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H I P IN T E RNAL A N D E XTE R N A L R OTATION BY ANTHONY LETT

The focus of this article is on the hip joint in internal and external rotation. Hip Rotation When standing in the anatomical position, internal and external rotation occur in a horizontal plane about a longitudinal axis of rotation. With the foot planted on the ground, the pelvis rotates round a fixed leg. This is described as pelvic on femoral rotation. During pelvic on femoral external rotation, the iliac crest on the side of the nonsupport hip rotates backward in the horizontal plane. Internal rotation of the support hip occurs as the iliac crest on the side of the nonsupport hip rotates forward in the horizontal plane. Femoral on pelvic rotation occurs where the pelvis remains stable and the femur is rotated. It is commonly called an open chain movement and can be either internal or external (see Image one).

IMAGE 1

If the pelvis is rotating beneath a relatively stationary trunk during pelvic on femoral rotation, the lumbar spine must rotate (or twist) in the opposite direction as the rotating pelvis.

An example of femoral on pelvic internal rotation


IMAGE 2

The small amount of axial rotation normally permitted in the lumbar spine significantly limits the full expression of horizontal plane rotation of the support hip. The full potential of pelvic-on-femoral rotation requires that the lumbar spine and trunk follow the rotation of the pelvis. Internal and external rotation occur across the transverse diameter of the joint surfaces (See Image two).

External Rotation Normal range is often given as 45 degrees, although there is large variation which will be discussed in class. Note the image at the top of the page which gives normal as 20 to 35 degrees. Limiting factors include: • The anterior portion of the joint capsule. • The iliofemoral and pubofemoral ligaments. • The internal rotator muscles. There are no primary internal rotator muscles in the anatomical position, however the muscles below all contribute to internal rotation. Each action assumes a muscle contraction that originates from the anatomic position. Several of these muscles may have a different action (in particular a stronger internal rotation torque) when they contract from a position other than the anatomic position. • Gluteus minimus (anterior fibers), Gluteus medius (anterior fibers), Tensor fasciae latae, Adductor longus, Adductor brevis, Pectineus.

Interestingly… An “ideal” primary internal rotator muscle of the hip would theoretically be oriented in the horizontal plane during standing, at some linear distance from the longitudinal or vertical axis of rotation at the hip. From the anatomic position, however, there are no primary internal rotators because no muscle is oriented even close to the horizontal plane. Several secondary internal rotators exist and are listed above. With the hip approaching 90 degrees of flexion, the internal rotation torque potential of the internal rotator muscles dramatically increases. This becomes clear with the help of a skeleton model and piece of string to mimic the line of force of muscles, such as the anterior fibers of the gluteus minimus or gluteus medius. Flexing the hip close to 90 degrees reorients the line of force of these muscles from nearly parallel to nearly perpendicular to the longitudinal axis of rotation at the hip.


This occurs because the longitudinal axis of rotation remains parallel with the shaft of the repositioned femur. Delp1 and coworkers have reported that the internal rotation moment arm of the anterior part of the gluteus medius, for example, increases eightfold between 0 and 90 degrees of flexion. Even some external rotator muscles (such as the piriformis,

anterior fibers of the gluteus maximus, and posterior fibers of the gluteus minimus) switch actions and become internal rotators beyond about 90 degrees of flexion. These changes in muscle action help explain why maximal-effort internal rotation torque in healthy persons has been shown to be about 50% greater with the hip flexed rather than extended.2

1. Delp SL, Hess WE, Hungerford DS, Jones LC: Variation of rotation moment arms with hip flexion, J Biomech 32:493-501,1999. 2. Lindsay DM, Maitland ME, Lowe RC: Comparison of isokinetic internal and external hip rotation torques using different testing positions, J Orthop Sports Phys Ther 16:43-50, 1992.

Biomechanics of the Adductor Muscles as Internal Rotators of the Hip In general, most of the adductor muscles are said to be capable of producing a modest internal rotation torque at the hip when the body is in or near the anatomic position.3 This action, however, may be difficult to reconcile considering that most adductors attach to the posterior side of the femur along the linea aspera. With normal anatomy of the hip, a shortening of these muscles would appear to rotate the femur externally instead of internally. Indeed, Dr Gerry, a professor of Medical Anatomy agues against this possibility when I questioned him.

Neumann, Donald A. in the Kinesiology of the Musculoskeletal System argues the following. “What must be considered, however, is the effect that the natural anterior bowing of the femoral shaft has on the line of force of the muscles. Bowing places much of the linea aspera anterior to the longitudinal axis of rotation at the hip. The horizontal force component of an adductor muscle, such as the adductor longus, lies anterior to the axis of rotation. Force from this muscle therefore acts with a moment arm to produce internal rotation.�

3. Dostal WF, Soderberg GL, Andrews JG: Actions of hip muscles, Phys Ther 66:351-361, 1986. 4. Lengsfeld M, Pressel T, Stammberger U: Lengths and lever arms of hip joint muscles: geometrical analyses using ahuman multibody model, Gait Posture 6:18-26, 1997.


The ROMA Test IMAGE 3A

IMAGE 3B

The ROMA test varies from traditional testing procedures like the ones above, image three A and B. They are usually performed lying pone or supine. Why don’t we use them? Because they yield imprecise results. This will be discussed in greater detail in class, but essentially: External rotation as a test for “internal rotator muscles” doesn’t test anything in particular, as we have seen above. Recall that there are no primary internal rotators because no muscle is oriented even close to the horizontal plane. Although the Gluteus minimus (anterior fibers), Gluteus medius (anterior fibers), Tensor fasciae latae do internally rotate the femur, there are more effective tests for these, and tightness in them will show up in these alternative tests. An example is in the hip flexor tests.

Internal Rotation Normal range is often given as between 30 and 45 degrees. Theoretically, internal rotation is limited by the following: • Joint capsule: posterior portion • Ligament: ischiofemoral • Muscles: external rotators (See image four)


IMAGE 4

The primary external rotator muscles of the hip are the gluteus maximus and five of the six “short external rotators.” The six “short external rotators” of the hip are the piriformis, obturator internus, gemellus superior, gemellus inferior, quadratus femoris, and obturator externus.

Unlike the internal rotators, the line of force of these muscles is oriented primarily in the horizontal plane. This orientation is optimal for the production of external rotation torque. In the anatomic position, muscles considered as secondary external rotators are the posterior fibers of the gluteus medius and minimus, obturator externus, sartorius, and long head of the biceps femoris. The obturator externus is considered a secondary rotator because in the anatomic position its line of force lies only a few millimeters posterior to the longitudinal axis of rotation.

Piriformis - particularly important for stretch therapists The piriformis attaches proximally on the anterior surface of the sacrum, among the ventral sacral foramina. Exiting the pelvis posteriorly through the greater sciatic foramen, the piriformis attaches to the superior aspect of the greater trochanter. In addition to the action of external rotation, the piriformis is a secondary hip abductor. The sciatic nerve usually exits the pelvis inferior to the piriformis. However, in up to 25% of the population the sciatic nerve may pass through the belly of the piriformis. A shortened or “tight” piriformis may compress and irritate the sciatic nerve, a condition known as “piriformis syndrome.” Refer to image four and Anthony’s article titled Stretching for Piriformis Syndrome.


ROMA When testing for internal rotation i.e testing the length of the external hip rotators in the ROMA, the femur is positioned in flexion and external rotation. Why is this? First, because as the femur is flexed and externally rotated, the insertions of the external rotators move away from their origins. See the image five and six below.

IMAGE 6

IMAGE 5

IMAGE 7

The lower fibers of gluteus maximus are probably stretched to a greater extent in the ROMA test in image 7. In a stiff client, this action will be enough to elicit a stretch. If not, leaning toward the foot takes the origins of the deep rotators on the sacrum further from their insertions on the trochanter. Lying supine and internally rotating the femur with the thigh flexed at 90 degrees is not a useful test generally for testing the length of the external hip rotator muscles. See image 3A. (Image 3B may be marginally better.) This is perhaps because as noted above some external rotator muscles such as the piriformis, anterior fibers of the gluteus maximus, and posterior fibers of the gluteus minimus switch actions and become internal rotators beyond about 90 degrees of flexion.


Often, 3A is a useful test for FAI, discussed in last week’s post. Watch this video for how to screen for Cam and Pincer type impingements. I will demonstrate one very clearly in class! > Video link: https://www.youtube.com/watch?v=7RvaGasiWXM

The second test in the ROMA protocol involves squaring the pelvis to the legs maximally and rotating the trunk and pelvis around the flexed thigh (see Image 8). Although difficult to be precise, this position probably places the gluteus medius and minimus and the upper fibers of gluteus maximus on greater stretch. It definitely feels different to the stretch above. Recall that with the hip approaching 90 degrees of flexion, the internal rotation torque potential of the internal rotator muscles (the anterior fibers of the gluteus minimus or gluteus medius) dramatically increases. IMAGE 8

Summary Testing internal and external hip rotation can be confusing. The line of force of many of the muscles active in producing torque at the hip changes considerably depending on the position of the femur. External rotation as a test for “internal rotator muscles” doesn’t test anything in particular, as we have seen above. Recall that there are no primary internal rotators because no muscle is oriented even close to the horizontal plane. External rotation is more useful as a stretch test for the external hip rotators, as described above. The important thing is to conduct both tests as they can produce entirely different results in the same person, on the same hip!


Enjoy the videos below!

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