Hexapods In Charcot Surgery: Current Concepts

For patients with Charcot neuroarthropathy, hexapod frames can be valuable in reconstructive surgery, offering gradual correction and realignment as well as quick post-op weightbearing. These authors discuss when and how to use hexapods for Charcot external fixation, and offer two compelling case studies.

Charcot neuroarthropathy is a challenging condition, which one can treat with and without operative intervention. The debilitating disease typically leads to a loss of normal pedal architecture, gait dysfunction and soft tissue compromise, often resulting in complex foot and ankle deformity.¹ If one chooses surgical intervention, the goal of surgical reconstruction for the Charcot foot is to create a stable plantigrade foot that is braceable for prolonged community ambulation.²

When one is considering surgical intervention, the clinical exam should evaluate for stability between the medial and lateral columns as well as the forefoot, midfoot, hindfoot and ankle segments. Adequate perfusion to the limb is a necessary component prior to any surgical intervention. One must address medical optimization and glycemic control with the interdisciplinary team that is involved in the patient’s care.

Also note the presence of partial to full-thickness wounds. Attempting to heal open wounds is ideal but not necessary prior to surgical intervention. Infected wounds pose a more complicated pre- and postoperative course, but do not eliminate the option of surgical correction.  

When To Incorporate Hexapod Frames In Charcot Reconstruction

External fixation in Charcot corrective surgery has proven to be beneficial in patients with the following indications:¹

• Soft tissue ulceration (with or without infection)
• Bony defect (with or without osteomyelitis)
• Instability of the ankle, hindfoot and/or midfoot
• Ambulatory dysfunction that cannot be corrected with bracing

Surgeons have utilized hexapods successfully for various types of complex foot and ankle conditions. Charcot joints of the foot and ankle pose a complex bony and soft tissue challenge. Hexapods can be beneficial in many Charcot joint cases by facilitating gradual realignment of segments of the foot that have become malaligned. One can utilize hexapods in patients with the above indications as well as those individuals with large angular deformities and patients with a consolidated deformity and/or subluxation without significant bone loss.³

The hexapod-assisted circular external frame fixation allows for:

• gradual correction and realignment of bony segments with a decreased risk of neurovascular compromise;
• maintenance of foot and ankle height/length;
• simultaneous multi-joint arthrodesis;
• early to immediate weightbearing;
• management/offloading of soft tissue defects; and/or
• delayed definitive treatment of active bony or soft tissue infection.

Typically, patients undergoing hexapod-assisted circular external fixation reconstruction will have a three-stage procedure for correction. During the first stage, the surgeon will utilize the hexapod for non-weightbearing bony realignment. Stage two consists of selective arthrodesis of joints and transitioning to weightbearing/load transfer in the external fixation device. The final step involves removing the external fixation to allow for the transition to community ambulation in a supported brace.

Determining who will benefit from hexapod-assisted surgery depends on various factors. Surgeon skill and comfort level with static and dynamic external fixation are necessary components when embarking on this method of correction. However, patient selection is critical to minimizing the many potential pitfalls and complications that are part of Charcot reconstruction surgery. For example, patients and/or surrogates who are unable to be active participants during the dynamic deformity correction stage would not be ideal candidates for reconstruction with this method. During this stage, the patient (or patient representative) must be willing to follow the strut adjustment prescriptions issued by the surgeon.  

How The Hexapod-Assisted Circular External Fixator Frame Works

The hexapod frame utilizes computer software and dynamic Ilizarov external fixation configurations for gradual correction via different constructs. Being familiar with the terminology can help determine the type of device that one needs to construct. The information gathered from applying the device transmits to a manufacturer’s web-based software.  

The “butt” joint construct allows for gradual correction of the forefoot/midfoot deformity on a fixed hindfoot and ankle. This construct is the most common application of the hexapod on the foot and is a very powerful method of correction for midfoot Charcot joint reconstructions. Surgeons can utilize the construct with internal fixation and it is very useful for offloading plantar wounds.  

A “miter” frame construct allows for simultaneous correction of the hindfoot and ankle deformity with concomitant correction of a midfoot/forefoot deformity. This setup presents as two separate six-axis frames on the same limb. The miter frame can be quite complex and technically more demanding for the surgeon.

When utilizing a hexapod device, surgeons should be ready to address challenges that may occur in the postoperative period.⁵ Pin site infections and soft tissue irritation are common examples of problems that may arise in the postoperative period. Other obstacles may require an operative intervention that does not affect the final outcome. Examples such as hardware exchange or strut adjustments are common obstacles that surgeons may need to account for during hexapod-assisted corrections. Complications include but are not limited to osteomyelitis, fracture and/or amputation.⁵

One must make patients aware of the risk of problems, obstacles and complications prior to embarking on the reconstructive journey. Discuss complications with the patient in detail, noting that external frame fixation with a hexapod system is not a risk-free surgery. Failure can result in limb amputation or long-term disability, especially in limb salvage cases.

We present two patients who we selected for complex Charcot reconstruction in the midfoot with a hexapod device.  

Case Study One: Addressing A Midfoot Charcot Deformity In A 72-Year-Old Patient With Persistent Pedal Edema

A 72-year-old male presented with midfoot Charcot deformity, persistent pedal edema and a pre-ulcerative lesion but no skin breakdown. The patient denied any pain to the left foot and had been ambulating in a controlled ankle motion (CAM) boot walker as recommended by another physician. His medical history was positive for type 2 diabetes, hypertension and hyperlipidemia, all of which his primary care physician managed well. His HgA1c was optimized and within normal limits prior to surgical intervention.  

Radiographic evaluation indicated midfoot Lisfranc and perinavicular Charcot joints with a collapsed Meary’s angle as well as bayonetting of the forefoot to hindfoot. Pedal pulses were palpable and light touch sensation was decreased but not completely diminished. The instability of the midfoot with equinus contracture started to create a plantar central lesion on the foot. However, no ulceration was present at the time of surgical intervention. After maintaining a brief period of immobilization to allow the Charcot joint to transition from an active to non-active phase, we decided to intervene surgically with the patient’s consent.    

We planned a two-stage correction with hexapod-assisted external fixation for operative intervention and correction of the deformity. The first stage consisted of application of the hexapod external fixator in a butt frame configuration and a gastrocsoleus recession. There was no attempt to create any open incisions or acute realignment of the midfoot as the patient had minimal fracture and a primary “bayonet” dislocation through the perinavicular portions of the midfoot. The goal was to allow for gradual distraction and medial/lateral column realignment of the midfoot onto the fixed hindfoot. The patient performed strut adjustments over a course of two weeks for anatomical realignment prior to returning the operating room for stage two of the procedure.

Stage two consisted of multi-level focused fusions of the forefoot, midfoot and hindfoot. We performed formal joint prep of the medial and lateral columns through small incisions. We converted the patient’s dynamic external fixation device to a static device and permitted immediate weightbearing. Large axial fixation screws maintained alignment of the medial and lateral columns. Evidence of radiographic healing was present at 10 weeks, which permitted safe removal of the external fixation.  

Multiple years after surgery, the patient has a solid, plantigrade and stable construct for daily ambulation in a custom-molded Arizona brace without any new pre-ulcerative lesions or wound breakdown.  

Case Study Two: When A Patient Has An Equinocavovarus Deformity And Midfoot Charcot

A 57-year-old male presented with a chronic wound on the plantar lateral aspect of his left foot. He had been receiving conservative local wound care for the past three years and had attempted to use offloading shoes and padding. After no improvement or signs of healing with his prior wound care specialist, the patient presented for a second opinion and expressed interest in operative intervention.

The patient’s past medical history consisted of diabetes mellitus, hypertension, hyperlipidemia, hypothyroidism, Charcot-Marie-Tooth disease and contralateral below-knee amputation. His history was unique since his pedal manifestations involved deformity due to Charcot-Marie-Tooth and consolidated midfoot/Lisfranc Charcot joints. The patient previously had a right below-knee amputation on his contralateral lower extremity due to a diabetic wound and infection. His primary care physician was adequately managing his medical comorbidities and prior to surgical intervention, the patient’s HgA1c was at an optimal level.

The left foot ulceration was to the plantar aspect of the left fourth and fifth metatarsals. A granular bed was present and the wound did not probe to bone. Prior bone biopsies revealed no osteomyelitis. His vascular status was intact with loss of protective sensation. The physical exam noted an equinocavovarus deformity with midfoot Charcot and soft tissue contracture at the posterior tibial tendon. Radiographic evaluation indicated subtalar joint osteoarthritis with a consolidated forefoot varus Charcot deformity.

Due to the presence of the left foot ulceration and need for surgical intervention, we planned a two-stage correction with hexapod-assisted external fixation for correction of the deformity. The first stage consisted of the application of the hexapod external fixator frame in a butt joint configuration, a realignment subtalar joint arthrodesis and a midfoot Gigli saw osteotomy. Due to poor skin quality and edema in the foot, we utilized a minimal incisional approach with a Gigli saw for midfoot osteotomies. Small incisions at the midfoot allowed for earlier initiation of correction with the hexapod-assisted circular external fixator.

After a few weeks of gradual correction, the patient returned to the operating suite for stage two of the procedure. During this stage, we converted the external fixator to a static device with compression across the midfoot. We overcorrected the midfoot and forefoot in dorsiflexion and eversion to prevent any pressure on the lateral column. After 10 weeks, the patient achieved radiographic union and we removed his external fixation device.   

Multiple years after surgery, the patient is doing well while ambulating in diabetic shoes with a custom ankle foot orthosis. No new pre-ulcerative lesions or wound breakdown are present at this time. Given the high morbidity associated with below-knee amputations, it was critical for this patient to salvage his Charcot limb. Preservation of this limb has made gait on his contralateral below-knee amputation significantly easier.  

In Conclusion

Charcot reconstruction with a hexapod-assisted circular external fixation frame is a powerful method to correct complex foot deformity. It allows the surgeon to correct multi-level and multiplanar deformities in the foot and ankle simultaneously. If one uses the hexapod with caution and precision, it can become a valuable method in the surgeon’s armamentarium for treating a very difficult condition.

More recently, many hexapod devices have become available for surgeons to incorporate into their Charcot reconstruction cases. Each manufacturer has their own computer platform and it is important to be familiar with the platform the surgeon has the most comfort and preference in using. Given the complexity of this method of correction, we recommend surgeons become familiar with Ilizarov principles prior to incorporating hexapod-assisted circular external fixation into their surgical cases.

Dr. Mayer is a second-year podiatry resident with the Department of Veterans Affairs Maryland Health Care System and the Rubin Institute for Advanced Orthopaedics at Sinai Hospital of Baltimore.

Dr. Siddiqui is the Director of the Podiatry Surgery Service at the Rubin Institute for Advanced Orthopaedics at Sinai Hospital of Baltimore. He is the Assistant Residency Director with the Baltimore VA/Sinai Hospital Surgical Residency Program.

References
1.    Siddiqui NA, Pless A. Midfoot and hindfoot Charcot joint deformity correction with hexapod-assisted circular external fixation. Clin Surg. 2017; 2:1430.
2.    Lamm BM, Siddiqui NA, Nair AK, LaPorta G. Intramedullary foot fixation for midfoot Charcot neuroarthropathy. J Foot Ankle Surg. 2012; 51(4):531-36.
3.    Lamm BM, Gourdine-Shaw MC, Thabet AM, et al. Distraction osteogenesis for complex foot deformities: Gigli saw midfoot osteotomy with external fixation. J Foot Ankle Surg. 2014; 53(5):567-576.
4.    Paley D. Problems, obstacles, and complications of limb lengthening by the Ilizarov technique. Clin Orthop Rel Res. 1990; 250:81-104.
5.    Fragomen AT, Rozbruch SR. The mechanics of external fixation. HSS J. 2007; 3(1):13-29.

For further reading, see “Pertinent Pearls On Using A Hexapod Frame For Charcot Fixation” in the May 2017 issue of Podiatry Today. For additional articles, visit the archives at www.podiatrytoday.com.