Can Scaling Theory Aid In Charcot Foot Reconstruction In Obese Patients?

Andrew J. Meyr, DPM, Kelly Pirozzi, DPM, and Corine Creech, DPM

   These findings underscore the incredible difficulty we have dealing with soft tissue loss of the plantar calcaneus. This area is challenging to offload and attempts to surgically reconstruct this tissue with autograft and allograft techniques are relatively ineffective unless one can restore sensate and structured plantar soft tissue. Graviportal findings point toward the incredible importance of the structure, function and maintenance of the plantar soft tissue, particularly about the calcaneus. Significant tissue loss from this location in humans may represent a contributing attribute to an “unsalvageable” limb in the obese, neuropathic patient with diabetes.

How Scaling Theory Relates To Beaming Technique For Charcot

In the graviportal osseous structure of animals, an immediate relative equinus deformity is present in comparison to the human osseous structure. Graviportal animals compensate for equinus with a tripod configuration within the metatarsals/forefoot. In comparison to other quadrupeds, all graviportal metatarsals are oriented more horizontally to the weightbearing surface. The second, third and fourth metatarsals serve as the primary supports while the first and fifth metatarsals are oriented slightly more vertically. Interestingly, the third metatarsal is the longest and the lateral metatarsals are relatively thicker in comparison to the medial metatarsals. Additionally, strong soft tissue structures rigidly anchor adjacent metatarsals to each other.

   When it comes to surgical reconstruction, these findings may correspond to the relative recent success of the medial and lateral column beaming technique for surgical deconstruction of midfoot Charcot neuroarthropathy.8,9 This may be particularly true when one performs the procedure in conjunction with arthrodesis of the subtalar joint to further exaggerate a tripod configuration of the human foot, which is inherently present in graviportal animals.

   The length of the third metatarsal and relative thicknesses of the lateral metatarsals are also interesting when considering the human metatarsal parabola. We tend to think of human biomechanics as a transfer of weight across the metatarsals in a lateral to medial orientation with the first being the thickest and extending the farthest distally as weight transfers through the first metatarsophalangeal joint during propulsion. This graviportal construct appears to accept and distribute more weight laterally and centrally during this process.

What The Graviportal Tendinous Structure Reveals About Offloading The Diabetic Foot

Further differences are present within the tendinous structures of graviportal animals. The tendons of pronation/supination are reduced with decreased thicknesses and insertions that are actually more consistent with flexion/extension. Another interesting finding is that the Achilles tendon is of a very small size and represents a small relative percentage of lower leg musculature in comparison to other animals.

   These findings may further support arthrodesis of the rearfoot and midfoot complexes with elimination of motion and the creation of a relatively stiff plantigrade structure. The pronatory/supinatory movements of the subtalar and midfoot joints may be paradoxically less necessary as body mass increases if motion transitions more closely to purely flexion/extension.

   It is also interesting to consider these tendinous findings when studying the relative successes and failures of offloading devices for the diabetic foot. Research has found that devices such as total contact casting and below-knee cast boots that immobilize the ankle and are better able to decrease subtalar joint range of motion are superior to those devices (surgical shoes and diabetic shoes) that allow for more motion at these joints.10

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