The knee joint connects the thigh bone (femur) to the shin bone (tibia), playing a significant role in lower limb function and stability. Proper alignment of the leg, known as the mechanical axis, is crucial for distributing body weight evenly across the joint surfaces. This mechanical axis is an imaginary straight line running from the center of the hip joint through the knee to the ankle. When this line deviates significantly from its neutral position, it results in mechanical axis deviation. Varus and valgus describe the two primary directions of this deviation, which alters the biomechanics of walking and standing, leading to uneven stress and potential joint damage over time.
Defining Varus and Valgus Alignments
Varus alignment, often referred to as genu varum, is characterized by the knee bowing outward, creating a “bow-legged” appearance. The mechanical axis shifts toward the inside of the knee joint, placing disproportionate stress on the medial (inner) compartment. The medial meniscus and the cartilage on the inner side of the joint bear an excessive load, increasing the risk of wear and tear in this area. A noticeable gap appears between the knees when the feet are placed together.
Valgus alignment, or genu valgum, is the opposite, commonly known as “knock-knees,” where the knees angle inward toward the midline. This inward bowing causes the mechanical axis to shift toward the outside of the joint, concentrating weight-bearing forces on the lateral (outer) compartment. The lateral meniscus and outer cartilage are subjected to higher mechanical loads. People with valgus alignment typically find that their knees touch or “knock” against each other.
Primary Causes and Contributing Factors
Misalignments often originate from issues that affect the growth and structure of the bones forming the knee joint. In children and adolescents, these alignments can be developmental; infants typically display a varus alignment that transitions to a slight valgus alignment before straightening by around age seven. When the bones fail to straighten, it is considered a persistent misalignment. Conditions that soften or weaken the bone structure are significant factors, such as Rickets (due to lack of Vitamin D) or Blount’s disease (a shin bone growth disorder), which can lead to varus alignment. In adults, severe, long-standing osteoarthritis is a major cause, as the loss of cartilage and bone in one compartment collapses that side of the joint, driving the leg into the corresponding varus or valgus position. Trauma can also disrupt the normal geometry of the femur or tibia, leading to a mechanical axis deviation.
Non-Surgical Management Strategies
The initial approach to managing varus or valgus alignment typically focuses on conservative, non-surgical methods to alleviate symptoms and reduce mechanical stress. Weight management is an important strategy, as reducing body mass significantly lowers the forces transmitted through the knee joint, potentially slowing the progression of cartilage wear. Even a small reduction in weight can decrease the load and associated pain, especially in varus alignment. Anti-inflammatory medications, such as NSAIDs, are often prescribed for short periods to manage pain and reduce inflammation associated with the condition.
Physical Therapy, Orthotics, and Bracing
Physical therapy is a core component, focusing on targeted exercises to strengthen the muscles surrounding the knee, such as the quadriceps and hamstrings, to improve joint stability. Gait training may also be used to optimize weight distribution during walking, thereby reducing excessive stress on the overloaded compartment. Orthotic inserts, specifically shoe wedges, are used to mechanically shift the weight-bearing line away from the distressed compartment. For varus alignment, a lateral (outer) wedge insert is used to push the load toward the healthier side of the knee, while a medial (inner) wedge is used for valgus alignment. Bracing may be recommended, particularly for growing children, to provide external support and gradually guide the leg toward a more neutral alignment. These non-invasive treatments are usually pursued until symptoms improve or until the misalignment progresses to a severity that requires a more definitive solution.
Surgical Correction Procedures
When conservative treatments fail to provide relief, or when the misalignment is severe and rapidly progressing, surgical intervention becomes necessary to restore the mechanical axis.
Osteotomy
A primary corrective procedure is an osteotomy, which involves surgically cutting and realigning the bone to shift the weight-bearing load away from the damaged side of the joint and onto the healthier side. For varus alignment, a High Tibial Osteotomy (HTO) is commonly performed on the shin bone to push the weight laterally. Conversely, for valgus alignment, a Distal Femoral Osteotomy (DFO) is typically performed on the thigh bone to shift the load medially. These procedures are often favored for younger, active patients with localized arthritis, as they preserve the natural joint and can delay the need for a total joint replacement.
Total Knee Arthroplasty (TKA)
Total Knee Arthroplasty (TKA), or total knee replacement, is the end-stage surgical option reserved for patients whose arthritis is widespread and severe across the entire joint. TKA involves removing the damaged joint surfaces and replacing them with metal and plastic components. While TKA is highly effective at relieving pain, it is generally considered after osteotomy has failed or is no longer a viable option due to the extent of the joint damage.