Implantable Knee Shock Absorber: 2-Year Outcomes

Led by Ohio State’s David Flanigan, M.D., a team of researchers from 10 centers have published 2-year outcome data for a novel, implantable shock absorber for patients with mild to moderate medial knee osteoarthritis.

The 10-center prospective study, “Implantable Shock Absorber Provides Superior Pain Relief and Functional Improvement Compared With High Tibial Osteotomy in Patients with Mild-to-Moderate Medial Knee Osteoarthritis: A 2-Year Report,” appears in the February 23, 2023 edition of Cartilage.

The study was designed by the research group to test an implantable shock absorber using a high tibial osteotomy as a control. “High tibial osteotomy is a well-accepted procedure with decades of clinical history,” explained co-author David Flanigan, M.D. an orthopedic surgeon with the Ohio State University in Columbus, Ohio. “Like the implantable shock absorber, high tibial osteotomy provides pain relief by unloading the diseased portion of the knee. It’s less common in the United States because it is a big operation with a long recovery period that can be intimidating to both patients and surgeons.”

For this study, the researchers looked at patients younger than 65 with symptomatic mild-to-moderate medial knee osteoarthritis (OA). There were 81 patients who received an implantable shock absorber (average age: 51.2 years); an equal number of patients were treated with high tibial osteotomy (average age: 52.5 years).

The team set a several study primary endpoints:

• pain,
• function,
• adverse events,
• implant or hardware integrity
• and conversion to subsequent surgery.

At the 2-year mark, patients who received the implantable shock absorbers “won the day” with 85.6% of them meeting all primary endpoint criteria compared with 65.5% of those undergoing high tibial osteotomy.

The research team set secondary endpoints as:

• Days to full weightbearing,
• Western Ontario and McMaster Universities Arthritis Index pain at 3 and 24 months,
• Western Ontario and McMaster Universities Arthritis Index function at 3 and 24 months.

Again, the research teams found evidence that the implantable shock absorber was superior to a high tibial osteotomy in terms of the secondary endpoints.

At 24 months, the proportions of subjects considered responders were 95.8% (implantable shock absorber) versus 87.9% (high tibial osteotomy) for pain and 91.7% (implantable shock absorber) versus 81.3% (high tibial osteotomy) for function. Patients in the implantable shock absorber group had 13.4 days to full weightbearing versus 58.0 days for those in the high tibial osteotomy group.

“As a principal investigator in the pivotal study,” Dr. Flanigan told OTW, “I’m very excited about the results of the study. The study demonstrated superiority of the implantable shock absorber over high tibial osteotomy and reported out high responder rates (96% of patients achieved clinically meaningful pain relief compared to baseline at two years). Combine the outcomes with a safety profile similar to a well-regarded control arm, and the implantable shock absorber is a very interesting technology.”

“As the study was designed as a non-inferiority study, the investigators were pleasantly surprised to see the final analysis that resulted in the implantable shock absorber achieving superiority of the primary endpoint. This is especially meaningful given the clinical history and acceptance of high tibial osteotomy as a viable treatment option.”

“My patients were happy with their experiences in the clinical study, and I continue to get requests from new patients asking about the procedure. The surgery is performed on an outpatient basis in my facility, and the surgical technique employs steps and techniques that will be familiar to orthopedic surgeons. I already know that many patients are excited to learn about this technology.”