The knee is a vulnerable joint. It carries the weight of the body. Stability is maintained by four ligaments and the muscles around the joint. The knee is susceptible to injury and disease processes, commonly osteoarthritis (OA). Injury is more likely in sports that involve twisting movements and sudden changes in direction of the knee, such as football, basketball, netball and skiing.¹ Taking a good history and performing a good examination can help to determine if a significant knee injury has occurred. A good assessment can help to guide further investigations and/or treatment.

If there is little or nothing abnormal to find despite the history, examine the hip and lumbar spine. Problems here may be causing referred knee pain. The hip as a cause of knee pain is common in children.

There is a separate article that covers Knee Pain.

Anatomy of the knee¹

• Joints - there are two joints in the knee:
  • Patellofemoral joint.
  • Tibiofemoral joint (the joint that is usually referred to as 'the knee joint').
• Patella - the patellar tendon (also called patellar ligament) passes anteriorly to the patella. The medial retinaculum also gives support to the patella.
• Ligaments - stability to the tibiofemoral joint is provided by various ligaments:
  • Anterior cruciate ligament (ACL) - controls rotational movement and prevents forward movement of the tibia in relation to the femur. Runs between attachments on the front (hence anterior cruciate) of the tibial plateau and the posterolateral aspect of the intercondylar notch of the femur.
  • Posterior cruciate ligament (PCL) - prevents forward sliding of the femur in relation to the tibial plateau. Runs between attachments on the posterior part (hence posterior cruciate) of the tibial plateau and the medial aspect of the intercondylar notch of the femur.
  • Medial collateral ligament (MCL) - prevents lateral movement of the tibia on the femur when valgus (away from the midline) stress is placed on the knee. Runs between the medial epicondyle of the femur and the anteromedial aspect of the tibia. Also has a deep attachment to the medial meniscus.
  • Lateral collateral ligament (LCL) - prevents medial movement of the tibia on the femur when varus (towards the midline) stress is placed on the knee. Runs between lateral epicondyle of the femur and head of the fibula.
• Menisci - the medial and lateral menisci are located within the knee joint, attached to the tibial plateau. They help to protect the articular surfaces by absorbing some of the forces transmitted through the knee. They also help to stabilise and lubricate the knee.

History

• Pain:
  • Is the pain unilateral or bilateral?
  • Was onset gradual or acute? OA comes on over years; ACL injury causes immediate pain.
  • If acute, was there trauma?
  • If there was trauma, what exactly happened? If the injury occurred in sport or an accident, get a precise history of the mechanism. Was there a direct blow causing vulgus or varus stress? Was there a twisting motion?
  • Where is the pain felt? Anterior, posterior, lateral or medial?
  • Is the pain persistent?
  • Is there any joint stiffness?
  • Are there any aggravating or relieving factors?
  • What was the degree of pain and disability at the time of injury? How does this compare to the current situation?
• Was there any sound? A 'popping' or 'snapping' sound may suggest rupture of a ligament.
• Did the knee swell immediately, gradually, or not at all? Rapid swelling (0-2 hours) suggests haemarthrosis which may, for example, be due to ACL or PCL rupture, patellar dislocation.¹ Gradual swelling (6-24 hours) suggests an effusion which may be due to meniscal injury.¹ Swelling over a 24-hour period with no history of trauma could be due to septic arthritis or an inflammatory arthritis.
• Does the knee lock or click? Suggests a loose body and may be due to meniscal injury.
• Does the knee give way? Suggests instability (e.g. ACL injury) or muscle weakness.
• Has the patient attended A&E? An X-ray may have been carried out to exclude a fracture.
• Ask about previous history of knee injury.
• Ask about past medical history, occupation and level of exercise.

Examination

Get the patient to lie comfortably on a couch. Pain or apprehension will make examination difficult. Always examine and compare both knees.

Inspection

• Look at the patient: a pyrexial and unwell patient may have septic arthritis.
• Look at the joint: is it swollen, red, or hot?
• Examine for muscle wasting: compare with the other side.

Examine for an effusion

• This is unnecessary if swelling is gross.
• Eliciting a patellar tap: extend the knee and empty the suprapatellar pouch by applying pressure from the palm of your hand above the knee. This will push fluid underneath the patella, lifting it. Maintain this pressure. Next, press down on the patella with the fingers of the other hand and the patella will be felt to move down and touch ('tap') the underlying bone if an effusion is present.
• The massage (bulge) test: with the knee in extension, use the palm of your hand to massage any fluid in the anteromedial compartment of the knee into the suprapatellar pouch. Next, stroke the lateral side of the joint and the lateral side of the suprapatellar pouch. This will push any fluid present back into the anteromedial compartment. Look for a fluid impulse.²

Examine for tenderness

Palpation should include:

• The medial and lateral joint line - palpate with the knee in 30° flexion.
• The patellofemoral joint.
• The medial collateral ligament (MCL) and the lateral collateral ligament (LCL).
• The popliteal fossa. This may be easier with the patient supine. Look for Baker's cyst, deep vein thrombosis, gastrocnemius pathology, popliteal artery aneurysm.³

Examine range of movement

• Examine active and passive flexion and extension.
• The examining hand on the kneecap may detect crepitus. This usually suggests osteoarthritis but is also found in chondromalacia patellae.
• Full range of movement is from 3° of hyperextension to 140° of flexion.³ For most activities of daily living 115° of flexion is needed.³
• Always compare both knees.
• Fixed flexion deformities can be due to torn cartilage or loose body.²

Examine stability

MCL and LCL

The valgus and varus stress tests can be used.⁴

• Flex the knee by 30°.
• Hold the ankle firmly between your arm and your side.
• With your other hand putting pressure above the knee, attempt to adduct and abduct the knee joint.
• More than minimal movement is abnormal.

Anterior cruciate ligament (ACL)

The anterior drawer test:

• Flex the knee to 90°.
• Hold the position by sitting on the patient's foot.
• Ensure that the hamstring muscles are relaxed.
• With both hands, grasp below the knee and pull the tibia forward.
• Compare the degree of movement with the other side.
• Excessive movement may indicate ACL disruption.

Lachman's test:

• Flex the knee to 15-20°.
• Hold the lower thigh in one hand and the upper tibia in the other.
• Push the thigh in one direction and pull the tibia in the other.
• Reverse the direction, pushing the tibia and pulling the thigh, and look for increased movement or laxity between the tibia and the femur.

Pivot shift test:²
This test is difficult to perform and is generally not recommended for use by GPs.⁴

• Hold the patient's heel with one hand.
• Internally rotate the foot and the tibia and, at the same time, apply an abduction (valgus) force at the knee.
• Flex the knee from 0° to 30° whilst applying this force and still holding the foot and tibia in internal rotation.
• Try to detect any palpable or visible reduction between the femur and the tibia.

Posterior cruciate ligament (PCL)

Posterior drawer test:

• Perform the same examination as the anterior drawer test but pushing backwards in relation to the tibia instead of pulling forwards.
• Compare the degree of movement with the other side.

Posterior sag test:¹

• Flex both knees to 90°.
• Look at the position of the tibia in relation to the femur.
• If there is rupture of the PCL, the position will be relatively posterior.

Other tests

McMurray's test for meniscal injury²

This test is no longer recommended because the diagnostic accuracy is low and it is thought that it may exacerbate the injury.⁴

• Flex the patient's hip and knee to 90°.
• Hold the heel with the right hand and steady the knee with the left.
• Slowly extend the knee, using the right hand and, at the same time, palpate the joint line with the left hand. Perform this with the tibia in external and then internal rotation at the various stages of flexion.
• A positive test is when a 'clunk' is felt with associated pain.

Patellar apprehension test to assess stability of the patella²

• The patient should be lying on their back with the knee extended.
• Apply pressure to the medial side of the patella.
• Keep this pressure applied whilst passively flexing the knee to 30°.
• Look for any lateral patellar movement and any 'apprehension' from the patient.

Examination of gait

Always remember to watch the patient in standing and in walking.

Investigations

• Knee joint aspiration can be both diagnostic and therapeutic. There is a separate article entitled Knee Injections and Aspirations.
• X-ray may reveal fracture of any of the bones or the calcium pyrophosphate crystals of pseudogout.
• Damage to cartilage or ligaments can be demonstrated by MRI or arthroscopy.
• The Direct Access Magnetic resonance imaging: Assessment for Suspect Knees (DAMASK) trial looked at the influence of early access to MRI of the knee, compared with referral to an orthopaedic specialist, on GP's diagnoses and treatment plans for people with knee problems. The trial found that access to MRI did not significantly alter their diagnoses or treatment plans but it did significantly increase their confidence in these decisions.⁵

Document references

1. Clinical Sports Medicine. Revised second edition. McGraw Hill. Chapter 23. Acute Knee Injuries
2. Macleod J, Munro JF, Campbell IW; Macleod's Clinical Examination. Churchill Livingstone, 2000
3. Wheeless on line; Examination of the knee
4. Knee pain - assessment, Clinical Knowledge Summaries (March 2011)
5. Brealey SD; Influence of magnetic resonance of the knee on GPs' decisions: a randomised trial. Br J Gen Pract. 2007 Aug;57(541):622-9. [abstract]

Internet and further reading

• Mr Fraz Hussain; Musculoskeletal Examination Video. Knee Examination Run Through. The Royal Orthopaedic Hospital. Accessed April 2011

Acknowledgements