The importance of the feet to the normal biomechanical functioning of the spine often is overlooked. Because the feet are seldom symptomatic, busy chiropractors frequently overlook examining and, consequently, treating them.
The Foot/Spine Connection
When we stand, walk, dance, jump and run, the feet are the foundation to the spine and the rest of the musculoskeletal support system of the body. This foundation must bear the weight of the entire body. If there is insufficient support from the pedal foundation, the spine will be exposed to less than optimal gait mechanics, which eventually can cause spinal joint dysfunction, postural deviations and back pain. Recognizing and responding appropriately to faulty foot biomechanics will allow chiropractic physicians to more effectively care for their patients.
Abnormal stresses on the pelvis and spine can be the result of, but not limited to, excessive shock transmission, abnormal joint motion, abnormal foot proprioception or a functional short leg. The cause of all four of these problems often is located in the feet. When a part of the foot is not moving properly (either insufficient or excessive joint motion), the resulting forces produce effects along the whole kinetic chain. Researchers have found, "Alteration of normal foot mechanics can adversely influence the normal functions of the ankle knee, hip and even the back."2
Shock Transmission
In ideal standing, posture with even feet forms an angle of 30 degrees and a plumb line dropped from the sacral promontory falls midway between the feet onto a line between the navicular bones.3 Pronation occurs when the superior aspect of the calcaneus tilts and rolls inward, which then brings the talus with it. This releases the navicular from arthrodial articulation with the talus and jeopardizes the medial longitudinal arch. When collapsed, it can begin serial distortion that may extend to the occiput.4 If the biomechanics of a foot tend to function in either hyperpronation or excessive supination, excessive shock is transmitted to the spinal joints. A high arched or cavus foot with limited range of motion attenuates shock poorly, and a hypermobile flat foot also does poorly on shock attenuation because of its function near the end of the range of motion.5 In either case, the forces may be felt in the joints of the pelvis and spine. In fact, enhancing shock absorption from the lower extremities may be one of the most significant long-term improvements that will be reported by patients with degenerative discs and spinal joints.
Light and his colleagues studied the "brief but sizeable deceleration transient, which travels up the human skeleton on heel strike during normal walking."6 In their classic investigation, they found significant stress that could be reduced with the use of visco-elastic heel pads. Regarding the spine, they warned, "While the transients will load the majority of joints primarily in compression, shear stress will predominate in others, such as spinal facet and sacroiliac joints."6 This may explain the rapid response of lumbosacral and sacroiliac pain with the use of orthotics that contains shock-absorbing materials.
Abnormal Joint Motion
When the foot and ankle biomechanically function in prolonged pronation, the entire lower extremity undergoes excessive internal rotation. This causes a range of altered biomechanics in the pelvis, sacroiliac joints and spine. Hammer has described the numerous consequences as follows: "Based on excessive internal femoral rotation due to hyperpronation, this may develop compensatory shortening of the iliopsoas, which would draw the spinal column downward, forward and rotate contralaterally. Unilateral iliopsoas involvement would cause a unilateral anterior pelvic tilt, while bilateral hyperpronation may result in an increased lordosis."7 The result is recurring abnormal joint motion affecting the sacroiliac and lumbar spine joints. These forces can be decreased significantly with the use of an orthotic that controls hyperpronation.8
Altered Proprioception
Proprioceptors are the sensory organs located in muscles and joints that provide information to the central nervous system regarding the status, function and position of the musculoskeletal system. With several small joints, ample layers of connective and articular tissues, and both intrinsic and extrinsic muscles, the feet are very well supplied with proprioceptive nerve endings. When there is biomechanical dysfunction, it is probable that inaccurate neurologic information is sent to the CNS from the feet. This can have a detrimental effect on coordination and balance throughout the spine and pelvis.9
Dropped Pelvis
When there is a discrepancy in the length of the legs (whether anatomical or functional), the pelvis is lower on one side. Leg-length asymmetry will cause vertebral rotation, recurrent subluxation and possibly a functional scoliosis, which in turn, produces strains to the pelvic and low back structures. These strains can cause not only chronic pain10,11 but also have been shown to result in specific degenerative changes.12 The most common cause of a functional short leg is a lowered medial arch and excessive pronation. The study by Rothbart and Estabrook found a correlation factor of 0.97 between asymmetrical pronation and a pelvic tilt to the same side.13 Because of these types of findings, it may be difficult to eliminate pelvic and spinal dysfunction without treating the feet.
What to Do
Every patient with spinal and pelvic-joint dysfunction should be checked for abnormal foot biomechanics. This evaluation can be quick and easy and is not painful to the patient. The feet may need to be adjusted so that numerous joints up the kinetic chain can move smoothly during each phase of gait. In addition, most patients with biomechanical foot problems will benefit from the long-term support provided by orthotics.
Conclusion
When a patient presents with spinal joint dysfunctions, especially ones that do not correct rapidly and completely, a search for contributing factors must include examination of the feet. Orthotics can be helpful in most cases needing long-term spinal stabilization. Even expertly applied, spinal corrections often will be only partially successful until the lower extremity problems are uncovered, corrected and supported for the long haul.
References
- Sychewska M, Oberg T, Karlsson D. Segmental movements of the spine during treadmill walking with normal speed. Clin Biomech, 1999;14:384-8.
- Katoh Y, et al. Biomechanical analysis of foot function during gait and clinical applications. Clin Orthop Rel Res, 1983;177:23-33.
- Steindler A. Kinesiology of the Human Body Under Normal and Pathological Conditions. Springfield, IL; Charles C. Thomas, 1970.
- Greenawalt, MH. Spinal Pelvic Stabilization. Roanoke, VA: Foot Levelers, Inc. 1990.
- Subotnick SI. Forces Acting on the Lower Extremity. In: Sports Medicine of the Lower Extremity. New York: Churchill Livingstone, 1989:189.
- Light LH, McLellan GE, Klenerman L. Skeletal transients on heel strike in normal walking with different footwear. J Biomech, 1980;13:477-80.
- Hammer WI. Hyperpronation: causes and effects. Chiro Sports Med, 1992;6:97-101.
- Dananberg HJ, Giuliani M. Chronic low-back pain and its response to custom-made foot orthoses. J Am Podiatr Med Assoc, 1999;89:109-17.
- Fitz-Ritson D. The anatomy and physiology of the muscle spindle and its role in posture and movement: a review. J Can Chiro Assoc, 1982;26:144-50.
- Giles, LGF, Taylor JR. Low-back pain associated with leg length inequality. Spine, 1981;6:510-21.
- Friberg O. Clinical symptoms and biomechanics of lumbar spine and hip joint in leg length inequality. Spine, 1983;8:643-51.
- Giles LGF, Taylor JR. Lumbar spine structural changes associated with leg length inequality. Spine, 1982;7:159-62.
- Rothbart BA, Estabrook L. Excessive pronation: a major biomechanical determinant in the development of chondromalacia and pelvic lists. J Manip Physiol Therap, 1988;11:373-9.
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