An arthrometer is a diagnostic tool used by doctors and physical therapists to measure joint range of motion and ligament flexibility. It is commonly used to evaluate knee ligament problems and can be used for initial diagnosis and postoperative assessments. The accuracy of the tool depends on proper placement and the experience of the user.
Doctors or physical therapists generally use an arthrometer, also known as a goniometer, as an orthopedic diagnostic tool to measure range of motion in joints. Manufacturers create each device to measure the flexibility and stiffness of the ligaments in a particular joint. Arthrometers can be made for shoulder, vertebral, or ankle joints, but most are used to evaluate knee ligament problems. Sensors on the device record joint movement and usually feed the information to a connected graph, providing a visual, paper-based view of joint articulation during assessment.
Healthcare providers might use an arthrometer for initial and postoperative assessments of an anterior cruciate ligament knee injury. The patient usually lies on a table with padded support under the legs. The support keeps the leg in proper alignment and provides the necessary amount of knee flexion, which is typically between 20 and 35 degrees. The arthrometer is positioned along the upper leg, from the knee to the shinbone, and is held in place with Velcro® straps.
A knee arthrometer usually has two sensors. One is in contact with the kneecap, or kneecap, and the other sits on the tibia, or shinbone. A force handle allows you to apply 15, 20, or 30 pounds of constant pressure below the knee during the stability assessment process. Using varying amounts of pressure, the lower leg can be moved or the patient can lift it himself, while the knee is supported. Several ranges of motion tests, often referred to as the drawer test, Lachman test, and pivot displacement, allow the doctor or therapist to determine abnormal motion between the tibia and the kneecap.
The amount of motion the tibia experiences to or from the kneecap determines the amount of damage to the ligaments. An injured knee often shows a greater degree of motion than a healthy knee. Practitioners can use the device on both knees, comparing the amount of movement of the injured leg to that of the unaffected leg. Arthrometer measurements on injured knees typically show 3 millimeters or more of displacement relative to the unaffected joint.
Physicians might choose to use an arthrometer for initial diagnostic purposes, as patients generally experience little or no knee pain with the device compared to the discomfort caused by conventional manual manipulation. An arthrometer might also be used during physical therapy as a means of monitoring progress. The accuracy of the tool depends largely on the training and experience of the individual using it. Improper placement can affect sensor contact and can give erroneous measurements.
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