Classifications In Brief: Salter-Harris Classification of Pediatric Physeal Fractures
- 1.6k Downloads
Fractures involving the epiphyseal plate, or physis, are common musculoskeletal injuries occurring in children with open growth plates. These fractures represent between 15% and 18% of all pediatric fractures [13, 24, 26] and present diagnostic and treatment challenges for orthopaedic surgeons. The first detailed description of injuries involving the epiphyseal plate was in 1863 by Foucher . In 1898, Poland classified these fractures into four types . Aitken further defined the characteristics of different types of physes with respect to structure, location, weightbearing status, and susceptibility to injury, suggesting that prognosis be considered on an individual basis .
An ideal fracture classification system should be reproducible, possess high inter- and intraobserver reliability, anticipate prognosis indicator, and guide clinical decision-making.
Physeal injuries have the potential for growth arrest and resulting deformity; however, not all injuries to the physis pose the same risk. Therefore, a classification system that is able to identify injury patterns that carry a high risk of physeal arrest and deformity would be desirable. Salter and Harris’  originally stated purpose was the accurate description of physeal injuries and prognosis relating to premature physeal closure.
To understand the pathomechanics of a physeal fracture, a basic understanding of growth plate histology is necessary. Salter and Harris  performed extensive histologic analysis of normal physeal anatomy, fracture patterns at the physis, and physeal healing after fracture.
The physis can be subdivided into four different zones, starting from the epiphysis and extending to the metaphysis (Fig. 1). Zone 1 is the “resting zone” and is located adjacent to the epiphysis and contains resting cells or germinal matrix, largely composed of relatively metabolically inactive chondroblasts. Zone 2 is the “proliferative zone” and contains more active chondrocytes that produce extracellular matrix proteins. Zone 3 is the “hypertrophic zone” and contains chondrocytes that are larger and more organized, but have decreased production of extracellular matrix proteins. This zone often is broken into three subzones: the zone of maturation, the zone of degeneration, and the zone of provisional calcification. The zone of provisional calcification constitutes a transitional area between calcified and noncalcified extracellular matrix proteins, effectively making this zone the weakest . Through histologic analysis, Salter and Harris showed that fracture propagation and physeal separation typically occur at this level. Zone 4 is the final layer—the “zone of calcification”—where cartilage is calcified and begins to be remodeled into bone.
The physis is encircled at is periphery by fibrocartilaginous tissue that includes the groove of Ranvier and the ring of LaCroix (Fig. 1). The groove of Ranvier is a microscopic stricture at the diaphyseal end of the physis. It contains chondroblasts, osteoblasts, and fibroblasts that support the peripheral growth of the physis. The ring of LaCroix is a strong fibrous structure that overlies the groove of Ranvier and connects the epiphyseal periosteum to the metaphyseal periosteum, adding stability to the physis .
Salter and Harris  reported that, in the majority of physes, the blood supply to the proliferating cells arises from the epiphysis via its periosteum. Since the zone of provisional calcification is metaphyseal relative to the proliferating cells of the physis, epiphyseal blood supply theoretically remains intact with Types I and II fractures. Conversely, Types III and IV fractures exit epiphyseal, violating and potentially devascularizing the proliferating cell layer. Salter and Harris recognized that certain physes were especially prone to devascularization, namely the femoral and radial head. The epiphyses in these locations are completely covered by articular cartilage and have no periosteal blood supply. Alternately, the blood supply is metaphyseal and laterally traverses the rim of the physis, easily disrupted by the shear forces seen in a Type 1 fracture .
This model provides a framework to think about the types of physeal fractures, however, clinical reality is somewhat more complex. Subsequent histologic studies have shown that, depending on the forces involved, physeal injuries commonly involve multiple layers of the physis and rarely are isolated to the zone of provisional calcification [9, 14]. This is clinically evident with Type II fractures. These fractures can result in growth arrest despite theoretically leaving the proliferating cells and their blood supply intact. Jaramillo et al.  reported that MRI has the ability to elucidate which physeal zones are involved in an injury, allowing for better understanding of the growth plate injury.
Although the Salter-Harris classification is in common use, there are relatively few formal validation studies. Thawrani et al.  examined the intra- and interobserver reliability of classifying pediatric distal tibia fractures and found very high rates of intraobserver reliability and fairly robust rates of interobserver reliability (Kappa coefficient, 0.57–0.67). Several studies have compared the ability to classify fractures involving the growth plate on plain radiographs versus three-dimensional (3-D) imaging [11, 19, 27]. These studies do not specifically use interobserver reliability as an endpoint, instead showing that fracture displacement is consistently underappreciated on plain radiographs [11, 19], and that 3-D imaging can better elucidate fracture patterns and change the classification of the fracture .
A high rate of interobserver reliability of the classification is important to its clinical utility. Despite a lack of formal validation, the Salter-Harris classification has stood the test of time and is in widespread use. One may speculate that this prevalence is attributable to its inherent simplicity and being nearly universally known in the orthopaedic community. There are limitations to using a poorly validated classification system and there may be some benefit to perform additional validation studies of the Salter-Harris classification.
The most significant limitation, as discussed above, is a paucity of studies formally validating the Salter-Harris classification, including interobserver reliability, intraobserver reliability, and accuracy in predicting fracture behavior. This validation is necessary to establish confidence in the classification and its implications. Lack of validation does not mean the classification is invalid, however, users should be aware of this limitation and use the classification accordingly. Future efforts to improve validation of the Salter-Harris classification could potentially resolve these concerns.
Another major limitation is that the Salter-Harris classification is not an independent predictor of a fracture’s prognosis. It is tempting to equate physeal arrest with prognosis when discussing fractures involving the physis, however, physeal arrest is only one component and is of variable clinical significance depending on remaining growth and the location of the deformity. Salter and Harris  recognized the complexity of this issue and commented that prognosis was not related to fracture classification alone, but also to the age of the patient, preservation of blood supply, presence of an open fracture, method of reduction, intraarticular displacement, quality of reduction, method and length of immobilization, and, of particular importance, the specific physis involved. Even if the outcome is limited to the presence of growth arrest alone, many authors agree that the Salter-Harris classification is not a good predictor of prognosis [2, 3, 7, 12, 23, 29]. For example, fractures involving the distal femoral physis tend to be high energy and have a rate of physeal arrest near 40% [2, 7]. Initial fracture displacement and accuracy of reduction have been found to be the most important prognostic indicators [2, 12]. Multiple studies examining physeal fractures at the distal tibia also have found that fracture displacement and mechanism of injury are the most significant prognostic indicators [10, 25, 28]. In a study of distal radius fractures, Cannata et al.  found that the rate of physeal arrest at the distal radius was less than 30% while the rate of physeal arrest at the distal ulna approached 80%, however, neither was significantly correlated to Salter-Harris classification and fewer than 5% of patients had residual symptoms or functional deficits. The most commonly reported predictors of physeal arrest appear to be initial fracture displacement, mechanism of injury, and accuracy of reduction.
Conclusions and Uses
The Salter-Harris classification continues to be relevant and serve an important purpose in orthopaedics despite substantial limitations. It is not a comprehensive system for classifying physeal injuries, guiding treatment, or determining prognosis. These limitation may be inherent to a classification that is intended to be generically applied to physeal fractures and does not attempt to account for anatomic variation between physes or unique clinical considerations of fractures in different locations. The Salter-Harris classification does provide a foundation to help clinicians understand how pediatric fractures relate to the anatomy and architecture of an open physis. Additionally, the generic nature of the classification allows it to be extremely simple and widely applied. The Salter-Harris classification has become part of the language used in orthopaedics, is nearly universally understood, and is used by orthopaedic practitioners, greatly facilitating communication. This is where the classification derives much of its utility. It may be more appropriate to think of the Salter-Harris classification as descriptive terminology with general clinical implications than a specific fracture classification that is expected to dictate treatment and prognosis. A thorough understanding of the scope of pediatric trauma and anatomy is necessary to guide treatment decisions and understand expected outcomes.
- 1.Aitken AP. The end results of the fractured distal tibial epiphysis. J Bone Joint Surg Am. 1936;18:685–691.Google Scholar
- 5.Cannata G, De Maio F, Mancini F, Ippolito E. Physeal fractures of the distal radius and ulna: long-term prognosis. J Orthop Trauma. 2003;17:172–179; discussion 179–180.Google Scholar
- 8.Foucher JT. De la divulsion des epiphyses. Cong Med France. 1863;1:63–72.Google Scholar
- 20.Poland J. Traumatic Separation of the Epiphyses. London, England: Smith, Elder & Co; 1898.Google Scholar
- 21.Rang M. The Growth Plate and Its Disorders. Harcourt Brace/Churchill Livingstone; 1968.Google Scholar
- 22.Rathjen KE, Birch JG. Physeal injuries and growth disturbances. In: Beaty JH, Kasser JR, eds. Rockwood and Wilkins’ Fractures in Children. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2010:91–119.Google Scholar
- 26.Salter RB, Harris WR. Injuries involving the epiphyseal plate. J Bone Joint Surg Am. 1963;45:587–622.Google Scholar