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Table 1 shows a list of anatomic locations considered high-risk for stress fractures. This distinction allows clinicians to quickly determine if they can be aggressive or conservative with the decision to return an athlete to training or competition.
Two key features of the Kaeding-Miller system are that it is generalizable and has been validated with intra- and inter-observer reliability. This classification system has been shown to have high inter- and intra-observer reliability. Coupling this fracture grade with the location of the fracture provides a more comprehensive description of the injury that takes into account both the extent of structural failure and healing potential of the injury. When reporting the stress fracture grade in this system, the imaging modality used should be reported. Almost perfect intra-observer agreement was found among fifteen evaluators of the classification system which included orthopaedists, primary care sports medicine specialists, and physician assistants. Substantial to almost perfect inter-observer reliability was observed for the classification grades among the same evaluators.
CURRENT CONCEPTS
Table 1: Anatomic Sites for High-Risk Stress Fractures
Femoral neck (Tension side)
Patella (Tension side)
Anterior Tibial Cortex
Medial Malleolus
Talar neck
Dorsal tarsal Navicular Cortex
5th Metatarsal Proximal Metaphysis
Sesamoids of the Great Toe
01
In addition to knowing the classification of whether a stress fracture is high risk or low risk as determined by its anatomic site, the extent of the structural failure or “grade” of the stress fracture is also needed to completely describe the injury and make appropriate treatment plans. As described above, stress injuries to bone occur on a continuum from simple bone marrow edema (stress reaction) to a small microcrack with minor cortical disruption to a complete fracture with or without nonunion. The management of bony stress injuries should be based on the location and grade of the injury.
02
Recently Kaeding and Miller proposed a comprehensive descriptive system for stress fractures. This includes a grading scale for classifying the extent of structural failure from Grade 1 to Grade 5. Grade 1 injuries are asymptomatic, usually incidental findings on imaging studies. Grade 2 injuries have imaging evidence of fatigue failure of bone, but no fracture line (Fig. 3). Grade 3 injuries have a fracture line with no displacement (Fig. 1 and 4). Grade 4 fractures are displaced (Fig. 5), and Grade 5 non-union of stress fracture (Fig. 3). This system is summarized in Table 2.
03
Low-risk stress fractures include the femoral shaft, medial tibia, ribs, ulnar shaft, and 1st through 4th metatarsals, all of which have a favorable natural history. These sites tend to be on the compressive side of the bone, and respond well to activity modification. Low-risk stress fractures are less likely to reoccur, develop nonunion, or have a significant complication should it progress to complete fracture.
High Risk Stress Fractures versus Low Risk Stress Fractures
ISAKOS NEWSLETTER 2015: Volume I 25