• Wallace J
• Gudgel JW

• Association of Chiropractic Colleges / congresses

Suprapelvic Muscle Hyperactivity: Normal movement dynamics in the affected spinal joints may be altered due to microtrauma or macrotrauma affecting the lumbar spine or lumbar postures as stabilization muscles fatigue to the point where the proprioceptors cease to function fully and correctly. Research indicates that excessive and uncontrolled movement is much more of a problem than restricted movement. It is the lack of support, protection, and control provided by the spinal stabilization muscles that allows these tissues to be placed in the condition that causes pain. As the nervous system experiences difficulty activating the stabilization muscles, it will increase the activity of the large global muscles of the back and trunk in an attempt to provide the stabilization. This accounts for the hypertonicity, and even spasm, often seen in the large back muscles during an acute back-pain episode. This “suprapelvic muscular hyperactivity” becomes chronic in that it is constantly being stimulated to compensate for the malfunctioning of small spinal stabilization muscles. Thus, when the patient is laid prone and the downward pull of gravity is eliminated, the pull of suprapelvic muscles on the pelvis is more effective at producing the unlevel pelvis that creates the short leg, as well as the other physical signs of the short leg.

The Feedforward Mechanism: Upon flexing of the patient’s knees, the proprioceptive input from the lower extremity, pelvic, and spinal joints that initiates the feedforward mechanism of spinal stabilization is activated. However, the feedforward mechanism is not effective in producing the stability and support needed in the spinal joints in the presence of dysfunction in both the neurological input and physical contraction of the stabilization muscles. This instability leads to activation of the global back muscles in an attempt to stiffen the spine and provide stability. This “suprapelvic muscular hyperactivity” prevents the ilia from moving noramlly when the rectus muscles of each anterior thigh are stretched via bilateral knee flexion. A normal functioning feedforward mechanism, along with adequate strength in the muscles activated by this system, would have limited excessive or uncontrolled vertebral movement with no activation of the global spinal muscles would have occurred. The spine would not have been “stiffened” by the activity of the global muscles in their attempt to limit the excess or incorrect movement and each ilium would have moved freely. Correction of the articular dysfunction will be reflected by improvement in the leg checks by improving the neurological function of the feedforward mechanism and its effect of increasing spinal stability.

Discussion: Even though Lawrence states, “there is no proof within the literature that (a functional short leg) exists”, the authors agree that most likely, the functional short leg is the product of suprapelvic muscular imbalance brought on by the body’s attempt to stabilize an unstable spinal or pelvic segment. It is the intent of the authors to spawn discussion and further clinical research of the feedforward mechanism and its relationship to leg length inequality, articular dysfunction and chiropractic practice.

This abstract is reproduced with the permission of the publisher.