Musculoskeletal Stability and Orthotic Support
by William M. Austin, DC, CCSP, CCRD
How can orthotics designed for the feet improve the function and stability of the entire musculoskeletal system? The list of conditions that have been attributed to biomechanical imbalances in the feet is extensive. While it is obvious that foot hypermobility can affect the lower extremities, problems in the pelvis and spine can also be helped with the use of foot orthotics. Over the past few decades, research investigations have contributed to our understanding of this phenomenon.
Normal gait causes predictable, repetitive motions to occur from the feet to the head. One recent study concluded that “there are small, but important, inter-segmental movements of the spine during gait.”1 The accurate timing of the many muscle contractions required to control these fine spinal movements during walking and running depends on stimuli from a symmetrical gait.
Pedal imbalances, such as excessive foot pronation (whether in one foot or bilaterally) will interfere with these carefully orchestrated movements and cause problems throughout the musculoskeletal system. In fact, investigators have found that “Alteration of normal foot mechanics can adversely influence the normal functions of the ankle, knee, hip, and even the back.”2 This is how biomechanical problems, such as excessive pronation in the feet, can be the cause of recurrent spinal subluxations, back pain, and degeneration.
Effects of Pedal Instability
Whenever the necessary structural support for the spine is lacking, chiropractic care suffers. The foundation provided by the feet and legs must bear the weight of the entire body. If there is either too much pronation or excessive supination in the feet, the spine is repeatedly exposed to abnormal stresses and strains that will eventually develop into low back pain.
These biomechanical excesses will affect musculoskeletal function in four specific ways: abnormal rotational stress, chronic sacroiliac joint dysfunction, excessive shock transmission, and pelvic unleveling. The use of custom-made functional orthotics will improve gait symmetry and help relieve these negative effects.
Abnormal Rotational Stress
As the foot pronates during the stance phase of gait, there is a normal inward (medial) rotation of the entire leg, into the pelvis. When the foot and ankle complex on one side stays too long in pronation (hyperpronation), the entire lower extremity undergoes excessive medial rotation. This can cause stress on the knee and hip joints, as well as into the pelvis, sacroiliac joints, and spine. The increased rotational forces are transmitted up the leg into the pelvis, and especially the sacroiliac joint.3
In response, various compensatory pelvic subluxation complexes develop. These include pelvic tilts (usually anterior or to one side), innominate rotations (usually postero-inferior), and other complex adaptations. Asymmetrical pronation also results in abnormal firing of muscles during the rotational component of gait. This causes inaccurate proprioceptive nerve impulses and mechanoreceptor responses, affecting skeletal muscle coordination and balance.
“Based on excessive internal femoral rotation due to hyperpronation,” Hammer writes, “there may develop compensatory shortening of the iliopsoas, which would draw the spinal column downward, forward, and rotate it contralaterally. Unilateral iliopsoas involvement would cause a unilateral anterior pelvic tilt, while bilateral hyperpronation may result in an increased lordosis.”4
Chronic Sacroiliac Joint Dysfunction
Because of their complex anatomy and unique axis of joint motion, the movement pattern of the sacroiliac joints is called “nutation.”5 With each step, one leg swings forward and the pelvis twists forward on that side. At heel strike, the leg is externally rotated and the ilium is posterior (PI).
As the foot and ankle pronate, the leg rotates inward, and the sacroiliac joint “contranutates.”6 The ilium moves anterior (AS) during mid-stance. As the foot and ankle supinate and the leg rotates outward, the opposite movement (“nutation”) brings the ilium posterior. If this complex movement pattern is disrupted by one foot pronating more than the other, recurring sacroiliac joint subluxations and pelvic region pain develop.
Excessive Shock Transmission
A foot in supination doesn’t absorb shock well. Interestingly, a foot that stays in pronation too long will also transmit excessive shock into the pelvis and spine. “A hypermobile flat foot does poorly on shock attenuation,” Subotnick writes, “because of its function near the end of the range of motion.”7 In both of these cases, shock forces are felt first in the lower extremities, and then in the pelvis and spine.
Light and his colleagues studied the “brief but sizeable deceleration transient which travels up the human skeleton on heel strike during normal walking.”8 They found this shock wave to be a significant stress that could be reduced by the use of viscoelastic heel pads. Regarding the spine, they warned that, “while the transients will load the majority of joints primarily in compression, shear stress will predominate in others, such as the spinal facet and sacroiliac joints.” This explains the rapid response of lumbosacral and sacroiliac pain to the use of orthotics that control pronation and also contain viscoelastic materials.
The loss of arch height that occurs with excessive pronation allows the pelvis to drop to the more pronated side during stance and gait. Rothbart and Estabrook found a correlation factor of 0.97 between asymmetrical pronation and a pelvic tilt to the same side.(9) The resulting pelvic tilt lowers the sacral base and drops the lowest freely moveable vertebra.
A lateral spinal curvature develops in response to the lack of solid support for the base of the spine. This “functional” scoliosis starts in the lumbar region, but can affect the entire spine. When uncorrected for a period of years, the leg asymmetry and pelvic misalignment produce sustained stress on the spinal joints, resulting in classical patterns of microtrauma, cartilage wear, and osteophytes.9
The most common cause of leg length discrepancy is a lowered medial arch and excessive pronation. In such cases, there is no possibility of eliminating the pelvic or spinal subluxations without correcting pedal imbalance. Using orthotics to reduce pronation can provide substantial correction for most short legs. It is very important to recognize the functional short leg, since providing a lift instead of an orthotic is likely to perpetuate the associated sacroiliac subluxations.10
Reducing Musculoskeletal Stress
A properly designed custom-made orthotic will provide the following corrections throughout the day and during all locomotor activities:
- Decreases the extent and speed of pronation (reduces the medial rotation force that is transmitted up the leg into the pelvis and spine)
- Improves alignment of the arches (permits smoother nutation of the sacroiliac joints during gait)
- Absorbs shock from viscoelastic materials (eases the impact at heel strike and reduces the abnormal forces on degenerated joints)
- Reduces calcaneal eversion with a “pronation wedge” and support the medial arch (limits the dropping of the pelvis during gait and the effects of a functional short leg)
Look to the Feet
While the feet are located at the far end of the musculoskeletal system, they are a vital part of overall stability. Both structural and neurological factors form this inter-related and integrated system. Posture, as well as balance, coordination, and efficient musculoskeletal function, depend on the smooth functioning of the foot and ankle complex.
Whenever a patient demonstrates evidence of musculoskeletal instability, we must always consider the importance of the lower extremities, and the feet in particular. Even expertly applied chiropractic adjustments to the musculoskeletal system will often be only partially successful until lack of stability from the feet has been addressed with custom-made orthotics.
About the Author
An enthusiastic speaker, Dr. William Austin provides an energetic approach to learning. He draws from over 37 years of healthcare experience, which includes Athletic Training, Chiropractic, and Chiropractic Research. He has developed two successful practices. He is a 1986 graduate of Logan College of Chiropractic.
1 Sychewska M, Oberg T, Karlsson D. Segmental movements of the spine during treadmill walking with normal speed. Clin Biomech 1999; 14:384-388.
2 Katoh Y et al. Biomechanical analysis of foot function during gait and clinical applications. Clin Orthop Rel Res 1983; 177:23-33.
3 Botte RR. An interpretation of the pronation syndrome and foot types of patients with low back pain. J Am Podiatr Assoc 1981; 71:243-253.
4 Hammer WI. Hyperpronation: causes and effects. Chiro Sports Med 1992; 6:97-101.
5 Kapandji IA. The Physiology of the Joints, Vol. 3: The Trunk and Vertebral Column. New York: Churchill Livingstone, 1974.
6 Magee DJ. Orthopedic Physical Assessment. Philadelphia: WB Saunders; 1987: 220.
7 Subotnick SI. Forces acting on the lower extremity. In: Sports Medicine of the Lower Extremity. New York: Churchill Livingstone, 1989:189.
8 Light LH, McLellan GE, Klenerman L. Skeletal transients on heel strike in normal walking with different footwear. J Biomech 1980; 13:477-480.
9 Rothbart BA, Estabrook L. Excessive pronation: a major biomechanical determinant in the development of chondromalacia and pelvic lists. J Manip Physiol Ther 1988; 11:373-379.
10 Giles LGF, Taylor JR. Lumbar spine structural changes associated with leg length inequality. Spine 1982; 7:159-162.