Learning Outcomes: Students will be able to:
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The knee joint complex consists of the Tibiofemoral joint (ginglymus/hinge joint) and the Patellofemoral joint (Arthrodial/gliding joint). The primary joint is the Tibiofemoral joint which is the articulation between the medial and lateral condyles of the femur and the medial and lateral plateaus of the tibia.
Closed Pack Position: Fully extended Open Pack Position: Flexed 25º
The Fibrous Joint Capsule of the knee joint extends from the distal femur to the proximal tibia. As such, when there is knee trauma the pattern of swelling can aid in determining what structures are damaged. Effusion: Intra-capsular tissue damage: Swelling will involve the entire knee and extend above the knee cap. Edema: Extra-capsular tissue damage: Swelling will be more localized. The capsule of the knee joint is somewhat lax allowing for significant range of motion. Therefore, it is reinforced by many ligaments, muscles, and fascia. They are:
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Joints and Connective Tissues of the Knee | |
Joints Tibiofemoral (ginglymus or ginglymotrochoidial) Patellofemoral (arthrodial) Ligaments Tibial (Medial) Collateral Ligament: A flat broad band ligament that attaches from the medial epicondyle of the femur to the proximal medial condyle of the tibia. (also has a medial meniscus attachment) This ligament becomes taut during knee extension, protecting against a valgus stress to the knee. Fibular (Lateral) Collateral Ligament: A cord-like ligament that attaches from the lateral femoral epicondyle to the styloid process of the head of the fibula. This ligament also becomes taut during knee extension, protecting against a varus stress to the knee. | Figure 2 |
Joints and Connective Tissues of the Knee cont . . . . |
Anterior Cruciate Ligament: Connects the anterior aspect of the intercondylar eminence of the tibia; runs superiorly, laterally, and posteriorly to attach to the medial aspect of the lateral femoral condyle. This ligament protects against anterior displacement of the tibia on the femur, and conversely, posterior displacement of the femur on the tibia. It also tightens on knee extension limiting hyperextension, and also extreme knee flexion. Provides rotary stability. Posterior Cruciate Ligament: Connects the posterior aspect of the intercondylar fossa of the tibia; runs superiorly, medially, and anteriorly to attach to the anterolateral aspect of the medial condyle of the femur. This ligament protects against posterior displacement of the tibia on the femur, and conversely, anterior displacement of the femur on the tibia. It also tightens on knee flexion. Provides rotary stability. Oblique Popliteal Ligament: Attaches posteriorly from the lateral femoral condyle to the distal tendon of the semitendinosus muscle. Reinforces the posterior knee joint capsule and resists full knee extension. Medial Meniscus (C shaped): Located on top of the medial tibial plateau. Has attachments to the MCL and capsule. Because of this, its movement is restricted and is more susceptible to injury. Lateral Meniscus (circular shaped): Located on top of the lateral tibial plateau. Has attachments to the arcuate popliteal ligament and popliteus muscle. Able to move more than medial meniscus and is less susceptible to injury. Menisci Both menisci are thicker on their periphery compared to the internal edge of the meniscus and as such serve to deepen the joint to enhance stability, congruency, and to absorb shock. They carry 70% of the weight bearing load on the tibia. Only the outer 1/3 has vascularization and therefore is very poor at healing. The open ends are named “horns” and are secured to the tibia via horn ligaments. Coronary ligaments attach the periphery of the menisci to the tibial condyles. The Transverse ligament attaches the anterior horns of the two menisci to each other. The menisci are somewhat mobile with the greatest mobility occurring in the lateral meniscus. They move posteriorly during flexion and anterior during extension. They tend to follow the femoral condyles during rotation. |
Figure 3 NOTE: ACL injury is often a non-contact event where the foot is planted, a valgus stress is applied at the knee while cutting combined with a later rotation of the knee. Hip adduction and internal rotation often accompanies this injury. Figure 4 |
Knee Joint Movements and Range of Motion |
Flexion: 135° , Extension: 0° Rotation (with knee flexed 30° or more):
Flexion: decreasing the angle between the femur and lower leg, characterized by the heel moving towards buttocks. Extension: increasing the angle between the femur and lower leg, characterized by heel moving away from buttocks. Internal Rotation: rotary movement of the lower leg medially toward the midline. External Rotation: rotary movement of the lower leg laterally away from the midline | Figure 5 |
Screw Home Mechanism: During the terminal degrees of knee extension, the tibia must externally rotate approximately 10º. Purposes: 1) align the femoral condyles with two knee joint menisci, and 2) to situate the foot/ankle so push off occurs at the 1st MTP joint for greater power. The combination of knee extension and external rotation results in tightening of both cruciate ligaments, which locks the knee for greater stability.
Note: The screw home mechanism does not need muscle contraction to occur during knee extension. However, “unlocking” the knee joint to perform knee flexion requires muscular contraction and is primarily accomplished by the popliteus muscle.
Figure 6 | ||
Accessory Structures of the Knee | ||
Patellar Fat Pad and Bursae
Knee Joint Complex Major Bursae
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Figure 7 Figure 8 |
Angulations and Deviations at the Knee Joint | |
Genu Varum (Bow Legged) Medial deviation of distal tibia Potential Causes:
Treatment: Braces, casts, special shoes Possible complications: Early knee arthritis | Figure 9
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Genu Valgum (Knock Knees) Lateral deviation of distal tibia Potential Causes:
Treatment: Bracing, but usually not treated Possible complications: Early knee arthritis | Figure 10
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Genu Recurvatum (Backward bow of legs) Potential Causes:
| Figure 11
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Q Angle (quadriceps angle) | |
The angle formed by the intersection of:
| Figure 12
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Patellofemoral Joint (arthrodial) |
The patellofemoral joint is formed by the articulation between the posterior surface of the patella and the intercondylar groove of the femur. The lateral surface of the patella is shallower than the medial surface of the patella. This is one of the reasons that patellar dislocations occur laterally. Movement of the patella in this groove is referred to as “tracking” and is a nonaxial gliding movement. If the proper sliding of the patella up and down in the intercondylar groove is altered, “improper tracking” will occur and can contribute to a breakdown of the patellar articulating cartilage surface and lead to a condition known as patellofemoral pain syndrome. Contributing factors to this condition include: Weak quadriceps, patella Baja, Q- Angle >20º.
The patella acts as an anatomical pulley, changing the line of pull and increasing the leverage and force that the quadriceps muscle group exerts on its insertion point at the tibial tuberosity. Without the mechanical advantage provided by the presence of the patella the quadriceps muscle group would lose approximately 30-50% of its torque. In addition, the patella’s dense, tough articular cartilage on its articulating surface helps protect against friction that would occur if the tendon itself had to slide across the distal surface of the femur, and is designed to properly tract or glide smoothly in the intercondylar tract.
Patellar Length to Patellar Tendon Length Ration The proper ratio is 1:1 (patella length equal to length of the patellar tendon). Patella Alta: Ratio >1:1 (patellar tendon longer)
Figure 15 Patella Baja: Ratio <1:1 (patellar tendon shorter)
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Figure 16 |
Femoral vs. Tibial Torsion | |
Internal Tibial, External Tibial, Internal Femoral, External Femoral
Step #1: Determine that a torsion is present while subject is standing (patella and feet do not line up) Step #2: Have subject sit on table with feet dangling free.
-Feet point out = external tibial torsion -Feet point in = internal tibial torsion Note: Combinations: Most common is external tibial-internal femoral torsion | Figure 17 |
A Few Knee Joint Review Questions |
you chose the position you did.
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