The lower limb spans the head of the femur to the toes. The leg lies between knee joint and ankle joint. Structures of the thigh are referred to as “femoral,” from Latin femur: “thigh,” such as fascia lata femoris: “broad fascia of the thigh,” and os femoris: “bone of the thigh,” or simply “femur.” Because two bones occupy the leg, its structures are referred to as “crural,” from Latin crus: “shank, leg,” such as crural fascia.

Unlike the hip, which commands its own treatise, the knee is difficult to extricate from the lower limb, save by an arthroscope (cf. Sports chapter).

The patella is conferred autonomy due to its size and functional importance. Hence, the term “ligamentum patellæ” when convention dictates “quadriceps tendon,” since the patella is lodged in this muscle as a sesamoid. The patella has a proximal base and a distal apex, referred to as superior and inferior poles. The anatomic terms aid understanding why children complain of pain rarely at the broad end (base) but frequently at the pointed end (apex), at which stress is concentrated. Anatomic terminology similarly aids remembering that the site of attachment of the lateral collateral ligament, known as fibular collateral ligament, differs from that of the medial collateral ligament, known as tibial collateral ligament.

Like the femur at the knee, the tibia has two condyles, which by being less rounded are less distinct. The raised space surrendered between the condyles for the cruciate ligaments is the “intercondylar eminence,” commonly referred to as “tibial spine” due to its sharp terminus. Like the proximal femur, with its trochanters, the proximal tibia has an apophysis termed “tubercle.” Unlike the femur, tibial apophysitis is common during growth.

Knee angle is defined between thigh and leg, or between femur and tibia. Popliteal angle (Latin poples: “ham, hollow of the knee”) specifies the angle subtended by the leg relative to thigh in the sagittal plane [C], where it is a measure of “hamstring” tension. Full extension is defined as 0 degree, while hyperextension is defined as negative.

A limp signifies abnormal gait, which may be due to pain (conscious or subconscious), deformity, or neuromuscular imbalance. The limping child need not be a diagnostic “black box.” It requires a thorough history and physical examination, which may be supplemented by laboratory and imaging studies. Transient synovitis is the most common cause [A]. The condition may be divided according to age and urgency. Different causes occur with different frequencies in different age groups [B]. Some are characteristic of certain ages (e.g., slipped capital femoral epiphysis circa puberty), while others are broadly distributed (e.g., lower limb length discrepancy). The varying causes may be divided into those that require urgent treatment (e.g., hip pyarthritis) and those that may be managed electively (e.g., developmental dysplasia of the hip). The hip dominates anatomically [D].

Gait Antalgic gait is defined by a shortened stance phase, of which the extreme is a refusal to walk [E]. A common theme in hip deformities producing limp is a Trendelenburg gait [C]. This results from a shift of the body over the affected hip in order to reduce the moment arm exerted on weak abductor muscles, which aids them in maintaining a horizontal pelvis during stance phase. In milder deformities, the gait may be apparent only after several cycles and may give way to pain as the hip abductors increasingly fatigue. This may be distinguished by its more lateral location from painful hip disorders, in which the pain is anterior in the region of the groin. Neuromuscular patients may exhibit an equinus gait, such as a hemiplegic who walks toe-toe. Equinus may drive the knee into recurvatum to plant the foot flat. Circumduction gait is characterized by incomplete knee flexion, actively (e.g., due to pain) or passively (e.g., due to contracture), which functionally lengthens the limb requiring swinging around the direction of walking to clear the ground.

Evaluation Age is the single most important discriminator of disease. Obtain a complete history. Is this acute, intermittent, or chronic? Are there associated symptoms (e.g., bruisability on leukæmia)? Is the limp local or a manifestation of a generalized condition (e.g., preceding illness)? Ask about milestones: delay may be an early tip-off of subtle neuromuscular disease [F]. Does the child complain of the limp? Long-standing, intermittent, milder pain may be suppressed in a child’s consciousness producing the so-called “painless” limp (e.g., established Legg-Calvé-Perthes disease).

Look at the whole child. Does she or he seem in distress (which may differentiate synovitis from infection), suggesting an urgent presentation? Are the upper limbs (e.g., hemiplegia) or back (e.g., diskitis) affected? Before examining where it hurts, go to the other side to gain the child’s confidence. The physical examination should be performed in both supine and prone positions. The supine position may show hip obligate lateral rotation with flexion as seen in slipped capital femoral epiphysis. The prone position has the distinct advantage of allowing uncoupling of the knee from the hip, which may masquerade one for the other. The knee may be ranged from extension to flexion without moving the hip. In the supine position, moving the knee requires flexion of the hip, making it difficult at times to tell which joint is the offender. In addition, as in examination for torsion, the prone position allows simultaneous comparison of hip rotation (especially medial), which is the most sensitive to disease. Finally, the prone position will reveal a hip flexion contracture that may be concealed by lumbar hyperlordosis without the physician manipulating the child. No room is big enough to evaluate gait in detail. In addition, running amplifies gait disturbances and impedes compensatory mechanisms.

Management This is in accordance with condition, of which the different types are discussed independently elsewhere. Röntgenogrammes are readily available, low morbidity, inexpensive, and useful for general screening. Ultrasonography is noninvasive. By contrast, needle aspiration is invasive and stressful to child and parent; however, it is of high diagnostic value. Do not let timidity or logistics delay or dissuade—the emergency setting offers the best opportunity. Specialized imaging focuses and elucidates, such as scintigraphy in radio negative case where occult fracture is
suspected. Obtain laboratory tests judiciously. C-reactive protein is more specific and sensitive for infection than is leukocyte count. Observation is an acceptable and prudent form of management. Before requesting a complex test, which may require anæsthesia or may be expensive, evaluate the child on another day if the presentation is not urgent. A final diagnosis may elude the most thorough investigator in up to 25% of cases.

Leg aches are “growing pains.” This may be explained as overuse in a child who lacks judgment to avoid repetitive injury and lacks consequence when injured (due to rapid recovery). Other mechanisms implicated include rapid, episodic skeletal growth stretching surrounding soft tissues, increasing body weight, participation in sports at higher levels with escalating expectations, and developing body mechanics. One-third of children experience leg aches, in addition to headaches and stomach aches. All of these may be stressful to the family but are physiologically benign, resolving without sequelæ. Extensive evaluation, including MRI of the brain, gastrointestinal contrast study, and multiple röntgenogrammes of the lower limbs, is negative. Recognize and reassure.

Evaluation Leg aches usually affect both legs, though one side may predominate [A]. If they produce limp, it is intermittent. They are worst at the end of a busy day or at night, interfering with falling asleep but not awakening from sleep. Long duration presents a paradox: while trying for a family, this lowers the physician’s concern (bad things do not linger without causing further trouble). They are not associated with other symptoms. They are poorly localized and may migrate from part to part within a limb or from side to side. This is consistent with benignity, but also calls for a broad physical examination. There are no “hard” objective signs, such as deformity, stiffness, swelling, discoloration.

Management Establish this diagnosis of exclusion, in order not to request unnecessary tests or tests that yield equivocal results, which may alarm a family and trigger further testing.

This presents the greatest disparity between familial concern and disease.

Anatomic description of angulation at a joint or fracture addresses the distal skeletal element. Genu valgum refers to pointing of the leg away from the midline, or apex medial angulation of the knee, in the coronal plane. Genu varum is the opposite. Genu valgum is known as “knockknee,” due to overlap of the joints during walking. Genu varum is known as “bowlegs,” after the arc formed by the lower limb.

Blount called this “tibia vara.” It represents a growth disturbance of the posteromedial proximal physis of the tibia. The growing tibia spirals into varus (medial tether) as well as medial rotation and procurvatum (posterior tether), thereby forming a complex multiplanar deformity. While the condition originates in the tibia, where signs are most striking, it also may involve the distal femur.