What are the key components of a comprehensive knee physical exam for an adult patient with no significant medical history presenting with knee-related symptoms?

Comprehensive Knee Physical Examination

A systematic knee physical examination should begin with inspection for effusion, deformity, and erythema, followed by palpation of specific anatomical structures, range of motion testing, and targeted provocative maneuvers based on the suspected pathology—always examining the uninjured knee first for comparison. 1

Initial Inspection and Observation

• Observe gait pattern for antalgic gait, limping, or inability to bear weight, which may indicate fracture, severe ligamentous injury, or joint infection 2, 3
• Inspect for joint effusion by observing for loss of normal contours around the patella and suprapatellar fullness 4, 3
• Look for erythema, warmth, or swelling which suggests infection, inflammatory arthritis, or acute trauma 3
• Check for visible deformity including valgus/varus alignment, patellar position, or gross anatomical disruption 4
• Examine both knees simultaneously to identify asymmetry in muscle bulk, particularly quadriceps atrophy 1

Systematic Palpation

• Palpate the joint line medially and laterally with the knee flexed to 90 degrees—joint line tenderness has 83% sensitivity and 83% specificity for meniscal tears 5
• Assess the patella for tenderness, crepitus with compression, and tracking during active knee extension 3
• Palpate the tibial tubercle for tenderness (Osgood-Schlatter disease in adolescents) and the patellar tendon insertion 2
• Examine the fibular head for focal tenderness, which is part of the Ottawa knee rules for fracture 6
• Check for effusion using the bulge sign (medial sweep test) for small effusions or ballottement of the patella for larger effusions 3

Range of Motion Assessment

• Test active and passive flexion and extension, documenting any loss of motion—normal knee flexion is approximately 135 degrees and full extension is 0 degrees 4, 1
• Note any crepitus during range of motion testing, which suggests osteoarthritis or chondromalacia 4, 5
• Assess for mechanical symptoms including true locking (inability to fully extend) versus pseudo-locking (pain-limited motion) 5, 3

Ligamentous Stability Testing

Collateral Ligaments

• Perform valgus stress testing at 0 and 30 degrees of flexion to assess medial collateral ligament integrity 1, 7
• Perform varus stress testing at 0 and 30 degrees of flexion to assess lateral collateral ligament integrity 1, 7

Anterior Cruciate Ligament

• Execute the Lachman test (knee at 20-30 degrees flexion, anterior translation of tibia on femur)—this is more sensitive and specific than the anterior drawer test for ACL tears 1, 6, 7
• Perform the pivot shift test for chronic ACL insufficiency, though this has lower sensitivity in the acute setting 1, 7
• The anterior drawer test (knee at 90 degrees flexion) is less reliable than the Lachman test 6

Posterior Cruciate Ligament

• Perform the posterior drawer test with the knee flexed to 90 degrees, applying posterior force to the proximal tibia 1, 7
• Check for the tibial sag sign by observing the tibial step-off with the knee flexed to 90 degrees 1

Meniscal Testing

• McMurray test: With the patient supine and knee fully flexed, internally rotate the tibia and extend the knee (tests lateral meniscus), then externally rotate and extend (tests medial meniscus)—this test is 52% sensitive but 97% specific for meniscal tears 5, 6
• Apley's grind test: With the patient prone and knee flexed to 90 degrees, apply downward pressure while rotating the tibia 1
• Joint line tenderness is 75% sensitive but only 27% specific for meniscal pathology 6

Patellofemoral Assessment

• Patellar apprehension test: Apply lateral pressure to the patella with the knee in slight flexion—patient apprehension suggests patellar instability 7, 3
• Patellar compression test: Compress the patella into the trochlear groove while the patient contracts the quadriceps—pain suggests patellofemoral pain syndrome or chondromalacia 3
• Assess patellar tracking during active knee extension from 90 degrees to full extension, observing for lateral subluxation or J-sign 7
• Anterior knee pain during squatting is 91% sensitive and 50% specific for patellofemoral pain 5

Critical Additional Examinations

• Always examine the hip with range of motion and impingement testing, as hip pathology commonly refers pain to the knee, especially in children and adolescents 4, 2
• Perform a focused neurologic examination including sensation, strength, and reflexes to exclude radiculopathy or neuropathy 2, 3
• Inspect the lumbar spine if knee radiographs are unremarkable and symptoms persist, as referred pain from the lower back must be considered 4

Key Clinical Pitfalls to Avoid

• Do not skip examining the contralateral knee first—this provides a baseline for comparison and helps identify subtle findings 1
• Avoid ordering MRI without recent radiographs (within the past year), as approximately 20% of patients with chronic knee pain undergo unnecessary MRI 4
• Recognize that asymptomatic meniscal tears are extremely common—the majority of people over 70 years have meniscal tears, and the likelihood of a tear in a painful versus asymptomatic knee is not significantly different in patients aged 45-55 years 4
• Physical examination for meniscal and ligamentous injuries is moderately sensitive (meniscus 87%, ACL 74%, PCL 81%) and highly specific (meniscus 92%, ACL 95%, PCL 95%), making it sufficient for initial decision-making about referral 6