What Role Might Minimally Invasive Surgery (MIS) Play In Charcot Reconstruction?
When offloading and bracing fail, one may need to explore surgical treatment options with the goal of creating a plantigrade foot with as minimal osseous prominences as possible. However, some patients who may need surgical intervention may not be a candidate for traditional open procedures due to associated comorbidities, such as elevated HbA1c or peripheral vascular disease (PVD).1 Many patients with Charcot neuroarthropathy have a tenuous soft tissue envelope and procedure selection should take this into consideration.
Surgical correction should only be undertaken following exhaustion of conservative measures including orthoses management and physical therapy modalities. When surgical correction is deemed appropriate, the goals for correction include: treatment of underlying forces; restoration of osseous anatomical alignment; remaining joint sparing when possible; and performing adjunctive soft tissue repair when necessary. Use of these basic tenets acts as a guide for procedure selection and deformity correction. The authors of our institution prefer to work in a stepwise fashion, working in order of hindfoot to forefoot, with additional soft tissue augmentation as needed.
MIS Approaches To Forefoot And Midfoot Charcot Deformities
Claw toe and hammertoe deformities are characterized by hyperextension and subluxation of the MPJ. These are typically associated with a flexion deformity at the proximal interphalangeal joint (PIPJ), leading to increased plantar pressures on the metatarsal heads. The Group of Research and Study in Minimally Invasive Surgery of the Foot (GRECMIP)2 recommends the following to address deformity at the PIPJ: MIS incision either medially or laterally with a plantar release; flexor digitorum brevis tenotomy; and osteotomy of the proximal phalanx. To address MPJ extension and subluxation one may utilize a MIS approach via extensor digitorum longus/extensor digitorum brevis tenotomy proximal to the MPJ, followed by distal metatarsal minimally invasive osteotomy (DMMO) with or without percutaneous capsular release.2,3
Many times, digital contractures occur secondary to midfoot Charcot collapse. These deformities can often lead to sub metatarsal ulcerations, dorsal digital wounds, or both requiring surgical intervention. The authors find the DMMO to be a powerful tool to relieve plantar pressures through both its ability to position the head both dorsally along with mild shortening. Key considerations on selecting a DMMO include whether beaming of the affected metatarsal is necessary for accompanying deformity. This often comes into question with the secondmetatarsal, where performing a DMMO to offload pressures may inhibit metatarsal beaming later if needed.
Percutaneous bone shaving or exostectomy of midfoot Charcot may take place through a minimally invasive approach in those with a stable foot or if the prominence overlies a previous flap with an altered vascular network. Often a small incision from the side along the glabrous junction avoids disruption of blood supply, and avoids scarring with potential for added risk of ulceration plantarly. If possible, avoiding disruption of tendinous tracts and insertions should be a consideration with incisional placement.
Intercalary resection, or internal pedal amputation, also represents a viable option to obtain a stable lower extremity. One can perform wedge resection, complete osteotomy and/or intercalary resection of all tarsals in a minimally invasive, percutaneous or limited open manner depending on fixation choice. The authors advocate for reduction of deformity with wedge resection. A percutaneous approach is possible, as endorsed by GRECMIP, with a burr along two K-wires set at angles determined for adequate reduction of deformity. Bone shavings are typically left as graft.2,3 Notably, a Gigli saw can also accomplish this approach.
Considerations For MIS Hindfoot Charcot Intervention
Equinus Deformity Correction. A lack of adequate ankle dorsiflexion may be seen in populations with Charcot neuroarthropathy and may often be associated with the accumulation of advanced glycation end products, which produces a decreased range of motion at the joint.4 “The Split Second Effect” described how, through direct tension of the gastroc-soleus complex by means of the Achilles tendon and indirect forces, equinus contracture is one of the main deforming forces seen in the lower extremity.5
Toolan and colleagues believed the contracture of the Achilles tendon complex was a primary deforming force on midfoot alignment by affecting calcaneal pitch and talar declination positioning.6 Additionally, Thordarson and colleagues found the Achilles tendon had a three-fold greater deforming effect to the medial arch complex as compared to the posterior tibial tendon directly.7
In the presence of equinus contracture, there is increased stress on the medial column of the foot, placing increased strain on the medial ligaments to maintain stability as well as on the posterior tibial tendon to invoke an inversion force on the hindfoot. In the setting of diseased posterior tibial tendon, ineffective eccentric contracture at the midtarsal joint will result in the midtarsal joint remaining unlocked following heel strike.8 This prevents the hindfoot from functioning as a rigid lever during push-off. Repetitive biomechanical alteration in the gait cycle leads to progressive midfoot collapse, forefoot abduction and hindfoot valgus as established previously.9
Therefore, identification and treatment of any gastro-soleal equinus is paramount to re-aligning the hindfoot during reconstruction. This lengthening restores anatomic calcaneal inclination and will manifest compensatory talar dorsiflexion. The authors at our institution prefer Strayer, Baumann or other midsubstance lengthenings using a posteromedial endoscopic or limited open approach. In cases with significant equinus, a percutaneous triple hemisection of the distal Achilles tendon may be preferable. One should note that midsubstance recessions are often preferable due to increased maintenance of plantarflexory force and push-off strength postoperatively.10
Calcaneal Varus/Valgus. MIS calcaneal displacement osteotomy with the aid of a low-speed, high-torque burr is well described in the literature.11,12 One first determines the intended osteotomy site using fluoroscopy and avoids neurovasculature in this area. One can fluoroscopically determine the safe zone for avoiding the sural nerve by tracing a line from the origin of the plantar fascia extending to the posterosuperior aspect of the calcaneal tuberosity. Placement of the burr should be in a region between this line and another line parallel and 11 mm anterior to it.13 This osteotomy also avoids the medial and lateral plantar nerves, however one should still take care when nearing the medial cortex to avoid excessive soft tissue disruption.
The surgeon then places the incision centrally between the superior and inferior aspects of the intended calcaneal osteotomy. A 2.5-mm Shannon burr is advanced across the calcaneus, perpendicular to the long axis. A calcaneal axial view ensures this orientation. The osteotomy may then take place either free-hand, or with the aid of a jig or guidance K-wires.12 This may shift either medially or laterally14 depending on the deformity to be corrected.
Key Concepts Related To The Distal Tibia
Distal tibial and ankle alignment deformities present unique challenges due to their complex and often chronic nature. Rarely are these deformities uniplanar or without concomitant deformity or compensation. Malposition of major functional joints leads to early articular degeneration, osteoarthritis, pain and reduced function. Multiple studies conclude end-stage arthritis in major functional joints can lead to early mental and physical decline.15,16 The supramalleolar osteotomy (SMO) is an extra-articular procedure designed to realign the mechanical axis of deformity, thereby restoring ankle function. SMOs and ancillary modalities are widely versatile, demonstrating ability to correct not only triplanar deformity but also chronic deformities such as equinus or limb length discrepancies through either acute or gradual correction.17,18 However, preoperative discovery and planning are critical.
Malunions of the distal tibia secondary to trauma or prior attempts at Charcot reconstruction are common sources of ankle malposition. Greater than 15° of angulation in the distal tibia can decrease tibiotalar contact area by 42 percent, and posttraumatic evaluations show similar reduction in contact area following as little as one mm of lateral talar displacement.19,20 For malaligned primary ankle fusions, one must also evaluate limb length discrepancies during correction planning. In severe instances, soft tissue integrity at the level of the deformity may be compromised secondary to multiple surgical procedures or local traumatic de-vascularization. In these instances, supramalleolar osteotomies may provide an alternative zone of deformity correction. Additionally, with chronic deformities, multiple distal and proximal compensatory mechanisms may be in place, which one should consider prior to surgical intervention.
When indicated, deformity correction begins with identification of the center of rotational angulation (CORA). Correct identification is imperative to deformity planning, as osteotomy characteristics are dictated by the location of the osteotomy site in relation to the level of the CORA. Importantly, corrective osteotomies performed at the level of the CORA permit the deformity to be corrected by angulation alone.18 When wedge osteotomies can be applied at the level of deformity, they alone will be sufficient for biplanar deformity correction. However if limitations prevent an osteotomy at the level of the CORA, osteotomy principles dictate inclusion of additional translation to achieve proper re-alignment.18 This mandate also states that any angular osteotomy performed outside of the level of CORA will contribute a translational force which one should account for prior to surgery.
For example, in procurvatum deformities with a CORA at the ankle joint, an anterior closing wedge osteotomy in the distal tibia may reduce the procurvatum deformity, but also contribute anterior translation. If one does not anticipate this anterior translation, the patient will in effect receive a net increase in the length of pedal arm lever, and have greater difficulty during ambulation. This is also apparent when correcting varus deformities of the distal tibia. With CORA at the ankle joint, a laterally based closing wedge of the distal tibia will also translate the tibial plafond laterally. Therefore, when fixating the osteotomy, one must translate the distal fragment medially to restore proper alignment of the mechanical axis of the tibia.
The metaphyseal zone of the distal tibia is ideal for supramalleolar osteotomies due to its robust healing potential. From the authors’ experience, it is best to avoid osteotomies greater than 2.5 cm proximal to the ankle joint and in the diaphysis of the distal tibia due to concern of delayed healing. Use of low-energy instruments such as osteotomes can also improve healing times when compared to high-powered instruments, which may contribute to thermal necrosis and osseous damage.
Respective length of the malleoli should also play a role in preoperative planning. When the tibia and fibula are not of equal deformity, one will note a disruption in the plafond malleolar angle (normal = 9°).21 Using an anterior-posterior radiograph of the ankle including proximal tibia, one should measure the tibial-fibular length differential. This will guide whether acute or gradual correction will equalize malleolar length and restore balance to the ankle mortise.
When correcting large sagittal or frontal plane deformities, there may be soft tissue entrapment or stretch, leading to neuropraxia or functional deficits. Corrections as little as 5° may place patients at great risk of pain or discomfort, therefore the authors recommend a low threshold for performing a prophylactic tarsal tunnel release.22 Our institution’s preferred guideline recommends all acute corrections greater than 10° or gradual corrections greater than 25° should receive prophylactic tarsal tunnel release prior to osteotomy.
Critical Concepts In Surgical Technique And Osteotomy Selection
One places the patient in a supine position with a bump under the ipsilateral hip to orient the patella upright and neutral. General anesthesia is optimal, however spinal anesthesia is an option when comorbidities are prohibitive. Tourniquets are not routinely utilized, as mild bleeding is beneficial for thermal cooling of power instrumentation. All draping and prepping is at least to the level of the mid-thigh to monitor alignment of the patella and anterior tibial crest to the foot and ankle.
An anterior approach is typical for sagittal plane deformities and medial or lateral incisions are preferrable for frontal plane deformity corrections. Minimal dissection can avoid unnecessary disruption of blood supply and prolonged tourniquet time. Specifically, periosteal dissection should be kept to a minimum during osteotomy preparation. When performing percutaneous supramalleolar osteotomies, multiple carefully placed stab incisions will avoid neurovascular bundles. If irrigation is not built into the hand-piece of the burr, the authors recommend having an assistant manually use drip irrigation to help prevent thermal necrosis of the soft tissues.
Wedge osteotomies are utilized when deformities lie in the sagittal, frontal or oblique planes of the distal tibia. If additional length is required, the authors prefer gradual distal tibial lengthening with Ilizarov method external fixation. When limb length equalization is not required, acute closing wedge osteotomies are often adequate for correction. Wedge osteotomies use an intraoperative wire-guided technique consisting of 1.8mm Ilizarov wires placed parallel to the ankle joint and perpendicular to the mechanical axis of the tibia. These wires should intersect at the apex of the deformity and indicate the level of ideal osteotomy when feasible. It is important to remember that osteotomies performed away from the apex of deformity (CORA) will require adjuvant translation which must be accounted for. When performing an opening wedge osteotomy, one should maintain the far cortex to act as a hinge, filling the defect with graft of choice. Otherwise through-and-through osteotomies may be required for complete correction, and fixation of choice can secure the corrected position.
When CORA is at the level of the ankle joint, focal dome osteotomies are an option using either open or percutaneous technique.18,23,24 Starting a few millimeters above the ankle joint, one places a half pin perpendicular and centered to the anatomic axis of the tibia using a tissue sleeve, confirming on fluoroscopy. A focal dome osteotomy guide may then assist in completing serial, contiguous drill holes in a dome-like fashion, extending to the medial and lateral cortices of the tibial metaphysis. Using fluoroscopic guidance, one connects these drill holes by a small Hoke osteotome, which when rotated or twisted will ensure completion of osteotomy and aid displacement of the distal fragment. A concomitant fibular osteotomy may also be performed distally using a similar multiple drill hole technique with 1.8mm Ilizarov wire. Supramalleolar osteotomies when combined with fibular osteotomies may result in increased coronal translation as compared to tibial osteotomies alone.25
Surgeons can also complete supramalleolar osteotomies using a Gigli saw through percutaneous incisions. Osteotomies through either tibia, fibular or both using this method are conducted through two small medial and one lateral incisions. Medial incisions are transverse with the first at the level of the osteotomy just medial to the tibialis anterior tendon. A periosteal elevator elevates the periosteum over the anterior aspect of the tibia until the elevator tents the skin over the fibula laterally. The second transverse incision is anterior to the tibialis posterior tendon where an elevator may be used to raise the periosteum posterior to the tibia and fibula. The third incision is longitudinal along the fibula where the prior elevator protrudes over the fibula.
With passages exposed, a curved hemostat passes the Gigli saw from medial to lateral. If encountering difficulty passing the saw, one may tie it to heavy suture, passing this first to dilate the canal and aid saw advancement. Once successfully passed from medial to lateral, the saw must then pass from the lateral incision to the transverse posteromedial incision. Using a sawing motion under manual strength, the Gigli saw should be free to cut from lateral to medial. When nearing the medial cortex, one should place small retractors and elevators into the incision to protect the medial soft tissue structures from damage at completion of the osteotomy.
Understanding Appropriate Fixation Methods And Distal Tibial Lengthening
There are numerous advantages and disadvantages to internal versus external fixation, most of which exist beyond the scope of this article. In short, advantages of internal fixation include a multitude of locations and options (plates, screws, staples, etc.) as well as ease of use and cost effectiveness. External fixation offers need for minimal dissection, early weight-bearing and opportunity for gradual correction of deformities such as limb length discrepancies or equinus. Disadvantages for external fixation include cost, pin site infections and patient frustrations during prolonged use. Selection of fixation methods should be based on the nature of required procedures, patient condition and preference as well as surgeon training and capabilities.
Distraction osteogenesis for limb length discrepancy secondary to hindfoot and/ or ankle Charcot neuroarthropathy is also an option. If no distal tibial angular deformity is present, one can make a corticotomy at the distal tibial meta-diaphyseal junction.26 One may initiate this through a medial small incision, with care taken to protect the neurovasculature posteriorly, with the aid of a low-speed, high-torque burr with irrigation. Once the corticotomy is complete, the site is distracted and intraoperative fluoroscopy can verify completion of corticotomy and maintained alignment of the distal extremity. Incremental lengthening then ensues after an appropriate latency phase, through the use of strut adjustments followed by an appropriate consolidation phase.
Concluding Thoughts
A multitude of options are available for surgical management of Charcot neuroarthropathy. Minimally invasive techniques continue to demonstrate increasing utility and safety in this highly comorbid and at-risk patient population. However, as with many other surgical skills, a steep learning curve is present with minimally invasive techniques, which one should consider during preoperative planning.
Dr. Furmanek is a third-year resident at Georgetown University/Medstar Health in Washington, D.C.
Dr. Miller is a Limb Salvage Fellow at Georgetown University/Medstar Hospital System in Washington, D.C.
Dr. Rahnama is a fellowship-trained foot and ankle surgeon and an Assistant Professor at Georgetown University School of Medicine.
Dr. Siddiqui is the Director of Podiatric Surgery at the International Center for Limb Lengthening and Chief of Podiatry at Northwest Hospital, in Baltimore.
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