USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 15-year-old boy comes to his general practitioner because of generalized right knee pain that has gradually worsened over the past five months. He does not recall any trauma or any inciting event. He says that the pain is accompanied by catching and clicking of the joint and is worsened by physical activity. He works on a farm and enjoys playing soccer with his siblings but has been unable to do so for the past month due to his symptoms. His knee appears swollen and is tender on palpation medial to the patella. Range of motion is limited and the knee clicks as it extends. The McMurray test is negative. Imaging cannot be obtained because the patient is unable to travel to an imaging center. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
It was once thought that the “itis” part of osteoarthritis was a misnomer, and that inflammation didn’t play a role in its development, and that it was mostly a degenerative disease resulting from simple “wear and tear”.
Nowadays, it’s thought that inflammation does indeed play an important role in the development of osteoarthritis.
Alright, so a healthy joint consists of two bones, each with its own layer of articular cartilage, which is a type of connective tissue that allows the two bones to glide against each other essentially without friction.
With Osteoarthritis, we’re really talking about one particular kind of joint which is a synovial joint.
Along with articular cartilage, another important component of synovial joints, and where they get their name from, is the synovium, which along with the surface of the articular cartilage, forms the inner lining of the joint space.
The synovium’s composed of loose connective tissue, blood vessels, lymphatic vessels, and on the surface—”Type A” cells that clear cellular debris and “Type B” cells that produce components of synovial fluid, which helps lubricate the two articular surfaces.
One of the main issues in osteoarthritis is the progressive loss of this articular cartilage, which means there’s not much separating the two bones anymore, which adds a significant amount of friction between them, which then generates inflammation, and triggers pain through the nerve endings in this joint space.
Maintaining healthy articular cartilage is the chondrocyte’s job, a specialized cell responsible for maintaining everything cartilage-related.
The chondrocytes produce and are embedded within a strong gel or extracellular matrix which contains type II collagen, a protein that provides structural support, as well as proteoglycans, which are aggregates of protein and sugar molecules like as hyaluronic acid, chondroitin sulfate, and keratin sulfate.
All of these extracellular components give the cartilage elasticity and high tensile strength, which help weight-bearing joints distribute weight such that the underlying bone absorbs the shock and weight, and