Anatomy and Kinesiology
The femur, the patella, the tibia and the fibula form the knee joint cavities [Figure 47]. The patella can in effect be considered a sesamoid bone in the tendon of the quadriceps femoris muscle. The femur and the patella form the patellofemoral joint, the femur and the tibia form the tibiofemoral joint and the fibula and the tibia form the proximal tibiofibular joint. The first two joints have a common joint cavity, the last joint is separated from the first two.
Figure 47
Ventral view of flexed knee (the capsule has been removed and the patella has been folded back distally):
- Patellar ligament.
- Collateral lateral ligament (fibular).
- Lateral meniscus.
- Medial meniscus.
- Collateral medial ligament (tibial).
- Patellar surface of the femur.
- Anterior cruciate ligament.
- Posterior cruciate ligament.
- Lateral condyle.
- Medial condyle.
- Transverse ligament of the knee.
- Articular surface of the patellar.
Proximally, the lateral and medial condyles can be distinguished on the tibia, with their joint surfaces separated by the intercondylar eminence of the tibia. The tuberosity of the tibia is located on the proximal anterior side. The proximal end of the fibula is referred to as the head of the fibula. Distally, the medial and lateral condyles can be distinguished on the femur. On both femoral condyles an epicondyle (medial and lateral) can be distinguished.
Both the medial and lateral compartment of the tibio-femoral joint contain a mensicus (medial and lateral). These menisci partially fill the space that arises due to incongruence of the femoral and tibial joint surfaces. Only the ‘central’ cartilaginous parts of the condyles are in direct contact with each other.
The anterior horn and posterior horn of both menisci are attached to parts of the intercondylar tibial eminence. Both anterior horns are also connected to each other via a transverse ligament of the knee. The medial meniscus is connected to the tendon of the semimembranosus muscle, and the lateral meniscus is connected to the tendon of the popliteus muscle. Some people assume that these muscles are pulled backwards when the knee is bent. The lateral meniscus posterior horn is usually connected by a ligament to the femoral insertion of the posterior cruciate ligament (anterior meniscofemoral ligament or posterior meniscofemoral ligament) [Figure 48].
Figure 48
Cross section of right knee joint:
- Patellar ligament.
- Transverse ligament of the knee.
- Medial meniscus.
- Lateral meniscus.
- Anterior cruciate ligament.
- Posterior cruciate ligament.
- Posterior meniscofemoral ligament.
The medial collateral ligament is located on the medial side of the knee and runs continuous with the joint capsule and the medial meniscus. The lateral collateral ligament is located on the lateral side. This last ligament is not continuous with the joint capsule and the lateral meniscus. The two cruciate ligaments are located between the femoral condyles and the intercondylar space outside the synovial membrane and therefore, outside the joint cavity.
The anterior and posterior cruciate ligaments are distinguished. During exorotation of the tibia on the femur, these cruciate ligaments rotate away from each other and consequently come to lie fairly parallel to each other. During endorotation of the tibia on the femur, the cruciate ligaments rotate towards each other.
The patella lies as a sesamoid bone in the tendon of the quadriceps femoris muscle (distally from the patella: the patellar ligament). The dorsal side of the patella is V-shaped as is the patellar surface of the femur. The joint cartilage is located on the inside of the patella. With this so-called articular patellar surface, the patella slides over the patellar surface of the femur cranially when the knee is extended and caudally when the knee is flexed (the patellofemoral joint) [Figure 47]. The congruence of both V-shaped joint surfaces is largest in the flexed position. The patella can then slide the least with respect to the femur. The patella does not articulate with the tibia. The medial and the lateral retinaculum connect the patella to the tibia. The patella has the tendency to move laterally, particularly during flexion. The strength of the vastus lateralis muscle is transferred via the lateral retinaculum to the lateral side of the patella and the lateral condyle of the tibia. The strength of the vastus medialis muscle is transferred via the medial retinaculum to the medial side of the patella and the medial tibial condyle. The patellar ligament proceeds from the apex of the patella to the tibial tuberosity. The infrapatellar adipose body (also known as Hoffa’s fat pad) is located behind this ligament and disappears in the joint cavity during flexion and protrudes on both sides of the patellar ligament during extension.
The popliteal fossa is located on the posterior side of the knee, the hollow of the knee. This is a diamond-shaped space enclosed proximally by the hamstrings and distally by the gastrocnemius muscle (and the plantaris muscle). It consists of lipid-rich connective tissue containing the popliteal artery and vein, continuations of the sciatic nerve and several lymph nodes. The posterior joint capsule of the knee is located more deeply.
Various bursae can be distinguished in and around the knee:
- The suprapatellar bursa or recess (protrusion of the joint cavity between the femur and the tendon of the quadriceps femoris muscle); this bursa always has an open connection with the joint cavity.
- The subpopliteal recess (protrusion of the joint cavity under the origin of the popliteal muscle), which also has an open connection with the joint cavity.
- The deep infrapatellar bursa (distal from the patella, between the patellar ligament and the tibia proximal to the tibial tuberosity).
- The superficial infrapatellar bursa (distal to the patella, between the skin and the patellar ligament).
- The prepatellar bursa (between the skin and the patella).
- Bursae are also usually located between the periosteum of the femur and the tibia and the tendons of the semimembranosus muscle, femoral biceps muscle, gastrocnemius muscle and the pes anserinus, respectively.
The movement possibilities of the knee are:
- Flexion (about 135°).
- Extension (about 0°).
- Endorotation (about 10°): with 90° flexion of the knee.
- Exorotation (about 10°): with 90° flexion of the knee.
The clinically most important muscles that have a functional effect on the knee are:
- Quadriceps femoris muscle (rectus femoris muscle, vastus lateralis muscle).
- Vastus medialis muscle and vastus intermedius muscle (in particular extension).
- Gastrocnemius muscle and plantaris muscle (in particular flexion).
- Biceps femoris muscle (in particular flexion and exorotation).
- Sartorius muscle, gracilis muscle, semitendinosus muscle and semimembranosus muscle (in particular flexion and endorotation).
Terminology
Genu Varum
Bow-leggedness, in other words with an extended leg the upper and lower leg form an obtuse angle that opens out in the medial direction. In clinical terms, the distance between both femoral condyles (intercondylar distance) is relevant. This should be measured when the patient is lying down. If this distance is greater than 8 cm, genu varum is present. Treatment is mostly indicated for a distance > 10 cm.
Genu Valgum
Knock-knees, in other words with an extended leg the upper and lower leg form an obtuse angle that opens out in the lateral direction. In clinical terms, the distance between both medial malleoli (intermalleolar distance) is relevant. This should be measured when the patient is lying down. If this distance is greater than 8 cm, genu valgum is present. Treatment is mostly indicated for a distance > 10 cm.
Genu Recurvatum
Hyperextended leg or a knee joint that bends backwards. Upon sideways inspection, the upper and lower leg form an angle that opens out in the anterior direction. This can be determined on the basis of an imaginary vertical line between the greater trochanter and the lateral malleolus. In the case of a ‘normal’ extended leg, this line passes through the fibular head whereas in a hyperextended leg, this line runs in front of the fibular head [Figures 55a, 55b].
Postural Knock-Knees
Functional knock-knees resulting from exorotation at the hip joint, combined with hyperextension in the knee joint. The patellae therefore, ‘point’ laterally.
Postural Bow Legs
Functional bow legs resulting from endorotation at the hip joint, combined with hyperextension in the knee joint. The patellae therefore, ‘point’ medially.
Quadriceps Angle
This is a cranially directed angle between two imaginary lines. One line runs from the anterior superior iliac spine to the middle of the patella, and the other line runs from the tibial tuberosity over the middle of the patella. For men, this angle may be about 10° and for women about 20°. The greater this angle, the greater the force with which the patella will be pulled laterally, which can result in palletofemoral complaints (in particular retropatellar chrondopathy) [Figures 49, 50].
Figure 49
Figure 50
Figures 49 and 50 Anterior view of the skeleton (male).
1. Imaginary connecting line between anterior superior iliac spine and middle of the patella.
2. Imaginary connecting line between tibial tuberosity and middle of the patella.
The angle formed by these two imaginary lines is called the ‘Q-angle’.
Bonnet’s Position
Favoured position of the knee joint in the case of substantial fluid accumulation or haemarthrosis. The patient will favour holding the knee in a flexed position (about 20-30°), as this creates the most space within the joint capsule.
Locked Rotation
Due to the specific shape of the tibia and femoral condyle joint surfaces, rotations occur during the flexion and extension of the knee. When the knee is flexed from a position of maximum extension, endorotation (about 10°) of the tibia on the femur occurs. During extension from the position of maximum flexion, exorotation (about 10°) of the tibia on the femur occurs. The tibial tuberosity and femoral condyles can be used as reference points for this.
Medial Plica
A fold of the synovial membrane between Hoffa’s pad and the medial capsule. It may cause a snapping sound during movement of the knee as a result of the plica sliding over the medial femoral condyle during flexion and extension.
Meniscus Cyst
Degenerative firm protrusion of the meniscus, mostly laterally in the joint space.
Baker’s Cyst
Sack-shaped protrusion of the synovial membrane in the adipose tissue medially in the hollow of the knee (popliteal fossa). The cyst is palpable as a fluctuating swelling.
Misalignment Syndrome
Abnormal tracking of the patella, which could represent a biomechanical cause for palletofemoral complaints.
Internal Derangement of the Knee
Blockage of movement in a certain direction due to entrapment of a loose part of the meniscus, as the result of a major rupture of the meniscus, for example. Accompanying fluid accumulation or haemarthrosis is typical for this complaint.
Ballottement of the Patella
When a person is lying down with extended legs, the patella cannot normally be pushed downwards as it is already lying on the femoral condyles. However, if fluid is present in the knee cavity, the patella will spring upwards again if an effort is made to push it onto the femoral condyles (‘floating’ or ‘dancing’ of the patella).
Lateral Patellar Dislocation
Lateral ‘tracking’ of the patella on the patellar surface of the femur during flexion and extension of the knee.
Referred Pain
The patient indicates pain at a location other than where the cause of the pain is located. For knee complaints the complaints are mostly indicated locally. Pain originating from a back or hip condition can be felt in the knee. In children with knee complaints, the possibility of hip complaints must always be considered and a basic function examination of the hips should always be performed.