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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.].

This chapter begins with providing an overview of the history and development of various orthopedic trauma devices, including dynamic compression plates, limited contact dynamic compression plates, and intramedullary nails. It then transitions into a discussion of the specific biomechanical properties of each design and how this allows each device to perform its necessary task effectively, as well has how these properties could potentially lead to failure. Understanding the biomechanics of each device may be helpful when choosing which devices best address the fracture being dealt with. Although all orthopedic trauma devices have a finite lifespan, this chapter documents the advantages and shortcomings of each device in order to help understand which devices may be most useful in specific types of fractures. Finally, retrieval studies for various devices are summarized to better understand the modes of failure for each type of device. Learning from failures and studying these retrievals may help to better understand these devices and could lead to development of better devices in the future.

Inflammatory cytokines have been proposed as potential biomarkers for damage in total knee arthroplasty (TKA). This study sought to compare the levels of inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-8, MCP-1, MIP-1α, MIP-3α, GM-CSF, and M-CSF) in synovial fluid of retrieved cadaveric primary TKAs, painful TKAs, and failed TKAs obtained at the time of revision. Twenty-five cadaveric specimens with primary TKAs were procured, and synovial fluid was collected. Seven synovial aspirates were collected during revision surgery from patients with failed primary TKAs, and twelve synovial aspirates were collected during clinic visits from patients with painful primary TKAs. Synovial samples were analyzed using a premixed Luminex Multiplex Screening Assay kit for detection of human inflammatory cytokines. A Kruskal-Wallis statistical test with Dunn's multiple comparison post hoc test and an assumed significance (p < 0.05) was used. Statistical analysis revealed a significant difference (p = 0.028) between IL-6 concentrations present in painful and cadaveric samples. No significant difference (p = 0.343) was found among the mean MCP-1 concentrations across the three sample groups. The cadaveric and painful samples had elevated MIP-3α compared to the revision samples upon initial inspection. Statistical analysis revealed a significant difference between cadaveric and revision sample groups. The cadaveric specimens had concentrations that were significantly elevated in comparison to the painful (p < 0.0001) and revision samples (p = 0.0015). IL-6 may be a potential biomarker for damage in a TKA. To better understand the role of MIP-3α, a future study should increase the sample size of the painful and revision groups. Future research will investigate the role of M-CSF concentrations as indicators in progression of TKA failure. Understanding the roles of these inflammatory cytokines throughout the progression of primary TKA complications may improve the diagnosis and treatment of painful TKAs.