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Imaging the Knee — Systematic Approach

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Imaging the Knee — Systematic Approach

Comprehensive guide to systematic knee imaging covering standard radiographic views, weight-bearing assessment, MRI for ligaments and menisci, and clinical applications for fellowship exam preparation.

Very High Yield
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Reviewed: 2026-03-11By OrthoVellum Medical Education Team

Reviewed by OrthoVellum Editorial Team

Orthopaedic clinicians and medical editors • Published by OrthoVellum Medical Education Team

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High Yield Overview

Imaging the Knee — Systematic Approach

From Weight-Bearing Radiographs to Advanced MRI Assessment

WBWeight-bearing views ESSENTIAL for OA assessment
RosenbergPA flexion view for posterior condyle wear
MRIGold standard for menisci, ligaments, cartilage
97%MRI sensitivity for ACL tears
SegondFracture = pathognomonic for ACL tear
Lipohaemarthros on lateral = intra-articular fracture
OttawaKnee rules determine need for radiograph
3THigher field MRI improves meniscal assessment

Knee Imaging Modality Selection

Radiography: First-line for ALL knee presentations. Weight-bearing AP + lateral minimum

Rosenberg view: PA flexion weight-bearing for posterior condylar cartilage assessment

Skyline view: Patellofemoral assessment (tilt, subluxation, OA)

MRI: Gold standard for internal derangement (menisci, ACL, PCL, cartilage)

CT: Fracture characterisation (tibial plateau), malalignment assessment

Ultrasound: Effusion assessment, popliteal cyst (Baker cyst), guided injection

Key: Weight-bearing views are mandatory for OA assessment — non-weight-bearing views are inadequate

Critical Must-Knows

  • Weight-bearing radiographs are ESSENTIAL for knee OA assessment — non-weight-bearing views OVERESTIMATE joint space width.
  • Rosenberg view (PA flexion weight-bearing) detects posterior condylar cartilage loss missed on standard AP views.
  • MRI is the gold standard for internal derangement: meniscal tears, ligament injuries, osteochondral lesions, and bone marrow oedema.
  • The Segond fracture (avulsion of the lateral tibial plateau) is pathognomonic for ACL tear.
  • Ottawa Knee Rules determine the need for radiography in acute knee injury — not all injured knees require X-ray.

Examiner's Pearls

  • "
    A lipohaeamarthrosis (fat-fluid level on horizontal beam lateral) = intra-articular fracture with marrow fat leaking into the joint.
  • "
    Meniscal tear on MRI: high signal on T2 extending to the articular surface (Grade 3). Grade 1-2 intrasubstance signal WITHOUT surface extension is degeneration, NOT tear.
  • "
    ACL tear MRI signs: non-visualisation of the ACL, horizontal/wavy course (loss of normal taut appearance), associated bone bruises (lateral femoral condyle + posterolateral tibial plateau).
  • "
    Pellegrini-Stieda lesion: calcification at the MCL origin (medial femoral condyle) = old MCL avulsion injury.
  • "
    PCL injuries: associated with dashboard mechanism. MRI shows increased signal or disruption of the normally dark, uniform PCL.

Exam Warning

Knee imaging is one of the most frequently tested radiology topics. You must know: the importance of WEIGHT-BEARING views for OA assessment, the Rosenberg view, the significance of lipohaeamarthrosis, the Segond fracture (pathognomonic for ACL tear), MRI criteria for meniscal tears (Grade 3 = surface extension), ACL tear signs including bone bruise pattern, and the Ottawa Knee Rules. Classic traps: ordering non-weight-bearing views for OA assessment and calling intrasubstance meniscal signal (Grade 2) a tear.

Mnemonic

ABCSSSystematic Knee Radiograph Assessment

A
Alignment
Mechanical axis, tibial plateau alignment, patella position (alta/baja). Varus/valgus angulation. Joint congruence (dislocation)
B
Bones
Trace all cortices: femoral condyles, tibial plateaus, patella, fibula head. Fractures, lytic lesions, avulsion fragments (Segond, tibial spine)
C
Cartilage spaces
Joint space width (medial vs lateral, patellofemoral). Weight-bearing views ESSENTIAL — non-WB overestimates joint space
S
Soft tissues
Suprapatellar effusion, lipohaeamarthrosis (fat-fluid level), Pellegrini-Stieda calcification, popliteal cyst, soft tissue swelling
S
Special views
Rosenberg (PA flexion WB for posterior condyle), skyline (PFJ), tunnel view (intercondylar notch for loose bodies and OCD)

Memory Hook:ABCSS: the systematic approach ensuring complete knee radiograph assessment.

Mnemonic

WARSWeight-Bearing Knee Views

W
Weight-bearing AP (standard)
Standing AP view with beam horizontal. Shows medial and lateral compartment joint space under physiological load
A
Alignment full-length (HKA)
Full-length standing views from hip to ankle for mechanical axis assessment. Essential for TKR planning and HTO assessment
R
Rosenberg (PA flexion 45 degrees)
Patient standing with knees flexed 45 degrees, PA projection. Preferentially loads the POSTERIOR condylar cartilage — detects wear missed on AP
S
Skyline (PFJ assessment)
Patient seated with knees flexed 30-45 degrees. Shows patella tracking, tilt, subluxation, and patellofemoral joint space

Memory Hook:WARS: Weight-bearing, Alignment, Rosenberg, Skyline — the four key views for comprehensive knee assessment.

Mnemonic

BLANDACL Tear MRI Signs

B
Bone bruise pattern (classic)
Lateral femoral condyle + posterolateral tibial plateau bone bruises = pivot shift mechanism, highly associated with ACL tear
L
Lax or horizontal ACL course
The normal ACL runs taut and parallel to Blumensaat line (intercondylar roof). A torn ACL appears horizontal, wavy, or completely invisible
A
Anterior tibial translation
More than 7mm anterior translation of the tibia relative to the femur on sagittal MRI = chronic ACL deficiency
N
Non-visualisation of ligament
Complete non-visualisation of the ACL on sagittal and coronal images = complete tear (most specific sign)
D
Deep lateral femoral notch sign
Depression more than 1.5mm deep in the lateral femoral condyle sulcus = impaction from pivot shift mechanism

Memory Hook:BLAND: the five MRI signs of ACL tear — any one raises suspicion, multiple confirm the diagnosis.

Overview

The knee is the most frequently imaged lower limb joint and one of the most commonly tested imaging assessment topics in fellowship examinations. The key principles of systematic knee imaging are: (1) appropriate view selection (weight-bearing views for OA, Ottawa Rules for trauma), (2) systematic radiograph reading, (3) understanding when advanced imaging (MRI, CT) adds value, and (4) accurate interpretation of MRI findings for internal derangement.

The single most important concept in knee imaging is the requirement for WEIGHT-BEARING views when assessing osteoarthritis. Non-weight-bearing radiographs significantly overestimate the remaining joint space because the cartilage surfaces are not compressed under load. This fundamental error can lead to underestimation of OA severity and inappropriate surgical decision-making.

Ottawa Knee Rules

Radiographs are indicated after acute knee injury ONLY if any of the following are present: (1) Age 55 or older. (2) Tenderness at the fibula head. (3) Isolated tenderness of the patella. (4) Inability to flex the knee to 90 degrees. (5) Inability to weight-bear for 4 steps immediately after injury AND in the emergency department. If NONE of these criteria are met, the probability of a clinically significant fracture is less than 1%, and radiographs can be safely deferred. The Ottawa Knee Rules have a sensitivity of approximately 99% for fractures requiring intervention.

The Rosenberg View

The standard AP weight-bearing view may MISS early to moderate OA because: cartilage wear often begins posteriorly on the femoral condyles, and the standard AP view projects through the anterior (thicker) cartilage, obscuring posterior wear. The Rosenberg view (PA projection with knees flexed 45 degrees) shifts the beam to project through the posterior condylar surface — where early cartilage loss occurs. Studies show the Rosenberg view detects joint space narrowing in up to 30% of knees graded as normal on standard AP views. This view is essential for assessing OA severity before osteotomy or arthroplasty.

Clinical Imaging

Imaging Gallery

MRI demonstrating meniscal pathology in coronal and sagittal planes
Click to expand
MRI of the knee demonstrating meniscal assessment in coronal and sagittal planes. Meniscal tears are diagnosed when high signal on T2-weighted images extends to the articular surface (Grade 3). Intrasubstance signal (Grades 1-2) without surface extension represents degeneration, not a clinically significant tear.Credit: Open-i (NIH) (Open Access (CC BY))
MRI showing meniscal root tear with three-panel comparison
Click to expand
Three-panel MRI comparison demonstrating meniscal root tear patterns. Root tears are functionally equivalent to a total meniscectomy because the meniscus can no longer convert axial load to hoop stress. Recognition of root tears on MRI is critical — they require surgical repair to prevent accelerated OA progression.Credit: Open-i (NIH) (Open Access (CC BY))

Systematic Approach

Systematic Knee Imaging Assessment

Knee Imaging Selection Guide

Clinical ScenarioFirst-Line ImagingAdvanced Imaging
Acute knee traumaRadiographs (if Ottawa Rules positive): AP + lateralMRI for suspected internal derangement (ACL, meniscus). CT for tibial plateau fracture characterisation
Osteoarthritis assessmentWeight-bearing AP + lateral + Rosenberg + skylineFull-length alignment (HKA) for osteotomy or arthroplasty planning. MRI only if diagnostic uncertainty
ACL injuryAP + lateral radiographs (Segond fracture, effusion, tibial spine avulsion)MRI: gold standard (sensitivity 97%). Assess associated meniscal and collateral injuries
Meniscal tearRadiographs usually normal (may show degenerative changes)MRI: gold standard. Grade 3 signal (extends to surface) = tear. Root tears are critical to identify
Patellofemoral problemsSkyline view (tilt, subluxation, OA)MRI for cartilage assessment, MPFL integrity. CT for TT-TG distance measurement (more than 20mm = abnormal)
Tibial plateau fractureAP + lateral radiographs (lipohaeamarthrosis on lateral)CT with 3D reconstruction: essential for Schatzker classification, fracture morphology, and surgical planning

Radiographic and MRI Assessment

Essential Radiographic Signs

Lipohaeamarthrosis: A fat-fluid level seen on a HORIZONTAL BEAM lateral radiograph. The fat (less dense) floats on top of the haemarthrosis (blood). This sign indicates an intra-articular fracture with marrow fat leaking into the joint through the fracture site. The most common cause is a tibial plateau fracture, but any intra-articular fracture can produce it. This is a pathognomonic sign and requires CT for full characterisation of the fracture.

Segond fracture: A small avulsion fracture of the lateral tibial plateau caused by traction on the lateral capsular ligament (meniscotibial portion) during pivot shift. This injury is PATHOGNOMONIC for an ACL tear — when seen radiographically, the probability of ACL rupture is nearly 100%. The fragment is a thin sliver of bone off the anterolateral tibial plateau, immediately below the articular surface.

Pellegrini-Stieda lesion: Calcification adjacent to the medial femoral condyle, representing ossification at the origin of the MCL. This indicates a previous (usually chronic) MCL avulsion injury. It may be seen incidentally and is usually asymptomatic, but can occasionally cause medial knee pain.

Tibial spine avulsion: An avulsion fracture of the tibial eminence (ACL footprint). Most common in children and adolescents (8-14 years). Meyers and McKeever classification: Type I (non-displaced), Type II (hinged with anterior elevation), Type III (completely displaced), Type IV (comminuted). Types III and IV require surgical fixation.

Joint space assessment: Kellgren-Lawrence grading on weight-bearing views: Grade 0 (normal), Grade 1 (possible osteophytes), Grade 2 (definite osteophytes, possible JSN), Grade 3 (moderate osteophytes, definite JSN), Grade 4 (large osteophytes, severe JSN, subchondral sclerosis, cyst formation).

MRI Internal Derangement Assessment

Meniscal tears: The key MRI criterion for a meniscal tear is high signal on T2-weighted images that extends to at LEAST one articular surface (Grade 3). The grading system: Grade 0 = normal (homogeneous low signal). Grade 1 = globular intrasubstance signal (NOT a tear — early degeneration). Grade 2 = linear intrasubstance signal without surface extension (NOT a tear — degeneration). Grade 3 = signal extending to articular surface (TEAR — clinically significant).

Tear morphology is described as: horizontal, vertical/longitudinal, radial, complex, or root tear. Bucket-handle tears (displaced vertical tears) show the classic 'double PCL sign' (the displaced meniscal fragment lies adjacent to the PCL) and 'absent bow tie sign' (normal meniscal body is not seen on sagittal images).

ACL assessment: The normal ACL runs from the posterolateral intercondylar notch of the femur to the anterior tibial plateau, parallel to Blumensaat line. On sagittal MRI, it should appear as a taut band of low signal. Signs of tear: BLAND mnemonic — Bone bruise pattern (lateral femoral condyle + posterolateral tibial plateau), Lax/horizontal course, Anterior tibial translation (more than 7mm), Non-visualisation, Deep lateral femoral notch sign.

PCL assessment: The PCL is normally uniformly dark (low signal) and smoothly curved. High signal within the PCL on T2, thickening, or complete disruption indicates injury. PCL injuries are associated with the dashboard mechanism (posterior force to the proximal tibia with the knee flexed).

Root tears: Meniscal root tears are functionally equivalent to total meniscectomy because the meniscus can no longer generate hoop stress. They are identified on MRI as: absence of the root attachment on coronal images, truncation sign on sagittal images, and associated meniscal extrusion (more than 3mm of meniscal body extending beyond the tibial margin on coronal images).

Evidence Base

MRI Accuracy for Internal Derangement

Meta-Analysis
Crawford R, Walley G, Bridgman S, Maffulli N • Journal of Bone and Joint Surgery (British) (2007)
Key Findings:
  • MRI sensitivity for ACL tears was 97% and specificity 97%.
  • MRI sensitivity for medial meniscal tears was 91% and specificity 86%.
  • MRI sensitivity for lateral meniscal tears was lower at 76%, with specificity of 93%.
Clinical Implication: MRI is highly accurate for ACL tears and medial meniscal tears. Lateral meniscal tears may be missed — clinical correlation is essential.
Limitation: Lateral meniscal tears, particularly small peripheral tears, have lower detection rates.
Source: Crawford R et al. JBJS Br 2007;89(6):761-8

Ottawa Knee Rules Validation

Prospective Validation Study
Stiell IG, Wells GA, Hoag RH, Sivilotti ML, Cacciotti TF, Verbeek PR, Greenway KT, McDowell I, Cwinn AA, Greenberg GH, Nichol G, Michael JA • Annals of Emergency Medicine (1997)
Key Findings:
  • The Ottawa Knee Rules had a sensitivity of 98.5% for clinically significant fractures.
  • Application of the rules would reduce radiograph requests by approximately 28%.
  • The only missed fracture was clinically insignificant (avulsion fragment with no change in management).
Clinical Implication: The Ottawa Knee Rules are a validated clinical decision tool that safely reduces unnecessary radiographs in acute knee injury.
Limitation: Not validated in children under 18 years. Should be used within 7 days of injury only.
Source: Stiell IG et al. Ann Emerg Med 1997;30(1):31-9

MRI and clinical rules provide evidence-based imaging pathways.

Rosenberg View for OA Detection

Comparative Study
Rosenberg TD, Paulos LE, Parker RD, Coward DB, Scott SM • Clinical Orthopaedics and Related Research (1988)
Key Findings:
  • The PA flexion weight-bearing (Rosenberg) view detected joint space narrowing in 30% of knees graded as normal on standard AP views.
  • The Rosenberg view was particularly sensitive for posterior condylar cartilage loss.
  • It provided better correlation with arthroscopic findings of cartilage damage.
Clinical Implication: The Rosenberg view should be included in all OA assessment radiographic series — it detects early posterior condylar wear missed by standard AP views.
Limitation: Requires patient cooperation (standing with knees flexed 45 degrees). May be difficult in patients with severe pain or instability.
Source: Rosenberg TD et al. Clin Orthop Relat Res 1988;231:229-35

Meniscal Root Tears and Outcomes

Cohort Study
Allaire R, Muriuki M, Gilbertson L, Harner CD • American Journal of Sports Medicine (2008)
Key Findings:
  • Meniscal root tears increased peak contact pressure by 25% — functionally equivalent to total meniscectomy.
  • Root tears led to loss of meniscal hoop stress, resulting in meniscal extrusion.
  • Unoperated root tears progressed to OA at a significantly higher rate than repaired root tears.
Clinical Implication: Meniscal root tears should be identified on MRI and treated as a high-priority finding — they are NOT benign and lead to progressive OA without repair.
Limitation: Not all root tears are repairable — patient age, cartilage status, and alignment affect treatment decision.
Source: Allaire R et al. Am J Sports Med 2008;36(8):1571-8

Segond Fracture and ACL Tear Association

Retrospective Study
Dietz GW, Wilcox DM, Montgomery JB • Radiology (1986)
Key Findings:
  • The Segond fracture was present in 9% of acute ACL injuries on radiographs.
  • When present, the Segond fracture had a 100% association with ACL tear at arthroscopy.
  • The fracture was often subtle — a thin cortical avulsion from the anterolateral tibial plateau.
Clinical Implication: The Segond fracture is pathognomonic for ACL tear — its recognition on radiographs should prompt MRI and orthopaedic referral.
Limitation: The fracture is present in only 9% of ACL injuries — its absence does NOT exclude ACL tear.
Source: Dietz GW et al. Radiology 1986;159(2):465-7

Specific findings guide management of meniscal, ligamentous, and articular pathology.

Australian Context

In Australia, knee imaging follows the evidence-based algorithmic approach. Plain radiographs are the standard first-line investigation, with weight-bearing views mandated for osteoarthritis assessment by both RANZCR and orthopaedic practice guidelines. The Rosenberg view is increasingly used in Australian radiology departments for pre-surgical OA evaluation.

MRI of the knee is widely available in Australian public hospitals and private radiology centres. Australian orthopaedic surgeons routinely request MRI for suspected internal derangement before considering arthroscopy — diagnostic arthroscopy without prior MRI has largely been abandoned in favour of pre-operative MRI assessment.

The Ottawa Knee Rules are the standard of care in Australian emergency departments for determining the need for radiography after acute knee injury. Their application has significantly reduced unnecessary radiograph ordering while maintaining diagnostic safety.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 65-year-old woman is being assessed for knee osteoarthritis. She brings non-weight-bearing AP and lateral knee radiographs that show mild changes. Her clinical symptoms suggest more severe disease."

EXCEPTIONAL ANSWER
The fundamental problem is that NON-WEIGHT-BEARING radiographs are inadequate for assessing knee osteoarthritis. Non-weight-bearing views significantly overestimate the remaining joint space because the cartilage surfaces are not compressed under physiological load. The articular cartilage is thickest when unloaded, so non-weight-bearing views make the joint appear more preserved than it truly is. This explains the discrepancy between her clinical symptoms (severe) and the radiographic appearance (mild). I would request a complete weight-bearing knee radiographic series: (1) Weight-bearing AP (standing) — the beam is positioned with the patient standing and weight-bearing equally on both legs. This shows the medial and lateral compartment joint space under physiological load. The joint space will likely show significantly more narrowing than the non-weight-bearing view. (2) Rosenberg view (PA flexion weight-bearing at 45 degrees) — this is CRITICAL because cartilage loss often begins on the POSTERIOR femoral condylar surface. The standard AP view projects through the anterior cartilage and may miss posterior cartilage loss entirely. The Rosenberg view directs the beam through the posterior condylar cartilage, detecting wear missed by the AP view. Studies show it detects additional narrowing in 30% of cases. (3) Skyline (Merchant) view — to assess the patellofemoral compartment. PFJ OA is a significant source of anterior knee pain and may be the primary compartment involved. (4) Lateral view — for tibial slope, osteophyte assessment (posterior condyle), and patellar height (Insall-Salvati ratio). If surgical intervention is being considered, I would also request: (5) Full-length weight-bearing HKA (hip-knee-ankle) alignment views — for mechanical axis assessment. This determines whether the patient is varus or valgus aligned, which influences the choice between unicompartmental knee replacement (medial compartment isolated disease with varus alignment) and total knee replacement. Kellgren-Lawrence grading should be applied to the weight-bearing views.
KEY POINTS TO SCORE
Non-weight-bearing views are INADEQUATE for OA assessment — overestimate joint space
Weight-bearing AP shows compartment narrowing under physiological load
Rosenberg view: PA flexion WB detects posterior condylar wear (missed in 30% on AP alone)
Skyline for patellofemoral compartment assessment
Full-length HKA alignment views for surgical planning (UKR vs TKR decision)
COMMON TRAPS
✗Accepting non-weight-bearing views for OA assessment
✗Not requesting the Rosenberg view (misses posterior condylar wear)
✗Not assessing the patellofemoral compartment (skyline view)
✗Not requesting alignment views when considering surgery
VIVA SCENARIOStandard

EXAMINER

"A 25-year-old footballer presents with acute knee injury after a twisting mechanism. The lateral radiograph shows a fat-fluid level in the suprapatellar pouch."

EXCEPTIONAL ANSWER
The fat-fluid level on the lateral radiograph is a LIPOHAEMARTHROSIS. This is a pathognomonic sign of an intra-articular fracture. The physiology: when an intra-articular fracture occurs, bone marrow fat leaks into the joint through the fracture surface. This fat is less dense than blood and floats on top of the haemarthrosis, creating a characteristic fat-fluid level on a horizontal beam lateral radiograph. Three layers may be identified: fat (supernatant), serosanguinous fluid (middle), and cellular blood (dependent). The differential when a lipohaemarthrosis is present: (1) Tibial plateau fracture — the most common cause in adults. Even a small cortical depression or split fracture can produce a lipohaemarthrosis. (2) Distal femoral fracture — may be subtle. (3) Patellar fracture — usually obvious on the lateral view, but sometimes a small marginal fracture can be missed. (4) Osteochondral fracture — from a patellar dislocation or direct impact. The osteochondral fragment itself may be visible as a loose body. My next step is to request a CT scan of the knee with 3D reconstruction. The CT scan will: (1) identify the exact fracture (tibial plateau, femoral condyle, or patella), (2) quantify the articular surface depression and displacement, (3) detect any loose bodies within the joint, (4) provide the information needed for fracture classification (Schatzker for tibial plateau) and surgical planning. If the CT confirms a tibial plateau fracture, I would assess: depression depth (more than 2mm is generally an indication for surgical management), fracture pattern (split vs depression vs combined), column involvement, and associated ligament/meniscal injury. MRI may be added later to assess soft tissue injuries.
KEY POINTS TO SCORE
Lipohaemarthrosis = fat-fluid level on horizontal beam lateral = INTRA-ARTICULAR FRACTURE
Marrow fat leaks through the fracture surface and floats on blood within the joint
Most common cause: tibial plateau fracture (often subtle on radiographs)
Next step: CT with 3D reconstruction for fracture characterisation
Schatzker classification for tibial plateau fractures guides surgical management
COMMON TRAPS
✗Not recognising the lipohaemarthrosis as evidence of intra-articular fracture
✗Not requesting CT for fracture characterisation
✗Not mentioning osteochondral fracture from patellar dislocation as a differential
✗Not knowing the clinical significance (surgical threshold of 2mm depression)
VIVA SCENARIOChallenging

EXAMINER

"An examiner shows you a knee MRI and asks you to systematically describe your assessment of the menisci and cruciate ligaments."

EXCEPTIONAL ANSWER
I will describe my systematic approach to assessing menisci and cruciate ligaments on standard knee MRI. Meniscal assessment: I assess the menisci systematically on SAGITTAL and CORONAL T2-weighted fat-suppressed images. Sagittal images: (1) I identify the medial meniscus first. On each sagittal slice, I look at the meniscal body, assessing for normal signal (homogeneous low signal) vs abnormal signal. (2) The normal meniscus has a 'bow-tie' appearance on sagittal images through the body (two consecutive bow-tie images should be visible). Absence of the bow-tie on two consecutive sagittal images suggests a displaced bucket-handle tear. (3) I trace anteriorly to the anterior horn and posteriorly to the posterior horn. (4) I repeat for the lateral meniscus. Coronal images: (5) I assess the meniscal body and root attachments. The posterior root is the most recently recognised critical structure — absence of the root attachment on coronal images suggests a root tear. (6) I check for meniscal extrusion: more than 3mm of meniscal body protruding beyond the tibial margin on coronal images suggests loss of root function (functionally equivalent to total meniscectomy). Meniscal tear grading: Grade 0 = normal (low signal). Grade 1 = globular intrasubstance signal (degeneration, NOT a tear). Grade 2 = linear intrasubstance signal not reaching surface (degeneration, NOT a tear). Grade 3 = signal extending to at least one articular surface (TEAR — the only grade that is clinically significant). Cruciate ligament assessment: ACL — I assess on sagittal and coronal images. The normal ACL runs from the posterolateral intercondylar roof to the anterior tibial plateau. On sagittal images, it should be taut and parallel to Blumensaat line. Five signs of tear (BLAND): Bone bruise pattern (lateral femoral condyle + posterolateral tibial plateau), Lax/horizontal course, Anterior tibial translation (more than 7mm), Non-visualisation, Deep lateral notch sign. On coronal images, the ACL should be visible as a low-signal band in the intercondylar notch. PCL — I assess on sagittal images. The normal PCL is a uniform dark (low signal) smoothly curved structure. It has a characteristic hockey-stick shape on sagittal MRI. High T2 signal within the PCL, thickening, or disruption indicates injury. The PCL is often split into anterolateral and posteromedial bundles on MRI.
KEY POINTS TO SCORE
Meniscal tear = Grade 3 ONLY (signal extends to articular surface). Grades 1-2 are NOT tears
Bow-tie sign: two consecutive sagittal bow-ties normal. Absent = bucket-handle tear
Root tears: check posterior root on coronal images, meniscal extrusion more than 3mm
ACL tear (BLAND): Bone bruise, Lax/horizontal, Anterior translation, Non-visualisation, Deep notch
PCL: normally uniformly dark with hockey-stick shape, high signal = injury
COMMON TRAPS
✗Calling Grade 1-2 intrasubstance signal a meniscal tear (these are degeneration)
✗Not assessing meniscal root attachments (root tears are functionally equivalent to meniscectomy)
✗Not looking for the bone bruise pattern associated with ACL tears
✗Not assessing anterior tibial translation on sagittal MRI

Knee Imaging — Exam Day Reference

High-Yield Exam Summary

Weight-Bearing Views (WARS)

  • •Weight-bearing AP: mandatory for OA assessment (non-WB overestimates JSW)
  • •Alignment (HKA): full-length for mechanical axis, surgical planning
  • •Rosenberg: PA flexion 45 degrees — detects posterior condylar wear (missed in 30%)
  • •Skyline: patellofemoral assessment (tilt, subluxation, PFJOA)

Key Radiographic Signs

  • •Lipohaemarthrosis: fat-fluid level on horizontal beam lateral = intra-articular fracture
  • •Segond fracture: lateral tibial plateau avulsion = pathognomonic for ACL tear
  • •Pellegrini-Stieda: medial epicondylar calcification = old MCL injury
  • •Tibial spine avulsion: ACL footprint avulsion (children), Meyers-McKeever classification

Meniscal MRI Assessment

  • •Grade 3 (signal to articular surface) = TEAR. Grade 1-2 = degeneration (NOT tear)
  • •Absent bow-tie sign: suggests bucket-handle (displaced) tear
  • •Double PCL sign: displaced bucket-handle fragment lies by PCL
  • •Root tear: absent root on coronal MRI + extrusion more than 3mm = functional meniscectomy

ACL Tear MRI Signs (BLAND)

  • •Bone bruise: lateral femoral condyle + posterolateral tibial plateau (pivot shift)
  • •Lax/horizontal ACL course (loss of normal taut appearance)
  • •Anterior tibial translation more than 7mm (sagittal images)
  • •Non-visualisation of ligament (most specific sign)
  • •Deep lateral femoral notch sign (more than 1.5mm)
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