Bow Legs and Knock Knees: When Is a Standing Scan Useful?

Many adults with bow legs or knock knees have simply got used to them. Perhaps someone pointed it out when you were young. Or you noticed it yourself over the years, but no one treated it as serious. Then the knee pain started. Slowly at first, then more often, until it became part of daily life. And somewhere along the way, nobody actually linked the two.

Bow legs and knock knees in adults are not just about how the legs look. They change the path your body weight takes every time you stand or walk. That change puts pressure on joints that were never meant to carry it unevenly. Year after year, this builds into pain, cartilage wear, and sometimes hip and back problems too. Knowing exactly where your alignment sits, measured while you are actually standing, is what makes real treatment possible. That is why a standing EOS scan at ScanAlign can be useful for adults who need clear leg alignment measurements.

What Are Bow Legs and Knock Knees?

Bow legs and knock knees are both forms of leg malalignment. The legs do not sit in a straight line from hip to ankle. They look different, load the knee differently, and need different treatment approaches. Both are more common in adults than most people think. Both can cause ongoing problems when nobody has properly assessed them.

• Bow legs, also called genu varum: The legs curve outward at the knee. Even with the ankles together, there is a gap between the knees. Body weight is pushed to the inner side of the knee joint.
• Knock knees, also called genu valgum: The knees angle inward and touch or cross when standing, while the feet stay apart. Body weight shifts to the outer side of the knee joint.

Both can be present from birth, or develop after an injury, from one-sided joint wear, or from conditions that affect bone structure over time. Many adults have some degree of either without it ever being measured.

Bow Legs vs Knock Knees: Key Differences

Can Bow Legs and Knock Knees Cause Knee Pain in Adults?

Every time you stand or take a step, body weight travels down a line called the mechanical axis. It runs from the centre of the hip, through the knee, and down to the ankle. When this line passes through the middle of the knee, the load spreads evenly across both sides. When the legs are bowed or knock-kneed, the line shifts off centre.

In bow legs, it swings inward and overloads the inner cartilage. In knock knees, it shifts outward and hits the outer side instead. This uneven load does not usually cause a sudden injury. It quietly wears the cartilage down on one side, year after year, until the knee pain is impossible to ignore. Most people blame age, but the real reason is often the alignment nobody measured.

Other Joints Affected by Leg Malalignment

The knee takes the most obvious strain, but the whole lower body can end up compensating.

• Hips: Abnormal leg rotation changes how the hip socket takes load, leading to one-sided hip pain over time.
• Ankles and feet: The foot may compensate for knee malalignment, often causing flat feet or ankle strain.
• Lower back: The pelvis can tilt to adjust around the leg misalignment, and this can build into ongoing back pain.
• Leg length differences: Untreated malalignment can create or worsen a leg length difference, adding more load imbalance.

Important Note: Knee pain from bow legs or knock knees is often mistaken for general wear and tear. The real cause, how body weight travels through a misaligned leg, only shows up clearly when the mechanical axis is measured in a standing, loaded position.

What Causes Bow Legs and Knock Knees in Adults?

Some adults have had this since childhood. It may be due to how the bones developed, or to conditions that affected bone growth early on. But leg malalignment does not always start young. It can develop or get worse in adult life for several reasons:

• Old fractures or injuries that healed with a slight angle in the bone
• Osteoarthritis wearing down cartilage on one side of the knee
• Obesity placing uneven load on one part of the knee over many years
• Meniscus damage removing the cushioning that keeps the joint space even
• Conditions like Paget’s disease or rickets that affect bone structure in the lower limb

Because it builds slowly, most people do not notice their alignment shifting. The pain gets blamed on other things long before anyone checks the actual position of the legs.

How Is Leg Alignment Normally Checked, and Where Does It Fall Short?

Standard assessment for bow legs and knock knees uses a few methods. But almost all of them share the same core problem. They do not always measure the mechanical axis accurately under real body weight. That is the one measurement that actually shows how serious the malalignment is and what should happen next.

What Standard Assessment Usually Includes

• A visual check of leg shape while standing or walking
• Physical measurements with a tape or goniometer in a clinic
• X-rays taken with the patient lying flat on a table
• A general clinical estimate of how much the legs bow or knock

Where It Falls Short

• Lying-down X-rays do not show how the knee takes load under body weight
• Visual estimates are not precise enough for treatment planning
• The mechanical axis cannot be calculated properly from a lying-down image
• Both legs are rarely compared at the same time in one image
• Moderate malalignment can be missed or underestimated

This is why weight-bearing imaging compared with traditional imaging is so important for checking alignment. Standing scans show how the body actually loads the joints in real life.

Why a Standing Scan Changes Everything

The mechanical axis only shows its true position when you stand with your full body weight going through the joints. When you lie flat, the muscles relax and pressure on the joint eases. The degree of bow or knock does not show the same way it does in real life. That difference in position can change how serious the malalignment looks. As a result, it can change which treatment is suggested.

What a Standing Scan Makes Possible

• Captures the true mechanical axis under real body weight
• Shows the actual degree of varus or valgus as it is day to day
• Measures both legs at the same time, so differences between the sides are clear
• Gives precise angles instead of visual estimates for surgical planning
• Shows the full lower limb as one connected system, not separate sections
• Picks up moderate malalignment that lying-down imaging may underestimate

What Is an EOS Scan and How Does It Measure Leg Alignment?

An EOS scan takes front and side images of your full lower limbs at the same time, from hip to ankle, while you stand naturally inside a scanning cabin. These images can be used to create a 3D skeletal model. This helps clinicians calculate the mechanical axis, the hip-knee-ankle angle, and the exact degree of bow or knock.

What Makes EOS Different for Leg Alignment?

• The standing position captures true weight-bearing alignment, not a lying-down approximation
• Both legs are scanned at the same time in one image from hip to ankle
• 3D modelling supports precise angle measurements instead of flat estimates
• Lower radiation exposure makes it useful when repeat monitoring is needed
• The scan is quick and open, and does not involve a tunnel

If you are worried about scan exposure, ScanAlign’s guide on EOS scan safety and radiation levels explains why EOS is often chosen for people who may need more than one scan over time.

What an EOS Scan Shows for Bow Legs and Knock Knees

A standing EOS scan gives your treating clinician details that change how bow legs and knock knees are managed. From the scan, a consultant radiologist can measure and report important alignment details.

• Mechanical axis deviation: How far the weight-bearing line has moved from the centre of the knee
• Hip-knee-ankle angle: Full alignment of the lower limb from top to bottom on each side
• Degree of varus or valgus: A precise measurement of how bowed or knock-kneed each leg is
• Joint space comparison: Which part of the knee is overloaded, and by how much
• Side-by-side lower limb comparison: Differences between left and right are clearly visible
• 3D skeletal model: A complete picture of how each leg lines up while standing

These details can help decide whether treatment should be conservative or surgical. ScanAlign’s guide on what an EOS scan report shows is also useful if you want to understand the kind of measurements you receive after the scan.

Who Should Get a Standing Leg Alignment Scan?

A standing EOS leg alignment scan is worth considering if any of these apply to you:

• You have visible bow legs or knock knees, and daily knee pain is developing
• You have one-sided knee pain with no clear injury, and your alignment has never been checked
• You have been told you have early knee osteoarthritis and want to know if malalignment is making it worse
• You are being assessed for, or considering, osteotomy surgery
• You are an athlete with persistent knee or hip pain on one side that a standard scan has not explained
• You have had knee surgery before and want to check how your alignment has settled since

At ScanAlign, you can refer yourself and get your measurements without needing a referral from your doctor.

Bow Legs in Adults Treatment: What Happens After the Scan?

Once the EOS report is ready and the degree of malalignment is clear, treatment options stop being guesswork. What is recommended depends on how significant the misalignment is and how much joint damage has already happened.

• Physiotherapy: Targeted work on the hip abductors, glutes and core to reduce uneven knee loading
• Orthotics and bracing: Offloading braces that shift weight away from the damaged part of the knee
• Weight management: Reducing the load through the knee matters, even with moderate malalignment
• High tibial osteotomy: For bow legs, realigning the tibia so the mechanical axis passes through the centre of the knee
• Distal femoral osteotomy: For knock knees, repositioning the lower femur to correct the valgus angle
• Knee replacement: For advanced joint damage, where saving the joint is no longer realistic

EOS data can make surgical planning far more precise, because the surgeon has exact correction measurements before treatment begins.

What Happens at a ScanAlign EOS Appointment?

The process at ScanAlign is simple from start to finish. You can also read the full guide on what happens during an EOS scan before your appointment.

1. Free Video Consultation

A specialist reviews your symptoms and history before you travel to London. This helps confirm whether EOS is the right next step.

2. Arrive at Harley Street Hospital

No preparation, injection or contrast dye is needed. Comfortable clothing is usually best, and you may need to remove metal items.

3. 15-Second Standing Scan

Both legs are scanned from hip to ankle while you stand naturally. There is no tunnel and no uncomfortable recovery period afterwards.

4. Consultant Radiologist Report

A UK-trained specialist writes a detailed report with mechanical axis measurements, angles and your 3D skeletal model.

5. Doctor Follow-Up

A doctor takes you through the findings, explains what the numbers mean, and talks through treatment options.

Important Note: EOS uses lower radiation than many standard X-ray methods. For adults who need repeat scans to track alignment changes or check results after treatment, that difference in exposure can matter over time.

FAQs

1. 1. Can bow legs in adults be treated without surgery? Yes. For mild to moderate bow legs, conservative treatment can make a real difference. Targeted physiotherapy, offloading knee braces and orthotics can all reduce pain and slow down joint damage. Surgery becomes more relevant when the malalignment is significant and conservative options are not enough to protect the joint.
2. 2. Do bow legs and knock knees get worse with age? They can, especially when arthritis develops on one side of the knee. As cartilage wears unevenly, the joint space narrows. The leg may then slowly bend further in the direction of the existing malalignment. Getting it measured early and monitoring it over time can be very useful.
3. 3. Can bow legs cause knee pain even if there is no injury? Yes. Pain from bow legs can come from uneven load, not a specific injury. With every step, the inner cartilage takes more force than it is designed for. Over time, that can cause pain and wear without any accident happening.
4. 4. What is the best scan to check leg alignment in adults? A standing full-length EOS scan is one of the most useful options. It captures the full mechanical axis from hip to ankle under real body weight. It also measures both legs at the same time and supports detailed 3D alignment assessment.
5. 5. How does an EOS scan measure bow legs or knock knees? EOS takes front and side images of both lower limbs at the same time while you stand. From those images, clinicians can calculate the mechanical axis, the hip-knee-ankle angle, and the exact degree of varus or valgus on each side.
6. 6. How do I book a standing leg alignment scan in London? You can book directly with ScanAlign, Harley Street Hospital, without a referral from your doctor. Start with a free video consultation, so a specialist can review your situation and confirm whether an EOS leg alignment scan is the right next step.