Differentials
| Presenting Feature | What might it be? | What might I find? | |
| Traumatic knee pain |
Meniscal tear |
Younger active patient with acute knee pain.
History of twisting injury e.g., whilst playing sport. Pain, swelling, giving way, locking. Positive McMurray and Apley grind tests. |
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Anterior Cruciate Ligament (ACL) tear |
Younger active patient with acute knee pain.
History of twisting injury e.g., whilst playing sport. May have been a ‘popping’ sound at time of injury. Instability, pain, swelling. Positive anterior drawer and Lachman tests. |
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Posterior Cruciate Ligament (PCL) tear |
History of direct blow to anterior knee e.g., dashboard injury.
Pain, swelling, instability. Positive posterior drawer test, evidence of posterior sag. |
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Collateral ligament tear |
Younger active patient with acute knee pain.
History of injury/impact to knee from the side. Medial or lateral knee pain, instability, swelling. Positive medial or lateral collateral stretch test. |
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| Atraumatic knee pain |
Osteoarthritis |
Older patient, history of manual work, high BMI.
Gradual onset of pain and stiffness affecting ROM. Reduced ROM, stiffness and crepitus on examination. |
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Meniscal tear |
Older patient, frailty.
Minor twisting movement, possible ‘pop’ followed by pain. Pain, swelling, reduced ROM, locking, giving way. |
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Osgood-Schlatter disease |
Adolescent patient, usually male and active.
Gradual onset anterior unilateral knee pain worse on activity. Painful bony swelling to tibial tuberosity. |
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Pre-patellar bursitis |
Patients who kneel a lot e.g., cleaners, plumbers, gardeners.
Repeated impact to anterior knee e.g., wrestling. Fluid filled swelling to anterior knee, warm and tender. Range of movement is maintained. |
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Patellofemoral pain (PFP) syndrome |
Young active female, frequent use e.g., running, athletics.
Gradually worsening anterior knee pain, worse with activity. Can be unilateral or bilateral. |
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Baker’s cyst |
Known existing knee pathology e.g., meniscus tear.
Pain, fullness, pressure and swelling in posterior fossa. May restrict ROM if large and may rupture. |
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Septic arthritis |
Systemically unwell patient with fever.
May have history of recent surgery or prosthesis. Rapid onset red, hot, swollen, tender joint with systemic upset. |
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Checklist
| Preparation | Wash – Name – Explain | |
| Position patient standing | ||
| Appropriate exposure of legs | ||
| General Inspection | Systemic appearance (well/unwell) | |
| Body habitus | ||
| Pain | ||
| Joint support | ||
| Clues in bed space | ||
| Look (standing) | Examination from all aspects (anterior/lateral/posterior) | |
| Gait | ||
| Asymmetry | ||
| Swelling | ||
| Scars | ||
| Muscle wasting | ||
| Varus/valgus deformity | ||
| Look (lying) | Reposition to reclining 45° | |
| Examination from all aspects (anterior/lateral)) | ||
| Asymmetry | ||
| Swelling | ||
| Scars | ||
| Muscle wasting | ||
| Skin colour | ||
| Fixed flexion deformity | ||
| Measure quadriceps circumference | ||
| Feel | Check for pain | |
| Temperature | ||
| Medial anterior joint line | ||
| Lateral anterior joint line | ||
| Patella | ||
| Patella tendon | ||
| Tibial tuberosity | ||
| Quadriceps tendon | ||
| Patella tap | ||
| Sweep test | ||
| Patella apprehension | ||
| Posterior fossa | ||
| Move | Active flexion | |
| Active extension | ||
| Passive flexion | ||
| Passive extension | ||
| Passive hyperextension | ||
| Special Tests | Anterior drawer | |
| Posterior drawer | ||
| Lachman | ||
| Collateral stretch | ||
| McMurray (offer) | ||
| Apley grind (offer) | ||
| Finishing | Neurovascular examination | |
| Examine joint above & below | ||
| Re-cover patient | ||
| Wash hands |
Explanation
Preparation
Wash, name, explain:
- Wash your hands
- Introduce yourself by name and role
- Check the patient’s name and date of birth
- Explain the procedure and get consent
“I have been asked to examine your knees. This involves looking at, pressing and moving your knees. You can ask me to stop at any time. Are you happy for me to do that?”
Ask the patient to expose their legs to above the knee (e.g., removing trousers and wearing small shorts).
Ask the patient to stand for the initial part of the examination.
General Inspection
Look at the patient and around the bed space for useful signs:
- Body habitus (e.g., overweight or underweight)
- Pain (e.g., holding or protecting joint)
- Joint support (e.g., brace or cast)
- Clues around the bed space (e.g., medication packets, walking stick or crutches)
Look (standing)
Inspect the anterior, lateral and posterior aspects or the knees, noting:
- Asymmetry (e.g., obvious deformity or swelling to one knee)
- Alignment of knees (e.g., varus (knees point outward) or valgus (knees point inward) deformity)
- Swelling
- Scars (e.g., from previous surgery or trauma)
- Muscle wasting (e.g., sarcopenia)
- Hypermobility – the knee joint hyperextends past 10°
Ask the patient to walk a short distance, observing for:
- Antalgic gait (limping) is caused by joint pain
- Reduced range of motion
- Hypermobility – the knee hyperextends while walking
Look (lying)
Reposition the patient to reclining on couch at 45° with legs extended. Observe for pain or difficulty when transferring to the couch.
Examine from anterior and lateral aspects. Perform a closer inspection of the knees, again looking for:
- Asymmetry
- Swelling
- Scars
- Muscle wasting
- Skin colour (e.g., erythema or bruising)
- Fixed flexion deformity – knee cannot fully extend and posterior aspect of the knee will not touch the couch
- Posterior sag – affected knee sags posteriorly compared with the other due to posterior cruciate ligament pathology
Measure the quadriceps circumference 20cm above the tibial tuberosity. A difference in size may suggest wasting of the quadriceps muscle.
Feel
Ask about knee pain before palpating the joint. Look at their face while palpating to check for pain or discomfort.
Feel for changes in skin temperature.
Start by palpating the anterior aspect of the knee, checking for swelling or tenderness of the:
- Medial joint line
- Lateral joint line
- Patella
- Patella tendon
- Quadriceps tendons
- Tibial tuberosity
Check for patellar apprehension by applying lateral pressure to the patella with the knee in extension and then slowly flexing the knee. If the patient feels that the knee is unstable and halts the test, this is considered a positive result, indicating patellar instability.
Check for effusions (fluid in the joint) using:
- Patella tap test
- Sweep test
The patella tap test is performed with knee in extension. Compress any supra–patellar fluid towards the patella with one hand. With the other hand, tap on patella. A knocking sound is heard when a joint effusion is present.
The sweep test is performed with the knee in extension. Using one hand, compress any fluid in the area inferomedial to the knee and sweep upwards to the superomedial area and maintain pressure to hold the fluid in this area. Then, using the other hand, sweep downwards from the superolateral area to the inferolateral area. When an effusion is present, the medial aspect will refill with fluid and a bulge will be seen below the first hand.
Palpate the posterior fossa, feeling for any tenderness or swelling behind the knee (e.g., Baker’s cyst).
Move
Examine active knee movements (ask the patient to move), comparing both sides for the range of motion and discomfort:
- Flexion (normal range: 140°)
- Extension (normal range: 180°)
Examine passive movements by repeating the above, moving the patient’s lower leg with one hand with the other hand placed on patient’s knee. Throughout all joint movement, check for discomfort, crepitus, and range of motion, comparing the results to active movements.
Examine for knee hyperextension. With the patient lying supine and relaxing the leg, lift the leg by the ankle, inspecting the knee joint for more than 10° of extension beyond 180°.
Special Tests
The special tests for the knee are:
- Anterior drawer test (anterior cruciate ligament tear)
- Lachman test (anterior cruciate ligament tear)
- Posterior drawer test (posterior cruciate ligament tear)
- Collateral stretch test (collateral ligament tear)
- McMurray test (meniscal tear – offer but do not perform)
- Apley grind test (meniscal tear – offer but do not perform)
The anterior drawer test starts with the patient’s knee flexed to 90°. Sit on the patient’s foot (check for pain first) to fix it in position. Interlock your fingers behind the knee with your thumbs over the tibial tuberosity. Pull the lower leg anteriorly towards you. The test is positive if the lower leg moves anteriorly, indicating anterior cruciate ligament instability, potentially caused by an ACL tear.
The Lachman test is performed the same way as the anterior drawer test, except with the knee flexed to 30°.
The posterior drawer test is performed the same way as the anterior drawer test, except the lower leg is pushed posteriorly. The test is positive if the lower leg moves posteriorly, indicating posterior cruciate ligament instability, potentially caused by a PCL tear.
The collateral stretch test is performed with the patient’s knee extended. One hand holds the ankle. With the other hand, apply an abducting force to the medial aspect of the knee while applying an adducting force in the opposite direction at the ankle, stressing the lateral collateral ligament of the knee joint. The test is positive if the patient experiences pain, indicating lateral collateral ligament pathology (e.g., a tear). Repeat the test with an adducting force to the lateral knee and an abducting force at the ankle to test the medial collateral ligament.
The McMurray test is performed with the patient’s knee and hip flexed at 90°. Place one hand around the posterior fossa with your thumb and fingers over anterior joint lines, and the other hand on the heel of the foot. Extend the knee with foot internally/externally rotated. The test is positive if the patient experiences pain, indicating meniscus pathology (e.g., tear).
The Apley grind test is performed with the patient lying on their front and the knee flexed at 90°. Press down and rotate the foot. The test is positive if the patient experiences pain, indicating meniscus pathology (e.g., tear).
Finishing
Thank the patient and allow them to cover themselves. Wash your hands.
Depending on the examination findings you may wish to carry out a full neurovascular assessment, examine the joint above and below as well as arrange further investigations including X-ray, ultrasound or MRI scanning.
Last updated Dec 2024
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