The MISHA Knee System (the “Knee Spring”): Why I Don’t Use It
The MISHA Knee System is a spring-loaded shock absorber attached to the outside of the knee to take pressure off arthritis on the inner side. Patients researching it are usually looking for something short of a knee replacement. I don’t use it, and here’s why, along with the options I believe do that job better.
Key takeaways
- The MISHA Knee System is a shock absorber screwed to the thigh bone and shin bone on the inner side of the knee, outside the joint.
- It was cleared by the FDA in 2023 for arthritis on the inner side of the knee in people who don’t want, or aren’t ready for, a knee replacement.
- I don’t use it. A part that flexes with every step can wear out, and it doesn’t treat the arthritis.
- Taking pressure off the inner knee is something we already do well, with an osteotomy or a partial knee replacement, both with long track records.
- Many insurers consider the MISHA experimental and won’t pay for it.
Patients who ask me about the MISHA Knee System, the “knee spring,” have usually done their homework. They have arthritis on the inner side of the knee, they’re often younger and active, and they want something that isn’t a knee replacement. That’s a reasonable thing to want. Here is how I think about the device, and why I choose other options.
What the MISHA Knee System is
The MISHA is a shock absorber, a spring-loaded piston, attached with plates and screws to the thigh bone and the shin bone along the inner side of the knee. It sits under the skin, outside the joint. With each step, it takes some of the pressure that would otherwise go through the worn inner half of the knee.
The appeal is easy to see: it doesn’t remove bone or cartilage, and it can be taken out later. The FDA authorized it in April 2023.
Who it’s designed for
It’s meant for arthritis on the inner (medial) side of the knee, in people whose pain continues despite other treatment and who don’t want, or aren’t yet eligible for, a knee replacement, often because of their age or because their arthritis isn’t advanced. In other words, a younger, active patient with arthritis mostly on one side of the knee.
That patient is exactly who I see for a partial knee replacement.
Why I don’t use it
I don’t offer the MISHA, and I haven’t met a patient I would recommend it for. My reasons are simple.
- Springs wear out. Bend a paper clip enough times and it breaks. A knee bends more than a million times a year. Anything that flexes with every one of those steps is working against that.
- It doesn’t treat the arthritis. The worn cartilage is still there. The device only tries to take pressure off it.
- We already know how to take pressure off the inner knee. A knee osteotomy realigns the leg so weight shifts away from the worn side, and it has been done for decades.
- The alternatives have a long track record. Partial and total knee replacements have decades of results behind them, and many last 20 years or more.
- It has already had a recall. In December 2024, the maker recalled certain implants because a part from a supplier could crack, which could mean removing the device.
What I use instead
For arthritis on one side of the knee, a partial knee replacement does the job, and I believe it does it better. It replaces only the worn part of the knee, keeps the healthy parts and your own ligaments, and patients often say it feels more like a natural knee. Recovery is usually quicker than a total knee replacement.
Not every knee is right for a partial. If the arthritis has spread beyond one side, a total knee replacement is the lasting answer. And if you’re not at the point of surgery, the first steps are still therapy, medication, a brace, and injections. For how long modern knees last, see how long a knee replacement lasts.
“Am I too young?”
Many patients look at the knee spring because they’ve been told they’re too young for a replacement. Age alone doesn’t decide it; your X-rays, your symptoms, and what you want to get back to do. See am I too young for a hip or knee replacement?
Insurance and cost
Several large insurers, including Cigna and Anthem, consider the MISHA experimental or investigational, and Medicare has no national coverage decision for it. For many patients, that means paying much or all of it out of pocket. Partial and total knee replacements are covered when they’re medically necessary.
If you’re considering it
If you’re looking into the knee spring, you’re trying to keep your knee and stay active. That’s my goal for you too. The best next step is to have your knee examined and your X-rays reviewed, so we can talk through which option fits your knee and what will last.
I see patients in Washington, D.C. and Germantown, Maryland. Request an appointment.
This article is general education and reflects my professional opinion. It isn’t advice about your specific knee.
Frequently asked questions
What is the MISHA Knee System?
It’s an implanted shock absorber, often called the knee spring. It attaches with plates and screws to the thigh bone and shin bone on the inner side of the knee, under the skin but outside the joint, and takes some of the load off the inner half of the knee with each step.
Is the MISHA Knee System FDA approved?
The FDA authorized it for marketing in April 2023 through its De Novo pathway, for arthritis on the inner side of the knee in patients who haven’t found relief with other treatment and are unwilling or not yet eligible to have a knee replacement.
Was the MISHA Knee System recalled?
In December 2024, the maker recalled certain small-size implants from specific lots because a part from a supplier could develop cracks, which could mean removing the device. The FDA classified it as a Class 2 recall. Ask your surgeon whether it applies to your implant.
Does insurance cover the MISHA Knee System?
Often not. Several large insurers consider it experimental or investigational, and Medicare has no national coverage decision for it. Check with your plan before scheduling. Partial and total knee replacements are covered by insurance when they’re medically necessary.
Is the MISHA better than a partial knee replacement?
In my opinion, no. Both are aimed at arthritis on the inner side of the knee. A partial knee replacement treats the worn surface directly and has decades of results behind it. The MISHA leaves the arthritis in place and relies on a moving part outside the joint.
Can the MISHA be removed?
Yes. Because it sits outside the joint, it can be taken out, and the knee can be converted to a knee replacement later. But removal is a second surgery, and that’s part of why I prefer to choose the lasting option first.
References
This article is for general education and is not a substitute for personalized medical advice. Recovery timelines vary by patient, procedure, medical history, and surgeon-specific protocol. Please consult Matthew Harb, M.D. about your specific condition.
What patients say
“A really smooth operation — I was discharged the same day and basically able to walk easily within a day.”
“I walked into the surgical center in great pain and walked out with a new knee and a renewed person.”
“My full knee replacement is a big success — six months after surgery I’m hiking and kayaking again.”
Keep learning
Partial (Unicompartmental) Knee Replacement
Not every arthritic knee needs the whole joint replaced. When arthritis is confined to just one part of the knee, a partial (unicompartmental) knee replacement resurfaces only that worn compartment and leaves the healthy parts — and your own ligaments — intact. For the right candidate it can mean a smaller operation, a more natural-feeling knee, and often a quicker recovery. The key word is candidate: careful selection is everything.
Read articleKnee ReplacementKnee Osteotomy: A Joint-Preservation Procedure for the Right Patient
A knee osteotomy is a joint-preservation procedure: the surgeon cuts and realigns the bone around the knee to shift weight off an overloaded, worn compartment and onto a healthier one — preserving your own knee instead of replacing it. In the right patient — younger, active, with significant malalignment, single-compartment pain, and otherwise preserved cartilage — it can delay knee replacement for years. But it does not replace damaged cartilage, so for established or multi-compartment arthritis, a knee replacement is usually the more predictable answer.
Read articleHip ReplacementAm I Too Young for a Hip or Knee Replacement?
One of the most common questions I hear is whether someone is too young — or too old — for a hip or knee replacement. The answer surprises many patients: the decision is rarely about age at all. It’s about how much arthritis is affecting your life, your overall health, and whether conservative treatments still help.
Read articleHave questions about your hip or knee?
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