Sprains to the knee are characterized by the stretching or tearing of noncontractile structures, such as the investing ligaments or of the joint capsule itself, whereas a strain refers to stretching or severing along the course of muscles or tendons. Both collateral ligament and cruciate ligament sprains, as well as muscular strains, are relatively common. Ligamentous (sprain) and muscular (strain) injuries may be classified according to the degree of impairment.
Grade I sprain - Stretching but no tearing of the ligament, local tenderness, minimal edema, no gross instability with stress testing, firm end point
Grade II sprain - Partial tears of the ligaments, moderate local tenderness, mild instability with stress testing (but firm end point), moderately incapacitating
Grade III sprain - Complete tear, discomfort with manipulation but less than expected for degree of injury, variable amount of edema (ranging from negligible to grossly conspicuous), clear instability with stress testing (expressing a mushy end point), severe disability
For more on the definition and grades of sprains and strains, read here.
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Cite this: James W. Pritchett. Fast Five Quiz: How Much Do You Know About Knee Pain? - Medscape - Dec 15, 2017.