Historical Background

Many investigators have devised classification schemes for femoral neck fractures that indicate prognostic differences according to fracture type. The first classification of femoral neck fractures was published in 1823 by Cooper, who divided these injuries into intracapsular and extracapsular fractures.⁵ Waldenström in 1924 and Cotton in 1927 classified these injuries as either abduction fractures and adduction fractures, according to their displacement features.^6,7 In 1955, Watson-Jones developed a system based on the age of the patient. He concluded that certain fracture types were typical in certain age groups.⁸ Enduring and meaningful classification systems were finally developed by Pauwels in 1935, Linton in 1941, and Garden in 1961.^3,4,9,10

Classification System of Garden

In 1964, Garden et al created a classification system for femoral neck fractures that consisted of four fracture types (Garden I to Garden IV), depending on the position and displacement of the femoral head in the anteroposterior (AP) projection (Fig. 6-1). In this system, type I includes fractures with an incomplete fracture line through the femoral neck and valgus position of the proximal fragment, type II comprises fractures with a complete fracture line through the femoral neck and no displacement between the proximal and distal fragments, type III includes fractures with a complete fracture line through the femoral neck and varus displacement of the proximal fragment that is less than 50% of the femoral neck diameter, and type IV comprises fractures with varus displacement of more than 50% of the femoral neck diameter or complete dissociation of the proximal and distal fragments.

Figure 6-1 Classification of Garden.

This classification scheme provides information about the likelihood of developing avascular femoral head necrosis. Patients with type I fractures have a probability of femoral head necrosis of less than 5%. In type II fractures, the likelihood of this complication is less than 10%. However, the probability of avascular necrosis is more than 50% in type III fractures and more than 80% in type IV fractures. The Garden classification is still the most important and commonly used scheme to classify femoral neck fractures and to determine individual strategies for treatment of these injuries.

Classification System of Pauwels

In 1935, Pauwels published a classification system of femoral neck fractures that included three types (Pauwels I to Pauwels III). The fractures were divided according to the angle between the fracture line and the horizontal line in the AP radiographic projection (Fig. 6-2). In this system, type I fractures have an angle smaller than 30 degrees between the fracture line and the horizontal line, type II fractures have an angle between 30 and 70 degrees, and type III fractures have an angle larger than 70 degrees.

Figure 6-2 Classification of Pauwels.

The prognostic value of this scheme includes the likelihood of fracture nonunion based on the vertical sheerness of the fracture. Type I fractures (0 to 30 degrees) are associated with a likelihood of fracture nonunion of less than 5%, type II fractures (30 to 70 degrees) have a less than 10% probability of nonunion, and type III (>70 degrees) fractures have a likelihood of nonunion of more than 25%.

AO Classification

The AO (Arbeitsgemeinschaft für Osteosynthesefragen, Switzerland, 1958) developed a simplified classification for femoral neck fractures including three subtypes (31 B1 to 31 B3). This system is arranged in order of increasing severity of these injuries according to complexity of the fracture, difficulty in treatment, and prognosis. These fractures are finally categorized by fracture site (subcapital, transcervical), as well as by impaction and displacement of the femoral head. Subtype B1 describes subcapital fractures with impaction and slight displacement, subtype II fractures are transcervical, and the subtype III category includes subcapital and nonimpacted fractures with strong displacement (Fig. 6-3).

Figure 6-3 AO classification.

Classification System of Linton

In 1941, Linton presented his classification scheme, which included three different types of femoral neck fractures based on the angulations between the median femoral neck trabeculae and the femur’s medial cortical trabeculae. This angle is normally 160 degrees in the AP projection (Fig. 6-4). Linton also considered the displacement of the central axis of the femoral head to the central axis of the femoral neck in the axial view, which is usually in a straight line of 180 degrees. Fractures were finally divided into the following categories: (1) fractures in adduction, with varus displacement and an angle between the median femoral neck trabeculae and the femur’s medial cortical trabeculae much smaller than 160 degrees; (2) fractures in abduction, with valgus displacement and parallel median femoral neck and femoral medial cortical trabeculae; and (3) intermediate fractures, corresponding to displacement halfway between adduction and abduction.

Figure 6-4 Classification of Linton.

Conventional Radiography

The initial diagnosis of patients with suspected femoral neck fractures includes three standard radiographs: (1) a pelvic radiograph, (2) an AP view of the affected hip, and (3) an axial view of the affected hip (Lauenstein projection). The standard radiographs usually allow sufficient assessment of the fracture type and estimation of fracture stability, as well as prognostic outcome, to determine individual strategies for treatment of these injuries. In patients with clinical evidence of femoral neck fractures that are not definitely verifiable on standard radiographs, changes in the trabecular lines may be observed and are indications for further imaging studies. In pathologic fractures, metastases usually become visible as rounded osteolytic or sclerotic lesions when more than 30% to 50% of bone resorption has already occurred.

Advanced Imaging

Further radiographic examinations are indicated in patients with clinical evidence of femoral neck fractures that are not obvious or verifiable on standard radiographs. In most of these cases, a computed tomography (CT) scan of the pelvis (with three-dimensional helical reconstruction) establishes the definitive diagnosis. Because delays in the diagnosis of these injuries occur with an incidence up to 15% and additionally increase morbidity in these patients, a CT scan of the pelvis should be considered obligatory in patients with a clear onset of symptoms but uncertain radiographic findings.

Further examinations, such as magnetic resonance imaging and bone scintigraphy, of the pelvis or the affected hip are usually reserved for particular questions and problems and are not considered in the primary evaluation of these injuries. Both techniques are commonly requested as screening methods for early detection of malignant metastases or other bone-weakening diseases.