Wound healing

Author: Dr Tony Williams, Consultant Occupational Physician, Working Fit Ltd.

Date: August 2015.

Wound healing time is the main factor affecting return to work times.  Healing time varies considerably depending on the reparative ability of the tissues, and it is mediated by growth factors known as cytokines.  Surgery always aims to create the optimum environment for wound healing, creating the initial incision in the optimum plane for strength and healing, avoiding unnecessary muscle damage, minimising infection, and removing dead tissue or old scar tissue that may impair healing.  Surgery after trauma is always a greater risk because of damage to surrounding structures and wound contamination, so delayed healing is more likely.

Healing time can be delayed by many factors including infection, ischaemia, and contamination with foreign bodies (including sutures and prosthetics).  The patient’s health may have a substantial impact, particularly if nutrition is poor, there is intercurrent illness such as malignancy or infection, diabetes mellitus, liver dysfunction, kidney dysfunction, or immune dysfunction.  External agents may also have a substantial impact, particularly smoking, past irradiation or irradiation after surgery, medication with immune suppressants (particularly steroids), and chemotherapy.

Velnar et al have published a useful overview of the wound healing process with multiple references.  A summary of the evidence base is outlined below (Velnar et al., 2009).

  • Coagulation - minutes.  Within minutes coagulation and haemostasis lead to blood clots within the wound, surface dehydration and scab formation.  The principle aim is to stop exsanguination.
  • Inflammation – 1-3 days. Within 24-36 hours the inflammatory phase begins with complement cascade, neutrophil infiltration, extrusion of dead and damaged cells.  Macrophages then appear and continue the process of phagocytosis.   Growth factors activate fibroblasts, keratinocytes and endothelial cells.  Lymphocytes arrive after 72 hours, and help regulate collagen remodelling.
  • Proliferation 3-14 days. On the third day the proliferative phase starts with the formation of granulation tissue.  Fibroblasts and myofibroblasts proliferate and migrate to the wound from the third day.  Collagen is synthesised to provide strength to the repairing tissues.  New blood vessels grow into and across the wound leading to swelling and thickening of the wound area.
  • Remodelling 2 weeks to 1 or 2 years.  The wound matrix matures, new epithelium develops, and collagen bundles increase in diameter.  As collagen bundles collect, wound strength increases up to approximately 80% of the strength of normal tissue.  The connective tissue shrinks to bring the wound margins closer together, blood flow declines and the thickened pink scar becomes thin and white.

Surgeons have traditionally recommended that patients refrain from strenuous physical activity for 4-6 weeks after surgical procedures, based more on traditional recommendations and animal models than any objective evidence base.  The foundation of current advice is a study by Levenson et al in 1965 which showed that wound healing follows a sinoidal trajectory with tensile strength increasing rapidly until about six weeks, after which it slowly reaches 80% of strength at three months.  Research shows that healing times are consistent among species so animal models are valid, with little or no strength developing in the first week.  Changes in collagen type and structure over the second week weaken any residual strength, so that the highest rate of wound dehiscence is in the second week.  Disruption of the healing wound in the second week can delay overall healing.  By four weeks the wound tensile strength is over 50% complete (Ireton et al., 2013).

These studies indicate that for normal surgical wounds in healthy individuals, great care should be taken over the first two weeks to avoid tensile forces across the wound margins or in healing tendons.  Very light activity is safe for week three, increasing progressively so that most normal daily activities should be safe from the fourth week onwards.  Many activities will not place stress on the wound itself, so it is important to assess the nature of employment and determine whether the activities undertaken are likely to place stress on the healing wound.  For example sedentary work using a computer will put no strain on a leg wound, very little strain on an abdominal wound but could affect healing tendons in the hands and forearms.

These studies relate to unsupported wounds.  Use of sutures, adhesives, mesh, bone anchors, screws and other prostheses can substantially alter the risk and make it much safer to return to physical activity at an early stage.

  • IRETON, J. E., UNGER, J. G. & ROHRICH, R. J. 2013. The role of wound healing and its everyday application in plastic surgery: a practical perspective and systematic review. Plast Reconstr Surg Glob Open, 1.
  • VELNAR, T., BAILEY, T. & SMRKOLJ, V. 2009. The wound healing process: an overview of the cellular and molecular mechanisms. J Int Med Res, 37, 1528-42.