Chapter 10 • Identify the bones and primary bony features of the knee. • Describe the primary supporting structures of the knee. • Describe the planes of motion and axes of rotation for the motions of the knee. • Cite the proximal and distal attachments of the muscles of the knee. • List the innervation of the muscles of the knee. • Justify the primary actions of the muscles of the knee. • Describe the factors that contribute to excessive lateral tracking of the patella. • Explain how patellofemoral joint compression force is increased or decreased relative to the depth of a squatting position. • Describe one biomechanical consequence associated with hamstring tightness. • Explain the principles of active and passive insufficiency with regard to the multi-articular muscles of the knee. • Describe the combined movements at the hip and knee that promote the most effective force production in the hamstrings and rectus femoris. The medial and lateral condyles (from the Greek kondylos, meaning “knuckle”) are the large rounded projections of the distal femur that articulate with the medial and lateral condyles of the tibia. The intercondylar groove is the smooth rounded area between the femoral condyles that articulates with the posterior surface of the patella (Figure 10-2). The intercondylar notch is located on the posterior-inferior aspect of the distal femur, separating the medial and lateral condyles. This notch forms a passageway for the anterior and posterior cruciate ligaments. The medial and lateral epicondyles (Figure 10-3) are palpable bony projections on the medial and lateral femoral condyles, respectively; these projections serve as attachments for the medial and lateral collateral ligaments of the knee. The patella, or knee cap, is a small, plate-like bone embedded within the quadriceps tendon. Because the patella exists within the quadriceps tendon, it is highly mobile and is at risk for abnormal gliding or subluxation. A portion of the stability provided to the patellofemoral joint comes from the fit of the posterior patella within the intercondylar groove of the femur (Figure 10-5, A). The base, or superior pole, of the patella accepts the quadriceps tendon; the apex, or inferior pole, accepts the proximal side of the patellar tendon (Figure 10-5, B). The posterior articular surface of the patella articulates with the intercondylar groove of the femur through medial and lateral facets. The lateral facet is steeper than the medial facet, matching the general shape of the intercondylar groove of the femur (Figure 10-5, C). As illustrated in Figure 10-7, A (and studied in Chapter 9), the 125-degree angle of inclination of the proximal femur directs the shaft of this bone toward the midline, for eventual articulation with the tibia at the knee. Because the tibia is oriented essentially vertically while standing, the articulation between the femur and the tibia does not typically form a straight line. As shown in Figure 10-7, A, the femur usually meets the tibia to form a lateral angle of 170 to 175 degrees (the femur projects 15 to 20 degrees laterally—relative to the tibia). This alignment is referred to as normal genu valgum. Variations of this angle are not uncommon because the knee must adjust to malalignment at either the hip or the ankle. A lateral angle of less than 170 degrees is considered excessive genu valgum, or knock-kneed (Figure 10-7, B). A lateral angle greater than 180 degrees is called genu varum, giving a bow-legged appearance (Figure 10-7, C). Functions and Mechanisms of Injury of the Supporting Structures of the Knee 2. “Dashboard injuries” (i.e., the tibia being forcefully driven posteriorly relative to the femur) 3. Severe hyperextension (with a large gapping of the posterior side of the joint) 4. Large valgus- or varus-producing forces with foot planted 5. Any of the above combined with large torsional force at the knee Table 10-1 summarizes the primary functions of the ACL and PCL, which are illustrated in Figures 10-9 and 10-10, respectively. The medial and lateral collateral ligaments strengthen the medial and lateral sides of the capsule of the knee (Figure 10-11, A). These ligaments are the primary frontal plane stabilizers of the knee, protecting against forces that produce excessive genu valgus. The wide, flat medial collateral ligament (MCL) spans the medial side of the knee between the medial epicondyle of the femur and the proximal medial tibia. The primary function of the MCL is to resist valgus-producing forces (Figure 10-11, B). Some fibers of the MCL attach to the medial meniscus of the knee; therefore, injury to the MCL may involve injury to the medial meniscus as well. The lateral collateral ligament (LCL) is a round, cord-like ligament that crosses the lateral side of the knee, attaching to the lateral epicondyle of the femur and the head of the fibula. The primary function of the LCL is to protect the knee from varus-producing forces (Figure 10-11, C). Internal and external rotation of the knee occurs within the horizontal plane about a vertical or longitudinal axis of rotation. This motion, also called axial rotation, refers to the rotation between the tibia and the femur (Figure 10-17). With the knee flexed, the knee joint permits 40 to 50 degrees of total rotation (Table 10-2); however, with the knee fully extended, essentially no rotation occurs between the two bones.
Structure and Function of the Knee
Osteology
Distal Femur
Patella
Arthrology
General Features
Normal Alignment
Supporting Structures
Table 10-1
Structure
Function
Most Common Mechanisms of Injury
Anterior cruciate ligament
Posterior cruciate ligament
Medial collateral ligament
Lateral collateral ligament
Posterior capsule
Medial and lateral menisci
Anterior and Posterior Cruciate Ligaments
Medial and Lateral Collateral Ligaments
Posterior Capsule
Kinematics
Osteokinematics of the Tibiofemoral Joint
Table 10-2
Motion
Axis of Rotation
Plane of Motion
Normal Range of Motion
Flexion
Extension
Medial-lateral through the femoral condyles
Sagittal
0-140 degrees
0-5 degrees of hyperextension
Internal rotation
External rotation
Vertical (longitudinal)
Horizontal
0-15 degrees (with knee flexed)
0-30 degrees (with knee flexed)
Structure and Function of the Knee
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