Exam Series: Guide to the Knee Exam

A 22 year old female comes to emergency department unable to walk. She was in the middle of a rugby game when she caught the ball while pivoting quickly, and was tackled shortly thereafter. She immediately heard a “pop” and says that the swelling in her right leg has increased substantially over the last hour.

Background:

The knee is a complex hinge joint and one of the most common sites of MSK injuries. Fortunately a diagnosis is usually possible with a good history and physical exam! Four ligaments – the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL) connect the femur to the tibial plateau, ensuring proper alignment and providing stability. Two menisci cushion the articulating surfaces while several bursa further reduce friction around the knee joint. The suprapatellar and posterior bursa communicate directly with the joint cavity and will be enlarged with a joint effusion, posteriorly this is known as a Bakers cyst. The popliteal artery, vein, peroneal and tibial nerve run through the popliteal fossa.

Approach to the History

A thorough history can provide several diagnostic clues and help to risk stratify patients. In some cases the physical examination may be limited by pain or a large effusion, so the history helps to form an overall impression of the case.

1. History of Presenting Illness: Understanding the mechanism of injury is essential in the assessment of knee pain. An acute and traumatic etiology suggests a structural cause of pain. It is also important to determine whether the patient has been able to weight bear, as this guides imaging decisions.
2. Pain characteristics: Identify the onset, position (anterior vs. posterior, medial vs. lateral), quality, radiation, severity, and duration of the pain.
3. Associated symptoms: Mechanical symptoms ex. popping, locking, clicking, and knee “giving way,” suggest a traumatic, structural injury. A joint effusion within hours of the time of the injury suggests a hemarthrosis or lipohemarthrosis from an intrarticular structure with vascularity i.e. ACL/PCL, tibial plateau fracture, or osteochondral injury. Generally meniscal tears have a delayed onset effusion.
4. Review of symptoms: Check for systemic symptoms including constitutional and infectious symptoms ex. fever, chills, night sweats, fatigue, rash. Is this knee pain monoarticular or are there other joints involved as well?
5. Past medical history: Determine if there is a history of injury or surgery to the affected knee. Medical history ex. Rheumatoid Arthritis may point to a chronic cause of knee pain.
6. Medications: Recent fluoroquinolone use, especially in combination with oral glucocorticoids, is associated with tendinopathy and tendon rupture.²

Approach to the Physical Examination – “Look, Feel, Move”

Throughout the physical examination compare the asymptomatic to the symptomatic knee. The knee exam should be conducted with the patient supine, examining a knee in a chair or wheelchair can significantly compromise your exam! Every patient will have a different laxity to their joints at baseline, use the asymptomatic knee to get a sense of the patients baseline laxity. Pain with provocative movements without associated laxity suggests a ligament strain rather than a tear.

Remember to assess the joint above and below the knee. Hip pathology can present as knee pain, and a proximal fibular fracture can be a Maisonneuve fracture that is associated with an ankle eversion injury.

1. Gait assessment: Look whether the patient is able to weight bear in the emergency department. From the standing position, assess whether they have Genu Varum (bow legs) or Genu Valgum (knocked knees – a Lateral force to the knee will knock the knees together in a VaLgum position).
2. Inspection: Look for a large joint effusion, which could represent a traumatic hemarthrosis or lipohemarthrosis, crystal arthopathy, septic arthritis, or other systemic illness. There is a low threshold for synovial fluid aspiration in a hot, swollen knee as septic arthritis is a can’t-miss diagnosis. Hemarthrosis represents bleeding into the knee joint, potentially from a traumatic tear to the ligaments or meniscus or an osteochondral fracture. Lipohemarthrosis occurs when fat and blood from the bone marrow pool in the joint capsule due to intra-articular fracture i.e. a tibial plateau fracture or extensive intraarticular soft tissue injury. Radiographically, lipohemarthrosis is characterized by a fat-fluid interface formed when the lighter fat floats on top of the denser blood.
   

   Lipohemarthosis with arrow indicating a fluid-fat interface³

3. Palpation: Use the back of the hand to assess temperature; the patella should feel cooler than the thigh or tibia. Palpate for joint line tenderness with the knee in flexion. Palpate for the popliteal pulse in the popliteal fossa and check for a Baker’s cyst. Try to elicit any subtle effusions by milking the joint.
4. Range of motion: Allow the patient to demonstrate their active range of motion, then move through their passive range while feeling for crepitus. The patient should be able to passively perform a straight leg raise; failure to do so may indicate injury to the extensor mechanism. Normal flexion is to 130° and normal extension should be <10 degrees. Internal and external rotation of the knees can be assessed by bending both the knee and hips to 90° while the patient lies supine, and then asking them to point their toes inwards (up to 30°) and outwards (up to 20°)
5. Power: Check for power bilaterally, assessing for any muscular atrophy or spasm.
6. Special tests:

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ACL Tear

• Anterior drawer test:Rest both of your forearms on the patient’s tibia with their knee flexed to 90° and foot resting on the table. Pull forwards to elicit any anterior displacement.
• Lachman: Place one hand on the femur and the other on the proximal tibia with the patient supine and knee flexed to 30°. Try to pull the tibia forwards and look for anterior displacement.
• Pivot shift sign: Position the knee in full extension with the leg internally rotated and under a valgus stress, then slowly flex the knee. If there is an ACL injury the tibia will initially be subluxed anteriorly and an appreciable reduction in its position occurs around 30°. The patient must be completely relaxed, so the test is best performed under anesthesia.

Test	Sensitivity	Specificity	Likelihood Ratio
Anterior drawer	49%	58%	1.4
Lachman	94%	97%	9.4
Pivot shift	32%	100%	1.3

Clinical Utility of Special Tests for ACL tear³ [bg_faq_end] [bg_faq_start]

PCL tear:

• Posterior drawer test: In the same position as the anterior drawer test push backwards to check for any possible posterior displacement.
• Posterior sag sign: Flex both hips and knees to 90°, supporting the patient’s ankles and knees. Compare the resting positions of the tibias; if one sags below the other it indicates a torn PCL.
• Quadriceps active test: Brace the patient’s foot on the bed with their knee flexed to 90° in a drawer test position. Ask the patient to extend to elicit a quadriceps contraction. Check for an anterior displacement of the tibia compared to the femur.

Test	Sensitivity	Specificity	Likelihood Ratio
Posterior drawer4	51-86%	Not reported	Not reported
Posterior sag5	79%	100%	79
Quadriceps activation6	54-98%	97-100%	Not reported

Clinical Utility of Special Tests for PCL tear [bg_faq_end] [bg_faq_start]

MCL tear:

• Medial collateral stress test: Apply a valgus force to the knee while the patient is supine with the knee slightly flexed, assessing for laxity and pain at the medial aspect of the knee. [bg_faq_end]

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LCL tear:

• Lateral collateral stress test: Similar to the medial collateral ligament stress test, apply a lateral varus force to the knee. [bg_faq_end]

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Meniscal tear:

• Joint line tenderness: Palpate for tenderness in the joint line while the knee is in a flexed position.
• McMurray’s test: Flex the knee and place your fingers along joint line. To test for a medial meniscus injury externally rotate the foot while applying a valgus force. Gently flex and extend the knee listening for a clicking sound indicative of a trapped meniscus. To test for a lateral meniscus injury internally rotate the foot while applying a varus force and try to trap the meniscus throughout movement.
• Apley’s compression test: Flex the patient’s knee to 90° and apply pressure on the patient’s foot towards the distal femur. Pain with pressure suggests a meniscal injury.
• Thessaly test: Support the patient while they stand on the injured leg flexed to 20°. Ask them to rotate on the tibia back and forth, assessing for joint line pain or mechanical symptoms.

Test	Sensitivity		Specificity		Likelihood Ratio
	MM	LM	MM	LM	MM	LM
Joint line tenderness	71%	78%	87%	90%	5.46	7.80
McMurray	48%	65%	94%	86%	8.00	4.64
Apley’s	41%	41%	93%	86%	5.85	2.93
Thessaly	89%	92%	97%	96%	29.7	23.0

Clinical Utility of Special Tests for Meniscal Injury^7,8  [bg_faq_end]

7. Neurovascular exam:

 It is essential, especially in the case of trauma or suspected knee dislocation, to conduct a neurovascular exam as injury to the popliteal artery can result in loss of limb in as little as 8 hours. At the bedside, this involves locating distal pulses (posterior tibial and dorsalis pedis) using palpation, Doppler, or bedside ultrasound. Serial physical examinations are necessary, with the addition of an Ankle-Brachial Index (ABI <0.9 is abnormal) as popliteal injury still occurs in up to 15% of patients with palpable peripheral pulses¹. CT angiography should be considered in all knee dislocations. Neurovascular exam should be documented before and after reduction of dislocations.

Nerve	Origin	Motor function	Sensory function	Reflexes
Deep peroneal	L4, L5. Derived from the common peroneal (fibular nerve)	Ankle dorsiflexion. Damage to this nerve results in foot drop	1st dorsal web space
Superficial peroneal	L5, S1	Foot eversion	Dorsum of the foot
Posterior tibia	L4, L5	Foot inversion
Tibial	S1, S2	Ankle plantar flexion	Plantar aspect of the foot arch	Achilles

Neurologic examination⁹

Investigations

The Ottawa Knee rule is 98.5% sensitive and 48.6% specific for identifying knee fractures in patients > 2 years old.¹⁰ It suggests that you obtain knee radiographs after acute injury for patients who have

• Age =>55
• Isolated tenderness at the patella
• Inability to flex the knee to 90 degrees
• Inability to bear weight immediately and in the emergency department for four steps

Children are more prone to fractures as their ligaments are stronger than bones, so there is a low threshold to order X-rays in children. If there is suspicion for a tibial plateau fracture three views should be ordered: AP, lateral, and tunnel view. A segond fracture – a small tibial avulsion fracture – may be indicative of an occult tibial plateau fracture or ACL tear.

CT imaging may be indicated if there is a traumatic mechanism and a high suspicion of fracture not seen on X ray. CT angiography may also be indicated if there is suspected popliteal artery injury and in all knee dislocations. MRI can be used to further assess for ligamentous injury. Although this does not guide management in the emergency department or acute setting it is often used to assess suitability for surgical repair. Arthroscopy can be both diagnostic and therapeutic. Bedside ultrasound may be helpful for appreciating an effusion, either intra-articular or bursal, and guiding a joint aspiration. Ultrasound can also be used to check for a popliteal cyst or deep vein thrombosis. Synovial joint aspiration is needed for a hot swollen joint in order to rule out septic arthritis.

Putting it all together

The combination of the history, physical, and ancillary test results can help to guide your assessment:

Injury	Mechanism	Signs and Symptoms	Investigations
Traumatic
ACL tear	Plant-pivot-pop,’ often without direct contact.	Felt a “pop” with immediate swelling. Instability with a positive Anterior Drawer, Lachman, Pivot Shift.	Segond fracture of X ray is pathognomonic for a tear.
PCL tear	Posterior force on the tibia ex. knee striking the dashboard in a car accident.	Pain with push off and descending stairs. Positive Posterior Drawer and Sag Sign.
LCL tear	Direct varus force on the medial aspect of the knee	Tenderness above and below the joint line, especially with stress.
MCL tear	Direct valgus force on the lateral aspect of the knee	Tenderness above and below the joint line, especially with stress.
Meniscal tear	Twisting force on the knee	Immediate pain, instability, locking. Delayed swelling. Joint line tenderness. McMurray, Apley’s, and Thessaly positive.
Extensor mechanism injuries (quadriceps tendon rupture, patellar tendon rupture)	Sudden forceful contraction of the quadriceps, or direct blow. Risk factors for tendon rupture include recent fluoroquinolone use, steroid use, DM, RA.	Patient cannot SLR. Palpation of a suprapatellar groove if the patella has shifted in position.	A lateral X ray may show the patella in a high riding position (alta) or a low riding position (baja), measured formally by the Insall-Salvati ratio. A sunrise view may show patellar fractures.
Dislocated knee	High impact trauma	Laxity in multiple ligaments. Most knee dislocations spontaneously reduce by the time the patient arrives to the emerg, however a reduction does not exclude vascular injury.	Neurovascular exam and possible ancillary investigations are required as there is a risk of limb-threatening popliteal injury. Consider imaging for assessment of associated fractures.
Fracture	High impact trauma	Inability to weight bear, pain, swelling.	Usually seen on X-ray, but a CT may be required to appreciate non-displaced fractures.
Atraumatic
Patellofemoral pain	Overuse syndrome, often linked to weakness of the quadriceps muscle. May be associated with other overuse syndromes including chondromalacia patellae, medial plica syndrome, Iliotibial band syndrome (lateral knee pain), popliteus tendinitis (posterior knee pain).	Vague history of anterior pain worsens after sitting (“theatre sign”). Pain with firm compression of the patella. No mechanical symptoms (eg, locking, catching). Commonly seen in young active female with high Q angle, as this increases the risk for patellar subluxation.	Clinical diagnosis, X rays are often normal.
Osteoarthritis	Chronic knee pain in patients >40	Aggravated by weight bearing and relieved with rest. Restricted ROM, crepitus.	X rays may show joint space narrowing, hypertrophic osteophyte formation and cystic changes but radiographic changes are not necessarily correlated to clinical symptoms.
Crystal arthropathy	No other infectious symptoms.	Unilateral, swollen joint, may have fever.	Crystals in synovial fluid AND a negative culture, as the presence of crystals can be co-morbid with septic arthritis.
Septic arthritis	Infection from hematogenous spread, open wound, or local spread through the joint space.	Unilateral, hot, swollen joint.	Synovial fluid showing WBC >25,000/mm3with a left shift. Fluid is typically opaque and yellow with a positive culture.
Bursitis	May be traumatic, crystal, or infectious, most commonly induced after repetitive kneeling on hard surfaces (“handmaid’s knee).	Pre-patellar effusion, tender to palpation. May mimic a joint effusion or a septic knee.	Ultrasound may help differentiate between bursitis and a joint effusion. Aspiration is required if there is any suspicion of infection.
Systemic disease (ex. Rheumatoid Arthritsi)	Known history of disease of systemic symptoms including fever, chills, night sweats, fatigue, or unintentional weight loss.	Insidious onset pain with morning stiffness. Often associated with effusions and Baker’s cysts.	Bony erosions, typically first seen in the PIPs and MCPs.

Management

The vast majority of knee injuries can be managed conservatively using RICE (restricted activity, ice, compression, and elevation). Topical therapies (ex. NSAIDs, capsaicin) can be used for pain relief in combination with regular Tylenol and/or NSAIDs.

Patients with suspected ligamentous injuries can be encouraged to weight bear as tolerated within limits of pain, using crutches as-needed for support. In the case of significant instability the patient should be non-weight bearing but should engage in daily ROM. Avoid immobilization with a Zimmer splint for ligamentous injuries as its use can delay rehabilitation, and contribute to atrophy and joint stiffness. Only patients with a soft tissue injury involving a quadriceps tendon rupture, patella tendon rupture, patellar dislocation, or fractured patella require a Zimmer immobilizer. Ligamentous, meniscal and osteochondral injuries can be referred for outpatient consultation to orthopedics, sports medicine or the patient’s family physician depending on local practice. The exception is an acutely ‘locked knee’ due to suspected meniscal tear which may require ED orthopedic consultation.

Fractures should be immobilized, referred to orthopaedics, and patients should refrain from weight bearing.

Management of osteoarthritis of the knee should involve physiotherapy referral for strengthening, low-impact aerobic exercise, weight loss, and analgesia including Tylenol and/or NSAIDs (topical or oral). Glucosamine and chondroitin are not recommended.¹²

Back to the Case

Given the history you immediately suspect an ACL injury. On your assessment she has a large effusion that limits her ROM. You are unable to conduct an appropriate Anterior Drawer Test or Pivot Shift Test secondary to pain, but she has a positive Lachman. You order an X-ray as she is unable to weight bear, and you see a small Segond fracture. She is diagnosed with an ACL tear and discharged home with suggestions for pain control, crutches, and advised to begin ROM exercises early. This young patient should be referred to orthopaedics for consideration of ACL repair before or after her MRI depending on local practice. ACL repair is generally delayed until near full ROM returns and the effusion resolves although this is surgeon dependent.

In summary for acute knee injuries take a good history, avoid examining the patient in a chair, ensure appropriate follow-up and discharge instructions including encouraging active ROM and weight bearing as tolerated for ligamentous and meniscal injuries. Reserve Zimmer splints for patients with patellar dislocations, patellar tendon or quadriceps tears.

Additional Resources

• Rheumtutor: MSK Clinical Skills Manuals and Instructional Videos
• Orthobullets: Quick reference orthopedic information
• Physiotutor: Youtube videos for clinical assessment
• EM Cases: Episode 91 Occult Knee Injuries Pearls and Pitfalls

This post was copyedited by Brad Stebner (@stebs444)

 References: