Key Answer
If the effect of long-term injection therapy diminishes and pain occurs even at rest, progressive joint space loss should be suspected.
If a knee that has received injection therapy for over 10 years has suddenly become much more painful over the past few weeks, the first thing to check is not simply worsening inflammation, but whether the cartilage loss stage (KL grade) has progressed further.
If the X-ray shows joint space loss and pain occurs even at rest, this is a stage where injections and braces are difficult to rely on.
At this stage, rather than repeating intra-articular injections further, I discuss with the patient the possibility of transitioning to robotic knee replacement surgery.
Questions This Article Answers
- Why would pain suddenly worsen after more than 10 years of injection therapy?
- What knee X-ray findings suggest knee replacement surgery should be considered?
- How does high tibial osteotomy (corrective osteotomy for bow legs) differ from knee replacement?
- How does Seoul One Hospital perform knee replacement surgery?
- What should be suspected if pain continues after surgery?
This is Dr. Yoon-Jong Choi, board-certified orthopedic surgeon and Director. Even when patients come in saying the same thing — "10 years of knee osteoarthritis" — some still have enough cartilage remaining to continue conservative treatment, while others have already reached a stage where the joint space is nearly gone and knee replacement is needed.
First, I want to acknowledge how much pain you must have endured. For patients who have tolerated pain for a long time, a single X-ray is often enough to clarify the situation.
Why Would Pain Suddenly Worsen After More Than 10 Years of Injection Therapy?
Intra-articular injections (hyaluronic acid, steroids) are a symptomatic treatment that reduces inflammation and relieves pain — they do not reverse worn cartilage.
According to the National Health Insurance Service's reassessment of intra-articular injection therapy, non-surgical injection therapy is treated in staged guidelines as a supplementary measure for early-to-mid-stage osteoarthritis.
Having relied on injections for 10 years also means cartilage has been gradually wearing away over that time. If pain has suddenly worsened recently, this may indicate progression to the stage where cartilage is completely worn away and bone directly contacts bone (KL grade 4).
At this stage, even if inflammation is reduced, the friction pain from bone-on-bone contact itself does not decrease.
If the effect of injections lasts shorter than before and pain is felt even at rest, this may be a sign that joint space loss has progressed — not simply a matter of injection dosage.
That is why, at Seoul One Hospital, when a patient reports that the nature of their pain has changed, we begin by reassessing joint space and cartilage condition with updated X-rays and, if needed, MRI.
| Stage | X-ray Findings | Representative Treatment |
|---|---|---|
| Grade 1 | Normal joint space, minor osteophytes | Exercise, weight management |
| Grade 2 | Clear osteophytes, pain after activity | Exercise, medication, early regenerative treatment |
| Grade 3 | Clearly reduced joint space, pain while walking | Intra-articular injections, braces; HTO if young |
| Grade 4 | Joint space loss, pain at rest | Knee replacement if conservative treatment fails |
caption: X-ray findings and representative treatment by KL grade stage
How to Choose Between Knee Replacement and High Tibial Osteotomy
For patients whose cartilage damage is confined to one side of the joint (medial compartment), who are relatively young and active, high tibial osteotomy (HTO, corrective osteotomy for bow legs), which preserves the patient's own joint, is also an option.
Conversely, for patients with extensive damage across the entire joint or who are elderly, total knee arthroplasty (TKA) is the more reasonable choice.
There have been cases where even the same meniscus root tear led to different treatment paths. A 56-year-old male patient with bowleg deformity underwent arthroscopic repair combined with high tibial osteotomy, while a 49-year-old female patient with neutral leg alignment had a good outcome with repair and cartilage regeneration treatment alone.
These cases show that even with the same type of injury, leg alignment and the extent of osteoarthritis progression determine the surgical approach.
In the case of a 48-year-old female patient, age alone might have suggested knee replacement as the first option, but she had a good outcome undergoing high tibial osteotomy combined with stem-cell cartilage regeneration (Cartistem), performed on each leg separately 3-4 months apart.
The clinical lesson from this case is that with good patient selection and appropriate rehabilitation, joint-preserving surgery can also lead to good outcomes.
My criterion is to recommend high tibial osteotomy for patients whose leg deformity is confined to one side (medial) and whose osteoarthritis is early-to-mid stage (KL grade 2 or below), and robot-assisted total knee arthroplasty for patients with more extensive overall joint damage.
| Category | HTO | TKA |
|---|---|---|
| Indicated Age | Active patients in 50s-60s | 65 and older |
| Extent of Damage | Medial compartment only, early stage (KL≤2) | Extensive, KL3-4 |
| Joint Preservation | Preserves own joint | Replaces joint surface |
| Recovery | About 6 weeks with brace after crutch walking | About 3 months without crutches |
caption: Comparison of indications and recovery between high tibial osteotomy and knee replacement
What Does Robotic Knee Replacement Make More Precise?
The core of robotic knee replacement surgery lies in pre-surgical planning and bone-cutting precision. While conventional surgery relies on the surgeon's experience and visual judgment, robotic surgery uses a CT-based 3D knee model for pre-surgical planning and provides real-time 3D imaging during surgery to confirm conditions.
I use the ROSA robotic system to establish a pre-surgical plan based on CT data, then perform bone resection within a 1mm margin of error using the robotic arm, adjusting ligament balance in real time throughout the procedure.
In knees with severe bone deformity, accuracy can decrease with conventional surgical methods, but the robot can predict the deformity angle and maintain correction accuracy — this is the key difference.
Asan Medical Center's guide to total knee arthroplasty also describes knee replacement as a surgery that replaces a damaged joint surface with an artificial implant.
The reason I choose robotic surgery is not the robot itself, but the fact that the implant used with it (PERSONA) offers narrow options and asymmetric left-right tibial components tailored to bone size, allowing a closer fit to the cut surface and easier rotational alignment.
I also take into account related research noting that systematic reviews have not yet confirmed that ceramic-coated implants have superior survival rates compared to standard implants.
That is why, at Seoul One Hospital, our dedicated knee team selects from 48 femoral component sizes, 16 polyethylene insert sizes, and 18 tibial component sizes to match each patient's joint shape when performing knee replacement surgery.
Limitations and Precautions
Knee replacement surgery is not the answer to all knee pain. I recommend checking the following first.
- ✓ Have you confirmed how much the joint space has narrowed on a recent X-ray?
- ✓ Do you have pain at rest at night, or only after activity?
- ✓ Has the duration of injection therapy's effectiveness become shorter than before?
- ✓ Is your leg developing a bowleg or knock-knee deformity?
- ✓ Has your ability to climb stairs or walking distance noticeably decreased?
If persistent pain, redness, or discharge appears at the surgical site, this is more likely a sign of suspected infection rather than a problem with the surgery itself, and requires immediate medical attention.
I once treated a 72-year-old female patient, two years after her knee replacement surgery, who developed gastroenteritis after eating raw oysters and came to the hospital a few days later with sudden knee swelling. Joint aspiration yielded 40cc of pus, and her white blood cell count was significantly elevated. A stool test done in consultation with internal medicine confirmed norovirus and rotavirus infection, and we determined that intestinal bacteria had spread to the joint through the bloodstream.
Because symptoms had only been present for a relatively short 2-3 days, we performed only a single-stage surgery with polyethylene insert exchange and debridement, instead of removing the entire implant. This case showed that a sudden worsening of pain is not always due to worsening of the arthritis itself.
Knee replacement surgery can be performed even in patients under age 50, but according to related research, implant survival rates are reported at 97% under 5 years, 95% between 5-10 years, and 87% beyond 10 years, so the possibility of revision surgery should be considered together for younger patients.
When warning signs (fever, swelling, discharge) are identified, I first perform joint aspiration and blood tests to rule out infection.
Graph showing changes in implant survival rate according to time elapsed since surgery · 출처: PMID 40840656
How Seoul One Hospital Approaches Knee Replacement Surgery
I treat knee joint replacement surgery alongside upper extremity conditions as part of my practice, and the knee joint field is managed jointly with the dedicated medical staff of our Joint Center.
Seoul One Hospital's Joint Center introduced the ROSA robotic system in May 2024 and reached 200 cases as of August 2026, with a cumulative total of 2,587 knee replacement surgeries performed.
Chief Director Dr. Young-Gon Na, who describes personally performing a double-check at every critical stage of robotic surgery, leads the dedicated knee team that selects implant sizes tailored to each patient's joint shape.
Pre-surgical evaluation includes multi-channel low-dose CT, X-ray, and ultrasound, and after surgery, joint range-of-motion recovery begins from day 1-2 in the inpatient ward using a continuous passive motion (CPM) device.
Inpatient meals are provided at 7 AM, 12 PM, and 5 PM, and the rehabilitation center has 9 physiotherapists handling manual therapy and exercise therapy.
Regarding cost, I generally explain that there is little difference between hospitals for insurance-covered items, and that differences arise mainly from non-covered materials and treatment items.
Before surgery, we assess joint space and degree of deformity with X-ray and CT, and design robot-assisted total knee arthroplasty for patients who have already reached the limits of conservative treatment.
For patients aged 60 or older who meet certain conditions, such as medical aid recipients, near-poverty status, or basic livelihood security recipients, we participate in the Elderly Medical Care Sharing Foundation's knee replacement surgery cost support program (1.2 million KRW for one knee, 2.4 million KRW for both), which can be applied for at the local community welfare center.
Frequently Asked Questions
How is the timing for knee replacement surgery determined?
We look at both whether joint space loss is present on X-ray and whether pain occurs at rest. If you have been managing with injections and physiotherapy but the duration of their effectiveness has shortened and pain occurs even at night, this is considered a sign that surgery timing may be approaching.
Why do some patients need surgery sooner than others, even with the same 10-year history of arthritis?
This is because the rate of cartilage loss, leg alignment (presence of bowleg deformity), and activity level differ from person to person. If damage is confined to the medial compartment alone, joint preservation is possible with high tibial osteotomy, but if damage is widespread, knee replacement is more appropriate.
How long does pain last after knee replacement surgery?
We generally explain that it takes about 3 months to be able to walk without crutches. The process of recovering range of motion through CPM exercise immediately after surgery is key to pain management.
Who is a good candidate for knee replacement surgery?
Candidates include those with severely worn cartilage causing difficulty walking and significant pain, those with severe leg deformity, and those with significant limitations in daily life due to reduced walking function. Conversely, for young, active patients with damage confined to one side (medial compartment) only, joint-preserving surgery is considered first.
Key Takeaways
- If the effect of injection therapy shortens and pain occurs at rest, progressive joint space loss should be suspected
- Medial compartment-only damage in younger patients points toward high tibial osteotomy, while extensive damage points toward total knee arthroplasty
- Redness, discharge, or fever at the surgical site are signs of infection requiring immediate medical attention
- Robot-assisted surgery is characterized by CT-based pre-surgical planning and 1mm-level bone resection precision
- As of 2026, Seoul One Hospital designs care from surgery through recovery using the ROSA robotic system and CPM rehabilitation equipment
About the Medical Staff
Dr. Yoon-Jong Choi, board-certified orthopedic surgeon, completed his orthopedic surgery residency at Severance Hospital, Yonsei University, and worked as a shoulder and elbow fellow in the Department of Orthopedic Surgery at Ewha Womans University Seoul Hospital. View Profile
Hospital Information
Seoul One Hospital is located on floors 6-10 of the Dongmyeong M Building, 179 Gangseo-ro, Gangseo-gu, Seoul, a 1-minute walk from Exit 8 of Hwagok Station (Seoul Subway Line 5).
If driving, parking is available in the underground parking lot (basement levels 1-2) at the rear of the building. For inquiries, please call the main line at 1544-5888.
If your knee pain has suddenly worsened, we recommend starting with a new X-ray to reassess your condition.