Union, Delayed Union, and Nonunion in Orthopaedics

1. Union (Normal Fracture Healing)

Phases of bone healing:

• Inflammatory phase: Haematoma formation, infiltration of granulation tissue containing osteoprogenitor cells
• Soft callus phase: Collagen, cartilage and woven bone laid down around the fracture site
• Hard callus phase: Progressive mineralisation and bridging callus
• Remodelling phase: The longest phase (can last years); callus is resorbed, trabecular bone formed along lines of stress, restoring original shape

No universally accepted, standardised definition of union exists in the literature. Attempts to define it are hampered by reliance on indirect means (radiographs, clinical signs) rather than direct measurement of fracture site strength. - Rockwood and Green's Fractures in Adults, 10th Ed 2025

Factors governing satisfactory remodelling:

• Young age
• Fracture near the end of the bone (metaphyseal)
• Angulation aligned with the plane of joint motion
• Minimal comminution

2. Delayed Union

"The definition of delayed union is arbitrary. Delayed union occurs when a fracture has not healed in the time frame that would be expected." - Campbell's Operative Orthopaedics, 15th Ed 2026

Time frame:

• Generally 3 to 6 months from the time of injury, though this varies by bone and injury severity
• The expected healing time depends on: bone involved, fracture location (metaphyseal heals faster than diaphyseal), energy of injury, soft tissue damage, host factors, and treatment method
• For example, delayed union of a closed tibial shaft fracture has a different threshold than a Gustilo type IIIB open tibial fracture

Key distinction from nonunion:

• In delayed union, healing has slowed but not ceased - the periosteal and endosteal healing response is still active
• On a cellular level, it has been proposed that cessation of the periosteal (but not endosteal) healing response prior to fracture bridging may define delayed union

Radiology:

• Minimal or progressive callus formation, but below what is expected
• No bridging yet, but no signs of healing arrest

Management of delayed union:

• Correction of metabolic/endocrine abnormalities (check vitamin D, thyroid, calcium)
• Optimise host factors: stop smoking, control diabetes, review medications
• Cast or brace immobilisation
• Bone stimulation: pulsed ultrasound (LIPUS), electrical/electromagnetic stimulation, extracorporeal shockwave therapy
• Surgical intervention if conservative measures fail (e.g. bone grafting, revision fixation)

Delayed union can be considered a precursor to nonunion. Timely intervention can prevent progression. - Campbell's Operative Orthopaedics, 15th Ed 2026

3. Nonunion

Definition:

1. Temporal (FDA) definition: A nonunion is "established when a minimum of 9 months has elapsed since injury and the fracture shows no visible progressive signs of healing for 3 consecutive months."
2. Physiologic (Brinker) definition - preferred clinically: "A fracture that, in the opinion of the treating physician, has no possibility of healing without further intervention."

The physiologic (Brinker) definition is probably more appropriate, as the FDA definition fails to include many fractures that have minimal or no chance of proceeding to union. - Campbell's Operative Orthopaedics, 15th Ed 2026

Classification of Nonunion (Weber-Cech Classification)

1. Location - epiphyseal, metaphyseal, or diaphyseal
2. Infection - septic vs. aseptic
3. Biology - hypertrophic, oligotrophic, or atrophic
4. Special type - pseudoarthrosis

A. Hypertrophic Nonunion ("Elephant Foot")

• Also called: hypervascular, viable, or vital nonunion
• Biology: Adequate vascularity and healing response - the fracture has adequate biology but inadequate stability
• The viable fibrocartilage at the fracture gap cannot mineralise due to excessive interfragmentary motion
• Radiology: Abundant callus on either side of the fracture gap (the classic "elephant foot" appearance), but with a persistent radiolucent gap
• Treatment: Stability alone - rigid fixation (plate/nail). Bone grafting is NOT required. Stabilisation allows the existing fibrocartilage to mineralise (usually by ~8 weeks)

B. Oligotrophic Nonunion

• Intermediate between atrophic and hypertrophic
• Biology: Viable, but with minimal radiographic healing reaction, often due to inadequate fracture approximation (distraction) or poor reduction
• Radiology: Little or no callus, no elephant foot appearance
• Treatment: Stabilisation + improve fracture contact. Bone graft may be considered

C. Atrophic Nonunion

• Also called: avascular, nonviable, or avital nonunion
• Biology: Poor or absent healing response - few or no bone-forming cells active at the fracture site, with poor blood supply
• Often related to: severe open fractures, surgical periosteal stripping, or significant host factors (diabetes, smoking)
• Radiology: No bone reaction, tapered/pointed bone ends (described classically as a "peppermint stick" or "icicle" appearance), no callus whatsoever
• Treatment: Requires a biological stimulus (autogenous bone graft or BMP) AND rigid stabilisation. Debridement of nonviable bone ends is also a key principle

D. Pseudoarthrosis (Synovial Pseudoarthrosis)

• A long-standing nonunion where a synovial-like joint forms at the fracture gap with a fluid-filled cavity and fibrocartilaginous "joint surfaces"
• Represents the end-stage of an untreated nonunion
• Requires surgical excision of the pseudoarthrosis, stabilisation, and bone grafting

Figure: Hypertrophic nonunion resulting after IM nailing of a distal tibial shaft fracture (A,B) treated with plate and screw fixation (C,D), achieving union without adjuvant bone graft (E,F). - Rockwood and Green's Fractures in Adults, 10th Ed 2025

Risk Factors for Nonunion

• High-energy mechanism with extensive periosteal stripping
• Open fractures (especially Gustilo IIIB/IIIC)
• Diaphyseal fractures (less blood supply than metaphyseal)
• Sites with watershed/limited blood supply: femoral neck, scaphoid waist, talar neck, 5th metatarsal base
• Bone loss/comminution

• Smoking (implicated by 81% of surgeons in one survey)
• Diabetes mellitus (59%)
• Peripheral vascular disease (53%)
• Osteoporosis, advanced age
• Medications: NSAIDs, corticosteroids, bisphosphonates, opioids (chronic opioid use implicated in 14.6% of nonunion cases in one large database study)
• Immunosuppression, malnutrition, vitamin D deficiency

• Inadequate stability (excessive interfragmentary motion)
• Excessive rigidity preventing secondary healing
• Distraction at the fracture site
• Infection
• Periosteal stripping during surgery

Summary Comparison Table

• Campbell's Operative Orthopaedics, 15th Ed 2026 - Definitions (p.3739), Etiology & Classification (p.3740-3743)
• Rockwood and Green's Fractures in Adults, 10th Ed 2025 - Introduction to Nonunions (p.986-996), Classification (Atrophic, Hypertrophic, Oligotrophic, Pseudoarthrosis)
• Tintinalli's Emergency Medicine - Fracture Healing (p. fracture healing section)