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Joint unloading implant improves joint space width in patients with OA

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Results from a small pilot study suggest a minimally invasive joint unloading implant can improve joint space width in the knees of patients with osteoarthritis.

Nine patients (median age: 53 years, mean BMI: 30 kg/m²) with 2-year follow-up data and adequate available imaging were randomly selected from the COAST study of 40 patients with osteoarthritis (OA) who received a KineSpring knee implant system for the treatment of unilateral compartment knee OA. Patients in the study were 25 years of age or older, had OA confirmed by radiograph and had failed at least 3 months of nonoperative care. The sample size was reportedly selected to provide 80% power to detect a minimum standardized pre-post effect size of 0.8 or greater. Clinical and radiographic disease severity was shown to be comparable to patients undergoing total knee arthroplasty.

All patients received the KineSpring implant system (Moximed). Pretreatment and 2-year follow-up radiographs were reviewed by an independent imaging core laboratory utilizing computer-aided detection methods. Mean image resolution was 0.12 µ per pixel. Statistical modeling was performed to provide quantitative measurements of subchondral trabecular integrity in the medial and lateral compartments of each knee. The software also calculated the minimum joint space width.

The morphology of vertically and horizontally aligned trabeculae was assessed by calculating the fractal dimension across a range of radii representing trabeculae from 0.4 mm to 3 mm in dimension. Differences in pixel width were standardized between patients using quadratic multiple regression with a noncentered polynomial. Under-the-curve methodology was used to analyze the radiographs from baseline and at 2 years.

The researchers found WOMAC scores were significantly improved at 2 years compared with baseline, with improvements of 92% for pain, 91% for function and 79% for stiffness. Minimum joint space width increased from a median of 0.9 mm at baseline to 3.1 mm at 2 years, with joint space width unchanged in the medial compartment of the untreated knee.

Fractal signatures in the vertically oriented trabeculae in the medial compartment decreased by 2.8% in the treated knee and increased by 2.1% in the untreated knee, which suggested OA modification in the treated knee, according to the researchers.

Implants are only available to those participating in research, and ongoing additional research is underway.

“To date, the device has been implanted in approximately 1,000 patients, and the first patient will achieve 7-year follow up this June,” Keith Fong, director of marketing for Moximed, said in an interview with www.Healio.com/Rheumatology. “Unloading therapy is starting to become established as a treatment category for knee OA, and the KineSpring system is a viable option for pre-arthroplasty patients.” – by Shirley Pulawski

Disclosure:  The researchers have no relevant financial disclosures.