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 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).
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 (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.
Types of knee dislocation: anterior (A), posterior (B), and lateral (C).
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.
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
Lateral dislocation of the right patella. [Photo contributed by Rob Hendrickson, MD, and Michael Martinez, MD.]
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
Quadriceps tendon rupture. Note the defect above the patella and prominence of the proximal edge of the patella. [Reproduced with permission of the Department of Emergency Medicine, Feinberg School of Medicine, Northwestern University.]
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.
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.