Internal / External Rotation

Overview:

Internal and external rotation of the hip has not bee extensively studied. The only really good piece of work (peer review) is by Lindsay et al. (1992). They compared 3 distinct positions, seated, supine with knee flexed and supine with knee extended. Seated tends to give the best strength scores.

These movements can be performed in either the lying (supine), or seated (modified) positions.  

The hip has the same degrees of freedom (movements) as the shoulder, however, unlike the shoulder the hip is bound tightly to the pelvic girdle making it much more stable. This stability gives the hip virtually no intrinsic motion. This limits the hips motion in each plane. This stable configuration reduces the possible contraindications and compensations (pelvic anterior / posterior rotation in hip rotation testing) are limited and easily identifiable. The bony landmarks are easy to find and the range of motion can be used without limitation as injury is unlikely.

The actions of the hip muscles are complex and often change in relation to demands. Any functional motion requires a coordinated effort by several muscles which may participate in many different actions together or individually. The function of some muscles (Medial gluteal is a good example as the posterior section rotates the hip inwards whilst the anterior section can rotate it outwards) changes depending on hip position and whether the position is weight bearing or not.

Lying position:

The least stabilised position for testing rotation.

To view a set up video press here 

Seated position:

The position of choice for patients and research (Lindsay et al. 1992).

To view a set up video press here 

Stabilisation:

Lying: In the lying position stabilisation normally only involves a pelvic strap to prevent the torso from influencing the results and a leg strap for the opposite (non tested) leg.

Seated: Stabilisation normally only involves a pelvic strap to prevent the torso from influencing the results

Attachments:

The footplate is normally used.

Axis of rotation:

The instantaneous axis of rotation is simply along the long axis of the femur

Anatomical zero:

With foot pointing to roof.

Range of motion:

Internal and external rotation of the hip. Although the hip has equal ROM to internal/external rotation of 45 degrees (Miller, 1985) isokinetic testing of these movements can be done over a much shorter arc. Dvir (1995) suggests a ROM from 5 degrees internal rotation to 25 degrees of external rotation.

Gravity correction:

Can be carried out if required but the influence is small some manufacturers supply a counter balance to use instead.

Speeds:

Once again debate rages over the speeds of motion of the leg during normal activities, however, slower speeds are normally chosen in the hip.

Generally it is accepted that speeds of 30 degrees/second and multiples of this should be used.

Protocols:

Interpretation:

In the hip it is normal to look at the ratio between the right and left sides there should be a 0-10% difference between the sides. Anything beyond this would indicate a muscle imbalance which would be best corrected.

Eccentric results are generally 30% higher than concentric within the same muscle.

Concentric/concentric ratio; external/internal rotation 0.80% this means the external rotators are only 80% of the extensors or the other way around is the internal rotators are 20% stronger than the external rotators

Normative values:

 Hip internal and external rotator concentric strength (based on Cahalan et al 1989 and Lindsey et al 1992)