An Alternative Unloading Implant for Medial Knee Oa in the Young and Active Patient

Introduction

Osteoarthritis (OA) represents a leading cause of disability and a growing burden on healthcare budgets. OA is particularly vexing for young, active patients who have failed less invasive therapies but are not ideal candidates for HTO or arthroplasty. Often, patients suffering in this wide therapeutic gap face a debilitating spiral of disease progression, increasing pain, and decreasing activity until they become suitable arthroplasty patients. An implantable unloading device was evaluated for the treatment of medial knee OA in this patient population.

Joint overload has been cited as a contributor to OA onset or progression. In response, the KineSpring® System (Moximed, Inc, USA) has been designed to reduce the load acting on the knee. The unloader is implanted in the subcutaneous tissue without violating the joint capsule, thus preserving the option of future primary arthroplasty. The implant may be particularly useful for young, active patients, given the reversibility of the procedure and the preservation of normal flexibility and range of motion.

Methods and Results

The KineSpring System was implanted in 79 patients with isolated medial knee OA, and the longest duration exceeds two and a half years. Treated patients were young and obese (mean age: 52 years, range 32–75; mean BMI: > 30 kg/m², range 21–45). Acute implant success, adverse events, and clinical outcomes using validated patient reported outcomes tools were recorded at baseline, post-op, 2 and 6 weeks, and 3, 6, 12 and 24 months post-op. All centers received ethics committee approvals prior to enrolling patients in the study.

Mean surgical time was 72 min (range 45–153 minutes), and all patients were discharged after a few days. Patients recovered rapidly, achieving full weight bearing within 1–2 wks and normal range of motion by 6 weeks. Most patients experienced significant pain relief and functional improvement by six weeks, with results sustained beyond the two-year follow-up visit. WOMAC Pain improved from 43 at baseline to 13 at 2 years (p<0.001), WOMAC Function improved from 43 at baseline to 11 at 2 years (p<0.001), and WOMAC Stiffness improved from 52 at baseline to 18 at 2 years (p<0.001). Patients reported satisfaction with implant and its appearance.

Conclusions

The KineSpring System provided pain relief and functional improvement in a young and obese patient population that may not be ideal for HTO or arthroplasty. This unloading device, with these successful results, fills a major gap in treatment options for young and active OA patients.