Tissue Healing Process

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A commonly asked question is how long the healing process takes after injury. While there is no simple answer, the process can be broken down by structure (muscles, bone, tendons, ligaments) and severity. Below we will give an overview of each, which can help define the timelines and expectations around healing.
Healing involves a three-step process that can be broken down into the inflammatory response phase, the fibroblastic repair phase, and the maturation remodeling phase. While we will not go you down with the minute details of the process but give you a general timeline for tissue healing and factors that affect healing.

Muscles

Muscle injuries are classified in grades by severity. The mildest form of these is termed delayed onset muscle soreness. This is due to micro-tearing of the muscle’s fibers from over-activation and usually only last 1-3 days. This tearing is normal for hypertrophy and muscle building.

Grade I:

  • Few muscle fibers are affected
  • Minimal swelling and discomfort
  • Healing rate: 3-14 days

Grade II:

  • Greater damage of the muscle or muscle fibers
  • Associated with pain, swelling, and loss of function
  • Healing rates: 14 days- 3 months depending on the amount of tissue damaged.

Grade III:

  • A tear extends across the entire cross-section of the muscle.
  • Most severe strain and can result in loss of muscle function
  • Healing rate: 4 weeks- 1 year and often require surgery.

Bones and Fractures

There are two main types of fractures: open, which fractures the entire cross-section of the bone and breaks the skin, and closed, which involves no displacement thus no skin damage. They are also considered complete, in which the bone is broken into at least 2 fragments, or incomplete, which the fracture does not completely split the bone.
We will examine a closed fracture healing time; closed fractures have many subsets but for the most part, will heal the same. Like soft tissue, bones bleed following a fracture. The blood quickly forms a clot and blood vessels form inside the fracture bringing in fresh new blood with healing qualities.
Starting at one week, soft callus forms called fibrocartilage which slowly ossifies. The final step is when cells called osteoclasts trim the access tissue and the bone resembles its original form. However, the strength of the bone must be strengthened just like any other tissue. In order for the bone to return to original strength, we must introduce force back into the system.
The timeline for bone healing depends on: severity and site of the fracture, as well as, age of patient. Casts and other immobilizations will range anywhere from 3 weeks for the small bones to 8 weeks for the long bones.
An injury occurs if muscles stretch too far or contract against too much weight. However, the muscle is not always the only tissue that gets injured, damage can occur to the muscle fibers, at the musculotendinous juncture, in the tendon, or at the tendinous attachment to the bone.
Tendons
Tendon healing is particularly challenging because the site of the tear needs a sturdy fibrous union but also, needs extensibility. Often times, collagen (the rebuilding fibers) gets excessive and creates bulky scar tissue. If the collagen adheres to the surrounding tissue, it can further decrease the extensibility of the tendon.
Like muscles, depending on the severity of the damage, tendons can take anywhere from 4 weeks to 6 months. Four weeks is the minimum due to muscles contracting on the healing tissue that could damage the tendon.

Ligaments

A very similar structure to tendons are ligaments which attach bone to bone. The most common ligament damage is seen with inversion ankle sprains. Like muscles, ligament injuries are graded on severity.

Grade I:

  • Involve excessive stretching and maybe slight tearing of the ligamentous fibers, with almost no joint instability
  • Little to no pain or swelling at joint
  • Healing time is 0-3 days

Grade II:

  • Involve some tearing and separation of the ligamentous fibers.
  • Increased pain swelling and moderate instability of the joint are seen.
  • Healing time is 3 weeks – 6 months depending on the amount of tissue damaged.

Grade III:

  • Complete rupture of the ligament
  • Severe pain followed by little to no pain
  • Healing time 3 months to a year and often surgery is required

*Special thanks to Daniel Lyons, SPT for helping to write this piece.
Järvinen TA, Järvinen M, Kalimo H. Regeneration of injured skeletal muscle after the injury. Muscles Ligaments Tendons J. 2014;3(4):337–345. Published 2014 Feb 24.
Prentice WE. Understanding and Managing the Healing Process Through Rehabilitation. In: Hoogenboom BJ, Voight ML, Prentice WE. eds. Musculoskeletal Interventions: Techniques for Therapeutic Exercise, Third Edition New York, NY: McGraw-Hill; 2013.