By P.K. Daniel
Windlass mechanism impairment is evident in patients with diabetic neuropathy and could contribute to increased plantar pressures and ulceration risk, according to research from the Washington University School of Medicine in St. Louis, MO.
The windlass mechanism allows the arch to move and be flexible, which helps to add stability to the foot. The essence of the principle is the shortening of the plantar fascia from hallux dorsiflexion during stance.
“It helps to maintain stability,” said David R. Sinacore, PT, PhD, who is the associate director of Postdoctoral Fellowships in Physical Therapy and professor of physical therapy at the university. “As we walk or confront uneven surfaces, the mechanism allows the foot to respond and function.”
Sinacore and colleagues studied individuals with diabetes mellitus and peripheral neuropathy (DMPN) as well as low medial longitudinal arch (MLA) height. The researchers defined low MLA as the presence of at least two of four criteria: navicular height less than 24 mm, arch index less than .263, longitudinal arch angle less than 130°, and weight-bearing calcaneal eversion greater than 5°.
Twelve participants with DMPN and low MLA and 12 healthy controls with normal MLA received weight-bearing radiographs in toe-flat and toe-extended positions. The study utilized these static measurements to imply dynamic function of the foot.
“It was our best attempt to take something dynamic and turn it into a static measurement that we could do with radiographs,” said study coauthor Mary Hastings, DPT, MSCI, a researcher at the Diabetes Research Center (DRC) and assistant professor of physical therapy and orthopedic surgery at the university.
The researchers obtained six radiographic measures of arch position for each patient and assessed whether each measure changed when the patient shifted from the toe-flat position to the toe-extended position. They categorized patients with DMPN into “severe” and “low” groups based on the extent of tarsal joint deterioration evident on radiographs.
Both DMPN groups demonstrated windlass mechanism impairment, manifested as an impaired ability to raise the arch from the toe-flat to toe-extended position compared to the control group. The DMPN severe group showed no change in alignment for half of the six radiographic measurements. The DMPN low group demonstrated change in five measures, and the control group was able to raise the arch in all six.
“It’s still intact, it’s just that it is impaired,” Sinacore said of the low and severe groups.
Hastings said the structural impairment in the severe group may have exacerbated the poor functioning of the plantar fascia.
“We do see some progression of [windlass mechanism] dysfunction here,” Hastings said. “The severe group also has bony changes. That may be part of why they don’t function as well.”
The findings, which were epublished by Foot & Ankle International on June 10, suggest that early identification of windlass mechanism impairment could potentially allow clinicians to prevent or delay joint deterioration, but Hastings noted that diabetic neuropathy is multifactorial.
“I think the windlass mechanism is just one part contributing to deformity,” Hastings said. “Perhaps if you could identify it earlier, you could prevent or delay it.”
Researchers also have yet to determine which comes first—the deformities or the change in the windlass mechanism. Further research is needed to examine the contribution of specific windlass mechanism components.
“That’s a chicken and egg thing,” Sinacore said. “In other words, we don’t really know what comes first.”
Intervention or compensation for an impaired windlass mechanism can involve orthotic devices, footwear modifications, or physical therapy. Hastings said tendon-lengthening surgery to increase toe and ankle range of motion also is a consideration.
“I think there are compensatory strategies that might be helpful, and there might also be some interventions to change some of the forces,” Hastings said. “The neuropathy, however, adds a critical component in that patient feedback does not provide insight about whether the intervention is working to relieve stress on the foot structures. Close monitoring of alignment would be required to prevent deformity onset [and] progression.”
Gelber JR, Sinacore DR, Strube MJ, et al. Windlass mechanism in individuals with diabetes mellitus, peripheral neuropathy, and low medial longitudinal arch height. Foot Ankle Int 2014 Jun 10. [Epub ahead of print]