March 2015

Hallux valgus and plantar pressure measurement

3PressureOpeningArtBy Hank Black

Researchers and clinicians have found that plantar pressure assessment can help document the dynamic effects of hallux valgus surgery, postoperative physical therapy, and footwear or orthotic interventions, particularly in cases involving less than optimal results after surgery.

From aboriginal trackers to Robinson Crusoe and on to modern clinicians, humans have found plenty of uses for the study of pressure patterns of the plantar surface of the foot. Once skilled observation of footprints could have been a matter of life and death for the hunter and the hunted; today it tells us about foot pathology. Perhaps this started when Boy Scout founder Lord Baden-Powell suggested that scoutmasters fill an evening in camp by having their troops provide an ink footprint in part to identify those boys whose feet may have been warped by ill-fitting shoes.1

Today the ill-fitting shoes are more likely to be a woman’s narrow-toed high heels,2 and in place of the footprint in ink, modern pedobarometrists are more likely using electronic plantar pressure measurements from sensor-embedded mats and in-shoe devices.

One common current use by researchers and clinicians is in the assessment of people with hallux valgus (HV), the structural deformity of the first ray that is often associated with the development of a reactive soft tissue bunion. The incidence of HV is more than 35% of adults older than 65 years, and women are twice as likely as men to be diagnosed with the disorder. Footwear, especially high-heeled or improperly fitting shoes, is implicated in HV development.

Researchers have used pedobarometric analysis to confirm the effectiveness of a surgical intervention for hallux valgus or to compare two different interventions.

Some 25 years ago,3 pressure distribution instruments were used to describe lateral forefoot load shifts in feet with hallux valgus (HV). Five years later, a study found high-heeled shoes were associated with lower loads under the heel and increased loads under the forefoot, with the higher medial forefoot loads potentially aggravating pain in patients with HV.4

“Pressure mapping is affordable, easy to use, and fast, depending on the format you choose to use,” according to Bruce E. Williams, DPM, a past president of the American Academy of Podiatric Sports Medicine who recently became director of gait analysis studies at Weil Foot & Ankle Institute in Chicago. “The smaller pressure mats are obviously less expensive than in-shoe systems, and for hallux valgus are adequate for pre- and postsurgical evaluation. In most instances, referral to a full-option gait lab would not be necessary.”

Figure 1. Plantar pressures of a chevron bunionectomy patient show a similar pattern before (A) and after (B) surgery. (Images courtesy of Christy King, DPM.)

Figure 1. Plantar pressures of a chevron bunionectomy patient show a similar pattern before (A) and after (B) surgery. (Images courtesy of Christy King, DPM.)

Comparing surgical outcomes

Researchers commonly employ pedobarometric analysis to compare outcomes of different surgical interventions. Christy King, DPM, who practices at Kaiser Permanente in Oakland, CA, collected pre- and postoperative pressure measurements for a study comparing Lapidus arthrodesis and chevron osteotomy in people undergoing hallux valgus surgery.5

“The decision for bunion correction surgery is multifactorial, including both clinical and radiographic evaluation,” she said. “Typically, a Lapidus bunionectomy is indicated in a patient with a larger intermetarsal [IM] angle, first ray instability, hypermobility, or all three of these. Chevron osteotomy is used in those with a lesser IM angle. In our study, while both sets of patients improved clinically after surgery, we found that the plantar pressures in those who underwent Lapidus bunionectomy were distributed more evenly across the five metatarsal heads and represented more of a tripod-like stability underneath the first and fifth metatarsal heads and the heel.”

Other researchers may gather plantar pressure measures before and after a single intervention to help determine effectiveness, as Kernozek et al did in analyses of characteristics before and after various chevron-type osteotomy procedures to correct for HV.6,7

And, while there are now a large variety of bunion surgeries, clinicians are always looking for different ways of helping patients with the HV conundrum. Wong et al recently described a successful HV surgery that used soft tissues and a cerclage wire around the necks of the first and second metatarsals to realign the first metatarsal. The force data suggested that the function of the hallux was restored by the procedure.8

Figure 2. Preoperative (A) and postoperative (B) images of a Lapidus bunionectomy patient show increased load sharing of the lesser metatarsals after surgery. (Images courtesy of Christy King, DPM.)

Figure 2. Preoperative (A) and postoperative (B) images of a Lapidus bunionectomy patient show increased load sharing of the lesser metatarsals after surgery. (Images courtesy of Christy King, DPM.)

Clinical utility

Researchers appreciate the data-gathering capabilities of modern plantar pressure measurements, but practitioners may vary in how clinically useful they consider the metrics to be for hallux valgus. King, for one, does not typically collect pressure measurements for assessment of hallux valgus prior to surgery, but views it as a valuable research tool.

“While the pedographic measurement device is easy to use, the pressure measurement collection is not typically part of our preoperative protocol, primarily due to staffing and time constraints,” she said.

Erin Klein, DPM, who, like Williams, is associated with the Weil Foot & Ankle Institute, collects plantar pressure data preoperatively on all patients with hallux valgus but does not make use of it unless a postoperative complication develops.

“Plantar pressures measurements do provide a more dynamic look at how the foot functions, but I tend to focus on the common radiographic variables when I’m fixing a bunion,” she said. “Nevertheless, if the patient has postoperative pain under the metatarsal heads, particularly the second metatarsal head, we can go back to the pressure data for guidance on developing an appropriate orthosis prescription for offloading that area.”

Williams said that correction of abnormal pressure distribution is vitally important in restoring overall foot and lower extremity function and symmetry. However, surgical intervention alone does not always result in a change in pressure pattern, particularly in cases involving unstable medial columns that rarely are associated with high pressures either pre- or postsurgery.9

“Simply reducing the angle of the hallux valgus deformity, although greatly beneficial to the patient, will not necessarily change the overall sagittal plane structure of the first ray or the stiffness of the first ray enough to change the pressure patterns,” Williams said. “However, most patients with bunions obtain pain relief and reduction of their angular deformity with bunion surgery regardless of the overall pressure pattern and whether or not the pattern has changed.”

bunion_bootie

Plantar pressure assessment can be useful in patients who do not experience optimal results after surgery, Williams said, particularly in determining the effect of an orthotic or footwear intervention.

“When I have tested patients who have complaints after bunion surgery, I can usually benefit them by modifying a custom foot orthotic for them that will improve their overall pressure profile and the timing of their force versus time curve,” he said.

Similarly, researchers have used pressure measurements to help assess whether foot orthoses can decrease pain associated with hallux valgus by offloading elevated medial forefoot pressures. In a 2014 Iranian publication, Farzadi et al used an in-shoe system to evaluate a medial arch support orthosis worn by female patients with mild-to-moderate hallux valgus. They found that the orthosis could reduce pressure under the hallux and first metatarsal head by transferring the load to the medial midfoot region.10

Klein, a clinical instructor of podiatric surgery at the William M. Scholl College of Podiatric Medicine in Chicago, collects mat-based plantar pressure measurements as part of her normal preoperative hallux valgus protocol, primarily with an eye toward using the data in retrospective outcomes studies.

“I don’t necessarily analyze the measurements before surgery, but they can be helpful if there is a complication postoperatively, such as when over-shortening of the metatarsal occurs following the Scarf osteotomy,”11 she said. “In that case, the plantar pressure measurements taken before surgery can augment x-rays in determining how to alter our prescription of orthoses.”

Differing results

Reports of subhallux pressure in people with HV have been inconsistent, with studies variously reporting reduced loading, increased loading, or no change in pressure at that site.12-14 Some of this inconsistency may be related to the different technologies used to assess plantar pressures in different studies, Williams said.

“Most studies [before and after] bunion surgery use pressure mats to evaluate the pressures. If an in-shoe pressure system were used instead of or in combination with a mat, a demonstrated change in pressure would be more likely, depending on the shoe worn and whether a custom foot orthotic was used during the testing as well,” he said. Some of the discrepancies in study outcomes may be explained by the progressive nature of the disease. In an analysis of how the magnitude and distribution of forefoot plantar pressures correspond with clinical and anthropometric determinants in mild disease, Martinez-Nova et al found significantly increased pressures under the hallux due to deviation of the first ray.12 Hurn et al, in a study published this year and also utilizing an in-shoe device, found no significant differences in plantar pressures between individuals with mild HV and controls, but did find that greater HV severity was associated with reduced loading under the hallux.14

Klein said she believes plantar pressure measurements to evaluate HV might be utilized more if the literature showed a more consistent correlation between plantar pressures and dysfunction.

“Many studies lack a description of the postoperative surgical and rehabilitation protocol, which plays an important role in outcomes. I’d like to see more single-surgeon, single-procedure studies with described and more standardized postoperative rehabilitation protocols, since there are many ways to fix hallux valgus and many variations in the postoperative protocols,” she said. “There’s also a need for a better way to standardize masks for plantar pressure zones to assure consistency within different sized feet.”

Marian Hannan, DSc, MPH, associate professor of medicine at Harvard Medical School in Boston, said inconsistent findings may result from small sample sizes in many studies along with failure to take into consideration coexisting foot disorders, degree of HV severity, and the age of participants.

“All of the studies are informative, but usually are looking at different parts of the elephant,” Hannan said.

Published studies of subhallux pressure in people with hallux valgus have been inconsistent, variously reporting reduced loading, increased loading, or no change in pressure at that site.

Framingham foot study

Hannan, who is also editor of Arthritis Care and Research, led a vast, population-based study of hallux valgus that was published in 2013.15 Her research group recruited 3205 participants from the Framingham Foot Study and collected biomechanical data on both feet for almost every participant. Those with HV (defined as a 15° or greater abduction of the hallux) were assigned to one of two groups, one with HV only and one with HV plus at least one additional foot disorder. A third group had no HV but at least one other foot disorder, and a reference group had no foot pathology. Using a pressure mat, the researchers found that, compared with the reference group, participants with HV had lower hallucal loading and higher forces at the lesser toes, and those with HV and another foot disorder also had abnormal rearfoot forces and pressures.

“It is a cross-sectional study, but it’s my suggestion that HV can change how a person walks, putting them at greater risk for other foot disorders,” Hannan said. “Our participants with HV, whether they had concurrent foot disorders or not, had a lower center of pressure excursion index, which we expect to see clinically in people with HV. However, they also had a higher arch as measured by the modified arch index [MAI]. That was contrary to what we were expecting, as typically HV is associated with a lower MAI.”16

The Framingham cohort is largely urban or suburban, white, and older. Hannan’s group is completing data collection on a similar study of HV and plantar pressure loading that involves about 2000 people in North Carolina, of whom one-third are African American.

“We will be interested to see how this rural, younger, and more racially diverse group differs from the Framingham group in regard to hallux valgus. We know, for example, that African Americans typically have lower arches than Caucasians,17 so that aspect will be especially interesting to follow,” she said.

Hannan hopes to secure funding to undertake a longitudinal study of both the Framingham and North Carolina cohorts.

“We want to look at them over three to five years and be able to describe any functional and structural changes that may be due to hallux valgus,” she said.

Therapy after intervention

Postoperative rehabilitation after hallux valgus surgery is increasingly being viewed as important for recovering physiological gait and foot function, 18 and plantar pressure measurement can confirm improved weightbearing after corrective bunion surgery. 19 Schuh et al evaluated plantar pressure in 29 patients with mild to moderate HV who had undergone chevron osteotomy, with half of them receiving physical therapy after surgery. They determined that physical therapy was able to increase the hallux plantar pressure to more normal values when compared with baseline levels, supporting the use of early first metatarsophalangeal joint range of motion exercises.19

“Many patients start asking when they can play sports and run. If patients don’t have sufficient motion in the big toe, their gait is altered. This can lead to changes in the pressure mapping of their feet,” Klein said.

Klein sees a possible role for the use of plantar pressure monitoring in physical therapy following HV surgery, particularly in the area of gait analysis.

“Pressure measurements could provide a new way of monitoring improvement if the therapist uses it periodically,” she said. “Initially, postoperative patients may walk with more lateral pressure because they are afraid to put their big toe on the floor or move their big toe. Pain may be a component of this as well. Over time the function of the hallux will normalize and strengthen, providing propulsion. This should normalize over the course of physical therapy.”

Pedobarometric analysis may also provide a way to influence patient satisfaction. The National Institutes of Health and specialty societies are placing a greater emphasis on collection of patient-based outcome measures in addition to clinical outcomes.

“We could show patients how pressure measures change pre- to postintervention. We show them x-rays before and after, so it would be an interesting concept to add the pressure data, too,” Klein said. “I am not quite sure if there is any connection, but patient perception of outcome is a complex and multifaceted issue. Pedobarometric measurements may be a part of this.”

Hank Black is a medical writer in Birmingham, AL.

REFERENCES
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  2. Hennig EM. Foot measurements. In: Goonetillake RS, ed. The Science of Footwear. Boca Raton; CRC Press; 2012.
  3. Blomgren M, Turan I, Agadin M. Gait analysis in hallux valgus. J Foot Surg 1991;30(1):70-71.
  4. Nyska M, McCabe C, Linge K, et al. Plantar foot pressures during treadmill walking with high-heel and low-heel shoes. Foot Ankle Int 1996;17(11):662-666.
  5. King C, Hamilton GA, Ford LA. Effects of the Lapidus arthrodesis and chevron bunionectomy on plantar forefoot pressures. J Foot Ankle Surg 2014;53(4):415-419.
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  9. Clough JG. Functional hallux limitus and lesser metatarsal overload. J Am Podiatr Med Assoc 2005;95(6):593-601.
  10. Farzadi M, Safaeepour Z, Mousavi ME, Saeedi H. Effect of medial arch support orthosis on plantar pressure females with mild-to-moderate hallux valgus after one month of follow distribution in -up. Prosthet Orthot Int 2014 Feb 10. [Epub ahead of print]
  11. Weil L Jr, Bowen M. Scarf osteotomy for correction of hallux abducto valgus deformity. Clin Podiatr Med Surg 2014;31(2):233-246.
  12. Martinez-Nova A, Sanchez-Rodriguez R, Perez-Soriano P, et al. Plantar pressures determinants in mild hallux valgus. Gait Posture 2010;32(3):425-427.
  13. Mickle KJ, Munro BJ, Lord SR, et al. Gait, balance and plantar pressures in older people with toe deformities. Gait Posture 2011;34(3):347-351.
  14. Hurn SE, Vicenzino, B, Smith MD. Functional impairments characterizing mild, moderate, and severe hallux valgus. Arthritis Care Res 2015;67(1):80-88.
  15. Galica AM, Hagedorn TJ, Dufour AB, et al. Hallux valgus and plantar pressure loading: the Framingham foot study. J Foot Ankle Res 2013;6(1):42.
  16. Schoenhaus HD, Cohen RS. Etiology of the bunion. J Foot Surg 1992;31(1):25-29.
  17. Dunn JE, Link CL, Felson DT. Prevalence of foot and ankle conditions in a multiethnic community sample of older adults. Am J Epidemiol 2004;159(5):491-498.
  18. Schuh R, Hofstaetter SG, Adams SB Jr, et al. Rehabilitation after hallux valgus surgery: Importance of physical therapy to restore weight bearing of the first ray during the stance phase. Phys Ther 2009;89(9):934-945.
  19. Schuh R, Adams S, Hofstaetter SG, et al. Plantar loading after chevron osteotomy combined with postoperative physical therapy. Foot Ankle Int 2010;31(11):980-986.
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