Current Concepts In External Fixation

While external fixation will not replace internal fixation in the surgical toolbox, it does offer a number of specific advantages. Using external fixation has become routine for initial reduction and stabilization of comminuted long bone fractures, and is often used in conjunction with a few judiciously placed lag screws. In the presence of compromised soft tissue, external fixation becomes essential. Unlike internal fixation, which becomes a fixed, static construct once you apply it, external fixation can be quite dynamic in certain forms. It is common during postoperative periods to adjust the fixators in order to improve skeletal alignment or apply compressive or distractive forces across joint fusions. In addition, one can gradually adjust Ilizarov frames to correct chronic angular and torsional deformities via bone callus distraction and ligamentotaxis. Severe deformities, such as untreated adult clubfoot, are often not acutely correctable because of neurovascular adaptation. However, one can achieve correction of these deformities through the Ilizarov method. Since many external fixation constructs are, by design, extremely rigid and stable, it’s possible for patients to have partial to full weightbearing status while they use the devices. It is not uncommon for an individual being treated for a segmental bone loss of the tibia with external fixation to be walking on his affected limb during lengthening. Furthermore, while managing fusions and comminuted fractures, once consolidation of the bone fragments has begun, one can gradually decrease the rigidity of the construct in order to allow the underlying bone to bear increasing loads (dynamization). Obviously, this would be impossible with internal fixation. Perhaps the most exciting application of external fixation is in the treatment of both acute and chronic Charcot neuroarthropathy. It has been shown that patients with this disorder have reduced bone mineral densities in the bones of their feet. As a result of this osteopenia, rigid internal fixation becomes a rather poor option in any reconstructive procedure. However, by using thin wires in a multi-planar array, one can apply rigid fixation to the foot and leg without significant risk of loosening of the implants. Other advantages of using external fixation include the following: • it provides neutralization or fixed distraction in limb length discrepancies; • it is ideal for treating infected joints in which arthrodesis is desirable or non-unions; and • it facilitates direct visualization of local wound status, flaps or skin grafts. Weighing The Potential Disadvantages However, one should also be aware that there are some distinct disadvantages to external fixation. Since there are multiple sites where you would apply both thin wires and thicker bone pins percutaneously, there is always the risk of pin tract infection. This risk approaches 100 percent when frames must remain in place for more than six weeks. When treating significant long bone deformities, keep in mind that it is not uncommon for fixators to remain on a limb for more than six months. Given the exposed hardware, the patient must play an active role in caring for his or her fixator, in terms of avoiding pin tract infections, not putting the frame at risk and notifying you if problems develop. External fixators, particularly circular frames, should be avoided when treating noncompliant patients. Indeed, patient acceptance of an external fixator for extended periods of time may wane during the period of treatment. Ensuring adequate preoperative education on the length of treatment as well as proper care of the device will help prevent the development of “cage rage.” However, there are certain patients who are not comfortable with the concept and would not be suitable candidates for external fixation. When using external fixation, another potential problem one may encounter is inadvertent neurovascular injuries. This may occur by a poorly placed wire or bone pin or occur during a lengthening procedure in which the rate of distraction exceeds the rate of growth of nerves in the area. One can avoid most of these complications by simply being cognizant of the location of the major neurovascular bundles, and by monitoring for sensory loss several times daily during lengthening procedures. One should monitor the presence of post-application pain. If the patient’s pain is increasing, it may signify a pin tract infection or a loosening of one or more of the pins, which produces vibration of the tissue and a reactive inflammatory response. Needless to say, extended immobilization of any joint will lead to stiffness. So it is essential for the patient to begin physical therapy as quickly as possible. External fixators, particularly circular frames, provide stress shielding to the bones that they pass over. As a result, those bones become osteopenic, proportional to the duration of the treatment. It is not uncommon for a patient to develop a stress fracture in the tibia or the calcaneus after the frame is removed. Therefore, it is important to protect the limb for a prescribed period after removing the frame. Also bear in mind that external fixators, particularly circular frames, are technically difficult to apply. As in all things, there is a learning curve that is quite steep and should not be underestimated by the novice. Fortunately, there are a number of courses offered by several manufacturers as well as courses offered through the American College of Foot and Ankle Surgeons that can provide a starting point. A final disadvantage to consider is the cost of external fixation. External fixators are expensive when compared to internal fixation. In order to justify the increased cost, the benefits to the patient must outweigh the financial concerns of the institution. What The Literature Reveals The application of external fixation in arthrodesis of the foot and ankle was inevitable. (See “A Brief Historical Overview Of External Fixation” on page 34.) It can be applied in any major joint of the foot as a primary or a salvage procedure. Other indications include infected nonunions, complex comminuted fractures, neuromuscular disorders, limb length discrepancies as well as acute and chronic Charcot neuroarthropathy. In 1955, Hulbert was the first to describe the compression clamp for arthrodesis of the first metatarsophalangeal joint.23 To date, rigid internal fixation is more common for arthrodesis of the aforementioned joint.24-26 However, employing external fixation is suitable for treating infected nonunions, septic arthritic and revisional cases. The tarsometatarsal articulation is a complex joint that is made up of the articulations between the metatarsals, the cuneiforms and the cuboid. The actual joint line is uneven due in large part to the recessed base of the second metatarsal. When there is degenerative arthritis of the Lisfranc’s joint without deformity, in situ fusions with internal fixation is most likely the technique of choice.27 Comminuted fracture-dislocations of the Lisfranc’s joint, infected non-unions and failure of internal fixation are best treated with external fixation. External fixation has also recently been used in the fixation of triple arthrodesis. It may take the form of a hybrid configuration or can be combined with a large lag screw in the subtalar joint with rails for the talonavicular and calcaneocuboid joints.28 One may use a series of rails with bone screws and transfixion pins or one may opt for a complete Ilizarov frame. In 1951, Charnley described the compression arthrodesis of the ankle and shoulder after he successfully used the same technique in arthrodesis of the knee.9,10 Ilizarov and Okulov reported on the use of external fixation in ankle arthrodesis in 1976.12 Since then, ring fixators have been commonly used for posttraumatic ankle arthritis, severely comminuted tibial plafond fractures, septic arthritis, osteomyelitis, Charcot ankle, nonunion and malunion of the ankle, equinocavus and osteonecrosis.29-36 Posttraumatic osteoarthrosis, neuromuscular disorders and painful rheumatoid ankle and hindfoot are some of the indications for pantalar and tibiotalocalcaneal arthrodesis.37-40 However, be aware that outcomes for pantalar fusions are not as good as the outcomes for ankle fusion or triple arthrodesis when they are performed alone.41 One may use a multiplanar ring frame or a hybrid system of rails to fixate all four joints and provide a stable environment for fusion. Certainly, using thin wires avoids the problems of trying to fuse the ankle and subtalar joint with large lag screws, which often compete for space within the talus. If one is considering external fixation for a pantalar or tibiotalocalcaneal arthrodesis, keep in mind that a circular frame is preferred over the other systems.42 This enables one to apply multiple motors to the connecting rods, which would allow postoperative adjustment in the event of a delayed union. Should You Consider External Fixation For Charcot’s Arthropathy? Multiplanar frames have been introduced for the treatment of Charcot’s arthropathy. Treatment of acute Charcot events has traditionally been conservative as physicians used casting and offloading with no attempt to reduce the deformity. Treatment of chronic deformities has involved the use of Crow walkers. Only recently have surgeons considered reconstruction via tarsal osteotomies as only a few papers have appeared in peer-reviewed journals describing the use of external fixation for such treatment. On the other hand, using internal fixation to treat Charcot patients can be problematic due in large part to the significant osteopenia associated with the disorder.43,44 By employing external fixation and multiplanar thin wires, the likelihood of fixation-induced collapse, at least intuitively, should be reduced. Additionally, using external fixation reduces the need for extensive surgical exposure in reconstruction and may provide a means of reducing acute Charcot deformities and maintaining the reduction during consolidation. When treating a patient who has Charcot neuroarthropathy with a significant forefoot abduction and plantar prominence at the Lisfranc’s joint, performing a wedge resection of the bases of the metatarsals and distal cuneiforms lends itself well to applying an external fixator. Using a single medial incision allows arthrodesis of the medial three joints as a unit, utilizing a ring fixator. In acute and chronic Charcot deformities with avascular necrosis, osteomyelitis or severe dislocation of the talus, a tibiocalcaneal fusion with an external skeletal frame is indicated. One may also consider combining a tibiocalcaneal arthrodesis with tibionavicular and calcaneocuboid fusions for patients with untreated rigid talipes equinovarus.45 While the incidence of nonunion of a tibiocalcaneal fusion is variable, a stable, fibrous nonunion is often a most acceptable alternative.46,47 Final Thoughts External fixation is gaining recognition in the management of foot and ankle pathology. Certainly, the advantages are well recognized but there are also some limitations. We also emphasize that this method should only be utilized by experienced surgeons who have a complete knowledge of the anatomical, structural and physiological properties of bones and soft tissue. Dr. Jolly is the Chief of Podiatric Surgery and is the Director of the PGY IV Fellowship in Reconstructive Foot And Ankle Surgery at New Britain General Hospital in New Britain, Ct. He is also a Clinical Professor of Surgery at the Des Moines University School of Podiatric Medicine and is the President-Elect of the American College of Foot and Ankle Surgeons. Dr. Blume is a Clinical Assistant Professor in the Department of Orthopaedics and Rehabilitation at the Yale School of Medicine. He is also a Fellow of the American College of Foot and Ankle Surgeons and is the Director of Limb Preservation at the Yale New Haven Hospital in New Haven, Ct. Dr. Zgonis is a Fellow in Reconstructive Foot And Ankle Surgery at the New Britain General Hospital in New Britain, Ct., and is a PostDoctoral Research Fellow within the Department of Orthopaedics and Rehabilitation at the Yale School of Medicine.
 

References:

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