Cadaveric Analysis of Plantar Fascia Tension and Windlass Mechanism and Development of Plantar Fascia-Specific Stretching Device
Authors: Momenzadeh Kaveh , Williams Caroline , Williamson Patrick M. , Kwon John Y. , Nazarian Ara , Miller Christopher P. 
Published: January 2022

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Introduction/Purpose:

Plantar fasciitis is the most common cause of heel pain in adults, affecting 1 out of 10 of the population at some point during their lifetime. Plantar specific stretching programs are popularity among foot and ankle surgeons consisting of passively dorsiflexing foot and using thumb to apply pressure. This technique is not without limitations. Certain patients are unable to properly perform the stretching techniques, such as limited mobility from advanced age, disability, or simply from performing stretching exercises incorrectly. The aims of this study are; first, identify what configuration of plantar-specific stretching combined with applied pressure to the plantar aponeurosis generates the greatest tensional force in the plantar fascia. And second, to construct a prototype device that could simulate these forces in a hands-free technique.

Methods:

Six (will be 10) fresh-frozen, morphologically normal cadaver feet (Medcure, RI) were utilized. Plantar fascia was exposed, ankle was fixed at 90-degree dorsiflexion using Calcaneo-Tibial Schanz Pin, specimen was then inverted and potted in a custom-made box (Smooth-Cast 300q, PA). Using an electromagnetic motion tracking system (Liberty, Polhemus, VT), the motion of sensors was recorded at 120 Hz. Utilizing tissue adhesive glue (Vetbond, 3M, Minnesota), the first sensor was attached to medial calcaneal tuberosity, and the second sensor was placed 5 cm distal to the first sensor on the plantar aponeurosis. Custom- built testing apparatus was made for induction of MTP dorsiflexion application of pressure on the plantar aponeurosis to mimic current conservative treatments. Weights were added to the custom build stretcher device in 10Lb increments. Strain percentage was calculated as the change in length divided by the baseline length position (condition 1) using the formula: ([L − Lo]/Lo) × 100

Results:

Dorsiflexion of 2nd-5th MTPs increases strain percentage more in comparison with 1st MTP dorsiflexion (Condition 3>4>2). This might show that dorsiflexing of 1st metatarsal is less effective at straining the plantar fascia because of the midfoot motion. By adding thumb pressure, strain percentages go higher, up to a point that in condition 7 (dorsiflexing all MTPs in combination of thumb pressure) it is significantly higher than our baseline condition (P=0.0385). It is noteworthy that, stretcher device itself (condition 8), cannot replicate conditions 4 or 7 strain percentages. When adding direct pressure and weight to the stretcher device (conditions 12 and 13), strains are even higher than condition 7 and also are significantly higher than the baseline (P= 0.0090 and 0.0291 respectively).

Conclusion:

The stretcher device itself is insufficient for stretching the plantar fascia, supporting the hypothesis of this study that we need a direct forceful pressure on the plantar aponeurosis as well. Our customized plantar stretcher not only can replicate the conventional stretching program, but also can produce higher strains on the plantar aponeurosis than the current manual application of plantar specific stretching. This device may impact the rehabilitation process in patients with advanced age as well as patients with spine mobility limitation who cannot perform manual stretching programs.