Starting position, left leg.
Starting position, left leg.
Patient: Sitting, with the knee flexed at and with leg in lateral rotation of tibia on a right angle femur.
Origin: Anterior part of the groove on the lateral condyle of the femur and oblique popliteal ligament of the knee joint
Insertion: Triangular area proximal to the soleal line on the posterior surface of the tibia and fascia covering the muscle.
Action: In nonweight bearing (i.e., with the origin fixed), the popliteus medially rotates the tibia on the femur and flexes the knee joint. In weight bearing (i.e., with the insertion fixed), it laterally rotates the femur on the tibia and flexes the knee joint. This muscle helps to reinforce the posterior ligaments of the knee joint.
Patient: Sitting, with the knee flexed at and with leg in lateral rotation of tibia on
Fixation: None necessary.
a right angle femur.
Test Movement: Medial rotation of the tibia on the femur.
Resistance: Seldom is resistance or pressure applied, because the movement is not used as a test for the purpose of grading the popliteus but, rather, merely to indicate whether the muscle is active.
Weakness: May result in hyperextension of the knee and lateral rotation of the leg on the thigh. Weakness is usually found in instances of imbalance between the lateral and medial hamstrings in which the medial hamstrings are weak and the lateral hamstrings are strong.
Shortness: Results in slight flexion of the knee and medial rotation of the leg on the thigh.
Weakness: Evidence of slight weakness of either the medial or lateral hamstrings is based on the subject's inability to maintain the rotation when asked to hold the test position. Weakness of both the medial and lateral hamstrings permits hyperextension of the knee. When this weakness is bilateral, the pelvis may tilt anteriorly, and the lumbar spine may assume a lordotic position. When this weakness is unilateral, a pelvic rotation may result. Weakness of the lateral hamstrings causes a tendency toward loss of lateral stability of the knee, allowing a thrust in the direction of a bowleg position in weight bearing. Weakness of the medial hamstrings decreases the medial stability of the knee joint and permits a knock-knee position, with a tendency toward lateral rotation of the leg on the femur.
Contracture: Contracture of both the medial and lateral hamstrings results in a position of knee flexion, and, if the contracture is extreme, it will be accompanied by a posterior tilting of the pelvis and a flattening of the lumbar spine.
Shortness: Restriction of knee extension when the hip is flexed, or restriction of hip flexion when the knee is extended. Shortness of the hamstrings does not cause a posterior pelvic tilt, but a posterior pelvic tilt and a flattening of the lumbar spine often are seen in subjects with hamstring shortness.
Note: Ordinarily, the hip flexors act to safeguard the hamstrings during knee flexion. Do not expect the subject to hold full knee flexion or to hold against the same amount of pressure with the hip extended in the prone position that could be resisted with a hip flexed in sitting. The frequent occurrence of muscle cramping during the hamstring test results from the muscle being in too short a position and attempting to hold against strong pressure. To test the hamstrings in full knee flexion, the hip must be flexed to take up some of the slack However, there will be assistance from the sartorius in both hip and knee flexion when the hamstrings are tested with the hip flexed.
Weakness of the popliteus and gastrocnemius may interfere with initiating knee flexion. Substitution of sartorius action will appear in the form of hip flexion as the knee flexion is initiated. A short rectus femoris, limiting the range of motion of knee flexion, will cause hip flexion as the motion of knee flexion is completed. (Hip flexion in the prone position is seen as an anterior tilt of the pelvis with lumbar spine hyperextension.) Assistance from the gastrocnemius in flexing the knee will be seen as an effort to dorsiflex the ankle, elongating the gas-trocnemius over the ankle to make it more effective in knee flexion.
Action of the gracilis as a knee flexor is illustrated. The muscle is brought into action by the test position and pressure as used for the medial hamstrings. The gracilis has its origin on the pubis, and the medial hamstrings arise from the ischium.
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