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Revision of Total Knee Replacement Often Caused by Stress Shielding

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July 1, 2013

More than 700,000 total knee arthroplasty (TKA) procedures are performed in the United States annually, and the number is predicted to steadily increase. The most common mechanical causes for revision of TKA are:

• Loosening (16.1%)
• Wear (4.9% )
• Periprosthetic osteolysis (3.2%) [2]

These factors can be interrelated. For example, mechanical loosening may be due to adverse periprosthetic bone remodeling following stress shielding, together with an osteolytic response to wear particles.

In one study, dual x-ray absorptiometry (DXA) was used to assess periprosthetic bone mineral density for 16 patients up to 2 years after cemented TKA. Bone loss of up to about 26% (in the central metaphyseal region) was found beneath the femoral component during the first 6 postoperative months.

Stress shielding is almost certainly the cause of this loss of bone density, either due to protection of the underlying bone from the forces normally transmitted across the patellofemoral joint, or to bypassing of the distal femoral bony structures as weight-bearing loads are transmitted through the stiff femoral component to the tibia.

Loss of bone density in the anterior femur and the proximal tibia is frequently seen when knee components are removed at revision surgery. This is often ascribed to osteolysis. Our model suggests that even if osteolytic changes are present, the prime cause of reduced bone density seen at revision is stress shielding resulting from a non-physiologic state of stress in the presence of metallic implants.

Although rarely the prime cause of revision at moderate follow-up intervals, the reduction in bone density caused by stress shielding may allow ingress of wear particles into fixation interfaces. For young patients who expect very long survivorship, the steady and increasing loss of bone may lead to stress shielding, becoming the root cause of arthroplasty failure.

As efforts continue to produce the "forgotten knee that will last for decades", our data suggest that the influence of stress shielding on bony structures should be taken into consideration in the implant development process.

Author:  Michael T. Manley, FRSA, PhD, is with the Homer Stryker Center for Orthopaedic Education and Research, Mahwah, New Jersey. He is also Visiting Professor, University of Bath, Bath, UK