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1850 SECTION 22: Orthopedics obtain secondary to patient discomfort. Anterior hip dislocations usu ally require reduction in the operating room.  DISLOCATIONS OF PROSTHETIC HIPS Prosthetic hips dislocate relatively easily and represent an overwhelming majority of hip dislocations seen by the emergency physician. Up to 10% of prosthetic hips dislocate, the majority in the first few months after surgery. 33 Total hip arthroplasties dislocate in the direction of the surgical approach taken. Because most hip arthroplasties are performed through a posterior approach, posterior dislocations are by far the most common. Dislocations through an anterior approach will also present to the ED, and recognizing that these require an entirely different reduc tion approach is critical. Posterior dislocations result from flexion, adduction, and internal rotation. This is common when going from a low-seated position to a standing position. Getting out of a booth, bending over to clip toenails, and standing up from the toilet are common mechanisms. Anterior dislocations occur from hyperextension of the hip, which is more awkward and less common in normal activities of daily living. This is one of the reasons some orthopedists advocate the anterior approach. Avascular necrosis of the femoral head is not a complication since there is no blood flow to the prosthetic joint. For this reason, reduction is not particularly time sensitive, although sciatic nerve injury or damage to the prosthesis may occur. Most posterior dislocations of prosthetic hips can be reduced using procedural sedation in the ED with the techniques described previously for posterior reductions of native hips. Anterior dislocations of total hip arthroplasties can often be reduced with simple gradual longitudinal traction on the dislocated leg while an assistant stabilizes the pelvis. This technique is known as the Allis leg extension method. A common cause for difficulty in reducing a dislocated total hip arthroplasty is the use of a “constrained cup. ” These acetabular components are often placed during revisions for chronic instability in patients prone to dislocations. The constrained cup has a locking ring that is intended to prevent the femoral cup from dislocating. When they do dislocate, they are essentially impossible to reduce using closed methods. Because of the variability of implants and approaches, an attempt to contact the surgeon who performed the arthroplasty should be made prior to any reduction attempts. A review of 410 prosthetic hip dislocations reported that emer gency physicians were successful at 79% of reductions in the ED, and orthopedists were successful at 71% of reductions in the ED—with no difference between emergency physicians and orthopedists in the proportion of successfully relocated hips in the ED and no difference in complications. The ED length of stay for ED-reduced prosthetic hip dislocations was about one third shorter than that for orthopedistreduced dislocations. This study did not describe the types of pros theses reduced. SPECIAL CONSIDERATIONS  PAIN CONTROL Patients with orthopedic injuries require early analgesia in the ED.35 Any patient with suspected fracture should immediately receive pain medications. Consider a femoral nerve block as a nonopiate option (See Video: Femoral Nerve Block). SPECIAL POPULATIONS  ATHLETES Stress fractures of the femoral neck are a common cause of hip pain in athletes, particularly runners and football players.

y patient with suspected fracture should immediately receive pain medications. Consider a femoral nerve block as a nonopiate option (See Video: Femoral Nerve Block). SPECIAL POPULATIONS  ATHLETES Stress fractures of the femoral neck are a common cause of hip pain in athletes, particularly runners and football players. The onset of pain is often insidious and may mimic other conditions such as bursitis or muscle strain. Patients reporting persistent pain in the groin, medial thigh, or knee or having pain with ambulation should undergo MRI. If imaging is not readily available, then the patient should be made non–weight bearing and told to avoid all athletic activities until ortho pedic evaluation can be obtained (optimally in the next 48 hours). 37 Dislocation has also been described in professional athletes with a high rate of avascular necrosis.  ELDERLY PATIENTS The majority of hip and femur injuries occur in the elderly. Consider elder abuse or self-neglect in patients with suspicious injuries. See Chapter 295, “ Abuse of the Elderly and Impaired, ” for a detailed discussion of elder abuse. Many older patients perceive these diagnoses as an end-of-life event. Emphasize that immobility and nonoperative management result in the majority of complications. Communication with family about potential loss of independence can allow for anticipatory planning. Appropriate early communication can alleviate patients’ fears and facilitate compli ance with physical therapy and rehabilitation, maximizing the potential for return to a preinjury quality of life. REFERENCES The complete reference list is available online at www.TintinalliEM.com. Knee Injuries Rachel Bengtzen ANATOMY The knee consists of two joints, the tibiofemoral joint and the patello femoral 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). FIGURE 274-1. The supracondylar and condylar areas of the femur, and the medial and subcondylar areas of the tibia. CHAPTER Tintinalli_Sec22_p1767-1880.indd 1850 8/2/19 6:20 PM

medial and lateral femoral condyles) articulates with the proximal tibia (comprised of the medial and lateral tibial condyles) (Figure 274-1). FIGURE 274-1. The supracondylar and condylar areas of the femur, and the medial and subcondylar areas of the tibia. CHAPTER Tintinalli_Sec22_p1767-1880.indd 1850 8/2/19 6:20 PM CHAPTER 274: Knee Injuries 1851 CLINICAL FEATURES Determine the mechanism of knee injury and review all prior orthope dic injuries or surgical procedures. Compare contralateral noninjured or normal joint with the injured joint, especially during ligament stress testing. The first examination is usually the easiest to perform and may be the most valid, as a patient’s anticipatory pain or an effusion limiting the examination may not have yet developed. Assess gait (if possible) and the ability to perform a straight leg raise (evaluates the extensor complex). Evaluate the knee for ecchymoses, swelling (extra-articular fluid), effusion (intra-articular fluid), 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. Include palpation of 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. Assess patellar mobility with the knee in extension for lateral and medial movement 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) (See Video: The Knee Exam). 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. Meniscus stress testing can include the McMurray test where the patient is supine with knee flexed to 90 degrees, and the examiner medially rotates the tibia and extends the knee stressing the lateral meniscus, and then repeats this laterally rotating the tibia and extending the knee again, stressing the medial meniscus. A positive test may elicit joint line pain or a painful click.  NEUROVASCULAR INJURIES Popliteal artery injury can occur from fractures about the knee, espe cially 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. 1-3 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. It is important to remember that vascular injury can be present even in the presence of normal pulses.

asure 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. 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 and duplex US (reported to be 95% sensitive and 99% specific for arterial injury, but can miss small intimal tears). 1,3 Patients with normal pulses and an ankle-brachial index ≥0.9 can be observed (See Video: Ankle-Brachial Index). Vascular compromise is suspected in patients with abnormal palpable and Doppler pulses and/or ankle-brachial index <0.9 and warrants further vascular imaging and consultation. Vascular surgery consultation can aid in determining the need for CT angiogram versus on-table angiography and can help monitor for the development of compartment syndrome, venous injury, and arterial thrombosis. Peroneal nerve injuries (stretch or, less often, transection) can result from severe ligamentous knee injuries or 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. FIGURE 274-2. Ligaments of the right knee joint. The articular capsule and the patella have been removed. FIGURE 274-3. Posterior knee: popliteal fossa anatomy. The medial and lateral menisci are situated between the articular sur faces, 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). Tintinalli_Sec22_p1767-1880.indd 1851 8/2/19 6:20 PM

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). Tintinalli_Sec22_p1767-1880.indd 1851 8/2/19 6:20 PM 1852 SECTION 22: Orthopedics DIAGNOSIS  IMAGING The Ottawa Knee Rules (Table 274-1) (See Video: Ottawa Knee Rules) are sensitive in identifying a clinically significant fracture, and their use reduces ED waiting times and costs. The Pittsburgh Knee Rules (Figure 274-4) are similar and may have greater specificity. 4-7 Sub sequent studies found barriers to implementation by physicians due to patient concerns or because specialists expect knee imaging. 5 It is reasonable to order radiographs on multisystem trauma patients with knee pain, especially those unable to undergo gait testing. According to the most recent meta-analysis available, the Ottawa Knee Rules are valid for children >5 years old. 8 For further discus sion of pediatric knee injuries, see Chapter 141, “Pediatric Orthopedic Emergencies. ” Anteroposterior and lateral radiographs are typically obtained if radiographs are needed. 9 Fat-fluid levels (lipohemarthrosis; Figure 274-5) suggest intra-articular fracture and may be identified on a lateral view of the knee. 10 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 visual izing the lateral plateau, and external oblique view is best for visualizing the medial plateau). 9 A tunnel or intercondylar view provides a clear image of the intercondylar region and is particularly useful in identify ing 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.  SPECIFIC INJURIES PATELLA FRACTURES Table 274-2 reviews the mechanisms of injury and treatment of patellar fractures. 11-14 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 274-6). 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 grav ity. Nonoperative management is indicated for fractures with an intact extensor mechanism and <2 mm of step-off and <3 mm of fracture displacement. 11,15 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 frac tures and include supracondylar, intercondylar, condylar, and distal femoral epiphyseal fractures ( Figure 274-1).

l 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 frac tures 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 thrombosis, fat embolus syn drome, delayed union or malunion, and the subsequent development of osteoarthritis. 12,16 TIBIAL SPINE AND TUBEROSITY FRACTURES Isolated injuries of the tibial spine are uncommon; however, 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 FIGURE 274-5. Lipohemarthrosis. Arrow points to lipid/blood interface. TABLE 274-1 Ottawa Knee Rules: Radiograph 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 after the injury and in the ED Fall or blunt-trauma mechanism Age <12 or age >50 years Able to walk four weight-bearing steps in ED No knee radiography No knee radiography Knee radiography Knee radiography Yes YesN o No Yes FIGURE 274-4. Pittsburgh Knee Rules for radiography. [Reproduced with permission from Seaberg DC, Yealy DM, Lukens T, et al: Multicenter comparison of two clinical decision rules for the use of radiography in acute, high-risk knee injuries. Ann Emerg Med. 1998;Jul;32(1):8-13. Copyright Elsevier.] Tintinalli_Sec22_p1767-1880.indd 1852 8/2/19 6:20 PM

Rules for radiography. [Reproduced with permission from Seaberg DC, Yealy DM, Lukens T, et al: Multicenter comparison of two clinical decision rules for the use of radiography in acute, high-risk knee injuries. Ann Emerg Med. 1998;Jul;32(1):8-13. Copyright Elsevier.] Tintinalli_Sec22_p1767-1880.indd 1852 8/2/19 6:20 PM CHAPTER 274: Knee Injuries 1853 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. 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. 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, often requires ORIF. Tibial tuberosity Sudden force to flexed knee with quadriceps contracted Incomplete or small avulsion fracture: immobilization. Complete avulsion: ORIF. 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) 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. Abbreviation: ORIF = open reduction internal fixation. FIGURE 274-6. Classification of patellar fractures. 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). 13 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. 17 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. 14 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.

atient 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. 9 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 pathogno monic for an anterior cruciate ligament injury, and it is important recognize and treat the ligament injury, rather than just the plateau fracture. 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 menisci. Functional instability of the knee can be determined by stress testing, which may demonstrate abnormal laxity. Functional stress testing assessment must be considered in the context of the composite history and complete physical exam as sensitivity and specificity of individual tests remain poor. 18-20  MEDIAL COLLATERAL LIGAMENT AND LATERAL COLLATERAL LIGAMENT INJURIES The medial stabilizers of the knee are tested by applying a valgus stress (Figure 274-7) to the knee at 0 degrees and in approximately 30 degrees of flexion to determine the integrity of the medial capsular and liga mentous 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 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 liga ments can include a strain, partial tear, or complete rupture. If there is no demonstrated laxity but the valgus or varus test reproduces pain, a grade 1 strain has likely occurred. If there is a laxity demonstrated without a firm end point compared with the other knee, this is concerning Tintinalli_Sec22_p1767-1880.indd 1853 8/2/19 6:20 PM

rain, partial tear, or complete rupture. If there is no demonstrated laxity but the valgus or varus test reproduces pain, a grade 1 strain has likely occurred. If there is a laxity demonstrated without a firm end point compared with the other knee, this is concerning Tintinalli_Sec22_p1767-1880.indd 1853 8/2/19 6:20 PM 1854 SECTION 22: Orthopedics 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 sig nificant lesion involving the entire medial collateral ligament complex and/or in association with a cruciate ligament and posterior capsule tear. 19,21 Laxity to varus stress in full extension likewise indicates a sig nificant 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. 18,19  ANTERIOR CRUCIATE LIGAMENT INJURIES The mechanism of injury to the anterior cruciate ligament is usually noncontact—a deceleration, hyperextension, or marked internal rota tion 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. 19 The history of this mechanism of injury combined with the presence of a traumatic effusion is very sug gestive of an anterior cruciate ligament disruption. The diagnosis of an anterior cruciate ligament injury is made using the Lachman test (Figure 274-8), the anterior drawer sign ( Figure 274-9), and the pivot shift ( Figure 274-10). The Lachman test is the most sensitive and specific test (81% for both). 19,22 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. The anterior drawer test is only approximately 38% sensitive and 81% specific. 19,22 This maneuver is performed with a 45-degree flexion at the hip and a 90-degree flexion at the knee. Then, an attempt is made 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, it can be difficult to perform on patients with large legs. The pivot shift (Figure 274-10) is the third maneuver by which the examiner can determine the integrity of the anterior cruciate liga ment. The pivot shift may be painful to the patient and is often most easily tested under anesthesia in the operating room. The pivot shift test without anesthesia was found to be only 28% sensitive but 81% specific.

) is the third maneuver by which the examiner can determine the integrity of the anterior cruciate liga ment. The pivot shift may be painful to the patient and is often most easily tested under anesthesia in the operating room. The pivot shift test without anesthesia was found to be only 28% sensitive but 81% specific. 19,22,23 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 30° FIGURE 274-7. Valgus stress in full extension (A) and in 30 degrees of flexion ( B). FIGURE 274-8. Lachman test, performed with the knee flexed between 15 and 30 degrees. One hand stabilizes the thigh, while the other moves the tibia anteriorly. 30° FIGURE 274-9. Anterior drawer test, performed with 45-degree flexion at the hip and a 90-degree flexion at the knee. Try to displace the tibia from the femur in an anterior direction. AB C 0° 20°– 30° FIGURE 274-10. A-C. The pivot shift is done with the knee in full extension with application of valgus and internal rotation stress. The clunk of reduction is felt in the first 20 to 30 degrees of flexion. Tintinalli_Sec22_p1767-1880.indd 1854 8/2/19 6:21 PM

bia from the femur in an anterior direction. AB C 0° 20°– 30° FIGURE 274-10. A-C. The pivot shift is done with the knee in full extension with application of valgus and internal rotation stress. The clunk of reduction is felt in the first 20 to 30 degrees of flexion. Tintinalli_Sec22_p1767-1880.indd 1854 8/2/19 6:21 PM CHAPTER 274: Knee Injuries 1855 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 com bination 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 pro vides initial resistance to posterior translation at all angles of flexion of the knee. The mechanism of injury then is usually an anterior-toposterior force applied to the tibia or lower leg. Nearly all posterior cruciate ligament injuries diagnosed in the ED are seen in association with other ligamentous injuries. A deficit of this ligament is identified by the posterior drawer test (Figure 274-11) 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 exam iner 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. 18,19,24 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 pos terolateral 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 poste rior 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.

ting 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), fracture, meniscus tear, osteoarthritis flare, or loose body. 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) 25 is a marker for anterior cruciate ligament rupture. 5,14 Cortical avulsion of the medial tibial plateau (very uncommon) is associated with tears of the posterior cruciate ligament and medial meniscus. Continued refinements in MRI have enabled this imaging method to produce high-quality images of the ligamentous and meniscal struc tures of the knee, which results in an accuracy rate of close to 90% to 95% in identifying meniscal and cruciate ligament disruption. 26 Such an MRI examination, however, is typically ordered 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 simple neoprene hinged brace (available over the counter), ice packs, elevation, NSAIDs, and ambulation as soon as is comfortable for the patient. 27 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 followup 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 (knee immobilizer or t-scope hinged brace if available) included as a part of the follow-up care. When knee immobilizers are placed, instruct the patient to perform daily range-of-motion exercises to avoid contracture and maintain mobility and reassess need within about 1 week as an outpatient. 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 (See Video: Knee Arthrocentesis). 28 Furthermore, recurrence of the effusion following aspiration is common. Arthrocentesis may be of assistance diagnostically if the effusion is not clearly due to trauma.

in patients with large, tense effusions of the knee; however, good evidence of its efficacy has not been reported (See Video: Knee Arthrocentesis). 28 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. Aspiration is also used to assess for a septic joint. In instance of clinical suspicion of an effusion, but a drip tap, point-of-care ultrasound can be used to confirm the needle is within hypoechoic intra-articular fluid, rather than FIGURE 274-11. Posterior drawer test. Tintinalli_Sec22_p1767-1880.indd 1855 8/2/19 6:21 PM

ation is also used to assess for a septic joint. In instance of clinical suspicion of an effusion, but a drip tap, point-of-care ultrasound can be used to confirm the needle is within hypoechoic intra-articular fluid, rather than FIGURE 274-11. Posterior drawer test. Tintinalli_Sec22_p1767-1880.indd 1855 8/2/19 6:21 PM 1856 SECTION 22: Orthopedics performing repeated needle placement attempts (Figure 274-12). The major complication of arthrocentesis is inducing 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. Many of the tears involve the peripheral posterior aspect of the meniscus. Many maneuvers have been described in the literature to determine whether a meniscus has been injured. However, most maneuvers have an unacceptable sensitivity and specificity (e.g., joint line tenderness has a sensitivity of 70% and specificity of 15% in the ED population). 18 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 one 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. Other signs of a meniscal tear include 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. At physical examination, attempt to identify atrophy of the quadriceps muscle as a result of disuse and joint-line tenderness. Various maneuvers, such as the McMurray test, have been described but yield positive results only about 50% of the time. 18,19,29 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. Defini tive 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 unsuc cessful, orthopedic consultation for operative arthroscopy is indicated. If the unlocking is successful, referral to an orthopedist for MRI and/or arthroscopy is appropriate. KNEE DISLOCATION Knee dislocation (Figure 274-13) primarily occurs in younger male populations.

pt to unlock the joint. If this maneuver is unsuc cessful, orthopedic consultation for operative arthroscopy is indicated. If the unlocking is successful, referral to an orthopedist for MRI and/or arthroscopy is appropriate. KNEE DISLOCATION Knee dislocation (Figure 274-13) primarily occurs in younger male populations. It is a result of tremendous ligamentous disruption due to either high-velocity mechanisms (motor vehicle crashes, fall from height) or low-velocity mechanisms (martial arts, walking, or trampo line falls); dislocations can also occur spontaneously in morbidly obese patients. 1,3,31 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. 2,31 Due to severe ligamentous damage, spontaneous reduction occurs in up to 50% of knee dislocations. 2,3 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 longitu dinal 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, in a manner that allows for serial vascular examinations. Reimage after splint application. Hospitalization is required along with emergent orthopedic FIGURE 274-12. Linear probe short axis view proximal to patella, with needle tip ( A) within hypoechoic knee effusion (B). Star depicts the femur. FIGURE 274-13. Types of knee dislocation: anterior (A), posterior (B), and lateral (C). Tintinalli_Sec22_p1767-1880.indd 1856 8/2/19 6:21 PM

d along with emergent orthopedic FIGURE 274-12. Linear probe short axis view proximal to patella, with needle tip ( A) within hypoechoic knee effusion (B). Star depicts the femur. FIGURE 274-13. Types of knee dislocation: anterior (A), posterior (B), and lateral (C). Tintinalli_Sec22_p1767-1880.indd 1856 8/2/19 6:21 PM CHAPTER 274: Knee Injuries 1857 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. Historically, arteriography was recommended for all patients with confirmed knee dislocations since there is a high incidence of popliteal artery injury (up to one third of patients) and poor outcomes associated with delays in vascular reconstruction. 1,32 Current recommendations include serial neurovascular exams and performing ankle-brachial index (see Chapter 61, “ Arterial Occlusion”) (See Video: Ankle-Brachial Index). Patients with distal pulses present before and after reduction and an ankle-brachial index ≥0.9 can be observed with serial neurovascular checks over 24 hours. 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. 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. 3,31 PATELLAR DISLOCATION Dislocation of the patella usually occurs from a twisting injury to the extended knee. The patella is displaced most commonly laterally over the lateral condyle, which results in pain and deformity of the knee (Figure 274-14). Tearing of the medial knee joint capsule often occurs. Reduction is accomplished with adequate analgesia then by flexing the hip, gently extending the knee, and guiding 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 radiographs of the patella and knee to exclude a fracture, and place a knee immobilizer after reduction 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. In the case of irreducible patellar dislocation, surgical correction is needed. Clues that a patient may have an irreducible patellar disloca tion include older age, preexisting patellofemoral arthritis, flexion of <45  degrees, anterolateral (rather than pure lateral) patellar position, and internal rotation of the patellar axis. 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.

UADRICEPS 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 use can increase risk of rupture. 11 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 do a straight leg raise, 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 274-15 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 274-16 ). Bedside point-of-care ultrasound using a high-frequency linear transducer can be used to visualize and diagnose a quadriceps or patella tendon rupture ( Figure 274-17). 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. 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 FIGURE 274-14. Lateral dislocation of the right patella. [Photo contributed by Rob Hendrickson, MD, and Michael Martinez, MD.] FIGURE 274-15. Quadriceps tendon rupture. Note the defect above the patella and prominence of the proximal edge of the patella. [Photo contributed by the Department of Emergency Medicine, Feinberg School of Medicine, Northwestern University.] Tintinalli_Sec22_p1767-1880.indd 1857 8/2/19 6:21 PM

d Michael Martinez, MD.] FIGURE 274-15. Quadriceps tendon rupture. Note the defect above the patella and prominence of the proximal edge of the patella. [Photo contributed by the Department of Emergency Medicine, Feinberg School of Medicine, Northwestern University.] Tintinalli_Sec22_p1767-1880.indd 1857 8/2/19 6:21 PM 1858 SECTION 22: Orthopedics 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 NSAIDs, eccentric quadriceps-strengthening exercises, and activity modification. Steroid injections predispose to tendon rup ture and thus should be avoided. FIGURE 274-16. Patella alta. FIGURE 274-17. Patella tendon rupture on ultrasound (high-frequency linear probe). Tendon remnant ends located at arrows. Star denotes patella. [Photo contributed of Dr. Craig Rudy and Dr. Bryson Hicks.] POSTARTHROSCOPY PROBLEMS Patients may present to the ED following arthroscopy because of pain and swelling. Effusions are common after arthroscopy, but joint infec tion 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. POSTARTHROPLASTY PROBLEMS Over 1 million total hip and knee joint arthroplasties are performed annually in the United States. Approximately 9.3% of patients who undergo elective total knee replacements visit the ED at least once within 90 days after discharge; readmission rates are around 5%. Leading causes for ED visits include pain, injuries, dislocation, deep vein thrombosis, cardiopulmonary events, physiologic decompensation, and infection (surgical site or elsewhere). 34-36 Assess with radiographs (anteroposterior, lateral, and axial patella views). If infection is sus pected, obtain laboratory testing for erythrocyte sedimentation rate, C-reactive protein, and synovial fluid evaluation. Gram stain has low sensitivity and specificity; a leukocyte count >2500/mm 3 and >60% polymorphonuclear leukocytes have a higher sensitivity and specificity for infection. 37 Dislocation of total knee arthroplasty is rare. When it occurs, complications are as above with native knee dislocations, with particular risk of associated neurovascular injury. Data are limited, but risk factors appear to be obesity, female sex, and presence of other neuromuscular problems. Total knee arthroplasty dislocations are managed initially with closed reduction, although there is a high rate of redislo cation without subsequent operative repair. 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 inju ries 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 proxim ity to joint spaces is discussed in Chapter 44, “Thigh, Leg, and Foot Lacerations. ” If a wound is periarticular, assess the integrity of the joint capsule, as joint involvement can lead to developing septic arthritis. One study found that open knee joint injuries had a mean periarticular wound size of approximately 4 cm and an infection rate ranging from 0% to 11.8%. CT scans can be useful if they detect intra-articular air; however, other diagnostic modalities such as the saline load test may be used initially. Perform the saline load test by injecting sterile saline into the joint where a penetrating injury is suspected, and assess for extravasation of the saline from the periarticular wound.

be useful if they detect intra-articular air; however, other diagnostic modalities such as the saline load test may be used initially. Perform the saline load test by injecting sterile saline into the joint where a penetrating injury is suspected, and assess for extravasation of the saline from the periarticular wound. Failure of extravasation is a nega tive saline load test. The traditional injection volume of the knee had been 60 mL; however, data suggest that load volumes of 155 and 194 mL help achieve a sensitivity of 95%. There was no added benefit of using methylene blue. 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 injure the cartilage and cruciate ligaments, and lead poisoning can occur. Antibiotics to cover streptococci and staphylococci are generally indicated for both penetrating knee wounds and foreign bodies. Administer tetanus prophylaxis as indicated. REFERENCES The complete reference list is available online at www.TintinalliEM.com. Tintinalli_Sec22_p1767-1880.indd 1858 8/2/19 6:21 PM