For Patients Who Can No Longer Sit in Seiza or Squat Due to Knee Osteoarthritis — Dr. Moriwaki Explains Deep Knee Flexion Load on the Posterior Meniscus and Patellofemoral Joint, and the Line Between What Stem Cell Conditioned Media Knee Injection Can and Cannot Restore2026.08.02
“The seiza posture and squatting motions that were once effortless have gradually become painful for my knees.” This is a story we hear frequently from middle-aged and older patients. Sitting on tatami mats, standing up from the floor, squatting in the garden, using a Japanese-style squat toilet — deep knee flexion motions occur far more often in daily life than most people realize, and losing the ability to perform them significantly diminishes quality of life. Behind these complaints lies the concept of deep knee flexion load. At flexion angles beyond 130 degrees, cartilage, menisci, and the patellofemoral joint experience unique mechanical stresses that do not occur at shallower angles. As knee osteoarthritis progresses, the joint can no longer tolerate this load, and in many cases patients first lose the ability to perform deep flexion before walking or climbing stairs becomes problematic. In this article, we organize — from a supervising physician’s perspective — the background of why seiza and squatting become painful, and the line between what a stem cell conditioned media knee injection can and cannot restore, particularly around whether “controlling pain” translates into “restoring deep flexion.”
Key Points of This Article
・Deep knee flexion load refers to the mechanical stress that concentrates on the posterior meniscal horn, posterior cartilage, and patellofemoral joint during seiza and squatting motions that exceed 130 degrees of knee flexion
・In knee osteoarthritis, a common mid-stage pattern is for patients to lose the ability to perform seiza and deep squats before stair climbing or walking becomes difficult
・Stem cell conditioned media knee injections may help modulate the intra-articular inflammatory environment, but they are not treatments that reverse joint deformity, meniscal defects, or osteophyte formation
・Even if pain diminishes, repeatedly forcing deep flexion in an already deformed knee can accelerate the wear of remaining cartilage and menisci
・Whether to “restore deep flexion” or to “protect the joint’s lifespan by converting daily activities to Western-style” is a decision to be made with a physician based on the degree of deformity, age, and lifestyle background
What Is Deep Knee Flexion Load — What Happens Inside the Joint During Seiza and Squatting
The area of the knee that bears load changes dramatically with the flexion angle. Level walking is completed within 0–60 degrees of knee flexion, and stair climbing within roughly 0–90 degrees. In contrast, seiza requires 140–150 degrees, and squatting for a Japanese-style toilet requires 130–140 degrees — postures that regularly use the extreme end of knee range of motion. The mechanical stress unique to this range is what we refer to here as deep knee flexion load.
Compressive Stress on the Posterior Meniscal Horn and Posterior Cartilage
During deep flexion, the posterior aspect of the femoral condyle is pressed firmly against the tibial articular surface. The structures that bear the greatest load here are the posterior femoral cartilage and the posterior horn of the medial meniscus. Biomechanical studies have repeatedly shown that contact pressure on the posterior meniscal horn rises sharply beyond about 120 degrees of knee flexion. For a meniscus that has lost elasticity through aging or degeneration, deep flexion is quite literally the “peak posture for damage.” This mechanical relationship also helps explain why medial meniscal posterior root injuries — common in women in their 40s and 50s — often begin with the episode of “a snap sound while squatting.”
Large Compressive Forces on the Patellofemoral Joint
Another factor that cannot be overlooked during deep flexion is the compressive force on the patellofemoral joint (the space between the kneecap and the femur). The deeper the knee bends, the more the quadriceps tension presses the patella against the femur. At 30 degrees of flexion this force is approximately 1–2 times body weight, at 90 degrees roughly 3–4 times, and in deep flexion beyond 130 degrees it has been reported to reach 6–8 times body weight. In a knee with osteoarthritis that also involves patellofemoral joint disease, this mechanical load appears clearly as “pain around the kneecap” or “anterior pain when rising from seiza.”
The Typical Course of “Deep Flexion Becoming Difficult First” in Knee Osteoarthritis
In clinical practice, we frequently encounter mid-stage knee osteoarthritis patients who can still manage stairs and walking, but have lost only the ability to perform seiza and deep squats. This reflects a state in which the posterior cartilage, posterior meniscal horn, and patellofemoral joint — loaded only during deep flexion — have already degenerated, while the anterior to central joint surfaces used at shallower angles remain relatively preserved. Deep knee flexion load first manifests in daily activities. This is also a relatively early sign of progressing knee osteoarthritis.
How Stem Cell Conditioned Media Knee Injection May Relate to Deep Knee Flexion Load
From here, we organize how stem cell conditioned media knee injections may relate to the problem of deep knee flexion load, and what they can and cannot achieve, from both the perspective of expectation and limitation.
Room for Pain Reduction Through Modulating the Intra-Articular Inflammatory Environment
Stem cell conditioned media is thought to contain growth factors secreted by mesenchymal stem cells (such as TGF-β, IGF-1, and HGF), anti-inflammatory cytokines, and miRNA carried within exosomes. These components are considered to potentially participate in suppressing chronic synovial inflammation and chondrocyte apoptosis, potentially acting to lower the “baseline inflammation” within the joint. When pain during deep flexion in a knee osteoarthritis patient arises as a synergy of chronic synovitis and contact pressure, there is indeed a clinical impression that calming the inflammation can reduce pain experienced during deep flexion.
The Line That This Is Not an Injection That “Restores” Deformity Itself or Meniscal Loss
On the other hand, a stem cell conditioned media knee injection is not a treatment that fully regenerates worn cartilage, reverses deformed bone morphology, or reattaches torn menisci. This distinction is extremely important. When symptoms of painful deep flexion are underpinned by structural changes such as joint deformity, posterior meniscal horn tears, or patellofemoral osteophyte formation, there is no guarantee that even successful inflammation control will return the patient to “performing deep flexion effortlessly as before.” Effects vary between individuals, and one must sincerely confront the gap between expectation and reality.
The Concern That “Forced Deep Flexion” After Pain Relief Can Accelerate Joint Destruction
One further point of caution: after pain has been reduced by injection, patients sometimes return to repeating seiza and deep squats as they did before. Even if intra-articular inflammation is suppressed, the mechanical load itself during deep flexion does not change. Repeating deep knee flexion load in an already deformed joint can accelerate the wear of remaining cartilage and menisci. Patients must clearly understand that “pain has gone away” does not equal “it is now safe to overuse the knee.” For details on indications and treatment design of stem cell conditioned media knee injection, please also refer to this page for more on joint injections with stem cell conditioned media.
Continue Seiza and Squatting, or Change Daily Habits — A Practical Framework for Deep Knee Flexion Load
How to face deep knee flexion load requires individualized judgment based on the degree of joint deformity, age, and lifestyle background. The following are frameworks we use in daily practice.
When Deformity Is Mild to Moderate and Deep Flexion Is Infrequent
For knees classified as Kellgren-Lawrence grade 1–2 on X-ray, and where seiza or squatting occurs only a few times per week rather than daily, there is room to maintain deep flexion within reasonable limits while combining stem cell conditioned media knee injection with quadriceps strengthening. However, if the knee swells or aches the day after deep flexion, this should be received as a signal that the joint is asking to “please stop deep flexion now.”
When Deformity Is Advanced and Deep Flexion Is Embedded in Daily Life
For knees at KL grade 3–4 in patients whose lives revolve around Japanese-style toilets, tatami living, or occupations that involve daily squatting (carpenters, farmers, childcare workers, and others), injection alone is insufficient to absorb deep knee flexion load. In such cases, environmental adjustments — converting to Western-style toilets, shifting to chair sitting, introducing tools that eliminate the need to squat — become as important as, or more important than, the injection treatment itself. For further information on joint diseases, please also refer to the Japanese Orthopaedic Association‘s reference pages.
“Giving Up Deep Flexion” Is Not a Defeat but an Active Choice
Many people feel reluctant to give up seiza or squatting. However, giving up deep flexion is a proactive choice that protects remaining cartilage and menisci and extends the lifespan of the joint. Shifting to Western-style habits, using shower chairs, and adopting kneeling pads for gardening — the accumulation of such small adjustments can dramatically change the state of the knee ten years down the road. Stem cell conditioned media knee injection functions as part of a comprehensive approach to deep knee flexion load only when combined with such lifestyle adjustments and exercise therapy.
Frequently Asked Questions
Q. If I receive a stem cell conditioned media knee injection, will I be able to perform seiza again?
There are indeed patients whose pain during deep flexion decreases as intra-articular inflammation is controlled. However, in a knee where structural changes from osteoarthritis have progressed, the injection does not guarantee that “seiza can be performed effortlessly as before.” Pain improvement and complete recovery of deep flexion motion should be considered separately. Effects vary between individuals, and it is important to share realistic goals with your physician in advance.
Q. If only seiza is painful and walking is fine, is treatment still necessary?
The stage where only deep flexion is painful often corresponds to mid-stage knee osteoarthritis, and beginning interventions at this point — quadriceps strengthening, weight management, and modulating the intra-articular inflammatory environment — carries meaningful value. There is no need to wait until walking becomes painful. Please consult a physician after evaluating the joint’s condition through X-rays and physical examination.
Q. After a stem cell conditioned media injection, when can I resume seiza and squatting motions?
Because the intra-articular state is prone to fluctuation for several days immediately after injection, deep flexion is typically avoided during that period. Timing and frequency of resumption thereafter are judged individually according to the degree of joint deformity. Please do not self-judge that “the pain is gone, so it’s fine,” but follow the guidance of your attending physician.
Q. Changing my lifestyle to avoid deep flexion feels excessive. Is it really necessary?
Deep flexion is reported to place a compressive force of 6–8 times body weight on the patellofemoral joint. If this load is repeated in an already deformed joint, it can accelerate the wear of remaining cartilage and menisci. Shifting daily habits to Western style is not excessive — it is reasonable to view it as part of an active treatment that extends the lifespan of the knee.
Q. Is a stem cell conditioned media knee injection alone sufficient, without any other treatment?
No — the injection is one part of the overall treatment. Only when combined with exercise therapy centered on the quadriceps, weight management, lifestyle adjustments that avoid deep flexion, and orthotic or cane use as needed, does it function as comprehensive conservative therapy for knee osteoarthritis. Please move away from the assumption that injection alone can resolve everything.
──────────────
Medical Supervisor: Shin Moriwaki, MD (Supervising Physician)
Member, Japan Society of Aesthetic Surgery (JSAS) / Member, American Academy of Aesthetic Medicine
ECFMG Certificate (US Medical Licensing Qualification)
──────────────
📍AVAN TOKYO Ginza Regenerative Medicine
AVAN TOKYO Ginza Regenerative Medicine
Available in English / 中文 / Tiếng Việt
Inquiries welcome via DM / LINE / Website / Phone.