SPORTS INJURIES REFRESHER KNEE JOINT

legs straight out. I place a hand on the quads, the other hand under their heel. I test for hyperextension by lifting the heel, keeping the back of the knee in contact with the bed. I examine the end-feel (see bullet point at end of article) - it should be firm. n I then bend the knee to 90o

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Video 2: Examination of hyperextension of the knee

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Video 4: The Lachman test

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Video 3: The anterior draw test

Compare with the other knee. Limitation of hyper-extension usually indicates an intra-articular obstruction to that hyper- extension. Note that an injured MCL will also cause lack of hyperextension. n I then ask the patient to move the heel towards their buttocks. Flexion should cease with the hamstrings abutting the upper gastrocnemius, at approximately 20-30o

. This assesses

the movements of the tibio-femoral joint. An intra-articular problem causes equal limitation of both flexion and extension (this is the capsular pattern of the knee) (2). However the lack of hyperextension is often an early sign of an intra-articular problem. Occasionally the knee is very lax as in hyper-mobility syndrome and hyper-extension may be 20o

plus, so check the other knee. I

observe the position of the patella in full extension (invariably mid-line) and in full

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ACL n Firstly the patient lies on the couch,

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Video 5: Sagging arthritic PCL deficient knee (compare this with a normal knee shown in video 3)

flexion (should be midline), often it glides laterally - a common problem in anterior knee pain (AKP).

Tests

The knee is a ligament-dependant joint. By that I mean the knee in neutral can be kept in place only by the tension of the ligaments. This is opposite to the shoulder which requires a constant background activity of the rotator cuff to remain in a correct neutral position.

testing with an appropriate force. Remember a 17-stone rugby player needs more force that a 6-stone gymnast!

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KEY POINT: Testing the ligaments correctly is vital for correct diagnosis. Remember the knee is tough. It needs

PCL

A posterior cruciate ligament injury is much less common and probably less crucial to diagnose. Often the anterior draw is ‘positive’ as the tibia may slip into a posterior position, the examiner then just pulls it into a normal position, appearing to be a positive anterior draw (video 5). The Lachman test is usually negative, or at least the relative movement of femur and tibia is better appreciated. A confirmatory test is to put the proximal arm underneath both tibial heads, (both knees bent to 90o

)

supporting the feet with the distal arm. The examiner then lets support of both tibial heads go suddenly. The affected

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the foot flat on the bed. I tell the patient then sit on their foot. Facing the knee I place my thumbs on their tibial tubercule and my hands around the proximal end of the tibia. I then give the tibia an exploratory pull gently. I then increase the force and velocity depending on the response (hopefully no pain). The tibia will often move anteriorly 0.5-1cm normally (you can always check the other knee to establish normality). A complete rupture of the ACL may allow the tibia to move anteriorly 2-4cm without pain. An injured ACL is usually painful, even without shift. This test is known as the anterior draw test (video 3). n A more accurate test for the ACL is the Lachman test. This involves securing the femur with the proximal hand, placed across the quads, just proximal to the patella. The distal hand is cupped behind the tibial head grasping the gastrocnemius muscle. A sharp jerk forward is given by the distal hand looking for anterior shift of the tibia or pain (video 4). The end-feel should be firm/strong. n Performed in this order neither type of ACL injury should be missed. This is vital as the ACL is considered the key internal ligament of the knee. If the leg being examined is too large to hold, lay the thigh flat over the side of the couch and repeat the procedure. This is often easier with a large patient and a petite doctor!