Grading the strength of muscle groups is an important feature of the physical exam. The data gathered from this portion of the examination might be helpful in diagnosing a condition, characterizing a range of symptoms, and as a marker for physical development or decline. For instance, after a stroke, patients are commonly examined for weakness in major muscle groups to determine the extent of damage caused by the stroke.
Anatomy and Function
The quadriceps muscle group is required for extension of the knee joint. Composed of four individual muscles, the quadriceps muscle group spans and impressive length overall, connecting the ilium of the hip to the superior edge of the knee bone. The rectus femoris is in the middle of the thigh, superficial to the other three muscles, which include the vastus lateralis, vastus medialis and vastus intermedius. These groups correspond to the most outer, inner and middle positions along the thigh.
In order to assess the strength of this muscle, the examiner will instruct the patient to extend her leg against a range of forces. When sitting atop the examination table with her legs hanging over the edge, the most basic demonstration of strength would require the patient to extend her legs so they are fully perpendicular to the floor. If this is the patient’s greatest level of strength, their quadriceps would be rated as a 3/5. Based on the results of this test, the examiner will proceed to either apply increasing resistance to leg extension or decrease the physical demands on the leg until a successful result is obtained.
According to the textbook “Clinical Neurology,” motor strength is a measurement of the ability of a muscle to contract against force. The grading system is based on a rating of 0-5 for each muscle group. Full strength in the quadriceps would be rated as a 5/5. A score of four would be given when the patient demonstrates movement against gravity and resistance applied by the examiner. As mentioned previously, movement that is only possible against gravity qualifies as a 3/5. A 2/5 strength grade indicates that the patient is able to extend her leg only when laying on her side, horizontal to the surface of the bed, thus removing the force of gravity. A 1/5 is given when contraction is evident when palpating, or inspecting with touch, but little or no effective motion is visible in the muscle. Finally, a zero is given when no muscular contraction is detected.
Formal testing of quadriceps strength may require follow up with what is known as a functional test. For instance, instructing the patient to rise from a squatting position, or stand from a low stool without using their arms, would both be useful tests for uncovering subtle weaknesses in these important leg muscles.