In adults 50 years of age and older, 25% have frequent knee pain, affecting their quality of life, recreational activities, and activities of daily living (ADL). Knee injuries are best evaluated by a physician's physical exam, x-rays, and a magnetic resonance imaging (MRI) test.
What structures make up the knee joint?
The knee joint is a complex arrangement of different structures (see diagram below):
- Four bones, including the femur (thigh bone), tibia (shin bone), fibula (calf bone on the outside of the tibia), and patella (kneecap).
- Ligaments, including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL, medial collateral ligament (MCL), and the lateral collateral ligament (LCL), on the outside but not labeled in the image.
- Many tendons but the most important being the quadriceps tendon and patellar tendon.
- Cartilage (firm, fibrous material that cushions the joint), including the medial meniscus and lateral meniscus.
- Synovial fluid is the thick liquid that lubricates the joint.
What types of knee injuries are caused by trauma?
Sudden trauma can cause injury to any knee structure:
- A fracture (break) of the bones
- Tearing of the ligaments, which can be a partial tear or complete
- Not only can tendons tear, but they can be overstretched, called a strain
- Cartilage can become damaged in what is called a chondral injury
What are other causes of knee pain?
Osteoarthritis is a degenerative disease that develops from wear and tear on the knee, leading to a breakdown of cartilage. It is the primary factor precipitating knee replacement surgery (discussed below). Obesity and aging are the main risk factors for osteoarthritis.
Gout is a condition in which there is an excess of uric acid in the bloodstream, leading to uric acid disseminating into the joint and crystalizing, forming uric acid crystals.
Rheumatoid arthritis is an autoinflammatory disease, meaning the body mistakes its own tissues for a foreign pathogen, such as a bacteria or virus, and attacks itself.
Tendonitis, inflammation of the tendons
Dislocations of the knee occur, with the tibia moving in different directions. Usually, there is some ligament damage with dislocation. In addition, the patella (kneecap) can dislocate to the sides, which prevents it from its normal up and down motion.
What are the symptoms associated with knee pain?
Besides pain, additional symptoms associated with knee pain vary depending on the structural issue. Other symptoms include decreased range of motion, clicking, popping, swelling, and warmth (mostly with gout and rheumatoid arthritis).
Knee buckling means the knee cannot support the weight of the posture; it can also be referred to as giving out and is usually related to a meniscal or ligament tear.
What is the diagnostic workup for a knee injury or pain?
A history is essential to inquire about any history of trauma. In addition, a family history of gout or rheumatoid arthritis can help with the diagnosis.
The Physical exam needs to evaluate for areas of tenderness and swelling. Redness or warmth is present with gout and infections.
In addition, the physician can perform special knee tests called the anterior and posterior “drawer” tests, in which the tibia is pulled forward and backward, respectively. While a positive anterior drawer test indicates an anterior cruciate ligament (ACL) tear, a positive posterior drawer test indicates a posterior cruciate ligament (PCL) tear.
The McMurray test is a special test for a medial meniscus injury, in which the physician flexes (bends) your knee first, then extends (straightens) it while placing pressure towards the middle: a clunk indicates a positive test.
Laboratory tests include a white blood cell level (WBCs) for infection, a rheumatoid factor for rheumatoid arthritis, and a serum uric acid for gout.
Imaging studies such as plain x-rays should be done first to evaluate for bony abnormalities, including fractures, osteoarthritis, spurs, or osteoporosis (bone thinning).
Computed tomography (CT) and magnetic resonance imaging (MRI) scans evaluate soft tissue structures not seen on x-rays, including the muscles, tendons, and ligaments.
Nowadays, MRI is the “gold standard” for knee evaluation.
What is the treatment for adult knee injury and pain?
The treatment varies depending on the condition. Once a fracture is ruled out, knee pain issues can be treated like any other musculoskeletal disorder.
However, some additional treatments are specific for knee injuries and pain.
A knee brace can be very helpful. Knee brace material varies from elastic to neoprene (wet suit material) to firm materials, like plastic. There are large braces with straps that completely immobilize the knee. Some braces have metal knee hinges on the sides to stabilize sideways movement.
Crutches may be used to prevent any weight bearing on the knee.
Different substances can be injected into the knee joint to help with pain and assist with knee function:
- Hyaluronic acid, a thick, gooey substance that acts as a lubricant
- Platelet rich plasma (PRP), a substance that is derived from the person’s own blood, with the red blood cells centrifuged out
Surgery is needed sometimes, including:
- Arthroscopy (involves small incisions and the use of a scope) to repair partially or fully torn cartilage, ligaments, or tendons
- For severe cases of osteoarthritis, a partial or total knee replacement
- An osteotomy, a procedure when one or more bones are cut
Dislocations can be manually placed back into place, especially the patellar types.
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Henrichs, Andrew, ‘A Review of Knee Dislocations’, Journal of Athletic Training, 39.4 (2004), 365–69
‘Knee Buckling in Older Adults’, Annals of Internal Medicine, 147.8 (2007), I–41 <https://doi.org/10.7326/0003-4819-147-8-200710160-00003>
Nguyen, Uyen-Sa D. T., Yuqing Zhang, Yanyan Zhu, Jingbo Niu, Bin Zhang, Piran Aliabadi, and others, ‘Increasing Prevalence of Knee Pain and Symptomatic Knee Osteoarthritis’, Annals of Internal Medicine, 155.11 (2011), 725–32 <https://doi.org/10.1059/0003-4819-155-11-201112060-00004>