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’
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!).
Look for 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
Scars from previous surgery
Feel the temperature with the back of your hand. If it is warm, state there is a local rise in temperature.
Fell 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.
Bulge test – can be sensitive for a small effusion.
- put 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
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.
- Extension – check both legs. Ask the patient to extend their knee as far as possible. Normally about 10’ of hyperextension is normal.
- Flexion – ask the patient to bring their foot to their bottom. About 140’ is normal.
- 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
- Medial ligament – apply varus force
- 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
- Posterior cruciate ligament - runs from a more anterior aspect of the femur to the anterior posterior of the tibia. Prevents the tibia slipping backwards
- Flex the leg to 30’
- 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 pathology
- 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.
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