Inversion / Eversion

In this position there is the increased innate thoracic and pelvic stability (little rotation occurs) but the angle of the knee has to be considered. Porter and Kaminski have shown that a knee angle anywhere from 15 to 45 degrees is acceptable for testing. The position of dorsi flexion at the ankle should also be considered. Any angle from neutral to 20 degrees plantar flexion can be used as Zachazewski and Browne (1990) showed no significant change in peak torque when comparing the degree of plantarflexion. Best for research.

To view a set up video press here 

Modified Seated position:

In this position there is even more increased innate thoracic and pelvic stability (little rotation occurs) and the subject is generally more comfortable. The angle of the knee still has to be considered. Porter and Kaminski have shown that a knee angle anywhere from 15 to 45 degrees is acceptable for testing. The position of dorsi flexion at the ankle should also be considered. Any angle from neutral to 20 degrees plantar flexion can be used as Zachazewski and Browne (1990) showed no significant change in peak torque when comparing the degree of plantarflexion. Best for patients.

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Stabilisation:

Seated: in the seated position stabilisation usually involves holding the bed handles. Most manufacturers supply a thigh / calf stabiliser which can be used to limit knee movement (the knee normally tries to rotate inwards). Whether it is used on the calf or thigh make little difference to the test

Attachments:

The footplate supplied with the machine should fully stabilise the foot it is likley the foot will pull to dorsi flexion during the test so car should be used to full tighten any straps

Axis of rotation:

The axis of rotation goes from the machine and extends through the center of the calcaneous (see below). To check the alignment simply invert and evert the ankle and ensure the heel does not lift from the footplate.

Anatomical zero:

Foot points to roof.

Range of motion:

Inversion and eversion takes place at the subtalar joint. Large individual variations exist in the amount of movement. The ROM should be between 30-50 degrees inversion and 15-20 degrees eversion (Miller, 1995). For eversion between 15-20 degrees is suitable remember not to go too far as the evertors tire very quickly. If you set too large a range of motion the muscles will suffer from muscular inefficiency and the test will stop as the end of range can not be attained. The range of motion for inversion is normally between 30 and 50 degrees  (remember these are the values shown on the machine they are not necessarily the true range of motion)

Gravity correction:

The effects of gravity are negligable in this position in fact some manufacturers use a counter balance rather than instrumented correction.

Speeds:

Speeds tend to be lower in the ankle with multiples of 30 being common. However, any speed from 30-240 degrees/second could be considered representative of the speed of subtalar movement during walking/running. A mid range speed for ordinary subjects is 45 degrees per second which will offer good results.

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

Protocols:

Interpretation:

In the ankle 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. In pathology of the lateral ankle complex the eccentric results can be drastically reduced. Restoration of this imbalance is crucial.

Concentric/concentric: Inversion/eversion ratio should show a invertor dominance of 30 percent.

Normative values:

Values for invertor and evertor group concentric and eccentric strength (in Nm). Based on Ivey et al (1985), Cahalan et al (1991) and + Shkiar & Dvir (1994) sedentary subjects.