Varus stress describes a force applied to the inner side of the knee, pushing it outward. This can lead to a “bow-legged” appearance, known as varus knee alignment or genu varum. This alignment alters how forces are distributed across the knee, increasing the load on the inner (medial) compartment. It also places tension on structures on the outer side of the knee, primarily the Lateral Collateral Ligament (LCL), which connects the thigh bone (femur) to the smaller shin bone (fibula).
Causes and Symptoms of Varus Knee Alignment
The reasons for a varus knee alignment are varied. While a bow-legged stance is a normal part of development for many infants, in older children and adults it can stem from conditions like rickets, a disease caused by vitamin D deficiency, or Blount’s disease, which affects the growth plates of the tibia. Previous injuries or bone tumors can also alter the knee’s alignment.
A structural cause in adults is the gradual wear of cartilage on the inside of the knee joint, which can cause the leg to bend outward. This creates a cycle where the varus alignment accelerates cartilage wear, and the cartilage loss worsens the alignment. Muscle imbalances, such as weakness in the hip abductor muscles, can also contribute to poor leg alignment and increased knee stress.
The most apparent sign of varus alignment is a visible bow-legged posture. Individuals often experience pain concentrated on the inner side of the knee, which can worsen with activities like walking or climbing stairs. A feeling of instability, or the sensation that the knee might “give way” outwards, is another frequent complaint. This instability arises because the altered alignment compromises the joint’s normal stability, putting extra strain on the supporting ligaments.
Potential Knee Injuries from Varus Stress
Chronic varus stress places excessive pressure on the medial compartment of the knee. This sustained overload can accelerate the wear of the articular cartilage, the smooth tissue that cushions the ends of the bones. Over time, this can lead to medial compartment osteoarthritis, a condition characterized by pain, stiffness, and joint space narrowing. The progressive loss of cartilage further exacerbates the varus alignment.
While chronic stress leads to degenerative changes, a sudden and forceful varus stress can cause acute injuries. A blow to the inside of the knee can stretch or tear the Lateral Collateral Ligament (LCL). The LCL is the primary stabilizer against this type of outward force, and an injury to it can range from a mild sprain to a complete rupture.
In more severe trauma, the injury may not be isolated to the LCL. The force can also damage other structures on the outer back portion of the knee, an area known as the posterolateral corner (PLC). An injury to the PLC, often occurring alongside an LCL tear, can lead to significant rotational and varus instability of the knee. This combined injury pattern is more complex and often results in greater functional impairment if not properly addressed.
Diagnosis and Treatment Pathways
Diagnosis begins with a physical examination where a healthcare provider will observe the patient’s gait and leg alignment. A maneuver called the varus stress test is performed, where a clinician applies an outward force to the lower leg to check the integrity of the LCL. Increased gapping on the outside of the knee during this test suggests an LCL injury.
Imaging studies are also used to get a clearer picture of the joint’s condition. X-rays are useful for assessing bone alignment and can reveal joint space narrowing, a sign of osteoarthritis. When soft tissue damage is suspected, an MRI scan provides detailed images of ligaments like the LCL, cartilage, and the menisci.
Treatment is tailored to the underlying cause and severity of the injury, and non-surgical approaches are often the first line of treatment. This includes:
- Physical therapy focused on strengthening the muscles around the hip and knee.
- Activity modification to avoid aggravating movements.
- Weight management to reduce load on the joint.
- The use of a supportive brace to provide relief.
For severe cases, such as a complete LCL rupture or significant osteoarthritis, surgery may be considered. In younger, active patients with varus malalignment but without advanced arthritis, a high tibial osteotomy may be performed. This procedure realigns the tibia to shift pressure from the damaged medial compartment to the healthier lateral one. For older individuals with severe arthritis, a total knee replacement is an effective option to relieve pain and restore function.