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Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8e

Chapter 274: Knee Injuries Rachel R. Bengtzen; Je�rey N. Glaspy; Mark T. Steele

ANATOMY

The knee consists of two joints, the tibiofemoral joint and the patellofemoral joint. Within the tibiofemoraljoint, the distal femur (comprised of the medial and lateral femoral condyles) articulates with the proximaltibia (comprised of the medial and lateral tibial condyles) (Figure 274-1). The medial and lateral menisci aresituated between the articular surfaces, and the menisci provide cushion, lubrication, and resistance toarticular wear (Figure 274-2). In the patellofemoral joint, the patella articulates with the distal femur alongthe anterior depression called the patellofemoral groove during flexion and extension of the knee. Thepatella is stabilized by the patellar tendon and medial retinaculum.

FIGURE 274-1.

The supracondylar and condylar areas of the femur, and the medial and subcondylar areas of the tibia.

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FIGURE 274-2.

Ligaments of the right knee joint. The articular capsule and the patella have been removed.

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There are four ligaments in the knee: the anterior cruciate ligament, the posterior cruciate ligament, and themedial and lateral collateral ligaments (Figure 274-2). These ligaments provide strength and stability to theknee. The posterior aspect of the knee, the popliteal fossa, contains the popliteal artery and vein, thecommon peroneal nerve, and the tibial nerve (Figure 274-3).

FIGURE 274-3.

Posterior knee: popliteal fossa anatomy.

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CLINICAL FEATURES

Determine the mechanism of knee injury and review all prior orthopedic injuries or surgical procedures. Aswith all orthopedic examinations, compare the noninjured or normal joint with the injured joint during allaspects of the examination, but especially during palpation and stress testing.

The first examination is usually the easiest to perform and may be the most valid, because the patient doesnot anticipate pain and may not guard against the examination, and because inflammation and e�usionlimiting the examination may have not yet developed.

Assess gait (if possible), functional range of motion, and the ability to perform a straight leg raise (evaluatesthe extensor complex). Evaluate the knee for ecchymoses, swelling, e�usion, masses, patella location andsize, muscle mass, erythema, and evidence of local trauma. With the patient supine, determine whether leglengths are equal or unequal. Ask the patient to demonstrate the best possible active range of motion. Assessdistal neurovascular function. Palpate the nontender areas first and work toward the tender area to minimizepatient apprehension. Palpate the patella, patellar facets, proximal fibula, and femoral and tibial condyles for

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pain and crepitus. Make note of joint e�usion, tenderness, increased temperature, strength, sensation, andlocation of pulses.

Examine the patella for size, shape, and location with the knee in flexion. Check patellar mobility with theknee in extension, making sure it can move laterally and medially without apprehension. Palpate thepopliteal space for masses, swelling, and pulses. With the knee in flexion, palpate both the medial and lateraljoint lines and the medial and lateral collateral ligaments, because tenderness at those locations suggeststhe possibility of a meniscal or ligamentous injury, respectively. The final phase of the examination of theknee is stress testing (see "Ligamentous and Meniscal Injuries" below). This is the most di�icult aspect of theexamination, although potentially the most informative. The patient must be relaxed and made ascomfortable as possible. Testing is o�en easier if the patient sits up with the leg hanging over the side of thebed and with the bed supporting the posterior thigh. Examine the uninjured, presumably normal, oppositeknee first to determine the patient's normal laxity.

NEUROVASCULAR INJURIES

Popliteal artery injury can occur from fractures about the knee, especially femoral condyle fractures ordisplaced tibial plateau fractures, and from ligamentous injuries such as isolated posterior cruciate ligament

injuries, multiple ligamentous injuries, or knee dislocation.1,2 Popliteal artery circulation must be restoredwithin 8 hours to avoid amputation, because collateral circulation is insu�icient to maintain blood flow tothe leg. Measure distal pulses on ED admission and a�er any manipulation, and compare pulses to those inthe noninjured leg. A diminished pulse raises concern for vascular injury and should not be interpreted asvascular spasm. An abnormal finding on pulse examination is reported to have a sensitivity of only 79% and a

specificity of 91% for arterial injuries that require surgical intervention,2 so it is important to remember thatvascular injury can be present even in the presence of normal pulses. Ancillary studies include measurementof ankle-brachial index (<0.9 in a patient with peripheral vascular disease or vascular injury) and duplex US

(reported to be 95% sensitive and 99% specific for arterial injury).1 Vascular surgery consultation is requiredfor any potential popliteal arterial injury to determine the need for angiography, as well to monitor for thedevelopment of compartment syndrome, venous injury, and arterial thrombosis.

Peroneal nerve injuries can result from severe ligamentous knee injuries and knee dislocations. Nearly half offibular head fractures or avulsions are associated with peroneal nerve injury. The deep peroneal nerveprovides sensation to the first dorsal web space of the toes and allows dorsiflexion of the foot and extensionof the toes. Injury results in foot drop and gait di�iculty. Prognosis is variable, depending on the severity ofinjury.

DIAGNOSIS

IMAGING

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The Ottawa Knee Rules (Table 274-1) are sensitive in identifying fracture, and their use reduces ED waiting

times and costs. The Pittsburgh Knee Rules (Figure 274-4) are similar and may have greater specificity.3,4

TABLE 274-1

Ottawa Knee Rules: X-Ray if One Criterion Is Met

Patient age >55 y (rules have been validated for children 2–16 y of age)

Tenderness at the head of the fibula

Isolated tenderness of the patella

Inability to flex knee to 90 degrees

Inability to transfer weight for four steps both immediately a�er the injury and in the ED

FIGURE 274-4.

Pittsburgh Knee Rules for radiography. [Reproduced with permission from Seaberg DC, Yealy DM, Lukens T, etal: Multicenter comparison of two clinical decision rules for the use of radiography in acute, high-risk kneeinjuries. Ann Emerg Med. 1998;Jul;32(1):8-13. Copyright Elsevier.]

Both rules are applicable to children >2 years old and adults.4 It would be reasonable to order radiographs ona higher number of patients with knee pain who are multisystem trauma patients, and thus immobilized andunable to undergo gait testing.

Anteroposterior and lateral radiographs are typically obtained if radiographs are needed.5 Fat-fluid levels

(lipohemarthrosis) suggest intra-articular fracture and may be identified on a lateral view of the knee.6

Consider weight-bearing radiographs when tolerated, which allows for a functional assessment. Additionalradiograph views can be very useful. Oblique views are particularly helpful for detecting subtle tibial plateau

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fractures (internal oblique view is best for visualizing the lateral plateau, and external oblique view is best for

visualizing the medial plateau).5,7 A tunnel or intercondylar view provides a clear image of the intercondylarregion and is particularly useful in identifying tibial spine fractures. A sunrise (skyline, axial, or tangential)view is most useful in detecting nondisplaced vertical or marginal fractures of the patella, which may bemissed with the conventional views. The sunrise view is indicated if patellar subluxation or fracture issuspected. CT may be necessary to fully delineate the extent of tibial plateau fractures. MRI is also helpful inthis regard and has the added benefit of being able to assess so� tissue (i.e., ligamentous and meniscal)

injury.5

SPECIFIC INJURIES

PATELLA FRACTURES

Table 274-2 reviews the mechanisms of injury and treatment of patellar fractures. Patellar fractures may betransverse, comminuted, or of the avulsion type when the quadriceps or patellar tendon pulls o� a smallportion of the patella (Figure 274-5).

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TABLE 274-2

Mechanisms of Knee Injury and Treatment

Fracture Mechanism Treatment

Patella Direct blow (i.e., fall, motor vehicle crash)

or forceful contraction of quadriceps

muscle

Nondisplaced fracture with intact extensor

mechanism: knee immobilizer, rest, ice,

analgesia. Follow-up for serial radiographs.

Displaced >3 mm, articular incongruity >2 mm,

or with disruption of extensor mechanism:

above treatment plus early referral for ORIF.8

Severely comminuted fracture: surgical

debridement of small fragments and suturing of

quadriceps and patellar tendons.

Open fracture: irrigation and antistaphylococcal

antibiotics in the ED; debridement and irrigation

in the operating room.

Femoral

condyles

Fall with axial load with

valgus/varus/rotational forces, or a blow to

the distal femur

Incomplete or nondisplaced fractures in any age

group or stable impacted fractures in the

elderly: long leg splinting and orthopedic

referral.

Displaced fractures or fractures with any degree

of joint incongruity: splinting and orthopedic

consult for ORIF.9,10

Tibial

spines

and

tuberosity

Force directed against flexed proximal tibia

in an anterior or posterior direction (i.e.,

motor vehicle crash, sporting injury)

Incomplete or nondisplaced fractures:

immobilization in full extension (knee

immobilizer) and orthopedic referral in 2–7 d.

Complete or displaced fracture: early orthopedic

referral, o�en requires ORIF.11

Tibial

tuberosity

Sudden force to flexed knee with

quadriceps contracted

Incomplete or small avulsion fracture:

immobilization.

Complete avulsion: ORIF.8

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Abbreviation: ORIF = open reduction internal fixation.

Fracture Mechanism Treatment

Tibial

plateau

Valgus or varus forces combined with axial

load that drives the femoral condyle into

the tibia (i.e., fall, leg hit by car bumper)12

Nondisplaced, lateral fracture: knee immobilizer

with non–weight bearing and orthopedic

referral in 2–7 d.

Depression of articular surface: early orthopedic

consult for ORIF.12

FIGURE 274-5.

Classification of patellar fractures.

Transverse fractures of the patella are most common, followed by stellate and comminuted fractures.Patients with nondisplaced fractures may be ambulatory. On examination, there is focal patellar tenderness,swelling, and e�usion. Check the integrity of the extensor mechanism of the knee by having the patientperform a straight-leg raise against gravity. Nonoperative management is indicated for fractures with an

intact extensor mechanism and <2 mm of step-o� and <3 mm of fracture displacement.8,13 Transversefractures are more likely to be displaced and to be associated with a disrupted extensor mechanism.Di�erential diagnosis of patellar fractures radiographically includes bipartite patella. This condition involvesthe superior lateral corner of the patella, is typically bilateral, and is di�erentiated from fracture by thesmooth cortical margins.

FEMORAL CONDYLE FRACTURES

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Fractures of the femoral condyles account for 6% of femur fractures and include supracondylar,intercondylar, condylar, and distal femoral epiphyseal fractures (Figure 274-1). Table 274-2 reviews themechanisms of injury and treatment for femoral condyle fractures. Examination reveals pain, swelling,deformity, rotation, shortening, and an inability to ambulate. Although neurovascular injuries areuncommon, the potential for popliteal artery injury exists, so the status of distal sensation and pulses mustbe checked. Test the space between the first and second toes, innervated by the deep peroneal nerve, forsensation. In addition, search for associated injuries, including ipsilateral hip dislocation or fractures anddamage to the quadriceps apparatus. The overall outcome of these injuries is fair. Complications includedeep venous, fat embolus syndrome, delayed union or malunion, and the subsequent development of

osteoarthritis.9

TIBIAL SPINE AND TUBEROSITY FRACTURES

Although isolated injuries of the tibial spine are uncommon, they usually result in cruciate ligamentinsu�iciency. Table 274-2 reviews the mechanism of injury and treatment for tibial spine and tuberosityfractures. Fracture of the anterior tibial spine is about 10-fold more common than fracture of the posteriorspine. Examination shows a painful, swollen knee secondary to hemarthrosis, inability to extend fully, and a

positive finding on the Lachman test (see "Ligamentous and Meniscal Injuries" below).11 The quadricepsmechanism inserts on the tibial tubercle. A sudden force to the flexed knee with the quadriceps musclecontracted may result in a complete or incomplete avulsion of the tibial tubercle. The fracture line mayextend into the joint. Examination reveals pain and tenderness over the proximal anterior tibia with pain onpassive or active extension.

TIBIAL PLATEAU FRACTURES

Fractures of the tibial plateau are seen more commonly in the older population and can be very di�icult todetect. Table 274-2 reviews the mechanism of injury and treatment for tibial plateau fractures. Both medial

and lateral plateaus may be fractured simultaneously, although the lateral plateau is more o�en fractured.12

Direct trauma to the lateral aspect of the knee may account for the preponderance of lateral tibial plateaufractures. The patient may experience painful swelling of the knee and limitation of motion. Radiographsmay demonstrate a fracture, but o�en show only a lipohemarthrosis on the lateral view. Consider adding ananteroposterior view in the plane of the plateau (10 to 15 degrees caudal) or oblique views to help assess fordisplacement. If the patient cannot tolerate the additional views, or there are negative radiographs but the

patient cannot bear weight, consider obtaining a CT scan.5 So� tissue injuries associated with tibial plateaufractures may influence outcomes. Anterior cruciate ligament and medial collateral ligament injuries areassociated with lateral plateau fractures, whereas posterior cruciate and lateral collateral ligament injuriesoccur with medial plateau fractures. A Segond's fracture (see below) is pathognomonic for an anteriorcruciate ligament injury, and it is important recognize and treat the ligament injury, rather than just the

plateau fracture.12 Potential complications of tibial plateau fractures include popliteal artery injury withhigh-energy displaced fractures, the development of deep venous thrombosis, and osteoarthritis.

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LIGAMENTOUS AND MENISCAL INJURIES

The knee joint depends on ligaments and muscles for support (Figure 274-2). It is frequently subjected toinjuries from traumatic forces, including hyperextension, valgus and varus stresses, and anteroposteriordisplacement. By far the most common forces are valgus, which produce injuries to the medial side of theknee. Injuries to the lateral side of the knee are produced by varus stresses. Such forces may result in a strainor rupture of the medial or lateral collateral ligaments, the anterior or posterior cruciate ligaments, or thecapsular structures, or a tear in the medial or lateral meniscus or both. Functional instability of the knee isdetermined by stress testing, which may demonstrate abnormal laxity when properly done. Table 274-3summarizes the reported sensitivity, specificity, and positive and negative likelihood ratios for diagnosis of

ligamentous and meniscal injury.14

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TABLE 274-3

Reliability of Physical Examination for Diagnosis of Knee Ligamentous and Meniscal Injuries

Structure Maneuver

Mean

Sensitivity

(range)

Mean

Specificity

(range)

Positive

LR

(95%

CI)

Negative

LR (95%

CI)

Comments

Anterior

cruciate

ligament

Composite

examination*

82% (62–

100)

94% (56–

100)

25 (2.1–

306)

0.04

(0.01–

0.48)

When limited to

acute injury (one

study), 62%

sensitivity and 56%

specificity.

Anterior

drawer test

62% (9–

93)

67% (23–

100)

3.8

(0.7–

22.0)

0.3

(0.05–

1.5)

Variability of studies

may be due to small

sample sizes.

Lachman

test

84% (60–

100)

100%

(100)

42 (2.7–

651.0)

0.1 (0.0–

0.4)

Only one study

commented on

specificity.

Therefore

specificity and LRs

may be inaccurate.

Lateral pivot

shi�

38% (27–

95)

NA NA NA No study

commented on

specificity.

Posterior

cruciate

ligament

Composite

examination*

95.5%

(91–100)

89.5%

(80–99)

21 (2.1–

205.0)

0.05

(0.01–

0.50)

Results limited to

two studies.

Posterior

drawer test

55% (51–

86)

NA NA NA No study

commented on

specificity.

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Abbreviation: LR = likelihood ratio; NA = not applicable.

*These studies reported a "composite examination" without giving data on the specific examination maneuvers.

Structure Maneuver

Mean

Sensitivity

(range)

Mean

Specificity

(range)

Positive

LR

(95%

CI)

Negative

LR (95%

CI)

Comments

Medial

collateral

ligament/lateral

collateral

ligament

NA NA NA NA NA No study was

identified that

adequately

examined

diagnostic accuracy

for these injuries.

Meniscal injury Composite

examination*

77% (64–

82)

81% (78–

84)

NA NA Only three of five

studies commented

on specificity.

Joint-line

tenderness

79% (76–

85)

15% (11–

43)

0.9

(0.8–

1.0)

1.1 (1.0–

1.3)

Only two of four

studies included

acute injuries, all

four included

chronic injuries;

consequently,

applicability to ED

is limited.

McMurray

test

53% (29–

63)

59% (29–

100)

1.3

(0.9–

1.7)

0.8 (0.6–

1.1)

MEDIAL COLLATERAL LIGAMENT AND LATERAL COLLATERAL LIGAMENT INJURIES

The medial stabilizers of the knee are tested by applying a valgus stress (Figure 274-6) to the knee inapproximately 30 degrees of flexion to determine the integrity of the medial capsular and ligamentousstructures. The medial collateral ligament supplies the majority of restraint to valgus deformities of the kneein all stages of flexion. A varus force is then applied to the lateral aspect of the knee, again withapproximately 30 degrees of flexion, to ascertain the integrity of the lateral structures. The lateral collateral

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ligament, analogous to the medial collateral ligament, is the major restraint to varus laxity on the knee at allpositions of flexion. Injuries to these ligaments can include a strain, partial tear, or complete rupture. If thereis no demonstrated laxity but the valgus or varus test reproduces pain, a strain has likely occurred. If there isa laxity demonstrated without a firm end point compared with the other knee, this is concerning for acomplete tear of the medial or lateral collateral ligament. If there is laxity with the varus or valgus testperformed with 30 degrees of flexion, similar maneuvers should be applied with the leg in full extension, ifpossible. Laxity to valgus stress while in full extension indicates a significant lesion involving the entiremedial collateral ligament complex and/or in association with a cruciate ligament and posterior capsule

tear.15 Laxity to varus stress in full extension likewise indicates a significant injury that may involve theposterolateral corner of the knee as well as the cruciate ligaments. Peroneal nerve injuries may also occur inlateral injuries. Although these tests may aid in the diagnosis of medial collateral ligament and lateralcollateral ligament injuries, there are no adequate published reports to allow comment on their sensitivity

and specificity.14

FIGURE 274-6.

Valgus stress in full extension (A) and in 30 degrees of flexion (B).

ANTERIOR CRUCIATE LIGAMENT INJURIES

The mechanism of injury to the anterior cruciate ligament is usually noncontact—a deceleration,hyperextension, or marked internal rotation of the tibia on the femur resulting in an injury to this ligament.Injury is o�en associated with a "pop," swelling that develops within hours, and a sense of instability. The

pop is considered pathognomonic for anterior cruciate ligament injury.16 The history of this mechanism ofinjury combined with the presence of a traumatic e�usion is very suggestive of an anterior cruciate ligamentdisruption.

The diagnosis of an anterior cruciate ligament injury is made using the Lachman test (Figure 274-7), theanterior drawer sign (Figure 274-8), and the pivot shi� (Figure 274-9). The Lachman test is the most sensitive

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and specific test (84% and 100%, respectively).14 For this test the examiner places the knee in 30 degrees offlexion and stabilizes the femur above the knee with his or her nondominant hand. The dominant hand isplaced grasping the lower leg at the level of the tibial tubercle, and the examiner introduces an anteriorforce, attempting to displace the tibia anteriorly on the femur. If a displacement compared with the oppositeknee is found, or if there is a so� end point, then a tear in the anterior cruciate ligament has occurred.Although the anterior drawer sign has been used for a long time, its sensitivity is only approximately 62%.The maneuver is done with a 45-degree flexion at the hip and a 90-degree flexion at the knee. Then attemptto displace the tibia from the femur in an anterior direction. A displacement of >6 mm compared with thenormal, opposite knee indicates an injury to the anterior cruciate ligament. False-negative findings may beassociated with this maneuver. False-positive results may occur when there is a posterior cruciate ligamenttear as the tibia will start out in a more posterior position, thus allowing for a perceived increase intranslation when moved anteriorly. Although the Lachman test is more sensitive than the anterior drawertest and is able to identify partial tears in the anterior cruciate ligament when the examiner is skilled, it canbe di�icult to perform on patients with large legs. The pivot shi� (Figure 274-9) is the third maneuver bywhich the examiner can determine the integrity of the anterior cruciate ligament. The pivot shi� may besomewhat painful to the patient and is o�en most easily tested in the operating room. The pivot shi� test

without anesthesia was found to be only 24% sensitive but 98% specific.17 With the patient supine andrelaxed, li� the heel of the foot to approximately 45 degrees of hip flexion with the knee fully extended. Theopposite hand grasps the knee with the thumb behind the fibular head. Then internally rotate the ankle andknee, apply a valgus force to the knee, and flex the knee. If an anterior subluxation of the tibia is present, asudden visible, audible, and palpable reduction of the subluxation occurs at about 20 to 30 degrees offlexion. This indicates a deficit in the anterior cruciate ligament, which is required to stabilize the knee in thisposition. Other tests are described in the literature to determine the integrity of the anterior cruciateligament, including the jerk test and dynamic extension testing.

FIGURE 274-7.

Lachman test, performed with the knee flexed between 15 and 30 degrees. One hand stabilizes the thighwhile the other moves the tibia anteriorly.

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FIGURE 274-8.

Anterior drawer test, performed with 45-degree flexion at the hip and a 90-degree flexion at the knee. Try todisplace the tibia from the femur in an anterior direction.

FIGURE 274-9.

A through C. In the pivot shi� of Galway and MacIntosh, the test is done with the knee in full extension withapplication of a valgus and internal rotation stress. The "clunk" of reduction is felt in the first 20 to 30 degreesof flexion.

POSTERIOR CRUCIATE LIGAMENT INJURIES

The posterior cruciate ligament can be injured in isolation or in combination with other ligamentousstructures of the knee. In contrast to anterior cruciate ligament injuries, isolated posterior cruciate ligament

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injuries are much less common. The posterior cruciate ligament provides initial resistance to posteriortranslation at all angles of flexion of the knee. The mechanism of injury then is usually an anterior-to-posterior force applied to the tibia or lower leg. Posterior cruciate ligament injuries are seen in associationwith other ligamentous injuries when a serious injury has occurred to the knee. A deficit of this ligament isidentified by the posterior drawer test (Figure 274-10) and the sag sign. The posterior drawer test isperformed with the knee and hip in flexion as described for the anterior drawer test. The physician applies aposterior force to the tibial tubercle. If there is displacement posteriorly, then the examiner can diagnose aninjury to this ligament. One might also notice a sag sign, where there is a posterior sag or drop back of thetibial tubercle because of loss of integrity of the posterior cruciate ligament when observing the knee with45-degree flexion at the hip and 90-degree flexion at the knee. Results of this test can be misleading,however, if there is a straight anterior instability resulting in a subluxation of the knee forward. Thisabnormal position gives the false impression of too much posterior play when the posterior drawer test isperformed, because the knee is reduced to its normal anatomic alignment from the forwardly subluxedposition. Although the posterior drawer test has only a 55% sensitivity, the composite history and physical

examination findings are much more accurate in the diagnosis of posterior cruciate ligament injuries.14,18

FIGURE 274-10.

Posterior drawer test.

Combined ligamentous laxity of the knee is o�en seen, especially in acute athletic injuries. Combinedanteromedial and anterolateral laxity occurs most frequently, but virtually any combination of medial andlateral laxity of the knee can occur.

POSTEROLATERAL INJURY

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One knee injury that is especially di�icult to detect is injury to the posterolateral structures. Posterolateralinstability usually involves a tear of the popliteus–arcuate complex, which may occur in combination withlateral ligament injury and possible anterior cruciate ligament or posterior cruciate ligament injury. Isolatedinjuries to the popliteus–arcuate complex are rare. Isolated posterolateral instability is demonstrated bytesting at 0 to 30 degrees of flexion for maximal posterior translation and at 90 degrees of flexion for maximalexternal rotation compared with that of the normal opposite knee. Further testing to determine the integrityof the lateral collateral ligament and anterior or posterior cruciate ligaments must be done as well.

HEMARTHROSIS OR EFFUSION

The presence of a hemarthrosis can suggest an underlying ligamentous injury to the knee, most commonlythe anterior cruciate ligament. Serious ligament injuries, however, may present with minimal pain and nohemarthrosis because of complete disruption of the ligamentous and capsular fibers, which allows leakageof the blood into the so� tissue spaces. Hemarthrosis can also be caused by osteochondral fractures orfractures that extend into the joint line, or peripheral meniscal tears. Traumatic hemarthroses usually occurwithin minutes to hours of injury, in contrast to chronic e�usions of the knee due to synovial inflammation,which occur 1 to 2 days a�er strenuous use of the joint.

With ligamentous injuries, plain radiographs are typically normal or reveal only an e�usion. An avulsionfracture at the site of attachment of the lateral capsular ligament on the lateral tibial condyle (Segond's

fracture) is a marker for anterior cruciate ligament rupture.7,12 Cortical avulsion of the medial tibial plateau

(very uncommon) is associated with tears of the posterior cruciate ligament and medial meniscus.19

Continued refinements in MRI have enabled this imaging method to produce high-quality images of theligamentous and meniscal structures of the knee, which results in an accuracy rate of close to 90% to 95% in

identifying meniscal and cruciate ligament disruption.20 Such an MRI examination, however, is typicallyordered by the patient's primary care provider, sports medicine physician, or orthopedist in follow-up.

TREATMENT OF SPECIFIC INJURIES

LIGAMENTOUS INJURIES

Injuries involving a single ligament with a minor strain can be managed with a knee immobilizer, ice packs,

elevation, nonsteroidal anti-inflammatory drugs, and ambulation as soon as is comfortable for the patient.21

When knee immobilizers are placed, instruct the patient to perform daily range-of-motion exercises to avoidcontracture and maintain mobility. Contractures are more common in the elderly and can occur a�er only afew days of immobilization. Although there is no universally accepted regimen for range-of-motion exercise,one procedure is first to apply ice to relieve pain and then to perform 10 to 20 knee flexion-extensions (noweights should be added) three or four times a day. Refer patients to an orthopedic surgeon, sports medicinephysician, or primary care provider within the next few days to a week for follow-up examination.

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Complete rupture of an isolated ligament can initially be treated conservatively in the same fashion, withstraight leg quadriceps strengthening, range-of-motion exercises, and functional bracing included as a partof the follow-up care. Professional athletes with single-ligament ruptures or patients with more than onetorn ligament need urgent orthopedic consultation so that definitive surgical management can be planned.

Arthrocentesis may be of therapeutic benefit in patients with large, tense e�usions of the knee; however,good evidence of its e�icacy has not been reported. A systematic review to ascertain whether aspiration

improves symptoms in patients with acute traumatic hemarthrosis found no conclusive data.22 Furthermore,recurrence of the e�usion following aspiration is common. Arthrocentesis may be of assistance diagnosticallyif the e�usion is not clearly due to trauma. The presence of blood and glistening fat globules ispathognomonic of lipohemarthrosis, which indicates intra-articular knee fracture. The major complication ofarthrocentesis is septic arthritis.

MENISCAL INJURIES

Meniscal injuries of the knee occur by themselves or in combination with ligamentous injuries. For example,anterior cruciate ligament injuries are commonly associated with meniscal injuries. Cutting, squatting, ortwisting maneuvers may cause injury to the meniscus. The medial meniscus is approximately twice as likelyas the lateral meniscus to be injured. Four fi�hs of the tears involve the peripheral posterior aspect of the

meniscus.23 Many maneuvers have been described in the literature to determine whether a meniscus hasbeen injured. Most of these tests, however, have an unacceptable sensitivity and specificity (e.g., joint line

tenderness has a sensitivity of 70% and specificity of 15% in the ED population).14 Although the diagnosis ofa meniscal tear is di�icult to make in certain patients, the combination of a suggestive history and physicalfindings on examination should lead the emergency physician to consider the diagnosis. Ask if the patientexperiences painful locking of the knee joint on either flexion or extension and if this limits further activity.This sign clearly points to the diagnosis of a torn meniscus. E�usions that occur a�er activity; a sensation ofpopping, clicking, or snapping; a feeling of instability in the joint, especially with activity; and tenderness inthe anterior joint space a�er excessive activity suggest the diagnosis of a meniscal tear.

At physical examination, attempt to identify atrophy of the quadriceps muscle because of disuse and joint-line tenderness. Various maneuvers, such as the McMurray test or the grind test, have been described but

yield positive results only about 50% of the time.14,24 If a tentative diagnosis of a meniscal tear is considered,refer to an orthopedic surgeon or the patient's primary care provider and instruct partial weight bearing, astolerated. Definitive diagnosis can be made by MRI or arthroscopy, with the latter also allowing for definitivesurgical treatment (usually partial meniscectomy or meniscal repair).

LOCKED KNEE

The "locked knee" describes when a knee cannot actively or passively fully extend. A patient who presents tothe ED with a locked knee can experience a great deal of pain along with loss of mobility. The most commoncause of an acutely locked knee is a torn meniscus. The di�erential diagnosis also includes anterior cruciate

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ligament rupture, patella dislocation, loose bodies, or foreign body. Historically the treatment includes oneattempt at closed reduction under procedural sedation. A�er procedural sedation is initiated, one canattempt to unlock the knee. Position the patient with the leg hanging over the edge of the table and the kneein 90 degrees of flexion. A�er a period of relaxation, apply longitudinal traction to the knee, along withinternal and external rotation, in an attempt to unlock the joint. If this maneuver is unsuccessful, orthopedicconsultation for operative arthroscopy is indicated. If the unlocking is successful, referral to an orthopedist

for MRI and/or arthroscopy is appropriate.25

KNEE DISLOCATION

Knee dislocation (Figure 274-11) is a result of tremendous ligamentous disruption due to hyperextension orapplication of direct posterior force to the anterior tibia, force to the fibula or medial femur, force to the tibiaor lateral femur, or rotatory force resulting in anterior, posterior, lateral, medial, or rotatory dislocation. Thisinjury typically occurs following high-velocity mechanisms such as motor vehicle crashes or low-velocity

mechanisms in sports; however, dislocations can also occur spontaneously in morbidly obese patients.1,26

An anterior dislocation is most common, occurring about 40% of the time, with posterior dislocations (33%),

lateral dislocations (18%), medial dislocations (4%), and rotary dislocations also occurring.2,26 Because of

severe ligamentous damage, spontaneous reduction occurs in up to 50% of knee dislocations.2 Therefore, aseverely injured knee that is unstable in multiple directions raises suspicion of a spontaneously reduced kneedislocation. Maintaining awareness of the possibility of this injury is important because of the high incidenceof associated complications, including popliteal artery injury and peroneal nerve injury (mostly withposterolateral dislocations), in addition to ligamentous and meniscal injury.

FIGURE 274-11.

Types of knee dislocation: anterior (A), posterior (B), and lateral (C).

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Timely reduction of the dislocated knee is essential. Apply longitudinal traction to the a�ected knee.Document neurovascular status of the extremity before and a�er reduction. Splint the lower extremity withthe knee at 20 degrees of flexion a�er dislocation reduction to prevent redislocation. Reimage a�er splintapplication. Hospitalization is required along with emergent orthopedic and vascular surgery consultation. Ifthe patient is neurovascularly intact and vascular and/or orthopedic surgery consultation is unavailable,then transfer the patient prior to reduction to the nearest hospital with those clinical services. Timelyreduction can occur at that time.

There are no clear guidelines for arteriography in patients with knee dislocation. Because of the highincidence of popliteal artery injury (up to one third of patients) and poor outcomes associated with delays invascular reconstruction, some authors recommend arteriography for all patients with confirmed knee

dislocations.1,27 Another option a�er reduction of a knee dislocation is to repeat the neurovascular exam and

perform Doppler pressure indices28 (ankle-brachial index; see chapter 61, "Arterial Occlusion"). Patients with

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distal pulses present before and a�er reduction and an ankle-brachial index >0.9 can be observed with serialneurovascular checks. The orthopedist may want a CT angiogram prior to ligamentous reconstruction. Forpatients in whom distal pulses are asymmetric, the ankle-brachial index is <0.9, or there is any other clinicalconcern of vascular injury (including ischemia, hemorrhage, or an expanding hematoma), proceed with CTangiogram or angiography. Patients with absent pulses before reduction with a return of a pulse a�er

reduction need measurement of an ankle-brachial index and emergent vascular surgery consultation.2

Patients with an open knee dislocation, absent distal pulses a�er reduction, or any other signs of vascularinjury, as above, need emergent vascular surgery consultation for surgical exploration and possible

angiography in the operating room.2,26,28

Close observation of patients with suspected knee dislocation is essential, because the presence of normaldistal pulses does not rule out a popliteal artery injury. Splint the a�ected knee in 20 degrees of flexion, withcare taken to construct the splint in a manner that allows for serial vascular examinations.

PATELLAR DISLOCATION

Dislocation of the patella usually occurs from a twisting injury to the extended knee. The patella is displacedlaterally over the lateral condyle, which results in pain and deformity of the knee (Figure 274-12). Tearing ofthe medial knee joint capsule o�en occurs. Reduction is accomplished with the patient under conscioussedation by flexing the hip, hyperextending the knee, and sliding the patella back into place. This results inimmediate relief of pain; however, caution patients that they will have residual soreness from the medialpatellofemoral retinacular tissue injury. Obtain x-rays of the patella and knee to exclude a fracture, and place

a knee immobilizer a�er reduction10 and provide crutches. Give instructions for partial weight bearing andstraight leg raises to strengthen the quadriceps. Arrange follow-up with an orthopedist within 1 week.Recurrent lateral dislocation of the patella occurs in approximately 15% of patients, and superior, horizontal,

and intercondylar dislocations require referral to an orthopedic surgeon for possible surgical intervention.29

FIGURE 274-12.

Lateral dislocation of the right patella. [Photo contributed by Rob Hendrickson, MD, and Michael Martinez,MD.]

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In the case of irreducible patellar dislocation, surgical correction is needed. Clues that a patient may have anirreducible patellar dislocation include older age, preexisting patellofemoral arthritis, flexion of <45 degrees,

anterolateral (rather than pure lateral) patellar position, and internal rotation of the patellar axis.30

QUADRICEPS OR PATELLAR TENDON RUPTURE

Rupture of the quadriceps or patellar tendons can occur from forceful contraction of the quadriceps muscleor falling on a flexed knee. Quadriceps tendon rupture is most frequent in those >40 years of age. Patellartendon rupture occurs most commonly in individuals <40 years of age. A history of tendinitis or past oral or

injected steroid can increase risk of rupture.8 Quadriceps or patellar tendon rupture disrupts the extensormechanism of the knee. There is severe pain and di�use swelling, and the patient is unable to actively extendthe knee or maintain a passively extended knee against gravity in both types of tendon rupture. Dependingon the tendon ruptured, a defect may be palpable proximal or distal to the patella. Figure 274-13 shows aquadriceps tendon rupture. A high-riding patella (patella alta) may be seen on a lateral radiograph of the

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knee in the setting of a patellar tendon rupture (Figure 274-14). The treatment of a complete tear is surgicalrepair of the involved tendon. Orthopedic consultation in the ED is indicated. Incomplete tears with an intact

extensor mechanism can be treated with immobilization and close follow-up.8

FIGURE 274-13.

Quadriceps tendon rupture. Note the defect above the patella and prominence of the proximal edge of thepatella. [Reproduced with permission of the Department of Emergency Medicine, Feinberg School ofMedicine, Northwestern University.]

FIGURE 274-14.

Patella alta.

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PATELLAR TENDINITIS

Also known as jumper's knee, patellar tendinitis is primarily seen in runners, high jumpers, and basketballand volleyball players. Pain is located at the patellar tendon and is worsened when going from sitting tostanding, jumping, or running up hills. Evaluate the extensor mechanism to rule out tendon rupture. Pointtenderness can be found at the distal aspect of the patella or proximal part of the patellar tendon. Treatmentconsists of nonsteroidal anti-inflammatory drugs, eccentric quadriceps-strengthening exercises, and activitymodification. Steroid injections predispose to tendon rupture and thus should be avoided.

POSTARTHROSCOPY PROBLEMS

Patients may present to the ED following arthroscopy because of pain and swelling. E�usions are commona�er arthroscopy, but joint infection is very uncommon. Perform diagnostic arthrocentesis if joint infection is

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1. 

2. 

3. 

4. 

5. 

6. 

suspected. Arthrocentesis and then injection of bupivacaine may be helpful therapeutically for large, tensee�usions and may reduce the need for systemic analgesia.

PENETRATING KNEE INJURY AND JOINT FOREIGN BODIES

The history should elicit information to re-create the position of the knee when the penetrating injuryoccurred. Many occupational injuries occur with the knee flexed, and failure to appreciate the trajectory ofinjury with the knee flexed can lead to misdiagnosis and failure to anticipate joint penetration. Managementof lacerations in proximity to joint spaces is discussed in chapter 44, "Leg and Foot Lacerations," in thesection "Wound Management."

Radiopaque foreign bodies (i.e., metal, glass) can be visualized on conventional radiographs. In general,foreign bodies in the knee joint need to be removed. A bullet in the joint can destroy the cartilage, and lead

poisoning can occur.31 Antibiotics to cover streptococci and staphylococci are generally indicated for bothpenetrating knee wounds and foreign bodies. Administer tetanus prophylaxis as indicated.

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