CHAPTER 12 Structure and Function of the Knee


257


Suprapatellar synovial bursa


Flexion Extension


Subcutaneous prepatellar bursa


Bursa under lateral head of gastrocnemius muscle


Deep


Subcutaneous infrapatellar bursa


(subtendinous) infrapatellar bursa


Lateral rotation


Medial rotation


Figure 12.11 Superior view of the movement of the menisci during knee flexion, extension, lateral rotation, and medial rotation.


The medial and lateral menisci have a blood supply that is adequate at the peripheral borders. In contrast, the internal borders are relatively avascular with little blood supply. This anatomical difference comes into play when the menisci are torn or injured. Meniscal injuries are the most common knee injury, with the medial menis- cus being twice as likely as the lateral meniscus to be injured. Injury can result from an axial rotational force as the body pivots over a planted foot and from valgus or varus forces at the knee in the frontal plane. They often are associated with injuries to the anterior cruciate liga- ments. Often surgical treatment is used to repair the torn meniscus rather than remove it. If the injury occurs in the avascular zone of the meniscus, surgical repair is less successful. Surgical removal of a meniscus is associated with increased stresses to the articular cartilage of the knee joint and the development of osteoarthritis of the knee. Even a partial meniscectomy increases the stresses to the articular cartilage and signifi cantly increases the risk for development of osteoarthritis. Because of the avascular nature of the internal borders of the menisci, surgical repair is often not a viable option.


Bursae


There are 14 bursae in the knee complex that reduce the friction between structures. Some of the bursae are formed from extensions of the synovial membrane of the joint capsule. Others are extracapsular and are often located between the muscle tendon and the bony insertion. The suprapatellar bursa is located behind the patellar tendon, whereas the deep infrapatellar bursa is between the patellar ligament and the tibial tuberosity.


Figure 12.12 Sagittal view showing some of the major bursae in the knee. (From Levangie P, Norkin C. Joint Structure and Function: A Comprehensive Analysis, 5th ed. Philadelphia, PA: F. A. Davis Company, 2011: p. 412, with permission.)


Fat pads associated with these two bursae further reduce friction between the moving components in the area. These bursae can become infl amed secondary to exces- sive compression by the quadriceps muscle group or from malalignment and poor tracking of the patellofemoral joint. The subcutaneous prepatellar bursa lies between the skin and the patella, and the subcutaneous infrapatel- lar bursae lie between the skin and the patellar ligament (Fig. 12.12). The most common knee bursae and their locations are listed in Table 12.2.


Capsule and Ligaments


The fi brous joint capsule of the knee encompasses the tibiofemoral and patellofemoral joints. Posteriorly, it attaches to the femur proximal to condyles and distal to the popliteal surface. Ligaments, fascia, and muscles reinforce the capsule to increase the external stability of the knee joint.


On the anterior aspect of the knee, the capsule is rein- forced by medial and lateral patellar retinacular fi bers. These are connective tissue fi bers that extend from the medial and lateral vastus muscles and the IT band. The IT band is the long, fl at, wide tendon of the tensor fasciae latae muscle (see Chapter 11) that provides additional stability to the lateral side of the knee (Fig. 12.13).


Medial and Lateral Collateral Ligaments Laterally, the cord-like lateral collateral ligament (LCL) reinforces the capsule along with the retinacular fi bers, bicep femoris muscle, tendons of the popliteus, and lateral head of the gastrocnemius. The LCL is a strong ligament attaching the lateral femoral epicondyle to the fi bular head (Fig. 12.13B).


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