Michael S. Pinzur
DEFINITION
Charcot foot arthropathy is a destructive process that primarily affects the foot and ankle of patients with longstanding diabetes (10-plus years) and peripheral neuropathy (PN).4,5,8
The resulting disabling deformity impairs walking, can be painful, and makes patients prone to develop overlying skin ulceration, leading to deep infection and eventual amputation. Outcome data derived from the AOFAS Diabetic Foot Questionnaire have revealed that Charcot foot arthropathy has a severe negative impact on health-related quality of life in affected individuals.6
Historically, clinical management has been dictated by anecdotal observation, with little data that would stand up to current evidence-based medicine standards.
Treatment has classically been passive and accommodative. Acute active-phase management has been accomplished with a non–weight-bearing total-contact cast until the active destructive phase has resolved. This has been followed by accommodative bracing with custom therapeutic shoes, accommodative foot orthoses, ankle–foot orthoses, and a special accommodative orthosis, the Charcot Restraint Orthotic Walker (CROW; FIG 1).
Based on similar anecdotal observation and level IV scientific evidence, most recent publications in peer-reviewed literature recommend universal correction of deformity combined with arthrodesis.7,14,22,23
This chapter will present an evidence-based algorithm for use in the management of Charcot foot arthropathy at the level of the midfoot.
ANATOMY
The foot is a unique end organ adapted for weight bearing.
The multiple linked small bones normally allow the uniquely durable soft tissue envelope of the plantar surface to be prepositioned to accept the load of weight bearing.
The destructive process associated with Charcot foot arthropathy impairs the ability of this mechanism to orient the foot in an optimal position to take advantage of its durable soft tissue envelope.
The ensuing deformity produces weight bearing through less durable tissues, leading to tissue failure, deep wound formation, destructive osteomyelitis, and systemic sepsis.
PATHOGENESIS
The primary risk factor for the development of Charcot foot arthropathy is longstanding peripheral neuropathy as measured by insensitivity to 10 grams of applied pressure (FIG 2).
While other causes of absence of protective sensation have been associated with the development of Charcot foot arthropathy, longstanding diabetes is present in well over 95% of affected individuals.
The majority of diabetics who develop foot-associated morbidity are morbidly obese.18 Glycemic management can be with insulin, oral medications, or diet. As with all of the morbidities associated with diabetes, the risk for foot-associated morbidity is decreased with tight glycemic management.
Trauma appears to be an important inciting factor. The trauma can be significant, seemingly trivial, or due to repetitive mechanical stress.
The neurotraumatic theory suggests that patients with longstanding PN and a loss of protective sensation develop a mechanical “stress” fracture. Due to the absence of protective sensation, they continue weight bearing, leading to a condition that mimics a hypertrophic nonunion.
The neurovascular theory suggests that a vasomotor PN leads to high-flow arteriovenous shunting, causing bony depletion of calcium, leading to bone weakening and the well-known deformities.
While the presence of sensory PN is well recognized, the accompanying motor and vasomotor neuropathies are often overlooked. The motor neuropathy affects the smaller nerves and muscles of the anterior leg (foot and ankle dorsiflexors) earlier in the disease process than the posterior leg compartments. This motor imbalance is currently appreciated as an important component leading to breakdown of the foot at the midfoot level during the terminal stance phase of gait. The autonomic neuropathy is likely involved as a component of the neurovascular theory.
FIG 1 • Charcot Restraint Orthotic Walker (CROW). The custom-fabricated clamshell ankle–foot orthosis is lined with a pressure-dissipating material. It is designed to both optimize positioning of the deformed Charcot foot and dissipate local pressure to bony prominences over a wide surface area.
FIG 2 • The Semmes-Weinstein 5.07 monofilament applies 10 grams of pressure. The inability to “feel” this amount of pressure appears to be the threshold of peripheral neuropathy associated with the development of the two major foot morbidities associated with diabetes: diabetic foot ulcers and Charcot foot arthropathy.
Baumhauer has demonstrated, via histochemical studies, the cytokines involved with the development of the destructive process, which resembles acute rheumatoid pannus.2
The answer is likely a combination of both pathologic theories. Trauma, or some unknown inciting factor, initiates a process that releases specific cytokines. These cytokines lead to the development of destructive gray tissue that histologically resembles rheumatoid pannus.2
NATURAL HISTORY
Most of the background observations in common orthopaedic textbooks are based on anecdotal observation, with little information that would comply with current evidencebased medicine standards.
Eichenholtz8 in 1966 published a detailed monograph based on his observations in 66 patients. This objective clinical, radiographic, and histologic information provides objective benchmark data. This monograph objectively describes the destructive disease process as well as the progression of deformity.
The AOFAS Diabetic Foot Questionnaire provides objective data to support Eichenholtz's appreciation of the severe negative impact on health-related quality of life in affected individuals.6
This very negative clinical observation has prompted many experienced clinical researchers to arbitrarily advise, without evidence-based medicine support, correction of deformity and arthrodesis at the onset of symptoms.7,14,22,23
PATIENT HISTORY AND PHYSICAL FINDINGS
The classic presentation is a grossly swollen, painless foot, without a history of trauma, in a longstanding diabetic. In fact, better than half of patients will remember a specific traumatic event, although it might be trivial. Most patients are in their mid-50s to mid-60s, and most are obese (FIG 3).15,17–20
Affected individuals generally have longstanding (10plus years) diabetes with evidence of PN, as measured by insensitivity to the Semmes-Weinstein 5.07 (10-gram) monofilament (FIG 1).
FIG 3 • Patients classically present with a grossly swollen, nonpainful foot without a history of trauma. In fact, most remember an episode of trauma, often trivial, and many are painful. Patients generally do not have a draining wound, supporting the presence of a diabetic foot abscess. The erythema is generally greatly lessened with elevation, which clinically differentiates it from infection.
Patients often describe a feeling of “crunching” and instability at the involved site.
On clinical examination, the foot is very swollen and warm. There is often gross nonpainful instability at the site of clinical involvement.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Treatment can generally be determined based on clinical examination and plain radiography.
Weight-bearing biplanar radiographs of the foot and ankle are essential.
Eichenholtz8 arbitrarily categorized the timeline of the disease process into three stages.
Stage I is the early active stage of the disease process. Radiographs will be normal.
Stage II is entered when there is sufficient destruction of the ligamentous structures of the involved joints to allow joint dislocation or periarticular fracture. A healing response will often develop during this destructive phase of the disease process, prompting other authors to divide the disease process into more stages. This is when the radiographs take on the characteristic appearance of hypertrophic destruction with or without bony repair and the appearance of a hypertrophic nonunion.
Stage III is the consolidation of the destructive process, characterized by a “burning out” of the bony destruction. This is the stage when the foot assumes the characteristic deformities with hypertrophic reactive bone formation.
Nuclear scanning is rarely helpful in distinguishing acute Charcot foot arthropathy from diabetic foot infection or abscess.
MR imaging is occasionally beneficial when it demonstrates bony destruction contiguous to a wound.
DIFFERENTIAL DIAGNOSIS
In the least destructive presentations of the disease process, patients are frequently misdiagnosed with a deep venous thrombosis, cellulitis, acute gout, or tenosynovitis.
Doppler ultrasound studies are normal, and patients do not respond to antibiotic therapy.
The critical differential is foot abscess.
Patients with a diabetic foot abscess, or infective cellulitis, will feel ill.
The first sign of occult infection in the diabetic is increasing blood sugar or increasing insulin demand. White blood cell count may not increase, as these patients are often poor hosts and are not capable of mounting a normal immune response.
Patients with deep infection will generally have an entry portal for infection, which might be as simple as an infected ingrown toenail, or a crack or pinhole between the toes.
Patients with acute Charcot foot arthropathy do not experience malaise, they have normal blood sugar levels (for the individual patient), and they do not have any purulent drainage. The erythema often disappears with elevation, in contrast to the patient with a diabetic foot infection.
NONOPERATIVE MANAGEMENT
Classically, treatment has been accommodative with a nonweight-bearing total-contact cast during the acute phase.
Long-term management has been accomplished with accommodative bracing.
Surgery was only advised for bony infection or when orthotic management could not accommodate the acquired deformity.
Based on clinical observations in patients who were not clinically plantigrade or would or could not use a CROW, we started to develop a clinical algorithm (FIG 4).
We defined a desired clinical outcome as remaining ulcerfree and maintaining walking independence with commercially available depth-inlay shoes and custom accommodative foot orthoses.
It has been determined that patients who are clinically plantigrade at the time of presentation and have a colinear lateral talar–first metatarsal axis, as determined from weightbearing dorsal–plantar radiographs, and have no bony prominences, can achieve the desired outcome without surgery.3,15
Patients who meet the criteria for nonoperative treatment are initially treated with a weight-bearing totalcontact cast.
The cast is changed every 14 days until the affected joint is clinically stable and the volume of the limb stabilizes.19
The patient is then progressed to a commercially available pneumatic fracture boot.
When the foot volume reaches a plateau, the patient is evaluated for long-term management with commercially available depth-inlay shoes and custom accommodative foot orthoses (FIG 5).1,21
The patient in FIGURE 6 demonstrates the difficulties in long-term management of the nonplantigrade patient without correction of the deformity.
The acute destructive process can be managed with a total-contact cast.
This patient was very compliant, wearing the therapeutic footwear full time. She returned for routine visits to the physician and pedorthist.
Despite close monitoring, she developed an ulcer in the skin overlying the head of the talus. When multiple surgical attempts failed, a transtibial amputation was necessary because of infection.
SURGICAL MANAGEMENT
There is disagreement whether the common midfoot location for the development of Charcot foot arthropathy is due to the mechanical forces produced by simple motor imbalance or to intrinsic contracture of the gastrocnemius–soleus muscle– tendon complex, which limits passive ankle dorsiflexion.11,12
FIG 4 • Treatment algorithm for acute Charcot foot arthropathy.
FIG 5 • A. This patient is clinically plantigrade with durable skin and connective tissue aligned for weight-bearing. B,C. Weight-bearing radiographs on presentation. Despite the deformity, treatment was accomplished with a weight-bearing total-contact cast until the acute destructive process subsided. Long-term management was accomplished with commercially available therapeutic footwear (depth-inlay shoes and custom accommodative foot orthoses).
Most experts agree that the first step in surgical treatment is a lengthening of the gastrocnemius–soleus motor group to create balance between ankle flexors and extensors. Whichever theory one subscribes to, it has become apparent that lengthening of the gastrocnemius–Achilles tendon motor unit by gastrocnemius recession or percutaneous Achilles tendon lengthening is important.
In most patients, the progressive deformity is biplanar. Correction of the bony deformity can generally be achieved by removing a sufficient wedge of bone at the apex of the deformity (ie, a partial tarsectomy) to create a plantigrade foot.
In patients who are clinically good hosts, have no evidence of open wounds overlying bony deformity and no deep infection, and appear to have a reasonable quality of bone
density, surgical stabilization can predictably be accomplished with internal fixation.10
Crossed large fragment screws (cannulated or noncannulated), long posterior-to-anterior screws, and plate and screw constructs have been advocated for maintaining the surgical correction.
Our preferred method of achieving surgical stabilization is with a tension-band 3.5-mm plate applied over the apex of the deformity. Due to the poor quality of local bone, 6.5-mm cortical bone screws are used to secure fixation (FIG 7).
In patients who clinically appear to be poor surgical hosts or have wounds or skin ulceration overlying bony deformity, deep infection, or poor-quality osteopenic bone, surgical stabilization is accomplished with a three-level ring external fixator (FIG 8).9,16
FIG 6 • This 55-year-old, extremely cooperative patient was successfully treated with a total-contact cast, progressing to therapeutic footwear. Despite very careful attention by the patient and close monitoring by her physicians, she developed this ulcer using therapeutic footwear 2.5 years after the development of a Charcot foot deformity.
FIG 7 • A. This 37-year-old diabetic had a nonplantigrade deformity. B–E. Photographs and radiographs at 5 years.
FIG 8 • A,B. This 50-year-old man had repeated lateral foot infections despite resection of the fifth metatarsal. Note the rotational deformity of the forefoot relative to the hindfoot. C,D. Initial weight-bearing radiographs. E,F.Percutaneous tendon Achilles lengthening was followed by a wedge resection of sufficient bone, through the ulcer, to correct the deformity. G. Photograph at 1 year.
TECHNIQUES
SURGICAL STEPS
The first step is a lengthening of the gastrocnemius musculotendinous unit by either percutaneous triple hemisection of the Achilles tendon or fractional muscle lengthening of the gastrocnemius (Strayer procedure).
Correction of the bony deformity is accomplished through an incision placed directly over or just inferior to the apex of the deformity. A biplanar wedge of bone is resected at the apex of the deformity, allowing correction of the deformity and creation of a plantigrade foot.
INTERNAL FIXATION
When stabilization is accomplished with internal fixation, a tension-band 3.5-mm bone plate is used with large fragment screws to optimize screw fixation in osteopenic bone (FIG 7).
EXTERNAL FIXATION
When surgical stabilization is accomplished with ring external fixation, a percutaneous smooth pin is sometimes valuable to establish temporary fixation while the ring external fixation frame is secured.
A neutral ring external fixation frame is assembled before surgery. The frame has limited adjustability to increase frame stability and minimize the risk for bolt or screw loosening.
The heel is safely positioned to avoid contact between the skin and the external fixator frame. Three oblique olive wire pins are initially applied through the calcaneus and then tensioned within the inferior ring. Three oblique olive wire pins are then placed through the metatarsal, with the forefoot aligned to the hindfoot in both plans, thus creating a plantigrade foot.
The ring is then secured to the tibia, first through the proximal ring and then through the middle ring. The rings are safely positioned to maintain alignment of the foot to the leg and to avoid contact between the limb and the frame (TECH FIG 1).
TECH FIG 1 • A,B. The hindfoot is initially secured to the frame with two or three 30-degree-oriented tensioned olive wires. Care is taken to avoid pressure between the skin and the frame. The forefoot is then secured in a similar fashion. Two upper levels are provided to dissipate the load. Patients are allowed to bear some weight for transfers.
PEARLS AND PITFALLS
Many of these patients are obese and have poor balance due to their PN. It is virtually impossible for them to maintain a non–weight-bearing status. Every effort should be made to allow them to bear some weight in order to assist in transfers.
Because of their diabetes, these individuals are poor surgical hosts. Large wounds with a great deal of soft tissue stripping should be avoided.
POSTOPERATIVE CARE
Patients undergoing nonoperative treatment (ie, those who are clinically plantigrade and have a radiographic colinear lateral talar–first metatarsal axis) are initially treated with a weight-bearing total-contact cast.
The cast is changed every 2 weeks to ensure bony immobilization and to avoid pressure ulcerations from a poorly fitting cast.
The total-contact cast is maintained until the foot is clinically stable and the limb volume is reasonably stable. This usually can be accomplished in 6 to 8 weeks (three or four casts).
Patients are then transitioned to a commercially available pneumatic diabetic walking boot until limb volume is sufficiently stable to allow fitting with commercially available depth-inlay shoes and custom accommodative foot orthoses.
The shoe is generally modified with a cushioned heel and rocker sole.
In the occasional patient whose foot becomes nonplantigrade or who develops a noncolinear lateral talar–first metatarsal axis or a painful nonunion, surgical stabilization is advised.
Patients undergoing surgical correction and maintenance with internal fixation are initially immobilized with a posterior plaster splint.
Weight bearing is initiated 7 to 10 days after surgery with a total-contact cast if the wound is secure.
The cast is maintained for 6 to 8 weeks, when patients are managed in a similar fashion to the nonoperative group.
Patients treated with surgical correction and immobilization with a ring external fixator are allowed to bear about 30 pounds of weight during treatment.
The external fixator is removed at 8 to 12 weeks, at which point a weight-bearing total-contact cast is applied for 4 to 6 weeks.
Progression to therapeutic footwear is accomplished in a similar fashion to the other groups.
OUTCOMES
During the past 10 years, only three patients treated nonsurgically developed a nonunion at the site of their Charcot arthropathy with sufficient pain to warrant surgical stabilization.15
The initial complication rate in the surgical patients was high compared with current standards. Infection rates have been greatly reduced with the use of the ring external fixator in high-risk, poor-host patients with open wounds or deep bony infection.
Mechanical failure and deep bony infection rates were high in the early experience with crossed-screw constructs, leading to a great deal of morbidity and three transtibial amputations.
In patients with adequate bone quality, the screw-plate construct can achieve successful outcomes in more than 90% of patients.
The absolute worst hosts undergo surgical correction through small incisions followed by immobilization with a ring external fixator. The complication rate in this group is surprisingly small.
Surgical correction of the deformity is accomplished before application of the external fixator, so the frame need not be adjustable. This absence of multiple connections appears to be responsible for the limited frame-associated morbidity.
COMPLICATIONS
Patients treated without surgery have had limited numbers of complications.
The rare cast-associated pressure ulcer generally resolves with local skin care and cast change. Changing the totalcontact cast every 14 days appears to avoid cast-associated morbidity.
Wound infection and mechanical failure were not uncommon during the early experience with internal fixation in this group. Wound infections are treated with surgical débridement, culture-specific parenteral antibiotics, and occasional management with a vacuum-assisted wound care system.
Mechanical failure was also more common when internal fixation was accomplished with crossed large fragment screws. It has been uncommon when the tension-band plate–large fragment screw construct has been used to accomplish internal fixation.
Stabilization of surgical correction with tensioned olive wires and ring external fixation has greatly decreased the incidence of wound infection and mechanical failure in the highest-risk group of patients.
Two patients in the ring external fixation group developed stress fractures months after removal of the ring external fixators. One healed with simple cast immobilization. One progressed to a nonunion. Uneventful healing was accomplished after closed antegrade intramedullary nailing.
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