Research Review By Christopher Howard ©


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Date Posted:

June 2011

Study Title:

Assessing Lateral Stability of the Hip and Pelvis


Grimaldi A

Author's Affiliations:

Physiotec Physiotherapy, Brisbane, Queensland, Australia

Publication Information:

Manual Therapy 2011; 16: 26-32.

Background Information:

Hip abductor muscle strength, activation, and functional control deficits have been implicated in osteoarthritis, patellofemoral pain and iliotibial band syndrome. For this reason, proper assessment of hip lateral stability and femoropelvic alignment is necessary. Ideal femoropelvic alignment in the frontal plane is the result of a balance between the lateral forces from the hip abductors and the medial forces imposed by body mass and the alignment of the trunk, pelvis and leg.

The hip abductors can be viewed in three layers. The gluteus minimus is the deepest layer, followed by the gluteus medius and piriformis/external rotators in the second layer, with the upper gluteus maximus and tensor fascia lata comprising the superficial layer.

The clinician’s ability to assess deficits, and tailor a management program that addresses specific alterations in muscle size, strength, activation patterns, and function is important to optimizing a patient’s lateral pelvic control. The focus of this paper was to review clinical and laboratory based research on the function of abductor muscles about the hip and pelvis.

Clinical Assessment:

Clinical assessment of hip abductor function aims at identifying abnormalities in posture, muscle tone and size, and movement patterns.

Standing Posture
  • Assessment of static posture has long been criticized for not associating well with dynamic function. It is important to note that often times in a clinical setting a patient’s static posture will be a reflection of what they think the clinician wants to see rather than their actual postural habits. The most common posture seen in those with hip abductor dysfunction will be a patient “hanging on one hip.” In this posture weight is shifted towards one side, and the pelvis is dropped on the other side, into a position of relative hip adduction. Inman (1) demonstrated that at 15 degrees of hip adduction in single leg stance, the forces of gravity were almost entirely resisted by fascial tension of the iliotibial band.
  • Florence Kendall’s text describes a “stretch weakness” of the hip abductor muscles as a result of standing in hip adduction (in relative adduction, the hip abductors are on stretch and in a lengthened position). These postural changes can lead to physiological changes over time and further hip dysfunction.
Resting Muscle Bulk and 'Stiffness'
  • Visual assessment of resting muscle bulk and tone should not be used alone in clinical evaluation as it would not hold up under academic examination. However, visual assessment of muscle size, asymmetry, and stiffness can provide supplemental information about muscle usage that can aid other assessments. For example, increases in TFL bulk are often associated with abductor dysfunction. Although, gluteus maximus and vastus lateralis should also be examined as they are part of the superficial layer of the abductor complex.
  • Abnormal asymmetry or hypertrophy of the superficial musculature is often an indication of muscle dysfunction. In addition, palpation of abnormal co-contraction, tonic activity, or stiffness of the superficial lateral musculature during quiet standing is also an indication of muscle dysfunction.
Dynamic Functional Assessment
  • Dynamic assessment may typically involve single leg stance, single leg squat, gait, stair-climbing, running, hopping, and/or other functional tasks specific to the sport played by an individual or activities of daily living. The primary goal of these assessments is to evaluate the ability of the individual to control femoropelvic alignment in the frontal plane.
  • Two tests have traditionally been used to assess femoropelvic control in the frontal plane: the Trendelenburg test and the modified Trendelenburg test. In the Trendelenburg test, an “uncompensated” positive test result occurs when a pelvic tilt occurs towards the unsupported side of the pelvis. A “compensated” positive test result occurs when the patient demonstrates trunk lateral flexion towards the weight bearing side. The modified Trendelenburg test involves maximal active elevation of the non weight bearing side of the pelvis, while the trunk is maintained in an upright position. An abnormal test result is an inability to maximally elevate the pelvis, or to maintain elevation for 30 seconds.
  • A limitation of both of the above assessments of pelvic tilt is that they do not take pelvic shift into consideration, and therefore may underestimate abductor dysfunction. Newer assessments use two dimensional kinematic data or the universal goniometer, which accounts for both lateral pelvic tilt and lateral pelvic shift.
  • Several authors have examined the increase in hip adduction that results when moving from bilateral to unilateral stance. DiMattia (2) reported the increase in hip adduction angle to be 5 degrees. Asayama (3) reported an increase of 2 degrees and Youdas (4) reported an increase of 7 degrees. However, Youdas noted that a change of 4 degrees would be the minimal change necessary to be statistically significant. Therefore, they concluded that due to inadequate sensitivity, the Trendelenburg test is questionable in its ability to asses hip abductor muscle performance. When transitioning from bilateral to unilateral stance, center of mass is moved over the base of support to maintain balance, which can be accomplished by hip adduction, but also changes in trunk and arm position. Therefore, simple measures of hip adduction are not enough and trunk and arm position must be taken into account.
  • Based on previous information, the authors of this review suggest methods to improve the value of the Trendelenburg test:
    1. The non-weightbearing leg should be between 0 and 30 degrees of flexion
    2. Arm position should be standardized – either at sides or crossed across the chest
    3. Trunk translation in the frontal plane relative to the pelvis should be quantified – establish relative positions of the sternal notch and midway between left and right ASIS.
    4. Have patient attempt to correct their position to determine whether their position of compensation is due to pain or changes in muscle function.
Abductor Muscle Strength
  • Isometric muscle strength testing is the most commonly employed tool for assessing abductor muscle function. This test provides information on the abductor mechanism’s ability to produce torque as a whole. However, it is important to understand that one member of the abductor mechanism could be inhibited while another is overactive, resulting in a net effect of zero. This can help to explain both the variability in the literature regarding abductor strength and hip osteoarthritis and the difficulty in correlating strength and performance on the Trendelenburg test.
  • To optimize the information gained from muscle strength testing, it is wise to test abductor function in multiple angles – neutral, 10 degrees adduction, and inner range abduction. In addition, pain should be noted prior to and during the testing procedure. This can be measured over time for a measure of progress.
  • A patient’s pattern of active movement can also be useful within the context of a battery of tests. The evaluation of active sidelying hip abduction is one such test. Lack of ability to maintain frontal plane alignment during the test will reflect the patient’s level of trunk control, but also substitution strategies.

Laboratory Based Assessments:

Magnetic Resonance Imaging (MRI) Assessment of Muscle Function
  • Information from functional MRI sheds a little more light on the discrepancies between functional and strength testing of the hip abductor muscles. In studying the activity of the gluteus minimus and gluteus medius, activity levels were affected by the degree of hip adduction in which the muscles were recruited. Gluteus minimus was substantially active regardless of frontal plane position, however the gluteus medius was much less active when activated from a position of abduction. This information further supports the need for clinicians to pay close attention to femoropelvic alignment during assessment and exercise
MRI Assessment of Muscle Size
  • Arokoski (5) showed that combined crossed sectional area of the abductor muscles was smaller around the worst effected hip in individuals with bilateral OA. Grimaldi demonstrated that in individuals with unilateral OA, the deeper abductor synergists (gluteus medius, piriformis, gluteus minimus), were smaller around the affected hip, while TFL and Upper Gluteus maximus maintained size.
  • Surface EMG analysis has shown that subjects with hip OA have increased gluteus medius activity during functional weightbearing tasks. This is opposite of normal clinical expectation of decreased gluteus medius activity.

Clinical Implications and Conclusions:

The assessment of hip abductor function should be based on a battery of tests, rather than just a single test. Information from each test should be taken into consideration when developing an overall treatment plan. In addition, it is important that the evaluator understands the objective of each test and how to perform the tests correctly. For instance, a multiangle test of muscle strength is more appropriate than testing at a single angle and both lateral pelvic tilt and lateral pelvic shift should be understood in the Trendelenburg test.

Additional References:

  1. Inman V. Functional aspects of the abductor muscles of the hip. Journal of Bone and Joint Surgery 1947; 29: 607-19.
  2. DiMattia M, Livengood A, Uhl T, Mattaclola C, Malone T. What are the validity of the single-leg-squat test and its relationship to hip-abduction strength? Journal of Sport Rehabilitation 2005;14:108-23.
  3. Asayama I, Naito M, Fujisawa M, Kambe T. Relationship between radiographic measurements of reconstructed hip joint position and the Trendelenburg sign. The Journal of Arthroplasty 2002;17:747-51.
  4. Youdas JW, Madson TJ, Hollman JH. Usefulness of the Trendelenburg test for identification of patients with hip joint osteoarthritis. Physiotherapy Theory and Practice 2010;26:184-94.
  5. Arokoski MH, Arokoski JPA, Haara M, Kankaanpaa M, Vesterinen M, Niemitukia LH, et al. Hip muscle strength and muscle cross sectional area in men with and without hip osteoarthritis. Journal of Rheumatology 2002;29:2185-95.