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  If a hip fracture is suspected in an elderly patient, but plain radiographs are negative, obtain a computed tomography scan or magnetic resonance imaging.

  
  
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  Delay in the reduction of a hip dislocation increases the likelihood of avascular necrosis of the femoral head.

  
  
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  The presence of normal distal pulses after a knee dislocation does not exclude popliteal artery injury.

  
  
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  A fracture at the base of the second metatarsal should raise suspicion for a Lisfranc fracture-dislocation.

Lower extremity injuries are frequently caused by motor vehicle collisions (MVCs), pedestrian auto accidents, sports, and falls. These mechanisms often involve large forces, so concurrent torso injuries may be present. Fractures in patients with osteopenia and pathologic fractures occur after minor trauma. This chapter reviews lower extremity injuries from the hip to the foot and highlights some of the pitfalls in managing these orthopedic emergencies.

Hip Injuries

Fractures at the hip are classified based on their location. Femoral neck (ie, subcapital) fractures are intracapsular and more likely to occur in elderly osteoporotic women. Displaced femoral neck fractures cause a hemarthrosis that compresses the femoral neck vessels and compromises the blood flow to the hip. This leads to avascular necrosis of the bone in 15–35% of cases and potential long-term disability. Intertrochanteric, subtrochanteric, and femoral shaft fractures are more likely to occur in young patients after a fall or direct blow to the knee (Figure 91-1).

Hip dislocations are posterior in 90% of cases. They are caused by high-energy trauma, such as striking the flexed knee on the dashboard during an MVC.

Knee Injuries

The knee is stabilized by 4 ligaments, the anterior and posterior cruciates and the medial and lateral collateral ligaments. Maneuvers such as cutting, squatting, and twisting motions can cause ligamentous and meniscus injuries. The popliteal fossa contains the popliteal artery and vein, the common peroneal nerve, and the tibial nerve, so fractures involving the femoral condyles or proximal fibula may be associated with popliteal artery or deep peroneal nerve injury, respectively. Likewise, popliteal artery injuries may be seen with knee dislocations, even if distal pulses are palpable.

Tibial plateau fractures, seen more commonly in older patients even after minor trauma, can be difficult to detect on plain radiography. A proximal fibula fracture occurs from direct impact or when an external rotational force is applied to the foot or ankle that tears the interosseous membrane between the tibia and fibula, also called a Maisonneuve fracture.

Ankle and Foot Injuries

Anatomically, the foot is divided into the hindfoot (talus, calcaneus), midfoot (cuneiforms, navicular, cuboid), and forefoot (metatarsals, phalanges). The Chopart joint separates the hindfoot from the midfoot, whereas the Lisfranc joint divides the midfoot from the forefoot. A fracture of the second metatarsal base is associated with disruption of the ligaments that stabilize the Lisfranc joint. This results in dislocation of the other metatarsal bones. A Lisfranc fracture-dislocation occurs after severe plantar flexion of the foot with an abduction force, such as stepping off a sidewalk curb. Calcaneus fractures are often bilateral because the most frequent mechanism is a fall from height, landing on both feet. Lumbar spine fractures occur in 10% of patients with calcaneal fractures.

The ankle is stabilized by the deltoid ligament, lateral ligament complex (anterior and posterior talofibular, and calcaneofibular ligaments), and syndesmosis. The most common injury is an ankle sprain, 90% of which are inversion injuries. Ligamentous injuries and laxity is difficult to detect hours after an acute injury because of the surrounding ligamentous tension and muscle spasm.

Other important lower extremity injuries to diagnose include Achilles tendon rupture and patella and quadriceps tendon rupture.

Patients with lower extremity injuries present with pain over the injured site, swelling, ecchymosis, deformity, limited range of motion, and/or inability to ambulate. During the primary survey, stabilizing the limb may limit blood loss, and reducing a fracture/dislocation may restore neurovascular function. The joints above and below the injury should be examined for deformities, shortening, rotation, lacerations, ligamentous instability, and neurovascular status. The physical exam can be very limited after an acute injury due to the pain associated with movement.

Intertrochanteric fractures of the hip may leave the leg shortened, abducted, and externally rotated because of traction on the iliopsoas. Patients with nondisplaced hip fractures may be ambulatory, so physicians should have a low threshold for obtaining imaging. A posterior hip dislocation presents with a shortened, adducted, and internally rotated leg.

A knee exam begins with inspecting for swelling, effusion, ecchymosis, and patella location, using the uninjured knee for comparison. Knee injuries, whether from a fracture, dislocation, or ligamentous injury, typically present with a hemarthrosis. Anterior cruciate ligament (ACL) tears cause the majority of hemarthrosis (75%), but other etiologies include meniscal tears and fractures. The mechanism of injury for an ACL tear is a deceleration, hyperextension, or internal rotation of the tibia on the femur, associated with a “pop” and swelling that develops within hours. Ligamentous testing of the knee is outlined in Table 91-1. A history of locking of the knee suggests a meniscal tear.

Knee dislocations are associated with tremendous ligamentous disruption. About half of all knee dislocations will have spontaneously reduced before presentation. Despite spontaneous reduction, there is still a high likelihood of popliteal artery and peroneal nerve injury. Palpation of the distal pulses is performed to assess the popliteal artery, but normal pulses are not sensitive enough to exclude arterial injury. In patients without evidence of vascular injury, an ankle brachial index (ABI) of >0.9 allows for safe observation without angiography. The deep peroneal nerve is assessed by testing sensation on the dorsal aspect of the foot between the first and second toes.

Some lacerations overlying the knee may be deep enough to extend into the joint capsule (ie, traumatic arthrotomy). The knee is the most common joint to be affected. Once an underlying fracture has been excluded, the joint will need to be injected with saline or dilute methylene blue. If fluid flows out of the laceration when the joint is injected, then the joint has been violated and requires a wash out in the operating room.

Patients with patella fractures and patella and quadriceps tendon rupture may be able to ambulate normally, but the extensor function of the knee is affected (ie, the patient would not be able to perform a straight leg raise). The position of the patella is notably altered on exam in patients with tendon rupture, particularly after a patella tendon rupture.

Posttraumatic compartment syndrome causes severe pain that starts within a few hours after the injury (but can occur up to 48 hours), worsens with passive range of motion, and is associated with progressive swelling around the injured area. In the lower extremity, the most common location to develop compartment syndrome is the leg, usually after a tibia fracture. The 4 compartments of the leg are the anterior, lateral, posterior, and deep posterior.