Review of Basic Principles

Malunion reconstruction is labor and resource intensive. So it is important to understand that it is much easier to stop a malunion from occurring than it is to repair the damage once it has occurred. It is typically possible to prevent a malunion from occurring by strict adherence to the basic principles of fracture care.6 It logically follows that when a malunion is being addressed, a review of the basic principles of fracture care will provide clarity as to why the failure has occurred.

A fracture fixation construct is a structure that consists of the combination of an implant and bone. The stability of that construct is defined as the motion that occurs when it is subjected to physiological loading.6 Construct stability is relevant because fracture care is always a race between fracture healing and construct failure. The goal in fracture care is to win that race. The means by which the race is won include maximizing the environment for fracture healing and limiting the potential for construct failure. Maximizing the healing environment entails using atraumatic surgical techniques and addressing patient comorbidities, including bone metabolism issues. Limiting the potential for construct failure entails optimizing construct stability and controlling patient loading. Components of construct stability include the bone quality (docking site for the implant and the ability to share load), the original fracture pattern (simple vs complex), the surgical technique (quality of reduction and loading of bone), and the chosen implant (plate, rod, external fixator). Unfortunately, the surgeon does not control all of these components. When one or more of the components of construct stability are unfavorable, then greater care must be given to the other components. For instance, when the fracture pattern is complex and the bone quality is marginal, the surgical technique and chosen implant take on more importance.

Directional loading also makes a difference in fracture care. Biomechanical principles must be considered when evaluating injuries and failed fixation attempts. Structures obey the laws of nature; therefore, the procedural preferences of the surgeon must correspond with basic physics. Internal forces and external loads act on all fracture fixation constructs. Any fixation construct has a limited number of load cycles prior to failure. By considering these forces and loads, it is possible to design a fixation construct that minimizes failure potential. Unbalanced forces create displacement and subsequent deformity. These forces must be characterized, and the plan for fracture treatment must include specific resistance to them. When the plan is unclear, the unbalanced forces win. This is the reason that malunion radiographs typically look like the original injury films with hardware or implant/bone junction failure.

Contributing Categories

To systematically evaluate the etiology of failure, it is useful to break the problem down into contributing categories, such as injury factors, patient factors, and surgeon factors.1

Injury factors are beyond the surgeon′s control. All of these factors are manifestations of the original energy of the injury. The law of energy conservation states that energy in a system remains constant but may change forms. To evaluate an injury, it is helpful to know how this transformation occurs. Translation of Newton′s laws into orthopaedic trauma language helps to explain the process. Newton′s first law states that objects in motion stay in motion unless acted upon by an unbalanced force. The second law states that when a force acts on an object, it causes an acceleration that is predictable based on the magnitude and direction of the force and the mass of the object. The third law states that for every action there is an equal but opposite reaction; but sometimes the object with the smaller mass may not be able to withstand the larger acceleration resulting from the interaction, and energy is transferred to a different form. To clarify, a car that hits a reinforced brick wall will stop moving forward and the human inside will absorb excess energy, overcoming the ultimate strength of his bones and soft tissue. This different form is recognizable radiographically by the complexity of the fracture pattern and the initial severity of displacement. It is recognizable clinically by the severity of soft tissue injury, the open or closed nature of the fracture, and the associated neurovascular insult. All of these serve as markers for the devitalization of bone fragments and the potential for a delayed healing response or a compromised healing environment.

When retrospectively evaluating these injury factors in malunion management, information should be gleaned from a review of the original injury films and a review of the operative records or discussion with the original surgeon. Failure to invest the time to do so may prevent a clear understanding of the cause of the malunion. More importantly, it places surgeons at a disadvantage for successful reconstruction of the malunion by limiting their understanding of the unbalanced forces that must be neutralized.

Patient factors are partially under the control of the surgeon. Some factors cannot be timely optimized but should be addressed nonetheless, such as obesity, traumatic brain injury, marginal bone quality, compromised immune function, systemic vascular diseases, hepatic/renal failure, and medications/treatments that affect bone and soft tissue quality and healing (corticosteroids, immunomodulators, anticoagulants, antibiotics, radiation therapy, etc.).7–13 Other factors can and should be optimized to maximize the chances of success, such as psychiatric disorders, endocrine/metabolic bone disorders, smoking, malnutrition, visual and balance abnormalities, syncope, limited upper extremity strength for protected weight bearing, bacterial carrier status, previous noncompliance, and family support/living situation.14–18 Discovery requires a thorough history and can be completed more efficiently via a focused nonunion/malunion type inventory (Table 7.2) that can be completed prior to arrival or with the assistance of ancillary personnel. Failure to take the time to discover and deal with these associated issues puts the surgeon at a disadvantage for future successful reconstruction of the malunion.

Surgeon factors include the additional energy imparted to the fracture by the original surgeon, and the violation of basic principles of fracture care. Fracture care can be challenging even for the most experienced traumatologist. As a malunion surgeon, it is important to recognize that even the best preoperative plans are not always effectively realized at the time of surgery. Surgery is a controlled form of trauma, and each additional step that must be taken has the potential to impart more energy to already compromised tissues. The energy imparted obeys the laws of energy conservation but can be more difficult to recognize and quantify. Telltale radiographic signs of overly aggressive surgery include unusual fixation montages, retained debris, implants placed in multiple planes that indicate circumferential stripping, and excessive screw density.19 Other common radiographic signs of the violation of basic principles include incorrect choice of desired stability for a given fracture (e.g., choosing absolute stability for a highly complex extra-articular fracture pattern), initial malreductions (Figs. 7.1 and 7.2), incorrect implant type (Fig. 7.3), incorrect implant sizing, imbalanced constructs, poor plate span width, irregular working lengths (Fig. 7.4), screws placed across malreduced fractures, disregard of directional loading (e.g., choosing an implant that commonly fails in the mode of the original fracture displacement), and unlocked intramedullary rods (Fig. 7.5). Clinical signs of potentially suboptimal surgery include unusually placed or irregular surgical scars, muscle atrophy secondary to denervation, and an asymmetric vascular examination not evidenced in the original history and physical. Discovering these surgeon factors requires a detailed study of the original documentation and radiographs as well as the early postoperative films. They can often be confirmed or clarified through communication with the original surgeon.

Management

There is no substitute for experience in failure analysis. An experienced trauma surgeon performs a proactive failure analysis when approaching both acute fractures and nonunion/malunion reconstruction. A goal for the end of the procedure should be established at the very beginning. The surgeon should be knowledgeable about historical failure modes, and should understand how specific patterns commonly displace and how specific implants commonly fail. The surest way of achieving success is for the surgeon to have as broad and deep an understanding as the problem requires. This good judgment typically evolves from experience, especially the experiences of past bad judgment. To optimize patient care, these learning curves should not be repeated. By explicitly studying failure, consulting more experienced surgeons, and studying the works of experts, good judgment can be achieved without patient harm.

Coronal or Frontal Plane

The frontal plane corresponds to the patella-forward position, with a few exceptions (e.g., altered patellofemoral mechanics, such as trochlear dysplasia or static patellar subluxation).21 This means that to adequately evaluate this plane, it is necessary to have a well-centered patellaforward radiograph, regardless of the position of the foot that this requires (Fig. 7.8). This necessitates either a knowledgeable X-ray technologist or the assistance of the operative surgeon. To ensure the image is ideal, the patella should rest in the center of the trochlea on the side being evaluated. Ideally both sides would be placed in the patella-forward position to facilitate comparison and determination of the patient′s normal anatomy. Occasionally, this bilateral position is impossible because of extreme rotational abnormalities or stiff joints.

Hip to ankle standing films are ideal for assessing the mechanical axis of the extremity. The mechanical axis of the extremity is the weight-bearing axis and is defined by a line drawn from the center of the femoral head to the center of the ankle joint. The mechanical axis should traverse the center of the knee joint (8 mm ± 7 mm medial to the center of the knee joint).21 If the mechanical axis traverses the knee joint more lateral than the value noted above, then there is a lateral mechanical axis deviation, and attention should be paid to discovering at what site(s) the valgus is occurring (Fig. 7.9). If the mechanical axis deviates more medial than the value noted above, then the extremity is in varus and attention should be paid to discovering at what site or sites the varus is occurring. For posttraumatic deformities, the varus/valgus would be expected to occur at the site of the previous fracture. This does not mean that other sites should not be explicitly evaluated by drawing out angles at each level and comparing them to the contralateral uninjured side or population norms. To clarify through an example, a bicondylar tibial plateau fracture may heal in varus after lateral locked plating, creating a posttraumatic deformity. This may have been set up in the beginning, even with an appropriate reduction of the tibial plateau fracture, secondary to a varus distal femur creating a mechanically unsound situation from a preexisting medial mechanical axis deviation. Although the additional deformities may not be corrected, discussion of these preexisting deformities with the patient will help set realistic expectations and help to explain one source of failure.

In cases in which the contralateral extremity was injured, it is extremely helpful to have baseline knowledge of population norms (Fig. 7.10). These norms should be either committed to memory or kept close by for reference even in acute fracture treatment. These norms have been defined based on mechanical and anatomic axis lines (anatomic axis lines are drawn by connecting multiple center positions of the canal for a specific bone). Anatomic axis lines are especially helpful intraoperatively during correction as the field of view for the fluoroscopy machine is limited.

A common way to radiographically define the angulation of a deformity is to draw the anatomic axis lines of the different segments of the deformed bone and measure the angle created by those lines. If the lines do not intersect in the bone at the deformity, then translation is also present (Fig. 7.11). When long segments are not present (e.g., metaphyseal deformity) or when the deformity occurs over a large area (e.g., bowing rather than acute angulation), then anatomic axis lines are difficult to draw. In these cases, it is useful to consider alternative methods of defining the deformity. One alternative way to radiographically define the angulation of a deformity is to superimpose the contralateral side image onto the deformed side. This can be done with a tracing, if the facility has a radiograph printer. This is an extremely powerful learning exercise in that it requires an intense focus on both normal anatomy and the deformity. Average dimensions, contours, and shadows become intuitive, and the gestalt is learned and clarified.22

Clinical evaluation of the patient with coronal plane angulation or translation is completed by observing the limb, preferably both in the supine and in the standing position. The standing position helps magnify the contribution of ligamentous laxity and muscle atrophy by providing dynamic loading. Observing just the unloaded limb in the supine position can lead to an underestimation of the functional deficit created by the deformity. The clinical findings and radiographic findings should logically correlate (e.g., if a patient appeared bow-legged, then the expectation is to find a medial mechanical axis deviation and varus occurring at one or more sites on the standing patella-forward radiograph). When the radiographs do not clearly correlate with the physical exam findings, care must taken to evaluate alternative sources of deformity (e.g., soft tissue contractures, ligamentous deficiencies, psychiatrically driven pseudodeformities).