The knee joint is the largest synovial joint in the body, primarily allowing flexion and extension, but also some degree of internal and external rotation in the flexed knee (as a modified hinge joint). The joint consists of two articulations: the tibiofemoral and patellofemoral joints. The articular surfaces are covered by a thin layer of hyaline cartilage, and two articular disks (the medial and lateral menisci) partly divide the tibiofemoral joint spaces. The peripheral outer thirds of the menisci are vascularized to some extent in adults (the “red zone”), but the central inner two-thirds (the “white zone”) are completely avascular ( ▶ Fig. 6.1a–c).
Fig. 6.1 (a–c) The knee joint.
The knee joint is stabilized by several extra-articular and intraarticular ligaments. The medial collateral ligament (MCL) is composed of two distinct parts, originating around the medial femoral epicondyle. The superficial part (sMCL) is an extra-articular ligament, with the fibers inserted around 5 cm below the joint line, next to the pes anserinus. The deep part (dMCL) is a capsular reinforcement, with the fibers inserted into the medial tibial condyle just below the joint line. The primary function of the MCL is to protect the knee from being bent open by stress applied to the lateral side of the knee (i.e., a valgus force).
In contrast, the lateral collateral ligament (LCL) is a complete extracapsular ligament running from its origin near the lateral femoral epicondyle to the head of the fibula. It protects the lateral side from being bent open by stress applied to the medial side of the knee (i.e., a varus force). The popliteal arcuate ligament (PAL) originates on the apex of the head of the fibula, crosses the popliteus tendon, and passes into the posterior capsule. It is an important element of the posterolateral corner (PLC) and acts mainly as a PL stabilizer in conjunction with the LCL. Similarly, the posterior oblique ligament, a distal expansion of the semimembranosus tendon, is the most important element of the posteromedial corner (PMC).
The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are found inside the knee joint. The ACL originates on the anterior intercondylar area of the tibia and inserts into the intercondylar notch on the lateral femur below the lateral transcondylar ridge. It consists of the anteromedial (AM) bundle and the PL bundle. The ACL is the main stabilizer of anteroposterior displacement, but is also important (especially the PL bundle) for rotational stability. The PCL originates on the posterior intercondylar area of the tibia and inserts into the inside of the medial femoral condyle and the notch roof, preventing posterior displacement of the tibia relative to the femur.
Anteriorly, the quadriceps tendon connects the quadriceps muscle group to the patella, and the patellar tendon connects the patella to the tibial tuberosity. Posteriorly, the single muscle in the knee joint, the popliteus muscle, and the neurovascular bundle are found. Laterally, the thick iliotibial band (ITB) covers the vastus lateralis muscle and inserts into Gerdy’s tubercle on the anterolateral tibial plateau. Finally, there are numerous bursae surrounding the knee joint, which can be either communicative (e.g., the suprapatellar bursa) or noncommunicative (e.g., the prepatellar bursa).
6.3 Clinical Examination
More significant knee injuries are sometimes difficult to examine in an acute setting owing to pain, swelling, and muscle spasms. It is therefore important to correctly identify the circumstances of the injury and the mechanisms involved by carefully establishing the relevant history. The examiner should aim to identify the following:
Information Relating to the Point of Injury
If there was player contact when the injury occurred or beforehand.
If the foot was free or planted on the ground.
If the player felt a “snap” or “pop” when the injury occurred.
If the player was able to continue playing or had to leave the pitch, etc.
If the player has previously suffered knee injuries.
If the player has previously undergone knee surgery.
Even when the injury history is more or less typical, 2 ACL injuries are often overlooked in a standard clinical setting ( ▶ Fig. 6.2). This is usually less of a problem in top-level football thanks to the qualified medical support at clubs. 3
Fig. 6.2 Even when the injury history is more or less typical, anterior cruciate ligament injuries are often overlooked in a standard clinical setting
Note: A “snap” or “pop” reported by the player at the incident usually means a ligament tear.
The key factor in injury diagnostics is a careful clinical examination of the joint. This examination should consist of the following:
Evaluation of range of motion (ROM).
Muscle strength tests.
Other knee-specific tests.
6.3.1 Visual Inspection
During the visual inspection, the examiner needs to look for gait disturbance, swelling, hematoma, muscle hypotrophy, lower limb malalignment, etc.
6.3.2 Evaluation of Range of Motion
Footballers’ ROMs vary widely, but habitual hyperextension of up to –10 degrees is sometimes seen, especially among female players. If the player has a pain-free and symmetrical active ROM, the value of additional passive ROM testing is limited.
6.3.3 Muscle Strength Tests
Muscle strength should be evaluated against resistance. This is usually done manually by the examiner, but hand-held dynamometers or other strength testing devices might be of value in some cases.
Always begin your palpation in areas where you have a low suspicion of tenderness. Important anatomical structures to palpate are the patella, the origins and insertions of tendons and ligaments, and the joint line. Additionally, the recesses should be compressed to evaluate any intraarticular effusion, with or without pressing the patella against the femur (“dancing patella” sign).
6.3.5 Laxity Tests
There are numerous manual laxity tests, 4 and it is impossible to be an expert on all of these. Instead, familiarize yourself with six to eight tests and use these routinely each time you examine a knee. It is important to remember that when evaluating laxity, side-to-side comparisons should always be carried out relative to the contralateral knee, which is often better than estimating the actual millimeters of laxity. It is often wise to start the examination with the unaffected knee, to ensure that the player is relaxed; having a relaxed player is imperative if proper laxity testing of the knee ligaments is to be achieved.
The laxity of the collateral ligaments are evaluated using valgus and varus stress tests at full extension and semiflexion (30 degrees). With the patient supine, the examiner holds the ankle with one hand and places the other hand on the lateral or medial aspect of the knee and applies a valgus or varus stress ▶ Fig. 6.3a, b. The tibia should be slightly externally rotated to uncoil the cruciate ligaments. Alternatively, the examiner may secure the lower leg between his/her waist and forearm, and simultaneously palpates the joint lines with the fingertips while the valgus and varus stress is applied. During testing, the opening of the joint line and the quality of the endpoint (firm, soft, or absent) should be evaluated.
MCL and LCL injuries are often graded as follows on the basis of their severity 5:
With a Grade I injury, there is tenderness over the ligament, but no (or only a minimal) increase in laxity (up to 5 mm).
With a Grade II injury, there is a moderate increase in laxity (5–10 mm) with semiflexion, but not extension.
With a Grade III injury, the increase in laxity with semiflexion is gross (>10 mm), without any endpoint, and is also seen, to some degree, with extension.
The grading of gapping in terms of millimeters has, however, been questioned, so this should be used with caution. 6 A practical description of isolated and combined collateral injuries based on the laxity testing can be found in ▶ Table 6.1.
Fig. 6.3 (a, b) Valgus and varus stress tests.
Medial opening with semiflexion
Medial opening with extension
Lateral opening with semiflexion
Lateral opening with extension
MCL intact or MCL injury; PMC intact
LCL intact or LCL injury; PLC intact
MCL and PMC injury
LCL and PLC injury
MCL and PMC injury; possibly ACL and/or PCL injury
MCL and PMC injury; possibly ACL and/or PCL injury
LCL and PLC injury; possibly ACL, PCL and/or ITB injury
LCL and PLC injury; possibly ACL and/or PCL injury
Abbreviations: ACL, anterior cruciate ligament; ITB, iliotibial band; LCL, lateral collateral ligament; MCL, medial collateral ligament; PCL, posterior cruciate ligament; PLC, posterolateral corner; PMC, posteromedial corner.
Anterior Cruciate Ligament
The anterior drawer, Lachman, and pivot-shift tests are all supposed to be routinely used for evaluating the laxity and the integrity of the ACL.
Anterior Drawer Test
The anterior drawer test is performed with the patient supine, the hip flexed at 45 degrees and the knee at 90 degrees ( ▶ Fig. 6.4). The examiner sits on the examination table in front of the knee in question, grasping the tibia just below the joint line of the knee. The thumbs are placed along the joint line on either side of the patellar tendon, and having ensured that the hamstring muscles are relaxed, the tibia is drawn forward. An increased anterior tibial translation and a lack of a firm endpoint indicate either a sprained AM bundle or a complete ACL tear.
Fig. 6.4 Anterior drawer test.
The Lachman test is considered the most sensitive test evaluating the integrity of the ACL, especially in an acute setting ( ▶ Fig. 6.5a, b). It is performed with the patient supine and the knee resting in the hands of the examiner, with around 30 degrees of knee flexion. Once the patient is relaxed, the examiner pulls on the tibia to assess the amount of anterior translation and the quality of the endpoint, as with the anterior drawer test. An increased anterior tibial translation and a lack of a firm endpoint indicate either a sprained AM or PL bundle or a complete ACL tear.
Fig. 6.5 (a, b) Lachman test.
The pivot-shift test is performed with the patient supine and the leg resting in the hands of the examiner with full extension. Once the patient is relaxed, the examiner lifts the leg and rotates it internally, then flexes the knee while applying a valgus stress ( ▶ Fig. 6.6). The pivot-shift phenomenon is caused by anterior subluxation of the lateral tibial plateau with full extension in the ACL-deficient knee, and when slowly flexing and abducting the knee from this position the joint is abruptly reduced at 30 to 40 degrees with a palpable, and sometimes audible, movement or “jerk.” With a Grade I injury, there is a smooth glide with a slight shift; with a Grade II injury, there is a marked shift and reduction; and with a Grade III injury, the tibia is locked anterior to the lateral femoral condyle initially, and there is a dramatic reduction with a gross shift. A positive pivot-shift test indicates either a sprained PL bundle or a complete ACL tear.
Fig. 6.6 Pivot-shift test.
Posterior Cruciate Ligament
The laxity and the integrity of the PCL are usually evaluated using the posterior drawer, the posterior sag, and the quadriceps active tests.
Posterior Drawer Test
The posterior drawer test is considered the most sensitive of these tests and is performed with the patient supine, the hip flexed at 45 degrees and the knee at 90 degrees ( ▶ Fig. 6.7). The examiner sits on the examination table in front of the injured knee, grasping the tibia just below the joint line of the knee. The thumbs are placed along the joint line on either side of the patellar tendon. Ensure that the patient is relaxed, and then move the tibia posteriorly. An increased posterior tibial translation and/or a lack of a firm endpoint indicate either a partial or a complete PCL tear.
Fig. 6.7 Posterior drawer test.
Posterior Sag Test
The posterior sag test is a static test where the patient lies supine with the hip flexed at 45 degrees and the knee at 90 degrees, as in the starting position for the drawer tests ( ▶ Fig. 6.8). The examiner looks at the knees from the side and evaluates any asymmetry in the anatomical positions of the tibias and femurs. A positive test is when the proximal tibia is found to “sag” posteriorly.
Fig. 6.8 Posterior sag test.
Quadriceps Active Test
The quadriceps active test is a dynamic laxity test where the patient lies supine with the hip flexed at 45 degrees and the knee at 90 degrees, as in the posterior sag test. The examiner asks the patient to attempt to slide the foot anteriorly. A “sagging” tibia will move in an anterior direction as a result of the contraction of the quadriceps when the patient attempts to slide the foot.
Posteromedial and Posterolateral Corners
A standard clinical examination of the injured knee joint must also include some tests that evaluate the PMC and PLC.
Slocum Drawer Test
The PMC can easily be tested by means of the Slocum drawer test, which is similar to an anterior drawer test, but with the foot rotated 30 degrees externally. In an ACL-deficient knee, the anterior tibial translation should be less pronounced with the foot rotated externally. Thus, a positive test involves external tibial rotation failing to reduce translation relative to the neutral position.
In this test, the patient lies prone with the knees flexed. While rotating the feet externally, the examiner checks for any asymmetrical external rotation with 90 and 30 degrees of knee flexion ( ▶ Fig. 6.9). The test is considered positive if there is more than 10 degrees of increased external rotation at 30 degrees (suggests PLC injury) and possibly also at 90 degrees (suggests combined PLC and PCL injury).
Fig. 6.9 Dial test.
Note: Certain laxity tests should always be used in a clinical examination of an acutely injured knee: valgus and varus stress tests, anterior and posterior drawer tests, and the Lachman test.
6.3.6 Meniscus Tests
The integrity of the menisci is typically evaluated using specific rotation tests; the most frequently used are the McMurray, Apley, and Thessaly tests. In addition, the knee is usually also moved into hyperextension and hyperflexion.
In the McMurray test, the examiner passively extends the supine player’s knee, starting from a completely flexed position, while simultaneously palpating the joint line and rotating the foot outward to test for medial meniscus damage and inward to test for lateral meniscus damage ( ▶ Fig. 6.10a, b). In a true positive test, there is both pain and clicking in the joint space where the meniscus is damaged. However, clicking is not always observed, and pain is the standard indicator.
Fig. 6.10 (a, b) McMurray test.
In the Apley test, the prone player has the knee flexed at 90 degrees, while the lower leg is rotated inward and outward by the examiner ( ▶ Fig. 6.11). With medial meniscus damage, there is pain over the interior joint space on outward rotation of the lower leg, while lateral meniscus damage is denoted by pain over the lateral joint space on inward rotation of the lower leg. The sensitivity of the test can be improved if the pain is increased while the examiner compresses the joint during lower leg rotation, and can be reduced by traction of the lower leg.
Fig. 6.11 Apley Test.
In the Thessaly test, the player is standing flat-footed with full weight-bearing on the side to be tested. The other leg does not bear weight and is flexed at the knee. The player holds the hands of the examiner in order to keep balance and flexes the knee to approximately 20 degrees. From this position, the player actively rotates the knee inward and outward three times. With meniscus damage, there is pain, and possibly clicking, over the joint space.
Hyperextension and Hyperflexion Tests
Another common strategy involves passively moving the knee into maximum hyperextension and hyperflexion in an effort to squeeze the menisci between the femur and tibia and thereby provoke pain. With hyperextension, the anterior horns are compressed, and with hyperflexion, the posterior horns are compressed.
6.3.7 Patellofemoral Tests
The most frequently used tests in assessing patellofemoral stability are the patellar tracking test, the (manual) patellar translation test, and Fairbank’s patellar apprehension test. 4 In addition, pain from the patellofemoral joint can often be elicited using the grinding test.
Patellar Tracking Test
In the patellar tracking test, the patella might be laterally subluxated in the extended knee at rest, and when the knee is actively flexed, the patella is engaged in the trochlear groove at approximately 30 to 40 degrees of flexion. In mild cases, this is seen as a smooth “jerk,” but it may also present with a gross reduction in which the patella follows a J-shaped path (positive “J sign”).
Manual Translation Test
The manual translation test evaluates lateral patellar hypermobility and is performed with the patient supine and the quadriceps relaxed ( ▶ Fig. 6.12a, b). With the knee extended or slightly flexed, the examiner gently pushes the patella laterally with both thumbs on the medial border of the patella. A translation of more than two quadrants of the patella’s width is usually considered pathological.
Fig. 6.12 (a, b) Patellar translation test.
Patellar Apprehension Test
The patellar apprehension test (sometimes also called the “Smillie test”) is a continuation of the manual translation test where the patient’s reaction is also noted. The test is positive if the patient is uncomfortable and apprehensive or expresses fear that the patella will dislocate. The testing can be reinforced by asking the patient to flex the knee, which will usually result in pain and/or quadriceps muscle contraction to resist the subluxation.
Patellofemoral Grinding Test
Pain from the patellofemoral joint can often be elicited using the patellofemoral grinding test (sometimes also called “Clarke’s test” or “Cleveland’s test”). In this test, the patient lies supine with both knees supported by a kneepad. The examiner presses the patella distally with one hand on the superior border of the patella and then asks the patient to contract the quadriceps muscle. If the patient’s pain is reproduced during this maneuver, the test is considered positive and is indicative of a patellofemoral disorder.
6.3.8 Other Tests
The tests used most frequently to diagnose runner’s knee are the Noble and Ober tests. Occasionally, the popliteus tendon also needs to be examined.
In the Noble test, the patient lies supine with the knee flexed at 90 degrees. From this position, the knee is extended, with concomitant pressure over the lateral femoral epicondyle. If the pain is reproduced at around 30 degrees, the test is considered positive.
The Ober test is used to assess the tightness of the ITB. The patient lies on the unaffected side with the knee flexed at 90 degrees. The examiner then abducts and extends the affected leg while stabilizing the pelvis and, from this position, tries to adduct the leg. The test is considered positive if the leg cannot be adducted and indicates tightness of the ITB.
Popliteus tendon pathology is usually evaluated in the prone position, with the knee flexed at 45 degrees and rotated internally against resistance, with concomitant palpation of the PL joint line. If pain and tenderness are reproduced during this maneuver, the test is considered positive.
6.4 Joint Aspiration
With intraarticular knee injuries (such as ACL injuries, patellar dislocations, and red zone meniscus lesions), the knee joint usually swells up within 6 hours of the injury occurring owing to bleeding (hemarthrosis). Approximately 70% of adult players with blood extravasation in the knee joint after rotational trauma will have damage to the ACL. 7 Consequently, patients with traumatic hemarthrosis should always be suspected of having an ACL injury, even if a clinical examination is difficult to perform in an acute setting ( ▶ Fig. 6.13). Rapid swelling should be evacuated by puncturing the knee joint under sterile conditions for diagnostic, therapeutic, and joint-protective reasons. The aspiration confirms the bleeding, but there might also be fat droplets in the blood, which usually indicates a concomitant osteochondral or bony injury (diagnostic purpose). The patient usually feels instant pain relief after aspiration, since the capsular distension is reduced (therapeutic purpose). Finally, iron from degraded hemoglobin has been shown to be chondrotoxic, 8 so the aspiration might have the effect of protecting the cartilage in the joint, as much of the blood is removed from the knee (joint-protective purpose).
Fig. 6.13 Patients with traumatic hemarthrosis should always be suspected of having an anterior cruciate ligament injury, even if a clinical examination is difficult to perform in an acute setting.