Variations in leg alignment are common, referring to an angular deformity where the lower limb does not follow a straight line from the hip to the ankle. This misalignment, known as a coronal plane deformity, can be present from childhood or develop later in life. While often perceived as cosmetic, these deviations alter the biomechanics of the knee joint and can lead to pain or degenerative conditions over time.
Defining Leg Misalignment: Bowed Legs and Knock Knees
The two primary types of angular leg misalignment are characterized by the direction the knees point when a person stands. Bowed legs, medically termed Genu Varum, present as an outward curvature where the knees remain apart even when the ankles are touching. This alignment places increased stress on the inner (medial) compartment of the knee joint.
The opposite presentation is Knock Knees, or Genu Valgum, where the knees touch or nearly touch while the ankles are separated. This inward angulation shifts the mechanical load to the outer (lateral) compartment of the knee. Both conditions affect how weight is distributed across the joint surfaces, which impacts long-term joint health.
Underlying Causes of Crooked Leg Appearance
The causes of angular deformities vary significantly depending on age, categorized into developmental or acquired issues. In toddlers, the most frequent cause of bowed legs is physiological bowing, a normal part of skeletal development that typically corrects itself by age three. If bowing persists, a pathological condition such as Blount’s disease may be present, involving an abnormal growth disturbance in the growth plate of the upper shin bone (tibia). Rickets, a bone-weakening disorder caused by insufficient Vitamin D, calcium, or phosphate, is another pediatric cause that leads to generalized softening and bowing of the long bones.
Acquired causes manifest later in life, resulting from trauma, disease, or mechanical wear. Fractures of the femur or tibia that heal in a non-straight position, known as malunion, can result in an angular deformity. In adults, degenerative arthritis, specifically osteoarthritis, frequently causes a gradual change in leg alignment. Osteoarthritis leads to progressive cartilage loss on one side of the knee joint, causing the leg to collapse into a varus (bowed) or valgus (knock-knee) position. Metabolic bone diseases, such as Paget’s disease, can also alter bone structure and integrity, leading to angular deformities.
Evaluating the Misalignment: The Diagnostic Process
Assessing leg alignment begins with a physical examination, where the physician observes the patient’s gait and measures the distance between the knees or ankles while standing. For Genu Valgum, the distance between the inner ankles is measured; for Genu Varum, the distance between the inner knees is recorded. This clinical measurement helps quantify the extent of the visible deformity.
The definitive evaluation relies on specialized imaging, primarily the full-length standing X-ray, also known as a long-leg alignment view. This image captures the entire leg from the hip to the ankle, allowing for precise measurement of the mechanical axis. The mechanical axis is an imaginary line drawn from the center of the hip joint to the center of the ankle joint, and in a perfectly aligned leg, this line should pass through the center of the knee.
The degree to which this line deviates is called the Mechanical Axis Deviation (MAD), a quantifiable measure of the deformity. Specialized measurements of joint angles are calculated from the X-ray to pinpoint whether the deformity originates in the femur, the tibia, or both. If a metabolic cause like Rickets is suspected, blood work is performed to check for deficiencies in Vitamin D, calcium, or phosphate levels.
Corrective and Management Strategies
Management of leg misalignment varies based on the patient’s age, cause, and severity. For infants and young children with physiological bowing, observation is the most common approach, as alignment frequently corrects spontaneously as the child grows. Non-surgical options for specific pediatric conditions, such as early-stage Blount’s disease, may include bracing to guide limb growth.
For adults or children with severe, progressive, or symptomatic alignment issues, surgical intervention is often necessary. Physical therapy strengthens muscles and improves gait mechanics but cannot correct the underlying bone structure. Weight management is a conservative strategy that reduces stress on the knee joint, which can slow the progression of arthritis associated with the deformity.
Guided Growth (Hemiepiphysiodesis)
In growing children, a minimally invasive technique called guided growth, or hemiepiphysiodesis, gradually corrects the angular deformity. This involves placing a small metal plate across the growth plate on the faster-growing side of the bone. This hardware temporarily slows growth on one side, allowing the untreated side to catch up and straighten the limb over months or years. Once the desired correction is achieved, the plate is removed in a second minor procedure.
Corrective Osteotomy
For adolescents with persistent problems or adults with misalignments, corrective osteotomy is the established surgical treatment. An osteotomy involves surgically cutting the bone, typically the tibia in a procedure known as a High Tibial Osteotomy, and then realigning it. The bone is fixed with plates and screws in the corrected position to shift the weight-bearing axis away from the damaged or overloaded compartment of the knee joint. This realignment aims to reduce pain, improve function, and slow the progression of degenerative arthritis by redistributing the mechanical load. The decision between guided growth and osteotomy depends on whether the patient’s growth plates are still open or have closed.