14 Subtrochanteric Fractures
The frequency curve of subtrochanteric fractures has two age-related peaks: the first peak appears in the third and fourth decades, and the second peak occurs in the seventh and eighth decades. The traumatic mechanism differs in these two age groups. Injuries in the younger population mostly result from high-energy impact, such as high-speed traffic accidents, sport accidents such as paragliding, or workplace accidents such as falls from heights. In contrast, injuries in the older group occur as a consequence of low-energy impact on poor-quality bone, given the increased incidence of severe osteoporosis in this burgeoning population of old and very old patients. The overall numbers of subtrochanteric fractures are steadily increasing, especially those injuries resulting from low-energy impact.
The treatment of subtrochanteric fractures remains a challenge because of the unique anatomic features of this area: the medial wall of the femur carries extremely high-pressure forces, whereas the lateral wall is subjected to strong tension forces. These anatomic and physiologic demands are induced by (1) the distribution of body weight through the femur into the hip and (2) the insertion of three major muscle groups to this region. These muscle groups are depicted in Figure 14-1. The strong abductor group of the gluteus medius and minimus muscles inserts into the major trochanter and comprises the major source of the pulling forces, the iliopsoas and adductor group at the lesser trochanter (piriformis, obturator externus, pectineus, adductor longus, and adductor brevis and magnus muscles).
(Adapted and redrawn from Russell TA, Taylor JC. Subtrochanteric fractures of the femur. In: Browner BD, Jupiter JB, Levine AM editors. Skeletal trauma. 2nd ed. Philadelphia: Saunders; 1992. p. 1836; drawing by Hella Thun.)
In the early days of the Arbeitsgemeinschaft für Osteosynthesefragen (AO), these fractures were all treated using widely open reduction with substantial detachment of soft tissue and plate osteosynthesis. The 95-degree condylar plate was the most successful device for this approach. However, the biologic consequences of soft tissue damage induced substantial numbers of postoperative infections, nonunions, and consecutive implant failures. Steady improvements in intramedullary implant design and the surgical implementation of the relative stability paradigm brought about an important change in treatment strategies in patients with subtrochanteric fractures. The major advantage of the use of intramedullary devices is that the patients can be mobilized much faster because they are able to resume almost full weight bearing after the surgical procedure. Despite these advances in intramedullary device use, two current demographic trends are increasing the demand for the use of plates in osteosynthesis of subtrochanteric fractures:
Lundy2 described subtrochanteric fractures as injuries of the proximal femur from the fossa piriformis to the isthmus. In older publications, the fracture was considered to occur more distally, between the lesser trochanter and 5 cm distal to it.3,4 The AO concentrated on an even smaller area, between the lesser trochanter and 3 cm distal to it.5
Biomechanically, the lateral cortical bone is subjected to high tensile forces, and the medial cortex is subjected to extremely high compressive forces.6 Hence, when developing potential therapeutic strategies, investigators must take into account that internal fixation techniques require substantial mechanical strength to support the significant forces exerted on the femur.
Several classifications for subtrochanteric fractures have been proposed.3,7 Most classifications distinguish between stable and unstable fracture types. Hence, the number of bone fragments and direction of fracture lines is the classifier for grouping injuries.
Within the AO classification system, Mueller8 proposed the designation 31 for the proximal femur and A3 for the extra-articular trochanteric region. According to this nomenclature, 31A3.1 represents the reversed fracture, which is considered unstable. The designation 31A3.2 represents a subtrochanteric fracture with a transverse fracture line visible on the anteroposterior radiograph, and 31A3.3 is a multiply fragmented comminuted subtrochanteric fracture with a separate fragment of the lesser trochanter (Fig. 14-2).
In the international literature, the Russell-Taylor classification is more widely used than the AO classification.9 This classification system is principally based on two issues: stability and fracture extension. Fractures without extension of the anteroposterior fracture line into the piriformis fossa are designated type I; the others are considered type II. In both types, fractures without comminution of the lesser trochanter are designated A, and those with comminution zone are B (Fig. 14-3).