The implantable shock absorber for medial compartment unloading of the knee: a scoping review

Abstract

Introduction

Management of early knee osteoarthritis in young, active populations remains challenging. The medial compartment sees the majority of load through the knee during ambulation and a significant population presents with unicompartmental disease. Traditional surgical options such as high tibial osteotomy (HTO) and arthroplasty pose limitations related to invasiveness, recovery, and long-term outcomes. The implantable shock absorber (ISA) offers a novel alternative that can reduce the load in the diseased compartment while offering a rapid rehabilitation protocol and future possibility for an osteotomy or arthroplasty revision.

Objectives

This review synthesizes current evidence on ISA as a treatment option for active patients with isolated medial compartment OA.

Methods

A comprehensive literature search identified peer-reviewed studies, abstracts, and regulatory documents related to medial knee OA, joint unloading devices, and ISA outcomes. Findings were categorized by biomechanical rational, clinical evidence, and surgical considerations.

Results

ISA offers biomechanical effects comparable to a 5° valgus-producing HTO, reducing medial tibiofemoral contact forces by up to 53%. Studies report significant improvements in pain, functional outcomes, and survivorship, including a 97.3% three-year survival rate and a 71% reduction in Western Ontario And McMaster Universities Osteoarthritis Index pain scores. ISA patients exhibit faster return to weight-bearing, lower revision rates (13.6% vs. 75.3% in HTO) and fewer serious adverse events. ISA preserves native anatomy, avoids bone resection. However, the current evidence is limited to shorter term, industry-sponsored trials.

Conclusion

ISA demonstrates promising, though limited clinical outcomes. Further independent studies are needed to understand the utility of ISA as a viable option for medial knee osteoarthritis.