Bow Legs, Knock Knees and Knee Arthritis: The Alignment Link

Bow legs and knock knees throw the knee out of alignment, so body weight loads one side of the joint far more than the other, which speeds up the wear of the cartilage on that side and is a common reason arthritis starts in just one compartment of the knee. The link between leg shape and knee arthritis is real and worth understanding, because it shapes both how the disease develops and which treatments suit you. This surgeon-reviewed guide explains the connection, what can be done about it, and when a knee replacement comes in.

My own arthritis was on the inner side of the knee, the classic pattern, and I remember the surgeon pointing out on the X-ray how my leg had gradually bowed as that side wore down. Seeing it made sense of years of one-sided pain. If your wear is one-sided too, it is worth knowing it can change your surgical options, which is part of the signs you may need a knee replacement.

How do bow legs and knock knees affect the knee?

Bow legs and knock knees shift body weight unevenly across the knee, so one side of the joint carries far more load than it should. In a well-aligned leg, the load passes evenly through the knee. When the leg is bowed or knock-kneed, the line of force moves to one side:

• Bow legs (varus alignment): the legs curve outwards, so the knees stay apart when the ankles touch, and load concentrates on the inner (medial) side of the knee.
• Knock knees (valgus alignment): the legs angle inwards, so the knees touch but the ankles stay apart, and load concentrates on the outer (lateral) side.

The knee has three compartments (inner, outer, and behind the kneecap), and this uneven loading wears out the overloaded compartment first¹.

Do bow legs and knock knees cause knee arthritis?

They do not directly cause arthritis, but they make it more likely and speed it up by concentrating wear on one side. Poor alignment is recognised as a risk factor for knee osteoarthritis, alongside age, extra weight, and previous injury². It works both ways too: once arthritis wears down one side of the joint, the leg can bow or angle further, which loads that side even more, so the shape and the wear feed each other over time.

The alignment itself is usually painless. The pain arrives when the uneven loading wears out the cartilage and arthritis develops on the overloaded side, bringing pain, stiffness, and swelling on that side of the knee.

How is alignment-related knee arthritis treated?

Treatment follows the same core path as any knee osteoarthritis: exercise, weight management, and pain relief first, which NICE recommends for everyone before surgery is considered³. Alignment adds a few specific points:

• Exercise: cannot straighten an adult’s bones, but strengthening the muscles around the knee and hip supports the joint and reduces pain.
• Weight management: especially valuable here, because less body weight means less force through the overloaded side. See losing weight before knee surgery.
• Braces and footwear: offloading supports can shift some load away from the worn side.
• Injections: a corticosteroid injection can settle a painful flare.

These and the other non-surgical options are covered in full in the alternatives to knee replacement.

Can surgery correct bow legs or knock knees?

Yes. In a younger, active person with significant misalignment and one-sided arthritis, an operation called an osteotomy can realign the leg by cutting and repositioning the bone to take load off the worn side and preserve the joint⁴. It is a joint-preserving option that aims to delay the need for a replacement. In older people with established arthritis across the joint, a knee replacement is usually the better answer, because it resurfaces the worn joint and corrects the alignment at the same time.

When is a knee replacement needed, and which type?

A knee replacement is considered when the pain limits everyday life and non-surgical treatments no longer help enough. Alignment matters here because it influences which type suits you:

• Partial (unicompartmental) knee replacement: resurfaces only the one damaged compartment, keeping the healthy bone and ligaments. Suitable for some people whose alignment problem has worn out just one side.
• Total knee replacement: resurfaces all three compartments and corrects the alignment; needed when the wear has spread across the joint.

Both are successful: around 90 to 95% of knee replacements are still in place at 10 years, and they typically last 15 to 20+ years¹. Which type suits you depends on how far the wear has spread, a decision made with your surgical team. The procedure, the types, the risks, and recovery are all set out in our complete guide to knee replacement surgery.