Fig. 1 A. Biomechanics of the axial bolt (beaming) technique. The bolt becomes a load-sharing device, much like a rebar in concrete. B/C. Postoperative radiograph of a Charcot midfoot dislocation repaired with the intraosseous bolt-and-nut construct for compression. Pinzur, M, Sammarco, VJ, Wukich, D. “The Charcot Foot: A Surgical Algorithm” In Volume 61 pages 423-440, American Academy of Orthopaedic Surgeons 2012 (Video Technique by VJS)

AAOS Now

Published 4/1/2018
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V. James Sammarco, MD

'Superconstructs' for Charcot Midfoot Dislocation

The treatment of midfoot fractures and dislocations in patients with diabetic neuropathy continues to pose challenges for the orthopaedist. Diabetes affects more than 250 million people worldwide and about 26 million Americans. The prevalence is estimated to have increased by greater than 15 percent since 2005 and the numbers continue to grow.

The complications of diabetes on the foot are profound. Peripheral sensory neuropathy leads to ulceration; in addition, the disease affects autonomic and motor neurons. Autonomic neuropathy can lead to drying and cracking of the skin, edema from venous stasis, and hyperemia of the limb with only minor trauma. Motor neuropathy can lead to contracture of the Achilles and other tendons, often resulting in progressive and rigid deformities of the foot and ankle. The combination of an insensate foot with significant deformity will often lead to intractable ulceration of the foot.

Deep infection can often develop in an untreated neuroarthropathic foot. These infections can extend beyond the soft tissues and into the osseous structures. Complications from diabetes are the most common cause of amputation in the United States; more than 60 percent of the 185,000 amputations in the United States are due to complications of diabetes.

Traditional treatment
Treatment strategies for the Charcot foot have evolved significantly during the past 10 years. Traditional treatment for the neuropathic foot dislocation has been to cast the foot during the initial phases of the Charcot process to try to control foot shape, then to treat residual deformity with accommodative bracing. This treatment is often effective and still offers a high success rate for many patients. If the foot remains plantigrade, this may be all that is needed. Residual bony prominence causing ulceration can be often treated with simple ostectomy.

Studies in the early 2000s questioned the validity and appropriateness of an indefinite nonsurgical approach for all cases. Although some patients do well with the standard nonsurgical approach, a subset of patients does not achieve a plantigrade, stable foot. Some patients continue to ulcerate despite expert treatment with bracing.

One study reviewed 115 patients (127 feet) with Charcot disease who were treated from 1983 to 2003. These patients were treated with a structured, standardized clinical protocol that emphasized nonsurgical care. The annual rate of amputation was 2.7 percent, the risk for extensive bracing that lasted more than 18 months was 47 percent and the risk of recurrent ulceration was 40 percent.

Another study of 15 patients who received conservative treatment used serial radiographs to measure progression of deformity over a two-year period. Researchers noted that progression of deformity first occurred in the medial column, then progressed into both columns, with worsening of all radiographic parameters during the two-year period. A report on early surgical treatment of 14 patients with Charcot midfoot deformity who were treated in Eichenholtz stage I disease found that correction of deformity and midfoot arthrodesis enabled all patients to return to a functional ambulatory status with standard diabetic and off the shelf shoewear. These studies suggest that a more active role in deformity correction by arthrodesis of the involved limb is beneficial to some patients.

What is a “Superconstruct”?
Reconstruction of Charcot foot deformity presents a significant challenge to the treating surgeon. Not only are extended healing times expected, but the Charcot process, the result of both sensory neuropathy and sympathetic denervation, leads to hypervascularity of the foot during the acute phase. Pathologically increased blood flow results in resorption of calcium and the development of osteoporosis in the area of the neuropathic fracture. Fixation in this area of “dissolution” is often not possible due to the poor mechanical qualities of this bone. Modern fixation techniques attempt to span the area of dissolution and to achieve fixation in less affected bone both proximally and distally.

A “superconstruct” describes techniques that prioritize stability and correction of deformity over sparing fusion segments. A superconstruct is defined by the following four factors:

  1. Fusion is often extended beyond the zone of injury to include joints that are not affected to improve fixation.
  2. Aggressive bone resection is performed to shorten the foot to allow for adequate reduction of deformity without undue tension on the soft tissue envelope.
  3. Stronger, thicker metal implants are used to avoid implant breakage.
  4. The positioning of the devices maximizes their mechanical stability through load sharing with the osseous structures.

Two techniques that have been developed to correct Charcot midfoot deformity are plantar plating and axial screw fixation (beaming).

Fig. 1 A. Biomechanics of the axial bolt (beaming) technique. The bolt becomes a load-sharing device, much like a rebar in concrete. B/C. Postoperative radiograph of a Charcot midfoot dislocation repaired with the intraosseous bolt-and-nut construct for compression. Pinzur, M, Sammarco, VJ, Wukich, D. “The Charcot Foot: A Surgical Algorithm” In Volume 61 pages 423-440, American Academy of Orthopaedic Surgeons 2012 (Video Technique by VJS)
Fig. 2 A. Biomechanics of plantar plate fixation. Load applied to the foot places the plate under tension and compresses the fusion site. B. Postoperative radiograph of a Charcot foot repaired with the plantar plating technique. Pinzur, M, Sammarco, VJ, Wukich, D. “The Charcot Foot: A Surgical Algorithm” In , Volume 61 pages 423-440, American Academy of Orthopaedic Surgeons 2012 (Video Technique by VJS)

Axial screw fixation
Axial screw fixation of foot fusions refers to the placement of long intraosseous screws or bolts that span the area of dissolution and fix the proximal and distal fusion segments. Distally, the screws are placed in the intramedullary canals of the metatarsals in the involved columns. Proximally, they can extend as far as the talus and/or calcaneus as needed. The technique creates a mechanical construct similar to reinforced concrete, where multiple axial screws act as “rebar” to improve distribution of the tensile and compressive forces generated by weight bearing (Fig. 1: A, B, and C).


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Biomechanically, the screws function as load sharing devices to achieve fixation proximally and distally to the zone of neuropathic bone. The technique was initially performed using large-diameter cannulated compression screws. Now, however, procedure-specific devices are available, reducing implant failures. Newer devices are more robust and, unlike bone screws, are designed to resist three-point bending along their horizontal axis. One device offers an intraosseous nut to achieve compression in poor quality bone.

Fusion procedures can be performed through a more limited approach with less osseous stripping than is needed for plating or other open techniques. Intraosseous positioning of the hardware diminishes the risk of infection in the event of poor wound healing. Axial fixation has been tested biomechanically and has proven to be a sound and robust method for achieving fixation. Two clinical studies of axial fixation techniques report good clinical results and a high rate of limb salvage.

Plantar plate fixation
The concept of using plates to achieve fixation for midfoot fusions is not new. Plate fixation has distinct advantages over simple lag screw compression in that longer plates can be used and fixation extended proximally and distally to achieve stable bone fixation away from the zone of neuropathic bone. Locking plate/screw constructs offer more stability in osteoporotic bone than their non-locking counterparts.

Credit for developing the concept of plantar plate fixation for arthrodesis of Charcot midfoot dislocation must go to Lew C. Schon, MD. He noted plantar plate application would create a stronger construct because weight bearing would place the plates under tension. Any deformation of the plate would then tend to compress the fusion site (Fig. 2: A and B). This provides both mechanical and biological benefits for osseous healing. In addition, a plate applied plantarly becomes a load-sharing device with weight bearing.


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Mechanical studies have validated this concept.  A study of 34 patients who underwent midfoot arthrodesis for Charcot foot disease found that the deformity was successfully corrected and eventual arthrodesis was achieved in all patients.

Conclusion
Charcot foot disease is a debilitating condition that requires aggressive treatment to prevent progression. Complications leading to amputation can be devastating to patients. Conservative management is often effective, but the progression of the disease may require surgical reconstruction with realignment and arthrodesis. Furthermore, newer techniques and devices offer promise for more successful surgical outcomes.

V. James Sammarco, MD, is a fellowship trained foot and ankle specialist at OrthoCincy in Cincinnati, Ohio, and is a member of the AAOS Now Editorial Board. He has clinical and research interests in the surgical correction of diabetic and neuroarthropathic foot and ankle deformity.

References

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