06. Approach to Knee Pain

Resident Editor: John Landefeld, MD

Faculty Editor: Carlin Senter, MD


✔ Ottawa Knee Rule is nearly 100% sensitive for detecting fracture as the cause of knee pain

✔ Suspicion for septic knee warrants immediate evaluation by orthopedist



  • Characterize pain: onset (rapid ­­­­or insidious), location (anterior, medial, lateral, posterior), duration, severity, quality (dull, sharp, achy)
  • Symptoms: Ask about locking (suggests meniscal tear), popping (suggests ligamentous tear), sensation of ‘giving way’ (suggest patellar subluxation or ligament rupture). Presence of effusion – if rapid, suggests ACL tear or tibial plateau fracture; if ~36hrs, suggests meniscal tear or other ligament rupture. 
  • Mechanism of injury
    • Direct blow? Anterior force can tear PCL, lateral force can tear MCL, medial force can tear LCL
    • Quick turns or stops? Can tear ACL
    • Sudden pivoting/twisting? Can injure meniscus
  • Medical history: 
    • Prior injuries to knee? Prior surgeries? 
    • What treatments have been attempted in the past? How successful were they?
    • History of gout, pseudogout, rheumatoid arthritis, or DJD? 



Patient standing: Inspection

  • Compare the affected knee to the contralateral, looking for asymmetry, swelling, erythema.
  • Evaluate alignment: varus, valgus or neutral?

Patient sitting at edge of table: Palpation

  • Find joint line and palpate 1 joint line at a time (medial or lateral) then the other, looking for tenderness. Isolated joint line tenderness raises concern for meniscus tear.
  • Palpate above and below the joint lines (femoral condyles above, tibial plateau below) looking for tenderness. Bony tenderness raises concern for arthritis or fracture.
  • Palpate patellar and quadriceps tendons to evaluate for tendinitis or tendinopathy. 

Patient supine:


  • Ballotement or milking to detect effusion
  • Temperature: knee should be cooler than rest of the leg
  • Patellar facets: tender in patellofemoral pain syndrome, chondromalacia patella, patellar arthritis
  • Patellar apprehension test: Apply lateral pressure to the medial aspect of the patella; if this reproduces pain, or gives sensation of ‘giving away’, patellar subluxation may be diagnosis
  • Palpate the Pes Anserine Bursa: Located just distal to the tibial tubercle and 2 fingerbreadths medial to it.  

Range of Motion

  • Extend and flex the knee as far as possible: normal ROM is 0° to 135°


  • Anterior Cruciate Ligament
    • Lachman Test: Patient in supine position, knee flexed to 30 degrees. Stabilize distal femur with one hand, and with other hand grasp tibia & translate anteriorly
  • Posterior Cruciate Ligament
    • Posterior Drawer: Patient in supine position, knee flexed to 90 degrees. Examiner attempts to translate tibia posteriorly. 

Collateral Ligaments

  • Medial Collateral Ligament
    • Apply valgus stress test at both 30 degrees and full extension
    • At 30 degrees, the joint is unlocked and valgus stress tests the MCL and joint capsule. At full extension, valgus stress tests the MCL, joint capsule, ACL, and PCL
  • Lateral Collateral Ligament
    • Apply varus stress test at both 30 degrees and full extension


  • Meniscal injuries generally present with tenderness along joint line
  • McMurray Test: Various techniques are acceptable. The following is one method – cup the heel of the affected leg in your dominant hand. With your other hand, grip the anterior knee along the joint line. While flexing and extending at the knee, flex and externally rotate at the hip, essentially ‘churning’ the leg as it flexes and extends like a piston. A positive test causes a thud, click, or pain. 
  • Thessaly Test: As the patient stands, hold her outstretched hands. The patient then rotates her knee and body, internally and externally, three times, keeping the knee at 5 degrees of flexion. Perform the same maneuver again at 20 degrees. First perform the test on the normal knee, then the affected knee. 
    • Patients with meniscal tears may experience joint line discomfort, or a sensation of locking or catching 



  • Ottawa Knee Rule* – Clinical prediction tool that is nearly 100% sensitive for detecting fracture as the cause of knee pain. Validated for patients > 2 years old. 
  • If radiographs are indicated, 3 views are sufficient (A/P, Lateral, and Merchant’s view) 
  • For knee OA, can order a weight-bearing, flexed P/A view (also known as ‘notch view’, more sensitive than non-weightbearing A/P view for OA)


Obtain knee x-ray series if any of the following apply:

  •  Age greater than or equal to 55 years
  •  Isolated tenderness of the patella (no other bony tenderness)
  •  Tenderness at the fibular head 
  •  Unable to flex the knee fully to 90 degrees
  •  Unable to bear weight, both immediately after the injury and in the ED (4 steps, limping is ok)


*Note: Rule may not be reliable in cases where patient assessment is difficult, as in intoxication, head injury, multiple painful injuries or diminished sensation due to neurological deficits. A liberal use of x-rays may be warranted to assess severity of extremity injuries in elderly patients, as they are more likely to fracture with relatively minor trauma.


Common Knee Problems

Patello-femoral Pain Syndrome

·      Vague history of mild-moderate anterior or peri-patellar pain frequently noticed after prolonged periods of sitting (aka the theater sign)

·      Usually is related to overuse in athletes, with other possible contributors include inappropriate footwear and performing squats & lunges. 

·      Usually without effusion, and pain can be reproduced by direct pressure on patella or with medial/lateral subluxation 



Pes Anserine Bursitis 

  • The bursa can become inflamed with overuse, causing anteromedial knee pain worsened with repetitive flexion/extension
  • No effusion on exam, but tenderness at the pes anserine bursa, distal and medial to the tibial tubercle 
  • Pain can be reproduced with valgus stress testing or resisted knee flexion 


Iliotibial Band Tendonitis

  • Due to increased friction between lateral femoral condyle and iliotibial band, and can be seen in any patients with increased repetitive knee flexion 
  • Patients report lateral knee pain worsened by descending or ascending hills or stairs. 
  • On exam, tenderness to palpation over the lateral femoral condyle, approximately 3cm proximal of the joint line


ACL Tear

  • Usually occurs without contact, but rather when the patient plants his/her foot and abruptly switches directions. The subsequent valgus strain leads to anterior tibial displacement and rupture of the ACL. 
  • Patients often report feeling or hearing a ‘pop’ in their knee at the time of injury
  • Swelling within 2 hours of the injury is often secondary to hemarthrosis after ligament rupture 
  • On exam, a moderate knee effusion limiting ROM may be present. The anterior drawer sign may be positive, but can also be negative due to swelling from hemarthrosis or guarding from hamstring muscles. Lachman’s test, however, is more sensitive and should be positive. 
  • Radiographs are indicated to detect possible tibial spine avulsion fractures, but an MRI will be necessary to confirm the diagnosis and for preoperative evaluation


MCL Sprain

  • Fairly common, and results from either a misstep or trauma leading to valgus (inward) stress on the knee
  • Immediately following the injury, the patient develops pain along the MCL
  • On exam there is point tenderness along the MCL, pain +/- laxity on valgus stress testing
    • A clearly defined end point on valgus stress testing indicates a Grade 1 sprain. Laxity with an endpoint is a Grade 2 sprain. Laxity with no endpoint, is a complete tear or Grade 3 sprain.


LCL Sprain

  • Less common than MCL sprains; typically occur with abrupt varus stress to the knee, leading to sudden lateral knee pain requiring cessation of activity
  • On exam there is point tenderness on the LCL with laxity and pain on varus stress testing 


Meniscal Tear 

  • Can occur with sudden twisting movement, such as when a runner changes direction, but may also occur over time in a patient with previous ACL injuries
  • Patients will complain of frequent ‘catching’ or ‘locking’ of their knee with pain, especially when squatting or twisting the knee 
  • On exam, there will be tenderness at the affected joint line. Negative McMurray alone does not rule out meniscal tear, so include multiple tests (joint line tenderness, Thessaly test, Squat test). 
  • MRI is imaging modality of choice 



  • Can occur at any age, but more common in patients with cancer, HIV/AIDS, diabetes, alcoholism, or those on chronic immunosuppression (including steroids). 
  • Patients report abrupt onset of pain, swelling, warmth without antecedent trauma
  • On exam, the knee is exquisitely tender, warm, erythematous, and swollen 
  • Arthrocentesis will find turbid fluid with >50K WBCs (>75% PMNs), elevated protein, and low glucose
  • Gram stain and culture may show the causative organism. Serum labs may show leukocytosis and elevated ESR. 
  • If suspicious, this is a surgical emergency, and the patient should be evaluated STAT by an orthopedist 



  • Knee pain that is aggravated by weight-bearing activity and relieved by rest. Patients may experience episodes of acute synovitis (including swelling) in addition to chronic joint stiffness and pain 
  • Exam may show effusion, bony tenderness, reduced range of motion, or crepitus 
  • When suspected, obtain radiographs (P/A weight-bearing view, Merchant’s and lateral non-weight-bearing views)



  • Patients will complain of acute inflammation, pain, and swelling without recent trauma suggest crystal-induced disease
  • On exam, the knee is erythematous, swollen, tender, and warm. Even minor movements evoke excruciating pain. 
  • Arthrocentesis will show clear or slightly-cloudy fluid, with 2K-75K WBCs and high protein content. Microscopy will show either negatively birefringent (gout) or positively birefringent (CPPD) crystals. 


Popliteal/Baker’s Cyst 

  • Insidious development of mild-moderate popliteal fossa
  • Palpable fullness in the medial aspect of the fossa 
  • Can be definitively diagnosed with arthrography, ultrasonography, or CT
  • Think of popliteal cyst as the same as an effusion. The cyst is not the problem in and of itself; it is a symptom of a knee problem (most often osteoarthritis but could be any knee problem leading to an effusion).



Calmbach WL, Hutchens M. Evaluation of Patients Presenting with Knee Pain Part 1: History, Physical Examination, Radiographs, and Laboratory Tests. Am Fam Physician 2003;68:907-912. 

Calmbach WL, Hutchens M. Evaluation of Patients Presenting with Knee Pain Part 2: Differential Diagnosis. Am Fam Physician 2003;68:917-922. 

Snoeker BA, Lindeboom R, Zwinderman AH, et al. Detecting Meniscal Tears in Primary Care: Reproducibility and Accuracy of 2 Weight-Bearing Tests and 1 Non-Weight-Bearing Test. J Orthop Sports Phys Ther. 2015;45:9,693-702.