Tibial varus is an angular orthopedic deformity where the tibia, the lower leg bone, bows inward, creating the appearance of “bow legs.” While genu varum describes general bow-leggedness, tibial varus specifically refers to the misalignment originating below the knee joint in the shin bone. This structural issue alters the mechanical axis of the leg, leading to uneven weight distribution. The abnormal alignment places excessive stress on the knee’s medial (inner) compartment, which can cause subsequent joint problems over time.
Identifying Tibial Varus
The most immediate sign of tibial varus is the visual presentation of an exaggerated outward curvature of the lower leg. The hallmark of the deformity is a significant gap remaining between the knees when a person stands with their ankles together. This bowing is often asymmetrical, affecting one leg more than the other.
Functional limitations often accompany the visual changes, including an abnormal gait pattern. The body may compensate for the misalignment, leading to a noticeable “lateral thrust” in the knee when walking. This mechanical stress concentrates the load on the medial compartment of the knee, resulting in chronic pain and premature cartilage wear.
The uneven pressure can also cause secondary issues due to compensatory mechanics in the foot and ankle. These include hip pain, shin splints, and Achilles tendonitis. Instability may also be reported, especially during activities involving running or pivoting. For many, the gradual onset of pain and difficulty with mobility is what ultimately prompts a medical consultation.
Underlying Factors Leading to the Condition
Developmental Causes
A primary developmental cause, particularly in children and adolescents, is Blount’s disease (tibia vara). This disorder involves a disruption in the growth plate of the proximal medial tibia. The inner part of the shin bone stops growing while the outer side continues, resulting in a progressive bow-legged deformity.
The infantile form of Blount’s disease typically manifests before age three and often affects both legs. The adolescent form occurs after age ten and is frequently associated with obesity or early walking. These factors place excessive compressive forces on the vulnerable growth plate, inhibiting normal bone formation on the medial side of the upper tibia.
Metabolic and Acquired Causes
Metabolic disorders, most notably rickets, are another underlying factor. Rickets is caused by a severe deficiency in Vitamin D or a genetic inability to metabolize it, leading to soft, weakened bones that bend under body weight. Rickets often contributes to the tibial component of the varus deformity.
In adults, tibial varus can be an acquired condition resulting from trauma or degenerative changes. A malunion, where a tibial fracture heals in an improper, angulated position, can directly create the deformity. Additionally, severe, long-standing osteoarthritis can cause cartilage and bone loss in the knee’s medial compartment, collapsing the joint space and driving the tibia into a progressively varus alignment.
Diagnostic Procedures and Assessment
Diagnosis of tibial varus begins with a detailed physical examination and medical history to assess the degree of bowing and identify underlying causes. The clinician visually assesses the patient’s standing alignment and gait, looking for signs like a lateral knee thrust during walking. Measuring the distance between the knees when the ankles are touching provides a preliminary measure of severity.
The definitive assessment relies on specialized radiographic imaging, specifically a full-length standing anteroposterior X-ray (long-leg alignment view). This image must be taken with the patient bearing weight and the patellae pointing forward to ensure an accurate representation of the limb’s true mechanical axis. The X-ray allows for precise measurement of angles that quantify the deformity.
A primary measurement is the Mechanical Axis Deviation (MAD), which tracks the line from the hip center to the ankle center. In varus, this line passes medial to the knee joint center, indicating the degree of malalignment. The Medial Proximal Tibial Angle (MPTA) is also measured to pinpoint the location and severity of the tibial deformity, guiding surgical planning. For complex cases, a CT scan or MRI may be used to evaluate bone torsion and joint cartilage health.
Managing and Correcting Tibial Varus
Management is determined by the patient’s age, the cause, and the severity of the malalignment. For very young children with mild, physiologic bowing, observation is often the initial strategy, as these cases may resolve naturally as the child grows. For established developmental conditions like Blount’s disease, observation alone is usually insufficient.
Non-Surgical Treatment
Non-surgical intervention focuses on managing symptoms and, in children, modulating growth. Physical therapy is prescribed to strengthen the muscles surrounding the knee and hip, improving dynamic stability and gait mechanics. While therapy cannot correct the bone deformity, it can alleviate pain and slow the progression of joint wear.
Bracing and orthotics are important, particularly for early-stage Blount’s disease in children under four years old. A Knee-Ankle-Foot Orthosis (KAFO) is a custom-fitted brace designed to apply corrective pressure to the medial side of the knee and tibia. The goal of bracing is to offload the medial growth plate, allowing the lateral side to catch up and correct the bowing.
Surgical Correction
If the deformity is advanced, progressive, or fails conservative management, surgical correction is the standard treatment. The most common procedure is an osteotomy, which involves cutting and realigning the bone to restore a normal mechanical axis. For tibial varus, a High Tibial Osteotomy (HTO) is typically performed near the top of the shin bone.
The HTO aims to shift the weight-bearing line from the damaged medial compartment of the knee to the healthier lateral compartment. This is often achieved using a Medial Opening Wedge HTO. A wedge-shaped cut is made in the tibia, and a gap is opened on the inner side, which is then filled with a bone graft or substitute. The newly aligned bone is secured with a plate and screws.
Recovery
Following surgery, recovery protects the healing bone while gradually restoring function. Patients are typically placed on partial weight-bearing restrictions for the first six weeks to allow the osteotomy site to consolidate. Physical therapy begins almost immediately to maintain joint range of motion and prevent muscle atrophy.
Full weight-bearing usually commences after six to eight weeks, depending on radiographic evidence of bone healing. The overall recovery and return to full activity can take several months. A successful osteotomy improves long-term function and alignment, and can delay the onset of severe osteoarthritis.