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HSS Researchers Lead Trial on New Surgical Option for Knee Osteoarthritis

Researchers at Hospital for Special Surgery in New York City are leading a pivotal clinical trial on a new investigational surgical treatment for osteoarthritis (OA) of the knee that is designed to offer improved mobility and reduced pain without the need for replacement of the joint. 

The multicenter Calypso Study will assess the safety and effectiveness of Moximed’s implantable shock absorber for the knee.  Moximed is a medical device manufacturer based in Fremont, California and is the sponsor of the study.   

The trial will enroll 80 men and women with medial knee OA, a painful, debilitating condition in which the cartilage barrier separating the ends of the femur and tibia deteriorates, allowing the two bones to rub against each other. Medial knee osteoarthritis can result from a variety of factors, including advanced age, the loss of estrogen after menopause for women, wear-and-tear from physical activity or obesity, and previous trauma to the joint, such as a torn ligament or meniscus. According to the CDC, an estimated 1 in 4 Americans suffer from some form of OA, and half are under the age of 65. 

Knee replacement surgery is an option for patients with medial knee osteoarthritis, but the procedure is relatively invasive and requires protracted recovery and rehabilitation. As a result, many patients opt for conservative care, which can entail the use of analgesics for pain, physical therapy and special insoles for shoes to help rebalance the affected joint—none of which prevent arthritis from progressing. 

"Many patients were injured when they were young, for example with anterior cruciate ligament (ACL) and meniscal tears, and these unfortunately lead to osteoarthritis in approximately 50% of them by 10 years after injury," said Andreas Gomoll, MD, sports medicine surgeon at HSS. "Since the original injury happens when patients are in their teens or 20s, they might have established osteoarthritis in their 30s and 40s, when knee replacement is not a great option since it has a high likelihood of wearing out during their lifetime and will have to be revised. Not surprisingly, doing a revision replacement is not as good as a primary replacement, and therefore we are looking for ways to delay these types of more invasive procedures for as long as possible. For some, conservative care helps, but not for everyone. That's where a device like the Calypso could fit in. If patients can buy years of improved pain and function, then knee replacement surgery can start later, requiring fewer possible revisions in the patient's lifetime. This device design is all about preserving options, since it can be removed with little-to-no permanent changes to the knee joint structure. Therefore, patients remain candidates for any other potential treatments that might be developed in the future."

The Calypso Study investigational device consists of a cylindrical shock absorber that is implanted along the side of the knee and reduces the amount of weight supported by the knee. 

"Nobody can wear a brace all the time for any length of time, and that's the advantage of an implantable device like Calypso," Dr. Gomoll said. "There is no other device like it and it offers a new approach for these patients."

"We are constantly pushing the biological envelope to preserve joints as long as we can," said Anil Ranawat, MD, sports medicine and knee joint preservation surgeon at HSS. "When a patient is young and has OA, it’s hard to know what the best procedure is. Injection therapy can relieve pain, but treatment benefit is only short term. More invasive surgical procedures, though effective in treating osteoarthritis, can inhibit treatment options down the road for young, active patients. The Calypso implant’s unique design maintains the anatomical structure of the knee while also treating the primary pain generator of OA. Our ultimate goal is to preserve motion and function in our patients."

The implantation surgery takes approximately one hour and can be performed on an outpatient basis, meaning patients can go home the same day. Rehabilitation is easier than for other knee surgeries, Dr. Gomoll noted.

The study will measure improvement over 24 months in pain and function based on a validated measure called the Western Ontario and McMasters University Osteoarthritis Index (WOMAC). The researchers also will track device safety and monitor the integrity of the implant over time using x-ray imaging. 

To participate in the study, patients must be between the ages of 25 and 65 and have had osteoarthritis pain on the inner side of the knee that has persisted for at least six months after trying non-surgical treatments. 

Patients are not eligible for the study if they have osteoarthritis in both sides of the same knee; if they have problems with the ligaments in their affected joint; if they have known allergies to certain metals; if they have been diagnosed with conditions that afflict the skeleton, such as rheumatoid arthritis and Paget’s disease; among other considerations.   

Two sports medicine surgeons at HSS are participating in the study: Andreas Gomoll, MD, and Anil Ranawat, MD.  

For more information about the trial, visit: www.calypsokneestudy.com.