Sprain or Strain...What's the Difference?

Many of us have suffered an injury and been diagnosed as having either a sprain or strain. I often hear patients and individuals outside of physical therapy using these two terms interchangeably when really they refer to two very different injuries that affect two very different tissue types.

Sprains are injuries that affect ligaments, which are the passive stabilizers of our joints and cross from one bone to another bone. They usually occur when a given joint is taumatically pushed beyond it’s normal range of motion and will often result in a “pop” type sound. Sprains can be graded into three groupings (grade 1, 2 & 3) based on the pain and the amount of laxity found in a given joint upon clinical inspection.

Grade 1: pain and no joint laxity
Grade 2: pain and some joint laxity
Grade 3: no pain and complete ligament tear (very lax)

The diagram below shows a grade III ligament injury



Strains refer to injuries of the musculotendinous unit, which includes a muscle and the tendon that secures it to the bone.

The diagram shows the calf muscles (gastrocnemius & soleus) and the achilles tendon, which attaches these two muscles to the calcaneus bone of the foot.




Strains occur when the length or strength of a given musculotendinous unit is exceeded. Basically, if a muscle is stretched beyond it’s normal length or asked to support a load that it is not strong enough to support. When either of these things occur, small microtears will occur within the muscle leading to soreness. In severe cases the tendon can actually be torn away from the bone, which is termed an avulsion.

Hopefully this clears up the difference!