Acute Muscle Injury – By Allan Kershaw

Anybody who has played sport knows how this feels even if didn’t happen to you. So, what goes on internally after an acute muscle injury and how do we plan the rehabilitation process.

Here is my favourite torn hamstring story. The link is pretty cringe worthy but still inspirational.

The strain happens most often at the musculotendinous junction (where the muscle joins onto the tendon) as a result of indirect trauma. This trauma happens when the two-joint muscle (e.g. the hamstring starts at your sitting bone and finishes below your knee, so it acts on the hip and knee) contracts eccentrically (into a lengthened position). The part of the muscle that is most vulnerable is the one that has the highest proportion of type II fibres (fast twitch fibres). The eccentric contraction causes great tension to be developed in the muscle as the muscle has to be controlled into this lengthened position.

Have you ever done a Nordic hamstring curl as part of your training? If you have you will know how hard work they are! They are a good example of how to work a muscle eccentrically…

Assessment
If the trauma is direct, the injury is typically a bruise visible at the point of contact. Passive injuries are produced by flexible overstretching loads an example of this would be my splits on an uneven surface (this tends to affect the muscle closer to its starting point and is slower to heal). The most common mechanism of injury is sprinting as documented above.So what happens when you get to the clinic? You tell us the story of running down the wing with nobody near you and bang you felt like you were kicked in the back of the leg. You may have been able to walk off the pitch and start your PRICE protocol (blog on this to come) or you may have needed assistance a la Derek Redmond. We then need to gauge the level of severity.Muscle injuries are classified as grade I, II and III<span “font-family:=”” “verdana”,sans-serif”=””>Grade I injury (strain)
Swelling and discomfort of muscle fibres
Minimal impairment of strength and function

Grade II (partial tear)
<1/3 of fibres are torn in low grade
1/3 to 2/3 fibres are torn in moderate lesions
>2/3 torn in high-grade injuries
You may need a scan to determine level of injury
Clinical findings: Muscle strength and high speed/high resistance athletic activities are impaired with a marked loss of function

Grade III injury (complete tear)
Most commonly occur with things like water skiing when the ski gets caught in the water causing your knee to straighten and hip to bend
Clinical findings – muscle function is lost
There will be a big haematoma and it is unlikely that you will be able to actively bend your knee.

What make us susceptible to muscle injuries.
<span “font-family:”verdana”,sans-serif;mso-fareast-font-family:verdana;=”” mso-bidi-font-family:verdana”=””>1.   Two joint muscles – the motion at one joint increases the passive tension of the muscle and leads to an overstretching injury.
<span “font-family:”verdana”,sans-serif;=”” mso-fareast-font-family:verdana;mso-bidi-font-family:verdana”=””>2.   Muscles contracting eccentrically – These tend to occur during the deceleration phase of activity which will have an effect on the muscle tension and cause overload of the muscle fibres
<span “font-family:”verdana”,sans-serif;mso-fareast-font-family:verdana;=”” mso-bidi-font-family:verdana”=””>3.   Muscles with a higher percentage of fast twitch fibres – These are responsible for developing high speed contractions.

Muscles tend to work in pairs such as the quadriceps and hamstrings (as the hamstrings contract to flex the knee the quadriceps relaxes). If there is a flexibility imbalance this may predispose you to injury. It is however the more flexible muscle that is more likely to be injured.

Previous injury makes muscles more vulnerable to re-injury which is generally caused by incomplete rehabilitation.
The other risk factor that none of us want to hear is age……

So we know from the nociceptive pain blog that we get an inflammatory response post injury. This acute inflammation does all the good stuff – it protects, localises and removes injurious agents from the body and promotes healing and repair so no anti-inflammatories please!!! Redness is caused by the chemical response and swelling due to the build-up of proteins and fluid in the extracellular space. The inflammatory process last 3 days and this is where optimal loading is so important. It may mean being on EC’s or in a moonboot so as to avoid stretching and irritating the weakened structures which may delay the healing process

Healing
When the inflammatory phase subsides, repair is started and continues for 3-4 weeks. During this phase immature collagen fibres (the building blocks of all connective tissue) are formed but these are easily injured if over stretched. Once these have undergone maturation and remodelling you will be able to return to sport pain free.

Treatment of acute injuries

Inflammatory phase
Follow the PRICE soon to be termed POLICE protocol for at least 48hours. The change is from rest to optimal loading as complete rest can be detrimental with the increase risk of DVT.

Repair phase
The inflammatory and repair phases overlap during the first week. When the building blocks of muscle (collagen) are formed they must be appropriately stressed to develop tensile strength. This can be done by contract relax / submaximal isometrics (these are where the muscles are activated but the length remains the same).  The frequency, intensity and duration can be monitored to ensure there are no signs of inflammation (pain, swelling, redness, warmth).

Maturation and remodelling
When the muscle building blocks are mature tension should be applied in the line of normal stresses (the direction that the muscle fibres travel) for proper remodelling. This is normally 2-3 weeks after injury and is characterised by

<span “font-family:”verdana”,sans-serif;mso-fareast-font-family:verdana;=”” mso-bidi-font-family:verdana”=””>1)   The absence of inflammation
<span “font-family:”verdana”,sans-serif;=”” mso-fareast-font-family:verdana;mso-bidi-font-family:verdana”=””>2)   Full, pain-free ROM
<span “font-family:”verdana”,sans-serif;mso-fareast-font-family:verdana;=”” mso-bidi-font-family:verdana”=””>3)   Pain after tissue resistance

Muscles must be stressed and overloaded in the manner in which they are used functionally. This means we tailor the rehabilitation to your sport – how do you use the injured muscle metabolically aerobically (long distance runner) or anaerobically (sprinter), do you move in straight lines or is there a lot of cutting and is there a lot of sudden stopping.

After you have regained full, pain-free active ROM and over 90% muscle strength on both sides full participation in sport is allowed.

In the next blogs: injury prevention and stretching.

References