Anatomy Msk · Year 1 · from Anatomy Msk
Case 1: Knee Osteoarthritis
Clinical Image
Source: Wikimedia Commons - Osteoarthritis of the Left Knee - CC BY-SA 3.0
Case Presentation
A 67-year-old retired postal worker presents with progressive left knee pain over the past 3 years. The pain is worse with activity, particularly climbing stairs and walking long distances, and improves with rest. She reports morning stiffness lasting about 15-20 minutes that "loosens up" as she moves around. She denies any history of knee trauma. Physical examination reveals a mild varus (bow-legged) deformity of the left knee with tenderness along the medial joint line. There is palpable crepitus with range of motion, which is reduced (5-110 degrees, normal 0-135 degrees). Small joint effusion is present. McMurray and ligamentous testing are negative. Weight-bearing radiographs demonstrate asymmetric joint space narrowing predominantly in the medial compartment, subchondral sclerosis, osteophyte formation at the joint margins, and subchondral cysts. The patient is started on conservative management including weight loss, physical therapy, acetaminophen, and a medial unloader brace. Understanding the synovial joint structure explains the pathophysiology and imaging findings of osteoarthritis.
Key Learning Points
- Synovial joints (diarthroses) allow free movement and contain articular cartilage, synovial membrane, and joint capsule
- Articular (hyaline) cartilage covers bone ends and provides a smooth, low-friction surface for joint movement
- Osteoarthritis involves progressive cartilage degradation, leading to joint space narrowing on imaging
- The four cardinal radiographic signs of OA are: joint space narrowing, subchondral sclerosis, osteophytes, and subchondral cysts
- Mechanical factors (alignment, weight) affect load distribution across the joint surfaces