Specific examination- ligament instability
- The following ligaments or ligament complexes can be examined individually or in combination and the pattern of instability determined:
Anterior Cruciate ligament
Posterior Cruciate ligament
Postero lateral corner
i) Collateral ligament examination
Understanding the anatomical structure and attachments of the collateral ligaments is important for accurate examination. The MCL is a fan shaped ligament radiating from the medial epicondyle on the femur to a broad attachment on the tibia whereas the LCL is a cord like structure from the lateral epicondyle to the head of the fibula. Tenderness following acute injury is examined with the knee at 900, applying deep palpation over the epicondyles and, for the MCL, over the tibial attachment.
Laxity and pain on stressing the collateral ligaments is detected at full hyperextension, 0 degrees extension and at 30 degrees with the purpose of detecting a difference to the other side. The patient should be asked whether the movement feels the same.
For detection of movement the knee is cupped by one hand using the fingers and the palm alternately as a fulcrum against the epicondyles, and the leg is levered to the side by firmly grasping the heel . Sometimes there is a clunk when pressure on the leg is removed and the joint closes again, reproducing any characteristic feeling of instability. Flexion beyond 20 – 30 degrees will result in rotation at the hip rather than opening of the knee.
Integrity of the LCL can be checked by palpation in the ‘figure four’ position, feeling the chord like structure running from fibula head to femur.
ii) Anterior Cruciate ligament examination
Again the purpose of examining the ligament is to detect asymmetry with the other side. Various methods need to be known in trying to get the patient to relax. Traditionally it is thought that it is difficult to diagnose ACL insufficiency in the awake patient due to voluntary and involuntary contraction of the hamstring tendons, which act as the main posterior dynamic restraint to the knee. This section outlines the detailed method for accurately detecting laxity of the ACL but, of course laxity may not necessarily mean that the patient has a non-functional ACL.
TABLE: Tips to encourage a patient to relax for ligament examination
- Resting the knee over a pillow at 10 – 15 degrees – this is useful in the acute injury stage as it keeps the thigh supported.
- Using a multitude of words of encouragement, not just relax!, relax!, relax!, expressed by the examiner with increasing anger.
- Repeated examination coming back to the stability tests after completing other parts of the examination
- Resting the patient in such a way that the patient can still see what is happening to their knee. They are naturally anxious, know it hurts, and actively lifting the head increases quads and hamstring activity.
- Repeatedly put the knee down and roll it on the couch to encourage the muscles to let go.
- Distraction with conversation
This detects increased AP movement in the knee at 10 – 15 degrees flexion i.e. when the posterior aspect of the knee is held a hands breadth off the couch. This Image shows positioning of the hands to exact a true anterior pull of the tibia on the femur, avoiding any rotational pull. The fingers of the lower hand should be directly posterior and the thumb of the upper hand directly anterior. The patient is encouraged to relax and firm AP force is applied, pushing back with the thigh hand and pulling forward with the tibial hand.
The test detects a difference between the two knees, assuming the other knee is innocent. The patient will often be able to tell the examiner if there is a difference. Two differences are sought:
- Increased anterior movement – it doesn’t matter how much, just that it is different to the other knee
- Quality of the end point: hard end point, indicating some fibres may be intact, or soft endpoint.
If the thigh is too big for the examiners hand then the thigh can be supported over the examiners own flexed knee at the same 15 degree flexion position. The thigh hand is then clamped on top of the patients thigh and the tibial hand used to exert the anterior force.
Pivot shift test
The pivot shift test is pathogmonic of ACL deficiency. In patients with recurrent giving way due to ACL injury it reminds them of the unpleasant feeling and this expression needs to be asked for, sometimes by asking the direct question ‘does this reproduce your feeling of instability?’
Various methods have been described and all involve supporting the tibia, applying valgus stress and flexing or extending the knee. Without adequate support the test can be very painful prohibiting either the first go or certainly any other attempt.
The method described here is painless and easily reproducible. It takes into account an understanding of the function of the ACL and three key observations:
- Abnormal sliding of the tibia on the femur occurs at around 20 degrees of flexion, not any more.
- The patient can relax their hamstrings by actively extending the knee contracting the quads,
- With the tibia adequately supported, the femur can drop posteriorly away from the tibia
Technique of the Patient Assisted Pivot shift test
The next image shows how the tibia is supported, between the examiners side and over the examiners forearm. The hand is then interlocked over the wrist of the other hand, which is applied against the lateral aspect of the proximal tibia and fibula. This is an active test involving participation of the patient. Initially their confidence is obtained by asking them to flex their knee from extension without the examiner applying any force on the leg.
Once the patient is comfortable the examiner then flexes the passive leg by lifting from the patients posterior calf. This exerts an anterior force on the tibia at the knee and in a positive test the tibia is felt to slide or jump back into place as the knee bends. This can be an obvious clunk or a subtle glide. To emphasise the test looking for reproduction of the patients distrust of their knee, increasing load is applied, both in valgus and by in-line compression, loading the lateral compartment to exaggerate the sliding of the femur over the dome of the lateral tibial plateau.
To encourage the patient to relax their hamstrings and to allow the femur to fall posteriorly, the patient is asked to push down on their knee straightening it. As it goes nearly straight the hamstrings have to relax and the examiner can push up again on the tibia eliciting the subluxation of the tibia on the femur as it goes back into flexion.
Anterior draw test
This test, in which the tibia is pulled anteriorly with the knee at 90 degrees , is much less reliable in the detection of ACL insufficiency. Probably its main purpose is to position the knee so that the step off sign for PCL insufficiency and posterior sag can be detected (see later section). The examiner sits against the foot and the palms grip the sides of the tibia exerting a strong anterior pull. The index fingers of both hands are used to ‘knock out’ posterior pull by the hamstrings. As for the Lachmans test, it is the difference from the other side that is important.
Active quads test
In this test the thigh is supported on a support such as a rolled up towel and the examiner gently holds the foot on the couch. The patient is asked to try to lift the foot off the couch and the tibia is seen to move anteriorly. Though very useful in the acutely injured knee this test is also positive in PCL injury as the tibia is pulled forward into its normal position.
iii) Posterior Cruciate Ligament examination
The Posterior Cruciate ligament acts to resist posterior translation of the tibia. Laxity is best examined with the knee at 90 degrees.
When both knees are viewed from the side, any sagging back of the tibial tubercle and upper tibia is noted as posterior sag. A straight edge such as an X-ray packet may be useful to demonstrate subtle sag . The edge is placed against the tibia just above the ankle and on the tibial tubercle. There should usually be a gap between the straight edge and the patella – any difference between the two knees indicates posterior sag.
Posterior draw test
With the knee at 800 – 900 degrees the tibia is pushed posteriorly to detect any increased posterior translation . The tibia needs to be pulled anteriorly to detect a firm endpoint from the ACL and to determine a starting point for the tibia otherwise, especially in chronic laxity the tibia tends to sit as far posteriorly as it can.
The step off sign
This is perhaps the most useful sign in detecting PCL laxity as it also helps to determine treatment.This image shoes the three grades based on the observation that as the examiners thumb is slid up the tibia there is usually a step-off ‘down’ to the anterior aspect of the exposed medial aspect of the femur. Grade II means the tibia is flush with the femur. The importance is that when grade III is detected (tibia posterior to femur) there is likely to be injury to the posterolateral corner. Note that this test was described by LARSON as a step ‘off’ and not a step ‘on’.
Posterior lachmans test
Increased posterior sag can also be detected at 150 – 200 flexion when the tibia is pushed posteriorly in relation to the femur.
iv) Postero-lateral corner examination
Injuries to structures of the postero-lateral corner results in increased external rotation of the tibia on the femur. Injuries can be isolated or in conjunction with PCL or ACL injury. Examination of this area is not easy and often the results of several tests are assimilated to decide on the final picture. The tests are unfortunately very subjective and are not easily taught. Different examiners provide differing amounts of rotational force and it is often difference in the quality of the end point of movement that indicates abnormality.
Dial test at 300 and 900
This is probably the easiest way to detect increased external rotation. The patient can be supine or prone (FIG 18), but prone is probably more accurate. The examiner supports the feet while an assistant keeps the knees together, to eliminate femoral rotation. The feet are rotated externally with equal force and the resultant ‘dialed’ position is then noted, looking for greater than 15 degrees difference to register as abnormal. Any element of rotation at the mid foot is minimised by trying to keep the ankle at neutral and by gripping the hind foot. The test needs to be performed at both 30 and 90 degrees of knee flexion.
Increased external rotation at 30 degrees suggests an isolated postero-lateral corner injury whilst increased external rotation at 30 and 90 degrees suggests injuries to both the postero-lateral corner and posterior cruciate ligament.
Lateral hypermobility at 900
With the knee at 900 the knee is rotated by gripping the proximal tibio-fibular joint and pushing it posteriorly in order to detect an increase in mobility compared to the other side joint. This indicates increased postero-lateral mobility of the knee.
This is similar to the dial test but is performed with the patient sitting on the edge of the couch. The examiner spins out the tibia while the patient keeps their knees together. Again the aim is to detect increased postero-lateral rotation by feeling and looking at the superior tibio-fibular joint.
External rotation recurvatum test
When the legs are picked up by the big toe or forefoot then the knees should sag back equally. If the PCL and postero-lateral corner are stretched out then the tibia falls into external rotation as the knee goes into hyperextension .
Reverse pivot shift test
This test detects the opposite of the pivot shift phenomenon in PCL insufficiency. The knee is supported in flexion with the foot externally rotated and the knee in compression and valgus. On moving into extension the lateral compartment reduces under the femur with a clunk . This is a difficult test to perform reliably.