Acute Knee Pain
Acute Knee Pain: Excerpt from Field Guide to Bedside Diagnosis
Differential Overview
❑ Osteoarthritis
❑ Patellofemoral pain
❑ Collateral ligament sprain
❑ Meniscal tear
❑ Anterior cruciate tear
❑ Infrapatellar quadriceps tendinitis
❑ Acute monoarticular arthritis
❑ Prepatellar bursitis
❑ Anserine bursitis
❑ Hamstring injury
❑ Baker cyst
❑ Septic joint
❑ Iliotibial band syndrome
❑ Hemarthrosis
❑ Patellar fracture
❑ Patellar dislocation
❑ Osteochondritis desiccans
❑ Osteonecrosis
Diagnostic Approach
Careful questioning about the mechanism of injury is most important. Overuse injury or undue stress caused by unbalanced walking is a common source. A sensation of “giving away” on stepping down is a symptom of posterior horn meniscus or anterior cruciate tear. Joint line pain is seen in osteoarthritis, high-grade collateral ligament injury, meniscal tear, and tibial plateau fracture. Pain located medially several centimeters below this is due to anserine bursitis or low-grade medial collateral ligament injury. Anterior knee pain is found in injury to the quadriceps mechanism or large joint effusions. Popliteal pain is usually due to a large knee effusion.
Systematically stress the knee in each direction, looking for pain and/or laxity, comparing with the contralateral side. The range of motion may be limited by effusion, by a meniscal tear, or by a loose body. True locking, with ability to flex but not extend fully, occurs 10 degrees short of full extension. A McMurray maneuver is performed by rotating the tibia on the femur medially with the knee flexed at 90 degrees and then extending the knee, then repeating the process with lateral rotation. A painful “clunk” with medial rotation indicates a lateral meniscus tear, and the same finding with lateral rotation suggests a medial meniscus tear. An anterior drawer sign is elicited as pain and a laxity when the tibia is pulled forward with the knee at 90 degrees, indicating anterior cruciate injury. A Lachman manuver, performed at 15 degrees flexion, is more sensitive. With effusion the hollows of the knee are filled, and a transmitted fluid wave can be elicited.
In acute knee injury, the Ottawa Knee Rule minimizes the number of x-rays without missing a significant fracture. Obtain an x-ray if: (a) age is >54, (b) there is tenderness at the head of the fibula, (c) there is isolated patellar tenderness, (d) there is an inability to flex the knee to 90 degrees, or (e) there is an inability to bear weight immediately and take four steps in the E.R.
Palpable clicks are not necessarily pathologic; they may be caused by the semitendinosus tendon slipping over the medial condyle or the iliotibial band slipping over the lateral condyle.
Clinical Findings
Osteoarthritis Early in the course there is mild stiffness on first arising that eventually resolves with use. Pain is most commonly localized to the anterior and medial aspects of the knee. Bony overgrowth of the knee, prominent crepitance on knee motion and lack of warmth are helpful clues. An acute flare is precipitated by overuse.
Patellofemoral pain This is a common cause of knee pain in joggers, producing retropatellar aching worse when climbing stairs. Pain can be elicited by downward pressure on the patella with the knee actively extended, and patellar crepitance can be felt on lateral movement of the patella.
Collateral ligament sprain Lateral force applied to the knee with the foot planted can cause collateral disruption. Test by stabilizing the lower leg and applying lateral (valgus) or medial (varus) force to the knee at varying angles of flexion. Pain and/or laxity are indicators.
Meniscal tear Twisting of the knee with the foot planted, flexed, and bearing weight is the usual mechanism. The joint line is tender, and the knee may lock or click. In acute injury, an effusion is usually found. When performing a McMurray maneuver, knee extension with internal rotation of the tibia stresses the medial meniscus and opens the lateral compartment. It may produce a painful click (palpated with a hand over the knee) with a lateral meniscus tear, or more often, pain due to pressure on the injured medial meniscus. External rotation produces stress on the contralateral menisci.
Anterior cruciate tear The mechanism of injury includes a noncontact deceleration, cutting, or hyperextension accompanied by a “pop.” An anterior cruciate tear produces a sensation of “giving away” of the knee as the tibia slips forward on the femur. Pain (with acute injury) and laxity may be found with the anterior drawer sign (forward movement of the tibia when pulled at 90 degrees of flexion) or the Lachman maneuver (forward shift of the tibia at 15 degrees flexion, a more sensitive finding).
Infrapatellar quadriceps tendinitis Pain and tenderness of the quadriceps tendon below the knee is accentuated by climbing stairs. A cystic/fluctuant swelling occurs with bursal inflammation. Osgood-Schlatter syndrome in adolescents produces similar pain over the anterior tibia.
Acute monoarticular arthritis The knee is warm, and there may be fever (especially, but not exclusively, in infection). The knee is a frequent site of rheumatoid arthritis, septic arthritis (especially staphylococcal and gonococcal), gout, Lyme disease, and rheumatic fever.
Prepatellar bursitis There is a history of trauma or repeated kneeling. There is a ballotable effusion over the lower half of the patella. Range of motion of the knee is not affected.
Anserine bursitis Medial knee pain occurs nocturnally and is exacerbated by walking. There is local tenderness over the tibial tuberosity. The medial collateral ligament is intact on stress.
Hamstring injury A hyperextension injury produces pain and tenderness in the popliteal space.
Baker cyst With a synovial cyst, there is midline popliteal swelling with the knee extended, which disappears when flexed. A large cyst causes tightness with knee flexion. It occurs in the setting of arthritis.
Septic joint The knee is hot and painful, and the patient appears ill and febrile. Gonococcal sepsis should be considered in young adults, accompanied by urethritis, pustular skin lesions, and tenosynovitis.
Iliotibial band syndrome Focal pain and tenderness over the lateral femoral condyle is accompanied by a palpable or audible tendon snap.
Hemarthrosis A rapidly filling, warm, and tense knee in the setting of trauma indicates a tear of a meniscus, ligament, or fracture. In patients with hemophilia, systemic anticoagulation, or leukemia, hemarthrosis can occur with more minor trauma.
Patellar fracture Suspect fracture when a patient falls directly onto the knee. The patella is exquisitely tender, and discrete fragments can be felt with the thumbnail.
Patellar dislocation There is excessive lateral patellar mobility, with a sensation of the leg “giving away.”
Osteochondritis desiccans Posttraumatic pain is located in the medial knee compartment in young adults. Locking may be caused by a loose body.
Osteonecrosis Sudden severe pain with weight bearing occurs in an elderly patient or one on steroids.
Pictures
Book Source Details
- Book Title: Field Guide to Bedside Diagnosis
- Author(s): David S. Smith
- Year of Publication: 2007
- Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2007 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Field Guide to Bedside Diagnosis
Authors: David S. Smith
Publisher: Lippincott Williams & Wilkins
Copyright: 2007
ISBN: 0-78178-165-5
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