Secrets To Biomechanical Considerations In Static Stance
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. This effect leads to an increased risk of symptomatology, according to Dr. Borgia. The forces of weightbearing in a normal foot would translate through the osseous structures with the windlass effect in motion. Dr. Borgia says the windlass effect provides a stable push-off, permitting the peroneal longus to plantarflex the first ray. He notes this effect stabilizes the subtalar joint and equalizes forces throughout the anatomical trabecular patterns of the foot. However, Dr. Stern says the pathomechanics of static stance should not have much of an effect on the biomechanics of dynamic gait. “Chronic use of the muscles to control balance in static stance should not affect their function and use in dynamic gait unless patients develop some kind of tendon problem like posterior tibial tendonitis,” contends Dr. Stern. Q: In your experience, what are the most common pathomechanics associated with static stance? A: Dr. Sol says it is common for patients to have joint stiffness, which often leads to secondary complaints associated with compensatory gait mechanics. When patients have stiffness in one lower extremity, Dr. Sol says they will typically compensate with a decreased support phase and increased swing phase in the symptomatic lower extremity and a correspondingly longer support phase in the opposite lower extremity. He notes this leads to relative overuse of the asymptomatic limb. These patients frequently present with unilateral pain in the overused limb and Dr. Sol says he often winds up treating the contralateral limb. When it comes to static stance pathomechanics, Dr. Borgia commonly notes complaints secondary to a collapsing arch. He says these complaints may evolve into posterior tibial tendon dysfunction, plantar fasciitis or Achilles tendonitis, which may lead to degenerative joint disease of the subtalar joint complex if left untreated. Static stance can vary depending on a patient’s occupation and different types of shoes can affect stance, according to Dr. Stern. For example, when patients who work on automotive assembly lines present to his office, Dr. Stern typically sees heel pain syndromes beyond just plantar fasciitis. He also sees heel bursitis, which patients experience when they are wearing hard-soled shoes and standing in place. Posterior tibial tendonitis and subsequent chronic posterior tibial tendon dysfunction (PTTD) are also problematic in patients who work on assembly lines. Dr. Stern says these conditions are caused by chronic use of the hard-soled shoes and compensations for trying to control the stability of the foot in static stance. When treating patients who work as greeters at a casino and wear heels, Dr. Stern sees some heel pain but less than he sees in an auto worker. He adds that he also sees some posterior tibial tendonitis in these patients. However, in Dr. Stern’s experience, the most common presentation in casino greeters is metatarsalgia, including neuroma-like symptoms and capsulitis, especially on the second MPJ. Q: What specific orthotic modifications do you incorporate for patients who spend a significant portion of weightbearing time in static stance? A: If a patient’s pathology is not that severe, Dr. Borgia uses a flexible type orthotic and gradually adds medial reinforcement as necessary. He opts for 1 to 2 degrees of rearfoot posting since he notes that more varus posting would increase the likeliness of the patient straining the Achilles. To prevent Achilles tendonitis, Dr. Borgia uses a 1/8- to 1/4-inch heel lift. He notes that patients with severely pronated feet do not tolerate rigid or semi-rigid orthotics, even when their feet are flexible, especially if body weight is a factor. For patients who are in static phase for a significant part of weightbearing time, Dr. Borgia will use a high density foam or a multicork and leather orthotic with a higher medial flange. In general, he will use a very inexpensive combination sport mold made of vinyl Styrene/Butadiene/Resin (SBR) and see these patients for three or four weekly visits. During these visits, Dr. Borgia says he gradually incorporates adhesive foam into the arch, which controls its height, and also posts the orthotic according to the patient’s specific need for control. At the last visit, he normally increases the heel height to a 1/8-inch foam adhesive pad in order to diminish pull on the Achilles. He emphasizes stretching exercises in the posterior muscle group during and after treatments. Temporary orthotics, which last over a year, cost patients about $30 and cost DPMs less than $12 for materials, notes Dr. Borgia. Dr. Sol advises emphasizing increased frequency of weight shifting and accommodation of ground reactive forces when correcting pathomechanics of static stance. For a patient without equinus or limb length discrepancy, he often uses a small heel lift of about 1/16-inch on both orthotics. For those with limb length discrepancy and/or equinus, Dr. Sol says he often intentionally overcorrects. In some of these cases, Dr. Sol notes he will adjust the heel lifts to a slightly undercorrected modification. Such an adjustment addresses joint stiffness by inducing more frequent left-to-right and front-to-rear weightbearing shifts. For these patients, he says one should stay aware of any changes in postural complaints, such as low back pain, and tailor modifications accordingly. As far as accommodating ground reactive forces, Dr. Sol notes one may need extra cushioning above and/or below the orthotics. If there is limited space in the shoe, he often uses a cushion insole under the orthotic and an accommodative forefoot extension that molds to the shape of the forefoot. Dr. Sol points out that left and right feet require different combinations of modifications. Dr. Stern says orthotic modifications depend on patients’ occupations. He notes a patient working on an assembly line requires support in the side-to-side plane to help stabilize the foot in static stance. Accordingly, one should try to control the heel position, the amount of lateral movement and any areas of pain such as heel bursitis or metatarsalgia, according to Dr. Stern. For these patients, he suggests employing a medial Shaffer plate to control abnormal side-to-side motion and a deep-seated heel cup to control rearfoot motion. Dr. Stern adds that a deep-seated heel cup will control rearfoot motion while a heel cutout filled with absorbent material can control heel bursitis. He notes that one can accommodate specific forefoot pain with a metatarsal pad or cutouts for specific areas. Dr. Sol founded the Walking Clinic, PC and practices in Colorado Springs, Col. He is a Fellow of the American College of Foot and Ankle Surgeons, and a Fellow of the American College of Foot and Ankle Orthopedics and Medicine. Dr. Borgia is Chief of the Podiatric Section, Department of Surgery, at University Medical Center in Las Vegas, Nev. He is a Fellow of the American College of Foot and Ankle Surgeons and a Diplomate of the American Board of Podiatric Surgery. Dr. Stern is a Fellow of the American College of Foot and Ankle Surgeons and a Diplomate of the American Board of Podiatric Surgery.