FDA Clears Shock-Absorbing Implant for Refractory Knee OA

The FDA has authorized marketing of an implantable shock absorber aimed at load reduction for people with refractory knee osteoarthritis (OA) who are not appropriate candidates for arthroplasty, the agency and maker Moximed announced.

Dubbed the MISHA Knee System, the newly cleared device is specifically indicated for patients with medial knee OA whose pain continues to interfere with daily life despite prior treatment, including surgery or non-surgical approaches. "These patients are also unwilling to undergo or are ineligible for total knee replacement due to age or absence of advanced osteoarthritis," the FDA added.

Implanted subcutaneously in the medial extra-capsular space, the device is affixed to the tibia and femur with screws -- a procedure that can be performed in the outpatient setting, according to the company.

Support for the authorization came primarily from CALYPSO, a nonrandomized, open-label prospective trial published in Cartilage earlier this year and detailed at the recent annual meeting of the American Academy of Orthopaedic Surgeons.

In the pivotal study of 81 younger patients (ages 25-65 years) with refractory medial knee OA, more participants achieved meaningful symptom relief at 2 years with the implanted shock absorber when compared with a historical (and propensity matched) control group of 81 individuals who had undergone high tibial osteotomy (86% vs 66%, P=0.01).

"I've been lucky enough to have been exposed to many major orthopedic innovations, most notably total knee arthroplasty (TKA). TKA is a phenomenal operation, but it has its limitations. I still see a clinical void between arthroscopic knee preservation and arthroplasty," investigator Anil Ranawat, MD, of the Hospital for Special Surgery in New York City, said in a statement from the device maker. "This system fills that void for both surgeons and patients."

The primary efficacy endpoint in CALYPSO included meeting all of the following five criteria: responses on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) for pain and function (at least 20% and 10-point improvements for both); no conversion to more invasive treatment such as arthroplasty or another joint-modifying surgery; no deep infections, neurovascular or ligament injuries, or non-union (in the osteotomy group); no implant or hardware breakage.

Additionally, all secondary endpoints showed superiority for the implanted shock absorber at 2 years versus high tibial osteotomy, including WOMAC response for pain (96% vs 88%, respectively) and WOMAC response for function (92% vs 81%).

While high tibial osteotomy is an established surgery for patients with mild to moderate knee pain that hasn't responded to other treatment, recovery can take weeks. In the study, full weight-bearing status was achieved at an average of 13 days with the MISHA system versus 58 days with high tibial osteotomy.

"Millions of people with symptomatic knee OA will now have an opportunity to achieve high levels of pain relief, enjoy the lifestyle and activities that are important to them, and preserve the option for a primary knee arthroplasty in the future," said Ranawat.

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