Presentation of the Classification
The alphanumeric classification consists of a m odular t opographic and m orphologic (MTM-) classification. To facilitate a more precise, reliable and reproducible fracture differentiation, initial radiological assessment, standardized plain x-rays in a.p. and axillary views were mandatory.
The Topographical Basis
The topographic basis is the division of the proximal humerus into two segments-the articular segment (with C-fractures from C = Caput = Humeral head) and the extraarticular segment. This extraarticular segment (with A-fractures) is further divided into the three subsegments metaphysis (M), Greater tuberosity (G) and Lesser tuberosity (L).
Both the articular and the extraarticular segments are divided by the anatomical neck (see Figure 1).
The fracture types
A-Fractures comprise fractures in the extraarticular segment. Two-part-A fractures are divided in two-part metaphyseal fractures (M) that extend through the surgical neck, two-part greater tuberosity (G) and two-part lesser tuberosity fractures (L). The tuberosity fractures are defined by a complete separation of the tuberosity from the metaphysis and the anatomical neck.
Three-part A fractures (MG and ML fractures) are a metaphyseal fracture (M) with a fracture of one tuberosity (G or L).
Four-part A fractures (MT fracture) are a metaphyseal fracture (M) with a fracture of both tuberosities (G+L = T) (see Figure 2a–f).
Type B: Incomplete Articular Fractures
Incomplete articular fractures show an incomplete fracture through the anatomic neck and extend into one of the extraarticular subsegments. This type describes a tuberosity or a medial wedge-shaped fragment, which is separated from the metaphysis and remains at the humeral head. Two-part B fractures are divided into three subtypes such as incomplete articular fractures with an medial metaphyseal wedge shaped fragment at the humeral head (MB), an incomplete fracture of the anatomical neck with the greater tuberosity at the humeral head (GB) and an incomplete fracture of the anatomical neck with the lesser tuberosity connected to the humeral head (LB).
The further division of type B fractures depends on the additionally occurring tuberosity fractures. These three-part B fractures are GB fractures with a separate fracture of the lesser tuberosity (GBL), LB fractures with a separate fracture of the greater tuberosity (LBG), MB fractures with a separate fracture of the greater tuberosity (MBG) and MB fractures with a separate fracture of the lesser tuberosity (MBL).
B fractures with four main parts (= 4-part B fractures) are MB fractures in combination with a fracture of both tuberosities (MBT) (see Figure 3 and 4).
Type C: Complete Articular Fractures
Type C articular fractures completely pass through the anatomic neck, but also may extend through the humeral head, which is completely separated from the extraarticular segment. Type C fractures are divided into five subtypes. Two-part C fractures with just one complete fracture through the anatomic neck are isolated articular fractures (SC).
Three-part C fractures showing a fracture of the greater tuberosity (CG), with a fracture of the lesser tuberosity (CL). Four-part C fractures show a fracture of both tuberosities fractures (CT). Along with four-part fractures there is often a fracture of the metaphyseal subsegment. These even more complex fractures are called (CTM) (see Figure 5).
Type D-Fractures (Fracture-Dislocations)
D fractures are fracture-dislocations. D fractures are divided in type C fracture-dislocations (DC), type B fracture-dislocations (DB) and type A fracture-dislocations (DA).
The further classification of DA fractures depends on the fractures in the extraarticular segment: fracture-dislocation with a metaphyseal fracture (DM), anterior fracture-dislocation dislocation and fracture of the greater tuberosity (DG) and posterior fracture-dislocation and fracture of the lesser tuberosity (DL).
The morphological basis
For morphological analysis, the MTM classification is based on four defined specifications, which are relevant for therapy and prognosis.
These specifications are organized by increasing fracture severity: minimally displaced and stable (S1), minimally displaced and unstable (S2), displaced (S3), displaced and comminuted (S4). In fractures with several parts, each part has to be classified individually. (see Figure 6).
S1: Minimally Displaced and Stable
The minimally displaced fractures (S 1) are defined as fractures with angulations up to 25°, a displacement of the tuberosities and the anatomical neck up to 5 mm, and a metaphyseal fracture displacement of 10 mm. Up to this extent of displacement, a real impairment of shoulder function is not to be expected.
Fracture stability is given if – through impaction of the main parts and preserved soft tissues – mobility between the main parts resulting in further displacement is unlikely. Thus, the fracture position, induced by the trauma, is not changing by careful functional strain of the shoulder.
Therefore, minimally displaced and stable fractures are amenable to nonoperative treatment including early functional exercises. Regardless of fracture type and the number of main fragments, those fractures can be grouped together as S1 fractures since they are almost analogous in treatment and prognosis.
S2: Minimally Displaced and Unstable
The displacement of S2 fractures is defined similar to S1 fractures as a displacement of the tuberosities and the anatomical neck up to 5 mm, and a metaphyseal fracture displacement of 10 mm. Those fractures were defined as unstable when fractured parts were not impacted into each other resulting in instability between the fractured parts. Thus, through muscle pull and shoulder mobilization further displacements beyond the initial radiographically diagnosed extent may occur.
Assessment of Stable and Unstable Fractures
If the above-defined criteria for stability and instability cannot clearly be applied radiologically, an additional fluoroscopic examination of the fracture is recommended. In this examination, a gentle abduction and rotation is applied in true a.p. view. If mobility can be visualized between fractured parts, the fracture is defined as unstable.
S3: Displaced
S3 fractures always show a stronger malalignment and fragment separation, and, thus, the interfragmental soft tissue is ruptured more strongly, mostly induced by a combination of angulatory, rotatory and translatory displacement. Often, a compression mechanism leads to strong displacement with impaction. In displaced C fractures, the blood supply to the humeral head is completely destroyed. In cases with translatory and rotatory displacement of the humeral head, there is no integrity of the medial hinge and capsular and periosteal vessels ascending intraosteally to the humeral head are ruptured[18, 20].
S4: Displaced and Comminuted
In addition to the displacement, S4 fractures show comminution of the main part complicating the therapeutic procedure and worsening the prognosis. For example displaced head-splitting fractures define the fracture of the humeral head in several single fragments (C4).
The application of the classification
Due to its modularity, the classification can be applied in several ways depending on application purposes.
The short topographic version allows to classify into main types (A, B, C, D) or into the number of main parts (2, 3, 4) or into a combination of both the main-fracture-type and parts (2-p-A-fracture to 4-p-C-fracture).
A more detailed approach evaluated individual fracture types (M to CTM) or fracture types in combination with the individual specification (M to CTM and S1 to S4).
For example, a stable fracture of the anatomical neck with a displaced fracture of the greater tuberosity could be classified as C1G3.
To allow the comparism with other studies we also classified the fractures according to the determination between minimal-displaced and displaced fractures (S1/S2 to S3/S4).