I had an X-ray in Gangseo-gu and was told my bow-leg angle is "borderline": how does Seoul One Hospital decide between watchful waiting and immediate correction with osteotomy?
A borderline bow-leg angle is judged based on age and the presence or absence of accompanying arthritis.
The Core Answer
A borderline angle is distinguished by age and growth plate status, along with whether arthritis is present.
In children whose growth plates (physis) are still open, a large proportion of deformities correct themselves naturally as the child grows, so surgery is not decided based on the angle alone.
On the other hand, in adults whose growth plates have closed, if medial knee arthritis is progressing concurrently, high tibial osteotomy (HTO) is actively considered even if the angle is borderline.
Questions This Article Answers
- Why isn't surgery decided immediately when the bow-leg angle is borderline?
- Why do the criteria differ between children and adults?
- Why can't the angle measurement (MDA) serve as a single standard?
- At what point is the effect of osteotomy considered no longer permanent?
- How does Seoul One Hospital follow up on borderline cases?
I am Dr. Young-Min Lee, a board-certified orthopedic surgeon and Chief Director of Seoul One Hospital.
If you've been told your angle is "borderline" after bringing in a single X-ray, you're probably at a loss over whether you need surgery right away or whether it's safe to keep watching.
The worry is naturally greater if it's your child's leg, and if you're an adult, the concern is that it may lead to arthritis.
In this article, I'll explain step by step which indicators I actually look at in outpatient visits, when I recommend observation, and when I recommend high tibial osteotomy.
Why a Single Angle Measurement Cannot Decide Surgery on Its Own
The reason a borderline angle appears is that the measurement indicator itself has a gray zone.
The metaphyseal-diaphyseal angle (MDA), which distinguishes physiological genu varum in children from pathological Blount disease, shows a clear statistical distinction: physiological varus averages 9±3.9 degrees, while Blount disease averages 19±5.7 degrees.
The problem lies in the 9–16 degree range. In this range, false positives and false negatives exceed 5%, making it impossible to set a single cutoff value.
A recent study confirmed that even using an MDA of 16 degrees as the cutoff yields a sensitivity of only 50.6% (with a specificity of 100%), meaning that relying on this number alone could miss nearly half of early Blount disease cases.
Rather than judging by a single angle, combining it with other indicators reduces the chance of misjudgment in the borderline range.
That's why, for pediatric patients, I look not just at the angle value itself but also at age, body weight, left-right symmetry of the deformity, and the shape of the growth plate cartilage together.
Plain X-ray is usually sufficient for this assessment, and in rare cases, CT or MRI is added to further check the growth plate status.
This data reflects only the average values provided in the reference material (9 degrees and 19 degrees); for patients in the borderline 9–16 degree range, we explain additional indicators together with them.
Why the Criteria Themselves Differ Between Children and Adults
The biggest difference is that children have "room to wait," while adults do not.
A study tracking severe femoro-tibial deformities in growing children reported that a significant proportion of even severe deformities corrected naturally with growth (Vankka 1982, PMID 7102273).
A randomized trial on flexible flatfoot (pes planus) also found that radiologic indicators improved in both the group using corrective shoes/insoles and the control group, with no difference between the two groups. This means the improvement was due to growth, not treatment.
Based on this evidence, I explain to parents of pediatric patients that common beliefs such as "the legs became bowed because the child started walking too early" or "bow legs must always be corrected to prevent arthritis later" are not accurate. Physiological varus often corrects itself naturally, and only pathological deformity requires treatment.
Conversely, in adults whose growth plates have closed, natural correction can no longer be expected.
In this case, if weight is repeatedly concentrated on the medial side of the knee despite a borderline angle, causing pain and cartilage wear, high tibial osteotomy is considered to shift the mechanical axis of the lower limb slightly lateral to the center line of the knee, reducing medial load (PubMed Central).
For children, observation is the default even with a borderline angle, but for adults, when arthritis is also present, even a borderline angle factors into the decision for surgery.
Our Joint Center's Chief Director, Dr. Young-Gon Na, has researched high tibial osteotomy based on cadaveric experiments, published papers in international journals, and received his doctorate from Seoul National University College of Medicine, and he reviews all difficult outpatient cases together with me.
How Are the Indications for Osteotomy and the Weight-Bearing Recovery Schedule Planned?
Once osteotomy has been decided, the next design point is "how much to correct and when to allow weight-bearing."
One study reported that the osteotomy site united in all patients, and the 3 patients who showed delayed union improved at 6 to 8 months after surgery, with full weight-bearing possible by an average of around 8 weeks (PubMed, PMID 16493168).
However, with the method of opening a gap between the bones and inserting a spacer plate, even partial weight-bearing may be restricted until at least 6 weeks later (PubMed Central).
What must be clearly stated here is that the effect of osteotomy cannot be assumed to be permanent. Knee joint survival rate has been reported at approximately 71% at the 10-year mark (PubMed Central, related data).
Osteotomy is a procedure that slows the progression of arthritis, not one that permanently stops it, so precisely matching the timing of surgery and the correction angle determines the outcome 10 years later.
In fact, there was a case of a patient who had suffered from medial knee arthritis due to bow legs for 7 to 8 years and underwent high tibial osteotomy at our Joint Center. At the 3-month mark after surgery, the patient had almost no pain outside the surgical site and continued recovery management centered on walking and strength exercises. Cases like this serve as grounds for the judgment that, even with a borderline angle, it is better not to delay the timing of surgery if arthritis is progressing concurrently.
Progress indicators summarizing weight-bearing timing after osteotomy and 10-year joint s… · 출처: PMID 16493168; PMC4969364; PMC5906498
A Checklist to Distinguish Cases Safe to Observe From Those That Are Not
Self-checking is possible with the items below, but the final decision must always be made together with imaging studies and an in-person examination.
- Is the patient still at an age when the growth plate is open (child/adolescent)?
- Is the degree of bowing similar in both legs, or is one leg noticeably more severe?
- Is there pain or limping accompanying the gait?
- Has the angle widened over the past 1–2 years?
- Is there pain, swelling, or a sense of instability on the medial side of the knee when bearing weight?
Warning signs are clear left-right asymmetry, deformity that is severe relative to age, or accompanying pain. These cases require differentiation from simple physiological deformity.
Conversely, if a child only has a borderline angle with no pain, asymmetry, or gait abnormality, surgery is not immediately indicated. However, because variables such as permanent growth arrest or rebound after removal of a correction device exist, it is advisable to carry out follow-up observation together with an experienced specialist.
When warning signs are present, we first check the angle and the condition of the growth plate cartilage with X-ray, and only add CT or MRI for further evaluation when necessary.
How Does Seoul One Hospital's Approach Handle Borderline Cases?
The more borderline the angle, the more I believe cross-checking by multiple specialists is needed, rather than a single reading.
Our name "Seoul One" carries the meaning of being the "number one" graduates of Seoul National University College of Medicine, as well as the meaning of a one-stop solution where the whole family can resolve joint and spine problems in one place. Borderline bow-leg cases often need to be examined jointly by the Pediatric Orthopedics Center and the Joint Center, and because our Chief Directors have built trust over many years together as mentors and mentees, seniors and juniors, at Seoul National University Hospital's Department of Orthopedic Surgery, we discuss all difficult outpatient cases together.
For pediatric cases, Chief Directors Dr. Won-Joon Yoo and Dr. Hyuk-Ju Moon of the Pediatric Orthopedics Center review the images together; for cases involving adult arthritis, Chief Director Dr. Young-Gon Na and I review the images together to decide whether and when to correct.
Examinations start with X-ray as the default, moving to CT or MRI only when necessary, in a way that reduces cost and radiation exposure.
When surgery is decided, follow-up of osteotomy site union and adjustment of the weight-bearing schedule are managed with one accompanying caregiver during hospitalization, and since Saturday outpatient hours operate biweekly depending on the physician, we recommend checking the clinic schedule on our website before visiting.
The more borderline the angle, the more misdiagnosis is reduced by having the Chief Directors of Pediatric Orthopedics and the Joint Center confirm it together, rather than relying on a single reading.
| Category | Observation (pediatric physiological deformity) | Osteotomy consideration (adult + arthritis) |
|---|---|---|
| Growth plate | Open | Closed |
| Likelihood of natural correction | High (Vankka 1982) | None |
| Accompanying pain | Usually none | Accompanied by medial knee pain |
| Reassessment interval | Follow-up every 6 months to 1 year | Detailed imaging evaluation before surgery |
Frequently Asked Questions
How often should a borderline angle be re-measured?
For children, X-rays are usually retaken every 6 months to 1 year to track changes in the angle. For adults with accompanying arthritis, checks can be done at shorter intervals depending on changes in pain.
Why aren't children corrected with braces or insoles?
Studies have shown no difference in radiologic improvement between groups using corrective shoes or insoles and those not using them, in cases of flexible deformity. The improvement was due to growth itself, not the effect of treatment.
When is the most appropriate time to undergo osteotomy?
The standard is the point when medial arthritis is progressing and pain recurs due to abnormality of the mechanical axis. Since the joint survival rate has been reported at 71% at 10 years, correcting before arthritis progresses too far is considered advantageous.
Who should be consulted about a borderline angle?
Children should be seen by a pediatric orthopedic specialist, and adult cases with accompanying arthritis should be seen by a Joint Center specialist. Since our structure has the Chief Directors of both fields consulting together, we can gather opinions on borderline cases all at once.
Key Takeaways
- A borderline angle is distinguished by age (growth plate status) and whether arthritis is present.
- In children, a significant proportion of deformities correct naturally with growth, so surgery is not decided based on angle alone.
- In adults, high tibial osteotomy, which reduces medial load through mechanical axis correction, is considered, while explaining the limitation that the 10-year joint survival rate is approximately 71%.
- A single indicator such as MDA has false positive/negative rates exceeding 5% in the 9–16 degree range, so it must be viewed together with other indicators.
- At Seoul One Hospital, the Chief Directors of the Pediatric Orthopedics Center and the Joint Center cross-check borderline cases together.
Dr. Young-Min Lee, a board-certified orthopedic surgeon and Chief Director, completed his orthopedic surgery residency at Seoul National University Hospital and treats joint conditions including corrective surgery for bow legs of the knee joint. Profile
Seoul One Hospital is located at Dongmyeong M Building, 179 Gangseo-ro, Gangseo-gu, Seoul, a 1-minute walk from Exit 8 of Hwagok Station (Seoul Subway Line 5).
Underground parking is available at the rear of the building, and if you are concerned about a borderline angle, please feel free to contact us by phone (1544-5888) or book an appointment through our website.