Implantable Shock Absorber for Medial Compartment Osteoarthritis

Treating younger patients with isolated medial compartment osteoarthritis (OA) remains challenging, as these patients have often failed nonoperative treatment and wish to remain active, while surgeons are cautious using unicompartmental knee arthroplasty in young patients.

Patients (1) aged between 25 and 65 years, (2) with medial compartment OA Kellgren-Lawrence grades 1 to 4, (3) who have failed a minimum of 6 months of nonoperative treatments, and (4) who do not have large medial osteophytes.

The patient is positioned supine with a foot positioner for full extension, 90° of flexion, and deep flexion. A medial incision is made, and the medial collateral ligament is exposed. With standard instrumentation, Kirschner-wires are drilled in the tibia and femur, and a trial component is placed on the medial side of the knee. Then, in full extension, the absorber prevents varus collapse, whereas in flexion, the absorber does not engage, allowing for full flexion. The final implant is then placed with 6 locking screws, and closure is performed in layers. Rehabilitation consists of weightbearing as tolerated and a progressive range of motion.

Three trials with the implantable shock absorber have shown that the implant is generally safe and leads to clinical improvement in nearly all cases. Compared with a historical cohort of patients undergoing high tibial osteotomy, those in the present study have an earlier time to weightbearing (13 versus 59 days) and show greater improvement in functional and pain outcomes. Survivorship of the first 171 cases has been estimated to be 90% at 3 years and 85% at 5 years.

An implantable shock absorber is a suitable treatment option for younger patients with medial OA who wish to remain active. Rehabilitation typically involves weightbearing as tolerated. Short- to midterm outcomes in the literature are promising in this challenging patient cohort; however, longer follow-up is needed before recommendations can be made for this procedure to be a definitive surgery.

Level 3.

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