Sprain, Strain, What’s the difference?
In simple terms, muscles strain and ligaments or tendons sprain. Both cause a physical disruption to that tissue and both are generally graded according to how much of that tissue has been affected.
Grade 1: mild disruption <50% of fibres torn.
Grade 2: moderate disruption >50% of fibres torn
Grade 3: complete disruption
Why do I care?
If you’ve read this far then you’ve probably been injured before and that first question was worth answering. If injury is your enemy, then understanding the tissues that get injured, why it happens, and how you recover from it is the first step in addressing the issue.
What are ‘Soft Tissues’?
You may have heard of the phrase, ‘soft tissue injury’. The body’s soft tissues are those tissues that surround, support and protect organs and other tissues. Some of these include muscle, tendon, fat, nerves, fascia, cartilage and ligament but not bone. Lets examine a few we commonly see injured.
Skeletal Muscles move joints. Skeletal muscle fibres have many small protein filaments (actin and myosin) that are able to slide over each other to cause a muscle to shorten. Several hundred filament form a myofibril, hundreds of myofibrils make a muscle fiber, 20-80 fibers make a fascicle and several fascicles make a muscle. This is relevant because muscle only store enough energy for about 6 seconds of exercise. A large portion of ongoing energy is derived from aerobic metabolism meaning it needs a decent blood supply and the microvasculature of muscle extends to each individual fiber. When damaged it bleeds, potentially to its deepest portions, but a generous blood supply can also begin the repair process quickly.
Transmitting forces from muscle to bone is the role of the Tendon. Tendons are very strong and most of the time they are resisting stretching forces generated by the muscle and by leverage effects created by the joints they act on.
Ligaments are largely considered a passive support structure that join bone to bone to stabilise across joints. They can also provide feedback to muscles and therefore play a role in joint position sense (as is the case for the ACL of the knee).
Tendons and ligaments are generally made up of collagen fibrils. These are well organized parallel structures responsible for the mechanical strength of the tissue. Although there are different types of tendon and ligament, these tissues generally have less of a blood supply. Whilst tendons are the strongest, they are also the least vascular, with portions of some tendons relying on diffusion rather than perfusion (a true blood supply).
This basic level of knowledge is crucial in understanding the processes involved in tissue injury and repair.
Why do they get injured?
Biological tissues are incredible materials that are very unique. They are resistant to a number of different forces, as well as have an ability to repair and adapt to various loading conditions. Unfortunately, when loads are excessive, the result is a response that either weakens it or more still, causes the tissue to fail.
Muscles and ligaments are more commonly affected by trauma (‘abuse’); either sudden high magnitude ‘stretching’ forces or by direct impact. Strains are the most common type of sports injury. Muscles are weakest at the musculotendinous junction (where muscle tissue, meets tendon tissue) and this is a common site for strains.
All materials have a point at which they rupture and in the case of strains and sprains, these loads are generally very high and most commonly tensile (stretched). Below is one of our clients having his Pectoral muscle reattached after it ruptured following a rugby injury, landing on an outstretched arm (note the surgeon approximating the torn edge to the bone in preparation to reattach to the arm).
Tendons are often affected chronically over time (overuse, disuse, misuse) and these injuries are often long and irritable in nature. Rupture is not altogether uncommon but it often often associated with a degenerative process that has reduced the tendons ability to withstand stress, thus reducing its breaking point.
How do they heal?
Following acute injury most soft tissues heal by passing through 3 distinct phases. The length of this process is dependent on many factors including the severity (or size of disruption), the tissue (including where it is in the body), biological factors (age, pre existing conditions etc) but also environmental, which includes how well you take care of your injury.
1) Inflammatory (3-5 days). Following acute injury a clot is formed to stop further blood loss. Infiltration of cells to the area removes any dead material and cleans up the edges before other cells initiate the reparatory phase.
2) Reparatory (up to 6-8 weeks) phase is generally considered the time for ‘scar formation’ to occur. The scar is predominantly made from a disorganized meshwork of deposited collagen, but a number of other building blocks for connective tissue are deposited and reorganized.
3) Remodelling (weeks – months). Over time, under controlled load, the orientation of collagen becomes aligned along the lines of stress and stronger cross links form with neighbouring, healthy tissue. Eventually, cellularity and vascularity more closely resembles that of normal tissue and the fibrous scar becomes stronger.
What is a good result?
A good result is one in which these processes are allowed to progress uninterrupted. Normal physiological healing takes time and as Physiotherapists it is our aim to ensure that during this time, the smallest and strongest, functional repair is attained. Unfortunately, however, that tissue will never be the same. Scar tissue has different mechanical properties to normal tissue, often having more creep (extensibility under sustained load) and less stiffness. Healed tendons and ligaments may be half to two-thirds the strength of their former selves. A poor recovery from injury may predispose these tissues to further injury or through biomechanical means may place other structures at risk.
Chris Dillon, Sports Physiotherapist