Knee examination

In normally aligned legs, with the patellae pointing forwards, the knee and ankles should be gently touching together (FIG 1).

Fig 1. Examination for leg alignment in the static standing position

Varus (bowlegged) or valgus (knock-kneed) alignment is noted and the presence of increasing deformity as a lateral or medial thrust on walking is also checked for (FIG 2).

Fig 2. Lateral thrust of the Right knee on walking, indicating malalignment.

Mal-alignment may also be rotational. In normally aligned legs when the patella points forward then the feet should also point forward, nearly in parallel. There is clearly a wide range of what is normal and mild varus or hyperextension, for example, may be a physiological variant of normal.

Squinting patellae occur when the feet point forward but the knees squint towards each other representing abnormal femoral and tibial torsion. Isolated external tibial torsion may be noted if the patella points forward but the feet point outwards more than 10 –150.

If the patients’ complains of instability then it may be useful to ask the patient to demonstrate the direction they feel the knee moves into. This may elicit lateral or postero-lateral instability.

b. Supine

Examination supine involves a combination of look, feel and move. In order to look properly we need to feel the knee aiming to detect and confirm specific appearances and problems.

General inspection: This takes into account evaluating alignment, position of the knee, skin problems, scars, muscle wasting, bruising for site of trauma, and the manner in which the knee is held.

Presence of effusion: This may be obvious due to loss of the usual divot or dent on the medial aspect of the patella or it may need to be detected by the bulge test. In this test the flat palm of the examiners hand milks fluid from the medial side via the suprapatella pouch into the lateral gutter. This collection of fluid is then sharply pushed back to the medial side by stroking the lateral gutter with the back of the hand eliciting a bulge on the medial side. Squeezing the suprapatella pouch with one hand and balloting the patella may elicit the patella tap sign (FIG 3).

Fig 3. Patella tap sign, bouncing the patella off the trochlea to demonstrate effusion

• Fixed flexion deformity: The patient may be holding the knee in a flexed posture indicating true locking or pseudo locking due to pain. The knee can be gently straightened to full hyperextension looking for any loss compared to the other side. Full passive extension is determined by holding the knee flat and lifting the foot and heel off the couch – quantifying any difference between the two knees by number of fingerbreadths heel height difference. An alternative measure is heel height difference in cm on prone lying with the distal thigh supported by the couch (FIG 4).

Fig 4. Measuring heel height difference in prone lying to record loss of knee extension

Assessing extension in the acutely injured knee: In the acute phase initially resting the knee over a pillow to encourage the muscles to relax and then gradually lifting the heel off the couch can allow detection of any true loss of extension. Pain felt over the medial aspect while achieving full extension indicates MCL injury rather than meniscal locking. Simply holding the legs by the heels may also detect a difference in knee height.

Range of movement (ROM): After trying to detect loss of extension it is useful at this stage to examine for flexion, partly because the patient is expecting the knee to be moved but mainly because this will elicit how painful the knee is and therefore guide the remainder of the examination. In the obviously arthritic knee, range of movement is the most important sign and palpation of tender points less so. By convention ROM is expressed by three numbers: hyperextension or recurvatum, active extension and flexion eg 5/0/135.

2. Specific examination

a. The patello-femoral joint and extensor mechanism

Inspection of the patello-femoral joint is initially best performed with the patient sitting with the leg flexed over the edge of the couch, noting the following features or signs.

Position of the patellae: The patella normally faces forward and slightly up. Facing higher indicates patella alta, and lower indicates patella baja.
Position of the tibial tubercle: This should be directly inferior to the centre of the patella. Inspection gives a guide to the tibial tubercle trochlea groove (TT-TG) offset that is more formally quantified on CT or MRI scanning.
Patella tracking: On active extension the patella should track centrally toward the groin. Tracking laterally in extension as an inverted J-sign indicates lateral subluxation in extension and potential or real patella instability.
Feeling the articulation: Holding the hand gently over the patella detects crepitus.

With the patient lying supine the following tests can be performed:

Fig 6. The apprehension sign, illustrating nervousness of the patient when attempted subluxation is gently performed

Patello-femoral compression. Examined by compressing the patella into the groove and rocking the knee into flexion and extension, eliciting pain, catching, crepitus or bare-bone grinding.

Patella tendon movements. Tethering of the patella to the anterior tibia will reduce medial/lateral movement of the patella tendon.

With the knee flexed at 90deg, the knee is further examined.

• Palpation for trigger points (FIG 7)
• Fat pad tenderness either side of the patella tendon
• Lateral IT band syndrome. Deep tenderness 2cm proximal to the lateral jointline over the lateral epicondyle. This is then confirmed with the patient standing, facing away from the examiner and palpating over the lateral epicondyle while asking the patient to mini squat.
• Capsular irritation over a prominent osteophytic edge of the articular surface may be noted
• Tender nodules or points representing a neuroma or painful scar

b. Examination of the menisci

This is best performed with the knee flexed at 90 degrees. Both hands may be needed to palpate the specific trigger points around the knee while supporting the leg with the other hand. It is useful to ask the patient to indicate where the pain is felt, as meniscal problems tend to be point specific where as degenerative problems are more vague in distribution.

Palpation

• Meniscal tenderness: Palpation for tender trigger points involves targeted pressure over specific areas. Meniscal tenderness is particularly deep and therefore takes a fair amount of force, usually pushing the pulp of two fingers or sometimes the thumb to elicit the pain.
•  Medial meniscal tenderness is classically on the posteromedial part of the joint line (FIG 8).

Fig 8. Medial joint line tenderness – felt at the posteromedial part

•  Lateral meniscal tear tenderness is on the midlateral aspect (FIG9).

Fig 9. Lateral joint line tenderness is felt in the mid lateral part of the joint, also by deep firm palpation

• Swelling: An associated fullness or obvious swelling may be sensed due to either an associated cyst (usually lateral) or sometimes the flap of a meniscus (typically medial). Lateral meniscal cysts stay at the level of the joint line and tend to be very hard – enough to be mistaken for bony lumps. Medial cysts tend to be just below the joint line.

Pain on movement

• Meniscal pain on full flexion. Pressure on the meniscus is increased in full flexion and may be resisted by the patient
• McMurrays test. In this test rotation in forced flexion with compression over the medial joint line is positive if it elicits a clunk from a torn meniscus as the test was originally described. It is less reliable if used with simple detection of pain. (FIG 10).

Fig 10. McMurrays test performed holding the knee to achieve full flexion and by applying rotational movements by grasping the heel.

• Squat or duck walking. This mimics McMurrays manoeuvre, compressing the menisci in deep flexion. The patient is asked to squat and walk or waddle a few steps, eliciting their characteristic pain. This can be a very useful confirmatory test.
• Apleys grind test. This is less commonly used but the patient is positioned prone, the knee flexed to 900 and the tibia ground into the femur looking for pain from a meniscal tear.

c. Examination for ligament instability

The following ligaments or ligament complexes can be examined individually or in combination and the pattern of instability determined:
Collateral ligaments
Anterior Cruciate ligament
Posterior Cruciate ligament
Postero lateral corner
Postero-medial corner

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 90deg, 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 (FIG 11). 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.

Fig 11. Assessment of the collateral ligaments, achieved by cupping the knee and then applying medial and lateral movements of the leg by grasping the heel. The fingers and the palm are used as a fulcrum.

• 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

Fig 13 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 (FIG 14), 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

Fig 14. Anterior Draw test. The examiner sits just against the foot and exerts anterior pull on the tibia, holding the hamstrings out of the way with the index fingers while gripping the tibia with the palm of the hands

The Posterior Cruciate ligament acts to resist posterior translation of the tibia. Laxity is best examined with the knee at 90 degrees.

Posterior sag

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 (FIG 15). 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.

Fig 15 X-ray packet sign showing normal gap between the edge and the patella (b) and the loss of gap (c) in PCL insufficiency

Posterior draw test

With the knee at 800 – 900 degrees the tibia is pushed posteriorly to detect any increased posterior translation (FIG 16). 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.

Fig 16. Posterior draw test. The tibia is pushed posteriorly and the thumb is used to feel the step off between the tibial margin and the exposed articular end of the Femur

The step off sign

This is perhaps the most useful sign in detecting PCL laxity as it also helps to determine treatment. FIG 17 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.

Fig 17. The Step off sign classification in determining the amount of loss of the normal anterior position of the tibia in relation to the femur

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.

Fig 18. Dial test demonstrating increased external rotation of the left tibia at the knee joint

Lateral hypermobility at 90deg

With the knee at 90deg 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. (Fig 19)

Fig 19. Testing increased rotation externally of the tibia by rotating the tibia and noting the position of the tibial tubercle and the fibula head

Spin test

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 (Fig 20).

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 (FIG 21). This is a difficult test to perform reliably.

Fig 20. External Recurvatum test: the leg is picked up by holding just the big toe and the knee is seen to drop into varus, external rotation and hyperextension, indicating injury to the postero-lateral structures

d. Examination for arthritis or joint surface damage

The hallmark signs when examining for joint surface damage are signs associated with higher friction, felt on moving one joint surface on its opposing surface under compression.

Fine crepitus

Crepitus on joint movement can be heard but it usually needs to be felt. Active movement loads the joint and the examiner places a hand over the moving part, either feeling with the fingers or the flat of the palm.

Other noises

Popping, snapping or clunking may be felt on movement under load. The characteristic of these noises needs to be noted with specific reference to whether the sensations remind the patient of their symptoms. Many knees will make some form of noise on moving and painless noises are generally considered ‘safe’.

Bare Bone crepitus.

When two bare bone surfaces are forcibly compressed together then there is very high friction and the surfaces momentarily stick together before sliding in a juddering fashion. This sign has been described as the pepper mill sign for obvious analogous reasons. When the patient admits this is what happens when getting up from a chair or on stooping, giving them a feeling of not trusting the knee, then it confirms the extent of their osteoarthritis – even if subsequent x-rays still seem to show the presence of a gap between the surfaces.

It is worth remembering that on the medial compartment the worn surface is most at about 30 degrees flexion, in the lateral compartment wear is at slightly greater flexion. In the patello-femoral joint it is the lateral patella facet and trochlea groove that are most commonly affected.

Table 1: groups of diagnostic signs