Chapter 4 – Knee and leg emergencies

Chapter 4 Knee and leg emergencies

Arun Sayal

Knee injuries – general approach

Key facts

  • With its location between two long bones, the knee is exposed to significant forces in different planes (axial, anterior/posterior, medial/lateral, and rotatory)

  • Injuries range from minor soft tissue injuries to dislocations with limb-threatening arterial injuries

  • High-energy forces are often responsible for the more serious injuries; but for certain groups (e.g., elderly or morbidly obese), serious injury can be seen with a relatively low-energy mechanism

  • Because of the limitations of the ED assessment, the suspected discharge diagnosis is often unconfirmed, and close follow-up is required to confirm the diagnosis, monitor symptoms and guide further management

  • Important goals of the ED knee assessment are to:

    • Ensure proper anatomic alignment

    • Rule out an occult knee dislocation

    • Rule out a fracture around the knee

    • Rule out an extensor mechanism injury

  • ED follow-up is guided by the judgement of the clinician and local orthopedic resources/preferences

PEARL: Fifty percent of knee dislocations will spontaneously reduce before the patient is evaluated in the ED.

Clinical presentation

  • The history is often the most important part of the knee examination – particularly the patient’s age and the exact mechanism of injury

  • Other key points on history include: the knee “giving way” or feeling a “pop”, events post-injury, presence and timing of swelling, previous injury (to either knee)

  • Immediate swelling (within an hour or two) is a hemarthrosis; common causes include an anterior cruciate ligament (ACL) tear and fracture

  • Swelling that is delayed (6–12 hours after injury) is usually inflammatory and is often seen with meniscal injuries, capsular stretches, and other less severe soft-tissue injuries

  • Always consider that pain in the knee (especially distal anterior/medial thigh) can be referred from the hip or back – such pain without tenderness should prompt a search for a more proximal cause

  • Many important aspects of the history are noticed only days after the injury and therefore are unavailable to the clinician in the ED (e.g., swelling with activity, pain with squatting, intermittent locking or clicking, sense of the knee “giving way” with walking, etc

Physical examination

  • Physical exam of the acutely injured knee in the ED is often compromised by acute pain and swelling

  • An organized approach to the physical exam helps recognize those patients that need orthopedic consultation (timing of the referral based on the diagnosis)

  • Proper assessment requires the patient to be lying on a bed (not sitting in a chair) with the distal thigh and knee fully visualized

  • The opposite knee should routinely be inspected and examined for comparison

  • A “Look, Feel, Move” approach helps to remember important aspects of the knee exam

  • “Look”

    • To ensure the skin is intact – rule out the possibility of an open fracture

    • For alignment – knee or patellar dislocations will be clinically apparent (beware that many of these spontaneously reduce before arrival at the ED)

    • For swelling

      • Large effusions are noted by loss of the “dimple” on the medial side of the knee

      • Mid-sized effusions can be detected by patellar balottement (where one hand compresses the patella medially, inferiorly and laterally; while the other hand pushes posteriorly on the patella, testing for patellar balottement or cushioning – compare to the opposite side)

      • Small effusions are detected with a fluid-bulge sign (milk up the medial side of the knee; then down the lateral side, looking for a medial fluid “bulge”)

  • “Feel”

    • For warmth and temperature difference, and point(s) of maximal tenderness – specifically palpate for tenderness:

      • Anteriorly – at the patella, distal quadriceps, patellar tendon, tibial tuberosity

      • Medially – at the medial femoral condyle, medial joint line, proximal medial tibia

      • Laterally – lateral femoral condyle, lateral joint line, proximal fibula

    • Distal neurovascular assessment – any vascular compromise is an orthopedic emergency

  • “Move”

    • Range of motion (active and passive) – assess if the knee reaches full extension

    • Both passive and active straight leg raise with the patient lying supine

    • An important part of the knee examination is to ensure the extensor mechanism is intact

      • If equivocal, can repeat active knee extension with the patient sitting over the side of the bed

  • As indicated, special tests may be performed to assess for injury to the main knee ligaments – (anterior cruciate, posterior cruciate, medial collateral and lateral collateral)

    • Anterior cruciate ligament (ACL): Lachman test (flex the knee 20–30° and attempt to displace the tibia anteriorly on the femur) and anterior drawer (at 90° of knee flexion, attempt to displace the tibia anteriorly on the femur)

    • Posterior cruciate ligament (PCL): posterior drawer (at 90° of knee flexion, attempt to displace the tibia posteriorly on the femur) and posterior sag sign (with the patient supine, knees flexed and feet on the bed – when viewed from the side, the proximal tibia of the affected knee sags posteriorly)

    • Medial collateral ligament (MCL): Valgus stress (flex the knee 20–30° and apply to the lateral joint line a medially directed force)

    • Lateral collateral ligament (LCL): Varus stress (flex the knee 20–30° and apply to the medial joint line a laterally directed force)

PEARL: If laxity is found in testing three of the four knee ligaments, then a knee dislocation should be assumed to have occurred.

PEARL: Ligament stress testing in the ED is often compromised by pain and swelling causing muscle spasm, making ligament testing less reliable in the acute setting.

Other special knee tests in the ED

  • Patellar apprehension test: With the knee extended and the quadriceps relaxed, apply to the medial side of the patella a laterally directed force. A reflexive quadriceps contraction or facial grimace is abnormal for meniscal pathology (more difficult to perform in the acutely injured knee)

  • Apley’s test: Flex the knee 90°; examiner pushes up on the foot (axial compression to the tibia); pain with external rotation of the foot suggests medial meniscus pathology; pain with internal rotation of the foot suggests lateral meniscus pathology

  • McMurray’s test: Flex the knee 45°; combine valgus stress, external rotation and extension – a painful ‘click’ suggests a medial meniscal tear; with a varus stress, internal rotation and extension – a painful ‘click’ suggests lateral meniscal tear

  • Thessaly’s test: Patient stands on affected leg with the knee flexed at 20°; then rotates the knee and body, internally and externally, three times. Patients with suspected meniscal tears will experience joint-line discomfort

  • External rotation dial test: For post-traumatic lateral knee pain and posterolateral corner injuries (PLC); with the patient prone, test external rotation of the tibia at both 30° and 90° of knee flexion. A positive test is > 10° difference in external rotation compared to the opposite side

Diagnostic testing

  • Plain knee radiographs – only ∼7% in the ED are diagnostic

  • Ottawa knee rules and Pittsburgh knee rules – both are clinical decision rules that can reduce the number of ED radiographs, reduce ED wait times, and reduce costs. Pittsburgh knee rules may have better specificity

  • Ottawa knee rules: Radiographs of the knee are indicated if any of the following are noted:

    • Age > 55 years

    • Inability to flex 90°

    • Isolated tenderness of the patella

    • Tenderness at the head of the fibula

    • Inability to walk four steps both immediately after injury and in the ED

  • Pittsburgh knee rules

    • Fall or blunt trauma injury to knee plus:

    • Either age < 12 years or > 50 years

    • Inability to walk four steps in the ED

  • The sensitivity of knee radiographs is not 100%

  • Radiographic occult fractures can occur around the knee

    • Particularly small avulsion fractures, osteochondral lesions, patellar fractures and subtle, undisplaced tibial plateau fractures

  • Oblique views can increase the sensitivity for detecting a fracture

  • A “sunrise” or “skyline” view can increase the sensitivity for a patellar fracture (Figure 4.1)

PEARL: Ottawa and Pittsburgh knee rules can significantly reduce the number of radiographs needed in patients presenting with knee pain.

  • A lipohemarthrosis is a fat–fluid level that may be seen on a lateral radiograph; its presence is associated with an intra-articular fracture – even if the fracture is not seen on radiograph (the fat comes from the bone marrow) (Figure 4.2)

  • A fabella is a small sesamoid bone found in the lateral head of the gastrocnemius; it is a normal variant and is rarely symptomatic

  • Advanced knee imaging in the ED:

    • Computed tomography (CT) of the knee is uncommonly required by the ED provider – consultants may request CT imaging in the ED to define more clearly fracture patterns and treatment plans

    • CT angiograms or arteriograms may be emergently indicated in select knee dislocation cases

    • Magnetic resonance imagery (MRI) for acute knee injuries is rarely required by the ED provider, though may be requested by the physician providing follow-up care as an outpatient

Figure 4.1 “Sunrise” or “skyline” view: Additional view that can increase sensitivity of the radiograph for patellar fractures. Here a fracture is noted.

(Image courtesy of Arun Sayal, MD.)

Figure 4.2 Lipohemarthrosis. White arrow shows “fat–fluid line” (fat on top) – associated with an intra-articular fracture.

(Image courtesy of Arun Sayal, MD.)


  • The specific diagnosis of the acutely injured knee may be suspected, but often remains unconfirmed after ED assessment

  • For the acutely injured knee that is anatomically aligned and with negative radiographs (if done), management is based on the clinical suspicion of the ED provider

  • In the rare instance where a knee dislocation is suspected, then immobilization in 20–30°of flexion and immediate orthopedic consultation in the ED is indicated

  • When an occult, non-displaced fracture is suspected, then management should include immobilization in ∼30° of flexion, crutches, non-weight-bearing status, and follow-up with orthopedic surgery within a few days. Though not absolutely indicated, local practice patterns may elect to confirm the presence or absence of a fracture in the ED with advanced imaging (CT)

  • Most commonly, a “soft tissue injury” is diagnosed. In these cases, follow-up should be arranged to confirm the diagnosis, ensure clinical improvement, and guide further management

  • Relatively minor soft tissue injuries can weight bear as tolerated, should avoid returning to sports, and can typically be followed up by a primary care physician within a week

  • For more significant soft tissue injuries (ligament, meniscal, etc.), ED management depends on local referral patterns and consultant preferences

  • One ED strategy includes close follow-up with ice, compression, ROM exercises, protected weight-bearing as tolerated, crutches as needed, and immobilization only if needed – this reduces the incidence of stiffness and atrophy that often follow immobilization of the knee

  • However, some orthopedic consultants may prefer immobilization and non-weight-bearing status at ED discharge with close follow-up

  • Follow-up arrangements are determined by multiple factors including provisional diagnosis, consultant preferences, patient’s athletic demands, access to care, age, and co-morbidities


  • Prognosis of knee injuries in the ED can vary from minor injuries that recover fully and quickly, to injuries that may never return to baseline function and are destined to have operative management and/or premature osteoarthritis

  • In appropriate patients, encouraging range of motion exercises and allowing weight-bearing as tolerated reduces the complications of stiffness and weakness that often accompany knee immobilization

Knee dislocations

Key facts

  • Knee dislocations are an orthopedic emergency

  • It is a rare but potentially devastating injury that must be admitted and monitored closely by orthopedic specialists

  • Mechanism varies from high-velocity dislocations (e.g., pedestrian struck) to low-velocity dislocations in susceptible individuals (e.g., morbidly obese individual stepping down off a curb)

  • The popliteal artery is tethered proximally and distally as it passes behind the knee; as such, an arterial injury can be seen with any knee dislocation (up to 30% in all dislocations; up to 50% in anterior–posterior dislocations)

  • Common peroneal nerve injury (“drop foot”) found in ∼25% of dislocations, especially with lateral dislocations

  • Initial ED presentation of arterial injury varies – the limb can be pulseless, may have diminished pulses, or may have normal pulses. ED providers must have a high index of suspicion and rule out a dislocated knee since these patients need to have their vascular status closely monitored

  • An ankle brachial index (ABI) may help guide management in some cases

Clinical presentation

  • High-energy mechanisms are most commonly implicated – motor vehicle crash (MVC), pedestrian struck, high-velocity sports, etc. (Figure 4.3)

  • May also be seen in susceptible individuals with relatively low-velocity injuries – morbidly obese with twisting knee injuries

  • In morbidly obese patients, the dislocation may not be as clinically apparent and only detected on radiographs (Figure 4.4A, B). If the MCL is completely torn, then the joint effusion can extravasate medially and the knee may not appear as swollen

  • Passive straight leg raise – gross hyperextension can indicate an occult knee dislocation

  • Typically, with acute knee ligament injuries, gross laxity is not seen in the ED owing to acute pain and swelling

  • Even though acute ligament testing in the ED is less sensitive, it must be performed to ensure the patient has not suffered a knee dislocation that has spontaneously reduced

  • If, on ED assessment, three out of four ligament laxity is noted, then a knee dislocation must be presumed

  • Assess through distal neurovascular examination for foot drop, color, temperature, refill, etc

  • Pulselessness at any time (pre-reduction or post-reduction) requires an emergent vascular consultation

  • Ankle brachial index may be useful to predict vascular complications

    • ABI is the ratio of the doppler blood pressure at the ankle (use the higher reading of dorsalis pedis and posterior tibial artery) and the brachial artery

    • An ABI of > 0.9 is reassuring; < 0.9 is associated with increased risk of vascular complications; you can compare the value to the contralateral leg

  • Assess for compartment syndrome of the lower leg (see Chapter 8)

PEARL: If three out of four ligaments are unstable on knee examination, the diagnosis is a knee dislocation until proven otherwise.

Figure 4.3 Lateral knee dislocation during a soccer game.

(Image courtesy of Arun Sayal, MD.)

Figure 4.4 Antero-medial knee dislocation. In an obese patient, this can be occult both on history (low velocity) and on physical examination when assessing for alignment. A: AP view. B: Lateral view.

(Images courtesy of Arun Sayal, MD.)

Diagnostic testing

  • Plain radiographs – diagnostic if the joint is still subluxed/dislocated (Figure 4.5 A, B)

  • May be normal if reduced already

  • May see associated fractures of the femur or tibia, (including avulsion fractures)

Figure 4.5 Lateral knee dislocation compared to an anterior/posterior knee dislocation, a lateral dislocation is more likely to have a common peroneal nerve palsy, and less likely to have an arterial injury, though both complications can occur with any knee dislocation. A: AP view. B: Lateral view.

(Images courtesy of Arun Sayal, MD.)

Treatment (Table 4.1)

  • All patients with a documented or suspected knee dislocation require referral to orthopedics and admission

  • If the joint remains subluxed or dislocated, immediate reduction is indicated

  • Typically, a knee dislocation is so unstable that it reduces fairly easily with gentle traction and repositioning (the same reason why knee dislocations often reduce before they get to the ED)

  • Occasionally, soft tissue may be interposed and make the knee irreducible – this warrants emergent referral for open reduction

  • After reduction, recheck and document neurovascular status and apply a knee immobilizer (preferably removable) in ∼20° of flexion (as full extension can result in posterior subluxation)

  • Obtain radiographs post reduction to ensure anatomic alignment

  • In the past, angiography was recommended for all cases of knee dislocation

  • A selective approach to angiography is now favored by many, with indications based on the vascular assessment

  • If definite signs of arterial injury exist (pulseless, expanding popliteal hematoma, cold, white limb, etc.) – then vascular and orthopedic surgery consultations are indicated and the patient should go directly to the operating room

  • If signs of possible arterial injury exist (decreased pulses, cooler limb, delayed refill, etc.), then both immediate referral and angiography are indicated

  • If no sign of arterial injury (normal pulses, warm foot, normal refill), then orthopedic referral is indicated for admission to a facility with vascular surgery and the patient should have frequent neurovascular assessments

  • Evidence of compartment syndrome warrants emergent referral for fasciotomies

PEARL: Knee dislocations are rare but commonly missed (especially if the dislocation spontaneously reduces). The ED provider must consider the diagnosis of a spontaneously reduced knee dislocation in patients with significant knee injuries.

Table 4.1 Management of vascular injuries in knee dislocations.


  • A knee dislocation is a potentially devastating knee injury

  • Vascular complications are more commonly seen with dislocations in the anterior–posterior plane

  • Nerve palsies are more commonly seen with dislocations in the lateral plane

  • Neurovascular complications can occur with dislocations in any direction

  • If vascular injury has occurred, time to OR is predictive of amputation rate: < 8 hours, approximately 15% amputate rate; > 8 hours, approximately 80% amputated

  • ∼1/4 may suffer peroneal nerve damage – majority of which are permanent

  • Stiffness and instability are common complications

  • Heterotopic ossification may also occur

  • Compartment syndrome is common, especially if there is a concomitant arterial injury

  • Complete recovery to the patient’s baseline (pre-dislocation) level of activity is highly unlikely

Meniscal injuries of the knee

Key facts

  • Menisci are important cartilaginous structures involved in weight distribution and knee stability

  • As patients age, degeneration causes the menisci to become thinner and more susceptible to injury

  • The “typical” history for a meniscal injury also varies based on patient age

  • Many meniscal injuries will heal with conservative management

  • Urgent arthroscopy is recommended if the knee is locked (lacks full extension)

Clinical presentation

  • In young adults, the mechanism of injury is usually a significant twisting injury with pronounced pain

  • In older patients, the mechanism of injury is often a minor twist (e.g., getting up from a squat) and the initial pain can vary

  • Meniscal injuries often present with swelling over hours, indicative of inflammation

  • Tears in degenerative menisci often have less swelling

  • Peripheral rim tears may present with a fairly acute hemarthrosis – rim tears are far less common than central tears

  • Other symptoms suggestive of meniscal pathology include pain with squatting, twisting or stairs; swelling with activity, and painful clicking

Physical examination

  • The physical examination usually reveals:

    • A joint effusion

    • Joint-line tenderness (typically medial, though often lateral)

  • Pain with full flexion or extension

  • Joint effusions can present with “fluid bulge” sign for smaller effusions or “patellar ballottement” for larger ones

  • A variety of tests can be performed to look for meniscal pathology – Apley’s test, Thessaly’s test, McMurray’s test, etc. – many of these are difficult to perform in the acutely injured knee

  • It is important to rule out a “locked” knee (i.e., a knee that lacks full extension) since a locked knee is an indication for urgent arthroscopy (Figure 4.6)

  • A few important points regarding a locked knee:

    • Compare to the opposite side (younger patients often hyperextend; so an injured knee that can extend to 0° may actually be “locked”)

    • Acute pain and swelling may also prevent full extension – it is not always mechanical

    • Acute mechanical causes of a locked knee include a bucket-handle tear of the meniscus, the stump of the ACL, or a loose body (which often presents with intermittent locking)

    • One clinical tip to detect more subtle cases of locking (see Figure 4.6): Lie the patient prone, with the knees near the end of the bed and the feet hanging over; a persistent elevated heel height on the affected side can indicate a difference in knee extension

PEARL: Failure to extend the knee fully can be a sign of a “locked knee.” If caused by a mechanical problem, this is an indication for an urgent arthroscopy. Pain and swelling may also prevent full extension. If a “locked knee” is suspected in the ED, then close follow-up needs to be arranged to distinguish surgical from non-surgical causes.

Figure 4.6 Locked knee. The far (right) heel is elevated compared to the near heel – indicating the right knee does not fully extend. If pushing down on the knee results in a hard, “spring-like” recoil, this suggests a mechanical block (i.e., a true “locked knee”). If the endpoint is soft, and the knee slowly extends further, this suggests pain and swelling may be responsible for the lack of full extension. Subtle cases of a locked knee can be detected by this maneuver.

(Image courtesy of Arun Sayal, MD.)

Diagnostic testing

  • Plain radiographs are of limited value in the ED assessment of meniscal injuries

  • For meniscal pathology, studies suggest, a good clinical examination is equivalent to MRI on both sensitivity and specificity

  • MRI may miss meniscal injuries that are present; may detect meniscal injuries that are either asymptomatic or in fact are false positives

  • CT and US do not have enough sensitivity to be recommended for use in determining meniscal pathology


  • Meniscal injuries can be treated with ice, compression, elevation, weight-bearing as tolerated, and crutches as needed

  • NSAIDs may help reduce pain and swelling, which will help maintain range of motion and strength

  • Restricted activity (walking as tolerated, but no running, twisting or jumping motion) is initially recommended to prevent further injury to the knee

  • Sudden knee pain from an existing injury (e.g., a healing meniscal or ligamentous injury) can cause the quadriceps muscles to suddenly relax. If the patient is standing only on the injured leg when this occurs, all the force is put through the unsupported and recently injured knee; this can further damage injured structures (e.g., extend a meniscal tear) or can injure structures not previously injured (e.g., an acute ACL tear)

  • Appropriate follow-up should be arranged and documented

  • Follow-up examination(s) are required to confirm the suspected diagnosis, reassess for other possible injuries, ensure the knee is not “locked,” ensure symptom improvement (pain, swelling) and guide the return to baseline range of motion, strength, and activity level

  • Suspected meniscal injuries can be followed in a week or so by an appropriate physician (local resources and referral pattern help decide if that is an orthopedic surgeon, sports medicine physician or primary care physician)

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Jan 19, 2021 | Posted by in EMERGENCY MEDICINE | Comments Off on Chapter 4 – Knee and leg emergencies

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