How do arm fractures heal?

How Arm Fractures Heal

The Biological Healing Process

Arm fractures heal through a well-orchestrated sequence of three distinct phases: inflammatory, repair (callus formation), and remodeling, ultimately restoring the original bone structure through either direct or indirect healing pathways. 1, 2

Phase 1: Inflammatory Phase (Days 1-7)

• An acute inflammatory response begins immediately after fracture, involving immune cells and molecular factors that initiate the repair cascade 3, 2
• Hematoma formation occurs at the fracture site, creating the initial scaffold for healing 4
• Inflammatory cells (neutrophils, macrophages) infiltrate the area and release cytokines and growth factors essential for subsequent healing 3, 5
• This phase is critical—insufficient or excessive inflammation can impair the entire healing process 3

Phase 2: Repair Phase (Weeks 2-12)

The repair phase proceeds through two distinct pathways depending on fracture stability:

Indirect Healing (Most Common)

• Occurs when fractures are not anatomically reduced or rigidly fixed 2
• Mesenchymal stem cells are recruited to generate a primary soft callus composed of cartilage and fibrous tissue 1, 2
• This cartilaginous callus undergoes revascularization and calcification to form a hard callus (bony bridging) 1, 4
• The hard callus provides initial stability but lacks organized bone structure 2

Direct Healing (Less Common)

• Requires anatomical reduction and rigidly stable conditions, typically achieved only through open reduction and internal fixation 2
• Bone regenerates immediately as anatomical lamellar bone and Haversian systems without intermediate cartilage formation 2
• No remodeling steps are necessary when direct healing occurs 2

Phase 3: Remodeling Phase (Months 3-24+)

• A slow remodeling process gradually reconstitutes the original bone structure and strength 1, 4
• Osteoclasts resorb excess callus while osteoblasts deposit organized lamellar bone 4
• The bone eventually returns to its pre-fracture architecture, though this can take months to years 1, 2

Critical Factors Influencing Healing

Biomechanical Stability

• Fracture fixation stability is the primary determinant of healing pathway and success 3, 2
• Stable fixation promotes direct healing; unstable conditions require indirect healing through callus formation 2
• Insufficient biomechanical stability can impair early local inflammation and delay healing 3

Blood Supply

• Revascularization after trauma is essential for delivering nutrients, oxygen, and healing cells to the fracture site 3
• Compromised blood supply significantly delays or prevents healing 3

Local Factors That Impair Healing

• Degree of local trauma and bone loss 4
• Type of bone affected (cortical vs. cancellous) 4
• Degree of immobilization 4
• Local pathologic conditions (infection, tumor) 4

Systemic Factors That Impair Healing

• Systemic inflammation from conditions like rheumatoid arthritis, diabetes mellitus, multiple trauma, or sepsis increases healing time and complication rates including non-unions 3
• Advanced age slows the repair process due to accumulated inflammatory damage and changes in cytokine levels 5
• Nutritional status affects bone quality and healing—deficiencies delay the process 5
• Hormonal factors and medications (polymedication in elderly patients) 4, 5

Common Pitfalls to Avoid

• Do not assume all arm fractures heal the same way—proximal humerus fractures often heal well non-operatively, while displaced fractures may require surgical intervention 6
• Avoid inadequate immobilization in unstable fractures, as this prevents proper callus formation 4
• Do not overlook systemic inflammatory conditions that can significantly impair healing 3
• Ensure adequate pain management and early mobilization when appropriate to prevent stiffness while maintaining fracture stability 6