Leg alignment is defined by the body’s mechanical axis, also known as the Mikulicz line, which represents the path of weight transmission from the hip to the ankle. This line runs from the center of the hip’s femoral head down to the center of the ankle joint. For a leg to be considered perfectly straight, this axis must pass directly through the center of the knee. Perfectly straight alignment is rare, and most people have slight, harmless variations. The term “not straight” refers to an angular deviation where the weight-bearing line shifts inward or outward from the knee joint’s center, medically described as an angular deformity.
Common Forms of Leg Misalignment
Angular deformities are broadly classified into two main types that determine how the legs appear. These conditions are defined by the knee’s relationship to the body’s midline.
The first type is Genu Varum, commonly known as bow legs, where the knees angle outward away from each other. When standing with feet and ankles together, a noticeable outward arc is visible, and the knees remain separated. This configuration places increased pressure on the inner (medial) compartment of the knee joint.
The second form is Genu Valgum, recognized as knock knees, where the knees angle inward toward the midline. When standing, the knees touch or overlap, but the ankles and feet remain apart. This alignment shifts the mechanical load to the outer (lateral) compartment of the knee.
Underlying Causes of Angular Deformity
The causes of leg misalignment range from expected phases of growth to underlying health conditions. Most angular deformities in childhood are physiological, meaning they are a normal part of development and self-correct over time.
Infants are typically born with genu varum (bow legs), which is most prominent until 18 to 24 months old. As the child grows, alignment shifts to genu valgum (knock knees), peaking around age four. The legs gradually straighten, achieving the adult configuration by age seven or eight. Observation is often the only management required for mild cases that follow this predictable sequence.
Misalignment is considered pathological when it is severe, progresses rapidly, or occurs outside of the expected age ranges. A common pathological cause is Rickets, a condition stemming from a nutritional deficiency of Vitamin D, calcium, or phosphate. Without these minerals, bones soften and bend under the body’s weight, leading to severe or persistent bowing.
Growth plate disturbances can also create angular deformities, most notably Blount’s disease (tibia vara). This condition affects the growth plate on the inner side of the upper shin bone, causing uneven growth that results in progressive bowing below the knee. Trauma or infection that damages a portion of the growth plate can similarly lead to asymmetrical growth and subsequent angular deformity.
Diagnosis and Assessing Severity
Diagnosis begins with a thorough physical examination. The first step involves measuring the distance between the knees or the ankles while the patient is standing.
For suspected bow legs (genu varum), the intermalleolar distance (space between the inner ankle bones) is measured when the knees are pressed together. For knock knees (genu valgum), the intercondylar distance (space between the inner knee prominences) is measured when the feet and ankles are placed together. These measurements quantify the degree of angulation. A long-leg alignment X-ray is the definitive diagnostic tool used to precisely assess the mechanical axis.
This specialized X-ray captures the entire lower limb, allowing doctors to draw the weight-bearing line and measure its deviation from the knee’s center. The results distinguish between a physiological variation and a pathological condition requiring intervention. Signs that raise concern include significant asymmetry, persistence of the deformity beyond the normal age range, or the presence of associated pain or limping.
Medical Interventions and Management
The course of action depends on the patient’s age, the cause, and the severity of the misalignment. For most children with physiological bowing or knock knees, the primary management is observation and monitoring. The healthcare provider tracks the child’s alignment with periodic physical exams to ensure the condition self-corrects according to the normal developmental timeline.
Non-surgical treatments, such as specialized braces or orthotic devices, are occasionally used for specific pathological conditions in young children, such as early-stage Blount’s disease. These devices apply corrective pressure to the growing bone to guide development toward straighter alignment. Braces are generally ineffective for physiological variations.
Surgical correction is considered when a pathological condition is severe or if a physiological deformity fails to correct by late childhood. For children with open growth plates, the preferred method is guided growth, or hemiepiphysiodesis.
This minimally invasive procedure involves temporarily placing hardware on one side of the growth plate near the knee. The hardware slows growth on the tethered side, allowing the limb to gradually straighten over time. Once alignment is achieved, the hardware is removed. For adolescents or adults with closed growth plates, or for very severe deformities, an osteotomy may be performed. This involves surgically cutting and reshaping the bone, followed by internal fixation, to immediately realign the limb.