The Motion of the Ocean
Motion is life. Motion is also stimulus. After injury or surgery, scar tissue forms unless motion is applied. Here is how it works.
When tissues are injured, a cascade of events occurs. These include inflammation and the release of chemical signals to recruit new cells. Some of these cells remove damaged tissue, while others form collagen: the fibrous material that makes up skin, bones, muscles, and all connective tissue.
At first, the eruption of the tissue repair process creates a tangled mess of collagen fibers. While normal tissues are made of a mixture of small and large collagen fibers, this new tissue contains only small-diameter fibers and has the biomechanical and structural properties of scar tissue. Over time, the body can either remodel this scar tissue into normal tissue (as it does with bone) or form the familiar scar tissue we often see with healed skin.
This remodeling process can be steered along more normal pathways using both chemical and physical factors. Motion is the most forceful of healing strategies.
Here is a typical example: When a football player’s knee joint is hit from the side, the medial collateral ligament can rupture. In the past, the knee was placed into a cast or a fixed splint and the ligament healed over a six-week time frame. But the physical properties and strength of the healed ligament were weak, leaving it—and the player—vulnerable to a repeat injury.
We have since learned that if motion is applied early in the healing process, the ligament heals with a more normal appearance. The motion has to be enough to provide stress, but not so much that it disrupts the healing fibers. This motion stimulates the repair cells to produce fibers that are oriented along the lines of stress. The motion-aligned fibers also have a more normal distribution of large and small diameters, rather than the tangled variety of fibers formed when the knee is placed in a cast.
More than ligaments benefit from motion. The bearing surfaces of the joints are called articular cartilage. When injured, these surfaces do not heal on their own, and arthritis—the wearing down of injured cartilage—progresses. When the injury is repaired using techniques such as articular cartilage paste grafting, followed by the application of motion (with the use of a continual passive motion machine), the healed cells of the articular cartilage look like normal cartilage tissue. Without the motion, only fibrous scar tissue forms.
The lesson that motion is critical for tissue repair applies widely in medicine and in life. Whether we are talking about physical trauma or mental injury, recovery from surgery or adapting to pharmaceutical treatments, the advice of the past—when patients were told to “go home and rest in bed”—is rarely used today. Even head colds seem to improve with gentle exercise. The key is modulating the activity enough to stimulate repair, but not so much that it induces further injury.
But how do you know exactly how much motion is enough and not too much? As physicians and physical therapists, we make educated guesses. We know impact exercises are often too much, and cycling is often just right. We wish the data were more specific to each tissue and each type of repair. The evaluation techniques of the future may involve extremely high-field, localized MRI machines that can focus on very small areas of tissue and provide real-time information on their healing status.
For now, it is not the size of the injury that determines your recovery—it is the motion of the ocean of all the healing factors.