Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

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absorption. They also help to stabilize the knee by deep- ening the tibial socket and maintaining the femur and tibia in proper position. In addition, the meniscus assists in joint lubrication and serves as a source of nutrition for articular cartilage in the knee. Meniscus injury commonly occurs as the result of a rotational injury from a sudden or sharp pivot or a direct blow to the knee, as in hockey, basketball, or foot- ball. It is often associated with other injuries, such as a torn ACL. The type and location of the meniscal tear are determined by the magnitude and direction of the force that acts on the knee and the position of the knee at the time of injury. Meniscus tears can be described by their appearance (e.g., parrot-beak, bucket handle) or their location (e.g., posterior horn, anterior horn). The injured knee is edematous and painful, especially with hyperflexion and hyperextension. A loose fragment may cause knee instability and locking. Diagnosis is made by examination and confirmed by MRI. A regular radiograph may be needed to rule out osteoarthritis. Initial treatment of meniscal injuries may be conservative. The knee may be placed in a removable knee immobilizer. Isometric quadriceps exercises may be prescribed. Activity usually is restricted until complete motion is recovered. Arthroscopic meniscectomy may be performed when there is recurrent or persistent lock- ing, recurrent effusion, or disabling pain. There is evidence that loss of meniscal function is associated with progressive deterioration of knee func- tion and osteoarthritic changes. 13 Damaged articular cartilage has a limited capacity to heal because of its avascular nature and inadequate mobilization of regen- erative cells. Meniscal reconstruction procedures have been developed to preserve these functions before sig- nificant degenerative changes develop, thus preventing the need for a total joint replacement later in life. 14 Patellar Subluxation and Dislocations. Recurrent subluxation and dislocation of the patella are common in young adults. 5,8 Sports such as skiing or tennis involve external rotation of the foot and leg with knee flexion, a position that exerts rotational stresses on the knee. Congenital knee variations are also a predisposing fac- tor. There is often a sensation of the patella “popping out” when the dislocation occurs. Other complaints include the knee giving out, swelling, crepitus, stiff- ness, and loss of range of motion. Treatment measures include immobilization with the knee extended, brac- ing, administration of anti-inflammatory agents, and isometric quadriceps-strengthening exercises. Surgical intervention often is necessary. Patellofemoral Pain Syndrome. Patellofemoral pain syndrome is the most common cause of anterior knee pain. 5,10,15 It is caused by imbalances in the forces con- trolling movement of the patella during knee flexion and extension, particularly with overloading of the joint. The patellofemoral joint is composed of the patella and the central groove in the proximal femur, which is referred to as the patellar groove or femoral trochlea (see Fig. 43-3). Stability of the joint involves dynamic and

Femoral trochlea

Femur

Patella (removed for clarity)

Lateral collateral ligament

Femoral condyles Anterior cruciate ligament

Lateral meniscus

Meniscus tear

Tibia

Medial meniscus

Lateral meniscus

Medial meniscus

and the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). Ligamentous Injuries. Ligamentous injuries of the knee are among the most serious of all knee injuries. The mech- anism is usually one of forceful stress against the knee when the extremity is bearing weight. A “pop” or tear- ing sensation along with sudden pain is often described, especially with ACL ruptures. After injury, the ability to bear weight on the extremity is often lost, and the knee becomes swollen because of hemorrhaging into the joint. Initial treatment includes rest, ice, and use of crutches until the person is able to ambulate without a limp. A knee immobilizer or range-of-motion brace may be used for comfort until the acute pain subsides. Range-of-motion exercises are important. Definitive treatment depends on the ligaments that are involved, the person’s age and activ- ity level, and any associated injuries. Most isolated lateral ligament injuries and isolated ACL and PCL ruptures are treated nonsurgically, at least initially. Surgical reconstruc- tion may be required in young, active persons. Older and less active individuals may be treated with physical ther- apy aimed at controlling the instability. A well-constructed brace may provide an option in some persons. Meniscus Injuries. The menisci are C-shaped plates of fibrocartilage that are superimposed between the con- dyles of the femur and tibia. There are two menisci in each knee, a lateral and medial meniscus 5,8,12,13 (see Fig. 43-3). The menisci are thicker at their external mar- gins and taper to thin, unattached edges at their inte- rior margin. They are firmly attached at their ends to the intercondylar area of the tibia and are supported by the coronary and transverse ligaments of the knee. The menisci play a major role in load bearing and shock Front View FIGURE 43-3. The knee, showing the lateral and medial condyles and menisci.The lateral and medial femotibial condyles are located between the lateral and medial femoral condyles and the tibial condyles (not shown). Inset (lower left) shows meniscus tear. Patella