External Fixation of Rearfoot and Ankle Arthrodeses

Bradley M. Lamm

External fixation has been used for more than a century. Codivilla (1) is the first to report the use of external fixation for limb lengthening in 1905. During the 1950s, Professor Gavril Abramovich Ilizarov, operating in Kurgan in the Ural Mountains of Siberia, developed the use of a modular circular fixator with transosseous tensioned wire fixation. He also developed a method of inducing bone growth with a minimally invasive corticotomy. He applied his techniques to the treatment of deformities, limb-length discrepancies, nonunions, osteomyelitis, fractures, and bone defects. Ilizarov worked in relative obscurity until 1967, when he treated an infected nonunion sustained by a Russian Olympic high jump champion, Valery Brumel. In 1973, the Journal of the American Podiatry Association (currently called the Journal of the American Podiatric Medical Association) was one of the first to document Ilizarov’s technique in the English language literature (2). However, it was not until 1996 that another article about Ilizarov’s technique was published in the podiatric literature (3). An Italian Professor, A. Bianchi-Maiocchi, introduced Ilizarov’s methods to the western world in 1981. External fixators were introduced to North America in 1986 through the early efforts of Drs. James Aronson, Victor Frankel, Stuart Green, and Dror Paley. Today, the Ilizarov technique is widely used by a variety of surgeons.

In 1994, Dr. J. Charles Taylor and his brother, engineer Harold Taylor, developed the Taylor spatial frame (TSF) (Smith & Nephew, Inc., Memphis, Tennessee) (4). The TSF, which modified the Ilizarov system, is an apparatus that uses a Stewart platform with a computer program to allow for precise gradual bony or soft tissue correction in any plane. New rings made of aluminum and specific and smaller foot and ankle rings have been developed. The advantage of the TSF over the Ilizarov device is the ease of construct whereby no hinges, translation boxes, or rotation apparatuses are required. This newer technology increased the potential applications for complex deformity correction of the foot and ankle. The Internet-based computer software program for use of the TSF for foot and ankle deformity correction was created in 2004. The current version is spatialframe.com version 3.1 by Smith & Nephew (www.spatialframe.com).

Circular external fixation (Ilizarov fixation, TSF fixation, and others) is typically preferred for static or dynamic (gradual) correction of rearfoot and ankle deformities because of the versatility of the components and strength for weight-bearing. Bilateral (Sidekick Stealth Rearfoot Fixator, Wright Medical Technology, Inc., Arlington, Tennessee), unilateral (Limb Reconstruction System; Orthofix Orthopedics North America, McKinney, Texas), and hybrid (Multi-Axial Correction Fixation System; Biomet, Inc., Warsaw, Indiana) external fixators can also be used to achieve the same goals as those achieved with circular fixators. The Limb Reconstruction System has been used for decades to manage fractures and bone lengthening. The Sidekick Stealth Rearfoot Fixator is a newer bilateral external fixator especially designed for the rearfoot and ankle. The Multi-Axial Correction device, developed by Richard Davidson, is a unilateral external fixator that performs correction about the apex of the deformity, or the center of rotation of angulation (CORA). A pin is inserted into the CORA of the deformity, and the fixator is then built around the pin. The Multi-Axial Correction Fixation System has been used to correct deformities in the femur, tibia, forearm, and foot. Regardless of the type of external fixation used, the surgeon’s understanding of external fixation principles and mechanics is required.

External fixation has many advantages over internal fixation, such as better fixation of osteoporotic bone, small bone segment fixation, and greater strength for weight-bearing, especially for patients with neuropathy, obesity, and upper extremity weakness. Also during external fixation treatment, access to soft tissues for wound care is advantageous. External fixation allows for fine-tuning of residual deformity correction during the postoperative period and can allow for joint range of motion and early weight-bearing. Theoretically, the advantages should lessen disuse osteoporosis and maintain joint range of motion and cartilage nutrition. Despite the use of “walking rings,” disuse osteopenia of the foot still occurs during treatment. A disadvantage of external fixation is the specialized surgical expertise that is required for construction and postoperative management. Complications, such as pin-site infections, are common; however, most complications are minor and can be addressed nonoperatively. Major complications, such as osteomyelitis, malunion, and nonunion, can occur with external fixation just as with internal fixation. With external fixation, when operative intervention is required for a complication, treatment typically can continue while the complication is being addressed (5).

Patients who require fusion for rearfoot and ankle deformities are at the end stages of joint degeneration from congenital, dysplastic, developmental, or traumatic conditions. Correction has likely been previously attempted, and various considerations are thus necessary. Patients might have isolated or combined osseous malalignment and soft tissue contractures of the rearfoot and/or ankle. In addition, limb-length discrepancies caused by rearfoot or ankle deformity can be present and should be properly measured via preoperative long leg (erect leg) radiography. Varying degrees of adjacent joint arthritis is a common finding with these rearfoot and ankle deformities and should also be evaluated preoperatively. A comprehensive clinical examination and stance and gait analysis of the rearfoot and ankle deformity with accurate assessment of joint compensation are essential for preoperative surgical planning correction.

Limb deformity principles are the foundation for proper surgical planning and correction. They provide accurate reference points and angles for producing predictable results. The geometrically based principles originate from a standard set of radiographic angles and reference points (6). The use of external fixation for correction of rearfoot and ankle deformities requires extensive surgical experience because multiple factors must be considered and addressed for a successful outcome. Limb deformity and external fixation principles and considerations regarding surgical realignment of the rearfoot and ankle are presented in this chapter.

EVALUATION, DIAGNOSIS, AND FUNCTIONAL ANATOMY

In addition to pertinent medical and surgical histories, a detailed history of the cause and resultant effects of the rearfoot or ankle deformity should be elicited. Knowing the cause of the rearfoot and/or ankle deformity is essential to understanding the current condition. Performing a thorough physical examination to include clinical evaluation, observing the patient during gait and stance, and determining the patient’s goals are very important. Radiographs should include anteroposterior, lateral, and axial views and, when necessary, stress or fluoroscopic images. In addition, advanced imaging is important in some cases to accurately execute a preoperative plan.

It has been well documented that an understanding of radiographic angular relationships is critical for appropriate evaluation and identification of the level and extent of deformities (6,7). Obtaining accurate radiographs is essential for surgical planning. Erect lower limb radiographs (full lower extremity, including pelvis, femur, tibia, fibula, and foot) and long lateral view radiographs (full lower extremity, including femur, tibia, fibula, and foot) are important for measuring overall lower extremity alignment, joint orientation angles, and limb-length discrepancies. To assess limb-length discrepancy and proximal deformity, the long radiographs should be obtained even though deformity is isolated to the rearfoot and/or ankle. If no proximal deformity or limb-length discrepancy is suspected, the radiographs should at least include the entire tibia. On the erect lower limb radiograph, a limb-length discrepancy cannot be accurately measured for patients with fixed ankle equinus or fixed knee flexion deformity.

In addition to the routine anteroposterior and lateral view radiographs of the foot and ankle, axial view radiographs are invaluable for assessing frontal plane alignment (8,9,10 and 11). The long calcaneal axial and rearfoot alignment views obtained in the frontal plane provide essential information regarding the relationship of the tibia to the calcaneus and to the subtalar and ankle joint positions, respectively. Stress radiographs can also be obtained to differentiate soft tissue abnormalities from osseous deformities. Real-time fluoroscopy adds a fourth dimension to the evaluation of ankle, subtalar joint, and midfoot motion (7,12).

SELECTION OF PROCECURE

After exhausting attempts or ruling out joint salvage options with a patient, the determination for arthrodesis should be critically evaluated. Arthrodesis of the rearfoot and/or ankle is required as a result of multiple conditions (trauma, congenital abnormality, avascular necrosis, previous surgery, nonunion, infection, and malunion). The goal of rearfoot or ankle arthrodesis is to achieve a successful fusion in proper alignment. Thus, the basic building blocks, AO principles, need to be strictly adhered to: atraumatic technique, good bone preparation, alignment, and early mobilization. The alignment principle can be best quantified by using a foundation of accurate radiographic reference points and angles called principles of limb deformity. The surgeon should embrace the principles of both arthrodesis and deformity correction because they are universal and independent of the type of fixation system used.

Rearfoot and/or ankle fusions achieved with external fixation typically are performed because the patient has other conditions that contribute to the complexity of the case or because the rearfoot and/or ankle condition is complex. Patients with other conditions contributing to the complexity of the case who can benefit from external fixation include those with neuropathy, obesity, upper extremity weakness, and inability to be non-weight-bearing. Conditions treated with external fixation typically are complex and include revision surgery, failed internal fixation, multiplanar deformity, osteoporotic bone, and small bone segments. Therefore, the choice of external fixation is dependent on multiple factors, including the surgeon’s familiarity with the external fixation system and the techniques of application. Some surgeons prefer external fixation to internal fixation, even for primary joint fusion, based on the aforementioned advantages of external fixation. In developing countries, the cost and availability of external fixation can be prohibitive and thus limit its use.

Unilateral and circular fixators are the most common types of external fixators available. As external fixation has evolved, these two types of fixators have been combined so that circular fixators offer unilateral attachments and vice versa. The combined external fixation devices are known as hybrid fixators. Unilateral fixators use threaded half-pins, whereas circular fixators use both threaded half-pins and smooth wires. External fixation can be constructed to conform to the shape of the foot, ankle, and/or limb deformity. In general, unilateral external fixation is preferred for correction of a limb deformity, so the pins do not interfere with the contralateral limb. Rearfoot and ankle deformity corrections can be achieved with either a ring (Ilizarov device, TSF) or unilateral external fixator. Typically, multiplanar and oblique deformity corrections are achieved with ring fixators and unilateral fixators are used for singleplane corrections.

External fixation has multiple uses: multilevel osseous and soft tissue gradual and acute deformity correction, osseous and joint distraction and compression, angulation, rotation, translation, and maintaining joint range of motion. Ultimately, these versatile characteristics provide very accurate corrections. With internal fixation, the precise deformity correction must be obtained at the time of surgery and cannot be altered during the postoperative period. With external fixation, the deformity can be continuously adjusted until the optimal clinical and radiographic result is obtained. Another advantage of external fixation is immediate postoperative weight-bearing. This is important because functional loading of the bone and joints minimizes osteoporosis. Pediatric patients heal quickly, and the need for fixation is therefore of short duration. For that reason, external fixation might be preferable for pediatric
patients, especially considering that no hardware is retained at the end of treatment. In addition, external fixation can avoid the physis in growing children; fixation across the physis is not recommended for pediatric patients. With external fixation, the patient can shower, bathe, and even swim in a chlorinated pool. These postoperative activities are not possible with internal fixation, secondary to a cast. Another advantage of external fixation is that it allows for access to the soft tissues for wound care while the deformity is corrected. Disadvantages of external fixation include bulky apparatuses, pin-site infections, and poor appearance. External fixation is not as popular with surgeons because it is labor-intensive and requires frequent follow-up visits, specialized surgical expertise, and lengthy treatment times. Increased knowledge and improved technology have tremendously expanded the indications and applications of external fixation (5,6).

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