Mastering Complications In External Fixation

Author(s): 
By David Kanuck, DPM, and Gary Jolly, DPM

   Any surgical procedure carries a risk of complications. Whether one opts to utilize internal or external fixation, there is both a common and yet unique set of problems based on hardware design and usage. Therefore, it is imperative to obtain an intimate working knowledge of the equipment and its capabilities in order to maximize the true potential of each method and hopefully minimize the risk of complications.    The ability to control an internal surgical environment by external manipulation is a powerful tool that is unique to external fixation. This “third dimension” empowers the surgeon to perform functions such as distraction, compression and neutralization in order to address suboptimal positioning postoperatively. It also enables one to extend the surgical procedure intentionally into the postoperative phase to facilitate gradual correction of deformities. Specifically, surgeons can accomplish this through frame morphing and adjustments via wire and ring modification. This distinction allows surgeons to address many problems in a “bloodless” fashion.    Therefore, it is not unreasonable for the initial frame setup to vary in construction prior to its final removal. This article focuses on the wire, the single most important component of external fixation. After all, it is the interface of wire and human tissue where most common complications occur.    The wire serves as an interface between an internal biological environment and an external mechanical one. This marriage between two subsystems results in the creation of a new entity that exists in a delicate balance. One should view the wire as the foundation to frame construction. A poor foundation will ultimately result in an unstable structure and lead to complications. Pin tract infection, nonunion, malunion, delayed union, hardware failure and neurovascular embarrassment are all complications that can be traced to this frame component.    The wire’s anatomic location serves as a passageway for organisms to colonize and possibly infect soft tissue and bone. This unique feature is why pin tract infections (PTI) are considered the most common complication associated with external fixation.    The key to treating and reducing the number of PTIs is understanding the etiology. A loose wire has a tendency to toggle, which irritates the bone and surrounding soft tissue. This action may provoke an inflammatory response and increases the susceptibility and passage of opportunistic pathogens. Therefore, one should strive to prevent wire loosening. One can reduce the incidence of PTIs through the judicious application of wires in terms of location, attachment to the ring, crossing angle and having a sufficient number of wires to produce a stable construct.

Key Insights In Designing The Ex-Fix Device

   After the patient has agreed to undergo the procedure (see “Why Appropriate Patient Selection And Education Are Essential” below), one should form a preoperative plan. Evaluate clinical and radiographic exams, and proceed to address decisions regarding components (such as wires and rings) of the frame construct.    The type of wire one selects is important because not all bones and not all parts of a bone have the same density (medullary vs. cancellous). Wires, by design, are engineered to cut bone differently, generating variations in heat production. Therefore, when one is working with the metaphyseal sections of long bones, use trochar tipped wires and bayonet tipped wires for diaphyseal bone if the choice is available.    Wire size is also an important factor that one should not overlook when selecting wires. The most commonly used wires are 1.5 and 1.8 mm but they also exist in 1.0 mm and 2.0 mm diameters. Improper size can lead to broken hardware, loss of compression and instability. A broken wire further burdens the remaining wires and can lead to premature loosening and infection. In addition, hardware failure might result in an unplanned visit to the operating room. Therefore, the criteria for selecting wire size should include the type of procedure, the patient’s weight, bone quality and the location on the extremity.    The ring is another component of an external fixator that requires preoperative consideration. It not only shares an intimate relationship with the wire but directly contributes to the construct’s stability. Variations in limb size require variations in ring size. The closer the ring is to the extremity, the more stable the construct.    However, spacing between the ring and limb is necessary to accommodate the routine ebb and flow that is endemic to postoperative swelling. As a general rule, a distance of two to three finger breadths is considered adequate at the posterior leg. A small ring can lead to constriction of edematous soft tissue, resulting in pain and ulceration. When this occurs, the surgeon faces sectioning out a part of the ring to prevent further deleterious effect. On the other hand, a ring that is too large may cause undue stress on the wires with subsequent breakage.

Emphasizing The Importance Of Proper Wire Handling And Insertion

   The role of the surgical assistant is of equal importance to the job of the surgeon. This point cannot be overstated. The success of frame construction and, ultimately, the surgical outcome depends greatly on the feedback and cues an assistant provides. For example, flexing and extending the toes, midfoot and ankle at appropriate moments during wire driving and frame construction magnifies the clarity of the anatomic landscape. The surgeon cannot effectively perform both tasks and both are important.    Proper wire handling emphasizing sterile technique is essential. When a wire is passed from the technician to the surgeon and is subsequently inserted, the wire should not directly touch gloves. Instead, one should pass wires with a dampened saline/alcohol gauze pad. This will not only clean the wire but prevent contamination and serve as a method of wire cooling during the insertion process. After establishing an anatomic location for wire insertion, an assistant cleans the area with solution. This action reduces the bacteria load from exposure and prior handling.    The wire insertion process involves three steps. First, one should press the wire through soft tissue until the surgeon engages the bone. Proceed to pulse drill the wire. Do not run the drill continuously as this will generate more heat and possibly lead to thermal necrosis of bone. The pulse sequence can be based on a five-second count.    After exiting the far cortex of the bone, substitute the drill for a mallet and continue with the insertion process. The benefit of the mallet is twofold. It reduces the amount of heat production and prevents the damage to soft tissue structures such as neurovascular bundles and tendons. As the wire exits the tissue, the assistant should once again use a dampened gauze pad to cool the wire directly.    If two cortices are not engaged during wire insertion, remove the wire and reinsert it. The engagement of a single cortex is a far more unstable construction and will likely result in early wire removal. This error commonly occurs when one tries to achieve larger crossing angles in the tibia and the wire winds up riding along the medial face of the bone. In this scenario, the wire enters and leaves a single cortex.    One can maximize crossing angles without compromising stability by adding a wire in either a dropped or raised fashion 4 cm above or below the ring. Then use a post to connect the wire to the ring. This technique avoids the potential injury of structures by offsetting the site of fixation.

Attaching The Wire To The Frame: How To Prevent Excessive Tensioning And Other Complications

   Attaching the wire to the frame is a critical technique often overlooked, equally misunderstood and mistakenly executed. One must consider how axial loading will place stress on this subsystem (wire/bolt/nut construct). Understanding this factor helps one appreciate the importance of the wire tightening/tensioning sequence. This includes the slotted side of the bolt into which one places the wire, the direction one should turn the bolt and nut, and the alternative use of locking nuts. Poor fixation and tensioning will result in instability, which leads to wire loosening and inflammation.    A technique that may reduce the incidence of soft tissue irritation involves pulling the skin and soft tissue away from the point where one would introduce the pin. Whether performing bone lengthening, gradual deformity correction or bent wire compression, if the surgeon anticipates positioning the wire at the end of the procedure, he or she can predict the location of skin tension.    For example, if performing a lengthening procedure, pull the tissue located at the proximal wire site in a distal direction prior to insertion. Conversely, one should pull tissue located at the distal wire site proximally. This produces a redundancy of tissue similar to an accordion in the central area between two rings. As the bone lengthens, the soft tissue will stretch and unravel. The prior knowledge and preparation prevents excessive tensioning at the skin/pin interfaces, which could lead to skin necrosis.    If one is to achieve compression by using a bent wires technique such as in a triple arthrodesis, the surgeon can also mobilize tissue to prevent kinking at the skin/wire interface. For example, prior to inserting the talar wire, push the skin distally so when the wire moves proximally on the ring, the redundancy of tissue distal to the wire will unfold and avert an area of excessive tension.    When the patient begins to ambulate, he or she may encounter muscle irritation during the loading cycle when the patient begins to ambulate. However, when it comes to pain and pin site inflammation secondary to “asymmetric tensioning,” the process of fixing opposing muscles in an unbalanced position, one needs to address this intraoperatively. In regard to the anterior and posterior compartment of the leg, when entering or exiting soft tissue from a posterior position, one should dorsiflex the foot. This maneuver tensions the posterior muscle group.    Conversely, when entering or exiting the muscle that is located in an anterior position, one should place the foot in a plantarflexed position. This enables two antagonistic muscle groups to function harmoniously through equal extension and flexion. This balance has a direct effect at both the skin-wire interface and on the overall stress absorbed by the wire.

What About Potential Nerve Injuries?

   Injury to neurovascular structures is a major complication of external fixation. Accordingly, one should consider established anatomic safe zones when inserting wires. Nonetheless, there is a potential for injury of these structures and it does happen occasionally. Early recognition is key to preventing permanent damage. Obvious insult to a nerve by wire often results in a sudden twitching or contracture at the foot or ankle. If this occurs, extract the wire from that site and reinsert it.    However, not all nerve injuries are as readily apparent. Injury to nerves can present with subtle clinical manifestations, such as light twitching or contracture at the level of the digits, that can escape even a perceptive surgeon’s eye. In order to prevent such oversights, an assistant should place one hand on the plantar aspect of the foot, including the toes, while driving each wire. If one suspects nerve impingement once again, extract the wire and reinsert it. Injury to a nerve will present as neurogenic pain in the postoperative period. This is often difficult to manage with pain medication and will usually require an early trip back into the operating room.    After one has applied the frame, the surgeon should inspect the wire-skin interfaces for tension and release them appropriately. Re-check the components of the frame. At this time, one should accordingly secure, tighten or tension loose parts, some of which may have been overlooked during the procedure. Clean the extremity. Proceed to apply the dressing initially with the use of rubber stoppers in order to facilitate compression and reduce tissue expansion over the wire.

Pertinent Points On Pin Tract Infections

   Scabbing and erythema around pin sites invites exploration and curettage if necessary. Curettage decompresses the site and facilitates an alternative route for a brewing infection in a direction diverted away from the bone. It is more common to see irritation at wires in a proximal position because the larger muscle mass has a greater effect on the wire. Lastly, reserve dressings for areas of drainage and early postoperative care. Once one has established a natural seal between wire and skin, the need for dressings is superfluous.    In regard to treating pin tract infections, we have adapted a simple classification.1 The sequence of grades 3 and 4 is variable.    Grade 1: local treatment    Grade 2: antibiotics (po)    Grade 3: antibiotics (iv)    Grade 4: pin removal    Grade 5: pin removal and surgical debridement    Grade 6: bone resection    It is common to prescribe oral antibiotics during the postoperative period and surgeons should not necessarily view this as a failure on their part. However, prevention remains the best weapon in the arsenal to address this type of complication.

Understanding The Impact Of Post-Op Weightbearing

   After addressing pin care, one should focus on the fixator and its components. Loading the limb and ambulating are very dynamic actions. The cycle of loading and unloading the limb during weightbearing activities stresses the interface among the wire, frame and the limb. It is therefore imperative to check these points of contact routinely and tighten and retension the wires appropriately. One should start by tightening the ring and rod connections. Once they are secured, proceed to tighten the wire bolt fixation sites. This ensures a stable ring-to-ring and wire-to-ring construct.    The practice of framing a patient and not incorporating some degree of weightbearing over the course of treatment relegates the frame to nothing more than an expensive cast. Joint stiffness and muscle atrophy are often associated with extended immobilization. One commonly observes these dilemmas with internal fixation and lengthy casting. Incorporating physical rehabilitation as part of the postoperative period can combat the negative effects associated with extended immobilization.    Although early weightbearing and range of motion are well known advantages of external fixation, patients are not immune from joint stiffness and muscle atrophy if one does not consider a joint sparing or early rehabilitation strategy prior to applying the frame. For example, if one incorporates a surrounding joint in the frame design and the joint is not directly involved in the traumatic or pathologic condition (i.e., ankle joint in a nonarticular calcaneal fracture or triple arthrodesis), the surgeon should consider using hinges to connect one ring to another.    During the first three weeks after surgery, the hinges can remain locked to provide stability. After three weeks, one can unlock the hinges during physical therapy to mobilize the ankle. Upon completing physical therapy, return the hinge to a locked position. With time, one can unlock the ankle joint during weightbearing activities. An alternative to using hinges is designing a ring construct that does not incorporate the surrounding joint(s) at all, abbreviating the frame.

In Conclusion

   In isolation, each of the fundamentals of frame building might have a marginal effect on frame construction and outcome success. However, when one combines these basic techniques, there are additive benefits for patients. When one routinely applies these frame building fundamentals, there will be less need to enhance the frame stability and a reduced occurrence of wire irritation, edema and pain. Initial application of external fixation can be both a challenging and intimidating undertaking but these concerns subside with proper training and repetition.    It is important to remember that external fixation is not about how many components one can utilize in a single frame or how elaborate a construct one can fabricate. Instead, the surgeon should follow the principles, laws and rules that make up the “Ilizarov system.” Adhering to these basics of frame building will result in a more stable construct and reduce the risk of complications. Dr. Kanuck is a Revisional/Reconstructive Fellow at New Britain General Hospital in New Britain, Ct. Dr. Kanuck’s e-mail address is drdamikan@yahoo.com. Dr. Jolly is a Fellow, Past President and Director of Fellowship Training of the American College of Foot and Ankle Surgeons. He is the Chief of Podiatric Surgery and the Director of the PGY IV Fellowship in Reconstructive Foot and Ankle Surgery at New Britain General Hospital in New Britain, Ct. Dr. Jolly is also a Clinical Professor of Surgery at the Des Moines University School of Podiatric Medicine and Surgery. Dr. Jolly’s e-mail address is gjolly8060@aol.com. Editor’s Note: The authors acknowledge the skilled teaching faculty, surgeons and staff at the Ilizarov center in Kurgan, Russia. They note the article and photos could not have been possible without the sharing of their knowledge, experience and wisdom.
 

 

References:

1. Sims M, Saleh M. Protocols for the care of external fixator pin sites. Professional Nurse 1996; 11(4):261-264.

 

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