Postmortem Retrieval Analysis of Metallosis and Periprosthetic Tissue Metal Concentrations in Total Knee Arthroplasty.

BACKGROUND: The purpose of this study is to determine the preferred sampling location for tissue analysis in total knee arthroplasty (TKA) and to evaluate metal concentrations, inflammatory cytokines, component damage, and tissue metallosis. METHODS: Twenty TKA systems were collected at necropsy along with tissue samples from 5 distinct locations. Inductively coupled plasma mass spectrometry (ICP-MS) analysis was performed to determine cobalt (Co), chromium (Cr), and titanium (Ti) concentrations. Synovial fluid cytokine analysis was preformed using a Magnetic Luminex Screening Assay. Femoral components were assesed for damage and tissues were visually scored for metallosis. RESULTS: The median metal concentrations were 16 ppb for Co, 46 ppb for Cr, and 9.8 ppb for Ti. There was no association between the tissue collection site and the metal concentration for Co (P = .979), Cr (P = .712), or Ti (P = .854). Twelve of 20 of the necropsy-retrieved TKAs had metallosis, but there was no correlation between Co (P = .48), Cr (P = .89), or Ti (P = .60) concentration and metallosis. Increased Co was associated with decreased tumor necrosis factor alpha (ρ = -0.56, P = .01) and interleukin 1 beta (ρ = -0.48, P = .03). Increased Cr was associated with decreased tumor necrosis factor alpha (ρ= -0.47, P = .03), interleukin 6 (ρ= -0.43, P = .04), and macrophage inflammatory protein 3 alpha (ρ= -0.47, P = .03). CONCLUSION: We observed elevated Co, Cr, and Ti concentrations in tissue from necropsy-retrieved TKA. Our findings did not support the hypothesis that tissue metal concentrations were associated with inflammatory cytokines. The results of this research will be useful for the design of future prospective studies.

Is Soft Tissue Laxity Associated with Tissue Metal Concentrations after Total Knee Arthroplasty?

Increased joint laxity is associated with excessive polyethylene wear, but the correlation between laxity and metal wear has not been established. Fifteen necropsy-retrieved primary total knee replacements were mounted into a custom knee-testing machine that measured anterior-posterior, varus-valgus, and internal-external rotational laxity at 0°, 30°, 60°, and 90° of flexion. Inductively coupled plasma-mass spectrometry analysis was performed to measure the cobalt (Co), chromium (Cr), and titanium (Ti) concentrations in periprosthetic tissue samples. Spearman's rank correlations were performed to determine whether a significant correlation (p < 0.05) existed between soft tissue laxity and tissue metal concentrations. At 0° flexion, decreased posterior displacement was negatively correlated with elevated Co and Cr concentrations. At 30° flexion, decreased external rotation and varus deflection was negatively correlated with elevated Ti concentrations. At 60° flexion, decreased anterior displacement was negatively correlated with elevated Cr concentrations and decreased varus deflection was negatively correlated with increased Ti concentrations. At 90° flexion, decreased anterior displacement was negatively correlated with elevated Co and Cr concentrations. To our knowledge, this is the first study to investigate the correlation between tissue metal concentration and laxity. Decreased laxity was associated with elevated metal concentrations in periprosthetic tissue.

Total Knee Post-Cam Design Variations and Their Effects on Kinematics and Wear Patterns.

Post-cam designs for posterior-stabilized total knee arthroplasy (TKA) implants have evolved over the last 2 decades. These designs have evolved from symmetric post and cam to asymmetric designs that include anterior post interactions to affect a kinematic change in full extension. All design changes have consequences on the resulting femorotibial contact kinematics and, depending on the amount of constraint built into the design, these changes may have significant consequences on the wear patterns on the tibial polyethylene insert. The current authors review the kinematic effects of symmetric and asymmetric cam designs and use a retrieval database of TKA implants obtained at the time of necropsy to show how different design variables may affect polyethylene wear patterns after 10 or more years of implantation or from modeled wear in simulators. More modern designs seem to have moved the post posteriorly and sloped the anterior aspect to avoid impingement of the anterior post in terminal flexion on the inferior aspect of the patella button. [Orthopedics. 2016; 39(3):S45-S49.].