STABILITY ASSESSMENT

an extensor function, and should work in a coordinated partnership with the others in the chain. However, Gmax commonly presents as weak and underactive in many patients, and this causes the other links in the extensor chain, the hamstrings, paraspinals and even adductor magnus, to compensate by becoming overactive at times when they should not normally be firing at such high levels. These “muscular martyrs” do not take on this increased workload with good grace however, they complain bitterly by becoming chronically tight and susceptible to injury (7).

Gmax has an intimate and highly coordi- nated relationship with the hamstrings in gait, and the role of each is determined by the phases of the gait cycle. Under nor- mal circumstances, the hamstrings will activate just prior to heel strike to increase stabilisation of

IMPORTANT

Athletes who present with chronic hamstring “tears” or unusual levels of tightness in hamstrings and paraspinal muscles often exhibit poor Gmax function on testing. If this is not corrected, treatment will have limited success in the long term.

implicated in knee, hip, pelvic, groin, lower back and even shoulder pain.

the sacroiliac

joints. This is possibly due to the fascial continuity of the hamstrings with the sacrotuberous ligament, which crosses the sacroiliac joint and when tensioned by hamstring contraction will help to “lock” the joint in preparation for weight bear- ing. Gmax then provides major support to the pelvis in early and mid stance by increasing sacroiliac joint compression via its attachments and via the posterior oblique myofascial sling (8) (see fig.3b).

This being the case, once you move from heel strike into midstance, hamstring activity should decrease, and Gmax should increase its contribution. However, if Gmax is weak, underactive or exhibits poor timing, the hamstrings will remain active in order to maintain pelvic stability. This puts them under abnormal strain in ranges of the gait cycle where they would not normally be under such loading.

Gmax is therefore a consideration in a range of patient presentations. Taking a good history is critical - the problem that your patient presents with now could have had its origin in the past. Gmax may not have recovered from past knee surgeries even if they were several years previously; sacroiliac dysfunction can influence Gmax and Gmed, and even ankle sprains have been found to decrease the activation of Gmax on both the injured and uninjured sides (9). Pain elsewhere in the body may be the result of biomechanical compensa- tion over a period of time, and with its variety of relationships, Gmax can be

14

GLUTEUS MEDIUS Although thought of as abducting the femur against the static pelvis, gluteus medius (Gmed) is a primary stabiliser of the pelvis in the coronal plane. It acts in reverse against the fixed foot to maintain a level pelvis in stance which allows the trunk to orientate itself vertically above the pelvis, decreasing the amount of pos- tural muscle activity necessary to main- tain equilibrium.

If walking normally, the spine should respond to the force of heel strike by rotating and counter-rotating around a vertical axis, which keeps the trunk cen- tred over the pelvis. Without adequate Gmed activity and strength, the body will respond in one of two ways during gait:

either the pelvis will tip down on the opposite side to the stance leg, giving the appearance of a swagger on that side (see Fig.4), or the individual will adopt a pen- dulum style of gait by shifting their whole trunk excessively over the weak hip (see Fig.5). If adopting the pendulum style of walking to compensate for weak hip abductors, the trunk is only centred over the pelvis for a short moment in the gait cycle, and appears more like a side-to-side movement that markedly decreases effi- ciency and increases the activity of the trunk side flexors such as quadratus lum- borum. This pattern is seen commonly in patients with osteoarthritis of the hip.

When standing on one leg, a relatively horizontal pelvis over the limb requires activation of the lateral system, which involves gluteus medius and minimus, TFL and adductors (10) co-contracting either side of the proximal femur. As in the case of the posterior oblique system, when one element of the system weakens, others will increase their contribution in order to maintain the system integrity. Athletes with Gmed insufficiency often present with intractable tightness and associated palpatory tenderness in their ITB. Unlike the hamstrings however, the ITB itself will often not directly present with tears and pulls; instead its tightness interferes with

Figure 4: Trendelenberg or “swag- ger” gait

Figure 5: Compensated Trendelenberg or “pendulum” gait

Figure 6: Iliotibial band with gluteus medius appearing beneath

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