The sartorius, gracilis, semitendinosus and semimembranosus tendons (with associated bursae) are next palpated. The pes anserinus tendons often become inflamed after overuse. Localised pain with lack of effusion is suggestive of extra-articular causes.

The lateral collateral ligament is palpated. This is running from the lateral femoral epicondyle to the fibular head, being at its tightest in extension. It is rarely torn as a single entity; varus stress on a fully extended knee is the most likely cause of injury.

The lateral joint line is palpated anteriorly to posteriorly. Tenderness anteriorly is common, particularly in bucket handle tears of the lateral meniscus. Mid-joint line tenderness is often due to a ‘parrot beak’ or transverse tear and may be associated with a pseudocyst or cyst. Tenderness posteriorly is often due to a cleavage tear of the posterior horn of the meniscus, and must be differentiated from:

1. Popliteus tendonitis; lack of effusion with lateral pain is suggestive of this condition.
2. The characteristic capsular tenderness seen after an episode of ‘giving way’ due to anterolateral rotatory instability. The joint line may generally be tender due to degenerative disease of the lateral compartment, osteochondral fracture, inflammatory joint conditions, or after an episode of anterior cruciate ligament instability.

The iliotibial band is palpated. This is both a dynamic and lateral stabiliser of the knee, originating as a fascial extension of the tensor fasciae latae and the gluteus maximus muscle, and inserting into Gerdy’s tubercle below the lateral joint line. It is course it runs across the lateral femoral condyle.

In athletes (particularly distance runners, cyclists and skiers), a friction syndrome of the iliotibial band over the lateral femoral condyle can take place, with severe pain on the lateral side of the knee. Contributing factors include genu varum, tightness of the iliotibial band, a prominent lateral femoral condyle and subtalar pronation. The condition often appears after a change of footwear, a sudden increase in the running schedule or prolonged downhill running.

Tenderness over the lateral femoral condyle, increasing with the pressure of extension and 30 to 60 degree flexion of the knee, suggests the diagnosis. Crepitus may also occur.

Ober’s test should be performed to assess iliotibial band tightness; the modified Ober’s test may confirm the diagnosis.

The popliteus is palpated. This is a musculotendonous structure which runs from the lateral femoral condyle to the tibia and deeply into the lateral collateral ligament, with attachments to the posterior horn of the lateral meniscus and the posterior aspect of the fibula.

The popliteus muscle assists the posterior cruciate in retarding the forward displacement of the femur on the tibia at stance, and in maintaining internal rotation of the tibia onto the femur shortly before heel strike and whilst three-quarters through the stance phase. This prevents the lateral femoral condyle from rotating off the lateral tibial plateau. The popliteus also retracts the posterior arch of the lateral meniscus.

The popliteus tendon is best examined in the ‘figure of 4’ position, where it is found just anteriorly to the lateral collateral ligament on the joint line. Pulling the ankle at the buttock in this position often causes pain.

Popliteus tendonitis (lateral pain) is common in runners and mountain climbers, particularly after prolonged downhill work. Pronatory changes in the feet contribute to this condition. It is often difficult to distinguish popliteus tendonitis from a lateral meniscal tear, although lack of an effusion in the joint and the characteristic tender area would point to the former.

The biceps femoris muscle that goes into the fibular head is palpated. The distal tendon may become tender with overuse tendonitis.

The ligaments are examined for laxity. The importance of early accurate assessment of ligament damage must be stressed, particularly as early surgical repair is becoming a recommended mode of treatment for some third degree tears. The following points should again be remembered:

• Comparison with the other side is mandatory prior to confirming the presence of laxity.
• A gentle approach leads to more information.
• Most ligament injuries are combined.
• Laxity may be masked by muscle tightness due to the patient’s apprehension or spasm. If in doubt, the examiner may need to perform the examination under anaesthesia.
• A gross effusion should be drained, to allow accurate assessment of the ligaments. If the fluid drained contains blood, the anterior cruciate is considered torn until proven otherwise. Fat globules in the aspirate indicate fracture of bone.
• Each testing for straight instabilities should be an open/shut or forwards/back movement, so as to assess the degree of laxity.

The following is a summary of Hughston’s classification of instability:

Straight: Medial, lateral, anterior, posterior.

Rotatory: Anteromedial (AMRI), anterolateral (ALRI), posterolateral (PLRI),

combined (usually AL&PL, or AM&AL).

Assessment of instability is important in determining the extent of ligament injury and whether the damaged ligament, once healed, will provide stability to the joint.

In first degree ruptures minimal numbers of fibres of the ligament are torn, with localised tenderness and often swelling, and no laxity on ligament stress.

In second degree ruptures more fibres are disrupted, usually accompanied by an effusion; on ligament stress there is a +1 laxity and the joint surfaces separate up to 5mm. If there is a +2 laxity, the joint surfaces separate between 5-10mm.

In third degree ruptures there is complete ligament disruption, and often no pain on stressing the ligament; the resulting effusion may leak into the surrounding tissues, causing a gross haematoma. Ligament stress testing will show lack of a definite endpoint and a +2 to +3 ligament laxity, with the joint surfaces separating over 10mm. Radiographic examination may show avulsion of a ligament insertion. Stress films are helpful in determining the degree of laxity.

Examination involves abduction and adduction stress tests to the fully extended knee. This should be totally stable due to the tight fit of the femoral and tibial condyles, meniscal wedge effect and taut ligaments. Significant laxity in this position indicates that the posterior cruciate ligament is torn and the collateral ligament stressed.

The medial stabilisers are twofold: the medial capsular ligament and the medial collateral ligament.

The medial capsular ligament is made up of the anterior capsule, the medial capsule and the posterior oblique ligament; it is connected to the coronary ligament, which is made up of a weak meniscofemoral component and a strong meniscotibial component. The medial collateral ligament (tibial collateral) is overlying this, and is phylogenically derived from the adductor magnus tendon, extending from the medial femoral condyle to its distal attachment below the pes enserinus. The fibres are arranged such that parts of the ligament remain taut in all joint positions.

The abduction stress at 30 degrees flexion is performed by holding the femur with the outer hand; as this tests the medial stabilisers, laxity will represent a tear particularly in the medial collateral ligament .

With the leg over the bed for maximum relaxation and the femur stabilised by the innermost hand, the leg is adducted at 30 degrees flexion. The main stabiliser laterally is the collateral ligament (fibula), which runs from the lateral femoral epicondyle to the fibular head. This ligament is taut in full extension, but at 30 degrees it has some laxity which can be confirmed by reaching an endpoint. This can give the inexperienced examiner a chance to detect ‘opening’ and ‘closing’ of the joint, and to actually feel the laxity.

In these tests, a torn meniscus may be compressed and pain elicited. Therefore, pain on compression of the lateral compartment in abduction suggests a torn lateral meniscus, whereas pain on compression of the medial compartment in adduction suggests a torn medial meniscus.