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

Abstract Management of early knee osteoarthritis in young, active populations remains challenging. Osteoarthritis is a multifactorial process, with chronic aberrant load contributing to disease progression. The medial compartment sees the majority of load through the knee during ambulation and a significant population presents with unicompartmental disease. Nonoperative treatment options for medial knee arthritis include oral and injectable preparations, weight loss, physical therapy and exercise, and off-loading bracing. Surgical options include restoration of meniscal integrity, cartilage repair, and offloading osteotomy to reduce contact forces in the compartment. Valgus-producing high tibial osteotomy (HTO) provides good patient reported outcomes and durable survivorship, but may present challenges to future knee arthroplasty and requires significant amount of time for recovery. Unicompartmental arthroplasty offers good outcomes in appropriately selected patients, while total knee arthroplasty remains the gold standard for advanced and/or multicompartmental disease. Despite their proven benefits, arthroplasty options may be less desirable for young, active patients. The challenges of treating patients with high physical demand and isolated medial compartment knee arthritis have led to the development of an alternative surgical option - the implantable shock absorber (ISA), which reduces the load in the diseased compartment, has a rapid rehabilitation protocol, and can be revised to osteotomy or arthroplasty if needed. This scoping review focuses on emerging technology in ISA, which has demonstrated promising, though limited, clinical outcomes. Further clinical use and study is needed to understand the utility of ISA in the armamentarium of treatment options for the young, active patient with focal knee osteoarthritis.