The Knee

Published on 16/03/2015 by admin

Last modified 22/04/2025

Print this page

This article have been viewed 2457 times

Chapter 11 The Knee

The knee is the largest joint in the body. The lower portion of the femur and upper aspect of the tibia articulate at only two points where the rounded femoral condyles bear weight on the flat tibial plateaus. The knee joint is subject to a wide variety of traumatic, mechanical, and inflammatory disorders.

Anatomy

The knee joint consists of medial and lateral, femoral and tibial condyles; and the patella. It is essentially a round bone sitting on a flat bone with no intrinsic bony stability and depends completely on its ligaments, muscles, menisci, and capsule for support. The most important ligaments of the knee are the medial and lateral collateral ligaments (LCLs) along with their associated posterior capsular structures and the anterior and posterior cruciate ligaments (Fig. 11-1). The medial collateral ligament originates below the adductor tubercle and attaches to the upper medial tibia. It limits abduction and assists in controlling rotation. The LCL attaches to the lateral epicondyle of the femur and head of the fibula and controls adduction. The cruciate ligaments attach to the intraarticular portions of the femur and tibia. The anterior cruciate ligament (ACL) prevents anterior displacement of the tibia and helps control rotation of the tibia on the femur. The posterior cruciate ligament (PCL) prevents backward displacement of the tibia on the femur.

FIG. 11-1 Ligaments of the knee. A, Anterior cruciate ligament; P, posterior cruciate ligament; L, lateral collateral ligament; M, medial collateral ligament; T, patellar tendon; ME, medial and lateral menisci.

The muscles about the knee also play important roles in its function. The quadriceps group is the most important. These muscles control extension and prevent dislocation of the patella. The medial and lateral hamstrings provide posterior support to the knee and control flexion. Additional support is provided by the popliteus muscle and the iliotibial band.

Normal knee motion consists of a combination of rotation and either extension or flexion. Normally, as the knee flexes, the tibia internally rotates. Extension of the knee is accompanied by lateral or external rotation of the tibia. These rotational motions are controlled by the ligaments and menisci of the knee. This rotation is reflected in the course that the patella takes with flexion and extension movements (Fig. 11-2). Thus, damage to the knee (such as a torn meniscus, which prevents normal tibial rotation) can cause patellar symptoms resulting from abnormal patellar excursion. These patellar symptoms are typically aggravated by walking up and down stairs, an activity that puts the greatest strain on the patella and knee extensors.

FIG. 11-2 Excursion of a patella with knee flexion.

Roentgenographic Anatomy

Anteroposterior and lateral views are essential in the diagnosis of knee disorders (Fig. 11-3). A tunnel view visualizes the intercondylar notch, and tangential views are helpful in diagnosing patellar disorders. With patients over the age of 40, the anteroposterior view should always be performed with the patient standing. This may reveal subtle joint space narrowing if osteoarthritis is present.

FIG. 11-3 Anteroposterior (A) and lateral (B) roentgenograms of a normal knee. M, Medial femoral condyle; L, lateral femoral condyle; T, tubercles of the intercondylar eminence; P, medial and lateral tibial plateaus; F, head of the fibula. Note that the medial femoral condyle projects more distally on both views.

Lesions of the Meniscus

INJURIES OF THE MENISCUS

The menisci, or semilunar cartilages, are two C-shaped structures composed of fibrocartilage that help act as cushions between the femur and tibia. They also assist in the control of normal knee motion. If the normal rotation of the tibia is forcibly prevented as the knee is flexed or extended (that is, if flexion occurs with external rotation or extension occurs with internal rotation), a tear in the meniscus can occur. The injury may be isolated or in conjunction with ligamentous ruptures. Meniscus tears are the most common of all knee injuries, and the pathologic characteristics of the tear are variable (Fig. 11-4). When an injury occurs that produces free fragments or tears, healing to the main body of the meniscus may not take place. The fragment often remains permanently detached but viable because nourishment for the meniscus is provided by the joint fluid. This joint fluid circulates around the tear and often prevents healing from taking place. Persistent symptoms are the result. The medial meniscus is injured 10 times more frequently because it is more firmly attached and less mobile than the lateral meniscus. In long-standing disease, articular cartilage erosion of the tibiofemoral and patellofemoral joints may even result.

FIG. 11-4 A, Normal meniscus. B, Longitudinal, or “bucket-handle,” tear. C, Tear of the posterior horn.

CLINICAL FEATURES

The history is usually one of a twisting injury to the knee with the foot in the weight-bearing position. Occasionally, the injury is slight. A “popping” or “tearing” sensation is often felt, followed by severe pain. The pain is frequently well localized medially or laterally, depending on which meniscus is injured. Locking from mechanical blockage of motion by the meniscus may occasionally occur, but restricted motion after meniscus injury is usually caused by other factors, such as hamstring guarding or swelling, that produce a pseudolocking effect. Swelling from joint effusion gradually occurs over several hours. This is in contrast to ligamentous injury, where the swelling is immediate because of hemorrhage. The swelling from meniscus injury is frequently maximal on the day following the injury. The acute symptoms may subside within a few days, only to be replaced by intermittent episodes of locking, buckling, giving out, swelling, and mild pain. Walking up and down stairs is frequently difficult, and squatting may be painful.

The examination usually reveals a joint effusion (Fig. 11-5). Its presence indicates acute or chronic synovial irritation. Its absence by history or examination should cause another diagnosis to be considered. This fluid may cause the patella to be ballotable. A click may also be present when the patella is pressed against the femur.

FIG. 11-5 Checking for joint effusion. Milking the suprapatellar pouch with downward and distal pressure will frequently reveal fluid that might not otherwise be apparent (arrow). Pressure against the patella may produce a “click” as the patella strikes the femur.

Pain and tenderness at the joint line either medially or laterally may be present. The range of motion is frequently limited. This may be caused by swelling, pseudolocking, or occasionally the interposition of the torn meniscus. In long-standing disease, atrophy of the quadriceps muscle, especially the vastus medialis, occurs rapidly (Fig. 11-6).

FIG. 11-6 The circumference of the thigh is measured 10 cm above the proximal pole of the patella (the medial joint line is marked).

The McMurray test is sometimes helpful in detecting a meniscus tear, although it is difficult to perform on a painful, swollen knee, and the results are often inconsistent (Fig. 11-7). Full knee flexion, which increases pressure on the posterior horns, may cause pain with many meniscus tears.

FIG. 11-7 McMurray test. A, To test for medial meniscus injury, the hip and knee are flexed maximally, and a valgus (abduction) force is applied to the knee. B, The foot is externally rotated, and the knee is passively extended. An audible or palpable snap during extension suggests a tear of the medial meniscus. To test for lateral meniscus injury, the procedure is performed with a varus, internal rotation stress applied.

DISCOID MENISCUS

Because of a failure in normal development, a meniscus, usually the lateral, may be elliptical rather than semilunar. The most common clinical finding in this disorder is an audible click that occurs with motion of the knee joint. The click may be present in infancy, but the disorder is usually not otherwise symptomatic at this age. The meniscus frequently wears away, so the clicking disappears. Occasionally, however, symptoms persist into adulthood, with clicking and aching pain at the lateral joint margin being common complaints. A palpable degenerative cyst may even form in the meniscus. Local tenderness at the lateral joint space is usually present.

Partial meniscectomy may be necessary in an adult with persistent symptoms. Infants usually require no treatment.

CALCIFICATION OF THE MENISCI

The meniscus can become calcified from a variety of causes (Fig. 11-10), the most common being degeneration and trauma. However, calcification can also occur in several other conditions, including degenerative arthritis, ochronosis, and pseudogout. The calcification itself is usually not painful. The symptoms are those that result from the primary disorder, and treatment is directed at that disorder.

FIG. 11-10 Calcification of the meniscus.

Cysts

Only two types of cystic lesions, the popliteal cyst and the cyst of the semilunar cartilage (meniscus), occur with any frequency around the knee joint. The popliteal or Baker’s cyst is an enlargement of the semimembranous bursa that is normally present in the medial aspect of the popliteal space. This bursa usually connects with the knee joint. Small asymptomatic popliteal cysts are common in the general population and are often discovered incidentally, usually during testing for other problems.

Baker’s cysts develop in any age group. In children, the cyst appears to be a primary lesion, in contrast to adults, in whom most of these cysts are secondary to some intraarticular pathology involving the knee. This abnormality, frequently a posterior tear of the medial meniscus or rheumatoid or degenerative arthritis, causes an increase in joint fluid. This chronic effusion opens the normal anatomic communication between the joint and cyst and allows fluid to escape into the semimembranous bursa. The cyst may reach an enormous size in rheumatoid patients with severe synovitis and even dissect distally into the calf.

Occasionally, the Baker’s cyst may rupture in the adult, allowing the escape of the fluid into the soft tissues. The fluid can be irritating and can cause the development of a clinical picture (pain, swelling, and tenderness) resembling thrombophlebitis, referred to as the “pseudothrombophlebitis syndrome.” Homan’s sign may even be positive. Sometimes, blood from rupture of the cyst will dissect distally toward the ankle, where it can reach the surface, creating an ecchymotic area around the malleoli. Differentiation of cyst rupture from venous thrombosis is critical in that thrombophlebitis may require anticoagulation, which is contraindicated in the ruptured cyst (or rupture of the medial head of the gastrocnemius muscle, which can also present with similar findings). Venous ultrasound, MRI, or venography may be needed to distinguish the disorders.

CLINICAL FEATURES

In children, the symptoms are usually related to the effects of direct pressure of the cyst on the adjacent soft tissues. Local discomfort may be present. In adults, the symptoms are related not only to the effects of the pressure of the cyst but also to the primary intraarticular abnormality. (Many cysts are asymptomatic, however.) The cyst commonly changes in size, depending on the activity of the patient and the amount of swelling in the knee.

Examination will reveal a cystic mass of variable size lateral to the medial hamstrings in the popliteal fossa (Fig. 11-11). The lesion may be locally tender. Other findings of primary joint disease may be present, especially in adults.

FIG. 11-11 The popliteal cyst in its usual medial location inferior to the knee crease and lateral to the medial hamstrings.

Except for occasional osteoarthritis, the roentgenogram is usually normal. Ultrasound studies are easy and can document the cystic nature of the lesion when the diagnosis is in doubt. They are also cost effective. MRI can identify underlying joint pathology as well. Occasionally, the cyst may even form multiple calcific loose bodies (Fig. 11-12).

FIG. 11-12 Multiple calcific loose bodies in a Baker’s cyst.

TREATMENT

In children with primary cysts, treatment should be conservative. There is a high rate of spontaneous disappearance of the cyst in this age group and an equally high rate of recurrence following surgical excision. Aspiration and injection of the cyst may be attempted, but they are usually not necessary because the cyst frequently disappears in 1 to 2 years. The easily performed ultrasound study can reassure the family of the benign nature of the lesion.

Adult patients are primarily treated nonsurgically. The cyst may be aspirated to reassure the patient of its benign nature. Aspiration, sometimes with injection of 1 mL of steroid, is often performed to relieve symptoms, and although recurrence is common, the symptoms are usually more tolerable. An intraarticular injection may also be needed to suppress the synovitis. If surgery is being considered, every attempt should be made to detect any underlying joint abnormality. Cyst excision without correction of the intraarticular abnormality is followed by a high rate of recurrence of the cyst. Correction of the intraarticular condition also frequently renders cyst excision unnecessary because the cyst becomes asymptomatic following elimination of the cause of the chronic effusion. Most patients are treated successfully by aspiration alone, or simple observation if the cyst is not symptomatic.

Comments

Popliteal cysts are usually separated from the midline neurovascular structures by the medial head of the gastrocnemius muscle. Whether or not the typical soft cyst is capable of compressing these structures is controversial.

CYSTS OF THE MENISCUS

Cysts may also develop in a meniscus, usually the lateral, as a result of degeneration or trauma. The patient is generally a young adult who has a history of pain and a gradually enlarging mass over the lateral joint line (Fig. 11-13). A knee effusion may be present. Treatment consists of aspiration or meniscectomy and cyst excision if the patient is symptomatic.

FIG. 11-13 Cyst of the lateral meniscus.

Lesions of the Ligaments

Ligamentous injuries to the knee are among the most serious of all knee disorders. The management of these injuries has evolved over the years and continues to evolve. These injuries may occur alone or in combination and are sometimes associated with meniscal tears. Although men have the greatest number of ACL injuries, the female athlete is at much greater risk, possibly because of a combination of hormonal and neuromuscular factors.

CLINICAL FEATURES

The mechanism is usually one of forceful stress against the knee when the extremity bears weight. Direct contact may be involved, although the ACL in particular is often injured without contact. A valgus stress against the knee may sprain or tear the medial collateral ligament, and a varus stress will injure the LCL. Cruciate injuries often occur as a result of a twisting injury, and a “pop” or tearing sensation is often described, especially with ACL ruptures.

After the injury, the ability to bear weight on the extremity is often lost. Swelling from an acute ligament or capsular tear is usually immediate because of a hemorrhage. If a cruciate injury has occurred, the joint fills rapidly with blood. If a collateral or capsular tear has occurred, localized ecchymosis may become visible in a few days. Incomplete tears or sprains are often more painful than complete ligamentous ruptures.

The examination is of utmost importance in the acute injury. Any swelling or discoloration is noted. The lesion can frequently be localized by palpation alone. Palpation should begin away from the suspected area to promote cooperation. A point of maximum tenderness is often present along the course of the collateral ligament or capsule.

The knee should always be tested for stability with the patient relaxed in the supine position. The injured knee is always compared with the opposite, uninvolved knee. The tests are performed in the following sequence:

1 Valgus–varus stress testing at 30 degrees of knee flexion. With the knee flexed 30 degrees, the cruciate ligaments are relaxed. This prevents them from producing a false-negative test result. The medial and lateral ligaments can then be tested by applying valgus and varus stresses to the knee (Fig. 11-14). If laxity exists in either direction with testing, the test reflects an injury to the involved collateral ligament. Sometimes, the test is graded according to the amount of laxity. A grade I injury is present when the joint opens 5 mm more than the normal, and a grade III or “complete” rupture is present when the joint opens more than 1 cm.

2 Valgus–varus stress testing at 0 degrees. Valgus and varus stresses are applied in the same manner as when the knee was tested at 30 degrees of flexion. If the knee was stable at 30 degrees, it will also be stable at 0 degrees because the collateral ligaments are intact. However, with the knee in extension, the cruciate ligaments tighten and by themselves can prevent the joint from opening despite a collateral ligament tear. Therefore, if the knee is unstable in extension, a more serious knee injury has occurred. Posterior capsular and cruciate damage may also be present in this case. (When the knee is extended, the cruciate and posterior capsular structures play a greater role in preventing varus and valgus opening.)

3 Drawer signs. Anteroposterior and rotatory instability are tested by determining how much abnormal excursion of the tibia is present when anterior and posterior stresses are applied to the tibia with the knee in a flexed position (Fig. 11-15). Anterior drawer testing is performed with the foot in external rotation, neutral rotation, and internal rotation. Abnormal forward excursion of the tibia with the foot in either position is highly suggestive of a significant injury to the ACL and joint capsule. The posterior drawer test is then performed by applying backward pressure against the tibia. Abnormal laxity with this test is present with posterior cruciate and posterior capsular injuries. The tibia will also “sag” posteriorly with the hip and knee flexed 90 degrees if the PCL is ruptured.

4 The ACL can also be assessed by the Lachman test (Fig. 11-16). This is essentially an anterior drawer test performed with the knee close to full extension. The femur is stabilized with one hand while firm pressure is applied to the proximal portion of the tibia in an attempt to translate it forward. A positive test result is one in which there is palpable and visual anterior movement of the tibia with a characteristic soft end point. This test is probably more accurate than the traditional anterior drawer sign and has the other advantage that it can be performed in the position of comfort of the acutely injured knee.

Roentgenographic examination may reveal avulsion fractures pulled off by the injured ligament (Fig. 11-17). Roentgenograms should always be obtained, especially in the growing child younger than 15 years of age with open epiphyses to rule out a fracture of the distal femoral epiphysis that may simulate collateral ligament injury (Fig. 11-18). MRI is helpful in assessing cruciate ligament status.

FIG. 11-14 Abduction (valgus) stress test at 30 degrees of knee flexion. To test the lateral collateral ligament, a varus stress is applied. The test is repeated in full extension. Collateral ligament injuries are graded by the amount of joint space opening.

FIG. 11-15 The drawer tests are performed with the hip flexed 45 degrees and the knee flexed 90 degrees. The hamstrings should always be relaxed.

FIG. 11-16 Lachman’s test. This is essentially an anterior drawer test performed with the knee in approximately 30 degrees of flexion. The femur is stabilized with one hand, and the tibia is drawn forward with the other. An increase in the forward motion and lack of a definite end point suggest a rupture of the anterior cruciate ligament.

FIG. 11-17 The lateral capsular fracture (arrow). A small avulsion fracture of the lateral ligament, which usually signals a severe joint injury commonly in combination with an ACL rupture.

FIG. 11-18 Stress roentgenography of the knee reveals an epiphyseal fracture of the lower portion of the femur that may be misdiagnosed as a ligamentous injury clinically.

TREATMENT

Most isolated collateral ligament injuries are now treated nonsurgically, even those that are complete (except severe LCL ruptures). Rest, ice, compression dressing, protection, and early rehabilitation are recommended. Functional hinged braces are used, and healing is usually good. Complete LCL injuries are often treated surgically to prevent late instability.

Treatment of cruciate injuries varies, depending on the age and activity of the patient and the presence of any additional injuries. Isolated ACL and PCL ruptures are generally treated nonsurgically, at least initially, in many cases. Reconstruction is usually required in patients with high demands. A well-constructed brace may provide an option in some patients. The treatment of combined cruciate/collateral injuries is unsettled. Surgery may be required to improve joint stability in the patient with multiple ligament involvement.

Minor ligament sprains are treated in the same manner as meniscus injuries (Fig. 11-19). Immobilization in a compression dressing with ice and elevation for 2 to 3 days are followed by exercises to promote absorption of swelling and restoration of motion and strength.

FIG. 11-19 Algorithm for investigation of the acute knee injury.

CHRONIC INSTABILITY

Patients often present with episodes of the knee “giving way” or “going out,” especially with activities that require cutting or changing directions. A chronic effusion may be present in the knee. Although a torn meniscus can cause similar symptoms, the most common cause of this problem is chronic instability caused by ACL deficiency. Although the initial disability from isolated ACL injuries may seem minimal, the injury may result in progressive deterioration with increasing knee laxity, tears in either meniscus, and articular cartilage degeneration. The ACL rupture has been referred to as “the beginning of the end” of the athlete’s knee.

Older injuries often cause the knee to “give out,” a term usually called the pivot shift. This usually occurs when the patient comes to a sudden stop or changes directions quickly. The pivot shift is a sign that the tibia is subluxing on the femur. A synovitis is often present. The findings are often suggestive of meniscal injury (which may also be present), but the pivot shift test is usually diagnostic (Fig. 11-20).

FIG. 11-20 The pivot shift test. A, With the knee slightly flexed, the proximal portion of the tibia is lifted forward and internally rotated, and the knee is then extended. (This subluxes the tibia forward, and the femur falls backward.) B, Valgus force is then applied, and the knee is flexed. At about 30 degrees, the subluxation will suddenly be reduced with a palpable sensation and reproduce the patient’s symptoms of instability.

TREATMENT

The treatment is individualized. The athlete usually needs referral for evaluation (MRI or arthroscopy), followed by surgical reconstruction and augmentation or ligament replacement. This is followed by several months of rehabilitation and exercise.

Treatment of the recreational athlete is often nonsurgical. Exercises, bracing, and occasionally, modification of activities usually allow a relatively normal lifestyle. If sufficient symptoms of instability develop later, surgical reconstruction to prevent subluxation is indicated. Surgery in these cases does not relieve pain but may eliminate symptoms of “giving out” and prevent secondary arthritis from developing.

PELLEGRINI–STIEDA DISEASE

Occasionally, a sprain or repeated trauma of the medial collateral ligament is followed by the formation of a calcified mass at the site of the ligament injury, usually the femoral attachment (Fig. 11-21). This area of dystrophic calcification may remain tender and swollen for an extended period of time. Ossification of the mass may even occur. The symptoms gradually subside, and symptomatic treatment is usually all that is necessary. The mass rarely needs to be removed.

FIG. 11-21 Pellegrini–Stieda sign.

Although the disease is relatively rare, ossification by itself (the Pellegrini–Stieda sign) is a fairly common radiographic finding.

Disorders of the Extensor Mechanism

The extensor mechanism of the knee consists of the quadriceps muscles and tendon, the patella, and the patellar tendon. Several painful disorders may alter its function, and some of them are difficult to cure.

PATELLOFEMORAL PAIN SYNDROME

This term describes a condition in which there is pain over the anterior aspect of the knee in the absence of other specific identifiable pathology. Over the years, pain around the patella has been attributed to a variety of structural abnormalities, including malalignment and chondromalacia (softening of the articular cartilage). Historically, “chondromalacia of the patella” was the diagnosis commonly given to patients with nonspecific pain in the front of the knee, but with the present state of knowledge, this term is now used to describe only the pathologic lesion of cartilaginous softening and fibrillation sometimes visualized surgically and not to describe a clinical entity. The anatomic lesion of chondromalacia is a frequent finding in the normal knee, but it is unclear whether or not it is ever associated with symptoms. The same syndrome of patellofemoral pain (also called anterior knee pain) is frequently present when the articular cartilage is normal.

The patellofemoral syndrome is one of the most common causes of pain in adolescents and young adults, but it can occur at any age. Its cause is unknown, but several factors may play a role in its development.

Any injury or anatomic abnormality that predisposes to an irregular pattern of movement of the patella can lead to this syndrome. Quadriceps imbalance (weak vastus medialis), a high-riding patella (patella alta), and angular deformities about the knee (genu valgum) may be associated with patellofemoral pain. Direct trauma, such as that which occurs with a fall or a dashboard injury to the patella, may also predispose to patellofemoral pain. It may develop because of repeated trauma, such as vigorous squatting during weightlifting, or in conjunction with simple overuse. The disorder is mainly a diagnosis of exclusion.

CLINICAL FEATURES

The majority of patients are teenagers or young adults. Crepitus is often the symptom of most concern. Pain beneath or near the patella is usually present, but many patients are unable to pinpoint the spot of maximal discomfort. Symptoms are characteristically aggravated by walking up and down stairs, an activity that puts the patella under the greatest flexion load. Squatting and prolonged sitting with the knee flexed (such as at the movie, the so-called “movie sign”) are also uncomfortable. This discomfort is often relieved by extension of the knee. Symptoms of giving way or locking may be present, and a history of previous trauma is common. The disease is frequently bilateral and may be confused with a meniscus injury or tendinitis.

Examination will reveal generalized tenderness around the patella, but the site is often not consistent or specific compared with the tenderness seen when quadriceps or patellar tendinitis is present. Direct pressure against the patella may be painful, and contraction of the quadriceps against patellar pressure is often uncomfortable (Fig. 11-22). Effusions are rare, unless the condition is associated with another problem such as a meniscal injury. Crepitus may be palpable during flexion and extension, although this finding is of debatable significance. There may also be signs of malalignment or an unstable patella, but commonly the examination is completely normal, except for tenderness around and beneath the patella. Roentgenographic examination is usually normal unless patellar subluxation is present.

FIG. 11-22 Examination for retropatellar pain. A, With the knee slightly flexed, pressure against the patella as the knee is actively extended may produce typical pain. B, With the knee extended, the patella is displaced medially or laterally. Pain is reproduced by digital pressure under either the medial or lateral patellar facet.

TREATMENT

Most management programs emphasize conservative treatment. The patient is reassured of the benign nature of the problem. Treatment is directed toward the underlying cause, if any is present. “Flexion loads” should be avoided, especially improperly performed quadriceps exercises. Otherwise, nonsteroidal anti-inflammatory drugs (NSAIDs), ice after activities, moist heat, and an exercise program addressing flexibility and strength are advised (Table 11-1). Referral to physical therapy may be helpful, but any exercise program should be pain free. Most cases eventually recover spontaneously. Activities, including athletics, are allowed as tolerated. If symptoms persist, surgery may rarely be indicated. It usually consists of some procedure to realign the patella, if needed, to prevent abnormal motion or to release excessive lateral patellar pressure. Shaving or removal of “abnormal” articular cartilage is often only of limited value. Surgery has a high failure rate, probably because the cause of the disorder is not clearly understood. Arthroscopy may even trigger a sympathetic dystrophy in some cases. Anterior knee pain itself does not appear to lead to patellofemoral arthritis, but symptoms may persist for years.

Table 11-1 Treatment for Anterior Knee Pain

Stretch	Quads, hamstrings, triceps, heel cord
Strengthen	Quads (short arc)
Modalities	Ice, heat, massage?
Medication	NSAIDs

NOTE: Eliminate overuse, flexion loads.

RECURRENT SUBLUXATION OF THE PATELLA

Recurrent subluxation of the patella (patellofemoral instability) is a common disorder that is often undiagnosed because the symptoms are similar to other derangements of the knee. In this condition, the patella subluxes or dislocates laterally. The onset is usually without any specific trauma, although it may follow an acute patellar dislocation that fails to heal properly. The disorder is frequently bilateral. The cause is often complex. Conditions that predispose the patella to not remain centralized in the femoral groove and track too far laterally are: (1) a shallow lateral femoral condyle; (2) a high Q angle (see Chapter 15); (3) inadequate development of the oblique portion of the vastus medialis muscle; (4) genu valgum; (5) ligamentous laxity; and (6) internal femoral torsion.

CLINICAL FEATURES

The symptoms are pain, swelling, and a sensation of the knee giving out. Acute dislocation may even occur, but more commonly, the symptoms are caused by recurrent subluxation. The patient may be able to describe the direction of movement of the patella. Physical examination usually reveals local tenderness over the medial facet of the patella and in the soft tissue medial to the patella. The patella may appear laterally displaced and higher than normal when the knee is slightly flexed (patella alta). Passive hypermobility with lateral displacement is often noted when pressure is applied against the patella with the knee relaxed in slight flexion (Fig. 11-23). This maneuver reproduces the sensation that the patient feels when the patella subluxes and often causes apprehension. Reflex contraction of the quadriceps muscle may also occur when the patella is manipulated. A joint effusion and mild quadriceps atrophy may be present. There are often findings of malalignment and mild laxity as well.

FIG. 11-23 The “apprehension” test. Abnormal lateral hypermobility may be noted when attempting to displace the patella laterally with the knee relaxed and slightly flexed. The patient may even become apprehensive and grab the examiner’s arm to prevent further displacement.

Roentgenographic studies are frequently helpful. A “sunrise” view taken with the knee relaxed in slight flexion will often reveal lateral displacement (Fig. 11-24).

FIG. 11-24 A “sunrise” view of the knee reveals abnormal lateral displacement of the patella.

TREATMENT

Treatment is directed at improving extensor muscle tone. Short arc quadriceps exercises are begun, and frequently, the vastus medialis portion of the quadriceps will strengthen enough to prevent recurrent lateral subluxation from occurring. The hamstrings are stretched if needed. Cycling may be helpful, and patellar stabilizing braces are sometimes prescribed.

Surgery may be indicated to reconstruct the extensor mechanism to prevent recurrence. A variety of procedures are available. All of them attempt to realign the patella to prevent abnormal lateral excursion from occurring. Exercise seems as successful as surgery with a 10% to 15% failure rate with either treatment.

ACUTE DISLOCATION OF THE PATELLA

A sudden valgus strain to the knee or a direct blow against the medial aspect of the patella may cause the patella to dislocate laterally (Fig. 11-25). The deformity is usually obvious, with the patella displaced in the lateral position and the knee held in slight flexion. There are usually no predisposing anatomic factors such as those seen with recurrent subluxation. Roentgenographic examination should always be performed to rule out any associated osteochondral fracture.

FIG. 11-25 A and B, Lateral dislocation of the patella.

Reduction can be accomplished by lifting the heel of the extremity off the table. This extends the knee and flexes the hip, thereby relaxing the entire quadriceps mechanism. Gentle pressure against the patella may be necessary to complete the reduction.

Occasionally, intravenous sedation may be needed. The knee is immobilized for 2 to 3 weeks by a knee immobilizer. Quadriceps exercises are begun as soon as possible. Traumatic dislocation is always accompanied by a partial rupture of the medial retinaculum and supporting structures of the patella. This may rarely lead to recurrent episodes of subluxation or dislocation. If it does, surgical reconstruction of the extensor mechanism may be necessary.

NOTE: Acute hemarthrosis after a twisting knee injury often means an ACL tear, but an acute patellar dislocation that spontaneously reduced can look the same. The dislocation is usually associated with medial retinacular tenderness due to damage to this tissue.

RUPTURES OF THE EXTENSOR MECHANISM

The extensor mechanism occasionally ruptures as a result of attrition. (Healthy, young tendon rarely ruptures.) Often, the rupture occurs during the course of normal activities, such as stair walking. The rupture may take place in the quadriceps or patellar tendon (Fig. 11-26). Patellar tendon ruptures are usually at its attachment to the patella. Active extension is immediately lost, but pain may be minimal, especially in an older patient with chronic degeneration of the muscle–tendon unit. Bilateral spontaneous quadriceps ruptures may be associated with diabetes, gout, and oral steroid use.

FIG. 11-26 Sites where the extensor mechanism commonly ruptures, usually close to the patella. The patella will displace proximally if the patellar tendon ruptures.

CLINICAL FEATURES

Clinically, hemorrhage and a palpable sulcus are present in the area of the rupture. Extension of the knee is markedly weakened or even completely absent. The patient is usually unable to perform a straight leg raise. A lateral roentgenogram taken with the knee in 90 degrees of flexion usually reveals proximal displacement of the patella (patella alta) when the rupture has occurred in the patellar tendon (Fig. 11-27). Roentgenograms are usually not helpful when the rupture has occurred proximal to the patella in the quadriceps mechanism.

FIG. 11-27 Rupture of the patellar tendon with marked proximal displacement of the patella (patella alta).

Incomplete tears are not uncommon. They are usually associated with pain and local tenderness. MRI is valuable in these cases.

TREATMENT

Treatment is usually by surgical repair followed by immobilization and rehabilitation. Incomplete tears respond to extension bracing for 6 weeks followed by slow rehabilitation.

OSGOOD–SCHLATTER DISEASE

Osgood–Schlatter disease is a disorder that involves the growing tibial tuberosity of adolescents. The cause is unknown, but the disorder is generally considered to be a traumatically produced lesion that occurs at the attachment of the patellar tendon to the tibial tuberosity. It is a self-limited condition that ends with closure of the upper tibial epiphyseal plate. The disorder usually becomes evident between the ages of 8 and 15 years and is frequently bilateral. Males are affected three times as often as females.

CLINICAL FEATURES

Local pain, swelling, and tenderness over the tibial tubercle are characteristic clinical features. The pain is accentuated by activity. Stair walking and squatting on the knees may be especially uncomfortable. The pain is also increased by extension of the knee against resistance.

Although usually normal, a lateral roentgenogram of the upper portion of the tibia with the leg slightly internally rotated may reveal variable degrees of separation and fragmentation of the upper tibial epiphysis. Occasionally, the fragmented area fails to unite to the tibia and persists into adulthood (Fig. 11-28).

FIG. 11-28 Osgood–Schlatter disease. A portion of the epiphysis has failed to unite. The patient was asymptomatic.

TREATMENT

Removing the stress on the tendon is usually sufficient treatment. Stretching, NSAIDs, and ice after exercise are advised. Simple abstinence from physical activity will relieve the symptoms in most cases, although several months may be needed to relieve symptoms. On the other hand, adverse outcomes are rare, even if the patient remains active despite the discomfort. Temporary immobilization in a knee splint may be necessary in resistant cases. Surgery is rarely indicated. The prognosis for complete restoration of function and relief from pain is excellent. The condition usually heals when the epiphysis closes, which may take 1 to 2 years. The prominence of the tibial tubercle often persists into adulthood, but symptoms are rare other than minor pain when kneeling.

LARSEN–JOHANSSON DISEASE

This is another disorder that can present as anterior knee pain in the adolescent. It appears to be the result of chronic traction (overuse) at the cartilaginous junction of the patella and either the quadriceps tendon or patellar tendon. Most commonly, it occurs at the junction with the patella and thus resembles “jumper’s knee” in the adult. Clinically, tenderness is present at the affected site. Roentgenograms may occasionally reveal ossification of the tendon at its attachment to the patella.

The treatment is similar to that of Osgood–Schlatter disease, and the symptoms usually cease at the time of skeletal maturation.

Osteochondritis Dissecans

Osteochondritis dissecans is a condition of unknown cause in which a segment of subchondral bone undergoes avascular necrosis. This portion of bone, with its overlying articular cartilage, may even separate or become detached from the joint surface and become a loose body. The knee is the most common joint affected (the talar dome and elbow are other sites), and the lateral surface of the medial femoral condyle is the area that is most often involved, although usually not the weight-bearing surface. The condition is primarily a disorder of young adults, but it may also be seen in children. Males are more commonly affected, and the disorder may be bilateral. Juvenile and adult forms are described. The term is probably a misnomer in that no inflammation is present. Osteochondrosis is probably a better term.

CLINICAL FEATURES

The symptoms consist of pain, stiffness, and swelling that are worsened with activity. A painful limp is frequently present, and locking may even occur if the fragment has become detached. Diminished motion, swelling, and medial joint tenderness are usually present. This tenderness may be well localized and is best elicited by deep local pressure over the affected area with the knee flexed 90 degrees. Thigh atrophy may be seen, and Wilson’s sign may be abnormal (pain with knee extension and internal rotation of the foot).

The roentgenogram is usually diagnostic (Fig. 11-29). A fragment of avascular bone is seen that is demarcated from the adjacent femur by a radiolucent line. Occasionally, a loose body may be present. Bone scanning and MRI may be helpful in management decisions.

FIG. 11-29 Osteochondritis dissecans of the knee (arrow). The “tunnel” view is frequently helpful in visualizing the defect. This fragment may become detached and form a loose body. This area should not be confused with the normal irregularity of the distal femoral epiphysis in young children.

TREATMENT

Undisplaced lesions in children are treated conservatively. The prognosis is usually good at this age. The joint is protected from weight bearing by the use of crutches. Several months are required for complete healing. In the older child or adult, the lesion is less likely to heal, and surgery is frequently indicated. Lateral lesions have a worse prognosis, and if a major portion of the weight-bearing surface is involved, osteoarthritis may develop in the adult.

Loose Bodies

Loose bodies, commonly referred to as “joint mice,” are often found in the knee joint. They may be present as the result of osteoarthritis, osteochondral fractures, or osteochondritis dissecans or secondary to primary disease of the synovium. Usually, no source is found.

CLINICAL FEATURES

Loose bodies may cause swelling and intermittent locking of the joint. There is frequently a feeling of weakness and instability. The loose body is occasionally palpable and freely movable. The roentgenogram is usually diagnostic (Fig. 11-30). A primary lesion such as osteochondritis dissecans may be detected, but frequently no joint abnormality other than the loose body is visualized.

FIG. 11-30 Osteocartilaginous loose body (arrow) in the suprapatellar pouch.

TREATMENT

Treatment is surgical removal if symptomatic. Sometimes, movement of the loose body and symptoms will cease when it becomes attached to the synovium.

Degenerative Arthritis

The knee is the joint most commonly affected by osteoarthritis. The main factor in its development is the aging process, and although the cause is unknown in most cases (primary osteoarthritis), obesity and malalignment of the lower extremity may play some role. Secondary or posttraumatic arthritis often develops after ligamentous injuries or severe trauma. The pathologic features were described in Chapter 10.

CLINICAL FEATURES

The symptoms are similar to those that occur with osteoarthritis in any other joint. The medial compartment is most commonly involved, which typically leads to increased bowing over time. Pain with activity that is relieved by rest is characteristic. Morning stiffness that is relieved by activity is also usually present. A chronic effusion is not uncommon. Crepitus and grating are also frequent complaints. Restriction of motion, joint swelling, local tenderness, and deformity are common clinical findings. Late stages are associated with pain at rest. The roentgenographic features consist of joint space narrowing, osteophyte formation, and sclerosis in the subchondral region (Fig. 11-31).

FIG. 11-31 Degenerative arthritis of the knee. The joint space is severely narrowed.

TREATMENT

Symptoms are often relieved by conservative treatment consisting of weight loss, rest, analgesics, and quadriceps exercises. NSAIDs are commonly used, although cellular and tissue evidence of inflammation is usually absent. A cane is frequently helpful to relieve the weight-bearing stress. An occasional intraarticular injection of steroid may be very helpful to relieve pain. This can be repeated three to four times per year as needed. When pain is diminished, gentle range-of-motion exercises are begun to overcome contractures. Viscosupplementation (injection of fluid containing hyaluronan derivatives) and unloading braces have been tried with uncertain benefit.

Surgical treatment involves elimination of the painful weight-bearing articulation. Arthrodesis in the active young adult eliminates the pain, but patients find the permanent stiffness disturbing, and it is rarely performed any longer. Realignment osteotomy and joint replacement are the most beneficial surgical procedures. Cartilage transplantation remains in the investigational stage.

Osteonecrosis

Avascular necrosis of bone occurs in many joints and under many conditions. The femoral head, humeral head, and talus are common sites. It may be spontaneous (idiopathic) or secondary to known causes such as chronic steroid therapy, gout, and chronic alcoholism. It may be seen in divers and workers who use compressed air (caisson disease). Most of the time, the cause is unknown. As in osteochondritis dissecans, the medial femoral condyle is the most common site of involvement in the knee. Secondary osteoarthritis frequently develops.

CLINICAL FEATURES

This disorder is more common in patients older than 50 years of age. The onset is usually gradual with progressive pain and swelling. The medial femoral condyle may be locally tender.

ROENTGENOGRAPHIC FINDINGS

Initially, films are usually normal or show minimal degenerative arthritis consistent with the patient’s age. An early bone scan may show well-localized increased uptake over the involved area. MRI will also reveal the lesion. Eventually, radiolucency from a subchondral zone of sclerosis appears. The necrotic area frequently fragments and collapses, and this results in secondary osteoarthritis (Fig. 11-32).

FIG. 11-32 Osteonecrosis of the distal femur. Note the large defect in the femoral articular surface. Also present are diffuse sclerotic bone changes in other regions of the knee. The patient was on long-term steroid use for scleroderma. Joint replacement was necessary.

TREATMENT

Strengthening exercises, NSAIDs, and reduction of weight bearing will allow healing within a few months in more than half the cases. Surgery is eventually required in the remainder, usually in the form of an osteotomy or joint replacement.

Bursitis

Protective bursal sacs are present wherever soft tissue, such as muscle or tendon, moves over a bony prominence. They can become painful as a result of irritation or direct trauma. One such bursa that is frequently symptomatic in the knee is the anserine bursa. This bursa is located deep to the insertions of the semitendinosus, gracilis, and sartorius tendons medially (Fig. 11-33). Anserine bursitis is often difficult to separate from medial joint osteoarthritis. (Sometimes they occur together.) The tenderness from anserine bursitis is below the joint line.

FIG. 11-33 Bursae of the knee. A, Anserine bursa; P, prepatellar bursa; S, semimembranous bursa. The latter may become enlarged and form a Baker’s cyst.

Treatment measures include moist heat, rest, and the injection of a steroid/lidocaine mixture into the tender bursa (Fig. 11-34). NSAIDs are given to control pain and inflammation. Recurrent anserine bursitis is often related to osteoarthritis of the knee.

FIG. 11-34 Pes bursitis injection. Approximately 2 finger breadths below the joint line (J) is the usual site of maximum tenderness. For injection, 1 mL of steroid plus 3 to 4 mL of lidocaine are used. The needle should encounter bone, and half of the injection is given there. The remainder is injected around the area for 1 to 2 cm.

The prepatellar bursa lies between the skin and the patella. Direct trauma may cause if to fill with blood acutely. It may also become irritated from recurrent trauma, especially kneeling (housemaid’s knee), and it is occasionally involved in infection. Chronic traumatic changes may occur with permanent thickening of the bursa, which makes it more prone to recurrent injury.

Acute traumatic prepatellar bursitis usually responds to rest. Aspiration may be performed for pain relief, but the fluid often returns. The fluid should be cultured if suspicious for infection. If infection develops, aspiration or open drainage followed by the appropriate antibiotic coverage is indicated. Incision and drainage should never be performed for sterile recurrent swelling because a chronic draining sinus tract may result. Recurrent bursal effusions may be aspirated repeatedly (Fig. 11-35). Eventually, most will “dry up” on their own. A chronic, swollen bursa that is vulnerable to repeated injuries may need to be excised.

FIG. 11-35 Swollen prepatellar bursa. To aspirate, a large needle (16- or 18-gauge) is needed. The skin may need to be infiltrated first with local anesthetic. During aspiration, additional fluid can be removed by manually expressing it towards the tip of the needle.

Tendinitis

Concepts regarding the fundamental underlying pathology in disorders commonly called tendinitis continue to evolve, as has the terminology. The idea that inflammation is the cause of these chronic conditions is gradually being replaced with more precise pathologic information that shows collagen degeneration and neovascular change as the primary abnormalities present in the involved tissues. Although a distant inflammatory event or old traumatic injury with ischemia may have led to the condition, inflammatory cells are commonly absent. Hence, terms such as tendinosis and tendinopathy are now often used in describing these painful disorders.

Several tendons adjacent to the knee joint may develop chronic pain. The tendons of the extensor mechanism (patellar and quadriceps) are the ones most commonly involved, and the etiology is usually overuse. The disorder is often seen in weightlifters and athletes who jump. The quads tendon may be affected at its insertion. The patellar tendon may be involved anywhere along its length (jumper’s knee), although it is most often affected at its patellar attachment. Flexor tendons are less frequently affected. Pain with activity and local point tenderness are characteristic clinical features. Patients often complain of stiffness after sitting with the knees flexed for a long period of time such as at the movie (“theatre sign”) or on long plane rides. The knee usually feels better when it is extended. As in most cases of tendinitis (tendinopathy), the pain is aggravated by passive stretching of the tendon as well as by forceful contraction of the muscle–tendon unit against resistance.

The treatment is symptomatic, with rest, heat, stretching, and strengthening. A properly designed program of physical therapy may help although it should be pain free. Even though there are unanswered questions regarding the etiology of these disorders, anti-inflammatory medication often relieves symptoms. Steroid injections may be helpful, but the patellar tendon should never be injected.

Arthroscopy

Arthroscopy is a valuable tool in the diagnosis and treatment of many disorders of the knee. It has also been used in the shoulder, elbow, hip, and ankle joint, but is most useful in problems of the knee. The procedure is safe and relatively minor with little morbidity. It is usually performed on an outpatient basis. Its diagnostic accuracy approaches 100%, and by using separate puncture holes of entrance, small instruments may be passed into the knee to perform a variety of functions. The most common are removal or repair of meniscus tears and removal of loose bodies. It is used to evaluate the knee of patients with Baker’s cyst to determine whether any intraarticular abnormality is present that may have caused the cyst to develop. In this case, the intraarticular problem might require treatment rather than the Baker’s cyst. Arthroscopic surgery is also frequently used to remove damaged articular cartilage from the patella in patients with chondromalacia, but the results in this condition are often inconsistent and unpredictable.

Diagnostic arthroscopy is also helpful in evaluating acute injuries of the knee to determine whether ligamentous repair may be necessary. It is also useful in difficult diagnostic problems in those symptomatic knees with vague symptoms and few physical findings.

PLICA SYNDROME

The synovial plicae are four (suprapatellar, infrapatellar, medial, and lateral) membranous folds or bands that may be an occasional source of chronic knee pain. They have become items of interest mainly because of the increasing use of arthroscopy. The plicae may become symptomatic when irritated by direct trauma, overuse, or inflammatory disorders, although the relationship between plicae and disease and symptoms remains uncertain. The most common clinical features are chronic aching, usually medial to the patella, and local tenderness. When the medial plica is visualized arthroscopically, it is released by partial excision. The other folds are not commonly symptomatic.

Fractures of the Knee

Many fractures about the knee are intraarticular. They may occur through the femoral condyles or tibial plateaus. Open reduction with internal fixation is usually indicated if any displacement is present that would cause the articular surface to be irregular or lead to instability. Otherwise, traumatic arthritis may develop.

FRACTURES OF THE TIBIAL PLATEAU

A common fracture in the knee is an injury to the lateral tibial plateau (Fig. 11-36). This injury results from a force applied to the lateral aspect of the knee with the leg in the extended weight-bearing position. This is often caused by being struck by the bumper of a car. Undisplaced, impacted fractures are easily treated by a compression dressing and early motion with avoidance of weight bearing for 6 to 8 weeks. Displaced fractures require open reduction and internal fixation with elevation of the depressed plateau fragment.

FIG. 11-36 Depressed fracture of the lateral tibial plateau.

FRACTURES OF THE PATELLA

Fractures of the patella are usually transverse and result from a fall onto the knee or a direct blow. They are classified as undisplaced or displaced (Fig. 11-37). Undisplaced (less than 8 mm) fractures are easily treated nonoperatively. A compression dressing followed by a removable splint may be all that is necessary in the conscientious patient. Otherwise, a cylinder cast or brace is applied and maintained for 5 to 6 weeks. This is followed by an active exercise program to restore strength and mobility.

FIG. 11-37 Displaced fracture of the patella.

Displaced fractures usually require surgery. Comminuted fragments are removed, and the patellar fracture and extensor mechanism of the knee are repaired.

Patellar fractures are not to be confused with a bipartite patella (Fig. 11-38). This is a developmental variant that is often bilateral and usually asymptomatic. It is most often located in the superolateral pole of the patella and represents failure of this ossification center to unite with the main patella.