The basic mechanics of gait and propulsion dictate that the extensor chain mechanism must operate in an integrated way to convert ground reaction force into forward momentum.  From a clinical perspective we are interested in the integrated activity of ankle plantar flexion, hip and knee extension and controlled but stable trunk alignment on the propelling limb.  There are a number of potential mechanisms of breakdown in this region, which can be broadly categorised as:

motion impairment deficiencies

muscle power deficiencies.

Impairment of ankle dorsi flexion range inhibits the ability of the foot to act like a pivot and allow body weight to transfer in front of the axis of the ankle joint in order to facilitate propulsion.

Impairment of knee extension effectively shortens the length of the standing leg and reduces the efficiency of forced transmission through the lower limb.  Typically in association with impaired knee extension is an increased co-activation of the hamstrings and quadriceps with the net result of a stiffening of the limb and reduction in “fluidity” of knee motion.

The next component of the extensor chain is the ability to extend the hip.  In cases where postural alignment tends to be flexed the centre of gravity remains anterior to the axis of the hip joint producing a perpetual flexion moment.  This is perpetuated by sustained hip/flexor muscle activity in conjunction with the anterior abdominal wall.  In order for the hip to function freely there needs to be passive range of hip extension and sufficient power within the prime hip extensors (gluteus maximus) to generate the propulsion.

In clinical practice impairment of this fundamental component of gait is exceedingly common and often  results in a combination of compensatory strategies.  One compensatory strategy for impairment of hip extension is to induce excessive sacroiliac torsion producing increased anterior rotation of the innominate bone.  This may subsequently produce secondary strain through the lumbosacral junction or induce a motion pattern of lumbar hyperextension in order to bring the leg behind the body.  Not only is this movement pattern inefficient but produces a high risk of tissue overload in the zones of compensation.

Clinical Thought

1. How can we detect breakdowns in the extensor chain function?

1. What are the implications of a hyperlordotic strategy for hip extension in relation to trunk stability?

1. What are the implications of anterior innominate rotation as part of the facilitatory mechanism of leg extension?

Share your thoughts and …..

Rise to the clinical challenge.
David

© David for PhysioDigest - an educational resource for the musculoskeletal rehabilitation community, 2009. | Permalink | One comment | Add to del.icio.us
Post tags: back extension, dysfunction, extension, extension exercise, extension exercises, extensor chain, hip dysfunction, hip extension, joint dysfunction, knee extension, low back pain, motion impairment deficiencies, muscle power deficiencies, pelvic dysfunction, sacroiliac dysfunction, sacroiliac joint dysfunction, si dysfunction spine extension, tissue overload

Feed enhanced by Better Feed from Ozh