Do Medial and Lateral Knee Osteoarthritis Change the Aim of Stem Cell Conditioned Media Knee Injection? Dr. Moriwaki Organizes Treatment Design from the Load Imbalance Shown by Varus and Valgus Knees2026.07.19

Knee osteoarthritis tends to be discussed as a single entity, but in reality it splits broadly into a “medial type” — where the inside of the knee hurts under a varus (O-shaped leg) tendency — and a “lateral type” — where the outside of the knee hurts under a valgus (X-shaped leg) tendency. Even under the same diagnosis of knee osteoarthritis, when the way load is distributed differs, so does the main source of inflammation and the part of the joint that is most damaged. Designing where and how to deliver a knee joint injection of stem cell conditioned media must therefore start by distinguishing medial from lateral type.

Key Points of This Article

・Knee osteoarthritis splits into “medial type (varus tendency)” and “lateral type (valgus tendency)”, with different load imbalance and different sites of pain and damage

・Even at the same KL grade, the target of knee joint injection and the combined therapies differ between medial and lateral types

・Intra-articular delivery of stem cell conditioned media addresses the overall inflammatory environment, while peri-articular delivery targets localized bursal or entheseal inflammation

・Reduce the load imbalance itself with braces, insoles and exercise therapy before evaluating the effect of the injection

・When severe varus/valgus deformity, joint instability, or signs of infection are present, orthopedic evaluation takes priority over injection

Why Do Medial and Lateral Types Diverge?

Among Japanese patients, knee osteoarthritis is predominantly the medial type. This originates from the fact that the load axis (lower-limb alignment) passes slightly medial to the center of the knee, so load is structurally concentrated on the medial cartilage. As varus (O-leg) progresses, the contact area between the medial femoral condyle and medial tibial plateau narrows each time weight is borne, and cartilage wear, synovial inflammation and osteophyte formation advance on the medial side. Complaints such as medial knee pain on initial gait or when descending stairs, and medial tightness when kneeling, are typical.

The lateral type, on the other hand, is more common in patients with valgus (X-leg) tendency, and it is not unusual for a history of rheumatoid arthritis, inflammatory joint disease, post-traumatic deformity, or old sports injuries to lie in the background. Load concentrates on the lateral femoral condyle and lateral tibial plateau, and this can be accompanied by degeneration of the lateral meniscus, tension around the lateral collateral ligament, and friction of the distal iliotibial band. Lateral knee pain and a sense of the knee giving way outward on stairs or slopes are signs that suggest the lateral type.

Confirm the “Type” with Imaging and Examination

On a frontal X-ray, we check the femorotibial angle (FTA) and which side shows greater joint-space narrowing, and — when needed — evaluate load-bearing alignment with standing and full-length lower-limb radiographs. On palpation, we assess the involvement of the meniscus and collateral ligaments through the tender site (medial or lateral joint line), range-of-motion limitation, varus/valgus stress tests, and the McMurray sign. MRI is useful for confirming synovitis, bone-marrow edema, and meniscal extrusion. Rather than judging by the visual appearance of O- or X-legs alone, it is essential to evaluate the type objectively by combining imaging and clinical examination.

Does the Aim of Knee Joint Injection Change with the Type of Knee Osteoarthritis?

Knee joint injection of stem cell conditioned media broadly falls into two approaches: “intra-articular injection” and “peri-articular injection.” Which of these to make the central axis depends on whether the case is medial or lateral, and on whether the source of pain is primarily intra-articular synovitis or peri-articular entheseal/bursal inflammation.

Injection Design for the Medial Type

In medial-type knee osteoarthritis with strong intra-articular synovitis, stem cell conditioned media is delivered intra-articularly, with the expectation that cytokines and growth factors related to anti-inflammatory and tissue-repair processes act on the inflammatory cycle. However, in the medial type, pes anserine bursitis (enthesitis of the sartorius, gracilis, and semitendinosus) and tension of the medial collateral ligament often contribute to the pain; in those cases we combine peri-articular injection as well. When intra-articular injection alone does not adequately relieve medial pain, we must suspect the scenario in which the real source of pain lay outside the joint.

Injection Design for the Lateral Type

In the lateral type, in addition to inflammation of the lateral compartment inside the joint, the load on the distal iliotibial band (a condition adjacent to runner’s knee) and around the lateral collateral ligament often adds up, making it realistic to combine peri-articular injection with intra-articular injection. In patients with strong valgus, lateral deviation of the patellofemoral joint (front of the knee) may coexist, so pain on the anterior or upper-lateral aspect of the knee can be mixed in, and care is required in differential diagnosis and selection of injection sites.

Only Meaningful When Combined with Bracing and Exercise Therapy

For either type, the idea that injection alone will suppress pain over the long term is not realistic. By running in parallel efforts to reduce the load imbalance itself, we create room to prolong the inflammation-lowering effect obtained from knee joint injection of stem cell conditioned media.

For the medial type, options such as a lateral-wedge insole, a soft knee brace that distributes varus load, exercises to strengthen the hip abductors (gluteus medius), and stretching of the adductors come up. For the lateral type, candidates include a medial-wedge insole in the opposite direction, a brace to suppress valgus, strengthening of the vastus medialis obliquus (VMO), and exercises to control hip internal rotation and adduction. Weight management is a common important factor for both, and because impact on the knee during walking reaches several times body weight, even a small weight loss contributes to reducing joint load.

Do Not Judge Effect by “Pain” Alone

The effect after injection is evaluated comprehensively — not just by pain scores (VAS/NRS), but also by range of motion, activities of daily living (stair climbing, kneeling, walking distance), the course of swelling and warmth, and, when needed, changes in imaging findings. A guide for effect assessment is 4–8 weeks after injection; when response is poor we move on to re-examining injection site, dose, combined therapies, and even the diagnosis itself. Information from the Japanese Orthopaedic Association is also useful for deepening overall understanding of knee osteoarthritis.

Factors That the “Type” Alone Cannot Decide, and Situations Unsuited for Injection

In reality, the knee does not divide neatly into either the medial or lateral type. Age, the course of trauma, sports history, body build, alignment of adjacent joints (hip and ankle), and even spinal posture — the whole-body linkage — largely determine the picture, and there are diverse patterns such as cases with lesions on both medial and lateral sides, cases dominated by patellofemoral osteoarthritis, or cases progressing rapidly due to meniscal extrusion.

In joints with active infection, uncontrolled systemic disease, near-end-stage joint destruction, or strong joint instability, orthopedic evaluation and consideration of surgical indication take priority over knee joint injection of stem cell conditioned media. Joint injection is not a universal treatment; it is a meaningful option only when indication is narrowed down after proper diagnosis. For related information on treatment options, please also refer to our page on joint injection with stem cell conditioned media.

Frequently Asked Questions

Q. I don’t even know whether I have O-legs or X-legs — can medial vs lateral type still be identified?

By combining a standing frontal X-ray with palpation, range-of-motion evaluation, and — when necessary — full-length lower-limb radiographs, we can objectively assess the tilt of the load axis and which side shows greater joint-space narrowing. The visual appearance of O- or X-legs does not necessarily match the actual load distribution inside the joint, so judgment is made through both imaging and examination.

Q. Do the number and volume of stem cell conditioned media knee joint injections change between medial and lateral types?

The basic dosing protocol does not change dramatically, but whether peri-articular injection is combined, the design of bracing and exercise therapy, and the timing of effect assessment are adjusted according to type and pathology. Rather than a simple “the type is different so the number of sessions increases,” the concept is to individually design a combination that fits the source of pain.

Q. I have been continuing hyaluronic acid injections for medial-type knee pain. Should I switch to conditioned media?

If symptoms are stable on hyaluronic acid and there is no interference with daily life, there is no need to force a switch. When signs such as a plateau in effect, shortening injection intervals, or repeated joint effusion appear, it becomes realistic to consider a different approach — knee joint injection of stem cell conditioned media.

Q. In lateral type, I have mixed pain on the lateral knee and the distal iliotibial band. Do you inject both?

When intra-articular inflammatory findings and peri-articular tenderness of the attachment site and distal iliotibial band coexist, combined intra-articular and peri-articular injection becomes a candidate for consideration. However, we first assess which is the main source of pain from examination, imaging, and response to analgesics, and design an order so as not to naively chase two rabbits.

Q. Even in advanced medial-type cases with quite strong varus, can we hold out with knee joint injection of stem cell conditioned media?

In cases close to end-stage KL grade IV, with instability that cannot withstand valgus stress, or with severe deformity pain and difficulty walking in daily life, there is a limit to “holding out” with injection, and consideration of surgical indication such as total knee arthroplasty takes priority. Judgment on whether to persist with injection or to steer toward surgery is made by combining the degree of deformity, the extent of interference in daily life, and general condition.

──────────────

【Medical Supervisor】Shin Moriwaki (Supervising Physician)

Member, Japan Society of Aesthetic Surgery (JSAS) / Member, American Academy of Aesthetic Medicine

ECFMG Certificate (U.S. Medical Licensing Qualification)

──────────────

📍AVAN TOKYO Ginza Regenerative Medicine

AVAN TOKYO Ginza Regenerative Medicine

English / 中文 / Tiếng Việt available

Inquiries welcome via DM / LINE / Website / Phone.