Identify the flat medial surface of the tibia—the shin. Follow its anterior border upward to the tibial tuberosity (A). Mark this point with a dot of ink. Now follow the medial border of the tibia upward until it merges into a bony prominence—the medial condyle of the tibia (B). This is somewhat higher than the tibial tuberosity. In a comparable location on the other side of the knee, find a similar prominence—the lateral condyle (C). Mark both condyles with ink. These three points form an isosceles triangle. On the lateral surface of the knee, somewhat below the level of the lateral tibial condyle, find the head of the fibula.
The patella rests on the anterior articulating surface of the femur, midway between the epicondyles, embedded in the tendon of the quadriceps muscle. This tendon continues below the knee joint as the patellar tendon and inserts on the tibial tuberosity.
Joints. Two condylar tibiofemoral joints are formed by the convex curves of the medial and lateral condyles of the femur as they articulate with the concave condyles of the tibia. The third articular surface is the patellofemoral joint. The patella slides in a groove on the anterior aspect of the distal femur, called the trochlear groove, during flexion and extension of the knee.
With the knee flexed about 90°, you can press your thumbs—one on each side of the patellar tendon—into the groove of the tibiofemoral joint. Note that the patella lies just above this joint line. As you press your thumbs downward, you can feel the edge of the tibial plateau, the upper surface of the tibia. Follow it medially, then laterally until you are stopped by the converging femur and tibia. By moving your thumbs upward toward the midline to the top of the patella, you can follow the articulating surface of the femur and identify the margins of the joint.
Muscle Groups. Powerful muscles move and support the knee. The quadriceps femoris extends the leg, covering the anterior, medial, and lateral aspects of the thigh. The hamstring muscles lie on the posterior aspect of the thigh and flex the knee.
Additional Structures. Two important pairs of ligaments, the collateral ligaments and the cruciate ligaments, and the menisci provide stability to the knee (see drawing on pp. 480 and 481).
■ The medial collateral ligament (MCL), not easily palpable, is a broad flat ligament connecting the medial condyles of the femur and the tibia. To locate the anatomic region of the MCL, move your fingers medially and posteriorly along the joint line, then palpate along the ligament from its origin to insertion.
■ The lateral collateral ligament (LCL) connects the lateral femoral condyle and the head of the fibula. To feel the LCL, cross one leg so the ankle rests on the opposite knee and find the firm cord that runs from the lateral epicondyle of the femur to the head of the fibula. The MCL and LCL provide medial and lateral stability to the knee.
■ The anterior cruciate ligament (ACL) crosses obliquely from the lateral femoral condyle to the medial tibia, preventing the tibia from sliding forward on the femur.
■ The posterior cruciate ligament (PCL) crosses from the lateral tibia and lateral meniscus to the medial femoral condyle, preventing the tibia from slipping backward on the femur. Since these ligaments lie within the knee joint, they are not palpable. They are nonetheless crucial to the anteroposterior stability of the knee.
■ The medial and lateral menisci cushion the action of the femur on the tibia. These crescent-shaped fibrocartilaginous discs add a cuplike surface to the otherwise flat tibial plateau. Palpate the medial meniscus by pressing on the medial soft-tissue depression along the upper edge of the tibial plateau. Place the knee in slight flexion and palpate the lateral meniscus along the lateral joint line.
Observe the concavities that are usually evident at each side of the patella and also above it. Occupying these areas is the synovial cavity of the knee, the largest joint cavity in the body. This cavity includes an extension 6 centimeters above the upper border of the patella, lying upward and deep to the quadriceps muscle—the suprapatellar pouch. The joint cavity covers the anterior, medial, and lateral surfaces of the knee, as well as the condyles of the femur and tibia posteriorly. Although the synovium is not normally detectable, these areas may become swollen and tender when the joint is inflamed.
Several bursae lie near the knee. The prepatellar bursa lies between the patella and the overlying skin. The anserine bursa lies 1 to 2 inches below the knee joint on the medial surface and cannot be palpated due to overlying tendons. Now identify the large semimembranosus bursa that communicates with the joint cavity, also on the posterior and medial surfaces of the knee.
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