral femoral notch so the whole ACL lies in one plane; it should be a straight dark line.

Posterior Cruciate Ligament

The ligament running from the posterior tibia up and forward to the medial femoral condyle, the main restraint to posterior tibial translation.

On MRI: A thick, curved, uniformly dark band in the intercondylar notch on sagittal, hooking forward like a comma; stronger and more obvious than the ACL.

Common pathology: PCL tears (often from dashboard injury) show thickening and bright signal; a buckled PCL is an indirect sign of an ACL tear.

Collateral ligaments

The side stabilizers spanning the joint line. Both are dark bands best shown on coronal; bright surrounding signal or fiber disruption indicates a sprain or tear.

Medial Collateral Ligament

The broad ligament on the inner side of the knee running from the medial femoral condyle to the proximal tibia, the main restraint to valgus stress.

On MRI: A thin dark band along the medial joint line, best seen on coronal running vertically from femur to tibia; its deep fibers blend with the medial meniscus.

Common pathology: MCL sprain/tear with edema along the ligament; part of the O'Donoghue triad (MCL, ACL, and medial meniscus injury).

Lateral Collateral Ligament

The cord-like ligament on the outer side of the knee running from the lateral femoral condyle to the fibular head, resisting varus stress.

On MRI: A thin dark cord on the lateral side on coronal, angling down to the fibular head where it joins the biceps femoris tendon (the conjoined insertion).

Common pathology: LCL tear is a key component of posterolateral corner injury; look at the fibular head attachment for avulsion.

Menisci

The C-shaped fibrocartilage cushions between femur and tibia. Normal menisci are uniformly dark (black) wedges; any bright line reaching an articular surface is a tear.

Medial Meniscus

The C-shaped fibrocartilage on the inner compartment that cushions and stabilizes the medial femorotibial joint.

On MRI: A dark triangular wedge between the medial femoral condyle and tibial plateau on coronal; its larger posterior horn is the most common tear site, best assessed on sagittal.

Common pathology: Posterior horn tears are the most common meniscal injury; the medial meniscus is less mobile, so degenerative and bucket-handle tears are frequent.

Lateral Meniscus

The more circular fibrocartilage on the outer compartment that cushions the lateral femorotibial joint.

On MRI: A dark wedge in the lateral compartment on coronal; the popliteus tendon grooves near its posterior horn and should not be mistaken for a tear.

Common pathology: Lateral meniscus tears (often with ACL injury), discoid lateral meniscus, and meniscal cysts.

Posterior Root of Lateral Meniscus

The posterior attachment of the lateral meniscus where it anchors to the tibial plateau near the PCL.

On MRI: The point where the back of the lateral meniscus fixes to the central tibia, seen on posterior sagittal slices and confirmed on coronal.

Common pathology: Root tears or avulsions cause meniscal extrusion and accelerate cartilage loss; commonly associated with ACL injury.

Extensor mechanism and soft tissue

The tendons that straighten the knee plus a key posterior muscle and vessel. Tendons are dark, ordered bands; the popliteal artery is a dark flow void on standard sequences.

Quadriceps Tendon

The strong tendon that joins the quadriceps muscles to the top of the patella, the upper half of the extensor mechanism.

On MRI: A thick, layered dark band running down to the superior pole of the patella on sagittal; it often shows a normal striated multilayer appearance.

Common pathology: Quadriceps tendon tear (more common in older patients) shows a gap with fluid; tendinosis shows thickening and intermediate signal.

Patellar Tendon

The tendon connecting the lower pole of the patella to the tibial tuberosity, the lower half of the extensor mechanism.

On MRI: A flat, uniformly dark band on sagittal running from the patellar apex to the tibial tuberosity, normally a couple of millimeters thick.

Common pathology: Patellar tendinopathy (jumper's knee) thickens the proximal tendon with bright signal; full tears show a gap and patella alta.

Medial Head

The medial head of the gastrocnemius muscle, arising from the back of the medial femoral condyle to form the inner bulge of the calf.

On MRI: A muscle belly on the posteromedial aspect on axial, with normal muscle signal; its origin tendon arises just behind the medial condyle.

Common pathology: Origin strain, and the medial-head bursa is the usual neck of a Baker (popliteal) cyst between it and the semimembranosus.

Popliteal Artery

The main artery behind the knee, the continuation of the femoral artery that supplies the lower leg.

On MRI: A round dark flow void in the popliteal fossa behind the joint on axial, and a vertical dark channel posteriorly on sagittal; bright on flow-sensitive or contrast sequences.

Common pathology: Popliteal artery aneurysm, entrapment syndrome, and adventitial cystic disease; also a landmark for posterior masses and Baker cysts.

Frequently asked questions

What structures are seen on a knee MRI?

A standard knee MRI shows the bones (distal femur, proximal tibia, fibula, and patella, including the tibial plateau and condyles), the cruciate ligaments (ACL and PCL), the collateral ligaments (MCL and LCL), the medial and lateral menisci, and the extensor mechanism (quadriceps and patellar tendons), along with the popliteal artery and the gastrocnemius origin. This page labels each one with its MRI appearance and the pathology technologists commonly encounter.

Which plane is best for studying knee anatomy?

Each plane has a job. Sagittal is the workhorse for the cruciate ligaments, the menisci (especially the posterior horns), and the extensor mechanism. Coronal is best for the collateral ligaments, the meniscal bodies, and comparing the medial and lateral compartments. Axial is best for the patellar cartilage and tracking, the retinacula, and the structures of the popliteal fossa.

What sequences are used for a knee MRI and how do you read meniscal tears?

Knee MRI relies heavily on fat-suppressed proton-density and T2 sequences, where fluid and edema are bright against dark bone, tendon, and meniscus. A normal meniscus is uniformly black; a tear shows a bright line that reaches an articular surface. Ligaments and tendons are normally dark bands, so bright fluid signal through their fibers signals a sprain or tear.

How do you tell the ACL from the PCL on MRI?

Both cruciate ligaments sit in the intercondylar notch and are best traced on sagittal. The PCL is the thick, smoothly curved, uniformly dark band that hooks forward like a comma and is easy to follow. The ACL is thinner and runs obliquely up and back toward the lateral femoral condyle; angling the sagittal slightly along the notch helps lay the whole ligament in one plane.

Do I need an account to use these knee MRI flashcards?

No. The interactive flashcards and this full labeled reference are open to use, with no account required to start. Creating an account lets you save your progress across devices and track which packs you have mastered.

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