Diagnosis
Comments
Hemarthrosis, bone infarct
History of hemophilia or sickle cell disease
Septic arthritis
Fever, unwillingness to bear weight or range a knee held constantly around 30° of flexion. Neisseria gonorrhoeae type common in sexually active young individuals
Acute osteomyelitis
Fever and constitutional symptoms especially in association with immunocompromised (HIV, sickle cell, diabetes, alcoholism, chronic corticosteroid use), intravenous drug abuse, or children
Neoplastic
Constitutional symptoms, typically more insidious onset (except acute fracture through tumoral bone); acute fracture across a benign preexisting bone lesion or cyst would not be distinguishable from ordinary fracture without imaging studies
Inflammatory
History of rheumatoid arthritis (flare up) or crystalline arthropathy; focal tenderness over the affected area (bursitis, tendinitis)
Traumatic
Onset of pain at time of acute sporting or vehicular injury; fractures associated with unwillingness to bear weight more than ligamentous or soft-tissue injuries, but may occur together; acute patellar or quadriceps tendon rupture prevents ability to actively, fully extend knee despite adequate passive motion
Iatrogenic/drugs
History of recent knee injection (postinjection inflammation and/or infection)
Watch Out
Ligamentous injury classically presents with immediate swelling, while meniscal tears develops swelling the next day.
What Is the Most Likely Diagnosis?
In a young healthy male with sudden knee pain immediately following a skiing accident, a traumatic etiology is most likely. Since the patient is able to bear weight, fracture is less likely, though not entirely ruled out. Anterior knee laxity on physical exam suggests anterior cruciate ligament (ACL) disruption. Varus and valgus stability go against associated medial collateral ligament (MCL) and lateral collateral ligament (LCL) disruption. As the patient’s knee does not buckle despite a flexed knee gait during weight bearing in conjunction with no palpable tendon defects, quadriceps or patellar tendon rupture is less likely. Though commonly associated with ACL tears, meniscal tear is less likely in the presence of a negative McMurray sign (no pain, no palpable or audible snap with a compression and axial rotation maneuver of the knee while extending it from a fully flexed position).
History and Physical Exam
What are the Principle Components of the Knee Exam?
Component | Features |
|---|---|
Gait | Look for obvious gait abnormalities |
Observation | Fully expose and compare both knees, look for atrophy, past scars, swelling, bowing, and landmarks (e.g., patella, anterior tibial tuberosity) |
Palpation | Temperature (e.g., warmth) and effusion (e.g., patella floats and “bounces” back when pushed down) |
Range of motion | Active and then passive (e.g., clinician moves the joint), listen for crepitus |
Joint line tenderness | Evaluate for medial or lateral meniscal injuries |
Neurovascular | Check distal pulses and sensation of knee and lower legs |
Knee maneuvers | Lachman’s test, anterior drawer, McMurray’s test, and pivotal shift tests (see Table 27.1) |
What Are the Classical Physical Exam Signs for Knee Injuries and How Are They Performed?
Table 27.1 describes all the clinical tests to evaluate knee pain. All are performed supine. Side-to-side comparison is most important to determine the presence of laxity or a soft end-point. For the pivot shift, the leg is lifted off the table while supported under the ankle. A valgus and internal compressive stress is applied while flexing the knee from full extension. As the knee flexes past 30°, a sudden clunk will occur as the iliotibial band reduces a subluxated knee if the ACL is disrupted. This test is considered pathognomonic for ACL disruption.
Table 27.1
Knee maneuvers
Structure | Clinical finding/test | Description |
|---|---|---|
Anterior cruciate ligament (ACL) | Anterior drawer or Lachman’s test | Knee flexed at 90°, forward traction on the lower leg causes the tibial plateau to move forward relative to the knee suggests torn ACL |
Posterior cruciate ligament (PCL) | Posterior drawer test or “tibial sag” on 90° flexion | Knee flexed at 90°, posterior force on the lower leg causes the tibial plateau to move posteriorly relative to the knee suggests torn PCL |
Meniscal cartilage | McMurray’s test | Extending the knee from a fully flexed position (heels on buttocks) and simultaneously applying compression and axial rotation (torsion) across the joint; positive if pain or an audible or palpable snap (more specific) along the joint line signifying meniscal tear |
Lateral collateral ligament (LCL) | Varus instability | Knee pressed laterally, foot pressed medially, significant laxity in this maneuver suggests LCL tear |
Medial collateral ligament (MCL) | Valgus instability | Knee pressed medially, foot pressed laterally, significant laxity in this maneuver suggests MCL tear |
Watch Out
Don’t confuse McMurray’s sign with Murphy’s sign (stopping of inspiration with right upper quadrant palpation associated with acute cholecystitis).
What is the Classic History for the Various Ligamentous Injuries in the Knee?
Ligament | Classic history |
|---|---|
Anterior cruciate ligament | Posterior blow to the lateral knee |
Posterior cruciate ligament | Anterior blow to the lateral knee |
Medial collateral ligament | Lateral blow to the knee (varus stress) |
Lateral collateral ligament | Medial blow to the knee (valgus stress) |
What Does a History of Locking or Catching Signify?
Locking or catching with range of motion of the knee is often referred to as mechanical symptoms and may signify a mechanical blockage to motion. This is most often associated with meniscal tears, especially mobile flaps. Other loose osteochondral bodies in the joint space can cause the same effect.
Why Is It Important to Perform a Careful Vascular Exam?
Clinical entities like knee dislocation or proximal tibia fracture can pose a significant threat to the limb. Knee dislocations can damage the popliteal vessels creating a dysvascular limb which may lead to amputation if not recognized and treated. Pulses should always be assessed and ankle-brachial indices performed if there is any uncertainty.
Why Is It Important to Perform a Careful Neurologic Exam?
Global instability after knee dislocation, significant ligamentous disruption, or fracture can damage the major nerves or branches traversing the region. Foot drop with damage to the peroneal nerve is among the most common. More aggressive or immediate stabilization of an unstable knee may be indicated to protect from or prevent further damage to these structures. Surgical exploration and nerve repair is sometimes needed.
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