Bone & joints

• Articulates the tubular bones of the extremities; there are varieties of synovial joints in regard to the kind of motion (e.g., hinge joints, pivot joints, ball and socket joints, etc.)
• Characterized by the presence of a joint space, which is closed off by a capsule that holds the bone ends together
  • Capsule is lined by synovium
  • Synovial recesses increase the joint space and allow a greater range of motion
  • Normal synovial joint contains a scant amount of synovial fluid which lubricates the cartilaginous surface
• Articular cartilage, a specialized type of connective tissue, covers the area of functional contact between the opposed bone ends (within the joint capsule) and provides structural support, cushioning and gliding
  • At its periphery, the articular cartilage fuses with the joint capsule and with the periosteum
• Normal articular cartilage is devoid of blood vessels, lymphatics and nerves; chondrocytes receive their nourishment by means of diffusion, mainly from the synovial fluid
• In some synovial joints, the articular space is divided, completely or incompletely, by a disk or by menisci
  • Periphery of these intraarticular structures is continuous with the capsule
• Functional synovial joint depends on the normal function of all of its components

• Most commonly encountered joint specimens are hips and knees (from arthroplasty)
  • Each component of the joint (including subarticular bone) should be described if possible
• Hip joint (specimen consists of a femoral head with or without femoral neck and fragmented labrum):
  • Femoral head is round, the convex surface of which is lined by smooth and glistening hyaline cartilage
  • At the periphery of articular cartilage there is thin and smooth synovium
  • On cut section, the cartilage is yellow-white and ranges 2 - 3 mm in thickness
  • In a middle age individual, the subarticular bone contains yellow (fatty) marrow
• Knee joint (specimen consists of fragments of soft tissue, articular, cortical and cancellous bone of the femoral condyles, tibial plateau and patella articular surfaces):
  • Articular surfaces of the medial, lateral and patella femoral compartments are lined by smooth, glistening hyaline cartilage
  • Synovium is thin and smooth
  • Medial and lateral menisci are preserved

Contributed by Edward F. DiCarlo, M.D.

Contributed by Lingxin Zhang, M.D.

What are the articulating surfaces of the bone ends of synovial joints normally covered by?

1. Elastic cartilage
2. Fibrocartilage
3. Hyaline cartilage
4. No cartilage

C. Hyaline cartilage

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Reference: Histology-joints

Chondrocytes generally have a limited proliferating capacity. The phenomenon shown in the microphotograph is most commonly seen in which scenario?

1. 30 year old man presents with right knee pain and founded to have numerous loose bodies in the joint
2. 60 year old woman presents with progressive bilateral hip pain with limited range of motion
3. 25 year old man presents with an expansile, radiolucent mass in his proximal phalanx of left long finger, with no frank destructive radiological features
4. 55 year old woman has had increasing epigastric pain for 10 years; imaging reveals a 12 cm exophytic, partially calcified rib mass

B. 60 year old woman presents with progressive bilateral hip pain with limited range of motion. The clinical scenario is degenerative joint disease (osteoarthritis). Chondrocyte cloning can be seen in the other scenarios (A: synovial chondromatosis, C: enchondroma, D: chondrosarcoma) but they are far less common than degenerative joint disease.

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Reference: Histology-joints