The healing process entails a remodeling of injured tissues, and things don't always go as planned. Though tissues adapt well to normal stresses, chronic overuse results in maladaptation that includes an increase in scar tissue. This has a number of implications, but the end result is weakening of the tissue -- be it tendon or muscle -- and an inability for it to function optimally. Inadequate rest after an injury, an overly aggressive rehab program and/or premature return to activity sets the stage for this maladaptation.
A ligament generally remains lengthened after a significant Grade 2 sprain, and therefore no longer stabilizes a joint to the same degree it did before. Sufferers work to overcome injury by maximizing dynamic stability, muscle strength, and proprioception (see below), however re-injury in competitive athletics is common. Playing on an insufficiently healed sprain will place undue stresses on the damaged tissue as well as on other stabilizing structures, inviting further damage (see RG III).
After injury, there is also a loss of proprioception, or the body's position sense. Impaired balance is another issue, not only after lower body injuries but after upper body injury as well. Re-training balance and proprioception is included in rehab and - like strength, range of motion and flexibility - it takes time until they are at full capacity. Functional testing to determine a sufficient degree of recovery in all areas should be what dictates a return to competition.
Articular cartilage is the cartilage that lines and cushions the ends of bones, providing smooth gliding surfaces at the joints. It is known to be resistant to compression but with less than ideal tensile strength. Articular, or hyaline cartilage lacks vascularity (blood vessels), nerves and a lymphatic supply. It derives nourishment from the soft tissue that lies between the joint capsule and the joint cavity (the synovium). When overloaded, articular cartilage becomes irreparably damaged; it does not regenerate. Permanent and disabling defects can result from a premature return to sports.
The scenario might go like this: an athlete suffers a ligament sprain that results in a loss of joint position sense (proprioception). This deficit leads to altered mechanics, which would in turn place an excessive load on articular cartilage, resulting in an acute inflammation and lesions in the tissue. Wear and tear of the smooth hyaline cartilage is cumulative and, over time, the athlete's joint may end up losing this surfacing entirely, resulting in what is known as being "bone on bone".
The dreaded microfracture surgery - from which not all athletes emerge victorious - is one procedure often performed in an attempt to treat articular cartilage lesions. Holes are drilled through any remaining cartilage into the bone below in an effort to create a bleed. The intention is for blood and fat droplets to migrate into the defect, form a clot, and heal into a form of cartilage that will help protect the area. Rehab after microfracture initially requires a significant protective non-weightbearing phase and, even after a lengthy and cautious program, successful return to high-impact sports may not be possible (see Greg Oden).
Fibrocartilage, present in only several joints, is most recognized for its role at the knee. Known as the menisci, these structures act as the shock absorbers at the joint, also creating a better fit for the femur and tibia. Lacking a substantial blood supply, particularly in the central regions, significant injuries to the menisci (tears) may require surgery. Because of the lack of nourishment from blood, meniscal surgery is more often performed to remove a torn segment rather than to repair the damage. Return to sports too soon after arthroscopic surgery is likely to result in impaired performance. Of even greater significance, is that it may increase the likelihood of arthritic changes down the line.
Bone contusions, and even more so fractures, may seem to be scariest to an athlete. In fact, in most cases, because bone healing generally occurs in a four to six-week window, a simple fracture mends in a more straightforward fashion than soft tissue. Contusions also generally resolve by the six to eight week mark. In contrast, displaced fractures - where the ends of the broken bone are out of alignment - require surgery (typically an internal fixation with plates, rods and pins) in order to heal properly. Fractures may be accompanied by soft tissue injury as well. The time required for athletes to return to sports after fracture is obviously greater than the healing time of the bone, as it also entails restoring any joint mobility lost due to immobilization, as well as achieving all the parameters of healing and function required after other musculoskeletal injuries.
When reporters inform us how long an athlete is expected to be out of action from an injury, they are reporting what they've been told. No one should base a fantasy team or bet the under on these predictions. In contrast with how most of us have learned to set a low-end realistic bar on expectations in order to exceed them, pro teams generally set our expectations of their athletes' recovery too high, positioning them for failure. I've no idea why.
*Note: My thanks to Michael T. O'Donnell, PT, DPT and Stephen Reischl, PT, DPT, OCS for an excellent presentation on Musculoskeletal Tissue Healing at the APTA conference last week. I've taken the liberty of boiling down much of the information (while adding my own two cents) in the writing of this article.