UGANDA HEALTH PROFESSIONS ASSESSMENT BOARD

Long bones develop through a process called Endochondral Ossification, which replaces a cartilage model with bone:

1. Formation of the Cartilage Model: During embryonic development, mesenchymal cells cluster and differentiate into chondroblasts. These cells secrete matrix, forming a hyaline cartilage model shaped like the future bone, surrounded by a membrane called the perichondrium.
2. Growth of the Model: The cartilage model grows in length (interstitial growth) and thickness (appositional growth). The chondrocytes in the center hypertrophy (enlarge) and burst, changing the matrix pH which triggers calcification. The central cartilage cells die, leaving empty cavities.
3. Primary Ossification Center: A nutrient artery penetrates the perichondrium, prompting osteogenic cells to differentiate into osteoblasts. This turns the perichondrium into a periosteum. Osteoblasts secrete a bone collar around the diaphysis (shaft) and begin replacing the central calcified cartilage with spongy bone.
4. Medullary Cavity Formation: As the primary ossification center grows toward the ends, osteoclasts break down some of the newly formed spongy bone. This creates the hollow medullary (marrow) cavity in the center of the diaphysis.
5. Secondary Ossification Centers: Around the time of birth, blood vessels enter the epiphyses (ends of the bone), and secondary ossification centers form. Spongy bone is laid down here, but no medullary cavity is formed in the epiphyses.
6. Formation of Articular Cartilage & Epiphyseal Plate: The hyaline cartilage that remains covering the epiphyses becomes articular cartilage (reducing joint friction). Cartilage remaining between the diaphysis and epiphyses forms the epiphyseal plate, enabling the bone to continue growing in length until early adulthood.

• Ensure Scene Safety: Check for traffic hazards, ensure personal safety, and wear protective gloves to prevent cross-infection from blood.
• Assess ABCs: Perform a primary survey checking the Airway, Breathing, and Circulation before focusing on the leg injury.
• Control Hemorrhage: Apply gentle, indirect pressure around the wound using sterile dressings. Never press directly on the protruding bone fragments.
• Cover the Wound: Place a sterile, non-fluffy dressing loosely over the exposed bone to prevent further contamination and bacterial entry.
• Do Not Reduce the Bone: Strictly avoid pushing the protruding bone back into the leg, as this will drag dirt deep into the tissue and sever surrounding nerves/vessels.
• Immobilize the Limb: Manually support the leg above and below the fracture site to prevent any movement that could cause further internal tissue damage.
• Apply a Splint: Use available rigid materials (padded boards) or secure the injured leg to the uninjured leg to firmly immobilize the joints above and below the fracture.
• Treat for Shock: Keep the casualty warm with blankets or jackets to preserve body heat, and reassure them to keep them calm.
• Assess Distal Circulation: Check the capillary refill or pulses in the toes of the injured leg to ensure blood flow has not been completely cut off by swelling.
• Call for Immediate Transport: Dial for emergency ambulance services immediately and monitor the patient's vital signs until professional help arrives.

• Hypovolemic Shock: Severe internal or external bleeding from severed blood vessels around the broken bone.
• Osteomyelitis (Infection): High risk of severe bone infection, particularly in open fractures where the bone breaches the skin barrier.
• Fat Embolism Syndrome: Fat globules released from the yellow bone marrow entering the bloodstream and blocking blood vessels in the lungs or brain.
• Compartment Syndrome: Internal bleeding and severe swelling within a closed muscle compartment, crushing nerves and cutting off arterial blood supply.
• Nerve Damage: Jagged bone ends severing or compressing adjacent motor and sensory nerves, leading to paralysis or chronic pain.