Joint Function Overview

Illustration of a woman's ankle joint overlayed on a photo of the woman walking on a treadmill / Getty Images 

The term joint function comes up a lot in reports of results of medical and research studies. Researchers speak of joint function and how it is affected by diseases, such as arthritis, or by treatments for arthritis. What is joint function?

Joints and Joint Function Defined

A joint is defined as the juncture where two or more bones come together for the purpose of movement or for stability. Contraction of muscles crossing the joint causes it to move. Normal joint function is defined as a joint's ability to move throughout its range of motion, bear weight and perform work.

Doctors and physical therapists are trained in anatomy and physiology to know how a normal joint should look and act. They know the structure and function of the bones, muscles, ligaments, tendons, nerves, and blood supply for the joint. All of this can be shown in diagrams and in dissecting cadavers. But beyond that, they have to know how a normal joint works. That includes how far it should be able to flex, extend or rotate. The ability to bear weight or to resist pressure opposing the action of the joint are other aspects of joint function.

Assessing Joint Function

When you go to the doctor with a complaint about a bone, muscle or joint, she will perform a musculoskeletal examination that includes assessing joint function. Joint function can be affected by injury or inflammation, so she will look for redness, bruising, and how it compares with the opposite joint that may be uninjured. Are they the same size and shape?

The doctor will have the patient move the joint through its usual range of motion - flexing, extending, rotating. She will also manipulate the joint to move it. In both cases, she looks for restrictions on the range of motion and whether there is any pain during the movement. She places a hand on the joint to feel for crepitus (crackling) showing a degradation of the joint. She will perform some specific function tests for suspected injuries. She sees how well the patient can resist movement of the joint.

Example of Shoulder Joint Function Tests

The range of motion tests for the shoulder include abduction, lifting the arm from a lowered position, out to the side and up to above the head in an arc, and flexion tested with arms extended in front and raised to over the head, with a normal range from 0 to 180 degrees. Adduction and internal rotation and then abduction and external rotation are tested with one arm first reaching the back from below and then from above. Other tests include Neer's Test and Hawkin's test for impingement and the Empty Can and Gerbers Liftoff tests for rotator cuff injuries.

Example of Knee Joint Function Assessment

For the knee, the doctor will watch the patient walk and see if there is a limp, which would show the joint function is impaired. The doctor will look at the patient standing to see whether the legs are bowed or knock-kneed (varus vs. valgus deformity) which shows impaired knee function. How the patient gets out of a chair and if he can climb stairs also indicate joint function. The patient lays down, and the doctor has him bend the knee, which should extend to zero degrees and be able to flex to 140 degrees with normal joint function. The doctor also passively bends the knee.

Other tests for knee joint function include the McMurray's Test and Appley Grind Test for medial meniscus injury, stress tests for the lateral collateral ligament and medial collateral ligament, Lachman's test for the anterior cruciate ligament, Posterior Drawer Test and chondromalacia tests.

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  • Merck Manual, Consumer Version, 2015.
  • Musculo-Skeletal Examination, University of California, San Diego, October 2015.