Knee Joint Distraction and Implantable Shock Absorbers for Knee Osteoarthritis: A Systematic Review of Joint-Preserving Outcomes, Structural Changes, and Complications

ObjectiveTo systematically synthesize clinical, structural, biomarker, and safety outcomes of knee joint distraction (KJD) and implantable medial compartment shock absorbers (ISA) for tibiofemoral knee osteoarthritis (KOA), and to summarize comparative evidence versus arthroplasty, high tibial osteotomy (HTO), orthoses, and non-operative care.DesignA PRISMA-based systematic review of PubMed, EMBASE, Scopus, and Cochrane Library from inception to 1 October 2025 identified peer-reviewed clinical studies of KJD or ISA for tibiofemoral KOA. Two reviewers independently screened records, extracted data, and assessed risk of bias. Owing to substantial clinical and methodological heterogeneity and overlapping cohorts, a narrative synthesis was prespecified and no quantitative meta-analysis was performed.ResultsSeventeen studies (13 KJD, 4 ISA) reporting on approximately 400 patients met the inclusion criteria. KJD yielded clinically important 1- to 2-year improvements in WOMAC/KOOS and VAS pain, with arthroplasty-free survival of roughly 75% to 85% at 5 to 9 years in selected series, accompanied by increases in radiographic joint-space width and MRI-derived cartilage thickness in the most affected compartment. ISA consistently improved WOMAC pain and function and showed higher 2-year arthroplasty-free survival than HTO or non-operative comparators.ConclusionsCurrent evidence, based on small heterogeneous cohorts at low-to-moderate certainty, suggests that KJD and ISA can provide meaningful short- to mid-term symptom relief and delay arthroplasty in carefully selected patients. KJD and ISA address different indications and mechanisms and should be considered complementary rather than interchangeable joint-preserving strategies. Larger, independently replicated randomized trials with standardized structural and clinical endpoints are needed before widespread adoption.