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75th Annual Meeting Scientific Exhibits

Factors Affecting Loading in TKA: What Is Causing Implant Failure and Loosening?

Scientific Exhibit Number: SE34

Location: Moscone Convention Center

Adult Reconstruction Knee

Michael E Berend, MD Mooresville IN
Scott R Small, MS Terre Haute IN
Robert Michael Meneghini, MD Farmington CT
Merrill A Ritter, MD Indianapolis IN
Christine A Buckley, PhD Chicago IL
Kurt Dierking, MS Mooresville IN
James C Merk, MS Mooresville IN

Tibial strain in TKA is affected by metal backing, femoral component sizing, tibial resection depth, and coronal plane articular geometry.

Failure in TKR has been attributed to abnormal loading conditions. TKR loading is dependent on alignment, ligament balance, and implant design; however, the respective contribution of each factor to failure is not known. This study quantified the effect of metal backing, component size mismatch, depth of tibial resection, ligament imbalance, and coronal plane geometry on loading.

Composite tibiae were coated with photoelastic material allowing 'full field' dynamic strain quantification under 3X BW throughout the loading cycle when viewed through a polariscope. Changes in strain were quantified in 24 proximal tibial regions.

The data represent percent change in surface strain (all-polyethylene vs metal backing) circumferentially at depths of 0-10mm, 10-20mm, and 20-30mm, respectively; Anteromedial Peripheral: +211, +46, +21; Anteromedial Central : +636, +457, +101; Anterolateral Central: -30, -44, +30; Anterolateral Peripheral: +109, +146, +129; Posteromedial Peripheral: +75, +49, +51; Posteromedial Central: +192, +41, +46; Posterolateral Central: +484, +70, +71; and Posterolateral Peripheral: +41, +54, +25. All changes above +101 were statistically significant (p<.05). The largest percent change in strain was observed with all-poly vs. metal backed components (636 percent). Anterior strains increased more than posterior. Distal resection levels and resulting smaller tibial component sizes and relative posterior and peripheral component position significantly increases posterolateral, peripheral strains (583 percent). Larger femoral components exhibited increased peripheral strains (113 percent). Peripheral strains decreased with increased coronal plane dishing compared to flat on flat designs (9-27 percent). (Dramatic video loop images captured throughout the loading cycle will be displayed in the exhibit on video monitors.)

Edge loading and failure in TKA are multifactorial processes. This is the first study to quantify the influence of femoral component size, depth of resection, imbalanced loading, metal backing, and coronal plane dishing on tibial strain distribution. Better understanding of in vitro loading patterns will help prevent failure in the future.

A · to the left of the title indicates the FDA has not cleared the drug or device for the described purpose.

Wednesday - Friday 7:00 AM - 6:00 PM
Saturday 7:00 AM - 5:30 PM
Sunday 7:00 AM - 12:30 PM

A Scientific Exhibit graphically illustrates a study or a complex procedure. It differentiates itself from a poster presentation in the amount of material that is presented and uses audiovisual, interactive demonstration, or some other type of enhancement in its presentation.

The principal exhibitor will be available at the exhibit from 11:30 AM to 12:30 PM Wednesday through Friday to provide information and answer questions.

An alphabetical listing of disclosures is available.

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