When body weight is supported, alternately, on one leg, such as in walking, the body must be stabilized on the weight-bearing leg during each step. By reverse action (i.e., origin pulled toward the insertion), strong hip abductors can stabilize the pelvis on the femur in hip joint abduction, as shown in Figure A. The lateral trunk flexors on the left also act by pulling upward on the pelvis.
Figure B shows a position of hip joint adduction that results when hip abductors are too weak to stabilize the pelvis on the femur. The pelvis drops downward on the opposite side. Strong lateral trunk flexors on the left cannot raise the pelvis on that side, in standing, without the opposite abductors providing a counter-pull on the right.
Figure B also illustrates the test used to elicit the Trendelenburg sign. Originally, this test was used in the diagnosis of a congenital dislocated hip. The Trendelen-
burg gait is one in which the affected hip goes into hip joint adduction during each weight-bearing phase of the gait. The femur rides upward, because the acetabulum is too shallow to support the head of the femur. If the problem is bilateral, a waddling gait is observed.
Figure C illustrates a relaxed postural position in an individual with mild weakness of the right hip abductors. The gluteus medius is the chief abductor, and a test that emphasizes the posterior gluteus medius often demonstrates more weakness than the test for hip abductors as a group. Often, this weakness of the gluteus medius is found in association with other weaknesses in the handedness patterns. (See pp. 74, 75.)
Testing the strength of the gluteus medius is important in cases of pain in the region of this muscle or of low back pain associated with lateral pelvic tilt.
Origin: Posterior gluteal line of the ilium and portion of the bone superior and posterior to it, posterior surface of the lower part of the sacrum, side of the coccyx, aponeu-rosis of the erector spinae, sacrotuberous ligament and gluteal aponeurosis.
Insertion: Larger proximal portion and superficial fibers of the distal portion of the muscle into the iliotibial tract of the fascia lata. Deep fibers of the distal portion into the gluteal tuberosity of the femur.
Action: Extends and laterally rotates the hip joint Lower fibers assist in adduction of the hip joint; upper fibers assist in abduction. Through its insertion into the iliotibial tract, helps to stabilize the knee in extension.
Nerve: Inferior gluteal, L5, SI, 2.
Patient: Prone, with knee flexed 90° or more. (The more the knee is flexed, the less the hip will extend because of restricting tension of the rectus femoris anteriorly.)
Test: Hip extension, with the knee flexed.
Pressure: Against the lower part of the posterior thigh, in the direction of hip flexion.
Weakness: Bilateral marked weakness of the gluteus maximus makes walking extremely difficult and necessitates the aid of crutches. The individual bears weight on the extremity in a position of posterolateral displacement of the trunk over the femur. Raising the trunk from a forward-bent position requires action of the gluteus maximus, and in cases of weakness, patients must push themselves to an upright position using their arms.
Note: // is important to test for strength of the gluteus maximus before testing strength of back extensors (see pp. 181 and 182), and in cases ofCoc-cyalgia (see page 222).
When the back extensor muscles are weak or the hip flexor muscles are tight, it is often necessary to modify the gluteus maximus test. The above figure shows the modified test.
Patient: Trunk prone on the table, and legs hanging over the end of the table.
Fixation: The patient usually needs to hold on to the table when pressure is applied.
Test: Extension of the hip, either with the knee passively flexed by the examiner, as illustrated, or with the knee extended, permitting hamstring assistance.
Pressure: This test presents a rather difficult problem regarding application of pressure. If the gluteus maximus is to be isolated as much as possible from the hamstrings, it requires that knee flexion be maintained by the examiner; otherwise, the hamstrings will unavoidably act in maintaining the antigravity knee flexion. Trying to maintain knee flexion passively and applying pressure to the thigh makes it difficult to obtain an accurate test.
If this test is used because of marked hip flexor tightness, it may be impractical to flex the knee, thereby increasing the rectus femoris tension over the hip joint.
The extensive deep fascia that covers the gluteal region and the thigh like a sleeve is called the fascia lata. It is attached proximally to the external lip of the iliac crest, sacrum and coccyx, sacrotuberous ligament, ischial tuberosity, ischiopubic rami and inguinal ligament. Distally, it is attached to the patella, tibial condyles and head of the fibula. The fascia on the medial aspect of the thigh is thin, whereas that on the lateral side is very dense—especially the portion between the tubercle of the iliac crest and the lateral condyle of the tibia, which is designated as the iliotibial band. On reaching the borders of the tensor fasciae latae and the gluteus maximus, the fascia lata divides and invests both the superficial and deep surfaces of these muscles. In addition, both the tensor fasciae latae and 3 A of the gluteus maximus insert into the iliotibial band so that its distal extent serves as a conjoint tendon of these muscles. This structural arrangement permits both muscles to influence stability of the extended knee joint.
So-called "actual leg length" is a measurement of length from the anterosuperior spine of the ilium to the medial malleolus. Obviously, such a measurement is not an absolutely accurate determination of leg length, because the points of measurement are from a landmark on the pelvis to one on the leg. Because it is impossible to palpate a point on the femur under the anterosuperior spine, it is necessary to use the landmark of the pelvis. It becomes necessary, therefore, to fix the alignment of the pelvis in relation to the trunk and legs before taking measurements to insure the same relationship of both extremities to the pelvis. Pelvic rotation or lateral tilt will change the relationship of the pelvis to the extremities enough to make a considerable difference in measurement. To obtain as much accuracy as possible, the patient lies supine on a table, with the trunk, pelvis, and legs in straight alignment and, in addition, the legs close together. The distance from the anterosuperior spine to the umbilicus is measured on the right and on the left to check against lateral pelvic tilt or rotation. If a difference in measurements is found, the pelvis is leveled and any rotation corrected so far as possible before leg-length measurements are taken.
"Apparent leg length" is a measurement from the umbilicus to the medial malleolus. This type of measurement is more often a source of confusion than an aid in determining differences of length for the purpose of applying a lift to correct pelvic tilt. The confusion arises because the picture in standing is the reverse of that in lying, and occurs when the pelvic tilt is caused by muscle imbalance rather than by an actual difference in leg length.
In standing, a fault in alignment will result when a weak muscle fails to provide adequate support for weight bearing. For example, a weakness of the right gluteus medius allows the pelvis to deviate toward the right and also elevate on that side, giving the appearance of a longer right leg. If the postural fault has been of long standing, there is usually an associated imbalance in the lateral trunk muscles, in which the right laterals are shorter and stronger than the left. (See p. 74.)
In lying, a fault in alignment will more often result from the pull of a strong muscle. In the supine position, an individual with the type of imbalance described above (i.e., a weak right gluteus medius and strong right laterals) will tend to lie with the pelvis higher on the right, pulled upward by the stronger lateral abdominal muscles. This position, in turn, draws the right leg up so that it appears to be shorter than the left.
The need for an elevation on a shoe should be determined by measurements in standing rather than the lying position. Boards of various thicknesses (see p. 86) are used for this purpose. (See also apparent leg-length discrepancy caused by muscle imbalance, facing page.)
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