Lower Limb (Extremity)
Each lower limb (lower extremity) has 30 bones in four locations—(1) the femur in the thigh; (2) the patella (kneecap); (3) the tibia and fibula in
the leg; and (4) the 7 tarsals in the tarsus (ankle), the 5 metatarsals in the metatarsus, and the 14 phalanges (bones of the digits) in the foot (see
Figures 8.11 and 8.13). The bones of the lower limb are discussed in Exhibits 8.G through 8.I
Femur
The femur, or thigh bone, is the longest, heaviest, and strongest bone in the body (Figure 8.11). Its proximal end articulates with the acetabulum
of the hip bone. Its distal end articulates with the tibia and patella. The body (shaft) of the femur angles medially and, as a result, the knee joints
are closer to the midline than the hip joints. This angle of the femoral shaft (angle of convergence) is greater in females because the female pelvis
is broader. The proximal end of the femur consists of a rounded head that articulates with the acetabulum of the hip bone to form the hip (coxal)
joint. The head contains a small central depression (pit) called the fovea capitis (FO¯-ve¯-a CAP-i-tis; fovea pit, capitis of the head). The ligament
of the head of the femur connects the fovea capitis of the femur to the acetabulum of the hip bone. The neck of the femur is a constricted region
distal to the head. A “broken hip” is more often associated with a fracture in the neck of the femur than with fractures of the hip bones. The
greater trochanter (tro¯-KANter) and lesser trochanter are projections from the junction of the neck and shaft that serve as points of attachment
for the tendons of some of the thigh and buttock muscles. The greater trochanter is the prominence felt and seen anterior to the hollow on the
side of the hip. It is a landmark commonly used to locate the site for intramuscular injections into the lateral surface of the thigh. The lesser
trochanter is inferior and medial to the greater trochanter. Between the anterior surfaces of the trochanters is a narrow intertrochanteric line
(Figure 8.11a). A ridge called the intertrochanteric crest appears between the posterior surfaces of the trochanters (Figure 8.11b). Inferior to the
intertrochanteric crest on the posterior surface of the body of the femur is a vertical ridge called the gluteal tuberosity. It blends into another
vertical ridge called the linea aspera (LIN-e¯-a AS-per-a; asper rough). Both ridges serve as attachment points for the tendons of several thigh
muscles. The expanded distal end of the femur includes the medial condyle ( knuckle) and the lateral condyle. These articulate with the medial
and lateral condyles of the tibia. Superior to the condyles are the medial epicondyle and the lateral epicondyle, to which ligaments of the knee
joint attach. A depressed area between the condyles on the posterior surface is called the intercondylar fossa (in-ter-KON-di-lar). The patellar
surface is located between the condyles on the anterior surface. Just superior to the medial epicondyle is the adductor tubercle, a roughened
projection that is a site of attachment for the adductor magnus muscle.
Patella
The patella (little dish), or kneecap, is a small, triangular bone located anterior to the knee joint (Figure 8.12). The broad proximal end of this
sesamoid bone, which develops in the tendon of the quadriceps femoris muscle, is called the base; the pointed distal end is referred to as the
apex. The posterior surface contains two articular facets, one for the medial condyle of the femur and another for the lateral condyle of the
femur. The patellar ligament attaches the patella to the tibial tuberosity. The patellofemoral joint, between the posterior surface of the patella
and the patellar surface.
Tibia
The tibia, or shin bone, is the larger, medial, weight-bearing bone of the leg (Figure 8.13). The term tibia means flute, because the tibial bones of
birds were used in ancient times to make musical instruments. The tibia articulates at its proximal end with the femur and fibula, and at its distal
end with the fibula and the talus bone of the ankle. The tibia and fibula, like the ulna and radius, are connected by an interosseous membrane.
The proximal end of the tibia is expanded into a lateral condyle and a medial condyle. These articulate with the condyles of the femur to form
the lateral and medial tibiofemoral (knee) joints. The inferior surface of the lateral condyle articulates with the head of the fibula. The slightly
concave condyles are separated by an upward projection called the intercondylar eminence (Figure 8.13b). The tibial tuberosity on the anterior
surface is a point of attachment for the patellar ligament. Inferior to and continuous with the tibial tuberosity is a sharp ridge that can be felt
below the skin, known as the anterior border (crest) or shin. The medial surface of the distal end of the tibia forms the medial malleolus (malLE¯-o¯-lus hammer). This structure articulates with the talus of the ankle and forms the prominence that can be felt on the medial surface of the
ankle. The fibular notch (Figure 8.13c) articulates with the distal end of the fibula to form the distal tibiofibular joint. Of all the long bones of the
body, the tibia is the most frequently fractured and is also the most frequent site of an open (compound) fracture.