Anatomy of the Knee

The knee is the largest synovial joint in the body, consisting of patellofemoral joint and tibiofemoral joint. It is a hinge joint that allows mainly extension and flexion



    • Medial collateral ligament (MCL) - Prevents lateral movement of the tibia of the femur when valgus stress is placed on the knee
    • Lateral collateral ligament (LCL) - Prevents medial movement of the tibia of the femur when varus stress is placed on the knee
    • Anterior cruciate ligament (ACL) - Controls rotational movement & prevents anterior displacement of the tibia in relation to the femur
    • Posterior cruciate ligament (PCL) - Prevents posterior displacement of the femur in relation to the tibia
    • Patellar ligament - Continuation of the quadriceps femoris tendon



    • 2 of them: medial and lateral
    • Fibrocartilaginous C-shaped cartilages
    • Shock absorber
    • Stabilize and lubricate the knee
    • Lateral meniscus is more mobile than medial meniscus as it is not attached to the joint capsule



    • Wash hands
    • Introduction
      • “My name is ….. I am a ….year medical student. Can I confirm your name and date of birth?” 
    • Explain and consent
      • “I have been asked to perform a knee examination on you today. The examination will involve me looking at both knees, feeling the structures around the knees and moving your legs. The whole examination should take around five minutes. Are you happy for me to proceed?”
      • “Please stop me at any time if you don’t feel comfortable.”
      • “Do you have any pain at the moment?”



      General observation

      • Look for any bedside clues such as crutches, casts or plasters
      • Looking at the patient: well or unwell, comfortable at rest? in pain?



        MUST compare with the unaffected leg. Expose the patient adequately with the patient STANDING. Inspect from front, behind and whilst walking for:

        • Deformity – varus/valgus
        • Colouration – redness indicating inflammation
        • Swelling
        • Bruising
        • Masses – bursitis or Baker’s cyst
        • Muscle wasting
        • Leg shortening – may suggest hip fracture
        • Scars – may suggest previous injury or surgery



        • Ask patient to walk to the end of the room
        • Inspect for any signs of antalgic gait


          Feel (patient lying supine)



              • Compare both sides. 
              • Warm knee + cold foot may indicate Popliteal artery block


                Effusion (2 tests)

                1. Patellar tap - Used to detect moderate amount of fluid in the joint:

                • With the knee extended, empty the suprapatellar pouch by applying pressure with the index finger and the thumb above the knee. 
                • This manoeuvre pushes the fluid underneath the patella. 
                • Maintain this pressure whilst using the tips of the fingers of the other hand to tap the patella with downward force
                • Positive test if the patella can be felt touching (‘tapping’) the femur
                • Negative test if effusion is small or tense


                2. Bulge test

                • Only used to detect a small amount of fluid in the joint
                • With the knee extended, use the back of your hand to massage any fluid in the anteromedial compartment of the knee into the suprapatellar pouch
                • Fluid will be pushed back into the anteromedial compartment
                • Positive test if a ripple is seen on the medial aspect of the knee
                • Negative test if effusion is tense


                    Tenderness - Ask the patient to flex the knee (around 30°). Palpate:

                    • tibial tuberosity
                    • Medial and lateral joint lines
                    • Collateral ligaments
                    • Patellofemoral joint
                    • Popliteal fossa – look for Baker’s cyst, Popliteal artery aneurysm


                        Muscle wasting

                        • Feel the quadriceps - If muscle wasting is suspected, then measure the circumferences of both quadriceps at equal points. <3cm differences is normal



                          Assess range of movement by assessing active and passive movement.

                          • Active flexion - “can you try to bring your heel back to your buttocks as far back as you can?”
                          • Active extension - examiner places his/her hand underneath patient’s knee (and ask the patient) “can you try to straighten your leg so that the back of your knee can touch my hand?”
                          • Passive flexion - “Just relax your leg. I will try to push your leg as far back as I can to your buttocks.”
                          • Passive extension - “just relax your leg. I will try to straighten your leg a bit more.”
                          • Measure the difference in degrees between passive and active flexion and extension
                          • Any crepitus? Hold the knee cap whilst extending the knee/ Possible causes: osteoarthritis, chondromalacia patellae
                          • Hyperextension - Get to fully extend leg and then take patients heel and tell them to let you take their weight, should be a few degrees of hyperextension
                          • Full ROM: 3° of hyperextension  to 140° of flexion


                              Medial and lateral collateral ligament

                              Need to check for varus and valgus instability which indicates collateral ligament problems


                              1. Varus test (testing LCL)

                              • Flex the knee by 20-30°, with patient lying flat
                              • Place one hand over the lateral joint line and hold the lower leg firmly with the other hand
                              • Applying varus force to the knee by adducting the ankle


                              2. Valgus test (testing MCL)

                              • Flex the knee by 20-30°, with patient lying flat
                              • Place one hand over the lateral joint line and hold the lower leg firmly with the other hand
                              • Applying valgus force to the knee by abducting the ankle


                              Grading of collateral ligament damage

                              • Grade 1 sprain – no gapping but pain
                              • Grade 2 sprain – some gapping of the knee with an end point
                              • Grade 3 sprain – gapping of the knee with no good end point


                                Valgus/varus stress tests

                                  Anterior cruciate ligament (2 tests)

                                   1. Anterior drawer test

                                  • Flex the knee to 90°
                                  • Ask the patient if he/she has any pain in his/her foot
                                  • Sit on the patient’s foot
                                  • Ask the patient to relax the hamstring muscles
                                  • Grasp below the knee with both thumbs on either side of the tibial tuberosity
                                  • Pull the tibia forward
                                  • Compare degree of movement with the other side
                                  • Excessive laxity/giving way suggests ACL disruption (positive anterior drawer test)



                                    2. Lachman’s test (optional)

                                    • Flex the knee to 20°
                                    • Support the femur with one hand and pull the tibia forward with the other hand (thumb must be placed on the tibial tuberosity)
                                    • Feel for the endpoint
                                    • If it comes to a sudden stop = firm endpoint à normal
                                    • If it doesn’t come to a sudden stop = soft endpoint; associated with a tear of the ACL


                                        Posterior cruciate ligament - Posterior drawer test

                                        • Same as the anterior drawer test but push the tibia backward instead of forward
                                        • Compare degree of movement with the other side
                                        • Excessive laxity/giving way suggests PCL disruption (positive posterior drawer test)



                                            Patella Apprehension test


                                            • Keep the knee in full extension
                                            • Apply pressure from medial patella
                                            • Ask patient to tighten quadriceps muscle - positive if with pain



                                                Menisci - McMurray test

                                                • Flex the hip and knee to 90°
                                                • Support the heel with the right hand and steady the knee with the left hand
                                                • Slowly extend the knee using the right hand and palpate the joint line with the left hand at the same time
                                                • Perform this with the tibia in both internal and external rotation
                                                • Internal rotation – lateral meniscus
                                                • External rotation – medial meniscus
                                                • If pain is felt or a ‘click’ is heard à positive McMurray test



                                                  • Examine the contralateral knee
                                                  • Examine the hip joint and ankle joint (above and below)
                                                  • XR knee - If fracture or pseudogout is suspected
                                                  • MRI/arthroscopy - Damage to ligaments and cartilages can be seen


                                                  Please see the attached video for a knee examination demonstration from the Central Manchester Foundation Trust Undergraduate Medical Education’s Channel.



                                                  Drake, RL, Vogl, W & Mitchell, A 2005, Gray’s Anatomy for Students, Elsevier Churchill Livingstone, London p. 532-540














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