Knee Malalignment

The knee is made up of three compartments: the medial compartment on the inner side, the lateral compartment on the outer side, and the patellofemoral compartment behind the kneecap. Each is lined with smooth cartilage and, in the medial and lateral compartments, cushioned by a meniscus.

When a person stands, load travels down a line from the center of the hip through the knee to the center of the ankle, called the mechanical axis. In a well-aligned leg, that line passes near the center of the knee and the medial and lateral compartments share the work. In a bowlegged, or varus, knee, the line shifts inward and overloads the medial compartment. In a knock-kneed, or valgus, knee, it shifts outward and overloads the lateral compartment.

Alignment also has a front-to-back component. The top of the tibia is normally tilted slightly backward, which is called the tibial slope. When that slope is excessive, the tibia tends to slide forward on the femur, placing greater strain on the ACL.

Over years, concentrated pressure wears down cartilage in the overloaded compartment. As cartilage is lost, the deformity worsens, which increases the overload further. Left untreated, this cycle can lead to arthritis on the affected side of the knee.

Malalignment may be constitutional, meaning it reflects the way a person is built, or it may be acquired. Common causes include:

• Natural build: Many people have a mild bowlegged or knock-kneed alignment that is simply part of their anatomy and becomes symptomatic only after years of activity.
• Growth plate injury or developmental conditions: An injury or condition affecting the growth plates during childhood can cause one side of a bone to grow unevenly.
• Prior fracture: A fracture of the femur or tibia that healed in an imperfect position can shift the alignment of the entire leg.
• Loss of meniscus: Removal of meniscal tissue reduces the cushion in that compartment, allowing the joint space to narrow and the knee to tilt toward the affected side.
• Ligament injury: Chronic ligament insufficiency, particularly of the posterolateral corner in a bowlegged knee, can allow the knee to open up and shift with each step.
• Cartilage loss: Arthritis itself worsens alignment, as thinning cartilage allows the knee to collapse further toward the damaged side.

Malalignment matters well beyond arthritis. It places excess stress on cartilage repairs, meniscal transplants, and ligament reconstructions, and it is one of the more commonly overlooked reasons those procedures fail.

Symptoms usually develop gradually and are concentrated on the overloaded side of the knee. Dr. Rynecki Baker encourages patients to seek evaluation before cartilage loss becomes advanced, because the treatment options available to a well-preserved knee are considerably broader.

Common symptoms include:

• Pain on one side of the knee: Inner-sided pain in bowlegged knees and outer-sided pain in knock-kneed knees, often worse with walking, standing, or descending stairs.
• A visible change in leg shape: Bowing or inward angulation that a patient or family member notices progressing over time.
• Pain that limits distance: Discomfort that appears after a predictable amount of walking or activity and eases with rest.
• Swelling and stiffness: Recurrent swelling in the affected compartment, particularly after activity.
• A sense of the knee shifting sideways: A thrust during walking, in which the knee visibly shifts outward (or inward) with each step, reflecting significant overload and often some ligamentous laxity.
• Recurrent ligament graft failure: Repeated failure of an ACL reconstruction can be a sign of underlying malalignment or excessive tibial slope.

Accurate diagnosis begins with a thorough evaluation by Dr. Rynecki Baker. She will take a detailed history, including where the pain is located, how far a patient can walk comfortably, prior knee surgeries, and any history of fracture or childhood injury. She will then examine standing alignment, watch the patient walk to identify a thrust, and assess range of motion, ligament stability, and tenderness by compartment.

Imaging is central to this diagnosis. Standing full-length x-rays from hip to ankle are the standard, because alignment cannot be assessed accurately on a short film or on an image taken lying down. These allow Dr. Rynecki Baker to measure the mechanical axis precisely and determine exactly where the deformity originates, in the femur, the tibia, or both. Weight-bearing views of the knee show joint space narrowing by compartment, and a side view is used to measure tibial slope. MRI defines the condition of the cartilage, meniscus, and ligaments. A CT scan may be added to assess rotation or for surgical planning.

Malalignment is frequently missed, and its consequences accumulate quietly. Recognizing it early can change the trajectory of a knee, and correcting it can relieve pain, protect cartilage, and delay or prevent knee replacement in patients who are far too young for one.

Dr. Rynecki Baker’s training at both NYU Langone Health and Hospital for Special Surgery, combined with her published work in this area, including a widely used book chapter on the technique for high tibial osteotomy, means patients are receiving care from a specialist with deep knowledge of knee mechanics and joint preservation. She approaches every patient as an individual, taking the time to understand each person’s symptoms, activity level, and goals before recommending treatment.