Topic Overview

Ossification of Humerus, Radius and Ulna

Humerus

• Primary center: shaft (8th week intrauterine life).

• Secondary centers:

  • Head → 1 year.

  • Greater tubercle → 3 years.

  • Lesser tubercle → 5 years.

  • Capitulum → 1 year.

  • Trochlea → 9–10 years.

  • Lateral epicondyle → 12 years.

  • Medial epicondyle → 5 years.

• Fusion:

  • Upper end → ~20 years.

  • Lower end → ~16–17 years.

• Total = 1 primary + 7 secondary centers.

Radius

• Primary center: shaft (8th week IUL).

• Secondary centers:

  • Lower end → 2 years, fuses at 20 years.

  • Upper end (head) → 5 years, fuses at 17 years.

• Total = 1 primary + 2 secondary centers = 3 centers.

Ulna

• Primary center: shaft (8th week IUL).

• Secondary centers:

  • Lower end → 5 years, fuses at 18 years.

  • Olecranon → 10 years, fuses at 15–16 years.

• Total = 1 primary + 2 secondary centers = 3 centers.

Importance of Capsular Attachments and Epiphyseal Lines

General Principle

• The capsule of a joint is usually attached close to the articular margins of bones.

• The epiphyseal line (growth plate) is placed either within or outside the capsule → this has important clinical implications.

Upper Limb Examples

1. Shoulder Joint (Humerus)

   • Capsule attached beyond the anatomical neck of humerus.

   • Epiphyseal line of head lies inside the capsule.

   • Clinical importance → septic arthritis in children may spread to epiphyseal cartilage, leading to growth disturbances.

2. Elbow Joint (Humerus, Radius, Ulna)

   • Capsule attached away from epiphyseal lines.

   • Epiphyseal lines lie outside the capsule.

   • Clinical importance → infection of joint is less likely to damage growth plates.

3. Wrist Joint (Radius, Ulna, Carpals)

   • Capsule attached to articular margins.

   • Lower epiphyseal line of radius lies within capsule.

   • Clinical importance → osteomyelitis or septic arthritis can spread to epiphysis in children.

Clinical Relevance

• Intra-capsular epiphyseal lines → prone to growth disturbances in septic arthritis (e.g., shoulder, hip).

• Extra-capsular epiphyseal lines → relatively protected (e.g., elbow).

• Knowledge important in pediatric orthopedics and forensic medicine (age estimation).