Knee examination is an important clinical skill, and knee problems are a common presenting complaint to general practice and emergency departments. Knee examination is also a common OSCE station.
The knee is a hinge joint, but it depends on external structures for its stability, including the cruciate and collateral ligaments, and the menisci.
- Valgus deformity – ><
- Varus deformity – <>
- Recurvatum deformity – hyperextendibility of the knee beyond the normal 10’
- Limp and gait
- Wounds (including old surgical scars)
- Gross deformity
- Swelling – the three main causes of swollen knee are:
- Bony swellings
- Synocial thickening
- Fluid collection e.g. in inflammation. Can be generalised (effusion), or localised (inflamed bursa).
- Chronic diseases that can cause a swollen knee are:
- Check the character and location of the swelling:
- Localised – likely bursitis
- Generalised – likely other cause
- Translumination? – indicates presence of fluid
- Quadriceps bulk – quadriceps often wasted in painful chronic knee conditions. You may want to measure the circumference and compare to the other leg, or compare over time. In these cases you shoulder measure 10cm above the patella.
- Why do muscles waste in joint disease? – it is not solely due to lack of use of the muscle! The exact mechanism is not clear, however, it is thought that there is secondary nerve changes in the nerves around a diseased joint that mean the muscle wastes very quickly (perhaps within days!)
- Leg length – compare to opposite side
- Position – values and various, patella position
- Gross deformity, growths
- Feel the temperature with the back of your hand. If it is warm, state there is a local rise in temperature.
- Feel for the joint line – if you feel distal to the patellar, on both the medial and lateral aspects of the joint you can feel two soft triangular hollows. Pressing into the superior aspect of these hollows, you will be able to feel the joint line. Check for tenderness at the joint line.
- Patella Tap – tests for larger effusions.
- Similar to the bulge test, try to empty the suprapatellar bursa. Make sure you maintain constant downwards pressure on the thigh.
- Now put two fingers on the patella and press firmly and briskly downwards. If fluid is present you will feel the patella move downwards (it might feel ‘squishy’) before hitting the underlying bone. In a normal patient, there will be little movement of the patella, and you should not feel it hit the underlying bone.
- Also check the patella position and freedom of lateral movement
- Bulge test – can be sensitive for a small effusion.
- Place your hand about 15cm proximal to the knee joint on the anterior part of the thigh. Then slide your hand down towards the knee. This empties the suprapatellar bursa of fluid
- keeping the first hand in place, using your other hand, press on the medial side of the knee joint to empty the medial compartment. Now all of the bursal fluid should be in the lateral compartment
- Take your hand off the medial compartment, and press on the lateral compartment – you may see a bulge in the medial compartment as it fills with fluid. This shows a small effusion
- Soft tissues – check for tenderness
- Patellar tendon
- Quadriceps tendon
- Iliotibial band (ITB)
- Collateral ligaments
- Popliteal fossa
- Painful if ruptures bakers cyst or ligament rupture
- Ruptured Baker’s cyst – is an important differential for DVT. Both produce calf swelling, pitting oedema, pain and redness.
- The baker’s cyst is located in the popliteal fossa. If it rupture it causes sudden calf pain. Can only really be differentiated for DVT with ultrasound (checks veins in legs, and can also look for swelling of knee joint, and remnants of a baker’s cyst).
- Neruovascular examination
- Not often indicated
- Knee flexion – Sciatic nerve
- Knee extension – femoral nerve
- Foot plantarflexion – tibial nerve
- Foot dorsiflexion – deep perineal nerve
- Medial thigh – Obturator nerve
- Anterior thigh – Femoral nerve
- Dorsal foot – Peroneal nerve
- Plantar foot – Tibial nerve
- Knee – popliteal
- Ankle – (medial) poster tibialis
- Foot – dorsals pedis
- Patellar – L4
- Extension – check both legs. Ask the patient to extend their knee as far as possible. Normal range – 0 – 10 degrees
- Flexion – ask the patient to bring their foot to their bottom. About 125-135 degrees is normal.
- Rotation – 10-15 degrees of tibial rotation is normal (whilst holding the femur fixed with your other hand)
- Compare both sides!
Examining knee stability
Flex the knee to about 20’. Hold the ankle with one hand and the thigh with the other.
- Lateral ligament – apply valgus force – “valgus stress test”
- Medial ligament – apply varus force – “varus stress test”
- Feel for laxity of the knee joint
- As you are doing this, you might want to try to feel the joint line with the hand that is holding the thigh (usually left hand) – to see if you are abnormally opening up the joint on the stressed side. Any weakness or tear of a collateral ligament will result in a joint line that separates abnormally.
- Anterior cruciate ligament – runs from the posterior aspect of the femur to the anterioraspect of the tibia. Prevents the tibia slipping forward
- Abnormal movement anteriorly of the tibia in relation to the femur in Lachman’s or drawer tests suggests ACL injury.
- Posterior cruciate ligament – runs from a more anterior aspect of the femur to the anterior posterior of the tibia. Prevents the tibia slipping backwards
- Abnormal movement posteriorly of the tibia in relation to the femur in drawer test suggests ACL injury.
- Flex the leg to 30 degrees
- Hold the femur securely by holding the thigh securely
- Try to move the tibia forward on the femur. Normally little movement is possible. Movement >5mm is suggests an ACL injury
- Flex the leg to 90’
- Put your fingers of both hands into the popliteal fossa, and the thumbs of both hands on the front of the tibia.
- Try to pull the tibia forward relative to the femur – Some doctors suggest you sit on the foot as you do this to anchor the foot and ankle
- Normally, there will be little movement, movement suggests pathology
- Any rotation at the hip joint prevents this test from properly assessing the cruciate, and thus many people say this test is inferior to Lackman’s
- Same as the anterior draw test, except that you push instead of pulling on the tibia.
- Joint line tenderness is the most sensitive test for meniscal tear
- Lie the patient prone
- Flex the knee to 90 degrees
- Apply axial loading to the foot, whilst rotating the tibia
- A positive test is indicated by pain, clicking or popping sensation in the joint, or restriction of rotation
- A positive test indicates likely meniscal injury
Further special tests
- Assesses an fixed flexion deformity. As the patient to lie with their legs flat. If the knee does not fully extend, then there is fixed flexion deformity. Often occurs due to tight hamstrings in sportsmen and women. The calf will often not touch the couch. As you try to passively extend the leg, the resistance will come on gradually.
- Locked knee – as you try to passively extend the leg, resistance will occur suddenly. Often due to debris in the knee joint (e.g. meniscal tear) – requires urgent orthopaedic attention.
- Ask the patient to flex knee, and then life the heel off the couch. If the quadriceps is weak, there will be a delay before the heel lifts. This is called quadriceps lag. Compare both legs