91: Lower Extremity Injuries

Key Points

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

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

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

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

Introduction

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 ...