Knee — Fast Exam

Tap a diagnosis. Tests first, interpretation underneath.

30-second screen

Run this before any special testEffusion → where it hurts → ligament → meniscus

Red flags? Hot swollen joint, can't weight-bear after trauma, night pain — listed at the bottom.
Ask the effusion timing. Within hours → haemarthrosis, think ACL or fracture. Next day → meniscus, patellar dislocation, or cartilage.
Where does it hurt? Joint line → meniscus. Anterior, behind the patella → patellofemoral. Diffuse with locking → loose body.
Lachman first. It is the single best test for an ACL. Do it before the knee gets guarding.
McMurray and joint-line tenderness for the meniscus — but know they are weak.
Weight-bearing radiograph if the patient is over 40, or if they can't fully straighten after trauma.

The honest caveat: knee special tests are, as a group, worse than shoulder tests. Nearly all sit near 60% sensitivity. Use them to sort suspects, not to make a diagnosis — and never let a negative McMurray stop you treating a classic history.

Ligament

ACL ruptureImmediate haemarthrosis, giving way, pivot or valgus mechanism

Hallmark

Swelling within hours of the injury, a loud pop, and a knee that gives way on pivoting. The patient often can't continue the sport.

Tests

Lachman — 20–30° flexion, stabilise the femur, translate the tibia anteriorly. Positive: increased anterior translation with a soft or absent endpoint. the most sensitive ACL test: ~85%
Pivot shift — from extension, apply valgus and internal rotation while flexing. Positive: a visible clunk as the tibia reduces. the most specific: ~98%
Anterior drawer at 90° — the classic, but less sensitive than Lachman because of hamstring guarding.
Lever sign — heel on the examiner's fist, press down on the distal thigh. Positive: the heel lifts off the table.

Next: combine Lachman + pivot shift + lever sign. The combination beat MRI for ACL deficiency in one comparative series. A negative pivot shift on a swollen, guarded knee means nothing — re-examine in a week.

MCL / LCL injuryAcute valgus or varus mechanism with focal ligament tenderness

Tests

Valgus stress at 30° of flexion — MCL. Positive: laxity plus pain over the medial collateral ligament.at 0° a positive also implicates the posterior capsule and cruciates
Varus stress at 30° of flexion — LCL. Positive: lateral laxity and pain.

Next: grade by laxity endpoint, not by pain. A firm endpoint with pain is a low-grade sprain. Always check the cruciates too — a grade III MCL is a different injury and often sits alongside an ACL tear.

PCL rupturePosterior sag — dashboard injury or fall onto a flexed knee

Tests

Posterior drawer at 90° — push the tibia posteriorly. Positive: posterior translation beyond the other side, with a soft endpoint. the most reliable PCL test: Sn 90% / Sp 99%
Posterior sag sign — hip and knee flexed to 90°, thigh supported. Positive: the tibia sinks back under gravity. Watch for it before you touch the knee. Sn 79% / Sp 100%
Quadriceps active test — from the sagging position, ask them to contract the quadriceps. Positive: the tibia reduces anteriorly. most specific: Sp 97% / Sn 54%

Next: PCL is the injury most often missed, because it looks quiet and the patient often still walks. The posterior drawer is the most reliable test — but look for the sag while the knee is relaxed, before you provoke any guarding.

Meniscus

Meniscal tearJoint-line pain with clicking or locking, delayed swelling

Hallmark

Joint-line pain, mechanical clicking or true locking, swelling that arrives the next day, and pain on twisting or deep squatting. Degenerate tears in older knees are common and often incidental.

Tests

Joint-line tenderness — palpate the joint line with the knee flexed. Positive: focal joint-line pain. Classically quoted as present in 77–85%, but ~54% accuracy in a primary-care-style study. Start here, don't trust it alone.
McMurray — flex fully, rotate the tibia, extend while applying valgus or varus. Positive: click or pain at the joint line. medial: Sn 61% / Sp 62% · lateral: Sn 56% / Sp 96%
Thessaly at 20° — weight-bearing, hold the patient's hands, rotate the knee on the standing leg at 20° flexion. Positive: joint-line pain or catching.the original study claimed 94–96% accuracy; an independent primary-care replication found Sn 66% / Sp 39% — no better than the rest
Apley grind — prone, knee 90°, apply compression while rotating. Positive: joint-line pain.

Next: every meniscal test is around 60% sensitive, and a positive cluster plus a typical history beats any single manoeuvre. Beware MRI in patients over 40 — meniscal tears are common in asymptomatic knees, so the scan often finds an innocent bystander. Treat the patient, not the picture.

Patellofemoral

Patellofemoral painAnterior knee pain — worse on stairs, squatting, and sitting still

Hallmark

Diffuse anterior pain behind the patella, worse going down stairs and after prolonged sitting (the "movie sign"). Usually no effusion, no locking, no giving way. It is a clinical diagnosis — the examination is mainly to exclude other things.

Tests

Patellar compression / Clarke — press the patella distally and ask for a quadriceps contraction. Positive: anterior knee pain. traditionally taught, poor accuracyweak
Single-leg decline squat / step-down — a functional reproduction. Positive: familiar anterior knee pain.
Patellar glide and tilt — assess lateral mobility and tightness of the lateral structures.

Next: no special test diagnoses patellofemoral pain. Reproduce the patient's own pain with load — that is the test.

Patellar instability / dislocationApprehension with lateral glide — apprehension, not pain

Tests

Patellar apprehension — knee slightly flexed, glide the patella laterally. Positive: apprehension or the sense that it will dislocate — not pain. Same trap as the shoulder: accepting pain as a positive is the commonest error.
J-sign — track the patella through extension. Positive: it jumps laterally out of the trochlea in terminal extension → dysplasia or maltracking.
Lateral patellar glide — measure quadrants of lateral translation.

Next: first-time dislocation usually follows a twist with the knee near extension. Ask about previous episodes — recurrent instability changes the management completely.

Patellar tendinopathyFocal pain at the inferior pole, load-related, worse the day after

Tests

Single-leg decline squat — the diagnostic test. Positive: focal pain precisely at the inferior pole of the patella.
Palpation of the inferior pole — Positive: well-localised tenderness (unlike patellofemoral pain, which is diffuse).

Next: a clinical diagnosis — no validated special test. The location is the whole diagnosis: focal inferior pole versus diffuse retropatellar.

Other

Loose body / OCDTrue locking and catching — something is physically in the way

Hallmark

Episodes of true locking — the knee genuinely blocks and then releases — with intermittent catching and effusion. Different from the pseudolocking of a meniscal tear, where the knee feels stuck but can be moved.

Next: radiograph first; MRI or arthroscopy if the history is convincing. True locking is a mechanical problem and does not settle with physiotherapy.

Knee osteoarthritisOver 40, crepitus, activity-related pain, brief morning stiffness

Hallmark

Activity-related pain, crepitus, stiffness after rest that lasts minutes not hours, and reduced range — often losing full extension first.

Next: a weight-bearing radiograph is the test. Not a special-test diagnosis. Avoid MRI as a first step: incidental meniscal and cartilage findings are the norm in this age group.

Referred from hip or lumbar spineKnee pain with a normal knee examination

Hallmark

Anterior knee pain that is not reproduced by any knee test, especially with a limp or restricted hip rotation. Classic in slipped epiphysis and in hip OA.

Tests

Hip rotation and FADIR — always examine the hip in a child or adolescent with knee pain. Positive: restricted or painful hip rotation → the knee is a referred symptom.
Straight leg raise and lumbar screen — Positive: pain reproduced from the spine.

Next: an unexplained knee that hurts and does not examine badly is a hip or a spine until you have checked.

When to image

Choosing the imagingRadiograph first after trauma · MRI for ligaments and cartilage, with caveats

Radiograph first — after acute trauma, and for suspected osteoarthritis. Weight-bearing views for OA. Ottawa knee rules guide the trauma films.
MRI — ligament and cartilage detail, and surgical planning. for ACL rupture: Sp 92% but Sn only 75% — examination beat it in one series
Ultrasound — good for effusion, bursae, tendons and guided injection. Poor for intra-articular structures.

Worth remembering: MRI specificity for meniscal tears is low in the presence of other pathology, and meniscal tears are common in asymptomatic knees over 40. A scan finding is not a diagnosis.

Red flags — before you test

Re-route before you testSeven findings that take precedence over any special test

Stop and re-route

Hot, swollen, red joint with fever → septic arthritis. Aspirate. Higher risk with immunosuppression, diabetes, recent injection or surgery.
Cannot weight-bear after trauma, or an inability to flex the knee 90° → fracture. Radiograph, Ottawa knee rules.
Locked knee that will not extend → displaced bucket-handle meniscus or loose body. Surgical, not conservative.
Night pain, unexplained weight loss, or a history of cancer → malignancy. Urgent referral.
Sudden posterior thigh pain with a pop and bruising → hamstring rupture. Examine for a palpable defect.
Unilateral calf swelling and tenderness, especially post-operatively or with cancer history → deep vein thrombosis.
A child or adolescent with knee pain and a limp → examine and image the hip. Slipped capital femoral epiphysis and Perthes present as knee pain.

Built for Ruby — PRM & sports medicine knee reference.
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Sources. [1] McMurray's test accuracy against arthroscopy — diagnostic accuracy study (PMC12162387): medial Sn 60.9% / Sp 61.5%; lateral Sn 55.6% / Sp 96.3%. [2] Physical examination versus MRI in common knee injuries — MDPI Applied Sciences 2019: Lachman Sn 84.5%; pivot shift and lever sign most specific at 98.5%; McMurray Sn 87.5% for medial meniscus; Thessaly Sn 70% for lateral. [3] Thessaly test re-examined in a primary-care-style setting — NCBI Bookshelf NBK310283: Sn 0.66 / Sp 0.39, no better than McMurray, Apley or joint-line tenderness. [4] Thessaly test original description — Papadopoulos et al., claiming 94% medial and 96% lateral accuracy. Included because the later independent study in [3] contradicts it. [5] Meniscal special-test review — Pacific University dissertation (Horn et al.): McMurray and Thessaly at 20° had specificity above 93% in pooled analysis. [6] ACL examination and lever sign — as reported in [2]. Combine Lachman, pivot shift and lever sign; the combination outperformed MRI for ACL deficiency in that series. [7] PCL examination — Rubinstein et al., Am J Sports Med 1994 (the standard accuracy study for PCL): posterior drawer Sn 90% / Sp 99%; posterior sag sign Sn 79% / Sp 100%; quadriceps active test Sn 54% / Sp 97%.

Diagnostic accuracy figures are pooled from the cited literature and vary widely between studies and populations. Interpret alongside history and pre-test probability. Not a decision-support system, and not a substitute for your own clinical judgement or local protocols.