FDA Clears New Implant for Knee OA

“Shock absorber” implant for those who aren’t ready for a replacement.

By Linda Rath | April 25, 2023

The U.S. Food and Drug Administration (FDA) recently approved the first implantable shock absorber for people with early-stage knee osteoarthritis (OA). The device, called the MISHA Knee System, is intended for patients who have pain despite receiving nonsurgical treatments such as weight loss and physical therapy but aren’t ready for total knee replacement. By reducing one-third of the normal weight-bearing load on the medial (inner) side of the knee, the system relieves stress on the joint. The manufacturer says the device is designed to postpone arthroplasty in some patients, acting as a bridge between conservative treatment and knee replacement, especially for younger, active people. Anil Ranawat, MD, chief of the hip and knee division of the Sports Medicine Institute at Hospital for Special Surgery in New York City, adds that the device “fills a treatment gap for early arthritis in [these] patients.” 

How It Works

The MISHA system looks like a pint-sized version of a car shock absorber. Measuring just three-tenths of an inch by two inches, it has a steel piston on top that slides in and out of a polymer cylinder. Titanium plates attach it to the inner (medial) part of the thigh and shin bones outside the knee joint. When the piston drives down, the cylinder bulges outward, absorbing some of the force that would normally strike the knee. 

A Home Run in Clinical Trials

The nonrandomized clinical trial leading to FDA approval compared the MISHA system with high tibial osteotomy (HTO) — an operation that adds or removes bone to shift weight from the damaged side of the knee joint. The benefits of HTO last eight to 10 years, and the surgery is not considered a permanent stand-in for knee replacement. Dr. Ranawat, one of the study authors, notes that the shock absorber can be temporary or permanent.

In the trial, which took place in 10 centers in the U.S. and Europe, the 81 patients who received the shock absorber device fared better than those who had HTO, with greater improvement in both pain (96% vs. 88%) and function (92% vs. 81%) after two years. There were 15 complications in the implant group compared to 42 complications in the HTO group. Eleven patients had their implant removed due to discomfort, infection or dissatisfaction with the device but still showed improved pain and function after two years, suggesting that even a brief period of joint unloading may help prevent further damage, the study authors wrote. Sixty-one of the 81 patients who underwent HTO had their hardware removed, mainly due to pain.

Unlike HTO, where bone is cut, the implant is placed and anchored to bone through a single small incision. According to Dr. Ranawat, it’s easily removed and doesn’t affect converting to total knee replacement. For most people, it’s an outpatient procedure. The real bonus seems to be reduced recovery time — 13 days to full weight-bearing and a return to normal activities versus two months (58 days) for HTO. 

Dr. Ranawat says the implant is likely to cost as much or slightly less than HTO or partial knee replacement. It will vary depending on where you live and the prices of anesthesia and facility and physician fees. 

Stay in the Know. Live in the Yes.

Get involved with the arthritis community. Tell us a little about yourself and, based on your interests, you’ll receive emails packed with the latest information and resources to live your best life and connect with others.