Factors Affecting Healing: Local, Systemic, Mechanical and Environmental

Healing is determined by an interaction between biology, mechanics and care. A fracture with an excellent reduction may fail when blood supply is absent or infection is present; a well-vascularised fracture may fail when excessive motion, a large gap or premature loading persists. The same principles apply to skin, soft tissue and bone wounds, although this page emphasises fracture and wound healing relevant to emergency medicine.

Learning outcomes

By the end of this page, the learner should be able to classify factors that influence healing, explain their mechanisms, identify modifiable risks, assess a patient whose wound or fracture is not progressing and construct an emergency plan that protects both biology and mechanics.

1. Local biological factors

1.1 Blood supply and oxygenation

• Periosteal, endosteal and soft-tissue vessels deliver oxygen, nutrients and progenitor cells. Stripping periosteum, crushing muscle, avulsing skin or injuring a nutrient artery reduces the cellular response.
• Some regions have naturally vulnerable circulation, including the scaphoid waist/proximal pole, talar neck, femoral neck and selected tibial areas. A fracture there can develop avascular necrosis even with good alignment.
• Shock, hypoxaemia, severe anaemia, vascular injury, compartment syndrome, smoking-related vasoconstriction and excessive swelling further reduce tissue oxygen.

1.2 Soft-tissue injury

Skin, muscle and fascia provide blood vessels and cells for callus. High-energy crush, degloving, thermal injury and repeated surgical exposure enlarge the zone of injury. A small wound may therefore conceal a large area of devitalised tissue.

1.3 Contamination and infection

Soil, saliva, faeces, water, foreign bodies and devitalised tissue increase microbial load. Bacteria compete for oxygen, produce toxins and biofilm, and sustain inflammatory cytokines that inhibit osteoblasts. Infection can cause osteomyelitis, implant loosening, sinus formation and non-union. Early source control is more important than relying on antibiotics alone.

1.4 Bone and fracture characteristics

Local feature	Why it matters	Possible effect
Comminution or segmental fracture	Small fragments may lose their blood supply; reconstruction is mechanically demanding	Delayed union, infection or non-union
Large gap or bone loss	Progenitor cells and vessels must bridge a greater distance	Persistent fibrous tissue or atrophic non-union
Interposed muscle, periosteum or foreign body	Prevents contact and may harbour bacteria	Failure of reduction or union
Intra-articular extension	Cartilage has limited regenerative capacity and stiffness develops easily	Post-traumatic arthritis and impaired function
Pathological bone	Tumour, infection or metabolic disease changes matrix and blood supply	Unusual fracture pattern and poor healing

2. Mechanical factors

2.1 Stability and interfragmentary strain

Healing tissue tolerates only a limited amount of deformation. Controlled relative motion can promote callus, but excessive shear, rotation or distraction keeps the tissue in a fibrous state. Primary/direct healing needs very rigid, near-anatomic fixation; secondary healing needs relative stability with a manageable strain environment.

2.2 Alignment and contact

• Malrotation, severe angulation, shortening and translation alter load distribution and may produce malunion even when a bridge eventually forms.
• Excessive compression can compromise microcirculation, whereas a large gap may exceed the capacity of callus to bridge.
• Joint incongruity increases focal cartilage stress and long-term arthritis risk.

2.3 Fixation and loading

Loose screws, plate failure, inadequate cast moulding, broken external-fixator components or premature weight-bearing can create a mechanically unstable non-union. Conversely, prolonged complete immobilisation can cause stiffness, muscle wasting, thrombosis and delayed functional recovery. The correct loading plan is fracture- and fixation-specific and should be documented by the treating team.

3. Patient-related systemic factors

3.1 Age and hormonal state

Children generally have thicker periosteum, more active osteoprogenitor cells and better remodelling. Older adults may have reduced osteoblast activity, osteoporosis, vascular disease, lower activity and polypharmacy. Menopause, hypogonadism and endocrine disorders can affect bone turnover.

3.2 Diabetes mellitus

Hyperglycaemia impairs leukocyte function, angiogenesis and collagen formation and increases infection risk. Peripheral neuropathy can delay presentation and allow excessive loading. Optimise glucose safely, inspect skin and feet, and do not assume a painless wound is a healthy wound.

3.3 Vascular and respiratory disease

• Peripheral arterial disease reduces oxygen and nutrient delivery.
• Heart failure, chronic lung disease, sleep-disordered breathing and severe anaemia can reduce oxygen availability.
• Vasoconstrictive drugs or profound hypotension may worsen an already marginal flap or fracture fragment.

3.4 Renal, hepatic and endocrine disease

Chronic kidney disease disturbs calcium-phosphate and parathyroid hormone balance and may cause renal osteodystrophy. Liver disease affects protein synthesis and nutrition. Thyroid, parathyroid and sex-hormone disorders alter bone turnover. Consider these conditions when a low-energy fracture or delayed union is unexplained.

3.5 Immune status and infection

HIV with advanced immunosuppression, malignancy, corticosteroid therapy, chemotherapy, severe sepsis and other immunodeficiency states increase infection risk and may reduce tissue repair. Review vaccination, fever, recurrent infections and medication history without stigmatising the patient.

4. Nutrition and metabolic substrates

Repair requires energy, amino acids, essential fatty acids, iron, zinc, copper, vitamin C, vitamin D, calcium and phosphate. Deficiency may be overt or hidden by chronic illness, alcohol use, food insecurity or prolonged hospitalisation.

Nutrient/metabolic issue	Role in healing	Clues and response
Protein/energy	Collagen, enzymes, immune cells and muscle	Weight loss, low intake, pressure injury; dietitian support and adequate protein
Vitamin C	Collagen hydroxylation and antioxidant function	Poor diet, bruising or gum disease; correct documented deficiency
Vitamin D/calcium/phosphate	Mineralisation and skeletal metabolism	Low sunlight, malabsorption, renal disease; test and replace according to local guidance
Iron/anaemia	Oxygen transport and cellular metabolism	Fatigue, pallor, blood loss; identify and treat the cause
Zinc/copper	Enzymes, immunity and connective tissue	Malabsorption or prolonged restrictive diet; avoid indiscriminate megadoses

Routine high-dose supplements do not substitute for diagnosis and may be harmful. Ask about alcohol, restrictive diets, vomiting, diarrhoea and access to food, and use local nutrition pathways.

5. Smoking, alcohol and substance exposure

Smoking and nicotine

Nicotine causes vasoconstriction and can suppress osteoblast differentiation; carbon monoxide reduces oxygen delivery and smoke-related toxins impair immune function. Smoking increases wound infection, flap necrosis, delayed union and non-union. Document use non-judgementally, offer cessation support and explain that stopping during the healing window has measurable benefit.

Alcohol

Heavy alcohol use is associated with malnutrition, falls, liver disease, poor adherence and altered osteoblast/osteoclast activity. Screen for withdrawal risk in hospital and provide safe nutritional and psychosocial support.

Other substances

Stimulants, injected drugs and contaminated injection sites increase vascular, infection and nutrition risks. Ask sensitively and connect patients with harm-reduction and treatment services.

6. Medicines and treatment-related factors

• Systemic corticosteroids: prolonged exposure can suppress collagen and bone formation and increase infection risk; never stop chronic steroids abruptly without a safe plan.
• Anti-resorptive and anabolic bone medicines: effects depend on indication, dose and duration; coordinate with the treating specialist rather than stopping or starting empirically.
• Analgesics and anti-inflammatory drugs: balance effective pain control, renal and gastrointestinal safety and the individual fracture context; follow local protocol rather than using one universal rule.
• Chemotherapy, immunosuppressants and radiotherapy: may reduce marrow, immune or vascular function.
• Anticoagulants and antiplatelet drugs: do not usually “stop healing” directly, but bleeding, haematoma and peri-operative decisions require clinician-led risk assessment.
• Local anaesthetic, antiseptic and dressing misuse: tissue-toxic solutions or inappropriate repeated manipulation can damage granulation tissue.

7. Wound-specific factors

7.1 Moisture and temperature

Most healing surfaces do best in a clean, moist—not wet or macerated—environment. Desiccation damages migrating epithelium; excessive exudate macerates edges. Hypothermia causes vasoconstriction and impairs coagulation and immunity, especially during major trauma and surgery.

7.2 Pressure, shear and friction

Pressure ulcers, prolonged immobilisation, poorly fitted casts and friction over bony prominences compromise capillary flow. Repositioning, pressure-relieving surfaces, correct splinting and skin checks protect the wound.

7.3 Foreign bodies and dead space

Suture fragments, gravel, wood, glass, necrotic fat and undrained cavities maintain inflammation and harbour bacteria. Explore and image when indicated; document packing and remove temporary materials at review.

7.4 Wound edge tension

High tension strangulates capillary loops and causes edge necrosis or dehiscence. Choose closure methods that distribute tension, and do not close a contaminated or oedematous wound simply for appearance.

8. Care-system and behavioural factors

• Delayed presentation, poor transport, cost, language barriers, unsafe housing and limited access to dressings can turn a manageable injury into an infected chronic wound.
• Unclear discharge instructions, absent follow-up and fragmented referrals delay recognition of non-union, infection or compartment syndrome.
• Non-adherence is often a systems problem. Use plain language, demonstrate wound care, involve family when appropriate and document a reachable review plan.
• Occupational demands, caregiving, homelessness and fear of lost income affect weight-bearing and medication decisions; incorporate social work and rehabilitation support.

9. Emergency checklist: optimise what can be changed today

10. How to investigate unexpectedly slow healing

1. Confirm the diagnosis and timeline: review original films, reduction, fixation and serial imaging; consider CT when bridging is unclear.
2. Reassess mechanics: inspect cast/brace, hardware, alignment, gap, motion and weight-bearing.
3. Search for infection: wound examination, temperature, inflammatory markers and deep sampling when revision surgery is planned; a normal temperature does not exclude indolent infection.
4. Assess biology: pulses, soft-tissue viability, diabetes control, nutrition, smoking, renal/endocrine disease and medicines.
5. Check for systemic or pathological causes: malignancy, metabolic bone disease, stress injury or an incorrect original diagnosis.
6. Refer early: orthopaedic, vascular, plastic-surgical, infectious-disease, endocrine or nutrition input may be needed.

11. Common combinations and their consequences

Combination	Why risk is amplified	Practical response
Smoking + unstable tibial fracture	Reduced perfusion plus excessive motion	Cessation support and mechanical review
Diabetes + foot wound + neuropathy	Impaired immunity, pressure and delayed detection	Off-loading, vascular/infection assessment and close follow-up
Open fracture + devascularised flap	High bacterial load with poor host defence	Urgent debridement, antibiotics, soft-tissue and fixation plan
Malnutrition + pressure injury	Low substrate with ongoing ischaemic pressure	Pressure relief, wound care and nutrition support
Renal disease + low-energy fracture	Abnormal mineral metabolism and fragile bone	Metabolic assessment and specialist management

12. Cases

Case 1: “The cast is fine, but the fracture is not healing”

At four months a smoker has persistent pain and minimal callus. Review whether the fracture is mechanically stable, assess infection and vascularity, and address smoking and nutrition. Do not label it “biological” until the mechanical environment has been checked.

Case 2: Diabetic foot wound

A patient with neuropathy has a painless plantar ulcer over a bony prominence. The lack of pain is not reassuring. Assess perfusion, depth, pressure, infection and osteomyelitis; off-load the site and create a multidisciplinary plan.

Case 3: Open fracture after flooding

A contaminated wound after flood-water exposure may contain unusual organisms and foreign material. Cover, document, give local-protocol prophylaxis and arrange urgent debridement; do not irrigate repeatedly in an uncontrolled environment and send the patient home without a review plan.

13. Prevention principles

• Preserve blood supply and soft tissue; use gentle handling and appropriate surgical approaches.
• Prevent infection with timely cleaning, debridement, prophylaxis and source control.
• Provide stability without unnecessary devascularisation or prolonged immobilisation.
• Correct smoking, nutrition, diabetes, anaemia and vascular disease where possible.
• Give written return precautions and ensure follow-up is realistic for the patient’s resources.

References and further reading

• NCBI Bookshelf: Fracture healing biology.
• NCBI Bookshelf: Open fracture management.
• NCBI Bookshelf: Wound healing and chronic wounds.
• Follow local trauma, orthopaedic, antimicrobial, diabetes and wound-care protocols.