June 8, 2025, 6:21 am | Read time: 5 minutes
Bowlegs and knock-knees are both misalignments that put stress on the knee and promote the development of osteoarthritis. Who is more frequently affected? And what does this mean for treatment? Researchers at Saarland University have found a clear answer.
It has long been suspected in practice that people with bowlegs are more likely to develop knee osteoarthritis in the event of a meniscus injury than those with knock-knees. However, it wasn’t until 2022 that a research team led by Prof. Henning Madry from Saarland University scientifically confirmed this connection. The findings offer new approaches for better treatment options–and thus more quality of life for those affected.
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Overview
How to Recognize a Leg Axis Misalignment
A leg axis misalignment can be congenital or acquired. It is distinguished between knock-knees (medically: valgus position) and bowlegs (varus position).
Slight misalignments in childhood are normal and usually correct themselves by school age. In adults, however, they are permanent–and thus relevant to joint health. Bowlegs are visually apparent when the knees are apart with feet together. Knock-knees are identified when the knees touch but the feet are far apart. A definitive diagnosis can only be made via X-ray.1
Typical Complaints with Knock-Knees or Bowlegs
Leg axis deviations often initially occur without symptoms. Complaints arise later–primarily due to the unilateral stress on the knee joint.
- Bowlegs more often lead to pain on the inside of the knee
- Knock-knees on the outside
When the legs are misaligned, one side of the knee is more stressed than the other. This causes the meniscus–a type of shock absorber in the knee–to wear out faster or even tear. Additionally, fluid can accumulate in the bone, which is very painful. Typical complaints include pain when starting to walk (especially in the morning), in cold weather, or during sports.2
Also interesting: What is osteoarthritis and what are the signs of the disease?
Causes: Why Do Leg Axis Misalignments Occur?
In children, they are usually developmental and harmless. But in adults, the following causes are often behind them:
- Vitamin D deficiency in childhood (rickets)
- Accidents or poorly healed fractures
- Growth disorders or metabolic diseases
- Overweight or poor posture
- Foot deformities like flat feet, which affect the leg axis
The rule is: The longer the misalignment remains untreated, the more the joint surfaces are stressed on one side–which promotes the development of osteoarthritis.3
How Pressure from a Misalignment is Transferred to the Knee
The alignment of the leg axis is crucial, according to the study published in the journal “Science Translational Medicine.”4 If it is tilted inward, one has knock-knees. If it is curved outward, one has bowlegs. Both are not unusual and not unhealthy. Nevertheless, the pressure on the knee joints is excessively transferred inward or outward. A healthy knee can generally tolerate such axis deviations well. However, with a meniscus injury, the risk of osteoarthritis increases significantly.
Replication in Animal Models
Madry and his colleagues replicated both misalignments and the normal leg axis in animal models and examined the impact of a meniscus injury on the subsequent risk of osteoarthritis. “We were able to demonstrate very clearly in the study that a meniscus injury indeed measurably increases the risk of osteoarthritis in the knee joint,” Madry explains in a statement from the university.5 His most important finding: “Bowlegs are much riskier for the eventual development of osteoarthritis than knock-knees.”
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Bowlegs and Increased Osteoarthritis Risk–What This Means for Treatment
The finding is significant for common treatment methods. There are several approaches to correct the axis: shoe inserts and knee braces (special bandages and splints to stabilize the knee joint) or surgery to correct the axis of the natural knee joint. An artificial knee joint is also an option, “but for younger patients, who usually still want to be very active, it is, of course, very burdensome,” says the expert. Especially since these often need to be replaced after ten years. The fundamental insights from his study could now lead to more surgeries preserving the natural knee. This provides patients with bowlegs a good quality of life even without a knee prosthesis.
Like a Gothic Cathedral
The expert compares bowlegs to the arch of a Gothic cathedral–in this construction, the load on the pillars is also great. Ultimately, this scientific study behaves similarly to the progress in architecture. “Gothic builders also knew how to build the arch as a support for the cathedral’s load, based on experience. Today’s structural engineers, however, know exactly how to calculate the load-bearing capacity of a wall or arch to safely construct a building.” For Madry, this is the difference between empirical values and exact science.