Total knee replacement can correct bow legs in most cases, and for many people with severe knee arthritis, it’s the procedure that finally straightens their alignment. Surgeons routinely plan for this correction, using precise bone cuts and soft tissue adjustments to bring the leg back toward a straight mechanical axis. The degree of correction depends on how severe the bowing is, what’s causing it, and how the surrounding ligaments respond during surgery.
How Bow Legs Develop With Knee Arthritis
Bow legs, known clinically as varus deformity, often develop gradually as arthritis wears down the inner (medial) compartment of the knee. As cartilage disappears on the inside of the joint, the bones settle inward and the leg begins to angle outward. Over years, this process can worsen as the inner bone wears further and the ligaments on the outer side of the knee stretch. What starts as mild bowing can progress to a noticeable deformity that shifts your weight distribution, accelerates further joint damage, and changes the way you walk.
Some people also have a naturally bowed alignment that predates their arthritis. In either case, the mechanical axis of the leg, an imaginary line running from the center of the hip to the center of the ankle, no longer passes through the middle of the knee. Restoring that line is one of the central goals of knee replacement surgery.
What the Surgeon Actually Does to Straighten the Leg
Correction happens through a combination of bone cuts and soft tissue balancing. Before surgery, you’ll have weight-bearing, full-length leg X-rays taken while standing. These images let the surgical team measure the hip-knee-ankle angle, which tells them exactly how far your alignment has drifted from neutral. A perfectly straight leg measures about 180 degrees on this scale, and the traditional target for knee replacement is to land within 3 degrees of that mark.
During the procedure, the surgeon removes damaged bone from the end of the thighbone and the top of the shinbone, then cuts those surfaces at carefully calculated angles to accept the implant components. The thickness and angle of these cuts are what primarily reposition the leg into better alignment. In more severe cases, a technique called reduction osteotomy may be used: the surgeon shaves away a bony ridge on the inner side of the upper shinbone that acts like a tent pole, pulling the soft tissues tight and preventing full correction. Roughly 2 millimeters of bone removal from this area yields about 1 degree of additional correction.
Computer navigation is sometimes used to verify alignment in real time. Sensors attached to the thighbone and shinbone track the mechanical axis throughout surgery, allowing the surgeon to confirm each correction step before cementing the final components in place.
Soft Tissue Balancing in Bowed Knees
Bone cuts alone don’t always fully correct a bow leg. Years of varus deformity cause the ligaments and soft tissues on the inner side of the knee to contract and tighten, while the outer side stretches. If these imbalances aren’t addressed, the knee will either remain slightly bowed or feel unstable.
Surgeons manage this through a stepwise process of medial release, progressively loosening the tight inner structures until the knee sits straight and balanced. This typically starts with removing bone spurs (osteophytes) that have built up along the joint line. If tightness remains, the deep layer of the medial collateral ligament is released, followed by other structures as needed. In the most severe cases, the surgeon may partially release the superficial medial collateral ligament from its attachment on the thighbone, a technique that can be done in controlled increments (one-third of the attachment at a time) to avoid over-releasing. The goal is a knee that’s both straight and stable, with even tension on both sides.
How Much Correction to Expect
Most patients with moderate bowing (up to about 10 degrees of varus) can expect full or near-full correction to a neutral mechanical axis. The average change in alignment for people with pre-operative varus deformity is around 6 degrees. For severe bowing beyond 10 degrees, full correction is still the goal but becomes more technically demanding and carries slightly higher risks.
Your leg may also get slightly longer. About 59% of knee replacement patients experience a measurable increase in limb length. For those with varus deformity, the average increase is about 4 millimeters, which is typically unnoticeable. People with severe varus (greater than 10 degrees) see a larger average increase of roughly 8.5 millimeters, which you might notice initially but usually adjust to within a few months.
One important nuance: some surgeons now intentionally leave a small amount of residual varus rather than forcing the leg to perfectly neutral, particularly in patients whose natural anatomy was slightly bowed before arthritis set in. This “constitutional alignment” approach tries to match your original leg shape rather than an idealized straight line. However, research in the Knee Surgery, Sports Traumatology, Arthroscopy journal found that knees left in varus alignment after surgery had a significantly higher failure rate compared to those corrected to neutral, so this remains a balancing act.
How Walking Changes After Correction
Straightening a bowed leg meaningfully changes your gait. The most notable improvement is a reduction in the knee adduction moment, the inward force that drives wear on the inner compartment. This force decreases substantially after surgery, which is one reason the new joint lasts as long as it does.
That said, walking mechanics after knee replacement don’t perfectly match a healthy knee. The implant constrains some of the natural side-to-side motion of the joint, reducing it to about 37% of what people without knee problems experience. Gait speed tends to be somewhat slower than age-matched peers, and full knee extension during walking is often slightly limited. These are tradeoffs most patients accept willingly given the pain relief and improved alignment, but it’s worth knowing that the goal is a functional, comfortable knee rather than a biomechanically perfect one.
Risks Specific to Bow Leg Correction
The overall complication rate for knee replacement is relatively low, and correcting a bow leg doesn’t dramatically change the risk profile. One concern specific to alignment correction is peroneal nerve injury, which affects the nerve running along the outside of the knee below the kneecap. This nerve can be stretched when a severely deformed leg is straightened. Across a large review of nearly 48,000 knee replacements, peroneal nerve palsy occurred in 0.4% of cases. The highest risk factor is actually a knock-kneed (valgus) deformity of 12 degrees or more, which carries a twelve-fold increased risk. Bow-legged patients face a lower risk for this particular complication, though it’s not zero.
The greater concern with severe varus deformity is achieving balanced soft tissues. Over-releasing the inner ligaments can create instability that requires a more constrained implant design. Under-correcting leaves residual bowing that may accelerate wear on the inner side of the new components. Both scenarios can eventually lead to revision surgery, which is why pre-operative planning and intraoperative assessment are so critical for patients with significant bowing.
When Knee Replacement Isn’t the Right Fix
Knee replacement corrects bowing that originates at the knee joint itself. If your bow legs come from a deformity in the shinbone or thighbone (which is more common in younger patients or those with developmental conditions), a knee replacement alone won’t address the problem. In those cases, an osteotomy, where the bone is cut and repositioned above or below the knee, is typically the better option. This is especially true for younger, active patients whose joint surfaces are still in reasonable shape.
For older adults with arthritis-driven bowing, though, total knee replacement remains the most reliable way to simultaneously relieve pain, restore function, and correct the visible deformity. The vast majority of patients come out of surgery with a straighter leg, and that improved alignment is one of the key reasons modern knee replacements routinely last 15 to 20 years.