Examination of the Knee Joint

Anatomy Relevant to Examination

• Extensor mechanism: Quadriceps muscle - quadriceps tendon - patella - patellar tendon - tibial tuberosity
• ACL: Primary restraint to anterior tibial displacement
• PCL: Primary restraint to posterior tibial displacement
• MCL: Resists valgus and external rotation forces
• LCL: Resists varus forces
• Medial and lateral menisci: Load-bearing fibrocartilage; medial is injured more commonly than lateral

History

• Mechanism of injury: Direction and force of the blow determines likely structure injured
  • Blow to lateral side of knee with weight bearing → medial collateral ligament injury
  • Backward thrust on the anterior tibia with knee flexed → PCL injury (classic "dashboard injury")
  • Forced hyperextension → ACL injury (isolated ACL tears are uncommon)
  • Rotational injury with knee flexed and weight bearing → meniscal tear (medial meniscus injured by internal femoral rotation on tibia; lateral meniscus by external rotation)
• Haemarthrosis vs. effusion: Rapid swelling within 2 hours = haemarthrosis (suggests ACL tear, tibial plateau fracture, patellar dislocation); delayed swelling = serous effusion (meniscal tear, ligament sprain)
• Locking: Cannot extend the knee past a certain degree (not locking in flexion). Caused by a bucket-handle meniscal tear or loose body. The joint can flex freely but cannot fully extend.
• Giving way: Feeling of instability, especially on stairs or uneven ground
• Lifestyle: Activity level guides expectations and management

1. LOOK (Inspection)

Standing inspection

• Alignment (front view): Look for varus (bow-leg - measure interknee distance) or valgus (knock-knee - measure intermalleolar distance)
• Side view: Look for fixed flexion deformity or recurvatum (hyperextension)
• Skin: Scars (prior surgery/trauma), erythema (infection/inflammatory arthritis), sinuses
• Soft tissues: Quadriceps wasting (a hallmark of chronic knee pathology - measure thigh circumference 15 cm above the patella and compare sides)
• Swelling: Effusion produces a characteristic horseshoe-shaped fullness around the suprapatellar region and on both sides of the patella. Look for prepatellar bursitis (housemaid's knee - swelling directly over the patella) vs. infrapatellar bursitis (clergyman's knee - over patellar tendon)
• Patella height: Patella alta (high-riding - patellar tendon rupture) or patella baja (low-riding)

Gait inspection

• Antalgic gait: Short stance phase on the affected side (pain-related)
• Varus thrust: Sudden collapse into greater varus on weight bearing = lateral compartment disease
• Quadriceps avoidance gait: Walking with the knee in extension to avoid quadriceps activation = ACL deficiency

2. FEEL (Palpation)

Temperature

Soft tissues

• Palpate the quadriceps and patellar tendons for a palpable gap (tendon rupture)
• Palpate popliteal fossa for a Baker's cyst (posterior fullness)

Tests for effusion

1. Stroke fluid out of the medial gutter upward into the suprapatellar pouch
2. Place your hand over the suprapatellar pouch and stroke downward
3. Watch the medial gutter - a positive result is a ripple of fluid appearing on the medial side

• Place one hand on the suprapatellar pouch compressing fluid down; with two fingers of the other hand, briskly press the patella downward - a "tap" or ballottement of the patella against the femoral condyles confirms a tense effusion

Bony palpation

• Tibial tuberosity: Tenderness = Osgood-Schlatter disease in adolescents; tibial plateau fracture in trauma
• Patella borders: Gap = transverse fracture; bony irregularity = comminuted fracture
• Inferior pole of patella: Tenderness = jumper's knee (patellar tendinopathy)
• Joint line (medial and lateral): Best felt with knee at 90°. Medial joint line tenderness is the most sensitive test for a medial meniscal tear
• Collateral ligament origins/insertions: Tenderness at the femoral attachment of the MCL = MCL injury (sprain or tear)
• Femoral condyles: Tenderness = fracture or osteochondritis dissecans
• Fibular head: Tenderness = LCL avulsion or proximal fibula fracture; test by "springing the fibula" (compress tibia and fibula distally - pain at the fracture site)

Point of tenderness - key diagnostic guide (S Das)

Neurovascular assessment

3. MOVE (Range of Motion)

• Active then passive movements: Ask the patient to flex and extend first; then examine passively
• Hyperextension test: Place one hand on the anterior distal femur, lift the distal tibia with the other. Note the heel height off the couch or measure the angle - hyperextension >10° is abnormal
• Fixed flexion deformity: If apparent, sit the patient with knees hanging over the couch edge (eliminates hip flexion artifact). Attempt passive full extension - if not achievable, this is a true flexion deformity (common in OA)
• Extensor lag test: Ask the patient to straight-leg raise to 10°, then flex the knee and attempt to re-extend it in mid-air. Inability to maintain full extension = positive lag = quadriceps mechanism disruption (quadriceps tendon, patellar fracture, patellar tendon, or severe muscle weakness)

4. SPECIAL TESTS

A. Tests for Anterior Instability (ACL)

• Patient supine, knee at 20-30° flexion (heel rests on couch)
• One hand around the distal femur (thumb on lateral femoral condyle), the other around proximal tibia (thumb on tibial tuberosity)
• Apply a brisk anteriorly directed force to the tibia
• Positive: Excessive anterior tibial translation (>5 mm) with a soft end-point (no firm stop) = ACL tear
• Grading: 1+ (0-5 mm), 2+ (5-10 mm), 3+ (>10 mm)

• Knee flexed at 90°, hip at 45°; examiner sits gently on the patient's foot (ensure hamstrings are relaxed)
• Both hands encircle the proximal tibia and pull it anteriorly
• Positive: Tibia slides forward >5 mm on the femur = ACL tear (note: requires medial meniscus or meniscotibial ligament co-injury to be positive)
• A false-positive can occur if the posterior sag sign (PCL injury) is not first excluded

• Patient supine; examiner holds the patient's foot in slight internal rotation and applies a valgus force with the knee in extension
• Slowly flex the knee: at 20-30° of flexion, the lateral tibial plateau suddenly reduces with a visible/palpable clunk
• Positive: A "pivot shift" clunk = combined ACL + posterolateral corner injury
• This test is often easier to perform under anaesthesia

B. Tests for Posterior Instability (PCL)

• Knee at 90° flexion, foot stabilised
• Both thumbs on tibial tuberosity; push the tibia posteriorly
• Positive: Posterior tibial displacement >5 mm or soft end-point = PCL tear
• Positive in ~85% of operative PCL tears

• Patient supine, pillow under distal thigh, knee at 45-90°, heel resting on the stretcher
• Observe the tibial tuberosity from the side
• Positive: Tibia sags backward due to gravity = PCL insufficiency
• Important: A missed posterior sag can cause a false-positive anterior drawer test (tibia starts posterior, then moves forward to neutral when pulled)

C. Collateral Ligament Tests

• Knee at 30° flexion (relaxes the posterior capsule; at 0° the cruciates provide stability, masking a collateral tear)
• Apply a valgus force; palpate the medial joint line with the index finger
• Positive: Excessive medial joint line opening with a soft end-point = MCL tear
• Laxity also in full extension (0°) = injury to the posterior capsule and/or PCL as well

• Knee at 30° flexion; apply a varus force; palpate the lateral joint line
• Positive: Excessive lateral joint line opening = LCL tear
• Laxity in full extension = posterolateral corner (PLC) injury

• Grade I: Firm end-point, <5 mm opening (partial tear)
• Grade II: Soft end-point, 5-10 mm opening (partial/near-complete)
• Grade III: No end-point, >10 mm opening (complete rupture)

D. Meniscal Tests

• Patient supine, knee fully flexed, hip at 45°
• For medial meniscus: Palpate medial joint line; apply a valgus stress and externally rotate the tibia; slowly extend the knee
• For lateral meniscus: Apply varus stress and internally rotate the tibia; slowly extend
• Positive: A palpable or audible click at the joint line, or reproduction of pain = meniscal tear
• The click occurs as the torn meniscus flips over the femoral condyle during extension

• Simply palpate the medial and lateral joint lines with the knee at 90°
• The most sensitive clinical test for meniscal tears (though not very specific)

• Patient prone, knee flexed to 90°
• Apply downward compression and rotate the tibia (grinding the meniscus between the femur and tibia)
• Positive: Pain on compression + rotation = meniscal tear
• Compare with distraction: if pain is worse with compression than distraction, the meniscus (not the ligament) is implicated

E. Patellofemoral Tests

• Patient supine, quadriceps relaxed, knee at 30° flexion
• Gently push the patella laterally
• Positive: Patient shows apprehension (contracts quadriceps or grabs your hand to prevent lateral subluxation) = history of patella dislocation or patellar instability

• Patient sits with legs hanging over the edge of the couch, knees at 90°
• Ask the patient to slowly extend the knee
• Positive: Near full extension, the patella jumps laterally (tracing a "J" shape instead of a smooth straight path) = patellofemoral maltracking

• With the knee extended, press the patella inferiorly and ask the patient to contract the quadriceps
• Positive: Pain and/or crepitus = patellofemoral chondromalacia or OA

5. ASSESSMENT FOR EFFUSION CONTENT

• Clear/straw-coloured: Inflammatory arthritis, meniscal tear
• Haemarthrosis (blood): ACL tear, tibial plateau fracture, patellar dislocation
• Lipohemarthrosis (fat globules in blood): Intra-articular fracture (fat from medullary cavity enters the joint - visible on lateral X-ray as a fluid-fat level)
• Pus: Septic arthritis (emergency)

6. OTTAWA KNEE RULES (Deciding on X-Ray)

Summary Checklist

• Bailey and Love's Short Practice of Surgery, 28th Edition, pp. 512-515 - Clinical Examination of the Knee
• S Das: A Manual on Clinical Surgery, 13th Edition, pp. 207-210 - Examination of Injuries Around the Knee Joint
• Rosen's Emergency Medicine: Concepts and Clinical Practice - Knee Injuries Examination Maneuvers and Ottawa/Pittsburgh Rules
• Gray's Anatomy for Students - Examination of the Knee Joint, Special Tests