Chapter 274: Knee Injuries

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

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

Determine the mechanism of knee injury and review all prior orthopedic injuries or surgical procedures. As with all orthopedic examinations, compare the noninjured or normal joint with the injured joint during all aspects 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 does not anticipate pain and may not guard against the examination, and because inflammation and effusion limiting the examination may have not yet developed.

Assess gait (if possible), functional range of motion, and the ability to perform a straight leg raise (evaluates the extensor complex). Evaluate the knee for ecchymoses, swelling, effusion, masses, patella location and size, muscle mass, erythema, and evidence of local trauma. With the patient supine, determine whether leg lengths are equal or unequal. Ask the patient to demonstrate the best possible active range of motion. Assess distal neurovascular function. Palpate the nontender areas first and work toward the tender area to minimize patient apprehension. Palpate the patella, patellar facets, proximal fibula, and femoral and tibial condyles for pain and crepitus. Make note of joint effusion, tenderness, increased temperature, strength, sensation, and location of pulses.

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

NEUROVASCULAR INJURIES

Popliteal artery injury can occur from fractures about the knee, especially femoral condyle fractures or displaced 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 restored within 8 hours to avoid amputation, because collateral circulation is insufficient to maintain blood flow to the leg. Measure distal pulses on ED admission and after any manipulation, and compare pulses to those in the noninjured leg. A diminished pulse raises concern for vascular injury and should not be interpreted as vascular 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 that vascular injury can be present even in the presence of normal pulses. Ancillary studies include measurement of 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 required for any potential popliteal arterial injury to determine the need for angiography, as well to monitor for the development of compartment syndrome, venous injury, and arterial thrombosis.

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

IMAGING

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

Both rules are applicable to children >2 years old and adults.⁴ It would be reasonable to order radiographs on a higher number of patients with knee pain who are multisystem trauma patients, and thus immobilized and unable 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. Additional radiograph views can be very useful. Oblique views are particularly helpful for detecting subtle tibial plateau 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 intercondylar region 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 be missed with the conventional views. The sunrise view is indicated if patellar subluxation or fracture is suspected. CT may be necessary to fully delineate the extent of tibial plateau fractures. MRI is also helpful in this regard and has the added benefit of being able to assess soft tissue (i.e., ligamentous and meniscal) injury.⁵

PATELLA FRACTURES

Table 274-2 reviews the mechanisms of injury and treatment of patellar fractures. Patellar fractures may be transverse, comminuted, or of the avulsion type when the quadriceps or patellar tendon pulls off a small portion of the patella (Figure 274-5).

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 effusion. Check the integrity of the extensor mechanism of the knee by having the patient perform a straight-leg raise against gravity. Nonoperative management is indicated for fractures with an intact extensor mechanism and <2 mm of step-off and <3 mm of fracture displacement.^8,13 Transverse fractures are more likely to be displaced and to be associated with a disrupted extensor mechanism. Differential diagnosis of patellar fractures radiographically includes bipartite patella. This condition involves the superior lateral corner of the patella, is typically bilateral, and is differentiated from fracture by the smooth cortical margins.

FEMORAL CONDYLE FRACTURES

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 the mechanisms of injury and treatment for femoral condyle fractures. Examination reveals pain, swelling, deformity, rotation, shortening, and an inability to ambulate. Although neurovascular injuries are uncommon, the potential for popliteal artery injury exists, so the status of distal sensation and pulses must be checked. Test the space between the first and second toes, innervated by the deep peroneal nerve, for sensation. In addition, search for associated injuries, including ipsilateral hip dislocation or fractures and damage to the quadriceps apparatus. The overall outcome of these injuries is fair. Complications include deep 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 ligament insufficiency. Table 274-2 reviews the mechanism of injury and treatment for tibial spine and tuberosity fractures. Fracture of the anterior tibial spine is about 10-fold more common than fracture of the posterior spine. 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 quadriceps mechanism inserts on the tibial tubercle. A sudden force to the flexed knee with the quadriceps muscle contracted may result in a complete or incomplete avulsion of the tibial tubercle. The fracture line may extend into the joint. Examination reveals pain and tenderness over the proximal anterior tibia with pain on passive or active extension.

TIBIAL PLATEAU FRACTURES

Fractures of the tibial plateau are seen more commonly in the older population and can be very difficult to detect. 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 often fractured.¹² Direct trauma to the lateral aspect of the knee may account for the preponderance of lateral tibial plateau fractures. The patient may experience painful swelling of the knee and limitation of motion. Radiographs may demonstrate a fracture, but often show only a lipohemarthrosis on the lateral view. Consider adding an anteroposterior view in the plane of the plateau (10 to 15 degrees caudal) or oblique views to help assess for displacement. 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 Soft tissue injuries associated with tibial plateau fractures may influence outcomes. Anterior cruciate ligament and medial collateral ligament injuries are associated with lateral plateau fractures, whereas posterior cruciate and lateral collateral ligament injuries occur with medial plateau fractures. A Segond's fracture (see below) is pathognomonic for an anterior cruciate 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 with high-energy displaced fractures, the development of deep venous thrombosis, and osteoarthritis.

LIGAMENTOUS AND MENISCAL INJURIES

The knee joint depends on ligaments and muscles for support (Figure 274-2). It is frequently subjected to injuries from traumatic forces, including hyperextension, valgus and varus stresses, and anteroposterior displacement. By far the most common forces are valgus, which produce injuries to the medial side of the knee. Injuries to the lateral side of the knee are produced by varus stresses. Such forces may result in a strain or rupture of the medial or lateral collateral ligaments, the anterior or posterior cruciate ligaments, or the capsular structures, or a tear in the medial or lateral meniscus or both. Functional instability of the knee is determined by stress testing, which may demonstrate abnormal laxity when properly done. Table 274-3 summarizes the reported sensitivity, specificity, and positive and negative likelihood ratios for diagnosis of ligamentous and meniscal injury.¹⁴

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 in approximately 30 degrees of flexion to determine the integrity of the medial capsular and ligamentous structures. The medial collateral ligament supplies the majority of restraint to valgus deformities of the knee in all stages of flexion. A varus force is then applied to the lateral aspect of the knee, again with approximately 30 degrees of flexion, to ascertain the integrity of the lateral structures. The lateral collateral ligament, analogous to the medial collateral ligament, is the major restraint to varus laxity on the knee at all positions of flexion. Injuries to these ligaments can include a strain, partial tear, or complete rupture. If there is no demonstrated laxity but the valgus or varus test reproduces pain, a strain has likely occurred. If there is a laxity demonstrated without a firm end point compared with the other knee, this is concerning for a complete tear of the medial or lateral collateral ligament. If there is laxity with the varus or valgus test performed with 30 degrees of flexion, similar maneuvers should be applied with the leg in full extension, if possible. Laxity to valgus stress while in full extension indicates a significant lesion involving the entire medial 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 the posterolateral corner of the knee as well as the cruciate ligaments. Peroneal nerve injuries may also occur in lateral injuries. Although these tests may aid in the diagnosis of medial collateral ligament and lateral collateral ligament injuries, there are no adequate published reports to allow comment on their sensitivity and specificity.¹⁴

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 often 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 of injury combined with the presence of a traumatic effusion is very suggestive of an anterior cruciate ligament disruption.

The diagnosis of an anterior cruciate ligament injury is made using the Lachman test (Figure 274-7), the anterior drawer sign (Figure 274-8), and the pivot shift (Figure 274-9). The Lachman test is the most sensitive and specific test (84% and 100%, respectively).¹⁴ For this test the examiner places the knee in 30 degrees of flexion and stabilizes the femur above the knee with his or her nondominant hand. The dominant hand is placed grasping the lower leg at the level of the tibial tubercle, and the examiner introduces an anterior force, attempting to displace the tibia anteriorly on the femur. If a displacement compared with the opposite knee is found, or if there is a soft 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 attempt to displace the tibia from the femur in an anterior direction. A displacement of >6 mm compared with the normal, opposite knee indicates an injury to the anterior cruciate ligament. False-negative findings may be associated with this maneuver. False-positive results may occur when there is a posterior cruciate ligament tear as the tibia will start out in a more posterior position, thus allowing for a perceived increase in translation when moved anteriorly. Although the Lachman test is more sensitive than the anterior drawer test and is able to identify partial tears in the anterior cruciate ligament when the examiner is skilled, it can be difficult to perform on patients with large legs. The pivot shift (Figure 274-9) is the third maneuver by which the examiner can determine the integrity of the anterior cruciate ligament. The pivot shift may be somewhat painful to the patient and is often most easily tested in the operating room. The pivot shift test without anesthesia was found to be only 24% sensitive but 98% specific.¹⁷ With the patient supine and relaxed, lift the heel of the foot to approximately 45 degrees of hip flexion with the knee fully extended. The opposite hand grasps the knee with the thumb behind the fibular head. Then internally rotate the ankle and knee, apply a valgus force to the knee, and flex the knee. If an anterior subluxation of the tibia is present, a sudden visible, audible, and palpable reduction of the subluxation occurs at about 20 to 30 degrees of flexion. This indicates a deficit in the anterior cruciate ligament, which is required to stabilize the knee in this position. Other tests are described in the literature to determine the integrity of the anterior cruciate ligament, including the jerk test and dynamic extension testing.

POSTERIOR CRUCIATE LIGAMENT INJURIES

The posterior cruciate ligament can be injured in isolation or in combination with other ligamentous structures of the knee. In contrast to anterior cruciate ligament injuries, isolated posterior cruciate ligament injuries are much less common. The posterior cruciate ligament provides initial resistance to posterior translation 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 association with other ligamentous injuries when a serious injury has occurred to the knee. A deficit of this ligament is identified by the posterior drawer test (Figure 274-10) and the sag sign. The posterior drawer test is performed with the knee and hip in flexion as described for the anterior drawer test. The physician applies a posterior force to the tibial tubercle. If there is displacement posteriorly, then the examiner can diagnose an injury to this ligament. One might also notice a sag sign, where there is a posterior sag or drop back of the tibial tubercle because of loss of integrity of the posterior cruciate ligament when observing the knee with 45-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. This abnormal position gives the false impression of too much posterior play when the posterior drawer test is performed, because the knee is reduced to its normal anatomic alignment from the forwardly subluxed position. 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

Combined ligamentous laxity of the knee is often seen, especially in acute athletic injuries. Combined anteromedial and anterolateral laxity occurs most frequently, but virtually any combination of medial and lateral laxity of the knee can occur.

POSTEROLATERAL INJURY

One knee injury that is especially difficult to detect is injury to the posterolateral structures. Posterolateral instability usually involves a tear of the popliteus–arcuate complex, which may occur in combination with lateral ligament injury and possible anterior cruciate ligament or posterior cruciate ligament injury. Isolated injuries to the popliteus–arcuate complex are rare. Isolated posterolateral instability is demonstrated by testing at 0 to 30 degrees of flexion for maximal posterior translation and at 90 degrees of flexion for maximal external rotation compared with that of the normal opposite knee. Further testing to determine the integrity of 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 commonly the anterior cruciate ligament. Serious ligament injuries, however, may present with minimal pain and no hemarthrosis because of complete disruption of the ligamentous and capsular fibers, which allows leakage of the blood into the soft tissue spaces. Hemarthrosis can also be caused by osteochondral fractures or fractures that extend into the joint line, or peripheral meniscal tears. Traumatic hemarthroses usually occur within minutes to hours of injury, in contrast to chronic effusions of the knee due to synovial inflammation, which occur 1 to 2 days after strenuous use of the joint.

With ligamentous injuries, plain radiographs are typically normal or reveal only an effusion. An avulsion fracture 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 the ligamentous 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 typically ordered by the patient's primary care provider, sports medicine physician, or orthopedist in follow-up.

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 avoid contracture and maintain mobility. Contractures are more common in the elderly and can occur after only a few 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 (no weights should be added) three or four times a day. Refer patients to an orthopedic surgeon, sports medicine physician, or primary care provider within the next few days to a week for follow-up examination.

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

Arthrocentesis may be of therapeutic benefit in patients with large, tense effusions of the knee; however, good evidence of its efficacy 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 effusion following aspiration is common. Arthrocentesis may be of assistance diagnostically if the effusion is not clearly due to trauma. The presence of blood and glistening fat globules is pathognomonic of lipohemarthrosis, which indicates intra-articular knee fracture. The major complication of arthrocentesis 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, or twisting maneuvers may cause injury to the meniscus. The medial meniscus is approximately twice as likely as the lateral meniscus to be injured. Four fifths 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 has been 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 of a meniscal tear is difficult to make in certain patients, the combination of a suggestive history and physical findings on examination should lead the emergency physician to consider the diagnosis. Ask if the patient experiences 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. Effusions that occur after activity; a sensation of popping, clicking, or snapping; a feeling of instability in the joint, especially with activity; and tenderness in the anterior joint space after 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, as tolerated. Definitive diagnosis can be made by MRI or arthroscopy, with the latter also allowing for definitive surgical 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 to the ED with a locked knee can experience a great deal of pain along with loss of mobility. The most common cause of an acutely locked knee is a torn meniscus. The differential diagnosis also includes anterior cruciate ligament rupture, patella dislocation, loose bodies, or foreign body. Historically the treatment includes one attempt at closed reduction under procedural sedation. After procedural sedation is initiated, one can attempt to unlock the knee. Position the patient with the leg hanging over the edge of the table and the knee in 90 degrees of flexion. After a period of relaxation, apply longitudinal traction to the knee, along with internal and external rotation, in an attempt to unlock the joint. If this maneuver is unsuccessful, orthopedic consultation 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 or application of direct posterior force to the anterior tibia, force to the fibula or medial femur, force to the tibia or lateral femur, or rotatory force resulting in anterior, posterior, lateral, medial, or rotatory dislocation. This injury 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, a severely injured knee that is unstable in multiple directions raises suspicion of a spontaneously reduced knee dislocation. Maintaining awareness of the possibility of this injury is important because of the high incidence of associated complications, including popliteal artery injury and peroneal nerve injury (mostly with posterolateral dislocations), in addition to ligamentous and meniscal injury.

Timely reduction of the dislocated knee is essential. Apply longitudinal traction to the affected knee. Document neurovascular status of the extremity before and after reduction. Splint the lower extremity with the knee at 20 degrees of flexion after dislocation reduction to prevent redislocation. Reimage after splint application. Hospitalization is required along with emergent orthopedic and vascular surgery consultation. If the 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. Timely reduction can occur at that time.

There are no clear guidelines for arteriography in patients with knee dislocation. Because of the high incidence of popliteal artery injury (up to one third of patients) and poor outcomes associated with delays in vascular reconstruction, some authors recommend arteriography for all patients with confirmed knee dislocations.^1,27 Another option after 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 distal pulses present before and after reduction and an ankle-brachial index >0.9 can be observed with serial neurovascular checks. The orthopedist may want a CT angiogram prior to ligamentous reconstruction. For patients in whom distal pulses are asymmetric, the ankle-brachial index is <0.9, or there is any other clinical concern of vascular injury (including ischemia, hemorrhage, or an expanding hematoma), proceed with CT angiogram or angiography. Patients with absent pulses before reduction with a return of a pulse after reduction need measurement of an ankle-brachial index and emergent vascular surgery consultation.² Patients with an open knee dislocation, absent distal pulses after reduction, or any other signs of vascular injury, 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 normal distal pulses does not rule out a popliteal artery injury. Splint the affected knee in 20 degrees of flexion, with care 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 displaced laterally over the lateral condyle, which results in pain and deformity of the knee (Figure 274-12). Tearing of the medial knee joint capsule often occurs. Reduction is accomplished with the patient under conscious sedation by flexing the hip, hyperextending the knee, and sliding the patella back into place. This results in immediate relief of pain; however, caution patients that they will have residual soreness from the medial patellofemoral retinacular tissue injury. Obtain x-rays of the patella and knee to exclude a fracture, and place a knee immobilizer after reduction¹⁰ and provide crutches. Give instructions for partial weight bearing and straight 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

In the case of irreducible patellar dislocation, surgical correction is needed. Clues that a patient may have an irreducible 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 muscle or falling on a flexed knee. Quadriceps tendon rupture is most frequent in those >40 years of age. Patellar tendon 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 extensor mechanism of the knee. There is severe pain and diffuse swelling, and the patient is unable to actively extend the knee or maintain a passively extended knee against gravity in both types of tendon rupture. Depending on the tendon ruptured, a defect may be palpable proximal or distal to the patella. Figure 274-13 shows a quadriceps tendon rupture. A high-riding patella (patella alta) may be seen on a lateral radiograph of the knee in the setting of a patellar tendon rupture (Figure 274-14). The treatment of a complete tear is surgical repair 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

PATELLAR TENDINITIS

Also known as jumper's knee, patellar tendinitis is primarily seen in runners, high jumpers, and basketball and volleyball players. Pain is located at the patellar tendon and is worsened when going from sitting to standing, jumping, or running up hills. Evaluate the extensor mechanism to rule out tendon rupture. Point tenderness can be found at the distal aspect of the patella or proximal part of the patellar tendon. Treatment consists of nonsteroidal anti-inflammatory drugs, eccentric quadriceps-strengthening exercises, and activity modification. 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. Effusions are common after arthroscopy, but joint infection is very uncommon. Perform diagnostic arthrocentesis if joint infection is suspected. Arthrocentesis and then injection of bupivacaine may be helpful therapeutically for large, tense effusions 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 injury occurred. Many occupational injuries occur with the knee flexed, and failure to appreciate the trajectory of injury with the knee flexed can lead to misdiagnosis and failure to anticipate joint penetration. Management of lacerations in proximity to joint spaces is discussed in chapter 44, "Leg and Foot Lacerations," in the section "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 both penetrating knee wounds and foreign bodies. Administer tetanus prophylaxis as indicated.