Knee pain

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In Process

Author / Curator: Christopher Steele, MD MPH MS

Faculty Advisor:

The format of each page are recommended guidelines. They should be fluid as each topic will have a unique flow.

(1) Be concise.

(2) Be evidence-based. (Everything should have a reputable citation and resource)

(3) Be clinically relevant. (Avoid unnecessary discussion of pathophysiology and epidemiology if it does not help clinical decision-making).

Learning Objectives

  • Understand the basic anatomy of the knee joint and correlate it to clinical pathology.
  • Develop an organized approach to forming a differential on knee pain.
  • Become familiar with the knee exam, including specialized maneuvers.
  • Understand how to manage common knee pathology, including when to refer to a specialist.
  • Know when it is appropriate to order imaging for the knee.

Top Teaching Points

  • Knee pain is the 2nd most common musculoskeletal concern presenting to a primary care clinic and plagues 13%- 20% of the general population.[1] [2]
  • The key anatomy one should familiarize themselves with is the bones, ligaments, menisci, bursa, the iliotibial band and plica of the knee. Almost all pathology of the knee is from one of those structures being injured.
  • One approach to creating a differential for knee pain is based on location such as anterior, posterior, lateral, medial and generalized.[3]
  • Always examine the joint above and below during a physical exam. Sometimes knee pain can be masked by hip, back or ankle pathology.
  • The Ottawa knee rule can be used to determine when plain films should be ordered to rule out a fracture in an acute injury.[4]
  • Conservative therapy such as ice, rest, physical therapy, strength training, or NSAIDs and/or tylenol is usually the best treatment options for knee pain.[3]


Basic Anatomy of the knee[5]

Knee pain is the 2nd most common musculoskeletal concern presenting to a primary care clinic and plagues 13%-20% of the general population.[1] [2] In order to diagnose knee pain, one has to have a working understanding of clinical anatomy of the knee. The next section is an overview of relevant anatomy a clinician should know in order to diagnose knee pain properly.


The knee is a complex joint made up of multiple ligaments, bursa, and menisci. The tibiofemoral joint, or the space between the femur and tibia, has 4 main ligaments providing stability to the joint which are the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LCL). Within the knee itself, there are two menisci made of cartilage which are termed medial and lateral meniscus. The other important bony landmark is the patella, which is attached superiorly by the quadriceps tendon and inferiorly by the patellar. Patellofemoral syndrome is the most common cause of anterior knee pain which is the irritation of patella and femoral tendon.[6]

The knee is also composed of bursa that act almost like cushions for the tendons to glide against. There are 5 bursa in the knee and are called the suprapatellar, prepatellar, infrapatellar, pes anserine and popliteal bursa. Of the 5, the pes anserine bursa and prepatellar bursa frequently become irritated resulting in bursitis. The Pes anserine bursa is located on the medial aspect of the knee next to the gracillus and Sartorius tendons. For some patients, they may have left over embryonic folds called plica in their joint spaces which allow synovial fluids to move around freely. Typically only the medial plica causes pain.[7] The only other anatomical structure to note is the iliotibial band which runs laterally and is a frequent cause of leg pain in runners and exercises involving bending.


Differential Diagnosis

The differential diagnosis of knee pain can be approached based on anatomical position with respect to the 4 quadrants of the knee which are anterior, posterior, medial and lateral pathology. There is a final section labeled generalized which encompasses pathology that may effect the entire joint itself. The following table summarizes the pathology that can occur in each section.

Differential diagnosis of knee pain based on anatomical position [8] [1] [2] [3]
Diagnosis Typical Presentation Physical Exam Findings
Anterior ACL Tear Pivotal trauma, usually with swelling almost immediately after.[1] Positive Anterior Drawer or Positive Lachman Test*
Patellofemoral Pain Syndrome

(chondromalacia patellae)

Pain with increased force on the tendon such as stairs or squatting.[9] [6] Positive Patella Apprehension Test

Positive Clark or Patellar Grind Test*

Prepatella bursitis

(AKA just above patella)

Pain over the patella after injuring their patella. Tenderness at the bursa site upon palpation
Posterior PCL Tear Deceleration of a flexed leg (e.g. car crash with knee hitting dashboard).[1] Posterior Drawer Test
Baker’s Cyst Cyst like mass palpated in back of knee with or without pain.[10] Palpation of a cystic structure at the back of the knee
Deep Vein Thrombosis Unilateral swelling and pain at the site of the calf but can be felt at the knee. Palpable cord, unilateral leg edema
Medial Medial Meniscus Tear Pain after a pivotal trauma, but swelling usually hours to days after incident. More common than lateral meniscus.[1] Positive McMurray’s Test (external rotation)
MCL Tear Lateral blunt trauma Positive Valgus Test
Pes Anserine Bursitis Pain localized medially and felt with activity such as running or climbing stairs.[11] With knee flexed at about 60 degrees, pain on the medial tibial joint line near the gracillus tendon.
Medial Plica Syndrome Pain with an audible click at the medial site with localized effusion.[12] Audible clicking with pain felt moreso at the medial femoral condyle. [13]
Lateral Lateral Meniscus Tear Pain after a pivotal trauma, but swelling usually hours to days after incident. Less common than medial meniscus.[1] Positive McMurray’s Test (internal rotation of leg).
LCL Tear Medial blunt trauma. Positive Varus Test
Iliotibial Band Syndrome Report a history of running or riding a pedal bike with pain near the femoral epicondyle.[14] Positive Noble or Ober Test
Generalized Arthritis (e.g osteoarthritis, rheumatoid arthritis) and gout/pseudogout. Variable The three most specific findings for OA are palpated bony enlargements, genu varum and stiffness lasting less than 30 minutes.[1][1]
Trauma Variable Variable
Septic Arthritis Acute onset of severe knee pain with other symptoms suggestive of infection and/or sepsis. Severe leg pain, fevers, and signs of infection/sepsis.

*Indicate the most specific test and superior to others suggested for that diagnosis.

Physical Exam

One approach for the physical examination is to break it into three sections. First, the practitioner should inspect and palpate the knee which includes assessing for temperature and fluid. Next, the practitioner should assess for range of motion. Finally, the practitioner should assess the ligaments and menisci of the knee.

Inspection and Palpation[15]

  • Have the patient stand to look for asymmetry and appearance of the knee. Always use the opposite knee for comparison.
  • Palpate the back of the knee looking for Baker's cysts.
  • Next have patient lie on the exam table supine.
  • Temperature
    • Examine the temperature of the knee by placing the back of one's hand on the knee then distally to the anterior shin.
      • Findings: The knee should be colder than the distal leg. If warmer, suspect inflammatory vs septic pathology.
  • Fluid
    • Technique: The practitioner should press on the medial aspect of the kneecap while holding firm pressure on the lateral aspect of the knee. On the medial site, the practitioner should move their hand anteriorly.
      • Findings: A positive finding results in a "bulge" sign or noticeable accumulation of fluid.
  • Palpation while supine
    • Palpation is key to localize the pain further. Conditions like osteoarthritis can be diagnosed with certainty by palpating bony enlargement. Other conditions that have a characteristic location are summarized in the differential diagnosis table.

Range of Motion

  • Passive: With the unaffected knee, first bend and extend the knee. Repeat the same with the affected knee.
  • Active: After passive motion is tested, have the patient bend and extend their knee joint with both legs.
    • Findings:
      • Passive motion pain: Joint involvement. Usually accompanied by active motion pain.
      • Active motion pain only: Muscle or tendon involvement
    • Crepitus, or the crunching sensation that can be palpated on exam, is a finding that can be appreciated by putting one hand on the knee while the provider passively moves the leg. A positive finding suggests either patellofemoral or tibiafemoral osteoarthritis. This finding may be the first sign to identify patellofemoral osteoarthritis. [16]

Specialized Examinations

This section will highlight common exam techniques a practitioner should know to diagnose different knee pathology. The following videos are posted with permission from Eric Sorenson, the original creator. Please visit his YouTube channel for more in depth videos on joint exams:

Patella Apprehension Test

This test looks mainly for patella instability but also may suggest patellofemoral syndrome (not the best test for it).[17]

Clarke’s Test

This is the best test to look for patellofemoral syndrome, however, most experts argue none of the physical diagnosis maneuvers are that great at testing for this condition.[18]

Lachman's Test

Very specific and most superior test at diagnosing ACL tears.[1]

Posterior Drawer Test

The test of choice to diagnose PCL tears.

Varus Test

The test of choice to diagnose LCL tears.

Valgus Test

The rest of choice to diagnose MCL tears.

McMurray Test

The best test available to diagnose meniscus tears. Internal rotation tests the lateral meniscus while external rotation tests the medial meniscus.

Noble Test

One of the tests for iliotibial band syndrome.

Ober Test

One of the tests for iliotibial band syndrome.

Finally, make sure to always examine the joints below and above the knee. Knee pain frequently can mask as hip or back pain.


Diagnostic Imaging

  • In general, a good history and physical exam is all that should be needed to diagnose acute knee pathology. When appropriate, imaging can be used as a diagnostic aid.[19]
  • X-rays are good at diagnosing osteoarthritis and fractures.[20]
  • The Ottawa knee rule can be used to determine when practitioners should order imaging for concerns of an acute fracture.[4]
  • Ultrasound can be used to either diagnose or further characterize effusions, Baker's cysts or deep vein thrombosis.[21]
  • MRI should not ordered regularly for knee pain since most cases resolve spontaneously within 4-6 weeks of conservative therapy.[22] MRIs can show signal enhancements that are not causing true pathology, leading to unnecessary referrals and operations and arthroscopies.[23][24]
  • Consideration for an MRI to be done before 4 weeks should be made for an athlete under the age of 40 who cannot straighten their leg and has a suspected meniscus tear.[22]

Medication and Therapies

  • In general, most knee pain is treated with conservative therapy such as ice, rest, physical therapy, stretching, strength conditioning, Tylenol and NSAIDs (when no contraindications).[3]
  • Physical therapy should be offered for most causes of knee pain.
  • Steroid injections of at least 50 mg may result in 12-24 weeks of relief.[25]
  • Patients should have a referral to an orthopedic surgeon if a provider feels a patient should be considered for knee replacement, repair of ligaments or meniscus or in acute emergencies such as a septic joint. Orthopedic surgeons can offer therapeutic modalities such as cortisone injections, arthroscopy and even total knee replacement.
  • For patients over the age of 65 or older or with kidney disease, topical NSAID therapies such as diclofenac gel is a safer option that does not pose as high of a risk of NSAID induced kidney injury.[26]

Trial Summaries

  • The Lachman test has been shown to be superior to the anterior drawer test in ruling in and ruling out an ACL rupture.[27]

Ongoing controversies / New updates

External Resources


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 McGee, S. Chapter 57: Examination of the musculoskeletal exam. Evidence-Based Physical Diagnosis. 4th ed. Elsevier; Philadelphia, PA: 2018.
  2. 2.0 2.1 2.2 Jackson JL, O'Malley PG, Kroenke K. Evaluation of acute knee pain in primary care. Ann Intern Med. 2003 Oct 7;139(7):575-88.
  3. 3.0 3.1 3.2 3.3 CALMBACH WL, HUTCHENS M. Evaluation of Patients Presenting with Knee Pain: Part II. Differential Diagnosis. AFP 2003; 68: 917-922.
  4. 4.0 4.1 Stiell IG1, Greenberg GH, Wells GA et al. Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med. 1995 Oct;26(4):405-13.
  5. Illustration from Anatomy & Physiology, Connexions Web site., Jun 19, 2013.
  6. 6.0 6.1 Dixit S. Difiori JP. Burton M et al. Management of patellofemoral pain syndrome. Am Fam Physician. 2007 Jan 15;75(2):194-202
  7. Dupont JY. Synovial plicae of the knee. Controversies and review. Clin Sports Med. 1997 Jan;16(1):87-122.
  8. Calmback WL, Hutchens M. Evaluation of Patients Presenting with Knee Pain: Part I. History, Physical Examination, Radiographs, and Laboratory Tests. Am Fam Physician. 2003 Sep 1;68(5):907-912.
  9. Waryasz GR, McDermott AY. Patellofemoral pain syndrome (PFPS): a systematic review of anatomy and potential risk factors. Dynamic Medicine20087:9
  10. Frush, Todd J., and Frank R. Noyes. "Baker’s Cyst Diagnostic and Surgical Considerations." Sports Health: A Multidisciplinary Approach 7.4 (2015): 359-365.)
  11. Glencross PM. Medscape: Pes Anserine Bursitis. (accessed 4 March 2017).
  12. Plica Syndrome. Physiopedia (2017). Accessed on 4 March 2018
  13. Dupont JY. Synovial plicae of the knee. Controversies and review. Clin Sports Med. 1997 Jan;16(1):87-122.
  14. Fairclough J, Hayashi K, Toumi H, Lyons K, Bydder G, Phillips N, Best TM, Benjamin M. Is iliotibial band syndrome really a friction syndrome?; Journal of Science and Medicine in Sport (2007) 10, 74-76
  15. Knee Exam. Standford 25.
  16. Schiphof D, van Middelkoop M, de Klerk BM et al. Crepitus is a first indication of patellofemoral osteoarthritis (and not of tibiofemoral osteoarthritis). Osteoarthritis Cartilage. 2014 May;22(5):631-8
  17. Ahmad CS, McCarthy M, Gomez JA, Shubin Stein BE. The moving patellar apprehension test for lateral patellar instability. Am J Sports Med. 2009 
  18. Fredericson M, Yoon K. Physical Examination and Patellofemoral Pain Syndrome. Am J Phys Med Rehabil. 2006 Mar;85(3):234-43.
  19. Kocabey Y, Tetik O, Isbell WM, Atay OA, Johnson DL. The value of clinical examination versus magnetic resonance imaging in the diagnosis of meniscal tears and anterior cruciate ligament rupture. Arthroscopy. 2004;20(7):696–700.
  21. Frush, Todd J., and Frank R. Noyes. "Baker’s Cyst Diagnostic and Surgical Considerations." Sports Health: A Multidisciplinary Approach 7.4 (2015): 359-365.)
  22. 22.0 22.1 Pompan DC. Reassessing the role of MRI in the evaluation of knee pain. Am Fam Physician. 2012 Feb 1;85(3):221-224.
  23. Ryzewicz M, Peterson B, Siparsky PN, Bartz RL. The diagnosis of meniscus tears: the role of MRI and clinical examination. Clin Orthop Relat Res. 2007;455:123–133.
  24. Ben-Galim P, Steinberg EL, Amir H, Ash N, Dekel S, Arbel R. Accuracy of magnetic resonance imaging of the knee and unjustified surgery. Clin Orthop Relat Res. 2006;447:100–104
  25. Arroll B. Corticosteroid injections for osteoarthritis of the knee: meta-analysis. BMJ 2004;328:869.
  26. Baraf HS, et al. Safety and efficacy of topical diclofenac sodium gel for knee osteoarthritis in elderly and younger patients: pooled data from three randomized, double-blind, parallel-group, placebo-controlled, multicentre trials. Drugs Aging. 2011 Jan 1;28(1):27-40.
  27. Ostrowski JA. Accuracy of 3 Diagnostic Tests for Anterior Cruciate Ligament Tears. J Athl Train. 2006; 41(1): 120–121.
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Christopher Steele