Secrets To Biomechanical Considerations In Static Stance

Author(s): 
Guest Clinical Editor: Nicholas Sol, DPM, CPed

   Evaluating biomechanics in static stance poses unique challenges because of the differences between static stance and dynamic gait. In addition, one must take the occupation of patients into account when modifying orthotics for patients who spend a significant amount of weightbearing time in static stance. That said, let us take a closer look at what these expert panelists have to say on the subject.    Q: What are the key differences between approaching the biomechanics of static stance and dynamic gait?    A: Podiatry schools and most literature on biomechanics use dynamic gait as a model, says Milton Stern, DPM. As a result, he says DPMs have an awareness of how the foot interacts with the surface below it from heel strike through toe off. Likewise, he says DPMs know what muscle and tendon groups are active during each phase of ambulation and what an orthotic tries to control during each phase of gait.     “It has always been my belief that an orthotic controls heel strike and then foot motion,” comments Dr. Stern. “Additions to an orthotic can control secondary conditions such as metatarsalgia, different painful foot syndromes and excessive pronation.”    During static stance, Dr. Stern says one doesn’t see the normal heel to toe gait with associated muscle activity. Instead, muscle and tendon complexes control basic balance. The entire plantar surface makes more contact with the weightbearing surface, according to Dr. Stern. In static stance, Dr. Stern notes patients are using agonist-antagonist muscle groups at the same time. He also points out the peroneal complex counteracts the tibialis anterior and posterior, which provides mid-stance stability from side to side. To a lesser degree, Dr. Stern notes the anterior group opposes the posterior group to control front to back stability.    Static stance represents only a small percentage of the gait cycle, according to Anthony Borgia, DPM. However, he says static stance is still important since it initiates the dynamic phase of gait.    It is vital to avoid treating faulty biomechanics of static stance with the same treatment paradigms one uses for dynamic gait, according to Nicholas Sol, DPM, CPed. While a patient may have one or two characteristic gait patterns, Dr. Sol says he or she may have over 30 different standing postures. He recommends a strong emphasis on surface materials, sole materials, the shoe construct and the orthotic-shoe interface when correcting static stance pathomechanics.    Q: How do the pathomechanics of static stance affect the biomechanics of dynamic gait?    A: Dr. Sol commonly hears patients complain of joint stiffness as an effect of static stance. He believes this results from constant pressure between opposing joint surfaces, which causes a proportionate net loss of water from proteoglycan binding. Therefore, the articular cartilage loses some elasticity and its ability to resist mechanical loading and shear. Dr. Sol suspects that mechanical injury occurs in part because the “dehydrated” surface cannot function normally during ambulation.     “I suspect that the inclusion of glucosamine sulfate supplements is as beneficial for these patients as it can be for those with pathomechanics of dynamic gait,” says Dr. Sol.    If a patient has a flexible collapsing midfoot in static stance, Dr. Borgia says one can assume the patient has shortened posterior musculature (i.e. equinus). This leads to a shorter stride, according to Dr. Borgia, and it explains why the posterior leg muscles fatigue faster than if the foot were more arched. Dynamically, the foot will not flow from heel to toe and Dr. Borgia says this alters a patient’s gait accordingly as it takes the patient more steps to get from one point to another.

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