CLASSIFICATION OF PERIPROSTHETIC FRACTURES COMPLICATING TOTAL KNEE ARTHROPLASTY

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More total knee arthroplasties are being performed than in the past, and as the population ages, more and more are expected to be performed. As the total numbers of knee arthroplasties increase, the frequency with which complications will be encountered can be expected to increase as well. Periprosthetic fracture occurring in relation to total knee arthroplasty presents significant challenges to the orthopedic surgeon. Clear guidelines do not yet exist as to the best way to manage many of these fractures. An important aspect of the development of understanding of these problems is the classification of these fractures. Adequate classification systems allow accurate communication between researchers and comparisons to be made between different techniques. Classification systems also allow algorithms to be developed to guide the diagnosis, investigation, and treatment.

Classification systems abound in the orthopedic literature. For many orthopedic conditions, there are multiple classification systems, each of which has been proposed by the developers of that system as a step forward in the understanding of that particular aspect of orthopedics. Many classification systems were developed in the past in relation to a specific problem and then have been modified over time as the understanding, investigation, and treatment of that problem have changed. It has become apparent that many classification systems are difficult to apply to common clinical situations and that orthopedic surgeons apply them differently when looking at the same data at a different time (intraobserver variability) and differently from other surgeons looking at the same data at the same time (interobserver variability).

The ideal classification system is one that is specific for a particular problem and yet is inclusive of all of the most important aspects of that problem. It should describe the condition and act as a guide for the management of that condition if the classification is meant to be used by clinicians. The system should also provide information to allow prognostication to guide the clinician and the patient. If the classification system is designed to be used for research purposes, it needs to be more inclusive and descriptive than one aimed solely for clinical use. The classification system should be relatively easy to understand and apply, and it should be based on readily available investigations. It must be widely accepted, understood, and used so that orthopedic pathology, its investigation, its management, and results can be communicated to others. This communication allows comparisons to be made with the findings of others so that meaningful conclusions can be drawn.

Ideally, there should be a limited number of variables to input into the classification. This limitation means that some variables that may affect management would not be included in the classification. The most important factors must be recognized and included, however, while it is acknowledged that on occasions other factors need to be considered. The application of the classification system must be reliable and reproducible both by one surgeon at different times and by several surgeons. Finally and importantly, it must be recognized that because the nature of the human body and its diseases is for unlimited variability, any classification system is doomed to fail in its bid to described all possible situations.

The classifications used for periprosthetic fractures around knee arthroplasty, similar to many others, have evolved from a variety of sources. The classifications commonly used today share many of the deficiencies of other classification systems but on the whole have been modified over time to guide treatment successfully.

Specific classification systems have been developed regarding periprosthetic fractures complicating total knee arthroplasty. The fracture can also be classified in more general terms, defining factors such as the timing of the fracture, fracture location and description, the condition of the patient, and the quality of the surrounding bone (Table 1).

The factors outlined in Table 1 are important to consider when managing periprosthetic fractures. Many of these factors significantly alter the decision-making process regardless of how else the fracture is classified. For example, a periprosthetic fracture occurring in the presence of severe bone loss and osteoporosis may not be able to be treated with reduction and internal fixation, or a fracture in a patient whose medical condition makes any surgery unsafe requires nonoperative management. These factors are not included in most fracture classifications, but they need to be considered before selecting treatment.

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SUPRACONDYLAR FRACTURES

Supracondylar fractures are the most common fractures occurring around total knee arthroplasties. The incidence has been reported as 0.3% to 2.5%. Factors that can predispose to these fractures include intraoperative notching of the femur, osteolysis, osteoporosis, rheumatoid arthritis, corticosteroid use, increased age, female sex, and certain neurologic disorders.1, 2, 3, 4, 7, 11, 12, 15, 16, 17

The classification system of Neer13 has been used for these fractures. This system was originated

TIBIAL FRACTURES

Periprosthetic fractures of the tibia occur infrequently. They may occur intraoperatively as a result of impaction of a prosthesis with a stem that impinges on the cortex. They can also be caused by inadequate preparation of seating holes for pegs or fins.5, 6 Malalignment of the tibial component has been associated with stress fracture of the tibia. Rand and Coventry14 reported on 15 patients with tibial fractures after total knee arthroplasty and found that most were associated with axial

PATELLAR FRACTURES

Patellar fractures complicating total knee arthroplasty may occur as a result of excessive bone removed during the resurfacing procedure, malposition of the component, and avascularity of the patella.5, 10 Several factors have been identified as being important in guiding management and allowing prognostication in the case of a periprosthetic patellar fracture. Probably the most important are the degree of displacement of the fracture, whether the extensor mechanism is intact or not, and how

CONCLUSION

Classification of orthopedic conditions is important to allow communication among researchers and clinicians, to guide treatment, and to provide insight into likely outcomes. Several classification systems exist in relation to periprosthetic fractures complicating total knee arthroplasty. The important factors in relation to these fractures are the anatomic location of the fracture, the degree of displacement, the status of the implant, and whether the extensor mechanism is intact. The authors

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Address reprint requests to Cecil H. Rorabeck, MD, London Health Science Centre, University Campus, 339 Windermere Road, London, Ontario, Canada N6A 5A5

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Department of Orthopaedic Surgery, London Health Sciences Centre, The University of Western Ontario, London, Ontario, Canada

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