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Dynamic Chiropractic – February 26, 2008, Vol. 26, Issue 05

A Few Words About Pronation

By Shawn Allen, DC, DABCO, Ivo F. Waerlop, DC, DABCN and Robert Lardner, PT

A lot of folks seem to be on a mission to eliminate pronation, considering it the scourge of humanity and the source of most human ailment.

While we agree that over-pronation causes biomechanical faults in the lower kinetic chain, so does under-pronation.

Furthermore, some pronation through the various axes of the foot is necessary and required for normal locomotion. We would like to deepen your understanding and appreciation of pronation and its potential impact on the musculoskeletal practice.

When most people think of pronation, they think of midfoot pronation, or pronation involving the subtalar or transverse tarsal joints. Pronation actually can occur relative to any articulation or bone, but with respect to the foot, we like to generalize and think of rearfoot (i.e., talocalcaneal), midfoot (talonavicular) and forefoot (transverse tarsal) pronation.

Pronation, with respect to the foot, is loosely defined as a combination of movements of eversion, abduction and dorsiflexion that results in flattening of the planter vault encompassing the medial and lateral longitudinal arches.1 In a normal gait cycle, this begins at initial contact (heel strike) and terminates at midstance, lasting no more than 25 percent of the gait cycle.1,2

In a perfect biomechanical world, shortly following initial lateral heel contact with the ground, the calcaneus should evert 4 degrees to 8 degrees3,4 because the body of the calcaneus is lateral to the longitudinal axis of the tibia.5 This results in plantar flexion, adduction and eversion of the talus on the calcaneus as it slides anteriorly. At this point, there should be dorsiflexion of the transverse tarsal (calcaneocuboid and talonavicular) joints. Due to the tight fit of the ankle mortise and its unique shape, the tibial is driven into internal rotation (medial rotation).6 This translates up the kinetic chain and causes internal rotation of the femur, which causes subsequent nutation (anterior tilt) of the pelvis and extension of the lumbar spine.7-9 This should all occur in the lower kinetic chain through the first half of stance phase. The sequence should reverse after the midpoint of midstance, causing supination and creating a rigid lever for forward propulsion.10,11

Pronation, along with knee and hip flexion, allows for crucial shock absorption throughout the first half of stance phase.12 Pronation allows for the calcaneocuboid and talonavicular joint axes to be parallel, making the foot into a mobile adaptor so it can contour to irregular surfaces.13,14 Problems seem to arise when the foot either under-pronates (7 degrees rearfoot valgus results in internal tibial rotation), or over-pronates (greater than 8 degrees or remains in pronation for more than half of the stance phase), resulting in poor shock absorption.11

This all being well-established, what about asymmetrical pronation? It is rare that people over- or under-pronate exactly the same amount on each side. These asymmetries usually are driven by weakness, such as from old injuries, surgeries or compensations. Excess midfoot pronation on the right causes more internal rotation at the right knee and an increased valgus stress at that joint. This puts the quadriceps at a mechanical disadvantage and places an adverse load on the adductor group, often making them stretch weak (unable to develop necessary eccentric loading) and thus, reflexively and protectively alters the function of the abductors, glutes and others. These then often become weak from repeated eccentric loading in an attempt to help limit the degree and rate of internal limb rotation.

The right foot, since it is now a poor lever in its more pronated state, often will be externally rotated, with toes clawed or hammered (intrinsic muscle imbalance) because the center of gravity has moved medially and they are trying to make that limb and foot stable to bear weight so they can progress forward. They often will toe off ineffectively from the inside of the great toe (as often is evidenced by a pinch callus medially) and will do so with an unbalanced and uncoordinated effort of the hallucis flexors, abductors, adductors and extensors, causing functional instability of the medial foot tripod. The medial rotation of the lower leg (relative because of the externally rotated foot) causes internal rotation of the thigh and anterior nutation of the pelvis on that side, both of which now put the gluteus maximus and abdominal wall anchors at a mechanical disadvantage - thus limiting hip extension on that side.

In this scenario, the sagittal plane extension usually expected at the hip has to occur somewhere and is frequently passed either into the knee (hyperextension) or into the lumbar spine, along with rotation and lateral bending to that side, possibly increasing compression on the right facets. From a neurological perspective, the vestibular system now kicks in to level the head, the result being contraction of the left paraspinals (sometimes inadequately so). Arm swing usually increases on the contralateral side to assist in propulsion forward, all in the ongoing environment of unequal stride lengths from the asymmetries described above.

Perhaps one question that should be entertained is this: What effect could this have on spinal mechanics in the average person who takes more than 10,000 steps a day or, even more devastatingly, is an aggressive athlete? What effects are we placing on the nervous system and what neuroplastic changes are occurring? As you can see, gait is terribly difficult and complex, with little room for error and almost countless compensation possibilities. Given time, the body usually will find a compensation pattern that provides an adequate degree of stability to ambulate; however, this is not without a price and not without pain if the system is overburdened long enough.

Under- or over-pronation, regardless of cause, ultimately means other articulations, including the spine, will have to attenuate more shock.7,15-18 Over time, this may lead to back pain,7,12,15,17,19 knee pain,16,17,19-24 articular cartilage degeneration19-21 or ligamentous laxity16,21,22 due to repetitive stresses.

Understanding the mechanics of pronation and its effects on the kinetic chain should alert you to other possible causes of a patient's presenting symptoms or mechanics observed during the physical examination. Some pronation, just as some supination, is necessary for normal ambulation. When there is excessive or deficient pronation, the body must compensate in some other manner, which often results in a symptom that may be the reason the person sought your care in the first place.

Recognizing normal mechanics will help you to decide where the fault in the biomechanical chain is and which action - manipulation, exercise, stretching, prescription of an orthotic, etc. - would be appropriate.

References

  1. Minkowsky R. The spine, an integral part of the lower extremity. In: Clinical Biomechanics of the Lower Extremities, Valmassey R. St Louis: Mosby, 1996:105.
  2. Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Slack, 1992:73.
  3. Close JR, Inman VT, Poor PM, Todd FN. The function of the subtalar joint. Clin Orthop, 1967;50(1-2):159-79.
  4. Wright DG, Desai SM, Henderson WH. Action of the subtalar and ankle joint complex during the stance phase of walking. J Bone Joint Surg, 1964;46A(2):361-82.
  5. Perry J. Anatomy and biomechanics of the hindfoot. Clin Orthop, 1983;177:1-16.
  6. Mann RA, Baxter DE, Lutter LD. Running symposium. Foot Ankle, 1981;1(4):190-224.
  7. Cibulka MT. Low back pain and its relation to the hip and foot. J Orthop Sports Phys Ther, October 1999;29(10):595-601.
  8. Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Slack, 1992:152.
  9. Michaud T. Foot Orthoses and Other Forms of Conservative Foot Care. Newton, Mass.: Michaud, 1993;59-62.
  10. Wernick J, Russell V. Lower extremity function and normal mechanics. In: Clinical Biomechanics of the Lower Extremities, Valmassey R. St Louis: Mosby, 1996:11-2.
  11. Perry J. Gait Analysis: Normal and Pathological Function. Thorofare, NJ: Slack, 1992:76-80.
  12. Waerlop I, Allen S. Pedographs and Gait Analysis: Case Studies and Clinical Pearls. Victoria, BC, Canada: Trafford, 2006.
  13. Michaud T. Foot Orthoses and Other Forms of Conservative Foot Care. Newton Mass.: Michaud, 1993:29.
  14. Phillips RD, Phillips RL. Quantative analysis of the locking mechanism of the midtarsal joint. J Am Pod Med Assoc, 1983;73:518-22.
  15. Botte RR. An interpretation of the pronation syndrome and foot types of patients with low back pain. J Am Podiatr Med Assoc, May 1981;71(5):243-53.
  16. Zammit GV, Payne CB. Relationship between positive clinical outcomes of foot orthotic treatment and changes in rearfoot kinematics. J Am Podiatr Med Assoc, May - June 2007;97(3):207-12.
  17. Root RC, Orien WP, Weed JH. Normal and abnormal function of the foot. Clinical Biomechanics, 1977.
  18. Builder MA, Marr SJ. Case history of a patient with low back pain and cavus feet. J Am Pod Med Assoc, 1980;6:299-301.
  19. Rothbart BA, Estabrook L. Excessive pronation: a major biomechanical determinant in the development of chondromalacia and pelvic lists. J Manipulative Physiol Ther, 1988;11(5):373-9.
  20. Klingman RE. Foot pronation and patellofemoral joint function. J Orthop Sports Phys Ther, 1999;29(7):421.
  21. Ross FD. The relationship of abnormal foot pronation to hallux abducto valgus - a pilot study. Prosthet Orthot Int, August 1986;10(2):72-8.
  22. Woodford-Rogers B, Cyphert L, Denegar CR. Risk factors for anterior cruciate ligament injury in high school and college athletes. J Athl Train, 1994;29(4):343-6.
  23. Krivickas LS. Anatomical factors associated with overuse sports injuries. Sports Med, 1997;24(2):132-46.
  24. Renström AF. Mechanism, diagnosis and treatment of running injuries. Instr Course Lect, 1993;42:225-34.

Dr. Shawn Allen is a 1995 graduate of National University of Health Sciences. He practices in Westmont, Ill. For questions or comments regarding this article, contact the author at or www.homunculusgroup.com.
Dr. Ivo Waerlop is a 1996 graduate of New York Chiropractic College. He practices in Silverthorne, Colo. For questions or comments regarding this article, contact the author at www.homunculusgroup.com.


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