The femoral shaft is essentially a tubular structure. It flares posteriorly along the linea aspera, where its cortical thickness is the greatest

TOPIC________________________________________________________________________________
The femoral shaft is essentially a tubular structure. It flares posteriorly along the linea aspera, where its cortical thickness is the greatest. The linea aspera (Latin for rough line) serves as a site of attachment for the fascia. The proximal and distal metaphyseal widening of the tube in the subtrochanteric and supracondylar regions of the bone results in stress concentration at these levels. Pathologic fractures, especially in the elderly, commonly occur at these metaphyseal–diaphyseal junctions. The most prominent feature of the femoral shaft is its anterior bow or antecurvature. Wide individual variations exist in the magnitude of this bow. The normal physiologic bow often is increased in certain pathologic conditions, such as fibrous dysplasia and Paget disease. The clinical importance of the antecurvature of the shaft has long been appreciated. Most modern intramedullary nails are prebent, with an average 10- to 12-mm-high arch at their midpoints to accommodate the bow. Straight, stiff implants used in the early years of femoral nailing straightened the shaft, leaving a posterior gap at the fracture site. Straight nails also resulted in fracture comminution and occasionally even perforation of the anterior cortex.
The femoral shaft is subjected to major musculature forces that deform the thigh after a fracture (Fig. 27-2). The action of the gluteal musculature that inserts on the greater trochanter abducts the proximal femur after subtrochanteric and high proximal shaft fractures. These proximal-third fractures of the shaft also are flexed and externally rotated by the action of the iliopsoas muscle's pull on the lesser trochanter. The adductor muscles span most shaft fractures and exert a strong axial and varus load to the bone. Distal shaft fractures, especially those extending into the supracondylar region, tend to angle into flexion through the pull of the gastrocnemius muscle. Adjustments in traction or bracing devices are needed to counteract these deformity muscular forces.
The femur possesses a rich vascular supply. The arterial supply is derived mainly from the profundus femoris artery. Although some anatomic variations occur in humans, the nutrient vessel usually enters the bone proximally and posteriorly along the linea aspera. In his cadaver dissections of adult femora, Laing184 found that there was usually only a single nutrient vessel, and in none of his specimens did a major artery enter the lower third of the shaft. The maximum number of nutrient vessels that he noted in any femur was two. After penetrating the posterior cortex, the nutrient vessel arborizes proximally and distally to provide the endosteal circulation to the shaft.

Fig. 27-3 Sectiune transversala coapsa cu evidentierea celor trei compartimente

Most of the periosteal vessels also enter the bone along the linea aspera. They align themselves perpendicularly to the cortical surface with few, if any, traversing along the periosteum longitudinally. Because of this perpendicular orientation of the periosteal vessels, they seldom are extensively stripped during fractures except during severe open injuries. Preservation of this periosteal circulation is a high priority during any open surgical procedure on the femur. Damage to the vessels is minimized by avoiding any soft-tissue stripping of the linea aspera. Although broad bands or tapes around the shaft should be shunned, simple cerclage wires alone will not devascularize the cortex because there is little or no longitudinal flow in the periosteal vasculature. Severe traumatic or operative damage to the periosteal vessels will result in delayed fracture healing.
The microcirculation of the femur is similar to that of the diaphyses of other long bones. Although their contribution is controversial, endosteal vessels are thought to provide (under normal physiologic conditions) circulation to the inner two thirds to three quarters of the cortex.281,282,283 They anastomose with the scattered blood vessels of the periosteal circulation. The normal blood flow is centrifugal, although some blood returns to the large venous sinusoids of the medullary canal. The periosteal arteries normally provide flow limited to the outer one quarter of the cortex, especially posteriorly along the linea aspera at the site of their penetration into the bone.
After diaphyseal fractures, the circulatory pattern is radically altered. In the rare nondisplaced fracture of the shaft, the endosteal supply can be relatively undisturbed and remain dominant. With most fractures, however, the major fragments displace, resulting in complete disruption of the medullary vessels. Proliferation of the periosteal vessels is the paramount vascular response to the fracture. The rapidly enhanced periosteal circulation is the primary source of cells and growth factors for healing. The medullary supply eventually is restored later in the healing process. Once reconstituted, the medullary circulation again gains dominance.
The effect of intramedullary nails on the diaphyseal circulation has been studied extensively by Rhinelander and colleagues.283 Intramedullary nails have the theoretic disadvantage of preventing restoration of the normal endosteal flow during fracture healing. Cylindrical or tubular nails that completely fill the canal can have a deleterious effect on reconstitution of the medullary arterial and venous flow. The impedance of venous outflow may have as profound an effect on blood flow to the fracture as any damage to the arteries. Fortunately, no commercially available nails possess such a circular cross-sectional design. Cloverleaf, diamond-shaped, fluted, flanged, delta, and other nails provide potential space for neovascularization of the endosteum. Restoration of endosteal vessels occurs quickly after fracture when such nails are used. During the early stages of fracture healing, the periosteal circulation appears to be able to maintain vascularity to the outer half of the cortex, even with complete filling of the canal with an intramedullary nail.283 The rapid healing and remodeling of fractures after closed intramedullary nailing attest to the abundant collateral circulation to the femoral shaft.
Nearly all open procedures on the femoral shaft should be performed through a longitudinal lateral incision. For rare specific indications, the distal metaphyseal–diaphyseal junction can be approached medially by elevation of the vastus medialis obliquus muscle. The anterolateral approach to the shaft through the substance of the vastus intermedius muscle should be avoided. Postoperative adhesions between the individual muscles of the quadriceps resulting in knee contractures are common with this latter approach.
The lateral approach uses an incision of variable length over the lateral aspect of the thigh along a line from the greater trochanter to the lateral femoral condyle (Fig. 27-4). The fascia lata is incised longitudinally in line with the skin incision. The posterior part of the vastus lateralis muscle is exposed by anterior retraction of the muscle and dissection along the fascia posteriorly to the linea aspera. The muscle and fascia are split about 1 cm lateral to the linea aspera. The perforating branches of the profundus femoris artery are identified and ligated. These vessels course perpendicular to the long axis of the femur at intervals of about 3 cm. The periosteum is split and elevated anteriorly along the vastus lateralis muscle. Only a minimal amount of periosteal stripping and muscle elevation should be performed. The intermuscular septum should not be dissected off the linea aspera unless it is imperative for surgical exposure. This lateral approach to the shaft results in minimal scarring of the quadriceps and can be reused in future surgery on the shaft as may be indicated.

Fig. 27-4 Abord lateral si posterolateral 13 medie coapsa. A.Abordul posterolateral de-a lungul septului intermuscular este preferat deoarece este minima disectie prin vastul lateral. B. Abordul lateral cu incizia vastului lateral si intermediar de-a lungul fibrelor

MECHANISMS OF INJURY

A fracture of a normal femoral shaft requires major trauma. Most fractures are sustained by young adults during high-energy injuries such as motor vehicle accidents, auto–pedestrian accidents, motorcycle accidents, falls from heights, or gunshot wounds.
Epidemiologic studies show a correlation between the mechanism of injury and the types of associated injuries.343 Auto–pedestrian accident victims have a high prevalence of head, chest, pelvis, arm, and leg injuries. Motorcyclists tend to sustain associated pelvis and ipsilateral leg injuries. Fall victims less frequently sustain major associated injuries.343 Lesser degrees of trauma can fracture a femur with pathologic bone. Such pathologic fractures often start at the weak metaphyseal bone at the ends of the femur and propagate into the shaft.
Fatigue failure is a rare cause of fracture of the femoral shaft.273 Usually located in the proximal or midshaft areas, fatigue or stress fractures occur mainly in military recruits undergoing a marked and prolonged increase in physical activity.
The incidence of stress fractures of the femoral shaft in civilian populations appears to be rising with the recent emphasis on physical fitness. Running accounts for most such fractures, but they also have been seen after triathlon events and aerobic dancing.90 Most runners report an increase in their training during or immediately before the onset of their pain. Plain radiographs often are normal, and radioisotope scans have proven to be the most sensitive tests for the early detection of these injuries. Displacement of these stress injuries can occur occasionally, but most heal with rest or substitution of low-impact exercises such as cycling and aquatic exercise for running.
Like most bones, the femoral shaft fails under tensile strain.109 The most common mechanism of injury is bending load, resulting in a transverse fracture. Higher-magnitude injuries cause varying degrees of fracture comminution. It has been estimated that 250 Nm of bending movement are needed to fracture a normal adult femoral shaft.183 Additional force is dissipated on the soft tissues. Pathologic bones are prone to spiral fractures after minor torsional loads. Such fractures rarely are comminuted or associated with severe soft-tissue damage.

CLASSIFICATION

No universally accepted classification scheme exists for fractures of the femoral shaft. Most investigators categorize fractures according to specific variables that directly influence their preferred treatment. Such factors as soft-tissue injury, geographic location, fracture geometry, fracture comminution, and associated injuries are used most often in classifying these fractures.
Open wounds occur less frequently with femoral shaft fractures than with tibial fractures. Open fractures can be subdivided into the standard grades I, II, IIIA, IIIB, and IIIC, according to the Gustilo-Anderson method.130,131 The abundant soft-tissue coverage of the femoral shaft makes grade III, especially IIIC, open fractures relatively uncommon.
The interobserver agreement with the Gustilo-Anderson classification system for open tibia fractures is only moderate to poor.54 A similar problem with its reliability and reproducibility may exist for femoral fractures, although this issue has not been studied. The definitive grading of the soft-tissue wound should be delayed until thorough inspection and debridement of the soft tissues and bone are completed.
Femoral shaft fractures can be categorized geographically as proximal third, midshaft, or distal third. Because the isthmus of the medullary canal usually is located in the midshaft, distal-third fractures also are called infraisthmal fractures. The variable anatomy of the medullary canal and the different mechanical stresses in these three regions of the shaft influence the techniques and results of intramedullary fixation.
Fractures also can be classified according to the geometry of the major fracture line. The terms transverse, oblique, spiral, and segmental are self-explanatory. The AO/ASIF classification distinguishes simple (A), wedge (B), and complex (C) patterns in its scheme for femoral diaphyseal fractures240 (Fig. 27-5). The simple fractures are subdivided according to the obliquity of the single fracture line. The wedge fractures can be a spiral, bending or fragmented configuration. The complex fractures include segmental fractures and fractures with extensive comminution over a long segment of the diaphysis. It is unclear how this AO/ASIF scheme may influence the preferred treatment of any given fracture or be predictive of its outcome.

Fig. 27-5 Clasificarea ASIF

The degree of fracture comminution has implications for the preferred form of medullary fixation and locking of the major fracture fragments. The Winquist classification of comminution is widely used369 (Fig. 27-6). Type I comminution is defined as minimal or no comminution at the fracture site. Any small fragment that is present should have no effect on fracture stability after intramedullary nailing. Type II comminution involves a fragment larger than that in type I but has at least 50% of the circumference of the cortices of the two major fracture fragments intact. Because the broad cortical contact after fracture reduction and nailing prevents shortening and malrotation, simple intramedullary nails suffice for most type II fractures. Nevertheless, static locking is used routinely for these type II injuries because of the risk of postoperative loss of fixation secondary to unrecognized comminution.59