Implantable Shock Absorber for Knee Osteoarthritis in Older Patients: Evidence From Two Clinical Studies

Background Knee osteoarthritis (OA) is a common, chronic condition associated with significant pain and functional limitations. Patients who receive inadequate relief from conservative care and are not indicated for or are unwilling to undergo arthroplasty procedures have previously faced a significant treatment gap. To address this, we examined the implantable shock absorber (ISA) in a cohort of patients over 65 years old, at follow-up through five years. Methods Patients from two clinical studies (Atlas and Calypso) aged 65 and over during the five-year observation period were evaluated in this secondary analysis. Primary outcomes included pain and functional ability (measured via the Western Ontario and McMaster Universities Arthritis Index (WOMAC)). Secondary outcomes included return-to-activities and adverse events. Outcomes were collected at baseline and at routine follow-up assessments for five years post ISA treatment. Follow-up measurements are compared with baseline at each interval.  Results A total of 18 participants (12 females) were eligible for inclusion in the analysis (mean age at final follow-up: 68.0 years, mean body mass index (BMI): 28.1). Five years after treatment with ISA, pain scores had improved by 70% over baseline (mean of 17.1 (SD 19.3) vs. mean of 55.0 (SD 11.9); p<0.01), and function scores had improved by 64% (mean of 19.5 (SD 22.2) vs. mean of 53.4 (SD 17.0); p<0.01). Additionally, 13/14 (93%) of participants achieved a clinically meaningful improvement in pain, with an 11/14 (79%) incidence of functional improvement after five years. Patients reported limitations in the performance of desired physical activities at baseline; at five-year follow-up, 14/18 (77.8%) of participants were able to perform one activity with no or minimal limitations (p<0.0001 vs. baseline). One device malfunction was reported at 105 days post procedure. Three participants were elected for conversion to total knee arthroplasty (TKA) in the study period. Conclusions Our study demonstrates that the ISA is a viable intervention for a selected population of patients with knee OA aged 65 and older. In this particular population, ISA was associated with significant long-term and sustained improvements in pain and function without compromising joint integrity, thus preserving options for future arthroplasty. For patients suffering in the treatment gap between the limited effectiveness of non-surgical approaches and the finality of arthroplasty, treatment with ISA offers a viable and effective proven option.