Overall structure and attributes

Any classification system should be suitable for the acquisition, storage, and retrieval of data. The Müller system presents a way not only to document fractures but also to understand them in biomechanical and biological terms. The system is based on a well-defined terminology which allows the surgeon to consistently describe the fracture in as much detail as is required for the clinical situation. The description is the key to the classification and this then forms the basis for the alphanumeric code which makes it suitable for computerization, documentation, and research. The first aim of the surgeon is to identify what Müller has referred to as the “essence of the fracture.” This is the attribute that gives the fracture its particular identity and enables it to be assigned to one particular type.

Classification is an ongoing process which depends on the information available to the surgeon at any given time. This process of classification is known as the diagnostic method. To make a diagnosis, information concerning the anatomical location and morphological characteristics of the fracture is obtained. This consists of a description of the location (ie, which bone is fractured and which part of the bone is affected?), followed by a fracture type (ie, how many fragments are involved?), and finally the morphological characteristics of a fracture (ie, what does the fracture look like?). This process provides useful clinical information for the physician to determine treatment. Only when all information concerning the fracture is collected may the classification process be considered complete.

Fracture localization: bones and segments

Each major long bone (humerus, radius and ulna, femur, and tibia and fibula) is named and then numbered (Fig 2.2-1). It should be noted that the two-paired bones, that is the radius and ulna, and the tibia and fibula, are regarded as one entity or group. Each long bone consists of three segments. There are two end segments (proximal and distal) and these are joined by a middle portion known as the diaphysis or shaft. The end segment consists of the metaphysis and articular surface. The extent of the end segments is defined as a square whose sides are the same length as the widest part of the epiphysis of the segment in question. Each of the segments in the bones is also numbered (Fig 2.2-2). There is a final segment, the malleolar segment, which is an exception to the rule. The pattern of these ankle fractures is determined by the relationship between the bones of the ankle mortise and their associated ligaments. The rule of defining the end segment cannot be applied. The Weber classification is universally accepted for this segment.

To assign each fracture to a segment, the center of the fracture must be determined. For a simple fracture, where there are only two bone fragments, this is apparent. It is the midpoint of an oblique or spiral fracture, and in a transverse fracture it is obvious.

A wedge fracture has a center which is the broadest portion of the wedge or the mid portion of the fragmented area when reduced. For complex fractures, where there are many bone fragments, the center may well have to be determined after reduction when the full extent of fragmentation is determined. This may mean that the surgeon can only give a final classification after surgical treatment. A displaced articular fracture will always be classified in an end segment regardless of its diaphyseal extension, since the articular injury is the most important for treatment and prognosis.